Fig. 3.

(A) Our approach for the structure elucidation of jessenipeptin. (B) GC-MS traces of derivatized fatty acid moiety (top trace) and traces of the corresponding synthetic (R)- and (S)-configured 3-hydroxy decanoic acid derivatives (bottom trace). The fatty acid derivative obtained from jessenipeptin coelutes with the respective (R)-configured synthetic counterpart. (C) Scandium triflate-mediated peptide cleavage yields fragments F1 and F2. A single l-alanine is present in F1. (D) Stable-isotope labeling results in shifts of one mass unit for fragments containing l-alanine in MS/MS experiments. The MS spectra of unlabeled jessenipeptin are depicted in green; the corresponding spectra of the labeled peptide are depicted in red. The mass shifts observed in two indicative fragments (m/z 776 and 507) are shown.