The Mechanism of Alkylation at C-24 During the C₂₉ Sterol Biosynthesis in Cucurbita maxima Seedlings

Abstract

When sodium acetate [2-¹⁴C] was incubated with germinating seeds of Cucurbita maxima Duch, 49.9 °/o of the label in sterols was found in α-spinasterol, 45.5 % in 24β-ethyl-cholesta-7, 22,25-trien-3β-ol, 3.6 % in 24/3-ethyl-cholesta-7,25-dien-3β-ol and 1 % in 24, Z-ethylidene-cholest- 7-en-3β-ol. By contrast Δ7-stigmastenol, present in the seeds and in the seedlings of Cucurbita maxima, was not formed during the germination. Cycloartenol [24-³H] [26, 27-¹⁴C] was also incorporated into phytosterols by seedlings of Cucurbita maxima. From the ³H/¹⁴C ratio of the label in the sterol acetates and their degradation products, it was possible to show that the C-24 tritium atom was retained into the 24β-ethyl-cholesta-7, 22,25-trien-3β-ol and 24β-ethyl-cholesta-7,25-dien-3β-ol but it was lost in α-spinasterol.

These results are consistent with the pathway suggested in Clerodendrum campbellii for the 24β-ethyl-25-methylene sterols.

Key Word index

Cucurbita maxima - 24α- and 24β-alkyl Sterols - Phytosterol Side Chain Biosynthesis.