Methanol → n-Carbobenzoxy-s-phenyl-l-cysteine methyl ester

Participants

Reaction Conditions

Reaction Steps

In a nitrogen atmosphere, 150 ml of methanol was added to 30.01 g of N-benzyloxycarbonyl-S-phenyl-L-cysteine and 864 mg of p-toluenesulfonic acid monohydrate, and the reaction was allowed to proceed under reflux. After 6 reaction hours, the mixture was cooled to about 50° C., and the pH was adjusted to 5.5 by adding 8 ml of a 5% (by weight) aqueous solution of sodium hydrogen carbonate. Then, the methanol was replaced with toluene at about 50° C., to give 103.87 g of a toluene-substituted reaction mixture containing 30.97 g (concentration: 29.8% by weight; yield: 99%; optical purity: 99.7%) of N-benzyloxycarbonyl-S-phenyl-L-cysteine methyl ester (Example 4). Then, 15 ml of pure water was added to this toluene-substituted reaction mixture at room temperature, and the mixture was stirred for 15 minutes and then allowed to stand, whereupon the aqueous phase formed a large number of droplets, which remained dispersed or settled in the organic phase but did not unite with one another. This procedure thus failed to form two layers, namely the upper and lower layers, separable from each other, hence to enable phase separation (Reference Example 2).

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