A solution of (3R)-6-cyclohexyl-3-[3-(ethoxycarbonyl)-1,2,4-oxadiazol-5-yl]hexanoic acid (Preparation 4) (500 mg, 1.47 mmol) in ethanol (13 ml) was treated with a solution of isopropylamine (434 mg, 7.35 mmol) in ethanol (2 ml) and the resulting mixture was heated at 80° C. under a nitrogen atmosphere for 10 hours. The solvent was removed under reduced pressure and the residue was dissolved in hydrochloric acid (1M, 10 ml) then extracted with ethyl acetate (×2). The combined organic layers were dried over anhydrous magnesium sulphate, filtered and the solvent removed under reduced pressure. This residue (531 mg) was then dissolved in dichloromethane (15 ml), cooled to 0° C. and treated sequentially with N-methylmorpholine (180 μl, 1.63 mmol) and isobutyl chloroformate (210 μl, 1.62 mmol). This mixture was stirred at 0° C. under a nitrogen atmosphere for 1 hour, then treated with O-(trimethylsilyl)hydroxylamine (220 μl, 1.80 mmol) and stirring continued for 10 minutes at 0° then for 17 hours at room temperature. The mixture was then treated with trifluoroacetic acid:water (5 ml, 9:1) and the solution stirred for 30 minutes. The solvent was removed under reduced pressure and the residue azeotroped from toluene (×2). The residue was purified by reverse phase HPLCa to afford the title compound as a foam (43 mg).
