Metabolism of 24(R,S),25-epiminolanosterol to 25-aminolanosterol and lanosterol by Gibberella fujikuroi

Mycelia of Gibberella fujikuroi metabolized 2-tritio-24(R,S),25-epiminolanosterol, a novel fungal sterol biosynthesis inhibitor that regulates Δ²⁴-sterol methyltransferase, to 25-aminolanosterol (a new sterol) and lanosterol. The identities of the two sterols were established by cochromatography with authentic samples, mass spectroscopy, and isotopic dilution and recrystallization to constant specific activity. The newly biosynthesized tritiolanosterol was demonstrably introduced into the sterol pathway as evidenced by significant tritium label in the radiochemically purified sterols; 24(28)-methylene-24, 25-dihydrolanosterol and 14-norlanosterol. The results demonstrate for the first time the direct reduction in situ of an aziridine ring to a tertiary amine and the stereocontrolled deamination of a C-25 aminosteroid to produce a Δ²⁴, rather than a Δ²⁵⁽²⁷⁾, steroid.