Oxysporizoline, an antibacterial polycyclic quinazoline alkaloid from the marine-mudflat-derived fungus Fusarium oxysporum

During the course of our studies on bioactive constituents of marine-derived microorganisms, we isolated antibacterial cerebrosides, flavusides A and B, from the marine-derived fungus Aspergillus flavus, and determined their absolute stereostructures.¹

In a subsequent study of the antibacterial chemical constituents of the marine-derived fungi, we found that a crude extract from a small-scale culture (100 ml) of the marine-mudflat-derived fungus Fusarium oxysporum displayed in vitro antimicrobial activity against methicillin-resistant and multidrug-resistant Staphylococcus aureus (MRSA and MDRSA) in a primary screen. We used a large-scale culture (10 l) to purify the antibacterial metabolites from the broth extract. By fractionating the extract, we isolated a new antibacterial alkaloid, a tris-anhydrotetramer of anthranilic acid (α-aminobenzoic acid), named oxysporizoline (1); the alkaloid 1H-indol-3-butanamide (2)² and two polyketides, chlamydosporol (3)³ and butenolide (4-acetamido-4-hydroxy-2-butenoic acid r-lactone) (4).⁴ In this paper, we report the structural elucidation of these alkaloids and polyketides.

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