Aspergillus microcysticus

The A. A u. B are antibacterial and antifungal metabolites from Aspergillus microcysticus while A. C, D and E have no antimicrobial activity. They belong to the class of cytochalasins. The are formed biogenet-ically from leucine and a polyketide chain. A. A C24H33NO4, Mr 399.53, light yellow powder, [a]p -20°. 

Very recently Keller-Schierlein and Kupfer (1979) reported the isolation and structure of four new metabolites of Aspergillus microcysticus, the aspochalasins A (lO-isopropyl-14-methyl-[l l]cytochalasa-6,13-diene-1,17,18,21-tetrone), B (17-hydroxy-10-isopropyl-14-methyl-[1 l]cytochalasa-6,13,19-triene-l,18,21-trione), C (17,18-dihydroxy-10-isopropyl-14-methyl-[1 l]cytochalasa-6,13,19-triene-l,21-dione), and D. The latter is a diastereomer of aspochalasin C. The aspochalasins contain an isopropyl group at C-10 indicating leucin being a biogenetic precursor. The isolation of the aspochalasins has raised the number of natural cytochalasans from 24 to 28. 

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