WO2018178397A1

WO2018178397A1 - N-alkylated amino acids and oligopeptides, uses thereof and methods for providing them.

Info

Publication number: WO2018178397A1
Application number: PCT/EP2018/058488
Authority: WO
Inventors: Katalin BARTA; Tao Yan; Bernard Lucas Feringa
Original assignee: Rijksuniversiteit Groningen
Priority date: 2017-03-30
Filing date: 2018-04-03
Publication date: 2018-10-04

Abstract

The invention relates to the synthesis of amphiphilic amino acid derivatives, in particular to a method for the N-alkylation of an unprotected amino acid or the N-terminus of an oligopeptide substrate, comprising reacting said unprotected amino acid or oligopeptide substrate with an alcohol, e.g. a fatty alcohol, in the presence of a homogeneous transition metal catalyst.

Description

Title: N-alkylated amino acids and oligopeptides, uses thereof and methods for providing them.

The invention relates to the synthesis of amphiphilic amino acid derivatives, in particular to N-alkylation of amino acids and oligopeptides by the direct alkylation of amines with alcohols. It also relates to the use of the N-alkylated products as surfactant.

Long-chain alkyl amino acid-based surfactants are known in the art, including N-alkyl amino acids, N-acyl amino acids, N-alkyl amino amides and alkyl amino acid esters (Infante et al., C. R. Chimie, 2004, 7, 583-592). However, the synthesis of N-alkyl amino acids is relatively demanding (Bordes and Holmberg, Advances in Colloid and Interface Science, 2015, 222, 79-91). The traditional pathways including N-alkylation of amino acids with alkyl halides (Bordes et al., Journal of Colloid and Interface Science 2013, 411, 47-52) and reductive N-alkylation of amino acids with aldehyde (Meng et al., Catal. Lett., 2016, 146,1249-1255). These suffer from various drawbacks, including the production of stoichiometric amount of toxic halide salts as wastes and unstable substrates leading to complex side products, respectively. Furthermore, alkyl halides and aldehydes are mostly synthetized from alkanes and alkenes which are derived from fossil fuels.

It is also known that alcohols are abundant chemical reagents that can be derived from renewable resources through fermentation, depolymerization of lignocellulose (Barta and Ford, Acc. Chem. Res., 2014, 47, 1503-1512) as well as reduction of fatty acids contained in plants oil (Kreutzer, J. Am. Oil. Chem. Soc. 1984, 61, 343 - 348). Whereas alcohols have been already used as reagent to alkylate amines in industrial scale, these known alkylation processes require harsh reaction conditions. Hence, the present inventors set out to provide an improved method for the synthesis of N-alkylated amino acids which method is environmentally benign and preferably uses building blocks from renewable sources. In particular, they aimed at providing fully sustainable production of (novel) surfactants based on renewable resources i.e. amino acids and long chain alcohols that can be obtained from fatty acids.

It was surprisingly found that this is advantageously achieved by the direct N-alkylation of amino acids with alcohols using a variety of transition metal complexes as catalysts under mild conditions. The process is also highly selective, only produces water as byproduct and allows for much easier purification than other methods.

Accordingly, the invention provides a method for the N-alkylation of an unprotected amino acid or the N-terminus of an oligopeptide substrate, comprising reacting said unprotected amino acid or oligopeptide substrate with an alcohol in the presence of a homogeneous transition metal catalyst.

Direct alkylation of amines with alcohols has been achieved mainly with Ru- or Ir- based catalytic system. However, none of them were successfully applied to zwitterionic amines like unprotected amino acids (Yu et al., Chem. Soc. Rev., 2015, 44, 2305-2329).

Recently, the inventors developed the first Fe- based catalytic system for direct alkylation of amines with alcohols (Yan, Feringa, Barta, Nature comm. 2014, 5, 5602; Yan, Feringa, Barta, ACS Catal. 2016, 6, 381). Notably however, zwitterionic amines like unprotected amino acids were not tested. The present finding that unprotected amino acids and oligopeptides can be directly N-alkylated is highly surprising for at least the following reasons. First, it were to be expected that the alcohol would react with the available carboxyl-moieties such that ester formation would occur instead of or in addition to N-alkylation. Second, the reported Fe- catalyst system used low or medium polarity solvents such as toluene and cyclopentyl methyl ether (CPME) in which unprotected amino acids are not soluble. Hence, selective N-alkylation of unprotected amino acids or oligopeptides according to the present invention could not have predicted.

Leonard et al. (Org. Process Res. Dev. 2015, 19, 1400-1410) describe the use of the "borrowing hydrogen strategy" in the synthesis of a number of pharmaceutically relevant intermediates, such as the alkylation of a protected amino acid ((S)-amino acid ester compound 29) using a diol. In contrast to the present invention Hence, Leonard et al. does not relate to the N-alkylation of an unprotected amino acid.

As is demonstrated in the Examples herein below, the present inventors are the first to show direct N-alkylation of free ct-amino acids and simple peptides with a variety of alcohols using low loadings of a

homogeneous transition metal catalyst. The presented atom-economic transformation only results in water as byproduct, thereby significantly simplifying the purification procedure. The reaction is highly selective, and most products were obtained in quantitative yield. Reaction temperature as low as 60°C were used with several substrates. The method is modular and allows for the use of a range of alcohol reaction partners leading to functionalized amino acids with modular properties such as low or high hydrophilicity. Particularly, the use of long chain alcohols and amino acids as only reaction partners to obtain mono-N-alkyl amino acids, especially with a molecular iron catalyst, holds great potential for the fully sustainable production of completely bio-based surfactants.

Chiral amines, N-alkylated amino acids and peptides moieties are frequently used as substrates or key intermediates to produce high valued chemicals (e.g. drugs), A method of the invention will dramatically reduce the cost and potential pollution (e.g. halide salts are toxic compounds produced in the current methods). Importantly, it was found that in a method of the invention using a Ru- or Fe-based catalyst, no racemization occurred. Natural amino acids are chiral, and this chirality was maintained in the obtained corresponding N-alkylated products. The mild reaction temperature and selectivity of the method as provided herein thus offer a distinct advantage when chirality of the final product is important, e.g. for further application.

Herewith, the invention provides not only a significant addition to

sustainable homogeneous catalysis related to the atom economic

modification of challenging substrates such as amino acids, but also opens up new possibilities for material science for the production of surfactant as well as for the easy and selective chemical modification of proteins or peptides in biochemistry. Preferably, the alkylation is performed in the presence of a Fe- or

Ru-based catalyst. Very suitable Fe catalysts for use in the present invention include those according to one of the following Formula's A, B or C herein below.

wherein Rl and R2 are independently selected from the group consisting of: alkyl, aryl, -CH₂Ph and silyl moieties (e.g. TMS (trimethylsilyl), TBDMS (tertbutyldimethylsilyl), TIPS (triisopropylsilyl) or TBDPS

(tertbutyldiphenylsilyl))

R3 and R4 are independently selected from the group consisting of:

hydrogen, optionally substituted alkyl and optionally substituted, aryl (with broad range of substitution e.g. -OCH₃, CN, NO₂, COOR, Alkyl)

L is selected from the group consisting of CO, acetonitrile phosphine, phosphite, phosphoramidite, primary or secondary amine, primary, secondary or tertiary alcohol,

X is O, NH or N-R where R is an alkyl or aryl, preferably X is O.

B

wherein Rl and R2 are independently selected from the group consisting of: alkyl, aryl, -CH2PI1 and,

silyl moieties ((e.g. TMS (trimethylsilyl), TBDMS (tertbutyldimethylsilyl), TIPS (triisopropylsilyl) or TBDPS (tertbutyldiphenylsilyl));

R3 and R4 are independently selected from the group consisting of:

hydrogen, optionally substituted alkyl (with broad range of substitution), and optionally substituted aryl (with broad range of substitution e.g. H, - OCH3, CN, NO₂, COOR, Alkyl), silyl, or OH, O-R; NH₂, NH-R (where R can be alkyl, aryl, sulphonyl, tosyl, mesyl); Y = CH2; CH2-CH2; CH2-O-; CH2- NH-; 0; NH or NHR5.wherein R5=alkyl or aryl, sulphonyl, tosyl, mesyl;

X is O, NH or N-R6 where R6 is an alkyl or aryl, preferably X is

wherein Rl and R2 are independently selected from the group consisting of: alkyl, aryl, -CH₂Ph and silyl moieties (e.g. TMS [trimethylsilyl], TBDMS [tertbutyldimethylsilyl, TIPS [triisopropylsilyl] or TBDPS

[tertbutyldiphenylsilyl]) where R3 and R4 are independently selected from the group consisting of H, Alkyl (with broad range of substitution), silyl, Aryl (with broad range of substitution on the aromatic ring: e.g. H, -OCH3, CN, NO2, COOR, Alkyl); or OH, O-R5 (where R5=alkyl, aryl); NH₂, NH-R6 (where R6=alkyl, aryl, sulphonyl), or wherein R3 and R4 are connected to form a cyclic structure, Yl and Y2 = CH₂; O; NH; NHR7 (where R7=alkyl, aryl, sulphonyl, tosyl, mesyl); CH2-CH2; CH2-O-; or CH₂-NH- L is selected from the group consisting of CO, acetonitrile phosphine, phosphite, phosphoramidite, primary or secondary amine, primary, secondary or tertiary alcohol,

Preferably, in any of the structures A, B or C above, L is CO or acetonitrile. In one embodiment, L=CO and catalyst activation is with MesNO, base or UV light. In another embodiment, L=acetonitrile and catalyst activation is with heat

Preferably, in any of the structures A, B or C above, X is oxygen.

Exemplary Fe-based catalysts for use in the present invention include

R

R = H, CH₂Ph, TBDMS,

TIPS or TBDPS In a specific aspect, the catalyst is of the formula:

Cat 1 b

In another embodiment, a method of the invention involves direct N- alkylation catalyzed by a Ru catalyst.

Very suitable Ru catalysts for use in the present invention include those according to one of the following Formula's D:

wherein Ri, R2, R3 and R₄ are independently selected from the group consisting of alkyl, aryl, -CH2PI , optionally with one or more substitution on the aromatic ring, preferably wherein Ri, R2, R3 and R₄ are (optionally substituted) aryl or -CH2PI1.

In a preferred embodiment, the Ru-based catalyst is of the formula D.

For example, in a specific aspect, the catalyst is 1- hydroxytetraphenylcyclopentadienyl-(tetraphenyl-2,4-cyclopentadien-l-one)- μ-hydrotetracarbonyldiruthenium(II) (Shvo catalyst) of the formula

Furthermore, a Ru-based catalyst may be prepared in situ from a Ru precursor consisting of RuCl3, Ru3(CO)i2, [Ru(p-cymene)Cl2)]2, Ru(acac (acetylacetonate) and a ligand which is a monodentate (e.g. triaryl or trialkyl phosphine), bidentate (dcpe, dppf, DPEphos, Duphos.. etc) or tridentate phosphine (triphos and its derivatives).

Furthermore, an Fe catalyst may be prepared in situ from a Fe precursor consisting of Fe(CO)₅ , Fe₃(CO)i₂, Fe(BF₄)₂*6H₂0 [iron (II) tetrafluoroborate, hexahydrate] ; Fe(OTf)2 [Iron (II) trifluormethansulfonate] ; Fe(OAc)2 [iron (II) acetate]; FeCh; FeBr2 or iron salts with organic acids as anions and a ligand, consisting of monodentate, bidentate, tridentate, or tetradentate phosphines, N-heterocyclic carbenes or the combination thereof. In addition, the li and is that of a PNP pincer type E and E' shown below.

R = aryl, alkyl;

R' = aryl, alkyl, amino, alkoxyl.

E E'

Further, an additional base such as KOH or KOtBu (potassium tert- butoxide) may need to be added.

