Lactic acid (LA) is an interesting platform molecule in the biorefinery concept [1]. A particularly interesting application is its use as building block of poly lactic acid (PLA). Knowadays, LA is produced only as one enantiomer, namely the L-enantiomer. D-LA is currently not abundantly available at commercial scale. Still, both enantiomers should be available to make various PLA forms as for example thermomechanical superior stereocomplexes of PLLA and PDLA. On the other hand, commercial L-LA production is hampered by gypsum waste issues and low space time yields. Alternatively, racemic lactate esters, produced by chemocatalysis using heterogeneous Lewis acid catalysts, could be interesting as a novel source for PLA production [2].However, the L- and D-fraction should be separated to tune the PLA stereochemistry.  A productive and enantioselective hydrolysis of racemic mixtures of lactate esters with commercial Candida rugosa lipase was performed. This step contributes to a novel envisioned route for  stereoselective PLA production by combining the recent chemocatalytic developments with this biocatalytic contribution, foreseeing two separate L- and D-lactate enantiomer streams. A study of the hydrolysis kinetics identified an unexpected rate determining step, viz. the deprotonation of the histidine residu, at the origin of an unprecedented ester reactivity order. In subsequent research, we started to increase the intrinsic activity of the lipase by a rational design procedure to tune the histidine basicity. An economic assessment based on the obtained productivity, industrial product market prices and reported enzyme stability, in similar reaction conditions, suggests a profitable route towards PLA for specialty and medical applications and likely also for commodity applications [3].[1] M. Dusselier, P. Van Wouwe, A. Dewaele,  E. Makshina and Bert F. Sels. Energy and Environmental Sciences (2013) 6, 1415-1442[2] M. S. Holm, S. Saravanamurugan, E. Taarning Science (2010) 328, 602-605.[3] P. Van Wouwe,M. Dusselier,  A. Basi�  and Bert F. Sels. Green Chemistry (2013) 15, 2817-2824.

Bridging racemic lactate esters with stereoselective polylactic acid using commercial lipase catalysis

248th National Meeting (2014)

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