Viridicatumtoxins: Exploring structural diversity and antibiotic properties

Viridicatumtoxins are a rare class of antibiotics composed of a tetracycline scaffold and a geranyl-derived spirobicyclic ring. Chemical investigation of a fungus Paecilomyces sp. obtained from a marine mollusc Siphonaria sp. led to the isolation of three novel viridicatumtoxin lactones, named viridicatumtoxins D-F (4-6), together with two known compounds, viridicatumtoxins A (1) and B (2). Re-cultivation of this fungus on rice solid media afforded one new compound viridicatumtoxin C (3), together with two known metabolites, spirohexaline (7) and previridicatumtoxin (8). Compounds 4 and 5 were proved to be natural products by the acid stability study of 1. The antibacterial and cytotoxicity activities of 1-8 were also evaluated.