Synthesis and Conformational Studies of Taa-Containing o-Nitrobenzenesulfonamide- (o-Nosyl-) Protected GS Analogs to Prove the Importance of 6R Stereochemistry of Taa over 6S

Gramicidin S (GS) is long known broad range antibiotic but limited to only topical application clinically due to its adverse hemolytic activity. We are reporting here the synthesis of Gramicidin S analogs where the turn unit D-Phe-Pro was replaced by suitably designed C6 substituted Tetrahydrofuran amino acid (Taa) moiety and side chain amine was protected as o-nitro benzene sulfonamide group (o-Nosyl). The detailed conformational analyses were also carried out by evaluating the structure activity relationship. Variation in the side chain and modification in the stereocentres of Taa play an important role towards the structure activity relationship in this class of compounds.