Holland Sweetener Company, V.o.f.

Peter J Quaedflieg

Kiyotaka Oyama

Shigeaki Irino

Theodorus J Van Dooren

Shin-ichiro Nakamura

The invention relates to a process for the preparation of N-benzyloxycarbonyl-.alpha.-L-aspartyl-L-phenylalanine methyl ester by enzymatic coupling of N-benzyloxycarbonyl-L-aspartic acid and L-phenylalanine methyl ester in an aqueous medium with formation of a precipitate, the coupling reaction being effected with (virtually) equimolar quantities of N-benzyloxycarbonyl-L-aspartic acid and L-phenylalanine methyl ester under the influence of a neutral protease at an initial pH of from 4.5 to 6.0 and in the presence of from 3 to 25%, calculated as per cent by weight based on the total reaction mixture, of an alkali metal salt, alkaline earth metal salt or ammonium salt.

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Geleen, Netherlands

Peter J Quaedflieg