It was found that, when primary amino acids and secondary alcohols were used as reactants, both catalysts gave mono-N-alkylated products.

Surprisingly, when primary amino acids and primary alcohols were used, a Ru-based catalyst yielded di-N-alkylated products. In contrast, a Fe-based catalyst could be used to specifically produce mono-N-alkylated products, e.g. by control of reaction conditions including reaction time and/or substrate ratio. Herewith, by choosing the catalyst system, a method of the invention therefore also allows to selectively produce mono— or bis- alkylated products.

As will be appreciated by a person skilled in the art, a method of the invention is broadly applicable to a diverse set of unprotected amino acids and small unprotected peptides. Amino acids are biologically important organic compounds containing amine (-NH2) and carboxyl (-COOH) functional groups, along with a side-chain (R group) specific to each amino acid. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen, though other elements are found in the side-chains of certain amino acids. About 500 amino acids are known (though only 20 are based on the genetic code) and can be classified in many ways. They can be classified according to the core structural functional groups' locations as alpha- (a-), beta- (6-), gamma- (γ-) or delta- (δ-) amino acids; other categories relate to polarity, pH level, and side-chain group type (aliphatic, acyclic, aromatic, containing hydroxyl or sulfur, etc.). In one aspect, the invention involves the N-alkylation of a naturally occurring amino acid. As used herein, a naturally occurring amino acid is one of the 20 common ct-amino acids (Gly, Ala, Val, Leu, He, Ser, Thr, Asp, Asn, Lys, Glu, Gin, Arg, His, Phe, Cys, Trp, Tyr, Met, and Pro), and other amino acids that are natural products, such as norleucine, ethylglycine, ornithine, methylbutenyl-methylthreonine, and phenylglycine. Typically, the amino acid or oligopeptide substrate used in the present invention comprises or consists of a- amino acids. However, β- and γ- amino acids were also found to be suitable substrates for N- alkylation.

As to the side-chain, the amino acid or oligopeptide substrate preferably consists of or comprises an amino acid residue having an uncharged or hydrophobic side chain. In one embodiment, the oligopeptide substrate consists of from two to eight amino acids, preferably two to five amino acids, more preferably wherein the oligopeptide is a dipeptide or a tripeptide.

However, the N-alkylationof Asp, Glu, His, Lys and Arg may be achieved through technical adaptation of the catalytic system, such us pH tuning e.g. involving the addition of an organic acid or base such as AcOH or Et3N). Good results were obtained with all naturally occurring amino acids excluding acidic amino acids (Asp, Glu) and basic amino acids (His, Lys, Arg). Accordingly, the unprotected amino acid/oligopeptide is or comprises a natural amino acid other than aspartic acid, glutamic acid, histidine and/or arginine residue(s). In one embodiment, the amino acid residue is selected from the group consisting of Ser, Thr, Cys, Met, Phe, Try, Ala, Gly, Pro, Val, Leu, He, Gin and Asn. Preferred oligopeptides are those comprising or consisting of two or more residues selected from Ser, Thr, Cys, Met, Phe, Try, Ala, Gly, Pro, Val, Leu, He, Gin, Asn. For example, it is Gly-Ala, Ala- Gly, Gly-Gly, Leu-Gly, Ala-Leu, Leu-Gly-Gly, Ala-Gly-Ala, and the like.

According to a method of the invention, any alcohol can be directly coupled to the amino acid or oligopeptide substrate. Whereas alcohols containing a single reactive hydroxyl group are typically preferred, e.g. in the synthesis of surfactants, diols may also be used.

In one preferred embodiment, the alcohol is a fatty alcohol. Fatty alcohols (or long-chain alcohols) are usually high-molecular-weight, straight-chain primary alcohols, but can also range from as few as 4-6 carbons to a typical medium chain length of C10-C20 to as many as 26-34 , derived from natural fats and oils. The precise chain length varies with the source. Fatty alcohols usually have an even number of carbon atoms and a single alcohol group (-OH) attached to the terminal carbon. Some are unsaturated and some are branched.

In one embodiment, the alcohol is of the formula /OH n=2 - 30

^ Ι^ typically between 6-18

Preferred alcohols for use in the present invention include C8-C18 fatty alcohols, more preferably saturated fatty C8-C18 alcohols. Synthetic fatty alcohols from industrial processes that use syngas and an appropriate catalyst for 'higher alcohol synthesis' can also be used.

In a further aspect, in particular for synthesis of an amino acid based surfactant, the alcohol is an unsaturated long chain, primary alcohol. Many of them can be derived from natural triglycerides (such as sunflower, palm, cashew, rapeseed, coconut, almond, soy oil) or triglycerides or lipids derived from algae. The chain can have 1, 2 or 3 double bonds.

6-18

bond variable

Alternatively, the alcohol is a branched aliphatic alcohol, for instance of the formula

Still further, the alcohol is a long chain aliphatic diol without branching on the chain or a long chain aliphatic diol with branching of alkyl-or aryl substituents on the chain, or a long chain diol with

unsaturation in the chain.

In one embodiment, the diol is of the formula

Other embodiments of the invention involve the use of alcohols derived from monolignols (such as coniferyl, coumaryl and synapyl alcohol) or phenol- alcohols derived from lignin depolymerization.

For example, the diol is of the formula

In a specific embodiment, the alcohol is an optionally substituted linear, branched or aromatic C1-C6 alcohol. Suitable substituents include one or more of halogen, oxo, hydroxyl, -CN, alkoxy, amino, amido, phenyl, benzyl hetero-aryl, cyclo-alkyl, heterocycloalkyl, -C(=0)0-R, wherein R is H, C1-C6 alkyl or CH2-aryl. For example, the alcohol is selected from the group consisting of ethanol, isopropanol, 1-butanol, 2-chloroethanol, 2-butanol, cyclopropylmethanol, benzylalcohol and 4-chlorobenzyl alcohol.

Preferably, the alcohol is derived from biomass or other renewable source. Methods for obtaining (fatty) alcohols are known in the art. For example, US2012/0115195 discloses a method for the production of fatty alcohols from biomass, including cellulose, xylan, hemicellulose, lignin, mannan, and other materials commonly found in biomass. Non-limiting examples of renewable sources include grasses (e.g., switchgrass, Miscanthus), rice hulls, bagasse, cotton, jute, hemp, flax, bamboo, sisal, abaca, straw, leaves, grass clippings, corn stover, corn cobs, distillers grains, legume plants, sorghum, sugar cane, sugar beet pulp, wood chips, sawdust, and biomass. It is also known that alcohols are abundant chemical reagents that can be derived from renewable resources through fermentation, depolymerization of lignocellulose (Barta and Ford, Acc. Chem. Res., 2014, 47, 1503-1512). Preferably, linear long chain alcohols are derived from the reduction of natural fatty acids contained in plant oil (Kreutzer, J. Am. Oil. Chem. Soc. 1984, 61, 343 - 348)."

The reaction conditions for performing the N-alkylation method of the invention can be optimized using routine skills. Typically, the conditions are relatively mild. Suitable reaction temperatures are those up to about 110°C, preferably up to about 100°C, like 95°C, 90°C, 85°C or lower. For example, good yields could be obtained at a temperature of only up to 80°C, like about 70°C or even about 60°C. Reaction times can vary e.g. depending on reaction temperature, solvent, catalyst and/or desired yields. Typical incubation times are at least 12 hours, preferably at least 16 hours, like 18 or 20 hours, more preferably at least 24 hours. Preferably, the reaction is performed under an argon atmosphere. In one embodiment, about 0.1 to about 1 mmol amino acid or oligopeptide substrate is reacted with about 2-6 ml alcohol. In a preferred embodiment, CF3CH2OH (typically 1 - 4 ml) is added to increase the solubility of the amino acid or oligopeptide substrate. Additional toluene (or an other low polar solvent, e.g. THF, CPME) can be added to tune the polarity of the mixture to obtain a higher catalytic reactivity. The catalyst is preferably used at about 0.5 to 5 mol%. Preferably, the Fe- based catalyst is used at about 4-5 mol%. The Ru-based catalyst is preferably used at about 0.5-1 mol%.

A further embodiment of the invention relates to an N-alkylated amino acid or oligopeptide obtainable by a method according to the invention. For example, there is provided an N-alkylated amino acid or oligopeptide selected from the group consisting of the reaction products of Tables 1 to 6 shown herein below. In one embodiment, the invention provides an N- alkylated amino acid or oligopeptide selected from the group consisting of the compounds shown in Scheme 2 or 3. Preferred Ν-alkylated amino acid or oligopeptide compounds, e.g. for use as surfactant, include N,N-di-(5- hydroxypentyl)-phenylalanine (3dk), N,N-di-(n-pentyl)-glycine (3gm), N,N- (di-n-nonyl)-phenylalanine (3dj), N,N-di-n-nonyl- glycine (3gj), N,N-di- dodecylglycine (3gn), N,N-di-(5-hydroxy-pentyl)-glycyl-alanine (5ak), N,N-di- (n-dodecyl)-glycyl-alanine (5an), N-nonyl- glycine (3gj'), N-decyl- glycine (3go'), N-dodecyl-alanine (3gn'), N-tetradecylglycine (3gp'), N- hexadecylglycine (3gq'), N-octadecylglycine (3gr'), N-dodecyl-alanine (3fn') and N-nonyl-proline (3aj). A method of the invention has many interesting applications. However, it is especially advantageous in the synthesis of an amino acid-based surfactant, preferably in the synthesis of an amino acid-based surfactant from natural building blocks/renewable sources. Hence, in one embodiment the invention provides a method for the synthesis of an amino acid based surfactant, preferably a long-chain N-alkyl amino acid, comprising the N-alkylation of an unprotected amino acid or the N-terminus of an oligopeptide substrate by reacting said unprotected amino acid or oligopeptide substrate with a long chain (fatty) alcohol in the presence of a homogeneous transition metal catalyst. In a preferred aspect, the method comprises mono-N-alkylation using a Fe-based catalyst as described herein above or in the Examples.

N-alkyl amino acid-based surfactants carry a positive charge at low pH, are zwitterionic at intermediate pH and negatively charged at high pH. This not only affects their physicochemical behavior, for instance their ability to adsorb at charged surfaces, but it also brings about a special feature with respect to self-assembly in bulk and at surfaces. Therefore, the invention also provides the use of an N-alkylated amino acid or oligopeptide

obtainable by a method of the invention as a surfactant. Preferred

surfactants include compounds 3dk, 3gm, 3dj, 3gj, 3gn, 5ak, 5an and those shown in Scheme 3.

Other preferred compounds (obtainable by a method) of the invention include those of the formula R=alcohol as specified above

Also provided is the use of these compounds as surfactant or as

antimicrobial agent.

EXPERIMENTAL SECTION Materials and Methods General methods

Chromatography: Merck silica gel type 9385 230-400 mesh or Merck AI2O3 90 active neutral, TLC: Merck silica gel 60, 0.25 mm. Components were visualized by UV, Ninhydrin or I2 staining. Progress of the reactions was determined by NMR. Mass spectra were recorded on an AEI-MS-902 mass spectrometer (EI+) or a LTQ Orbitrap XL (ESI+). Ή- and ¹³C NMR spectra were recorded on a Varian AMX400 (400 and 100.59 MHz, respectively) using CDCI3, CD3OD, D₂O or DMSO-d6 as solvent. Chemical shift values are reported in ppm with the solvent resonance as the internal standard (CDCI3: 7.26 for Ή, 77.00 for ¹³C; CD3OD: 3.31 for Ή, 49.00 for ¹³C; D₂O: 4.79 for Ή; DMSO-d6: 2.50 for Ή, 39.52 for ¹³C). Data are reported as follows: chemical shifts, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, br. = broad, m = multiplet), coupling constants (Hz), and integration. All reactions were carried out under an Argon atmosphere using oven (110 °C) dried glassware and using standard Schlenk techniques. Toluene were collected from a MBRAUN solvent purification system (MB SPS-800). CF3CH2OH (>99.0%) was purchased from TCI without further purification. Complex Cat la was synthesized according to T. Yan, B. L. Feringa, K. Barta ACS Catal., 2016, 6, 381-388. Cat 2 was purchased from Strem. All other reagents were purchased from Sigma, TCI or Acros in reagent or higher grade and were used without further purification.

