Tianchimycins A–B, 16-membered macrolides from the rare actinomycete Saccharothrix xinjiangensis

Two new 16-membered macrolactone-type polyketides, Tianchimycin A (1) and B (2), were isolated from the rare actinomycete Saccharothrix xinjiangensis NRRL B-24321, together with one known compound, swalpamycin B (3). The isolated compounds were structurally characterized using 1D and 2D NMR and MS techniques. The antimicrobial activities of 1–3 were determined against a panel of Gram-negative and Gram-positive bacteria including five hospital isolates from NHS Grampian. Compound 3 displayed moderate antibacterial activity against three MRSA clinical isolates and Enterococcus faecalis ATCC 29212.