As the first stable tachysterol analogs, 14-epi-19-nortachysterol and its 2-substituted derivatives
were synthesized using the Stille coupling reaction between the A-ring precursor (three vinylstannanes) and
the CD-ring vinyl trifrate. Among them, the 2-methylidene group was hydrogenated with Wilkinson’s catalyst
regioselectively to obtain 2α- and 2β-methyl analogs after separation; therefore, five new 14-epi-19-
nortachysterols were constructed. All 14-epi-19-nortachysterols showed moderate to strong human vitamin D
receptor (hVDR) binding affinity except the 2α-(3-hydroxypropoxy) substituted analog. X-ray cocrystallographic
analysis of the [truncated hVDR]-[2-methyl-14-epi-19-nortachysterol] complex exhibited an unusual binding
structure that has not been observed previously.
Keywords: Crystal structure, 14-Epimerization, Stille coupling, Tachysterol, Vitamin D3, Vitamin D receptor.
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