COMPARISON OF THE POTENCY OF 8-L-ARGININE, 8-D-ARGININE AND 8-D-HOMOARGININE VASOPRESSIN ANALOGS WITH SUBSTITUTED PHENYLALANINE IN POSITION-2 .236.

An analysis of the uterotonic potencies of all analogs having substitu ted L- or D-tyrosine or -phenylalanine in position 2 and L-arginine, D -arginine or D-homoarginine in position 8 was made. The series of anal ogs already published was completed by the solid phase synthesis of te n new analogs having L- or D-Phe, L- or D-Phe(2-Et), L- or D-Phe(2,4,6 -triMe) or D-Tyr(Me) in position 2 and either L- or D-arginine in posi tion 8. All newly synthesized analogs were found to be uterotonic inhi bitors. Deamination increases both the agonistic and antagonistic pote ncy. In the case of phenylalanine analogs the change of configuration froM L to D in position 2 enhances the uterotonic inhibition for more than 1 order of magnitude. The L to D change in position 8 enhances th e inhibitory potency negligibly. Prolongation of the side chain of the D-basic amino acid in position 8 seems to decrease slightly the inhib itory potency if there is L-Substituted amino acid in position 2. On t he other hand there is a tendency to the increase of the inhibitory po tency if there is D-substituted amino acid in position 2.