Linear enzyme cascade for the production of (-)-iso-isopulegol

Biocatalysis has developed enormously in the last decade and now offers solutions for the sustainable production of chiral and highly functionalised asset molecules. Products generated by enzymatic transformations are already being used in the food, feed, chemical, pharmaceutical and cosmetic industry, and the accessible compound panoply is expected to expand even further. In particular, the combination of stereo-selective enzymes in linear cascade reactions is an elegant strategy toward enantiomeric pure compounds, as it reduces the number of isolation and purification steps and avoids accumulation of potentially unstable intermediates. Here, we present the set-up of an enzyme cascade to selectively convert citral to (-)-iso-isopulegol by combining an ene reductase and a squalene hopene cyclase. In the initial reaction step, the ene reductase YqjM from Bacillus subtilis selectively transforms citral to (S)-citronellal, which is subsequently cyclised exclusively to (-)-iso-isopulegol by a mutant of the squalene hopene cyclase from Alicyclobacillus acidocaldarius (AacSHC). With this approach, we can convert citral to an enantiopure precursor for isomenthol derivatives.