Novel formation of α-amino acid from α-oxo acids and ammonia in an aqueous medium

In the course of a study of possible mechanisms for chemical evolution in the primeval sea, we found the novel formation of -amino acids and N-acylamino acids from -oxo acids and ammonia in an aqueous medium. Glyoxylic acid reacted with ammonia to form N-oxalylglycine, which gave glycine in a 5–39% yield after hydrolysis with 6N HCl. Pyruvic acid and ammonia reacted to give N-acetylalanine, which formed alanine in a 3–7% overall yield upon hydrolysis. The pH optima in these reactions were between pH 3 and 4. These reactions were further extended to the formation of other amino acids. Glutamic acid, phenylalanine and alanine were formed from -ketoglutaric acid, phenylpyruvic acid and oxaloacetic acid, respectively, under similar conditions. N-Succinylglutamic acid was obtained as an intermediate in glutamic acid synthesis. Phenylacetylphenyl-alanineamide was also isolated as an intermediate in phenylalanine synthesis. Alanine, rather than aspartic acid, was produced from oxaloacetic acid. These reactions provide a novel route for the prebiotic synthesis of amino acids. A mechanism for the reactions will be proposed.     

A method for the separation of peptides and α-amino acids

1. Peptides and alpha-amino acids, occurring in mixtures from various sources, can be separated into one fraction containing the amino acids and several peptide fractions. This is achieved by chelation of the mixture with Cu(2+) ions and subsequent chromatography of these chelates over the acetate form of diethylaminoethylcellulose or triethylaminoethylcellulose. 2. The amino acid fraction is obtained by elution with 0.01m-collidine-acetate buffer, pH8.0. 3. Peptide fractions are eluted with 0.01m-collidine-acetate buffer, pH4.5, 0.17n-acetic acid and 0.1n-hydrochloric acid respectively. 4. With the exception of aspartic acid and glutamic acid, which are partly found in the acidic peptide fraction, the amino acids are completely separated from the peptides. 5. Contamination of the acidic peptide fraction with glutamic acid and aspartic acid can be largely avoided by previous addition of an excess of arginine. 6. Copper is removed from the eluates by extraction with 8-hydroxyquinoline in chloroform.     

Ammonia lyases and aminomutases as biocatalysts for the synthesis of α-amino and β-amino acids

Ammonia lyases catalyse the reversible addition of ammonia to cinnamic acid (1: R=H) and p-hydroxycinnamic (1: R=OH) to generate L-phenylalanine (2: R=H) and L-tyrosine (2: R=OH) respectively (Figure 1a). Both phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL) are widely distributed in plants, fungi and prokaryotes. Recently there has been interest in the use of these enzymes for the synthesis of a broader range of L-arylalanines. Aminomutases catalyse a related reaction, namely the interconversion of α-amino acids to β-amino acids (Figure 1b). In the case of L-phenylalanine, this reaction is catalysed by phenylalanine aminomutase (PAM) and proceeds stereospecifically via the intermediate cinnamic acid to generate β-Phe 3. Ammonia lyases and aminomutases are related in sequence and structure and share the same active site cofactor 4-methylideneimidazole-5-one (MIO). There is currently interest in the possibility of using these biocatalysts to prepare a wide range of enantiomerically pure l-configured α-amino and β-amino acids. Recent reviews have focused on the mechanism of these MIO containing enzymes. The aim of this review is to review recent progress in the application of ammonia lyase and aminomutase enzymes to prepare enantiomerically pure α-amino and β-amino acids.     

A preparation of N-Fmoc-N-methyl-α-amino acids and N-nosyl-N-methyl-α-amino acids

A convenient route for the synthesis of lipophilic N-Fmoc-N-methyl-α-amino acids and N-nosyl-N-methyl-α-amino acids, interesting building blocks to be used for the preparation of N-methylated peptides, is presented. Both nosyl- and Fmoc-protected monomers are accessible, so these compounds can be used in solution as well as in solid phase peptide synthesis. The methodology is based on the use of benzhydryl group to protect temporarily the carboxyl function of N-nosyl-α-amino acids and on the subsequent methylation of the N-nosyl-α-amino acid benzhydryl esters with diazomethane. The benzhydryl esters offer several beneficial features such as simple preparation, stability to methylation and selective deprotection under mild conditions. The overall procedure is highly efficient in that the adopted conditions keep the chiral integrity of amino acid precursors and the process does not require chromatographic purification of the methylated products.     

