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

High-resolution tandem mass spectrometry (HR-MS 2 )-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.