Targeted Isolation of Saalfelduracin B–D from Amycolatopsis saalfeldensis Using LC-MS/MS-Based Molecular Networking

High-resolution tandem mass spectrometry (HR-MS2)-based metabolomic studies of Amycolatopsis saalfeldensis, isolated from the "Saalfelder Feengrotten" caves in Germany, led to the isolation of three ribosomally synthesized and post-translationally modified type II thiopeptides, saalfelduracin B-D (1-3) and the known saalfelduracin A (4). The structures of all four compounds were determined by comparative two-dimensional NMR analysis and high-resolution tandem mass spectrometry.