Anju Chadha

Biocatalytic reduction of alkyl 2-oxopropanoates were carried out by utilizing the whole cells of Candida parapsilosis ATCC 7330 to form the optically enriched alkyl 2-hydroxypropanoates with good enantiomeric excess (ee) (≤91%) and isolated yields (≤68%). Enantiomerically enriched (S)-ethyl 3-bromo-2-hydroxypropanoate thus synthesized by biocatalytic reduction of ethyl 3-bromo-2-oxopropanoate is presented in this study for the first time in water under ambient reaction conditions in a reaction time of 4 h which is considerably less than earlier reported procedures.

Alcohol dehydrogenases (ADHs) catalyses reversible reduction of carbonyl group to its corresponding alcohols and have been widely employed as versatile biocatalyst due to its high enantioselectivity to produce chiral alcohols. In this study, the (S) - specific alcohol dehydrogenase (S-ADH) enzyme was purified from Candida parapsilosis ATCC 7330. It asymmetrically reduced acetophenone to (S)-1-phenylethanol with > 99% ee with an effective substrate coupled approach for cofactor recycling. In the reverse reaction, i.e., oxidation of 1-phenylethanol, S-ADH produced (R)-1-phenylethanol with > 99% ee via kinetic resolution. S-ADH is a zinc dependent medium chain dehydrogenase/reductase. It was found to be a tetramer in nature with subunit molecular mass of 40 kDa catalysing oxidation and reduction reactions only using NAD+ and NADH as the cofactors respectively with higher affinity for NAD+. Further biochemical characterisation indicated that His and Cys residues play a crucial role in the enzymatic catalysis and requires a reducing environment at the active site. S-ADH was stable at pH 6.0 in reducing acetophenone and pH 8.0 in oxidising 1-phenylethanol at 45 °C with the t1/2 of 6.8 h and 9.0 h respectively. Therefore, purified S-ADH would be a useful biocatalyst in the synthesis of enantiopure (S)- and (R)-1-phenylethanol which are used in the fragrance preparation.