Fujimoto Y, Morisaki M, Ikekawa N
Biochemistry. 1980 Mar 18;19(6):1065-9. doi: 10.1021/bi00547a003.
Studies on the stereochemistry of 24,28-epoxy-24-ethylcholesterol, a key intermediate in sitosterol to cholesterol conversion in insects, were undertaken. In nutritional experiments, the 24R,28S and 24S,28R stereoisomers (isofucosterol epoxides) were unable to support growth and development of silkworm larvae. Incubation of 3 alpha-3H-labeled (24R,28R)- and (24S,28S)-epoxide (fucosterol epoxides) with a cell-free preparation from silkworm guts resulted in effective conversion into desmosterol and cholesterol; (24R,28R)-epoxide was the slightly better substrate. Fucosterol incubation yielded (24R,28R)-epoxide and the 24S,28S isomer in approximately equal amounts, while slightly preferential formation of the 24R,28R isomer was observed in in vivo experiments. These results indicate that both the formation of the epoxide from fucosterol and its conversion to desmosterol proceed with a low degree of stereospecificity.
对24,28 - 环氧 - 24 - 乙基胆固醇（昆虫中豆甾醇向胆固醇转化的关键中间体）的立体化学进行了研究。在营养实验中，24R,28S和24S,28R立体异构体（异岩藻甾醇环氧化物）无法支持家蚕幼虫的生长和发育。用家蚕肠道的无细胞制剂孵育3α - 3H标记的(24R,28R)-和(24S,28S)-环氧化物（岩藻甾醇环氧化物），可有效转化为胆甾烯醇和胆固醇；(24R,28R)-环氧化物是稍好的底物。孵育岩藻甾醇可产生大致等量的(24R,28R)-环氧化物和24S,28S异构体，而在体内实验中观察到24R,28R异构体的形成略有偏好。这些结果表明，从岩藻甾醇形成环氧化物及其向胆甾烯醇的转化过程中，立体特异性程度都较低。
