Imidazole → 5(S)-(Boc-Amino)-4(S)-(tert-butyldimethylsilyloxy)-6-(p-benzyloxy-phenyl)-2(R)-[(p-benzyloxyphenyl)methyl]hexanoic acid

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Reaction Steps

2.44 g (3.90 mmol) of 5(S)-(Boc-amino)-4(S)-hydroxy-6-(p-benzyloxyphenyl)-2(R)-[(p-benzyloxyphenyl)methyl]-hexanoic acid in 14 ml of DMF are stirred, under an N2 atmosphere, together with 2.70 g (17.6 mmol) of tert-butyldimethylchlorosilane and 2.18 g (32 mmol) of imidazole at RT for 18 h. The reaction mixture is poured onto ice-water, and this mixture is extracted with 3 portions of ethyl acetate; the organic phases are washed with 10% citric acid solution, H2O and saline, dried with Na2 SO4 and evaporated. The resulting oil is taken up in 30 ml of methanol/THF/H2O 3:1:1, and this solution is treated with 3.2 g of K2CO3 and stirred at RT for 1 h. The reaction mixture is partially evaporated, and the aqueous residue is poured onto 10% citric acid solution and ice, and this mixture is extracted 3× with ethyl acetate; the organic phases are washed twice with H2O and, finally, with saline, dried with Na2SO4 and evaporated. Column chromatography (SiO2, hexane/ethyl acetate 2:1→1:1) of the crude product affords the title compound: TLC Rf (C)=0.53; FAB-MS (M+H)+ =740.

Provenance & Evidence