Synthesis of (24R)- and (24S)-24,28-epoxyergost-5-en-3β-ols. Substrate stereospecificity in their metabolism in the insect tenebrio molitor

(24R)- and (24S)-24,28-Epoxyergost-5-en-3β-ols have been synthesized and their configuration at C-24 assigned. When these 24,28-epoxides were tritium labelled and fed in separate experiments to Tenebrio molitor larvae, only the (24R) stereoisomer was effectively converted into cholesterol, indicating that in this step of phytosterol metabolism the insect exhibits a high degree of substrate stereospecificity.