New derivative of 1alpha,25-dihydroxy-19-norvitamin D3 with 3'-alkoxypropylidene moiety at C-2: synthesis, biological activity and conformational analysis

In pursuit of novel biologically active Vitamin D compounds of potential therapeutic value, 1alpha,25-dihydroxy-2-[3'-(methoxymethoxy)propylidene]-19-norvitamin D(3) (7) was efficiently prepared in a convergent synthesis, starting with (-)-quinic acid and the protected 25-hydroxy Grundmann ketone 16. The key synthetic step involved Lythgoe type Wittig-Horner coupling of 16, with the phosphine oxide 15. Molecular modeling was employed to establish the A-ring conformation of the synthesized Vitamin 7. Also, preliminary modeling of its complex with the rVDR was performed and interactions between ligand and the binding domain analyzed. Analog 7 was found to be only six times less potent than 1alpha,25-(OH)(2)D(3) (1) in binding to the rat recombinant Vitamin D receptor (VDR). In comparison with hormone 1, it also showed slightly lower cellular HL-60-differentiation activity. Preliminary in vivo tests indicated unusually high calcemic activity of 7.