Citric Acid → N-((1,1-Dimethylethoxy)carbonyl)-S-(triphenylmethyl)-L-cysteine

Participants

Reaction Steps

To a solution of S-trityl cysteine (see Hiskey and Adams, J. Org. Chem., 30:1340, (1965)) (36.3 g, 0.10 mol) in dioxane (200 ml) and 1M aqueous NaOH (100 ml, 0.10 mol) was added di-t-butyl carbonate (25.36 g, 0.12 mol). The resulting opaque solution became warm and effervesced and the pH fell from 12 to 8 over one hour. After stirring for 90 min, 50% aqueous citric acid (40 ml) was added and the resulting mixture (pH 4) was extracted with ether. The ether was washed with water, then saturated brine, dried (MgSO4), filtered and evaporated to give N-BOC-S-(triphenylmethyl)-cysteine as an oil. Half of this material was dissolved in ether (200 ml) and treated with dicyclohexylamine (10 ml, 50 mmol) to give compound (XX) as a white precipitate which was filtered off, washed with ether and dried (25.1 g, 78%), mp 205°-207°.

Provenance & Evidence