A solution of methyl 2-((1R)-1-{2-[(benzyloxy)amino]-2-oxoethyl}-4-cyclohexylbutyl)-5-methyl-1,3-oxazole-4-carboxylate (Preparation 72) (200 mg, 0.47 mmol) in dichloromethane (10 ml) was treated sequentially with 1-hydroxybenzotriazole hydrate (63 mg, 0.47 mmol), N-methylmorpholine (77 μl, 0.70 mmol) and 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (134 mg, 0.70 mmol) and the resulting mixture was stirred at room temperature under a nitrogen atmosphere for 10 minutes. Concentrated ammonia solution (0.88, 50 μl, 1.00 mmol) was then added and the mixture was stirred for 17 hours. The mixture was diluted with dichloromethane and washed sequentially with water, a saturated aqueous solution of sodium hydrogen carbonate and brine, dried over anhydrous magnesium sulphate, filtered and the solvent removed under reduced pressure. The residue was then purified by column chromatography on silica gel eluting with dichloromethane:methanol:0.88 ammonia (97:3:0.3) to afford the title compound as a white solid (140 mg).
