Preparation of optically active cyanohydrins from 2-substituted benzaldehydes using a hydroxynitrile lyase from Pouteria sapota seeds immobilized on celite

Abstract

Abstract The HNL from the defatted meal of the seeds of Pouteria sapota (PsHNL) was extracted with water, and the aqueous extract was immobilized over celite or lyophilized and used as semi-purified PsHNL. The aqueous extract was mixed with celite, ratios 1:1, 1:2 and 1:4, and lyophilized. The immobilized PsHNLdir-celite catalysed the addition of HCN to 1b in buffer saturated-DIPE (microaqueous system) with high enantioselectivity in the first cycle but diminished in the next two cycles, best results were obtained with the ratio 1:4. The reaction with PsHNLdir-celite in biphasic medium (5% citrates buffer) improved the conversion compared with the microaqueous system, but it was still lower to that obtained with the PsHNL. Other way of immobilization studied was the precipitation of the enzyme with acetone and immobilization on celite, the PsHNLpp-celite catalysed the enantioselective addition of HCN to 2-fluoro (1a), 2-chloro (1b), 2-bromo (1c), 2-methyl (1d) and 2-nitro (1e) benzaldehydes, in the biphasic medium (1:4 ratio, 5% citrates buffer). The enantiomeric excess (ee) of (R)-2a, (R)-2b, (R)-2c and (R)-2d were >98% and remained during the three cycles. The ee of 2-nitromandelonitrile was 82% and was raised to 95% in the third cycle. Compared with the PsHNL, the conversion of 1a and 1b diminished 6% and 40%, respectively, after third cycle; for 2c, conversion was almost 10% higher in the first two cycles and diminished 19% in the third; for 2d and 2e the conversion was between 18–13% and 31–18% higher, respectively.