Dibenzoyl-L-tartaric acid

The initial medicinal chemistry route to the azabicyclo[3.3.0]octane-3-carboxylic acid produced the azabicyclo system in a diastereoselective but racemic manner, and required a classical resolution to achieve enantioenriched material (Teetz et al., 1984a, b 1988). Reaction of (R)-methyl 2-acetamido-3-chloropropanoate (43) and 1-cyclopentenylpyrrolidine (44) in DMF followed by an aqueous acidic work-up provided racemic keto ester 45 in 84% yield (Scheme 10.11). Cyclization of 45 in refluxing aqueous hydrochloric acid provided the bicyclic imine, which was immediately reduced under acidic hydrogenation conditions. The desired cis-endo product 46 was obtained upon recrystaUization. The acid was protected as the benzyl ester using thionyl chloride and benzyl alcohol, providing subunit 47 as the racemate. Resolution of 47 was accomplished by crystallization with benzyloxy-carbonyl-L-phenylalanine or L-dibenzoyl-tartaric acid. 

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