Transaminase – carbonic anhydrase bi-enzymatic cascade for preparation of (R)-1-arylethan-1-amines and (S)-1-arylethan-1-ols

Abstract

In the present study, the development of a bi-enzymatic transaminase from Pseudomonas psychrotolerans (PpS-TA)–human carbonic anhydrase II (hCAII) cascade for the efficient conversion of various (±)-1-phenylethan-1-amines into the corresponding enantiopure (R)-amines and (S)-1-phenylethan-1-ols is described. The mixture HEPES–DMSO was found to be a suitable reaction medium for both enzymes. A DMSO content of 30% improved the solubilization of the substrates, intermediates, and phenylsilane as a reactant for the complete reduction of acetophenone even at a concentration of 250 mM with hCAII. The total transformation of the reactive stereoisomer of (±)-1-phenylethan-1-amine (up to 40 mM) to acetophenone with soluble PpS-TA in the first stage, was followed by the stereoselective reduction of the previously formed ketone to (S)-1-phenylethan-1-ol in the presence of hCAII. Compared with the procedure using soluble enzymes, the cellular cascade showed improved viability, as both biotransformations could be carried out with improved efficiency even at a 2.5-fold higher substrate concentration in phosphate buffer. Without altering the activities and selectivities of the enzymes, the cellular cascade allowed the gram-scale conversion of (±)-1-phenylethan-1-amine (1.2 g in 100 mL reaction mixture) to the enantiopure (R)-amine and (S)-1-phenylethan-1-ol, which were isolated in greater than 93% yield.