The dipeptide derivativesZ-Tyr-Leu-NH2 andMca-Tyr-Leu-NH2 were synthesized by α-chymotrypsin-catalyzed coupling reactions in solvent systems consisting of buffer and ethyl acetate. In comparison to a pure aqueous medium, in which only insignificant synthesis takes place, the product formation is greatly enhanced in a biphasic medium due to extraction of the dipeptide into the organic phase. The influence of several reaction parameters, such as buffer concentration, reaction time, volume ratio of organic and aqueous phase, and reagent concentration on the yield ofZ-Tyr-Leu-NH2 was investigated. Replacement of the hydrophobicZ-group by the more hydrophilic chloroacetyl group resulted in better dipeptide yields at higher reaction rates.