Representative procedures

General procedure: An oven-dried 20 ml Schlenk tube, equipped with stirring bar, was charged with amino acid (or peptide, given amount), Cat 1 or Cat 2 (given amount) and alcohol (given amount), solvent (or neat).

Amino acid (or peptide) and catalyst were added into the Schlenk tube under air, the Schlenk tube was subsequently connected to an argon line and a vacuum-argon exchange was performed three times. Alcohol and solvent was charged under an argon stream. The Schlenk tube was capped. Then the Schlenk was fast sequentially connected to vacuo and argon line, repeat 3 times, for degassing the mixture. And the mixture was rapidly stirred at room temperature for 1 min, then was placed into a pre-heated oil bath at the appropriate temperature and stirred for a given time. The reaction mixture was cooled down to room temperature and concentrated in vacuo. The residue was characterized by crude H NMR for determining conversion. Further purification was conducted through flash column chromatography or crystallization to provide the pure N-alkyl amino acid (or peptide) product. Esterification procedure (for preparation of methyl ester of alky amino acids 3gp', 3gq' and 3gr'): Continuing the General procedure, until the reaction mixture was cooled down to room temperature, then 3 ml benzene was added, and under stirring TMSCHN2 (2M in toluene) was added. The reaction can be monitored by TLC (S1O2, mono-N-alkyl amino acid, Rf = 0.3 in ethylacetate/MeOH = 1/1; methyl mono-n-alkyl amino acid ester, Rf = 0.3 in Et20). Then the corresponding methyl ester was purified by flash chromatography (tol/Et₂0 50/50 - 0/100). Preparation of Cat lb: Oven-dried 250 ml Schlenk was charged with 100 ml dry acetone and 2 ml dry CH3CN, degas with N2 for 20 min. Then 1 g Cat la (2.38 mmol) was added under N2, stirring for 1 min until it fully solubilized. 216 mg Me3NO (1.2eq) was added under N2. The direct color changing from yellow to orange was observed in 5 s. The conversion of Cat la can be monitored by TLC (pentane/ethyl acetate = 1/1, on silica gel, Rfcatia = 0.95, Rfcatib = 0.35). After lh, the solvent was removed by vacuum; Cat lb was purified through flash chromatography, and obtained as brown solid (0.91g, 88% yield). Ή NMR (400 MHz, CDCI3): δ 2.05 - 2.48 (m, 4H), 2.21 (s, 3H), 1.38 - 1.73 (m, 4H), 0.22 (s, 18 H). ¹³C NMR (100 MHz, CDCI3): δ 212.80, 180.12, 126.00, 106.58, 69.91, 24.83, 22.31, 4.43, -0.12. The physical data were identical in all respects to those previously reported. Cat la and Cat lb are slightly light sensitive but air stable.

EXAMPLE 1 : Direct N-alkylation of amino acids.

This example exemplifies direct N-alkylation of unprotected amino acids using proline (la) as exemplary substrate, ethanol (2a) as the alkylation reagent and Cat la as the catalyst (Table 1). Table 1: Optimization of reaction conditions for direct N-ethylation of proline (la) or leucine (lb) with ethanol (2a).

Cat 2

Entry 1 Cat. [mol %] 2a T. Temp. Conv. Sele. 3 [%]^«

[mmol] [ml] [h] [°C] 1

[%]°

1 la / 0.5 Cat la / 4, MesNO / 8 2 18 110 >99 >99

2 la / 0.5 Cat la / 4, MesNO / 8 2 16 90 >99 >99 (99)

3 la / 0.5 Cat la / 2, MesNO / 4 2 16 80 14 14

4 lb / 0.5 Cat la / 4, MesNO / 8 4 15 90 15 n.d.

5 lb / 0.2 Cat la / 10, MesNO / 5 24 90 60 n.d.

20

6 lb / 0.2 Cat la / 10, MesNO / 5 18 110 70 n.d.

20

₇t lb / 0.5 Cat la / 4, MesNO / 8 4 24 100 30 n.d.

8^b lb / 0.5 Cat lb / 4 4 24 100 70 n.d.

9^C lb / 0.5 Cat lb / 4 4 24 110 18 n.d.

10⁶ lb / 0.5 Cat lb / 4 4 24 110 90 n.d.

11» lb / 0.5 Cat lb / 4 4 42 110 >95 (49)

12 la / 0.5 Cat 2 / 0.5 2 18 110 >99 >99

13 la / 0.5 Cat 2 / 0.5 5 18 90 >99 >99 (99)

14 la / 0.2 Cat 2 / 1 5 18 60 53 53

15 lb / 0.5 Cat 2 / 1 4 14 90 >99 86

16 lb / 0.2 Cat 2 / 1 5 18 90 >99 >99 (99)

General reaction conditions: General procedure, 0.2 or 0.5 mmol la (or lb), 2 - 5 ml 2a, Cat la + MesNO, Cat lb, or Cat 2 (given amount), neat, 14 - 24 h, 60 - 110 °C, isolated yields in parenthesis. "Conversion and selectivities are based on crude H NMR. ^bl ml CF3CH2OH was added. ^cl ml H2O was added. Quantitative yield of N-ethyl proline (3aa) was obtained with 4 mol % of Cat la, under 90 °C for 16 h (Table 1, entry 2). However, when leucine (lb) was tried as the substrate, the results of producing N,N-diethyl leucine (3ba) turned out to be less satisfactory (Table 1, entry 4 - 7). Then Cat la's analogue, Cat lb was employed as the catalyst, full conversion of lb and

49% yield of 3aa were obtained, with using CF3CH2OH as the solvent, under 110 °C, for 42 h (Table 1, entry 8 - 11). The ruthenium catalyst (Cat 2) was also selected as the catalyst. Surprisingly, quantitative yields of both 3aa and 3ba from la and lb were observed (Table 1, entry 13 and 16). The Shvo catalyst (Cat 2) has been well studied in a variety of reactions including transfer hydrogenation. However, its ability to promote N-alkylation of amines with alcohols has not been suggested.

EXAMPLE 2: Retention of chirality of starting materials.

One important requirement for a method designed for the modification of amino acids is the retention of the valuable chiral information contained in the starting material. Enantiomeric excess (ee) is a measurement of purity used for chiral substances. It reflects the degree to which a sample contains one enantiomer in greater amounts than the other. A racemic mixture has an ee of 0%, while a single completely pure enantiomer has an ee of 100%. In this example the enantiomeric excess (ee) of the N-alkylation products was investigated (Scheme 1, Table 2).

Scheme 1. N-ethylation, iso-propylation of amino acids

General reaction conditions: General procedure 0.2 mmol 1, 4 - 5 ml 2, 1 mol % Cat 2, neat when using ethanol (2a), 1 ml CF3CH2OH (2d) when using tPrOH (2b), 18 - 28 h, 90 °C, yields are based on crude H NMR and mass balance, ee was measured through corresponding amide, unless otherwise specified; ^aee was measured through corresponding methyl ester; ⁶47h; ^cneat;

was used instead of 2d; ^eMeOH (2c) was used instead of 2d; 2 mol % Cat 2 was used; «100 °C;

isolated yield. For details see Table 2 and 3.

Table 2: Direct N-ethylation of free amino acid (1) with ethanol (2a) and the ee retention.

Entry 1 [mmol] 2a T. [h] Temp. Conv. 1 Sele. 3 [%] ^a ee [%]^b

[ml] [°C] [%]^a

1 la L-Proline / 0.2 5 18 90 >99 3aa >99 (99) 93.2

2^e la L-Proline / 0.5 5 18 90 >99 3aa >99 (99) 99.2

3 lb L-Leucine / 0.2 5 18 90 >99 3ba >99 (99) 98.5 lb L-Leucine / 0.5 4 42 110 >95 3ba (49) 79.7

5 lc L-Valine / 0.2 5 18 90 >99 3ca 55 n.d.

6 lc L-Valine / 0.2 5 24 90 >99 3ca >99 99.5

7 Id L-Phenylalanine / 5 18 90 >99 3da >99 97.2^C

0.2

8* Id L-Phenylalanine / 4 42 110 >90 3da (55) 72.0

0.5

9 le L-Serine / 0.2 5 18 90 >99 3ea >99 86.1

10 If L-Alanine / 0.2 5 18 90 >99 3fa >99 84.1

11 If L-Alanine / 0.2 5 47 60 >99 3fa >99 85.6 12 ig Glycine / 0.2 5 18 90 >99 3ga >99

13 lh Lysine 5 18 90 <1% 3ha /

14d lh Lysine 4 18 100 <1% 3ha /

15 li N⁶-Ac-lysine 5 18 90 >99 3ia <5%

16^d li N⁶-Ac-lysine 4 18 90 >99 3ia (74)

General reaction conditions: General procedure (see page S2), 0.2 mmol 1, 5 ml 2a, 1 mol % Cat 2, neat, 18 - 47 h, 60 or 90 °C, unless otherwise specified, isolated yields in parenthesis; Conversion and selectivities are based on crude H NMR; ^bee was measured through corresponding amide unless otherwise specified, see page S55 for detains of ee determination; ^cee was measured through

corresponding methyl ester; ^dl ml CF3CH2OH was added; ^e5 mol % Cat lb was used instead of Cat 2.

As can be seen in Table 2, Cat lb gave 3aa quantitative yield with 99.2 % ee retention, 3ba 45 % yield with 79.7 % ee retention (Table 2, entry 2 and 4). At the meantime, Cat 2 gave both 3aa and 3ba quantitative yields as described, with retention of ee of 93.2 % and 98.5 %, respectively (Table 2, entry 1 and 3). Phenylalanine (Id) was selected to react with 2a, catalyzed by both Cat lb and Cat 2 for further comparison. Cat lb gave 3da 55 % yield with 72.0 % ee retention, and Cat 2 gave 3da quantitative yield with 97.2 % ee retention (Table 2, entry 7 and 8). Thus Cat 2 was chosen for the further investigation.

Then, other ct-amino acids including valine (lc), serine (le) and alanine (If) were evaluated. Quantitative yields of corresponding di-ethylation products 3ca, 3ea and 3fa were obtained, with the retention of ee of 99.5, 86.1 and 84.1 %, respectively (Table 2, entry 6, 9 and 10). The racemization in the latter cases was probably due to the activity of the Shvo catalyst in the dehydrogenation/rehydrogenation of amines. A lower steric hindrance on the chiral carbons of 3ea and 3fa compared to 3ca presumably allows for easier dehydrogenation/rehydrogenation of amines. In order to improve the ee retention of 3fa, the temperature was lowered to 60°C from 90°C while prolonging the reaction time. A quantitative yield of 3fa was obtained, whereas the ee of the final product was improved slightly to 85.6 % (Table 2, entry 11).

Continuing exploring the reaction scope, the simplest ct-amino acid glycine (lg), also gave quantitative yield of N,N-di-ethyl-glycine (3ga) (Table 2, entry 12). On the other hand, lysine (3h) was unreactive, whereas N6-acetyl- lysine (3i) give 74 % yield of corresponding N2,N2-di-ethylation product 3ia (Table 2, entry 13 - 16). The above results clearly showed that all primary amino acids selectively gave di-N,N-ethylated products when reacted with 2a in neat condition.

EXAMPLE 3: N-alkylation using a secondary alcohol.

Following the results of N-ethylation of cc-amino acids with 2a, the secondary alcohol isopropanol (2b) was used applied to alkylate cc-amino acids (Scheme 2, Table 3).

