S-Protected tripeptide

A protected serine hydrazide was condensed by the azide method to an S-protected tripeptide H-Asn-Cys-Tyr-NHNH-Cbz to form a protected tetrapeptide Boc-Ser-Asn-Cys-Tyr-NHNH-Cbz 1.02 g of N-rerr-butoxycarbonylserine hydrazide (Boc-Ser-NH-NHj) >n DMF containing HCI in dioxane was mixed at -20 °C with reri-butyl nitrite. This mixture containing the azide Boc-Ser-Nj was neutralized with triethylamine, and a solution of 3.4 g asparaginyl-S-(ethylcarbamoyl)cysteinyl-tyrosinyl 2-(benzyloxy-carbonyl)hydrazide trifluoroacetate was added. After 72 hours at 4 °C a simple work-up procedure and precipitation from methanol-petroleum ether yielded 3 g of impure protected retrapeptide hydrazide. It... 

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