Replacement of the disulfide bond in oxytocin by an amide group. Synthesis and some biological properties of [cyclo-(1-L-aspartic acid, 6-L-.alpha.,.beta.-diaminopropionic acid)]oxytocin

As part of a continuing investigation of the steric and electronic functions of the disulfide group in neurohypophyseal hormones on their biological activity, the synthesis of "oxytocin lactam", [cyclo-(1-aspartic acid,6-alpha,beta-diaminopropionic acid)]oxytocin, has been undertaken. The protected nonapeptide was prepared in a stepwise manner by solution techniques; after removal of side-chain protecting groups, formation of the briding amide bonds was accomplished by oxidation-reduction condensation. The analogue possesses rat uterotonic, avian vasodepressor, and rat antidiuretic potencies of 16 +/- 2, 6.6 +/- 0.6, and 5.6 +/- 3.8 units/mg, respectively.