The hemolytic activity of all the synthesized cyclic peptides was determined against the human red blood cells (hRBCs) as an in vitro cytotoxicity indicator. In Series 1, among the peptides designed by replacing one residue at a time with its D-isomer (1a-7a), peptide 7a, having D-Arg at the first position, was found to be less hemolytic with HC50 = 165 µg/mL. A similar trend was observed for Series 2 peptides (1b-7b), with minimum hemolysis observed for 7b (HC50 = 170 µg/mL). Noticeably, compared to their parent peptides p1 and p2, 7a and 7b, respectively, displayed around twofold reduction in hemolytic activity (Figure ).