SYNTHETIC STUDIES ON PEPTIDES.

In an effort to devise a new protecting group amidino group for the thiol group of cysteine the reaction of N-benzyloxycarbonyl-L-cysteine with cyanamide was explored. A crystalline product obtained from the reaction between N-benzyloxycarbonyl-L-cysteine and cyanamide was shown to possess the elemental composition C12H13O3N3S. A cyclic sturcture Formula VI appears to represent the correct formulation for this compound. L-Cysteine hydrochloride was converted into S-ethylcarbamyl-L-cysteine by treatment with ethyl isocyanate in dimethylformamide solution. Exposure to benzyloxycarbonyl chloride and alkali at pH 7.6 transformed S-ethylcarbamyl-L-cysteine into N-benzyloxycarbonyl-S-ethylcarbamyl-L-cysteine. Similarly interaction of S-ethylcarbamyl-L-cysteine with t-butyloxycarbonyl azidoformate in presence of magnesium oxide gave the N-t-butyloxycarbonyl derivative. The p-nitrophenyl and 2,4,5-trichlorophenyl esters of N-benzyloxycarbonyl-S-ethylcarbamyl-L-cysteine were prepared and characterized. Using these activated esters the two protected dipeptide derivatives, methyl N-benzyloxycarbonyl-S-ethylcarbamyl-L-cysteinylglycinate and N-benzyloxycarbonyl-S-ethylcarbamyl-L-cysteinyl-L-theronine amide, were synthesized and characterized. Exposure of the threonine derivative to hydrogen bromide in glacial acetic acid gave S-ethylcarbamyl-L-cysteinyl-L-threonine amide. A route to benzyloxycarbonyldipeptide T-butyloxy-carbonylhydrazides was developed. Author