Transformation of Serine to Cysteine. β-Elimination Reactions in Serine Derivatives

O-Tosylated and O-diphenylphosphorylated serine derivatives undergo a β-elimination reaction on being treated with 0.1 N alkali or diethylamine in non-polar solvents, resulting in the formation of dehydroalanine derivatives. N-Carbobenzoxy-O-tosyl-l-serine methyl ester is converted to N-carbobenzoxy-S-trityl-dl-cysteine by reaction with tritylthiocarbinol sodium salt, followed by saponification. It has been observed that N-acyl-S-alkyl-l-cysteine esters are extensively racemized by saponification with alcoholic alkali, but little or no racemization is produced by alkali in 50% aqueous methanol or aqueous dioxane. © 1963, American Chemical Society. All rights reserved

A New Synthesis of Oxytocin Using S-Acyl Cysteines as Intermediates

The fully S,N-protected derivatives (VI-IX) of the nonapeptide amide, L-cysteinyl-L-tyrosyl-L-isoleucyl-L-glutaminyl-L-asparaginyl-L-cysteinyl-L-prolyl-L-leucylglycinamide, have been prepared by a step-by-step synthesis, using new N-protecting groups (the t-butyloxycarbonyl and the o-nitrophenylsulfenyl groups) in addition to the classical carbobenzoxy and new S-protecting groups (the S-benzoyl and S-carbobenzoxy groups). The selective removal of the S-protecting groups from compounds VI-IX by methanolysis afforded the N-protected oxytoceines (X-XII). Oxidation of the free thiol groups of X and XII by 1,2-diiodoethane led to the formation of N-carbo-benzoxy- (XIII), and N-t-butyloxycarbonyl-oxytocin, (XIV), respectively. The peptide obtained after decarbo-benzoxylation of the N-carbobenzoxy-oxytocin (XIII) was purified by countercurrent distribution and partition chromatography on Sephadex. The isolated material exhibited the chemical, physical, and biological activities of oxytocin. © 1966, American Chemical Society. All rights reserved

Transformation of L-Serine Peptides to L-Cysteine Peptides

The serine moieties of the peptides N-carbobenzoxy-L-serylglycine ethyl ester and N-carbobenzoxyglycyl-L-serylglycine ethyl ester were O-tosylated to give the corresponding O-tosyl derivatives IV and VI, respectively. Displacement of the O-tosyl groups of IV and VI by thiobenzoate anion afforded in excellent yields N-carbobenzoxy-S-benzoyl-L-cysteinylglycine ethyl ester (Va) and N-carbobenzoxyglycyl-S-benzoyl-L-cysteinyl-glycine ethyl ester (VIIa), respectively. A similar displacement by thioacetate anion afforded N-carbo-@r@nbenzoxy-S-acetyl-L-cysteinylglycine ethyl ester (Vb) and N-carbobenzoxyglycyl-S-acetyl-L-cysteinylglycine ethyl ester (VIlb). © 1965, American Chemical Society. All rights reserved

Some applications of the curtius rearrangement?

Pairs of optically pure enantiomers of substituted 1,1-diamines have been prepared from the azides of L-amino-acids via the Curtius rearrangement. This synthesis is based on the interchange of two groups attached to the asymmetrically substituted tetrahedral α-carbon atom of the parent amino acid. Such an interchange occurs without the intermediate formation of a racemate. In addition, some side reactions of isocyanates of N-benzyloxycarbonyl-L-amino acids in aqueous acidic solution have been elucidated