A new approach to preparative enzymatic synthesis (Reprinted from Biotechnology and Bioengineering, vol 19, pg 1351-1361, 1977)

A new approach to preparative organic synthesis in aqueous-organic systems is suggested. It is based on the idea that the enzymatic process is carried out in a biphasic system "water-wafer-immiscible organic solvent." Thereby the enzyme is localized in the aqueous phase-this eliminates the tradition al problem of stabilizing the enzyme against inactivation by a nonaqueous s olvent. Hence, in contrast to the commonly used combinations "water-water-m iscible organic solvent," in the suggested system the content of water may be infinitely low. This allows one to dramatically shift the equilibrium of the reactions forming water as a reaction product (synthesis of esters and amides, polymerization of amino acids, sugars and nucleotides, dehydration reactions, etc.) toward the products. The fact that the system consists of two phases provides another very important source for an equilibrium shift , i.e., free energies of the transfer of a reagent from one phase to the ot her. Equations are derived describing the dependence of the equilibrium con stant in a biphasic system on the ratio of the volumes of the aqueous and n onaqueous phases and the partition coefficients of the reagents between the phases. The approach has been experimentally verified with the synthesis o f N-acetyl-L-tryptophan ethyl ester from the respective alcohol and acid. P orous glass was impregnated with aqueous buffer solution of chymotrypsin an d suspended in chloroform containing N-acetyl-L-tryptophan and ethanol. In water (no organic phase) the yield of the eater is about 0.01%, whereas in this biphasic system it is practically 100%. The idea is applicable to a gr eat number of preparative enzymatic reactions.