Under neat conditions, 2a was quantitatively converted to N-isopropyl- proline (3ab) (Table 3, entry 1). However, in case of phenylalanine (Id), no significant formation of corresponding N-alkyl amino acid was observed due to the poor solubility of Id in isopropanol (2b). This prompted us to investigate using solvent like H₂O, MeOH (2c) or CFsCI^OH¹ (2d). While H2O or 2c gave a less satisfactory improvement, surprisingly, the use of 2d gave quantitative yield of N-isopropyl-phenylalanine (3db) (Table 3, entry 3 - 9). Only the mono alkylation product was observed in this case, probably due the steric hindrance created after the insertion of the first isopropyl- moiety inhibited the second alkylation step. Table 3: Direct mono N-isopropylation of amino acid (1) with isopropanol (2b).

Entry 1 [mmol] 2b Sol. T. Conv. 1 Sele. 3 [%]^a

[ml] [ml] [h] [%]^«

Ϊ la Proline / 0.2 2 / 18 >99 3cb >99 ^"

(99)

2^b la Proline / 0.5 2 / 16 88 n.d.

3 Id Phenylalanine / 5 / 18 <5 n.d.

0.2

4 Id Phenylalanine / 4.5 H₂0 45 <1 n.d.

0.2 0.5

5 Id Phenylalanine / 4.5 2c 0.5 45 15 n.d.

0.2

6 Id Phenylalanine / 4 2c 1 18 12 n.d.

0.2

7 Id Phenylalanine / 4 2c 1 18 85 n.d.

0.2

8 Id Phenylalanine / 3 2c 2 18 10 n.d.

0.2

9 Id Phenylalanine / 4 2d 1 24 >99 3db >99

0.2 (99)

10 lb Leucine / 0.2 5 / 18 <5 n.d.

11 lb Leucine / 0.2 4 2d 1 24 40 n.d.

12^c lb Leucine / 0.2 4 2d 1 28 >99 3bb >99

(99) 13 lb Leucine / 0.2 4 2d 1 42 <5 n.d.

14 lc Valine / 0.2 5 / 18 <5 n.d.

15 lc Valine / 0.2 4 2d 1 24 >99 3cb >99

(99)

16 le Serine / 0.2 5 / 18 <5 n.d.

17 le Serine / 0.2 4 2d 1 24 15 n.d.

18^c le Serine / 0.2 4 2d 1 24 40 n.d.

19^d le Serine / 0.2 4 2d 1 24 >99 3eb >99

(99)

20 If Alanine / 0.2 5 / 18 <5 n.d.

21 If Alanine / 0.2 4 2d 1 24 67 n.d.

52 If Alanine / 0.2 4 2d 1 28 >99 3fb >99

(99)

General reaction conditions: General procedure 0.2 or 0.5 mmol 1, 2 - 5 ml 2b, neat or with solvent (amount shown in the table), 1 mol % Cat 2, 16 - 28 h, 90°C, unless otherwise specified, isolated yields in parenthesis; Conversion and selectivities are based on crude H NMR; ^b4 mol % Cat lb was used instead of Cat 2; <=2 mol % Cat 2 was used; ^100 °C.

Following the same procedure, amino acids lb, lc, le and If were also successfully mono-isopropylated, forming 3bb, 3cb, 3eb and 3fb in quantitative yields, respectively (Table 3, entry 10 - 22). This method is advantageously used to easily obtain mono-N-alkylated amino acids (non- proteinogenic amino acids) e.g. for the synthesis of modified proteins with higher lipophilicity. Scheme 2. N-alkylation of amino acids and N-terminus of peptides with various alcohols.

General reaction conditions: General procedure, 0.2 or 0.5 mmol 1, 1 - 4 ml or 0.6 - 2 mmol 2, neat or 2d/tol as solvent, 1 mol % Cat 2, 18 - 24 h, 90 °C, isolated yields are shown, unless otherwise specified; "yields are base crude H MNR and mass balance; ⁶100 °C. For details see Table 4 and 5. After exploring the reactivity of various cc-amino acids with ethanol (2a) and isopropanol (2b), diverse alcohols were tried (Scheme 2, Table 4). As previously shown, MeOH (2c) or CF3CH2OH (2d) did not react with la, probably because they were not prone to be dehydrogenated under the present reaction conditions, which allowed for the possibility of using 2c or 2d as solvent. For other alcohol substrates such as 1-butanol (2e),

cyclopropylmethanol (2f) and 2-chloroethanol (2g), employed in the reaction with la, resulted in quantitative yield of 3ea, 55 % of 3af, and 71 % of 3ag, respectively (Table 4, entry 3 - 5). Also, benzyl alcohol (3h) and 4- chlorobenzyl alcohol (3i) were successfully applied to benzylate la with good yields of 68 % and 82 % (Table 4, entry 6 and 7). Here it needs to be pointed out that, the chloro- group on 3ag and 3ai would allow the further

functionalization of the obtained amino acid derivatives. Subsequently, the use of other amino acids such as phenylalanine (Id) and glycine (lg) were examined. Id reacted with 1-butanol (2e) to give 84 % yield of 3de (Table 4, entry 8). Surprisingly, instead of forming a 6-membered heterocycle, the reaction of Id with 1,5-pentane-diol (2k) gave a 35% yield of the di-alkylated 3dk as the major product (Table 4, entry 9). The introduced 2-hydroxyl groups on 3dk can not only be exploited for further functionalization, but also dramatically increase the hydrophilicity of the product.

Next, the functionalization of lg with various alcohols was further explored. Upon reaction with 3h the di-benzylation product 3gh was obtained in 52 % yield while when secondary alcohol 2-butanol (21) was employed to alkylate lg, selective formation of mono-alkylated product 3gl was obtained in quantitative yield (Table 4, entry 10 and 12). Table 4: Direct N-alkylation of free amino acid (1) with various alcohols (2).

Entry 1 [mmol] 2 Sol. T. Temp. Conv. Sele. 3 [%]^«

[ml] [h] [°C] 1 [%]^a

1 la Proline / 0.2 2c MeOH / 2 / 18 90 <1 3ac / ml

2 la Proline / 0.2 2d CF3CH2OH / / 18 90 <1 3ad /

2 ml

3 la Proline / 0.2 2e nBuOH / 2 / 24 90 >99 3ae >99 ml

4 la Proline / 0.5 2f / 18 90 >99 3af (55)

OH / 5

ml

5 la Proline / 0.2 2g ^CI^OH / 2 / 18 90 >99 3ag (71) ml

6 la Proline / 0.2 2h BnOH / 2 ml / 18 90 >99 3ah (68)

7 la Proline / 0.5 2i l. 20 90 >99 3ai (82)

2 mmol

8 Id Phenylalanine 2e nBuOH / 4 2d 2 24 90 >99 3de (84)

/ 0.5 ml

9 Id Phenylalanine 2j 1-nonanol / 2d/tol 24 90 >99 3dj (75)

/ 0.5 1 ml 2/2

10 Id Phenylalanine 2k 1,5- 2d/tol 18 100 >99 3dk (35)

/ 0.2 pentanediol 2/3

/ 2 mmol

12 ig Glycine / 0.5 2h BnOH / 2 2d/tol 18 90 / 3gh (52) mmol 2/3

13 ig Glycine / 0.5 2j 1-nonanol / 2d/tol 24 90 >99 3gj (91)

2 mmol 2/3

14 ig Glycine / 0.2 21 2-butanol / 4 2d 1 24 90 >99 3gl >99 ml

15 ig Glycine / 0.5 2m 1-pentanol / 2d/tol 18 90 >99 3gm (90)

2 mmol 2/3

16 ig Glycine / 0.5 2m 1-pentanol / 2d/tol 18 90 >99 3gm' (46)

0.6 mmol 2/3 3gm (29)

17 ig Glycine / 0.5 2n 1-dodecanol 2d/tol 18 90 >99 3gn (92)

/ 2 mmol 2/3

General reaction conditions: General procedure, 0.2 or 0.5 mmol 1, 0.6 - 2 mmol or 2 - 5 ml 2, neat or with solvent (amount shown in the table), 1 mol % Cat 2, 16 - 24 h, 90 or 100°C, isolated yields in parenthesis; "Conversion and

selectivities are based on crude H NMR. After this, the possibility of mono-alkylation with primary alcohols was also investigated. Using 4 eq. of 1-pentanol (lm), lg was successfully di- alkylated giving 90 % of 3gm. When the amount of lm was decreased to 1.2 eq., 46 % mono-alkylated product 3gm' was obtained, only giving 29 % of the di-alkylated product 3gm (Table 4, entry 15 and 16). As 3gm' is more basic than 3g, without enough steric hindrance on the nitrogen atom, the second alkylation step occurred immediately once 3gm' formed. Thus, mono-N- alkylated amino acids can be obtained from primary amino acids and primary alcohols, but with low selectivity.

Long-chain N-alkylated amino acids are widely used in surfactants, among which N-alkylated amino acids are not well studied because they are relatively difficult to be synthetized9. Envisioning the possibility of easily synthetizing long-chain N-alkylated amino acids with our methodology, 1- nonanol (2j) was selected to react with Id and lg. Di-alkylated compounds 3dj and 3gj were selectively obtained with good to excellent yields of 75 % and 91 %, respectively (Table 4, entry 9 and 13). The reaction also readily proceeded with 1-dodecanol (In) and lg as substrate, obtaining the corresponding product 3gn in an excellent yield of 92 % (Table 4, entry 17).

EXAMPLE 4: Direct N-alkylation of oligopeptides with alcohol.

Encouraged by the promising results with the functionalization of amino acids, we attempted the extension of this novel method to simple free oligopeptides, which possess similar physical properties and functional groups as the corresponding amino acids (Scheme 2, Table 5). First, the simple dipeptide glycylalanine (4a) was chosen to react with 2a.

Surprisingly, the corresponding di-ethylated product 5aa was obtained quantitatively (Table 5, entry 1). Based on this protocol, the hydrophobicity or hydrophobicity of peptides can be modulated by introducing either longer chain alkyl groups or more polar moieties such as hydroxyl groups. Indeed, when 1-dodecanol (2n) was reacted with dipeptide 4a, the corresponding dialkylated product 5an was obtained in 62 % yield (Table 5, entry 3). This type of lipophilic dipeptide can be used for transporting metal ions across membranes6. On the other hand, the reaction of diol 2k with 4a, afforded 36 % 5ak, bearing extra hydroxyl groups (Table 5, entry 2).

Following the successful and diverse functionalization of a dipeptide, a tri- peptide leucylglycylclycine (4b) was tested in the reaction with 2a, which resulted in the formation of the corresponding di-ethylated product 5ba in 67% yield (Table 5, entry 4 and 5). The above reactions represent the first example of the selective di-alkylation of unprotected oligopeptide substrates on their N-terminus using simple alcohols, allowing for good product yields and easy purification. This methodology can promote the protein N- terminus modification that affecting protein activation, conversion and degradation, further diversifying biological functions .

Table 5: Direct N-alkylation of free peptide (4) with alcohols (2).

Entry 4 [mmol] Sol. T. Temp. Conv. Sele. 5

[ml] [h] [°C] 4 [%]^a [%]^«

1 4a

H₂N^ 2a ethanol / 5 / 24 90 >95 5aa >95

0 ^{1 C00H} / ml (95)

0.2

2 4a 2k 1,5- 2d/tol 24 90 n.d. 5ak (36)

H₂N^ 0 ^{1 C00H} / pentanediol 2/3

0.5 / 2 mmol

0.5 2 mmol

4 4b anol / 5 / 24 90 n.d. 5ba (50)

5 4b anol / 5 2d 2 18 90 n.d. 5ba (67)

0.5

General reaction conditions: General procedure, 0.2 or 0.5 mmol 4, 2 mmol or 5 ml 2, neat or with solvent (amount shown in the table), 1 mol %

Cat 2, 18 or 24 h, 90°C, isolated yields in parenthesis; "Conversion and selectivities are based on crude H NMR. EXAMPLE 5: Synthesis of surfactants from natural amino acids and fatty alcohols.

