Methyl 5-[2-[(1,1-dimethylethyl)amino]-1-hydroxyethyl]-2-hydroxybenzoate → (-)-Salbutamol

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Several patents report synthetic routes using enantiomeric separation, however, the synthetic routes result in low yields of the enantiomerically pure product. Optically pure levalbuterol was synthesized by the borane-methylsulfide reduction of the enantiomerically pure precursor (Formula 2) as described in U.S. Pat. No. 5,399,765. The reaction dissolved a mixture of enantiomers of methyl 5-[2-[(1,1-dimethylethyl)amino]-1-hydroxyethyl]-2-hydroxybenzoate and a chiral acid selected from (−)-di-toluoyl-L-tartaric acid and (+)-di-toluoyl-D-tartaric acid in methanol, upon cooling one stereoisomer crystallized, which was separated, and recrystallized as a diastereomer from methanol, the diastereomer was separated, treated with base, and upon reduction formed optically active levalbuterol.

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