Regio- and stereoselective reduction of 17-oxosteroids to 17β-hydroxysteroids by a yeast strain Zygowilliopsis sp. WY7905

•Zygowilliopsis sp. WY7905 contained constitutive 17β-hydroxysteroid dehydrogenases.•It effectively catalyzed the reduction of androst-4-ene-3,17-dione to testosterone.•It also reduced other 17-oxosteroids to the corresponding 17β-hydroxysteroids.•It was not active toward steroids with only C-3 or C-20 carbonyl groups.

The reduction of 17-oxosteroids to 17β-hydroxysteroids is one of the important transformations for the preparation of many steroidal drugs and intermediates. The strain Zygowilliopsis sp. WY7905 was found to catalyze the reduction of C-17 carbonyl group of androst-4-ene-3,17-dione (AD) to give testosterone (TS) as the sole product by the constitutive 17β-hydroxysteroid dehydrogenase (17β-HSD). The optimal conditions for the reduction were pH 8.0 and 30 °C with supplementing 10 g/l glucose and 1% Tween 80 (w/v). Under the optimized transformation conditions, 0.75 g/l AD was reduced to a single product TS with >90% yield and >99% diastereomeric excess (de) within 24 h. This strain also reduced other 17-oxosteroids such as estrone, 3β-hydroxyandrost-5-en-17-one and norandrostenedione, to give the corresponding 17β-hydroxysteroids, while the C-3 and C-20 carbonyl groups were intact. The absence of by-products in this microbial 17β-reduction would facilitate the product purification. As such, the strain might serve as a useful biocatalyst for this important transformation.

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