Fungal products. Part II. Structure and stereochemistry of the acid C18H16O5, a degradation product of wortmannin

Degradation of the fungal metabolite, wortmannin, by dilute mineral acid yields, inter alia, an acid C18H16O5 to which structure (Ia) is assigned from the spectroscopic properties of its derivatives. The assigned structure (Ia) is supported by dehydrogenation of the methyl ether methyl ester (Id) to methyl 2,3-dihydro-10-methoxy-6-methyl-3-oxo-1H-cyclopenta[7,8]naphtho[2,3-b]furan-7-carboxylate (VII), a previously described degradation product of the fungal metabolite, viridin (VI; X = O).