合成路线1

Acylation of L-proline t-butyl ester (I) with 3,5-dichlorobenzenesulfonyl chloride (II) affords sulfonamide (III). The tert-butyl ester group of (III) is then cleaved by treatment with aqueous trifluoroacetic acid, yielding carboxylic acid (IV). Coupling of sulfonyl proline (IV) with the racemic 3-endo-amino-bicyclo[2.2.1]heptane-2-endo-carboxylate (V) leads to a mixture of four diastereoisomeric amides, resulting from carboxylate group epimerization. This mixture can be separated into two pairs of diastereoisomers (VI) and (VII) by flash chromatography. The desired diastereoisomeric mixture of esters (VII) is then hydrolyzed under alkaline conditions to furnish the title carboxylic acid along with its epimer (VIII).