Citric Acid → Z-Thr(tBu)-Tyr(tBu)-Thr(tBu)-Gln-Asp(OtBu)-Phe-OCH3

Participants

Reaction Steps

The acid is liberated from 2.85 g of Z-Thr(tBu)-OH.dicyclohexylammonium salt in ethyl acetate by means of citric acid as described under 23 and the resulting oil consisting of Z-Thr(tBu)-OH is stirred with 3.33 g of H-Tyr(tBu)-Thr(tBu)-Gln-Asp(OtBu)-Phe-OCH 3 in 80 ml of acetonitrile at room temperature. 1.20 g of dicyclohexylcarbodiimde are added thereto in the solid form and the mixture is stirred for 23 hours at room temperature. After filtering off the precipitated dicyclohexylurea, which is washed with three portions of acetonitrile each of 7 ml, the solution is evaporated in vacuo and the residue is three times precipitated from ethyl acetate/alcohol solution by means of petroleum ether.

Provenance & Evidence