A 20S Combined with a 22R Configuration Markedly Increases both in Vivo and in Vitro Biological Activity of 1α,25-Dihydroxy-22-methyl-2-methylene-19-norvitamin D3

Six new analogues of 1 alpha,25-dihydroxy-19-norvitamin D-3 (3a-4b, 5, and 6) were prepared by a convergent synthesis applying the Wittig-Horner reaction as a key step. The influence of methyl groups at C-22 on their biological activity was examined. It was established that both in vitro and in vivo activity is strongly dependent on the configuration of the stereogenic centers at C-20 and C-22. Introduction of the second methyl group at C-22 (analogues 5 and 6) generates the compounds that are slightly more potent than 1 alpha,25-(OH)(2)D-3 in the in vitro tests but much less potent in vivo. The greatest in vitro and in vivo biological activity was achieved when the C-20 is in the S configuration and the C-22 is in the R configuration. The building blocks for the synthesis, the respective (20R,22R)-, (20R,22S)-, (20S,22R)-, and (20S,22S)-diols, were obtained by fractional crystallization of mixtures of the corresponding diastereomers. Structures and absolute configurations of the diols 21a, 21b, and 22a as well as analogues 3a, 5, and 6 were confirmed by the X-ray crystallography.