This compound was prepared from the product of 15a (1.2 g; 3.2 mmol), 5-(Cbz-amino)-4-oxopentanoic acid (0.84 g; 3.2 mmol), 4-pyrrolidinylpyridine (50 mg), and N,N′-diisopropylcarbodiimide (0.50 g; 4.0 mmol) in dichloromethane (35 mL) according to Procedure D. The reaction time was 3 days. The crude product was purified on a 85×55 mm silica gel 60 column eluted with ethyl acetate-hexane (1:1) (1000 mL) collecting 13×50 mL fractions. Fractions containing the product (3-6) were evaporated and 0.57 g (29%) product was obtained (white solid, mp 78-81° C.).
