A solution of tert-butyl 4-(4-carboxyphenyl)-piperidine-1-carboxylate (1 g) in pyridine (3 mL) and DMF (3 mL) at 40° C. was stirred for 30 minutes, treated with carbonyl diimidazole (CDI, 0.55 g), stirred for 1 hour, treated with 2,3-diaminobenzamide dihydrochloride (synthesized as described in U.S. Pat. No. 6,737,421, 0.73 g), stirred for 1 hour at ambient temperature, treated with isopropanol, (10 mL), cooled for 18 hours at 0° C. and filtered. The filtrant was dissolved in water (10 mL), treated with 50% aqueous NaOH (0.26 mL), stirred for 3 hours at ambient temperature and filtered.
