AN EFFECTIVE CHIROSPECIFIC SYNTHESIS OF (+)-PILOCARPINE FROM L-ASPARTIC ACID

A short and efficient synthesis of (+)-pilocarpine (1) has been accomplished in 10 steps and 51 % overall yield from L-aspartic acid. The synthesis features a diastereoselective alkylation of a protected aspartic acid diester derivative and a selective hydrolysis of the alpha-methyl ester to give the corresponding amino acid. Subsequent replacement of the amino group with bromo, esterification, and a modified Reformatsky reaction with 1-methylimidazole-5-carboxaldehyde (8) afforded imidazole-substituted lactone 28. Details concerning this novel lactone synthesis are also described. Finally, hydrogenolysis of the lactone carbon-oxygen bond and selective reduction of the resulting monoester afforded pure (+)-pilocarpine (1).