P-Mercapto-a-amino acids

The a,p-double bond in amino acid derivatives and peptides represents, in addition to the amino and carboxy groups, the introduction of a third highly reactive function into the molecule. It is therefore pertinent in a discussion of the a,P-dehydroamino acids to devote some attention to their primary addition products, such as derivatives of a-mercapto- and a-hydroxy-a-amino acids. Further topics relevant in this context are their relationship to P-hydroxy- and P-mercapto-a-amino acid derivatives (elimination-addition sequence), as well as syntheses and reactions of pyruvoylamino acids, which result from the hydrolysis of dehydropeptides and can possibly serve as precursors of the latter by condensation with amino acid amides. On the other hand, p,y- and y S-dehydroamino acids will be excluded from the scope of this discussion. The isolated double bonds of these compounds undergo the normal olefin reactions and display no unusual characteristics. 

Chart 1. Possible Biological Relationship Between Dehydroamino Acids and Amino Acids, a- and p-Hydroxy-a-amino Acids, a- and P-Mercapto-a-amino Acids, a-Keto-acids and... 

Amino acids with appropriate 3-substituents have frequently been employed as a,p-dehydroamino acid precursors, particularly in the form of peptide chain subunits. Elimination reactions from derivatives of P-hydroxy- and P-mercapto-a-amino acids are the examples most often encountered. Of less importance are amino acid derivatives with P-halogen substituents (38, 132, 337, 386, 394, 395), as these require more drastic elimination conditions. Mannich bases of monoalkyl acylaminomalonates have also found use as precursors of dehydroalanine derivatives (177, 438). 

The double bond of N-acylenamino acids and their esters represents the locus minoris resistentiae . As a result of conjugation with the carboxyl group, the double bond is a good acceptor for nucleophilic addends under basic catalysis. The acylamino group makes electrophilic additions possible. It is thus possible to obtain a- or P-mercapto a-amino acid derivatives by selecting the appropriate reaction conditions for the addition of mercaptans. 

With Sulfur Nucleophiles N-Carboxy-protected aziridine-2-carboxylates react with thiols to give P-mercapto-ot-amino acid derivatives. The reaction is usually catalyzed by BF3 and the yields range from fair to excellent [15, 16, 108-111]. With N-unprotected 3-substituted aziridine-2-carboxylates, the ring-opening with thiols usually takes place with anti stereoselectivity, especially in the case of the C-3 aliphatic substituted substrates. In cases in which C-3 is aromatic, however, the stereoselectivity has been found to be a function of the substitution pattern on the aromatic ring 3-p-methoxy ph eri yl-su bs li In led aziridines 143a (Scheme 3.51) and... 

Contents J. M. BRAND, J. CHR. YOUNG, and R. M. SILVERSTEIN, Insect Pheromones A Critical Review of Recent Advances in Their Chemistry, Biology, and Application - M. McNEIL, A. G. DARVILL, and P. ALBERSHEIM, The Structural Polymers of the Primary Cell Walls of Dicots - U. SCHMIDT, J. HAUSLER, ELISABETH OHLER, and H. POISEL, Dehydroamino Acids, a-Hydroxy-a-amino Acids and a-Mercapto-a-amino Acids — Author Index — Subject Index. 

Preparations.—a-Mercapto-a-amino-acids R NHCR (SH)C02H are obtained from corresponding chloro-compounds or from 4-chloro-oxazol-5(4H)-ones. Conventional methods are also used for synthesis of thio-resorcinols (from benzene-1,3-disulphonic acids via sulphonyl chlorides, reduced with red P-Ir-AcOH, or from resorcinols via Newman-Kwart rearrangement of O-dimethylaminothiocarbonyl-resorcinols followed by alkaline hydrolysis ). Dithiols are unexpectedly obtained from ethyl a-acetonylacetate by treatment with H2S in acid solution at -40 "C. Mercapto-ethylation of aliphatic amines is best achieved by a modificaticm of the well-established method using episulphides, in aqueous solution in the presence of a silver salt. Methyl sulphides ArSMe may be demethylated by chlorination to ArSCCh followed by acid methanolysis, while aryl diphenylmethyl sulphides are susceptible to electrolytic reduction to the thiophenol. ... 

