PURPOSE: To provide a novel low-toxic compound having powerful vitamin D3-like activity, useful as a therapeutic agent for calcium dysbolism and osteoporosis.
CONSTITUTION: A compound of formula I (R is methyl or ethyl), e.g. (24R)-1α,25- dihydroxy-26,27-dimethylvitamin D2. The compound of the formula I can be obtained by the following processes: the protecting group of a compound of formula III produced from a compound of formula II as starting material is eliminated to form a compound of formula IV, which is, in turn, irradiated with light of rays using a medium-pressure mercury lamp and then thermally isomerized.
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