Studies on the Constituents of Asclepiadaceae Plants. XL. Absolute Configurations of Tomentogenin and Utendin

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The configuration at C-20 of tomentogenin and utendin was determined as s by means of the circular dichroism experiment of 20-O-o-nitrobenzoyl derivatives. From these results, the absolute configurations of tomentogenin and utendin were determined as 5α-pregnan-3β, 12β, 14β, 17β, 20α-pentol and pregn-5-ene-3β, 12β, 14β, 17β, 20α-pentol, respectively.