Calcitriol Derivatives with Two Different Side Chains at C-20. II. Diastereoselective Syntheses of the Metabolically Produced 24(R)-Hydroxygemini¹

Vitamin D derivatives containing two side chains emanating at C-20 are known as gemini. We have recently synthesized two gemini which are related to calcitriol and 19-norcalcitriol containing two identical side chains. The metabolism of these species involves 24(R)-hydroxylation on one of the side chains. To determine the outcome of this diastereospecific transformation, we synthesized both C-20 epimeric pairs containing the 24(R)-hydroxy group in the gemini and 19-norgemini series. On the basis of the availability of these reference compounds, it was shown that the metabolic hydroxylation occurred at the pro-R side chain in both gemini compounds. In comparison to the parent compounds, the 24-hydroxygemini required higher doses to increase blood calcium levels in mice and to suppress INF-γ release in MLR.