Preparation method of anti-allergic drug bepotastine

The invention discloses a preparation method of an anti-allergic drug bepotastine, and relates to the technical field of anti-allergic drugs. The technical point of the invention is that a compound (S)-(4-chlorophenyl)(2-pyridyl)-methanol (formula II) is adopted as an initial raw material and is subjected to a reaction with N-tert-butoxycarbonyl-4-halopiperidine, such that a compound (S)-N-tert-butoxycarbonyl-4-[(4-chlorophenyl)(2-pyridyl)methoxy]piperidine (formula III) is obtained; under an acidic condition, the protecting group of the compound represented by the formula (III) is removed, such that a compound (S)-4-[(4-chlorophenyl)(2-pyridyl)methoxy]piperidine (formula IV) is obtained; the compound represented by the formula (IV) is subjected to a nucleophilic substitution reaction with 4-chlorobutanamide, such that a compound (S)-4-[(4-chlorophenyl)(2-pyridyl)methoxy]-piperidinyl]-butyramide (formula V) is obtained; the amide group of the compound represented by the formula (V) is hydrolyzed, such that the target product which is the anti-allergic drug bepotastine is obtained. The method provided by the invention has the advantages of simple synthesis route and low cost, and is suitable for large-scale production of the optically pure anti-allergic drug bepotastine.