Figure 1.

HPLC–MS analysis of desertomycins A (1 a) and B (1 b). A) LC–ESI‐MS total ion current traces for mycelium methanol extracts from S. macronensis wild type and the ΔdstH deletion mutant. In the mutant, production of 1 a was abolished and replaced by guanidino compound 1 b. Inserts show mass spectra of [M+H]⁺ ions for 1 a (1192.7) and 1 b (1234.7). The 13.02 min and 14.27 min peaks labeled as 1 a* and 1 b* have the same MS and MS/MS as 1 a and 1 b, respectively, and may represent isomers of 1 a and 1 b of altered ring size, although this remains to be established. B) LC–ESI‐MS total ion current traces of DstH‐catalyzed conversion of desertomycin B 1 b (and putative isomer 1 b*) into desertomycin A 1 a (and putative isomer 1 a*) when Co²⁺ is present as the activating metal ion.