Synthesis of optically active lipidicα-amino acids and lipidic 2-amino alcohols

Summary Lipidic-amino acids (LAAs) are a class of compounds combining structural features of amino acids with those of fatty acids. They are non-natural-amino acids with saturated or unsaturated long aliphatic side chains. Synthetic approaches to optically active LAAs and lipidic 2-amino alcohols (LAALs) are summarized in this review. A general approach to enantioselective synthesis of saturated LAAs is based on the oxidative cleavage of 3-amino -1,2-diols obtained by the regioselective opening of enantiomerically enriched long chain 2,3-epoxy alcohols. Unsaturated LAAs are prepared in their enantiomeric forms by Wittig reactionvia methyl (S)-2di-tert-butoxycarbonylamino-5-oxo-pentanoate. This key intermediate aldehyde is obtained by selective reduction of dimethyl N,N-di-Boc glutamate with DIBAL. (R) or (S) LAALs may be prepared starting from D-mannitol or L-serine. LAAs are converted into LAALs by chemoselective reduction of their fluorides using sodium borohydride with retention of optical purity. Replacement of the hydroxyl group of LAALs by the azido group, followed by selective reduction leads to unsaturated optically active lipidic 1,2-diamines.Abbreviations Bn benzyl - Boc tert-butoxycarbonyl - DDQ 2,3-dichloro-5,6-dicyano-1,4-benzoquinone - DET diethyl tartrate - DIBAL diisobutyl aluminum hydride - DMAP 4-dimethylaminopyridine - DMF N,N-dimethylformamide - DMSO dimethyl sulfoxide - EDC N-ethyl-N-(3-dimethylaminopropyl)carbodiimide - Et₃N triethylamine - HMPA hexamethylphosphoramide - HOBt 1-hydroxybenzotriazole - KN(TMS)₂ potassium bis(trimethylsilyl)-amide - LAA lipidic-amino acid - LAAAl lipidic 2-amino alcohol - LDA lipidic 1,2-diamine - LP lipidic peptide - MPM-Cl p-methoxybenzyl chloride - MsCl methanesulphonyl chloride - MTPA -methoxy--(trifluoromethyl)phenylaccitc - PLA₂ phospholipase A₂ - TBIIP tert-butyl hydroperoxide - THF tetrahydrofuran - TMSCl trimethylsilyl chloride - Tr trityl - Z benzyloxycarbonyl     

Synthesis of α-trifluoromethyl α-amino acids with aromatic, heteroaromatic and ferrocenyl subunits in the side chain

Summary. 5-Benzyloxy-4-trifluoromethyl-1,3-oxazoles, obtained from 5-fluoro-4-trifluoromethyloxazoles and benzyl alcohols, are capable for rearrangements. A 1,3 shift of a benzyl group is the key step of a new general route toward α-trifluoromethyl substituted aromatic and heteroaromatic amino acids, demonstrating that 5-fluoro-4-trifluoromethyl-1,3-oxazole is a synthetic Tfm-Gly equivalent. On reaction with benzpinacol partially fluorinated oxazoles are transformed into bis(trifluoromethyl) substituted 2,5-diamino adipic acid and N-benzoyl-2-benzhydryl-3,3,3-trifluoroalanine.     

Helix induction potential of N-terminal α-methyl, α-amino acids

Summary A series of longer analogues of the C-peptide of RNAse A has been synthesized with the aim of assessing the helix induction potential in water of α-methyl, α-amino acids at the N-terminus of the chain. The circular dichroism data indicate that one isovaline residue is effective in increasing the helix content of the 13-residue peptide by about 7%.     

