Novel enantioselective esterases from yeasts and bacteria

The major goal of our research is the developement of synthetically useful selective biotransformations using “new” microbial enzymes by combining natural and non-natural conditions. Enantioselective hydrolysis of chiral or prochiral esters can be used in different fields (i.e. pharma, agrofood, materials) for obtaining optically pure alcohols or carboxylic acids. While a number of lipases is commercially available as free or immobilized enzymes, esterases are much less studied, although they show interesting features, such as: • Esterases show chemo-, regio- and stereoselectivity alternative or complementary to the ones displayed by lipases. • Esterases are much less used for the synthesis of optically pure products and their commercial availability is limited. We have built-up a library of 75 microorganisms belonging to different genera having cell-associated esterases selected after screenings carried out on chiral esters of primary alcohols which are hydrolysed with low enantioselectivity by commercial lipases. New cell-bound carboxylesterases from bacteria (i.e. Bacillus coagulans, Streptomyces sp.) and yeasts (i.e. Kluyveromyces marxianus, Pichia sp.) have been studied and partially characterised. They have been employed for different enantioselective hydrolysis of chiral esters (i.e. solketal and aminoacid esters), not easily and/or efficiently resolved with commercial enzymes. Different strategies of optimisation and developement of processes yelding multi-gram scale production will be also discussed.