P. which contain only amino acid residues are called homomeric P., whereas P. with non-amino acid constituents are known as heteromeric P. Each of these classes is further subdivided into homodetic P., which contain only peptide bonds, and heterodetic P, which contain other bonds, e.g. ester, thioether or disulfide. Heterodetic P. possessing one or more ester bonds as hetero link are called Depsipeptides (see). The classification of depsipeptides does not accord entirely with the homomeric/heteromeric system it has arisen from the fact that the synthesis of these peptides presents rather special problems. There are two types of homomeric depsipeptides O-peptides contain ester-linked hydroxyamino acids, and they may be linear or cyclic (i. e. lactones) in S-peptides or thiodepsipep-tides, the mercapto group of a cysteine residue is acy-lated with an amino acid. Heteromeric depsipeptides contain hydroxy acids as the hetero component, and they are also known as peptolides. P. with non-amino... 

Several crown ethers that possess side chains with terminal mercapto groups enhance the rate of transesterification of amino-acid p-nitrophenyl esters. Matsui and Koga (1978) reported the reactions of a number of amino-acid p-nitrophenyl ester hydrobromides dissolved in mixtures of ethanol and dichloromethane (1 4) and buffered with acetic acid and pyridine (pH 4.60 in... 

B. 2-Mercapto-4-hydroxy-5-cyanopyrimidine. The aqueous filtrate from which the crude 2-mercapto-4-amino-5-carbethoxy-pyrimidine separated is cooled overnight at 0°, and the cyano-pyrimidine that precipitates is collected on a suction filter. The crude product is recrystallized from about 200 ml. of 10% acetic acid with 1 g. of decolorizing charcoal added. Two additional recrystallizations done similarly give the pure cyanopyrimidine as faintly yellow crystals, m.p. 265-272° (dec.) (Note 3). The yield is 10-18 g. (7-12%). 

The concentrates are analysed by High Performance Liquid Chromatography (HPLC) coupled to a fluorescence detector. Elution is performed using a gradient of methanol in a phosphate buffer on a Cj g radial compression column. In order to render the amino acids amenable to fluorescence detection ( X Xgjjj = 455 nm), it is first necessary to derivatize them using orthophtaldialdehyde (O.P.A.) in the presence of mercapto-2 ethanol. Up to 20 amino acids can thus be analysed and quantified, and the complete analysis takes only 35 minutes. Table 2 presents the most commonly determined amino acids during the course of this study. 

SA " r R1 aliphatic and aromatic amines, hydroxy, ester, protected [109] a- and p-amino acids amino, furyl, thienyl aromatic and heteroaromatic aldehydes 2-mercapto acids... 

L-Alanine, 3-mercapto- 2-Amino-3-mercaptopropanoic acid, (R)- 2-Amino-3-mercaptopropionic acid L-2-Amino-3-mercaptopropanoio acid R)-2-Amino-3-mercaptopropanoic acid a-Amino-P-thiolpropionic acid a-Amino-p-thiolpropionio acid, L- a-Amino-p-mercaptopropanoic acid, L- AI3-26559 CCRIS 912 Cisteina Cisteinum Cystein Cysteine L-Cysteine L-(+)-Cysteine Cysteine, L- (R)-Cysteine Cysteinum EINECS 200-158-2 FEMA No. 3263 Half cystine HSDB 2109 NSC-8746 Thioserine. A nonessentiai amino acid biochemical and nutrition research, reducing agent in... 

Holmes et al. [33] reported the solution and polymer-supported synthesis of 4-thiazolidinones 3 and 4-metathiazanones 4 derived from amino acids. A three-component condensation of an amino acid ester or a resin-bound amino acid (glycine, alanine, j8-alanihe, phenylalanine, and valine), an aldehyde (benzaldehyde, o-tolualdehyde, m-tolualdehyde, p-tolualdehyde and 3-pyridine carboxaldehyde), and an a-mercapto carboxylic acid led to the formation of five- and six-membered heterocycles (Fig. 3b). 