Realizing that chirality is not an essential property for surfactant, the Fe- based Cat lb was employed for direct synthesis of surfactants from natural amino acids with fatty alcohols (Figure 1; Table 6).

General reaction conditions: General procedure, 0.5 mmol 1, 1 ml or 2 mmol 2, neat or 3 ml 2d as solvent, 5 mol % Cat lb, 24 h, 110°C, isolated yields are shown; "The products were isolated as corresponding methyl ester. For details see Table 6.

Glycine (lg) and 1-dodecanol (2n) were tried under 110 oC for 24 h with 5 mol % Cat lb. Surprisingly, 54 % mono-N-dodecylglycine (3gn') and 8 % Ν,Ν-didodecylglycine (3gn) were isolated (Table 6, entry 1). The inherent property of Cat lb leads to preferentially formation of mono-N-alkyl amino acids, which are one typical type of amino acid based surfactant9. After adding KOH and H2O to 3gn', a rich foam formation was clearly seen (Figure 1), indicating its amphiphilic property.

Table 6: Direct synthesis of amphiphiles through iron catalyzed N- alkylation of free amino acid (1) with fatty alcohols (2).

3

Entry 1 [mmol] 2 yield 3 [%]

1 Glycine / 0.5 2n 1-dodecanol / 54 Glycine (lg) and 1-dodecanol (2n) were tried under 110 oC for 24 h with 5 mol % Cat lb. Surprisingly, 54 % mono-N-dodecylglycine (3gn') and 8 % Ν,Ν-didodecylglycine (3gn) were isolated (Table 6, entry 1). The inherent property of Cat lb leads to preferentially formation of mono-N-alkyl amino acids, which are one typical type of amino acid based surfactant9. After adding KOH and H2O to 3gn', a rich foam formation was clearly seen (Scheme 3), indicating its amphiphilic property.

Entry 1 [mmol] 2 yield 3 [%]

1 lg Glycine / 0.5 2n 1-dodecanol / 3gn' 54

1 ml

3gn 8

2 lg Glycine / 0.5 2j 1-nonanol / 1 3gj' 51

ml

3 lg Glycine / 0.5 2o 1-decanol / 1 3go' 69

ml

4^» lg Glycine / 0.5 2p 1- 3gp' 32

tetradecanol

/ 2 mmol

4^« lg Glycine / 0.5 2q 1-hexadecano 3gq' 38

2 mmol

5° lg Glycine / 0.5 2r 1- 3gr' 39

octadecanol /

2 mmol 6 lg Alanine / 2n 1-dodecanol / 3gn' 49

0.5 1 ml

7 la Proline / 0.5 2j 1-nonanol / 1 3aj 52

ml

General reaction conditions: General procedure (see page S2), 0.5 mmol 1, 1 ml or 2 mmol 2, 3 ml CF3CH2OH, 5 mol % Cat 2b, 24 h, 110°C, isolated yields are shown; "The products were isolated as corresponding methyl ester.

Later on, various biomass derived fatty alcohols including 1-nonanol (2j), 1- decanol (2o), 1-tetradecanol (2p), 1-hexadecanol (2q) and 1-octadecanol (2n) were react3e with lg, and 32 - 69 % yields of corresponding mono-N-alkyl glycine 3gj', 3go', 3gp', 3gq' and 3gr' were isolated (Table 6, entry 2 - 5).

Alanine (If) and proline (la) were reacted with 1-dodecanol (2n) and 1- nonanol (2j), with 5 mol % Cat lb, 49 % of 3fn' and 52 % of 3aj were isolated respectively (Table 6, entry 6 and 7). Long-chain alcohols can be easily produced from natural fats and oils. The present findings open up important possibilities for the fully sustainable production of long-chain N-alkyl amino acid based surfactants completely from biomass, with iron based catalyst.

Spectral data of isolated compounds

N-ethyl-proline (3aa): Synthesized according to General procedure.

Quantitative yield has been obtained according to crude H NMR. Ή NMR (400 MHz, D₂0) δ 3.83 - 3.96 (m, 1H), 3.64 - 3.78 (m, 1H), 3.15 - 3.33 (m, 2H), 3.05 - 3.15 (m, 1H), 2.35 - 2.52 (m, 1H), 1.99 - 2.16 (m, 2H), 1.85 - 1.99 (m, 1H), 1.27 (t, J = 7.28 Hz, 3H). ¹³C NMR (100 MHz, MeOD) δ 173.46, 70.13, 55.45, 51.51, 30.32, 24.34, 11.31. HRMS (APCI+, m/z): calculated for C7H14NO2 [M+H]+: 144.10191; found: 144.10181. The physical data matches previous report.

N,N-di-ethyl-leucine (3ba): Synthesized according to General

procedure. Quantitative yield has been obtained according to crude H NMR. Ή NMR (400 MHz, D₂0) δ 3.58 - 3.67 (m, 1H), 3.08 - 3.30 (m, 4H), 1.67 - 1.78 (m, 1H), 1.51 - 1.67 (m, 2H), 1.26 (t, J = 5.24 Hz, 6H), 0.83 - 1.00 (m, 6H). ¹³C NMR (100 MHz, D₂0) δ 176.34, 68.56, 48.14 (br.s), 38.83, 27.77, 25.52, 23.04, 11.13 (br.s). HRMS (APCI+, m/z): calculated for C10H20NO2 [M- H]-: 186.14886; found: 186.15012.

N,N-di-ethyl-valine (3ca): Synthesized according to General procedure. Quantitative yield has been obtained according to crude H NMR. Ή NMR (400 MHz, D₂0) δ 3.45 - 3.52 (m, 1H) 3.05 - 3.35 (m, 4H), 2.22 - 2.40 (m, 1H), 1.15 - 1.40 (m, 6H), 0.99 - 1.10 (m, 3H), 0.86 - 0.99 (m, 3H) ¹³C NMR (100 MHz, D₂0) δ 174.31, 74.85, 49.85, 45.30, 28.02, 22.22, 18.81, 11.73, 9.62. HRMS (APCI+, m/z): calculated for C9H20NO2 [M+H]+: 174.14886; found: 174.14879.

N,N-di-ethyl-phenylalanine (3da): Synthesized according to General procedure. Quantitative yield has been obtained according to crude H NMR. Ή NMR (400 MHz, D₂0) δ 7.12 - 7.43 (m, 5H), 3.80 - 3.93 (m, 1H), 3.08 - 3.40 (m, 4H), 2.98 - 3.31 (m, 2H), 1.17 - 1.33 (m, 6H). ¹³C NMR (100 MHz, D₂0) δ 172.37, 135.44, 129.06, 128.80, 127.28, 67.81, 45.70 (br.s), 33.44, 8.42 (br.s). HRMS (APCI+, m/z): calculated for Ci₃Hi₈N0₂ [M-H]-: 220.13321 found: 220.13433.

N,N-di-ethyl-serine (3ea): Synthesized according to General procedure.

Quantitative yield has been obtained according to crude H NMR. Ή NMR (400 MHz, D₂0) δ 3.98 - 4.18 (m, 2H), 3.79 - 3.91 (m, 1H), 3.37 - 3.52 (m, 1H), 3.18 - 3.37 (m, 3H), 1.18 - 1.40 (m, 6H). ¹³C NMR (100 MHz, D₂0) δ 173.91, 69.38, 60.55, 50.29, 47.45, 11.81, 10.96. HRMS (APCI+, m/z):

calculated for C7H14NO3 [M-H]-: 160.09682; found: 160.09811.

N COOH N,N-di-ethyl-alanine (3ea): Synthesized according to General

procedure. Quantitative yield has been obtained according to crude H NMR. Ή NMR (400 MHz, D₂0) δ 3.77 - 3.92 (m, 1H), 3.19 - 3.39 (m, 2H), 3.00 - 3.20 (m, 2H), 1.38 - 1.52 (m, 3H), 1.17 - 1.37 (m, 6H). ¹³C NMR (100 MHz, D₂0) δ 174.31, 61.46, 47.04, 44.97, 11.47, 9.29, 8.32. HRMS (APCI+, m/z): calculated for C7H16NO2 [M+H]+: 146.11756; found: 146.11746. N COOH

N,N-di-ethyl-glycine (3ga): Synthesized according to General

procedure. Quantitative yield has been obtained according to crude H NMR. Ή NMR (400 MHz, D₂0) δ 3.66 (s, 2H). 3.22 (q. J = 7.31 Hz, 4H), 1.26 (t. J = 7.32 Hz, 6H). ¹³C NMR (100 MHz, D₂0) δ 173.50, 57.36, 52.14, 52.11, 11.13. HRMS (APCI+, m/z): calculated for C₆Hi₄N02 [M+H]+: 132.10191; found: 132.10180.

N⁶-acetyl-N²,N²-di-ethyl-lysine (3ha): Synthesized according to General procedure. N⁶-acetyl-lysine (0.094 g, 0.50 mmol) affords 3ha (0.090 g, 75% yield). White solid was obtained after column chromatography (S1O2,

EtOAc/MeOH 80:20 to 50:50).. Ή NMR (400 MHz, D₂0) δ 4.02 - 4.13 (m, 1H), 2.96 - 3.08 (m, 4H), 2.82 - 2.96 (m, 2H), 1.97 (s, 3H), 1.70 - 1.84 (m, 1H), 1.51 - 1.70 (m, 3H), 1.25 - 1.38 (m, 2H), 1.07 - 1.24 (m, 6H). ¹³C NMR (100 MHz, D₂0) δ 181.63, 176.06, 57.47, 54.04, 49.59, 33.75, 25.86, 25.15, 24.49, 11.12. HRMS (APCI+, m/z): calculated for C12H25N2O3 [M+H]+:

245.18597; found: 245.18593.

N-isopropyl-proline (3ab): Synthesized according to General procedure.

Quantitative yield has been obtained according to crude H NMR. Ή NMR (400 MHz, D₂0) δ 3.93 - 4.05 (m, 1H), 3.62 - 3.72 (m, 1H), 3.47 - 3.61 (m, 1H), 3.13 - 3.26 (m, 1H), 2.29 - 2.44 (m, 1H), 2.00 - 2.15 (m, 2H), 1.79 - 1.97 (m, 1H), 1.20 - 1.40 (m, 6H). ¹³C NMR (100 MHz, D₂0) δ 174.53, 65.80, 56.99, 52.28, 29.59, 23.59, 17.39, 17.26. HRMS (APCI+, m/z): calculated for C₈Hi6N0₂ [M+H]+: 158.11756; found: 158.11747.

N-isopropyl-phenylalanine (3db): Synthesized according to General procedure. Quantitative yield has been obtained according to crude H NMR. Ή NMR (400 MHz, D₂0) δ 6.87 - 7.24 (m, 5H), 3.24 - 3.34 (m, 1H), 2.71 - 2.80 (m, 1H), 2.45 - 2.65 (m, 2H), 0.74 - 0.93 (m, 6H). ¹³C NMR (100 MHz, D₂0) δ 181.45, 137.84, 129.08, 128.33, 126.40, 62.55, 45.96, 39.09, 22.57, 19.72. HRMS (APCI+, m/z): calculated for Ci₂Hi₈N0₂ [M+H]+:

ound: 208.13312.

N-isopropyl-leucine (3bb): Synthesized according to General

procedure. Quantitative yield has been obtained according to crude H

NMR. Ή NMR (400 MHz, D₂0-NaOH) δ 3.08 - 3.21 (m, 1H), 2.52 - 2.66 (m, 1H), 1.37 - 1.54 (m, 1H), 1.16 - 1.35 (m, 2H), 0.86 - 1.05 (m, 6H), 0.68 - 0.86 (m, 6H). ¹³C NMR (100 MHz, D₂0) δ 177.15, 61.65, 53.02, 42.23, 27.09, 24.64, 23.83, 21.72, 20.32. HRMS (APCI+, m/z): calculated for C₉H₂₀NO₂ [M+H]+: 174.14886; found: 174.14872.

