Synthesis and biologic activity of 3β-thiovitamin D₃

We synthesized 3β-thiovitamin D₃ from 7-dehydrocholesterol and tested its biological activity and protein binding properties. The thiovitamin was found to be a weak vitamin D agonist at high doses in vivo. It was poorly bound by both vitamin D-binding protein as well as by the intestinal cytosol receptor for 1,25-dihydroxyvitamin D. It did not increase the synthesis of calcium binding protein in the chick embryonic duodenum and did not block the activity of 1,25-dihydroxyvitamin D₃ in this system We conclude that 3β -thiovitamin D₃ is a weak vitamin D agonist in vivo with no agonist activity or antagonist activity to 1,25-dihydroxyvitamin D₃ in the chick embryonic duodenum.