Fig. 5. Structure elucidation of megapolipeptins from P. megapolitana RL18-039-BIC-B. (A) The structures of megapolipeptin A (1) and megapolipeptin B (2). (B) Key MS/MS fragments showing neutral losses of threonine amino acid residues on the peptidic terminus of 1 and 2. (C) Reaction scheme with TMS diazomethane in DCM/MeOH affording two diastereotopic epoxide-containing products via the Büchner–Curtius–Schlotterbeck reaction. (D) Structure of partial hydrolysis product used to determine configuration of threonine residues. (E) EIC traces of Marfey's derivative of threonine (m/z = 400.15) for partial hydrolysis product, and l-threonine and l-allo-threonine standards.
