Studies on vitamin D and related compounds IV: The pattern of the photochemical conversion of the provitamins D

Abstract

Abstract Solutions of about equal amounts of 7‐dehydrocholesterol‐3‐C 14 and (inactive) lumisterol 3 were irradiated with ultra‐violet light (265‐280 mμ) for short periods of time, resulting in approximately 10% conversion of the provitamin. Similar experiments were performed with labelled ergosterol (obtained by growing yeast in a medium containing acetate‐1‐C 14 ), admixed with inactive lumisterol 2 and tachysterol 2 . Isolation of the compounds present in the irradiated solutions was effected by precipitating the pro‐vitamin D with digitonin and separating the remaining components according to their different rates of reaction with maleic anhydride (tachysterol > vitamin D> lumisterol). The specific radio‐activities of the products isolated gave clear‐cut evidence that lumisterol does not play any part as an intermediate in the main route of the reaction provitamin D → tachysterol nor in the conversion provitamin D → vitamin D. Besides, lumisterol seems to be formed at a relatively low rate under the conditions employed, which are comparable with those generally used in vitamin D synthesis. As to tachysterol, here conclusions were somewhat less definite because this compound has rather a high rate of photochemical formation and decomposition and is difficult to purify. The specific activity measurements, however, strongly supported the conclusion that also tachysterol is not a necessary intermediate in the vitamin D formation. Thus the results are contradictory to the traditional scheme provitamin D magnified image lumisterol magnified image tachysterol magnified image previtamin D ⇄ vitamin D, and are strongly in favour of a reaction pattern of the following type: magnified image