Investigations on the Δ 23-, Δ 24(28)- and Δ 25-Sterols of zea mays

Abstract

The sterols of Zea mays shoots were isolated and characterized by TLC, HPLC, GC/MS and 1H NMR techniques. In all, 22 4-demethyl sterols were identified and they included trace amounts of the Δ 23-, Δ 24- and Δ 25-sterols, 24-methylcholesta-5, E-23-dien-3β-ol, 24-methylcholesta-5, Z-23-dien-3β-ol, 24-methylcholesta-5,25-dien-3β-ol, 24-ethylcholesta-5,25-dien-3β-ol and 24-ethylcholesta-5,24-dien-3β-ol. In the 4,4-dimethyl sterol fraction, cycloartenol and 24-methylenecycloartanol were the major sterol components but small amounts of the Δ 23-compound, cyclosadol, and the Δ 25-compound, cyclolaudenol, were recognized. These various Δ 23- and Δ 25-sterols may have some importance in alternative biosynthetic routes to the major sterols, particularly the 24β-methylcholest-5-en-3β-ol component of the C 28-sterols. Radioactivity from both [2- 14C]MVA and [methyl- 14C]methionine was incorporated by Z. mays shoots into the sterol mixture. Although 24-methylene and 24-ethylidene sterols were relatively highly labelled, the various Δ 23- and Δ 25-sterols contained much lower levels of radioactivity, which is possibly indicative of their participation in alternative sterol biosynthetic routes. (24R)-24-Ethylcholest-5-en-3β-ol (sitosterol) had a significantly higher specific activity than the 24-methylcholest-5-en-3β-ol indicating that the former is synthesized at a faster rate.