Ring-Extended Gramicidin S Analogs Containing cis δ-Sugar Amino Acid Turn Mimetics with Varying Ring Size

This article presents a series of ring‐extended gramicidin S derivatives, 9–14, that have four ornithine residues as polar protonated side chains and one modified turn region containing a mono‐functionalized cis‐δ‐oxetane, δ‐furanoid, or δ‐pyranoid sugar amino acid residue. Of the GS analogs evaluated, we identified compound 7, which contains the mono‐benzyloxy cis‐δ‐pyranoid sugar amino acid, as having a better biological profile than the clinically applied topical antibiotic gramicidin S.