A solution of tert-butyl(3R)-6-cyclohexyl-3-({[2-hydroxy-1-(methoxycarbonyl)propyl]amino}carbonyl)hexanoate (Preparation 171) (6.48 g, 15.69 mmol) in dichloromethane (60 ml) was treated with Dess-Martin periodinane [1,1,1-triacetoxy-1,1-dihydro-1,2-benziodoxol-3(1H)-one] (7.32 g, 17.26 mmol) and the resulting mixture was stirred at room temperature under a nitrogen atmosphere for 1 hour. A solution of sodium thiosulphate (6 g in 50 ml water) and a saturated aqueous sodium hydrogen carbonate solution (50 ml) were then added to the mixture which was stirred for a further 10 minutes. The layers were separated and the aqueous layer was extracted with dichloromethane. The combined organic layers were sequentially washed with water and brine, dried over anhydrous magnesium sulphate, filtered and the solvent removed under reduced pressure. The residue was purified by column chromatography on silica gel eluting with a gradient system of pentane:ethyl acetate (100:0 to 90:10) to afford the title compound as a colourless oil (4.86 g)
