Lactoquinomycin B, a novel antibiotic

Streptomyces tanashiensis IM8442T was found to produce lactoquinomycin B, a novel antibiotic, together with lactoquinomycin A. Lactoquinomycin B was purified, and the physico-chemical and biological characteristics were studied. Lactoquinomycin B, C24H27NO9, mp 149-152 degrees C (dec), FD-MS m/z 473 (M+), is a basic substance, showing UV lambda MeOHmax (epsilon) 239 (15,100), 287 (3,450) and 369 nm (5,300), and IR nu CHCl3max 1790 (gamma-lactone), and 1700 and 1650 (quinone) cm-1. The structure of lactoquinomycin B was elucidated by 1H NMR and 13C NMR in comparison with those of lactoquinomycin A, indicating that B is a 4a,10a-epoxide derivative of A. Lactoquinomycin B displayed inhibitory activity against bacteria, particularly Gram-positive organisms, and cytotoxicity against human and murine tumor cell lines. LD50 for mice was ca. 40 mg/kg by iv route.