N-Acetylcysteine-Conjugated Benzoxazomycins and Hydroxymycotrienin Derivatives from a Hymenoptera-Associated Streptomyces sp. SID10815.

As part of our continuing search for antifungal natural products, we investigated the secondary metabolites of Streptomyces sp. SID10815, an actinomycete isolated from a ground-nesting bee-associated environment that exhibited notable antifungal activity in preliminary screenings. Herein, we report the discovery of four new N-acetylcysteine-modified ansamycins (1-4) and three new hydroxymycotrienin analogues (5-7), together with six known ansamycins (8-13), produced by this strain. These metabolites were detected and prioritized through a metabolomics-guided dereplication strategy integrating LC-MS profiling and bioactivity correlation. Their structures were elucidated by comprehensive spectroscopic analyses, including 1D and 2D nuclear magnetic resonance (1H, 13C, COSY, HSQC, HMBC, and NOESY) in combination with high-resolution mass spectrometry. The newly identified metabolites expand the structural diversity of the ansamycin family and provide a basis for future structure-activity relationship studies of N-acetylcysteine-conjugated ansamycins. These findings define a distinctive ansamycin profile of Streptomyces sp. SID10815 that may serve as a useful chemical signature for future comparative studies of insect-associated actinomycetes.