Synthesis of medicinally useful lipidicα-amino acids, 2-amino alcohols and diamines

Summary The lipidic-amino acids (LAAs) are non-natural-amino acids with saturated or unsaturated long aliphatic side chains. LAAs and their derivatives (lipid mimetics) together with the lipidic peptides represent a class of compounds which combine structural features of lipids with those of amino acids and peptides. Racemic LAAs may be prepared by classical methods and resolved by chemical or enzymatic methods. LAA amides and esters with saturated or unsaturated long chain amines and alcohols respectively, as well as lipidic dipeptide derivatives inhibit both pancreatic and human platelet phospholipase A₂. Lipophilic peptide derivatives are inhibitors of human neutrophil elastase. LAAs and their oligomers have been used as drug delivery system. A Lipid-Core-Peptide system has been designed and used as a combined adjuvant-carrier-vaccine system. A variety of lipid mimetics such as lipidic 2-amino alcohols, lipidic 1,2- and 1,3-diamines have been prepared based upon LAAs. Some of them are potent inhibitors of phospholipase A₂. A general approach to enantioselective synthesis of LAAs and lipid mimetics is based on the oxidative cleavage of 3-amino-1,2-diols obtained by the regioselective opening of enantiomerically enriched long chain 2,3-epoxy alcohols.Abbreviations Boc tert-butoxycarbonyl - BSA bovine serum albumin - CD circular dichroism - DET diethyl tartrate - DIBAL diisobutyl aluminum hydride - DMF N,N-dimethylformammide - HMPA hexamethylphosphoramide - HNE human neutophil elastase - LAA lipidic amino acid - LAAL lipidic amino alcohol - LH-RH luteinizing hormone-releasing hormone - LCP lipid-core-peptide - LDA lipidic diamine - LP lipidic peptide - MAP multiple antigenic peptide - PLA₂ phospholipase A₂ - TBHP tert-butyl hydroperoxide - THF tetrahydrofuran - TRH thyrotropin-releasing hormone - Z benzyloxycarbonyl     

The production of extracellular and intracellular free amino acids during aerated fermentation of glucose by Baker’s yeast (Saccharomyces cerevisiae)

During a study of the effects of a high level of NaCl on the content of free intracellular amino acids in baker’s yeast grown in aerated fermentation of glucose it was found (Malaneyet al. 1988, 1989; Malaney and Tanner 1988) that 0.6 mol/L exogenous NaCl significantly increased the content of free intracellular citrulline, glutamine, ornithine, arginine and lysine (all basic amino acids) over that observed at zero mol/L exogenous NaCl. (Exogenous is defined as salt added beyond that present in the mineral salts in the culture medium.) This paper describes the production and relative relationships of both extracellular and free intracellular amino acids byS. cerevisiae under conditions of high NaCl content in the growth medium at pH 5 and 32 °C. For early culture times (6 h), the production of glutamine, citrulline, valine, isoleucine, ornithine, lysine and histidine were all enhanced by the addition of NaCl. For late times (24 h), except for ornithine, the early-time-enhanced amino acids continued to be enhanced by the addition of NaCl. In addition, the yields of several other amino acids also were increased by exogenous salt at this late time. These include aspartic acid, threonine, glutamic acid, cystine, methionine, tyrosine, phenylalanine and arginine. Deceased, August 12, 1988. This study was supported by theNational Science Foundation (Grant No. CPE8209945) in conjunction with the NSF United States — Taiwan Cooperative Science Program.     

Asymmetric synthesis of α-amino acids via homologation of Ni(II) complexes of glycine Schiff bases. Part 2: Aldol, Mannich addition reactions, deracemization and (S) to (R) interconversion of α-amino acids

This review provides a comprehensive treatment of literature data dealing with asymmetric synthesis of α-amino-β-hydroxy and α,β-diamino acids via homologation of chiral Ni(II) complexes of glycine Schiff bases using aldol and Mannich-type reactions. These reactions proceed with synthetically useful chemical yields and thermodynamically controlled stereoselectivity and allow direct introduction of two stereogenic centers in a single operation with predictable stereochemical outcome. Furthermore, new application of Ni(II) complexes of α-amino acids Schiff bases for deracemization of racemic α-amino acids and (S) to (R) interconversion providing additional synthetic opportunities for preparation of enantiomerically pure α-amino acids, is also reviewed. Origin of observed diastereo-/enantioselectivity in the aldol, Mannich-type and deracemization reactions, generality and limitations of these methodologies are critically discussed.     

