1-O-[(Z)-(1-amino-2-ethoxy-2-oxoethylidene)amino] 4-O-tert-butyl (2R)-2-(3-cyclohexylpropyl)butanedioate → ethyl 5-{(1R)-1-[2-(tert-butoxy)-2-oxoethyl]4-cyclohexylbutyl}-1,2,4-oxadiazole-3-carboxylate

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A solution of tert-Butyl(3R)-3-[({[(Z)-1-amino-2-ethoxy-2-oxoethylidene]amino}oxy)carbonyl]-6-cyclohexylhexanoate (Preparation 169) (21.0 g, 50.82 mmol) in xylene (400 ml) was heated at 130° C. for 17 hours, then allowed to cool to room temperature. The residue was purified by column chromatography on silica gel eluting with a gradient system of ethyl acetate:pentane (5:95) gradually changing to ethyl acetate:pentane (20:80) to afford the title compound as a colourless oil (20.0 g).

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