A super active cyclic hexapeptide analog of somatostatin.

The cyclic hexapeptide, cyclo (Pro-Phe-D-Trp-Lys-Thr-Phe), I, has been shown to have the biological properties of somatostatin. We now report structure-activity studies which optimize the potency of this cyclic hexapeptide series with the synthesis of cyclo (N-Me-Ala-Tyr-D-Trp-Lys-Val-Phe), II, which is 50-100 times more potent than somatostatin for the inhibition of insulin, glucagon and growth hormone release. The hydroxyl group of tyrosine is seen to lend a 10-fold enhancement to the potency.

Synthesis and conformational study of a cyclic hexapeptide analog of somatostatin containing dehydrophenylalanine.

A cyclic hexapeptide analog of somatostatin, cyclo-(Pro-delta z-Phe-D-Trp-Lys-Thr-Phe) (II) has been synthesized by a combination of solid phase and solution methodology. It shows a potency for inhibition of growth hormone release in vitro about one-tenth that of the corresponding saturated analog, cyclo-(Pro-Phe-D-Trp-Lys-Thr-Phe) (I). N.