Stereo-retained and stereo-selective lactonization of four diastereoisomers of 23,25,26-trihydroxyvitamin D3 in homogenates of kidney from vitamin D-supplemented chicks.

To elucidate the biosynthesis of 25-hydroxyvitamin D3-26,23-lactone, various vitamin D3 derivatives were incubated individually with kidney homogenates prepared from vitamin D3-supplemented chicks, a preparation known to produce the 25-hydroxyvitamin D3-26,23-lactone from 25-hydroxyvitamin D3. The 25-hydroxyvitamin D3-26, 23-lactone produced in vitro was then separated, purified, identified, and quantitated by consecutive analysis by high-pressure liquid chromatography. The naturally occurring 23(S), 25(R)-25-hydroxyvitamin D3-26,23-lactone was produced from 23(S),25-dihydroxyvitamin D3, 25(R),26-dihydroxyvitamin D3, and 23(S),25(R),26-trihydroxyvitamin D3. 23(S),25 (S)-25-Hydroxyvitamin D3-26,23-lactone was synthesized from 25(S),26-dihydroxyvitamin D3 and 23(S),25(S),26-trihydroxyvitamin D3. The relative amounts of 25-hydroxyvitamin D3-26,23-lactones generated from the following vitamin D3 derivatives used as substrate (23(S),25(S),26-trihydroxyvitamin D3; 23(R),25(R),26-trihydroxyvitamin D3; 23(S),25(R),26-trihydroxyvitamin D3; 23(R),25(S),26-trihydroxyvitamin D3; 23(S), 25-dihydroxyvitamin D3; 23(R),25-dihydroxyvitamin D3; 25(S),26-dihydroxyvitamin D3; and 25(R),26-dihydroxyvitamin D3) are, respectively, 15:1.7:24:3.3:2.5:0:1:1.7. These results indicate that when the lactonization at C-23 and C-26 positions of various vitamin D3 derivatives occurred the stereochemical configuration at their C-23 and/or C-25 positions was not changed and the difference of the stereochemical configurations determined the rate of lactonization.