Design and efficient synthesis of 2α-(ω-hydroxyalkoxy)- 1α,25-dihydroxyvitamin D₃ analogues, including 2-epi-ED-71 and their 20-epimers with HL-60 cell differentiation activity

A concise and efficient synthetic approach to 2α-(ω- hydroxyalkoxy)-1α,25-dihydroxyvitamin D₃ (4a-c), including 2-epi-ED-71, was developed starting from D-glucose as a chiral template for the construction of the 2α-modified A-ring precursors (11a-c). It was found that the best ligand for the bovine thymus vitamin D receptor (VDR) in this series is 4b, which has 1.8 times greater binding affinity for the bovine thymus VDR than that of the natural hormone 1. Interestingly, potency in the induction of HL-60 cell differentiation for 4a-c was almost the same or weaker than that of 1 despite the strong binding affinity for the VDR. Next, we were interested in the "double modification" of 1 based on 4a-c with C20-epimerization, affording 2α-(ω-hydroxyalkoxy)-20-epi-1α, 25-dihydroxyvitamin D₃ (20-epi-4a-c). All three 2α-substituted 20-epi analogues of 1 (20-epi-4a-c) exhibited stronger binding affinities for the VDR, and their conformations in the ligand binding domain of VDR were analyzed by molecular modeling. Double-modified analogues of 20-epi-4a-c showed marked HL-60 cell differentiation activity, and 20-epi-4a possesses an activity 58-fold higher than that of the natural hormone 1.