The predominant 4‐desmethylsterols from the leaves of 13 species in eight genera of the family Chenopodiaceae are 24α‐ethylsterols. In four species,Chenopodium ambrosioides L.,C. rubrum L.,Salicornia europaea L. andS. bigelovii Torr., the C‐22(23) double bond is introduced into more than 70% of the 24α‐ethylsterols producing spinasterol (24α‐ethylcholesta‐7,22E‐dien‐3β‐ol) in the first two species and mixtures of spinasterol and stigmasterol (24α‐ethylcholesta‐5,22E‐dien‐3β‐ol) in the latter species. The saturated side chain analogues predominate with more than 70% of the 24α‐ethylsterols in eight species.Salsola kali L.,Suaeda linearis (Ell.) Moq.,Kochia scoparia (L.) Roth., andBassia hirsute (L.) Aschers. synthesize sitosterol (24α‐ethylcholest‐5‐en‐3β‐ol), andAtriplex arenaria Nutt.,C. album L.,C. urbicum L. andC. leptophyllum Nutt. possess mixtures of sitosterol and 22‐dihydrospinasterol (24α‐ethylcholest‐7‐en‐3β‐ol). Sitostanol (24α‐ethyl‐5α‐cholestan‐3β‐ol) was isolated fromSuaeda linearis as an 18% component of the total 4‐desmethylsterol and in lesser amounts from four other species. In all species synthesizing 24‐ethyl‐Δ5‐sterols, a 24ξ‐methylcholest‐5‐en‐3β‐ol was also present at 1.0–20% of the total 4‐desmethylsterol. Avenasterol [24‐ethylcholesta‐7,24(28)Z‐dien‐3β‐ol], isofucosterol [24‐ethylcholesta‐5,24(28)Z‐dien‐3β‐ol), cholesterol (cholest‐5‐en‐3β‐ol) and 24ξ‐methyl‐5α‐cholestan‐3β‐ol also were isolated from several species. Species in the family Chenopodiaceae and the type genusChenopodium may be categorized into one of three groups based on sterol biosynthesis: the Δ7‐sterol producers; the Δ5‐sterol producers, and those producing mixtures of both Δ7‐ and Δ5‐sterols in relatively fixed percentage compositions.
The 4-desmethylsterols from the leaves ofBeta vulgaris are a mixture of Δ(7)-sterols (71%) and Δ(5)-sterols (29%). The Δ(7)-sterols isolated are spinasterol (24α-ethylcholesta-7,22-dien-3β-ol; 45%), 22-dihydrospinasterol (24α-ethylcholest-7-en-3β-ol; 24%), and avenasterol (24-ethylcholesta-7,24(28)-dien-3β-ol; 1.5%). The Δ(5)-sterols isolated are sitosterol (24α-ethylcholest-5-en-3β-ol; 15%), 24ζ-ethylcholesta-5,22-dien-3β-ol (7.5%), and 24ζ-methylcholest-5-en-3β-ol (7%).
The metabolism of three dietary 4,4-desmethylsterols and two 4 alpha-methylsterols was investigated in the free-living nematode Caenorhabditis elegans. Dietary cholestanol was converted mostly to lathosterol. Dietary lathosterol, 7-dehydrocholesterol, 4 alpha-methylcholest-7-enol and 4 alpha-methylcholest-8(14)-enol each remained largely unchanged. An absolute requirement for a substantial quantity of 7-dehydrocholesterol in C. elegans did not exist. C. elegans was unable to remove a 4 alpha-methyl group or introduce a double bond at C-5 and also demonstrated the lack of a delta 7-reductase. Its nutritional sterol requirement was satisfied by cholestanol, lathosterol or 7-dehydrocholesterol; growth was comparable to that obtained previously in media containing delta 5-sterols. However, the two 4 alpha-methylsterols appeared to be unsatisfactory sterol nutrients. The possible physiological importance of 4 alpha-methylsterols is discussed briefly.
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