A convenient synthesis of 7 alpha-hydroxycholest-4-en-3-one by the hydroxypropyl-beta-cyclodextrin-facilitated cholesterol oxidase oxidation of 3 beta,7 alpha-cholest-5-ene-3,7-diol.
The initial biosynthetic conversions of cholesterol to the bile acids involve sequential 7 alpha-hydroxylation (catalyzed by cholesterol 7 alpha-hydroxylase) followed by C-3 oxidation and concomitant double bond migration (to a delta 4-configuration, catalyzed by 3 beta-delta 5-C27-steroid oxidoreductase) to provide 7 alpha-hydroxycholest-4-en-3-one. A straightforward, and economical, preparation (on a 0.1 g scale) of this pivotal biosynthetic intermediate has been devised. Reduction of 3 beta-(benzoyloxy)-cholest-5-en-7-one with LiB(sec-butyl)3H provided a 4:1 mixture, respectively, of the 7 alpha- and 7 beta-hydroxy diastereomers, which were separated chromatographically. Solvolytic removal of the C-3 benzoyl group gave 3 beta,7 alpha-cholest-5-ene-3,7-diol. A suspension of the 1:1 (v/v) complex (formed by mutual dissolution in MeOH, followed by evaporation of the solvent) of this diol with hydroxypropyl-beta-cyclodextrin, at a concentration of 1 mg mL-1 (in neutral phosphate buffer), was converted by Brevibacterium sp cholesterol oxidase (0.25 U mg-1 of substrate) and catalase (70 U mg-1 of substrate, to recover O2 from the H2O2 produced by the enzymatic oxidation) to a suspension of 7 alpha-hydroxycholest-4-en-3-one and the hydroxypropyl-beta-cyclodextrin. The yield for the enzymatic conversion was in excess of 90%. A much poorer and less reproducible yield (< 20%) was seen in the absence of the hydroxypropyl-beta-cyclodextrin. Routine extraction of this aqueous suspension, and chromatographic purification (85:15 CHCl3/acetone v/v on silica) of the residue, gave pure 7 alpha-hydroxycholest-4-en-3-one in 68% isolated yield. This route is a significant improvement, in terms of reaction scale and convenience, over the previous procedures for the preparation of this steroid.
Alexander
D L
DL
Upjohn Laboratories, Kalamazoo Michigan 49007-4940, USA.
Fisher
J F
JF
D000073738:2-Hydroxypropyl-beta-cyclodextrin; D002783:Cholestenones / Q000737:chemistry / Q000378:metabolism*; D002789:Cholesterol Oxidase / Q000378:metabolism*; D003505:Cyclodextrins / Q000494:pharmacology*; D006888:Hydroxycholesterols / Q000378:metabolism*; D010084:Oxidation-Reduction; D013237:Stereoisomerism; D047391:alpha-Cyclodextrins; D047392:beta-Cyclodextrins
D002783:Cholestenones; D003505:Cyclodextrins; D006888:Hydroxycholesterols; D047391:alpha-Cyclodextrins; D047392:beta-Cyclodextrins; C479658:hydroxypropyl-alpha-cyclodextrin; D000073738:2-Hydroxypropyl-beta-cyclodextrin; C002656:7 alpha-hydroxy-4-cholesten-3-one; C011724:cholest-5-en-3 beta,7 alpha-diol; D002789:Cholesterol Oxidase