Patent ID: 7355064

Claim:
A method for preparing a 15-keto-prostaglandin E derivative represented by formula (I): wherein, R 1 is a saturated or unsaturated bivalent lower or medium aliphatic hydrocarbon residue, which unsubstituted or substituted with halogen, lower alkyl, hydroxy, oxo, aryl or heterocyclic, and at least one of carbon atom in the aliphatic hydrocarbon is optionally substituted by oxygen, nitrogen or sulfur; R 2 is a saturated or unsaturated lower or medium aliphatic hydrocarbon, which is unsubstituted or substituted with lower alkyl, lower alkoxy, lower alkanoyloxy, cyclo(lower)alkyl, cyclo(lower)alkyloxy, aryl, aryloxy, heterocyclic or heterocyclicoxy group; cyclo(lower)alkyl; cyclo(lower)alkyloxy; aryl; aryloxy; heterocyclic; or heterocyclicoxy group; B is â€”CH 2 â€”CH 2 â€”, â€”CH=CHâ€” or â€”Câ•Câ€”; Q is â€”CH 3 , â€”COCH 3 , â€”OH, â€”COOH or a salt, ether, ester or amide thereof; X 1 and X 2 are hydrogen, lower alkyl, or halogen; which comprises the step of hydrolyzing the compound represented by formula (II): wherein, A 1 is a protecting group for hydroxy group, R 1 , R 2 , B, Q, X 1 and X 2 are the same as above in the presence of phosphoric acid compound.