Biosynthesis of ergosta-4,6,8(14),22-tetraen-3-one. A novel oxygenative pathway

Specifically (tritium) labeled precursors (VIII, X, XIV, XV, and XVI), upon feeding to Penicillium rubrum, are incorporated into ergosta-4,6,8(14),22-tetraen-3-one (IV) to the extent of 14.2, 4.5, 11.4, 16.3, and 5.5% respectively. Proof that the ergostane skeleton was incorporated intact was afforded by a chemical-biosynthetic cycle, the latter stages of which entailed reduction of isolated (IV) to ergosterone (VIII), followed by removal of the label through base-catalyzed exchange. A search of the growth medium of P. rubrum revealed the presence of nonartefactual ergosterol epidioxide (XIII) and ergosta-6,22-dien-3β,5α,8α-triol (XVIII). The incorporation data are consistent with a set of multiple pathways with no unique biosynthetic sequence apparent.