For further studies, peptides were selected based on the therapeutic index. For each cyclic peptide, the therapeutic index was calculated by dividing HC50 values by the MICs against S. aureus (ATCC 29213). The therapeutic index values are presented as a bar graph, with peptides showing higher therapeutic index in each series (7a, 12a, 7b, 12b, 15c, 16c, 20c, 15d, and 16d) highlighted in green (Figure ). Peptides with higher therapeutic index were selected for broad-spectrum antimicrobial activity and cell cytotoxicity studies.