Synthesis of conformationally constrained hydroxy-α-amino acids by intramolecular conjugate addition

Summary. An efficient and easily applicable method for the synthesis of a variety of hydroxy-α-amino acids analogues of serine and phenylalanine has been established. The method involves the stereoselective intramolecular conjugate addition of the benzamide group to cyclohexenone promoted by Lewis acid. Subsequent transformations of functional groups pro-vide the conformationally constrained 2-hydroxy- and 2,4-dihydroxy-6-phenylcyclohexane-α-amino acids. Received February 5, 1999, Accepted May 16, 1999     

One-pot efficient synthesis of N α-urethane-protected β- and γ-amino acids

1-[(4-Methylphenyl)oxy]pyrrolidine-2,5-dione and 1-[(4-methylphenyl)oxy]piperidine-2,6-dione react in a Lossen-type reaction with primary alcohols in the presence of triethylamine to furnish corresponding N ^α-urethane-protected β-alanine and γ-aminopropionic acid (GABA), respectively, with excellent yields and purities, in an essentially “one-pot” procedure.     

Gas chromatographic enantioseparation of derivatized α-amino acids on chiral stationary phases--past and present

The historical development of the enantioseparation of derivatized α-amino acids by high-resolution capillary gas chromatography on chiral stationary phases derived from α-amino acid-derivatives and modified cyclodextrins is described. The pioneering work emerging from Emanuel Gil-Av and his associates at the Weizmann Institute of Science is reviewed. A bridge to more recent developments is spanned aimed at helping to select appropriate tools for contemporary chiral α-amino acid analysis by gas chromatography in different research areas.     

Pro-apoptotic activity of lipidic α-amino acids isolated from Protopalythoa variabilis

Lipidic α-amino acids (LAAs) have been described as non-natural amino acids with long saturated or unsaturated aliphatic chains. In the continuing prospect to discover anticancer agents from marine sources, we have obtained a mixture of two cytotoxic LAAs (1a and 1b) from the zoanthid Protopalythoa variabilis. The anti-proliferative potential of 14 synthetic LAAs and 1a/1b were evaluated on four tumor cell lines (HCT-8, SF-295, MDA-MB-435, and HL-60). Five of the synthetic LAAs showed high percentage of tumor cell inhibition, while 1a/1b completely inhibited tumor cell growth. Additionally, apoptotic effects of 1a/1b were studied on HL-60 cell line. 1a/1b-treated cells showed apoptosis morphology, loss of mitochondrial potential, and DNA fragmentation.     

The role of the delocalized α,α′-carbanion in vitamin B6 and Al(III) catalyzed transamination of α-amino and α-keto acids

The rates of the transamination reactions of α-amino acids and α-keto acids were followed by measurement of the 200 MHz proton NMR spectra of solution species as a function of time. Reaction systems measured in D₂O at 10 °C consisted of 1:1:1 molar ratios of pyridoxal:α-amino acid:Al(III) or pyridoxamine:α-keto acid:Al(III). Amino and keto acids employed are alanine, α-aminoisobutyric acid, valine, phenylglycine, pyruvic acid, and α-ketobutyric acid. A negatively charged deprotonated Schiff base coordinated to Al(III) was detected in all systems that undergo transamination (i.e., except α-aminoisobutyric acid). The intermediate resembles the aldimine Al(III) chelate with NMR resonances shifted upfield in accordance with its greater negative charge. Its equilibrium concentration is reached in the time required to reach transamination equilibrium and is maintained in solution at a ca. 10–20% of the aldimine Schiff base concentration.     

The use of β-amino acids in the design of protease and peptidase inhibitors

Summary The use of β-amino acids as peptidomimetics has emerged in recent years with significant potential in a number of applications. The incorporation of β-amino acids has been successful in creating peptidomimetics that not only have potent biological activity, but are also resistant to proteolysis. This article reviews the recent applications of β-amino acids in the design of protease and peptidase inhibitors. Given their structural diversity, together with the ease of synthesis and incorporation into peptide sequences using standard solid-phase peptide synthesis techniques, β-amino acids have the potential to form a new platform technology for peptidomimetic design and synthesis.