N-isopropyl-valine (3cb): Synthesized according to General procedure.

Quantitative yield has been obtained according to crude H NMR. Ή NMR (400 MHz, D₂0) δ 3.09 - 3.20 (m, 1H), 2.82 - 2.96 (m, 1H), 1.81 - 2.00 (m, 1H), 0.99 - 1.25 (m, 6H), 0.85 - 0.98 (m, 6H). ¹³C NMR (100 MHz, D₂0) δ 181.45, 69.24, 51.18, 32.88, 23.89, 21.59, 21.17, 20.60. HRMS (APCI+, m/z): calculated for C₈Hi₈N0₂ [M+H]+: 160.13321; found: 160.13307.

N-isopropyl-serine (3eb): Synthesized according to General procedure

Quantitative yield has been obtained according to crude H NMR. Ή NMR (400 MHz, D₂0) δ 3.85 - 4.01 (m, 2H), 3.72 - 3.79 (m, 1H), 3.38 - 3.52 (m, 1H), 1.24 - 1.36 (m, 6H). ¹³C NMR (100 MHz, D₂0) δ 174.36, 63.67, 62.42, 53.03, 21.26, 21.24, 20.58. HRMS (APCI+, m/z): calculated for CeHwNOs [M+H]+: 148.09682; found: 148.09671.

HN COOH

N-isopropyl-alanine (3fb): Synthesized according to General procedure. Quantitative yield has been obtained according to crude H NMR. Ή NMR (400 MHz, D₂0) δ 3.71 - 3.80 (m, 1H), 3.38 - 3.50 (m, 1H), 1.42 - 1.53 (m, 3H), 1.26 - 1.37 (m, 6H). ¹³C NMR (100 MHz, D₂0) δ 177.76, 57.76, 52.17, 21.17, 20.71, 18.14. HRMS (APCI+, m/z): calculated for C₆Hi₄N02 [M+H]+: 132.10191; found: 132.10181.

N-n-butyl-proline (3ae): Synthesized according to General procedure.

Quantitative yield has been obtained according to crude H NMR. Ή NMR (400 MHz, MeOD) δ 3.78 - 3.90 (m, 1H), 3.65 - 3.78 (m, 1H), 3.15 - 3.27 (m, 1H), 2.95 - 3.15 (m,2H), 2.30 - 2.46 (m, 1H), 1.99 - 2.15 (m, 2H), 1.82 - 1.98 (m, 1H), 1.56 - 1.76 (m, 2H), 1.30 - 1.47 (m, 2H), 0.83 - 1.04 (m, 3H). ¹³C NMR (100 MHz, MeOD) δ 173.50, 70.60, 56.38, 55.95, 30.30, 28.94, 24.34, 20.88, 13.96. HRMS (APCI+, m/z): calculated for C₉Hi₆NO₂ [M-H]-:

170.11756; found: 170.11876.

N-cyclopropylmethyl-proline (3fb): Synthesized according to General procedure. Proline (0.058 g, 0.50 mmol) affords 3fb (0.046 g, 55% yield). White solid was obtained after column chromatography (S1O2, EtOAc/MeOH 80:20 to 80:20). Ή NMR (400 MHz, CDCI3) δ 3.83 - 4.01 (m, 1H), 3.67 - 3.83 (m, 1H), 2.98 -3.14 (m, 1H), 2.70 - 2.95 (m, 2H), 2.22 - 2.38 (m, 1H), 2.05 - 2.22 (m, 1H), 1.86 - 2.05 (m, 2H), 0.95 - 1.09 (m, 1H), 0.49 - 0.70 (m, 2H), 0.18 - 0.40 (m, 2H). ¹³C NMR (100 MHz, CDCI3) δ 170.64, 68.63, 59.14, 53.96, 29.01, 23.06, 6.63, 4.45, 4.06. HRMS (APCI+, m/z): calculated for C9H14NO2 [M-H]-: 168.10191; found: 168.10321.

N-(2-chloroethyl)-proline (3ag): Synthesized according to General procedure. Proline (0.058 g, 0.50 mmol) affords 3ag (0.063 g, 71% yield). White solid was obtained after crystallization in MeOH/Et₂0. Ή NMR (400 MHz, D₂0) δ 4.45 - 4.65 (m, 3H), 3.76 - 3.93 (m, 2H), 3.33 - 3.54 (m, 2H), 2.38 - 2.55 (m, 1H), 2.15 - 2.32 (m, 1H), 1.97 - 2.14 (m, 2H). ¹³C NMR (100 MHz, D₂0) δ 169.50, 66.38, 59.35, 46.16, 41.59, 28.06, 23.07. HRMS (APCI+, m/z): calculated for C7H13CINO2 [M+H]+: 178.06293; found: 178.06289.

N-benzyl-proline (3ah): Synthesized according to General procedure. Proline (0.019 g, 0.20 mmol) affords 3ah (0.028 g, 68% yield). White solid was obtained after crystallization in Et₂0. Ή NMR (400 MHz, CDC1₃) δ 9.33 (br.s, 1H), 7.28 - 7.52 (m, 5H), 4.11 - 4.37 (m, 2H), 3.74 - 3.90 (m, 1H), 3.59 - 3.74 (m, 1H), 2.78 - 2.94 (m, 1H), 2.17 - 2.38 (m, 2H), 1.79 - 2.08 (m, 2H). ¹³C NMR (100 MHz, CDCI3) δ 171.02, 130.73, 130.53, 129.40, 129.04, 67.31, 57.61, 53.31, 28.89, 22.89. HRMS (APCI+, m/z): calculated for Ci₂Hi₆N0₂ [M+H]+: 206.11756; found: 206.11742.

N-(4-chloro-benzyl)-proline (3ai): Synthesized according to General procedure. Proline (0.058 g, 0.50 mmol) affords 3ai (0.098 g, 82% yield).

White solid was obtained after column chromatography (Si0₂, EtOAc/MeOH 90:10 to 50:50). H NMR (400 MHz, D₂0) δ 7.28 - 7.48 (m, 4H), 4.12 - 4.34 (m, 2H), 3.75 - 3.88 (m, 1H), 3.41 - 3.54 (m, 1H), 3.03 - 3.18 (m, 1H), 2.31 - 2.48 (m, 1H), 1.80 - 2.09 (m, 3H). ¹³C NMR (100 MHz, D₂0) δ 176.56, 137.60, 134.51, 131.87, 131.63, 70.76, 59.87, 56.86, 31.30, 25.17. HRMS (APCI+, m/z): calculated for Ci₂Hi₅ClN0₂ [M+H]+: 240.07858; found:

240.07854.

N,N-(di-n-butyl)-phenylalanine (3de): Synthesized according to General procedure. Phenylalanine (0.083 g, 0.50 mmol) affords 3de (0.116 g, 84% yield). White solid was obtained after column chromatography (Si0₂,

EtOAc/MeOH 90:10 to 80:20). Ή NMR (400 MHz, CDCI3) δ 9.36 (br.s, 1H), 7.10 - 7.35 (m, 5H), 3.83 - 3.94 (m, 1H), 3.42 - 3.56 (m, 1H), 2.88 - 3.07 (m, 3H), 2.70 - 2.85 (m, 2H), 1.52 - 1.67 (m, 2H), 1.36 - 1.52 (m, 2H), 1.05 - 1.27 (m, 4H). ¹³C NMR (100 MHz, CDC1₃) δ 170.49, 137.88, 128.76, 128.55, 126.65, 67.49, 51.45, 33.82, 26.82, 19.90, 13.49. HRMS (APCI+, m/z):

7H26NO2 [M-H]-: 276.19581; found: 276.19703.

N,N-(di-n-nonyl)-phenylalanine (3dj): Synthesized according to General procedure. Phenylalanine (0.083 g, 0.50 mmol) affords 3dj (0.147 g, 75% yield). White solid was obtained after column chromatography (S1O2, Pentane/EtOAc 50:50 to 0:100, then EtOH/MeOH 90/10). H NMR (400 MHz, CDCI3) δ 8.68 (br.s, 1H), 7.13 - 7.31 (m, 5H). 3.84 - 3.93 (m, 1H), 3.50 - 3.58 (m, 1H), 2.88 - 3.05 (m, 3H), 2.67 - 2.79 (m, 2H), 1.53 - 1.67 (m, 2H), 1.38 - 1.52 (m, 2H), 0.98 - 1.35 (m, 24H), 0.75 - 0.89 (m, 6H). ¹³C NMR (100 MHz, CDCI3) δ 170.49, 138.02, 128.75, 128.59, 126.67, 67.41, 51.76, 33.71, 31.67, 29.30, 29.05, 29.03, 26.70, 25.07, 22.50, 13.94. HRMS (APCI+, m/z): calculated for C27H48NO2 [M-H]-: 418.36796; found: 418.36763.

N,N-di-(5-hydroxypentyl)-phenylalanine (3dk): Synthesized according to General procedure. Phenylalanine (0.083 g, 0.50 mmol) affords 3dk (0.059 g, 35% yield). White solid was obtained after column chromatography (S1O2, EtOAc/MeOH 50:50 to 30:70). Ή NMR (400 MHz, D₂0) δ 7.23 - 7.45 (m, 5H), 3.91 - 4.03 (m, 1H), 3.47 - 3.65 (m, 4H), 3.13 - 3.32 (m, 4H), 2.95 - 3.13 (m, 2H), 1.58 - 1.79 (m, 4H), 1.45 - 1.58 (m, 4H), 1.21 - 1.43 (m, 4H). ¹³C NMR (100 MHz, D₂0) δ 172.40, 135.73, 128.94, 128.85, 127.27, 68.29, 61.15, 33.38, 30.56, 23.33, 22.13. HRMS (APCI+, m/z): calculated for

C19H32NO4 [M+H]+: 338.23258; found: 338.23176.

N,N-di-n-nonyl-glycine (3gj): Synthesized according to General procedure. Glycine (0.038 g, 0.50 mmol) affords 3gj (0.149 g, 91% yield). White solid was obtained after column chromatography (S1O2, EtOAc/MeOH 90:10 to 70:30). Ή NMR (400 MHz, CDCI3) δ 8.78 (br.s, 1H), 3.48 (s, 2H), 2.95 - 3.15 (m, 4H), 1.52 - 1.75 (m, 4H), 1.03 - 1.42 (m, 24H), 0.65 - 0.95 (m, 6H). ¹³C NMR (100 MHz, CDCI3) δ 167.42, 55.99, 53.92, 31.63, 29.26, 29.03, 28.99, 26.66, 23.71, 22.47, 13.90. HRMS (APCI+, m/z): calculated for

C20H44NO2 [M+H]+: 328.32155; found: 328.32095.

N,N-di-benzyl-glycine (3gh): Synthesized according to General

procedure. Glycine (0.038 g, 0.50 mmol) affords 3gh (0.066 g, 52% yield). White solid was obtained after precipitation in MeOH/Et₂0. Ή NMR (400 MHz, DMSO-d6) δ 7.20 - 7.40 (m, 10H), 3.73 (s, 4H), 3.15 (s, 2H). ⁱ³C NMR (100 MHz, DMSO-d6) δ 172.19, 139.00, 128.53, 128.24, 126.98, 56.79, 53.00 HRMS (APCI+, m/z): calculated for Ci6Hi₈N0₂ [M+H]+: 256.13321; found: 256.13325.

N-2-butyl-glycine (3gl): Synthesized according to General procedure.

