Imidazole → 5(S)-tert-butoxycarbonylamino-4(S)-tert-butyldimethylsilyloxy-7(S)-isopropyl-2(R)-methyl-8-[4-methoxy-3-(3-methoxy-propyloxy)-phenyl]-octanoic acid

Participants

Reaction Steps

4.45 g of 5(S)-tert-butoxycarbonylamino-4(S)-hydroxy-7(S)-isopropyl-2(R)-methyl-8-[4-methoxy-3-(3-methoxypropyloxy)-phenyl]-octanoic acid (crude) are stirred in 45 ml of dimethylformamide with 2.36 g of tert-butyldimethylsilyl chloride and 2.03 g of imidazole for 6 days at room temperature. The mixture is concentrated by evaporation and the residue is partitioned between 10% citric acid solution and ethyl acetate. The organic phase is concentrated and stirred in 20 ml of tetrahydrofuran, 8 ml of water and 20 ml of acetic acid at room temperature for 16 hours. After concentration by evaporation, ice/water is added to the residue and the mixture is then extracted with ethyl acetate. The title compound is obtained from the organic phase after FC (260 g of silica gel, ethyl acetate/hexane=1:1): Rf (ethyl acetate/hexane=1:1)=0.32.

Provenance & Evidence