Concise synthesis of dopexamine dihydrochloride via benzyl protecting protocol

Benzyl protecting protocol was first employed in two routes for the concise synthesis of dopexamine dihydrochloride. This protecting group could be cleanly removed under mild condition and no unacceptable ion was brought to the final product. The total yield of route I was 43.8% from phenylacetic acid, while it was 54.1% of route II from 2-(3,4-bis(benzyloxy)phenyl)acetic acid. The titration purity of the final product was more than 99.5%, while any single or total impurities met the known standard of the drug by HPLC analysis. The measured residual palladium met an acceptable limit (<1 ppm) as an API for injection.