Stereochemistry of hydrogen introduction at C-25 in ergosterol synthesized by the mevalonate-independent pathway

Feeding of [1-C-13]glucose to Prototheca wickerhamii followed by C-13 NMR analysis of the resulting C-13-labeled ergosterol demonstrated this yeast-like al,aa operates the mevalonate-independent pathway. Based on the C-13 NMR signal assignment of [2,6,11,12,16,18,19, 21,23,27-C-13(10)] egosterol synthesized from [1-C-13]glucose indicated the pro-Z methyl group of cycloartenol is derived from C-5 of IPP and that protonation at C-25 of the Delta(25(27))-sterol intermediate takes place from the Si-face of Delta(25) to form the isopropyl pro-R methyl group. (C) 2000 Elsevier Science Ltd. All rights reserved.