Six new degraded steroids including an unprecedented 4-methyl-androstane with oxabicyclo[3.2.1]octane moiety from Nodulisporium sp.

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Abstract 4-Methyl-androstanes are a class of rare steroid. A chemical investigation on Nodulisporium sp. led to the isolation of an unprecedented 4-methyl-androstane (nodulisporandrostane A, 1) with an ether linkage between C-4 and C-9 forming an oxabicyclo[3.2.1]octane ring system, along with five biosynthetic related new androstanes (nodulisporandrostanes B–F, 2–6). Their structures were determined by detailed NMR analyses, X-ray crystallography, and NMR calculations. Based on the isolated compounds and our previous works, a plausible biosynthetic pathway of 1–6 was also proposed.