Novel 12 alpha-hydroxysteroid dehydrogenases, production and use thereof

A process for the preparation of ursodeoxycholic acid (UDCA) of the formula (1)

• in which
• R represents alkyl, NR1R2, H, an alkali metal ion or N(R3)4+, in which the radicals R3 are identical or different and represent H or alkyl, where
• a) a cholic acid (CA) of the formula (2)
• in which R has the meanings indicated above, and the radicals Ra are identical or different and represent H or acyl, is oxidized in the presence of a 12α-hydroxysteroid dehydrogenase, wherein the 12α-hydroxysteroid dehydrogenase is recombinantly produced by expression of a polynucleotide consisting of SEQ ID NO:3 in a non-pathogenic microorganism, to the corresponding 12-ketochenodeoxycholic acid (12-keto-CDCA) of the formula (3)
• in which R and Ra have the meanings indicated above, and subsequently
• b) 12-keto-CDCA of the formula (3) is reacted by deoxygenation to give chenodeoxycholic acid (CDCA) of the formula (4)
• in which R and Ra have the meanings indicated above, and
• c) CDCA of the formula (4) is chemically oxidized in position 7 to the 7-ketolithocholicacid (KLCA) of the formula (5)
• in which R and Ra have the meanings indicated above;
• and
• d) KLCA of the formula (5) is reduced and
• e) the reaction product is optionally further purified.