Study of vitamin ester synthesis by lipase-catalyzed transesterification in organic media.

Immobilized lipase from Candida antarctica (Novozym 435) was used in organic media to catalyze esterifications of vitamins (ascorbic acid and retinol) from hydroxy acid. We described the synthesis of retinyl L-lactate by transesterification between retinol and L-methyl lactate with yield reaching 90% and the synthesis of ascorbyl L-lactate by transesterification between ascorbic acid and L-methyl lactate with yield reaching 80%. The kinetic study of the esterification of vitamins with L-methyl lactate in organic media has been carried out and agrees with ping-pong-ordered Bi-Bi when the initial vitamin concentration is low. When initial vitamin concentration is high, the kinetic is similar to a hybrid ping-pong-ordered Bi Bi or hybrid ping-pong-random Bi Bi mechanism. However, with high initial substrate concentration, change of the kinetic by other phenomena, such as interaction of substrates with molecular sieves, adsorption of the methanol formed, and decreases of substrate diffusion, could be considered. It is obvious that in these conditions, classical enzymology (i.e., Michaelian enzymology) cannot be used for the interpretation of results.