A novel active analogue of gramicidin S with smaller ring size.

A novel active gramicidin S analogue with smaller ring size, cyclo[-delta-Orn(-Val-Pro-D-Phe-H)-Leu-]2, was synthesized and examined the structure-activity relationship. Its analogue showed antibiotic activity against all Gram-positive microorganisms tested, and its activity was 1/2-1/8 of that of gramicidin S. The present results indicated that both structures of cyclo(-delta-Orn-Leu-)2 and H-D-Phe-Pro-Val sequence play the important role for showing the antibiotic activity.