A Continuous Lipase-Catalyzed Acylation Process for the Large-Scale Production of Vitamin A Precursors

Abstract

A continuous enzyme-catalyzed acylation process for the selective preparation of monoacylated Vitamin A precursors starting from a 1,6-diol on a large scale is reported. Screenings led to the selection of the commercially available immobilized lipase Chirazyme L2-C2 (lipase B from Candida antarctica) as the biocatalyst, different vinyl acylates as the acylating agents, and acetone as the co-solvent. Using a mixture of 70% (v/v) acetone and acylating agent allowed to increase the substrate concentration from 10 to 30% (w/w). Using a small fixed-bed reactor, this continuous process produced monoacylated product with >99% yield and >97% selectivity for the primary hydroxy group. The robustness of this system under different conditions was investigated. Consequently, the stability of the biocatalyst could be greatly improved by adding a protective pre-column and by adding small amounts of organic base and antioxidant to the substrate solution. This optimized laboratory process was used to selectively prepare monoacylated compounds in kilogram scales over one hundred days with only a minor decrease in conversion efficiency. The process was also implemented in an up-scaled mini plant for the continuous production on a kilogram-per-day scale, reproducing the results previously obtained on smaller laboratory scales.