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Synthesis of 24-Oxavitamin D3 and 1α-Hydroxy-24-oxavitamin D3.-The metabolite (Vd), the hormonally active form of vitamin D3 (Vc) is used for the treatment of certain cancers and skin diseases. Since its applicability is limited due to its secondary strong calcemic effects, it has been of interest to develop modified analogues with high cell differentiating ability and low calcemic action. In order to find vitamin D analogues with these types of properties, the title compounds (Va) and (Vb) are synthesized starting with the fragment ( III) (obtained from vitamin D2 (I)) via coupling with the appropriate A-ring fragments (IV) or (VI) as the key steps. -(SARANDESES, L. A.; VALLES, M. J.; CASTEDO, L.; MOURINO, A.; Tetrahedron 49 (1993) 3, 731-738;