A mixture of N-tert-butoxycarbonyl-4-(3-methylbenzyl)-isonipecotic acid (1.02 g, 3.00 mmol), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (0.64 g. 3.36 mmol), 1-hydroxy-benzotriazole hydrate (0.45 g, 3.31 mmol), ammonium chloride (0.33 g, 6.15 mmol), and diisopropylethylamine (1.15 mL, 6.60 mmol) in anhydrous dimethylformamide (10 ml) was stirred at room temp. overnight. The resultant solution was concentrated under vacuum and the residue was partitioned between ethyl acetate and water. The organic extracts were combined, washed with brine, dried over anhydrous magnesium sulfate, filtered, and concentrated under vacuum. The residual oil was subjected to column chromatography on silica eluting with 40% ethyl acetate in hexane. Collection and concentration of appropriate fractions provided the title product.
