Abstract: Based on the EDRF(endothelium derived relaxing factor)-like effects for polyarginine Arg-Arg-OH was selected as the lead compound and its derivatives Arg-Arg-OCH3. Arg Arg-Arg-OH, HO-ArgCOCH2CH2COArg-OH, HO-ArgCOCH2COArg-OH, were synthesized. These substances showed on bioassay various degrees of vasorelaxant activities. With protection for the C-terminal of Arg-Arg-OH with a methyl ester. The vasorelaxing activitv was decreased. In contrast.when the N-terminal of Arg-OH was protected with malonic acid or butane diacid. The biological activites were lower than those of Arg-Arg-OH due to the lowered metabolic rate. With protection of N-terminal of Arg-Arg-OH with L-Arg residue.Arg-Arg-Arg-OH was obtained, which showed a vasorelaxing activity better than that of Arg-Arg-OH. The bioactivities observed on the Wister's rats for the former com- pound become the experimental basis for prodrug design of EDRF.

Key words: Polyarginine oligopeptide, Structure-activity relationships, Endothelium derived relaxing factor (EDRF)-like activties