In a completely different context, an A-protected version of the amino acid cysteine has been found to be an excellent promoter for the intramolecular Rauhut-Currier reaction (Scheme 6.20)," in which an enolizable enone played the role of the Michael acceptor, adding to another a,p-unsaturated ketone moiety in already present at the substrate structure. The mechanism of the reaction involved the activation of the enone which has to play the role of the donor by the catalyst via sulfa-Michael addition through the mercapto functionality of the A-protected cysteine derivative. The formed enolate... 

The amino acid cysteine bears a relatively nucleophilic and acidic mercapto substituent (pTCa = 8.2, p/ = 5.1). In addition, thiols can be oxidized to disulfides under mild conditions (Section 9-10). In nature, various enzymes are capable of oxidatively coupling and reduc-tively decoupling the mercapto groups in the cysteines of proteins and peptides, thereby reversibly linking peptide strands (Section 9-10). We have highlighted previously the importance of this amino acid in biological function (see Really on p. 815 and Section 22-9). 

The use of an acidic solution of p-anisaldehyde in ethanol to detect aldehyde functionalities on polystyrene polymer supports has been reported (beads are treated with a freshly made solution of p-anisaldehyde (2.55 mL), ethanol (88 mL), sulfuric acid (9 mL), acetic acid (1 mL) and heated at 110°C for 4 min). The colour of the beads depends on the percentage of CHO content such that at 0% of CHO groups, the beads are colourless, -50% CHO content, the beads appear red and at 98% CHO the beads appear burgundy [Vdzquez and Albericio Tetrahedron Lett 42 6691 200]]. A different approach utilises 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (Purpald) as the visualizing agent for CHO groups. Resins containing aldehyde functionalities turn dark brown to purple after a 5 min reaction followed by a 10 minute air oxidation [Coumoyer et al. J Comb Chem 4 120 2002]. 

Benzenemethanethiol,a-(selenylmethylene)-metal complexes, 809 Benzeneselenic acid metal complexes, 807 Benzenetetrathiols metal complexes, 606 Benzenethiol, 2-amino-metal complexes, 799 Benzenethiol, o-hydroseleno-metal complexes, 809 Benzimidazole, 2-guanidinium-metal complexes, 283 Benzimidazole, 2-mercapto metal complexes, 802 Benzimidazole, 2-(2-pyridyl)-metal complexes, 93 Benzimidazoles metal complexes, 78, 85 P a, 11... 

Fig. 5 Nucleic acid immobilization onto (a) silica 60 nm particles, (b) amino terminated 0.31 xm latex beads and (c) poly(T) modified Dynabeads . MPTS 3-mercapto-propyltrimethoxysilane. (

Bidentate ligands containing OS donors, particularly in conjunction with carboxylate moieties, form strong complexes at pH values near the p/y, value for the thiol.584,602,687-689 The reduction of Viv to V111 by cysteine methyl ester in water has been found to be enhanced in the presence of amino polycarboxylates.690 The ligand 2-mercapto-4-methylphenol forms a square-pyramidal five-coordinate complex with the vanadyl cation (150) the reported crystal structure is of the cis isomer.691 The bidentate ligand 2-aminocyclopent-l-ene-l-carbodithioic acid forms non-oxo-Viv complexes based on spectroscopic studies and chemical precedence, an eight-coordinate vanadium atom is inferred.692... 

The stability constants of uranyl amino- and mercapto-acid complexes have been determined. Among the acids investigated were cysteine, methionine, P-alanine, anthranilic acid, serine, threonine, and JV-ac tylglycine. Stability constants of a series of chloro-, bromo-, iodo-, and nitro-substituted salicylic acid and of o-pyrocatechinic, y-resorcylic, and gentisic acids complexes of UOj" have been measured 1 1 and 1 2 species were identified. It was observed that there was a distinct dependence of stability constant on the charge of the central metal atom in UO ", NpO, and Pu " tropolonato complexes. ... 

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