Method for preparing 15-keto-prostaglandin E derivative

A. method for preparing a 15-keto-prostaglandin E derivative represented by formula (I):

• wherein,
• R1 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;
• R2 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 hetrocyclicoxy group;
• cyclo(lower) alkyl;
• cyclo(lower)alkyloxy;
• aryl;
• aryloxy;
• heterocyclic;
• or heterocyclicoxy group;
• B is —CH2—CH2—, —CH═CH— or —C≡C—;
• Q is —CH3, —COCH3, —OH, —COOH or a functional derivative thereof;
• X1 and X2 are hydrogen, lower alkyl, or halogen which comprises the step of hydrolyzing the compound represented by formula (II):
• wherein,
• A1 is a protecting group for hydroxy group, R1, R2, B, Q, X1 and X2 are the same as above in the presence of phosphoric acid compound.