4-Methylmorpholine → tert.-butoxycarbonyl-L-tyrosyl-D-phenylalanyl-glycine benzyl ester

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Reaction Steps

18.55 g (45 mmoles) of the protected dipeptide ester obtained in Step 1 above are dissolved in 60 ml of ethyl acetate containing 11-15% of hydrochloric acid. After 0.5 hours of standing the solution is evaporated, and the residue is dried in a vacuum desiccator above potassium hydroxide. The resulting substance, Rf3 =0.4-0.5, is dissolved in 40 ml of dimethyl formamide, and 5.0 ml (45 mmoles) of N-methylmorpholine and 26.2 g (49.5 mmoles) of tert.-butoxycarbonyl-L-tyrosine pentachlorophenyl ester are added. The reaction mixture is stirred for 16-20 hours. During the first two hours 5.5 ml (49.5 mmoles) of N-methylmorpholine are added to the mixture in five portions. The reaction mixture is evaporated under reduced pressure, the residue is dissolved in a mixture of 300 ml of ethyl acetate and 50 ml of water, the ethyl acetate phase is separated, washed twice with 50 ml of 1 n aqueous hydrochloric acid cooled with ice water and then twice with 50 ml of water, each, dried over sodium sulfate, decolourized with carbon, filtered, and the filtrate is evaporated under reduced pressure. The crystalline residue is suspended in diisopropyl ether, the solid is filtered off, washed with diisopropyl ether, and dried in a vacuum desiccator. 23.5 g (90.8%) of tert.-butoxycarbonyl-L-tyrosyl-D-phenylalanyl-glycine benzyl ester are obtained; m.p.: 169° C., Rf10 =0.45-0.55, [α]D20 +16.3° (c=1%, in dimethyl formamide).

Provenance & Evidence