Preparation of (R)-3-hydroxy-n-methylpiperidine, a synthetic key intermediate of (R)-mepenzolate, based on the lipase-catalyzed resolution of the racemic form

In this study, a two-step method for the gram-scale synthesis of (R)-3-hydroxy-N-methylpiperidine in 97.8% enantiomeric excess (ee) is reported. The key chiral synthetic intermediate of (R)-mepenzolate was formed in 22% yield over two steps using a commercially available and inexpensive racemic alcohol as the starting material. In the first step, Candida antarctica lipase B-catalyzed kinetic resolution of the racemic alcohol under acetylation conditions was performed to obtain the acetate form of the (R)-enantiomer in 82.1% ee (E 18). The second step involved enantio-enrichment using the same lipase to catalyze deacetylation. The ee of the product (R)-alcohol was further enriched to 97.8%.