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Chemical investigations into solid phase cultivations of an Australian sheep station pasture plant-derived Streptomyces sp. CMB-PB042, yielded the rare enamine naphthopyranoquinones BE-54238A (1) and BE-54238B (2), together with four new analogues, glenthenamines B–D (4–6) and F (8), and two handling artifacts, glenthenamines A (3) and E (7). Single crystal X-ray analyses of 1–2 resolved configurational ambiguities in the scientific literature, while detailed spectroscopic analysis and biosynthetic considerations assigned structures inclusive of absolute configuration to 3–8. We propose a plausible sequence of biosynthetic transformations linking structural and configurational features of 1–8, and apply a novel Schiff base "fishing" approach to detect a key deoxyaminosugar precursor. These enamine naphthopyranoquinone disclose a new P-gp inhibitory pharmacophore capable of reversing doxorubicin resistance in P-gp overexpressing colon carcinoma cells.

A marine-derived Streptomyces sp. (CMB-M0244) isolated from a sediment collected off South Molle Island, Queensland, produced mollemycin A (1) as a new first in class glyco-hexadepsipeptide-polyketide. The structure of 1 was assigned by detailed spectroscopic analysis, supported by chemical derivatization and degradation, and C3 Marfey's analysis. Mollemycin A (1) exhibits exceptionally potent and selective growth inhibitory activity against Gram-positive and Gram-negative bacteria (IC50 10-50 nM) and drug-sensitive (3D7; IC50 7 nM) and multidrug-resistant (Dd2; IC50 9 nM) clones of the malaria parasite Plasmodium falciparum.