New 2-alkylidene 1α,25-dihydroxy-19-norvitamin D3 analogues of high intestinal activity:: Synthesis and biological evaluation of 2-(3′-alkoxypropylidene) and 2-(3-hydroxypropylidene) derivatives

In a search for novel vitamin D compounds of potential therapeutic value, E- and Z-isomers of 1 alpha,25-dihydroxy-2-(3 '-hydroxypropylidene)-19-norvitamin D-3, as well as a derivative of the former compound possessing a 3 '-(methoxymethoxy)propylidene substituent at C-2, were efficiently prepared. All vitamins were obtained in convergent syntheses, starting with (-)-quinic acid and the protected 25-hydroxy Grundmann ketones. Quinic acid was converted into keto lactone 11, and a substituted hydroxypropylidene group was attached by Wittig reaction yielding pairs of isomeric compounds 12, 13 and 14, 15. These olefinic products were then transformed into phosphine oxides 32-34 which were subjected to Lythgoe type Wittig-Horner coupling with C,D-fragments 35a and 35b. An alternative route was also elaborated that comprised Julia coupling of sulfones 39a and 39b with the cyclohexanone derivative 23. The binding of all synthesized vitamins to the full-length rat recombinant vitamin D receptor (VDR) is either similar to or within one log of 1 alpha,25(OH)(2)D-3. The in vivo tests have revealed that the calcemic activity of all analogues in the E-series (5a, 6a, 6b) is considerably higher than that of the native hormone.