Imidazole → 5(s)-(Boc-amino)-4(s)-(tert-butyldimethylsilyloxy)-6-(p-methoxyphenyl)-2(r)-(phenylmethyl)hexanoic acid

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Reaction Steps

2.9 g (6.54 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-methoxyphenyl)-2(R)-(phenylmethyl)hexanoic acid in 7 ml of DMF are silylated, at RT for 20 h and under an N2 atmosphere, with 4.5 g (30 mmol) of tert-butyldimethylchlorosilane and 3.65 g (53.6 mmol) of imidazole. The reaction mixture is poured onto 500 ml of ice-water, and this mixture is extracted 3× with ethyl acetate. The organic phases are washed with 10% citric acid solution, 2× water and saline, dried with Na2SO4 and evaporated. Hydrolysis of the residue in 80 ml of methanol and 30 ml of THF with 5.4 g of potassium carbonate and 30 ml of water, working up after 3 h in analogy with Example 7c), and column chromatography (SiO2, hexane/ethyl acetate, 2:1), affords the title compound: TLC Rf (D)=0.13; tRet (II)=20.3 min.

Provenance & Evidence