Preparation and Disulfide Interchange Reactions of Unsymmetrical Open-chain Derivatives of Cystine

Preparation of mono-(carbobenzoxyglycyl)-L-cystine was achieved by treatment of an excess of L-cystine in aqueous alkali with carbobenzoxyglycyl chloride. Decarbobenzoxylation of the compound by the action of hydrogen bromide in glacial acetic acid permitted the subsequent isolation of pure, crystalline monoglycyl-L-cystine. The bis-methyl, bis-benzyl, monomethyl and monobenzyl ester derivatives of monocarbobenzoxy-L-cystine were prepared by the usual esterification procedures. Conversion of the first-mentioned derivative to Nα-carbobenzoxy-Nα'-trityl-L-cystine bis-methyl ester was effected by the action of trityl chloride in chloroform containing triethylamine. Treatment of such product with hydrazine did not lead to the expected α-monohydrazide but rather induced a rapid disulfide interchange with the formation of the symmetrical bis-trityl-L-cystine bis-methyl ester and bis-carbobenzoxy-L-cystine bis-hydrazide as the only isolable products. Comparable disulfide interchange of this same compound as well as of monocarbobenzoxy- and monoglycyl-L-cystine was catalyzed by alkali in both aqueous and methanolic solution. The rate and extent of such interchange in basic solution was shown to increase with an increase in pH. © 1959, American Chemical Society. All rights reserved

Structures of some acetyl-serine peptides from acetyl-chymotrypsin

IN 1958, two of us1 obtained, by enzymic degradation of acetyl-chymotrypsin labelled with carbon-142, five peptides containing labelled acetyl-groups. Subsequent sequence studies3 have shown that the largest of these peptides has the amino-acid sequence, Gly.Asp.Ser.Gly.Gly.Pro.Leu, identical with that already found4, by degradation of the di-isopropylphosphoryl-enzyme, to surround the reactive serine ; it may reasonably be concluded that the other four peptides contain the sequences Ser.Gly.Gly.Pro.Leu, Asp.Ser.Gly.Gly, Gly.Asp.Ser.Gly and Ser.Gly.Gly, respectively. © 1960 Nature Publishing Group