Quantitative yield has been obtained according to crude H NMR. Ή NMR (400 MHz, D₂0) δ 3.48 - 3.67 (m, 2H), 3.14 - 3.27 (m, 1H), 1.68 - 1.84 (m, 1H), 1.47 - 1.66 (m, 1H), 1.22 - 1.35 (m, 3H). 0.88 - 1.03 (m, 3H). ¹³C NMR (100 MHz, D₂0) δ 174.11, 58.44, 49.00, 28.27, 17.51, 11.47. HRMS (APCI+, m/z): calculated for C₆Hi₄N02 [M+H]+: 132.10191; found: 132.10181.

N,N-di-(n-pentyl)-glycine (3gm): Synthesized according to General procedure. Glycine (0.038 g, 0.50 mmol) affords 3gm (0.097 g, 90% yield). White solid was obtained after column chromatography (S1O2, EtOAc/MeOH 90:10 to 70:30). Ή NMR (400 MHz, D₂0) δ 3.68 (s, 2H), 3.05 - 3.25 (m, 4H), 1.56 - 1.80 (m, 4H), 1.20 - 1.40 (m, 8H), 0.75 - 1.00 (m, 6H). ¹³C NMR (100 MHz, D₂0) δ 173.36, 58.39, 57.49, 30.46, 25.61, 24.08, 15.65. HRMS (APCI+, m/z): calculated for C12H26NO2 [M+H]+: 216.19581; found: 216.19574.

N COOH H

N-n-pentyl-glycine (3gm'): Synthesized according to General procedure. Glycine (0.038 g, 0.50 mmol) affords 3gm' (0.033 g, 46% yield). White solid was obtained after column chromatography (S1O2, EtOAc/MeOH 60:40 to 30:70). Ή NMR (400 MHz, D₂0) δ 3.57 (s, 2H), 2.91 - 3.13 (m, 2H), 1.54 - 1.80 (m, 2H), 1.20 - 1.46 (m, 4H), 0.75 - 0.99 (m, 3H). ¹³C NMR (100 MHz, D₂0) δ 174.07, 51.74, 50.13, 30.40, 27.75, 24.05, 15.62. HRMS (APCI+, m/z): calculated for C7H16NO2 [M+H]+: 146.11756; found: 146.11751.

N,N-di-n-dodecyl-glycine (3gn): Synthesized according to General procedure. Glycine (0.038 g, 0.50 mmol) affords 3gn (0.189 g, 92% yield). White solid was obtained after column chromatography (S1O2, EtOAc/MeOH 90:10 to 70:30). Ή NMR (400 MHz, CDCI3) δ 8.36 (br.s, 1H), 3.49 (s, 2H), 2.95 - 3.15 (m, 4H), 1.52 - 1.75 (m, 4H), 1.03 - 1.42 (m, 36H), 0.75 - 0.95 (m, 6H). ¹³C NMR (100 MHz, CDC1₃) δ 167.51, 56.23, 54.01, 31.80, 29.51, 29.42, 29.38, 29.23, 29.11, 26.73, 23.74, 22.57, 13.99. HRMS (APCI+, m/z):

calculated for C26H54NO2 [M+H]+: 412.41491; found: 412.41482.

H

Nv^COOH

0

N-dodecyl-glycine (3gn'): Synthesized according to General procedure. Glycine (0.038 g, 0.50 mmol) affords 3gn' (0.066 g, 54% yield). White solid was obtained after column chromatography (S1O2, EtOAc/MeOH 70:30 to 40:60). Ή NMR (400 MHz, KOH, D₂0) δ 3.00 - 3.20 (m, 2H), 2.38 - 2.58 (m, 2H), 1.36 - 1.57 (m, 2H), 1.12 - 1.35 (m, 18H), 0.73 - 0.90 (m, 3H). ¹³C NMR (100 MHz, KOH, D₂0) δ 180.96, 55.23, 51.69, 34.63, 32.69, 32.61, 32.54, 32.40, 32.22, 31.93, 30.15, 25.28, 16.42. HRMS (APCI+, m/z): calculated for C14H30NO2 [M+H]+: 244.22711; found: 244.22711.

H

^N ^COOH

N-nonyl-glycine (3gj'): Synthesized according to General procedure. Glycine (0.038 g, 0.50 mmol) affords 3gj' (0.052 g, 51% yield). White solid was obtained after column chromatography (S1O2, EtOAc/MeOH 70:30 to 40:60). Ή NMR (400 MHz, KOH, D₂0) δ 2.90 - 3.18 (m, 2H), 2.30 - 2.56 (m, 2H), 1.28 - 1.55 (m, 2H), 1.02 - 1.38 (m, 12H), 0.65 - 0.91 (m, 3H). ¹³C NMR (100 MHz, KOH, D₂0) δ 181.71, 55.18, 51.50, 34.34, 32.09, 31.96, 31.80, 31.74, 29.78, 25.05, 16.31. HRMS (APCI+, m/z): calculated for C11H24NO2 [M+H]+: 202.18016; found: 202.18010.

H

^N ^COOH

8

N-decyl-glycine (3go'): Synthesized according to General procedure. Glycine (0.038 g, 0.50 mmol) affords 3go' (0.075 g, 69% yield). White solid was obtained after column chromatography (S1O2, EtOAc/MeOH 70:30 to 50:50). Ή NMR (400 MHz, KOH, D₂0) δ 3.00 - 3.15 (m, 2H), 2.36 - 2.58 (m, 2H), 1.36 - 1.54 (m, 2H), 1.05 - 1.35 (m, 14H), 0.73 - 0.90 (m, 3H). ¹³C NMR (100 MHz, KOH, D₂0) δ 181.42, 55.34, 51.67, 34.49, 32.45, 32.30, 32.22, 32.05, 31.99, 30.04, 25.18, 16.35. HRMS (APCI+, m/z): calculated for

C12H26NO2 [M+H]+: 216.19581; found: 216.19589.

H

^-N COO e

12

methyl N-tetradecylglycinate (methyl ester of 3gp': 3gp'-Me):

Synthesized according to General procedure and Esterification procedure. Glycine (0.038 g, 0.50 mmol) affords 3gp'-Me (0.046 g, 32% yield). Pale oily compound was obtained after column chromatography. Ή NMR (400 MHz, CDCI3) δ 3.72 (s, 3H), 3.41 (s, 2H), 2.52 - 2.64 (m, 2H), 1.42

- 1.54 (m, 2H), 1.15 - 1.36 (m, 22H), 0.83 - 0.91 (m, 3H) ¹³C NMR (100 MHz, CDCI3) δ 173.02, 51.71, 50.84, 49.67, 31.91, 30.04, 29.68, 29.66, 29.65, 29.64, 29.60, 29.57, 29.51, 29.34, 27.21, 22.68, 14.10. HRMS (APCI+, m/z):

calculated for C17H36NO2 [M+H]+: 286.27406; found: 286.27430.

H

^ N r iOMe

14

methyl N-hexadecylglycinate (methyl ester of 3gq': 3gq'-Me):

Synthesized according to General procedure and Esterification procedure. Glycine (0.038 g, 0.50 mmol) affords 3gq'-Me (0.059 g, 38% yield). Pale oily compound was obtained after column chromatography. *H NMR (400 MHz, CDCI3) δ 3.73 (s, 3H), 3.43 (s, 2H), 2.52 - 2.64 (m, 2H), 1.42

- 1.58 (m, 2H), 1.13 - 1.37 (m, 26H), 0.80 - 0.94 (m, 3H) ¹³C NMR (100 MHz, CDCI3) δ 172.71, 51.78, 50.65, 49.60, 31.92, 29.85, 29.68, 29.67, 29.65, 29.60, 29.57, 29.49, 29.35, 27.19, 22.68, 14.11. HRMS (APCI+, m/z): calculated for C19H40NO2 [M+H]+: 314.30536; found: 314.30540.

H

^ N ^COOMe methyl N-octadecylglycinate (methyl ester of 3gr': 3gr'-Me):

Synthesized according to General procedure and Esterification

procedure. Glycine (0.038 g, 0.50 mmol) affords 3gr'-Me (0.067 g, 39% yield). Pale oily compound was obtained after column chromatography. *H NMR (400 MHz, CDC1₃) δ 3.71 (s, 3H), 3.40 (s, 2H), 2.53 - 2.64 (m, 2H), 1.42 - 1.52 (m, 2H), 1.17 - 1.36 (m, 30H), 0.80 - 0.91 (m, 3H) ¹³C NMR (100 MHz, CDCI3) δ 173.01, 51.68, 50.83, 49.67, 31.90, 30.04, 29.67, 29.66, 29.64, 29.59, 29.57, 29.50, 29.34, 27.21, 22.67, 14.09. HRMS (APCI+, m/z): calculated for C21H44NO2 [M+H]+: 342.33666; found: 342.33681.

N-dodecyl-alanine (3gn'): Synthesized according to General procedure. Alanine (0.045 g, 0.50 mmol) affords 3gn' (0.063 g, 49% yield). White solid was obtained after column chromatography (S1O2, EtOAc/MeOH 70:30 to

40:60). Ή NMR (400 MHz, KOH, D₂0) δ 3.00 - 3.20 (m, 2H), 2.38 - 2.58 (m, 2H), 1.36 - 1.57 (m, 2H), 1.12 - 1.35 (m, 18H), 0.73 - 0.90 (m, 3H). ¹³C NMR (100 MHz, KOH, D₂O) δ 180.96, 55.23, 51.69, 34.63, 32.69, 32.61, 32.54, 32.40, 32.22, 31.93, 30.15, 25.28, 16.42. HRMS (APCI+, m/z): calculated for C15H32NO2 [M+H]+: 258.24276; found: 258.24302.

N-nonyl-proline (3aj): Synthesized according to General procedure. Proline (0.053 g, 0.50 mmol) affords 3aj (0.063 g, 52% yield). White solid was obtained after column chromatography (S1O2, EtOAc/MeOH 90:10 to 50:50). Ή NMR (400 MHz, CDCI3) δ 3.92 - 3.06 (m, 1H), 3.61 - 3.78 (m, 1H), 3.06 - 3.22 (m, 1H), 2.90 - 3.06 (m, 1H), 2.71 - 2.89 (m, 1H), 2.27 - 2.43 (m, 1H), 2.13 - 2.27 (m, 1H), 1.88 - 2.09 (m, 2H), 1.60 - 1.79 (m, 2H), 1.05 - 1.43 (m, 12H), 0.72 - 0.95 (m, 3H). ¹³C NMR (100 MHz, CDC1₃) δ 170.24, 69.66, 55.60, 54.77, 31.68, 29.38, 29.27, 29.05, 26.64, 25.66, 23.48, 22.53, 13.97. HRMS (APCI+, m/z): calculated for C14H28NO2 [M+H]+: 242.21146; found: 242.21144.

N,N-di-ethyl-glycyl-alanine (5aa): Synthesized according to General procedure. Quantitative yield has been obtained according to crude H NMR. Ή NMR (400 MHz, D₂0) δ 4.08 - 4.22 (m, 1H), 3.88 - 4.03 (m, 2H), 3.17 - 3.31 (m, 4H), 1.30 - 1.36 (m, 3H), 1.21 - 1.30 (m, 6H). ¹³C NMR (100 MHz, D₂0) δ 179.44, 164.77, 53.19, 51.17, 49.43, 16.92, 8.30. HRMS (APCI+, m/z): calculated for C9H19N2O3 [M+H]+: 203.13902; found: 203.13895.

