Polypeptides

The invention comprises the cyclic polypeptide of the formula p I, and the nonapeptide of the formula II, in which R and R1 each represents a protective group for the sulphhydryl group, with the proviso that R and R1 need not be dissimilar, and R11 and R111 each represents a protective group for the amino group with the proviso that R11 and R111 need not be dissimilar and with the further proviso that all of R, R1, R11 and R111 may represent hydrogen atoms and pharmaceutical compositions containing the polypeptide. The groups R and R1 are particularly benzyl groups, R11 a carbobenzoxy group and R111 a p-toluenesulphonyl group. The compounds of the invention may be prepared by condensing the hexapeptide VIII, after splitting off the carbobenzoxy group, with the azide of the tripeptide VIII, to give the nonapeptide II, treating this with an alkali metal in liquid ammonia to yield the free nonapeptide and oxidising this to the cyclic polypeptide I by air or hydrogen peroxide. The hexapeptide VIII is prepared by condensing N-carbobenzoxy-L-glutaminyl-L-asparaginyl- S-benzyl- L-cysteinyl -azide with L-propyl-e -N-p-toluenesulphonyl- L-lysylgylcinamide prepared by hydrolysis of N-carbobenzoxy-L -prolyl-e -N- p-toluenesulphonyl-L-lysylglycinamide with hydrobromic acid. The tripeptide azide VIII is prepared by condensing N-carbobenzoxy- S-benzyl-L-cysteinyl-L-phenyl-alanine with L-phenylalanine methyl ester and converting the tripeptide ester in the azide with hydrazine. Pharmaceutical compositions comprise the cyclic polypeptide in addition to an inert carrier. The compositions may be formulated as solutions for injection or as nasal sprays. The peptide may be stored in the dry state when mixed with a water soluble carrier, e.g. sodium chloride, to increase its stability. The compositions have vasopressor activity.