Practical and Sustainable Synthesis of Optically Pure Levocabastine, a H₁ Receptor Antagonist.

A practical and sustainable method for the synthesis of levocabastine hydrochloride (1), a H₁ receptor antagonist for the treatment of allergic conjunctivitis, that can be applied to the industrial production of the compound has been developed. Substantial improvements over the previously reported procedure are achieved via efficient preparation of an optically active key intermediate (5) without chiral resolution and with a more effective detosylation, which complements the previous procedure. Notably, our process requires no chromatographic purification and provides levocabastine hydrochloride in greater than 99.5% purity in a 14.2% overall yield.