N,N-di-(5-hydroxy-pentyl)-glycyl-alanine (5ak): Synthesized according to General procedure. Glycyl-alanine (0.073 g, 0.50 mmol) affords 5ak (0.036 g, 36% yield). White solid was obtained after column chromatography (S1O2, EtOAc/MeOH 60:40 to 30:70). Ή NMR (400 MHz, D₂0) δ 4.15 - 4.23 (m, 1H), 3.55 - 3.67 (m, 4H), 3.19 - 3.34 (m, 2H,), 2.52 - 2.71 (m, 4H), 1.47 - 1.66 (m, 8H), 1.28 - 1.44 (m, 7H). ¹³C NMR (100 MHz, D₂0) δ 182.21,

175.12, 64.25, 59.67, 57.15, 53.19, 33.76, 28.20, 25.58, 20.44. HRMS (APCI+, m/z): calculated for C15H31N2O5 [M+H]+: 319.22275; found: 319.22278.

N,N-di-(n-dodecyl)-glycyl-alanine (5an): Synthesized according to

General procedure. Glycyl- alanine (0.073 g, 0.50 mmol) affords 5an

(0.149 g, 62% yield). White solid was obtained after column chromatography (Si0₂, EtOAc/MeOH 90:10 to 50:50). Ή NMR (400 MHz, CDC1₃) δ 8.20 (br.s, 1H), 4.17 - 4.38 (m, 1H), 3.24 - 3.60 (m, 2H), 2.52 - 2.95 (m, 4H), 1.45 - 1.64 (m, 4H), 1.11 - 1.42 (m, 39H), 0.70 - 0.95 (m, 6H). ¹³C NMR (100 MHz, CDCI3) δ 177.93, 167.98, 56.32, 54.16, 49.95, 31.87, 29.64, 29.61, 29.58, 29.37, 29.31, 27.15, 25.34, 22.63, 18.39, 14.04. HRMS (APCI+, m/z):

calculated for C29H59N2O3 [M+H]+: 483.45202; found: 483.45170.

N,N-di-ethyl-glycyl-alanine (5ba): Synthesized according to General procedure. Leucyl-glycyl- glycine (0.123 g, 0.50 mmol) affords 5ba (0.101 g, 67% yield). White solid was obtained after column chromatography (S1O2, EtOAc/MeOH 60:40 to 30:70). Ή NMR (400 MHz, D₂0) δ 3.86 - 4.02 (m, 2H), 3.75 (s, 2H), 3.38 - 3.48 (m, 1H), 2.71 - 2.88 (m, 2H), 2.46 - 2.62 (m, 2H), 1.68 - 1.83 (m, 1H), 1.32 - 1.54 (m, 2H), 0.97 - 1.13 (m, 6H), 0.83 - 0.96 (m, 6H). ¹³C NMR (100 MHz, D₂0) δ 179.02, 177.83, 173.32, 64.90, 46.57, 45.81, 44.84, 40.43, 27.43, 25.57, 23.61, 14.04. HRMS (APCI+, m/z):

calculated for C14H28N3O4 [M+H]+: 302.20743; found: 302.20747.

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12 A recent example derived protected amino acids through C-H activation, see T. J. Osberger, D. C. Rogness, J. T. Kohrt, A. F. Stepan, M. C. White

doi:10.1038/naturel8941

13 Yasufumi Ohfune 1 , Natsuko Kurokawa 1 , Naoki Higuchi 2 , Masayuki Saito

2 , Masaki Hashimoto 2 , Takaharu Tanaka 2 CHEMISTRY LETTERS, 1984, 13, 441-444.

14 Graham Barrett, Chemistry and Biochemistry of the Amino Acids chapter 11, reactions of amino acids, page 360, 1985, Chapman and hall ltd, London

15 M. H. S. A. Hamid, P. A. Slatford, J. M. J. Williams, Adv. Synth. Catal. 2007, 349, 1555 - 1575.

16 G. Guillena, D. J. Ramon, M. Yus Hydrogen autotransfer in the N-alkylation of amines and related compounds using alcohols and amines as electrophiles. Chem. Rev. 2010, 110, 1611 - 1641.

17 G. E. Dobereiner, R. H. Crabtree, Chem. Rev. 2010, 110, 681 - 703

18 A. J. A. Watson, J. M. J. Williams, Science 2010, 329, 635-636

19 S. Bahn, S. Imm, L. Neubert, Dr. M. Zhang, H. Neumann, M. Beller.

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20 C. Gunanathan, D. Milstein, Science 2013, 341, 1229712.

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22 K. Barta, P. C. Ford, Acc. Chem. Res. 2014, 47, 1503 - 1512.

23 U. R. Kreutzer J. Am. Oil. Chem. Soc. 1984, 61, 343 - 348. 24 Industrial production of amines mostly based nucleophilic substitution mechanism. For example, methylamines can be produced under 350-500 °C and 15- 30 bar pressure using aluminum-based heterogeneous catalyst from ammonia and methanol. See: Weissermel, K.; Arpe, H.-J. Industrial Organic Chemistry, Fourth Completely Revised Edition, Wiley-VCH: Weinheim, 2003, p. 51.

25 C.-P. Xu, Z.-H. Xiao, B.-Q. Zhuo, Y.-H. Wang, P.-Q. Huang Chem. Commun, 2010, 46, 7834-7836

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33 Zon W Lai, Agnese Petrera2, Oliver Schilling Protein amino-terminal modifications and proteomic approaches for N-terminal profiling Current Opinion in Chemical Biology 2015, 24, 71-79

Claims

1. A method for the N-alkylation of an unprotected amino acid or the N-terminus of an unprotected oligopeptide substrate, comprising reacting said unprotected amino acid or oligopeptide substrate with an alcohol in the presence of a homogeneous transition metal catalyst, preferably wherein the transition metal catalyst is a Fe- or Ru-based catalyst.

2. Method according to claim 1, wherein the Fe-based catalyst is of one of the following formula's :

Formula A

wherein Ri and R2 are independently selected from the group consisting of: alkyl, aryl, -CH2PI1 and silyl moieties (e.g. TMS

(trimethylsilyl), TBDMS (tertbutyldimethylsilyl), TIPS (triisopropylsilyl) or TBDPS (tertbutyldiphenylsilyl))

R3 and R₄ are independently selected from the group consisting of: hydrogen, optionally substituted alkyl and optionally substituted, aryl (with broad range of substitution e.g. -OCH3, CN, N0₂, COOR, Alkyl) L is selected from the group consisting of CO, acetonitrile phosphine, phosphite, phosphoramidite, primary or secondary amine, primary, secondary or tertiary alcohol, preferably L is CO or acetonitrile

X is O, NH or N-R5 where R5 is an alkyl or aryl, preferably X is

Formula B wherein Ri and R2 are independently selected from the group consisting of: alkyl, aryl, -CH2PI1 and silyl moieties ((e.g. TMS

(trimethylsilyl), TBDMS (tertbutyldimethylsilyl), TIPS (triisopropylsilyl) or TBDPS (tertbutyldiphenylsilyl));

R3 and R₄ are independently selected from the group consisting of: hydrogen, optionally substituted alkyl (with broad range of substitution), and optionally substituted aryl (with broad range of substitution e.g. H, - OCH3, CN, NO₂, COOR, Alkyl), silyl, or OH, O-R; NH₂, NH-R (where R can be alkyl, aryl, sulphonyl, tosyl, mesyl);

Y = CH₂; CH2-CH2; CH2-O-; CH2-NH-; O; NH or NHR5, wherein R5=alkyl or aryl, sulphonyl, tosyl, mesyl;

L is selected from the group consisting of CO, acetonitrile phosphine, phosphite, phosphoramidite, primary or secondary amine, primary, secondary or tertiary alcohol, preferably L is CO or acetonitrile

X is O, NH or Ν-Re where R6 is an alkyl or aryl, preferably X is O.

Formula C wherein Ri and R2 are independently selected from the group consisting of alkyl, aryl, -CH2PI1 and silyl moieties (e.g. TMS

[trimethylsilyl], TBDMS [tertbutyldimethylsilyl, TIPS [triisopropylsilyl] or TBDPS [tertbutyldiphenylsilyl])

R3 and R₄ are independently selected from the group consisting of alkyl (with broad range of substitution), silyl, Aryl (with broad range of substitution on the aromatic ring: e.g. H, -OCH3, CN, NO2, COOR, Alkyl); or OH, O-R5 (where R₅=alkyl, aryl); NH₂, NH-R₆ (where R₆=alkyl, aryl, sulphonyl), or wherein R3 and R₄ are connected to form a cyclic structure,

Yi and Y₂ = CH₂; O; NH; NHR₇ (where R₇=alkyl, aryl, sulphonyl, tosyl, mesyl); CH2-CH2; CH2-O-; or CH2-NH- L is selected from the group consisting of CO, acetonitrile phosphine, phosphite, phosphoramidite, primary or secondary amine, primary, secondary or tertiary alcohol, preferably L is CO or acetonitrile

3. Method according to claim 2, wherein the Fe-based catalyst is

Cat 1 b

4. Method according to claim 1, wherein the Ru-based catalyst is of one of the following formula's :

D D' wherein Ri, R2, R3 and R₄ are independently selected from the group consisting of alkyl, aryl, -CH2PI , optionally with one or more substitution on the aromatic ring, preferably wherein Ri, R2, R3 and R₄ are (optionally substituted) aryl or -CH2PI1.

5. Method according to claim 4, wherein the Ru-based catalyst is of the formula D, preferably wherein the catalyst is

Cat 2

6. Method according to any one of the preceeding claims, wherein the amino acid or oligopeptide substrate consists of or comprises a- amino acids.

7. Method according to any one of the preceeding claims, wherein the oligopeptide substrate consists of from two to eight amino acids, preferably two to five amino acids, more preferably wherein the oligopeptide is a dipeptide or a tripeptide.

8. Method according to any one of the preceeding claims, wherein the amino acid or oligopeptide substrate consists of or comprises an amino acid residue having an uncharged or hydrophobic side chain, preferably wherein the amino acid residue is selected from the group consisting of Ala, Gly, Pro, Val, Leu, He, Gin, Asn.

9. Method according to any one of the preceeding claims, wherein the alcohol is a long-chain primary alcohol, preferably a Cs-Cis fatty alcohol.

10. Method according to any one of claims 1- 8, wherein the alcohol is an optionally substituted linear, branched or aromatic Ci-Ce alcohol, preferably selected from the group consisting of ethanol, isopropanol, 1- butanol, 2-chloroethanol, 2-butanol, cyclopropylmethanol, benzylalcohol and 4-chlorobenzyl alcohol.

11. Method according to any one of the preceeding claims, wherein the alcohol is derived from biomass.

12. N-alkylated amino acid or oligopeptide selected from the group consisting of the compound of formula N,N-di-(5-hydroxypentyl)- phenylalanine (3dk), N,N-di-(«-pentyl)-glycine (3gm), N,N-(di-«-nonyl)- phenylalanine (3dj), N,N-di-«-nonyl-glycine (3gj), N,N-di-dodecylglycine (3gn), N,N-di-(5-hydroxy-pentyl)-glycyl-alanine (5ak), N,N-di-(«-dodecyl)- glycyl-alanine (5an), N-nonyl- glycine (3gj'), N-decyl- glycine (3go'), N- dodecyl-alanine (3gn'), N-tetradecylglycine (3gp'), N-hexadecylglycine (3gq'), N-octadecylglycine (3gr'), N-dodecyl-alanine (3fn') and N-nonyl-proline (3aj).

13. A method according to claim 1 for the synthesis of an amino acid based surfactant, preferably a long-chain N-alkyl amino acid, comprising the N-alkylation of an unprotected amino acid or the N-terminus of an oligopeptide substrate by reacting said unprotected amino acid or

oligopeptide substrate with a long chain (fatty) alcohol in the presence of a homogeneous transition metal catalyst.

14. Method according to claim 13, comprising mono-N-alkylation using a Fe-based catalyst, preferably a catalyst mentioned in claim 2 or 3.

15. Method according to claim 13 or 14, comprising the synthesis of an amino acid-based surfactant from natural building blocks/renewable sources.

16. Use of an N-alkylated amino acid or oligopeptide according to claim 12 as surfactant.