Transesterification

Abstract

The peptidyl polymer (Z-Ala-Phe-resin, 4.0 g, 1 mmol) is washed with dimethylformamide [2] (40 ml, in several portions) and then suspended, without drying in a mixture of dimethylformamide (80 ml) and dimethylaminoethanol (80 ml). The suspension is stirred for about 24 hours, filtered and the resin washed with dimethylformamide (three times, 80 ml each time). The filtrate and washings are pooled and concentrated in vacuo at room temperature to about 10 ml. An equal volume of water and a catalytic amount of imidazole (about 7 mg, 0.1 mmol) are added and the mixture allowed to stand at room temperature for one day [3]. The solvents are removed in vacuo at room temperature and the residue dissolved in ethyl acetate (100 ml). The solution is washed with 0.01 N hydrochloric acid (twice, 50 ml each time) and the aqueous phases reextracted with ethyl acetate (twice, with 50 ml each time). The ethyl acetate solutions are pooled, dried over anhydrous MgSO₄ and evaporated to dryness in vacuo. The crude product is recrystallized from aqueous acetic acid.