(R)-2-[2-(tert-Butoxy)-2-oxoethyl]-5-phenylpentanoic acid cyclohexylamine salt (6.8 g, 17 mmol) and ethyl acetate (100 ml) were added to an aqueous solution of citric acid (10%, 100ml) and the organic phase was separated and washed with water (100 ml). Iso-propyl alcohol (20 ml) and 5% rhodium on alumina (51.6 g) were added and the mixture was stirred at 20-25° C., under hydrogen (10 atmospheres, 150 p.s.i.) for 48 hours and then filtered through celite. To the filtrate was added a solution of sodium hydroxide (0.67 g, 17 mmol) in water and the mixture was stripped and replaced with acetonitrile by distillation at atmospheric pressure to a volume of 30 ml. The mixture was allowed to cool to 20-25° C. and was stirred for 24 hours. The mixture was cooled to 0° C. and then filtered. The residue was washed with acetonitrile (2×10 ml) and then dried in vacuo at 45° C. for 2 hours to leave the title compound as a colourless solid (3.8 g, 69% yield, 95% pure by NMR).
