Accraspiroketides A-B, Phenylnaphthacenoid-Derived Polyketides with Unprecedented [6 + 6+6 + 6] + [5 + 5] Spiro-Architecture.

Two novel polyketides, accraspiroketides A ( 1 ) and B ( 2 ), which feature unprecedented [6 + 6+6 + 6] + [5 + 5] spiro chemical architectures, were isolated from Streptomyces sp. MA37 Δ accJ mutant strain. Compounds 1 - 2 exhibit excellent activity against Gram-positive bacteria (MIC = 1.5-6.3 μg/mL). Notably, 1 and 2 have superior activity against clinically isolated Enterococcus faecium K60-39 (MIC = 4.0 μg/mL and 4.7 μg/mL, respectively) than ampicillin (MIC = 25 μg/mL).