An easy stereoselective synthesis of 5(10)-estrene-3β,17α-diol, a biological marker of pregnancy in the mare

•5(10)-Estrene-3β,17α-diol is an essential reference material for doping analysis in horse-racing laboratories.•A stereoselective synthesis of this compound is described.•The 3β alcohol was obtained via asymmetric transfer hydrogenation using Noyori catalyst.•Final purification was performed according to a chemoenzymatic process.

5(10)-Estrene-3β,17α-diol is an essential reference material for doping analysis in horse-racing laboratories. It is used to detect misuse, for doping purpose, of the pregnancy status in the mare. Its stereoselective synthesis from 17β-estradiol-3-methyl ether (prepared from estrone or 17β-estradiol) was performed in four steps: (1) Mitsunobu inversion of the 17β-alcohol; (2) Birch reduction of the aromatic ring; (3) stereoselective reduction of the 3-ketone via Noyori asymmetric transfer hydrogenation; (4) chemoenzymatic purification.

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