Upcoming bio-refineries will be at the heart of the manufacture of future transportation fuels, chemicals and materials. A narrow number of platform molecules are envisioned to bridge nature's abundant polysaccharide feedstock to the production of added-value chemicals and intermediate building blocks. Such platform molecules are well-chosen to lie at the base of a large product assortment, while their formation should be straightforward from the refined biomass, practical and energy efficient, without unnecessary loss of carbon atoms. Lactic acid has been identified as one such high potential platform. Despite its established fermentation route, sustainability issues – like gypsum waste and cost factors due to multi-step purification and separation requirements – will arise as soon as the necessary orders of magnitude larger volumes are needed. Innovative production routes to lactic acid and its esters are therefore under development, converting sugars and glycerol in the presence of chemocatalysts. Moreover, catalysis is one of the fundamental routes to convert lactic acid into a range of useful chemicals in a platform approach. This contribution attempts a critical overview of all advances in the field of homogeneous and heterogeneous catalysis and recognises a great potential of some of these chemocatalytic approaches to produce and transform lactic acid as well as some other promising α-hydroxy acids.

Lactic acid as a platform chemical in the biobased economy: the role of chemocatalysis

Polymeric materials, natural and unnatural, are indispensable to the modern society. They are widely used from everyday life usages as commodity materials to industry and technology usages in the fields such as electronics, machinery, communications, transportations, pharmacy, and medicine as highly advanced materials. Today, it is hard to think of the present society without polymeric materials. Developments of various polymeric materials have been owed to epoch-making innovative works as exemplified typically by the discovery of Ziegler-Natta catalyst,1-3 the concept of living polymerization,4 the discovery of conducting polymers,5 and the discovery of metathesis catalyst.6,7 These observations demonstrate that new polymeric materials are often brought about by new production methods including polymerization catalysts. Historically, polymerization catalysts utilized classical catalysts of acids (Brønsted acids, Lewis acids, and various cations), bases (Lewis bases and various anions), and radical generating compounds since the 1920s, the early stage of polymer chemistry. In the following * To whom correspondence should be addressed. Fax/Tel: (+81)-75-7247688. E-mail: kobayash@kit.ac.jp. † Kyoto Institute of Technology and Emeritus Professor of Kyoto University. ‡ Kyoto University. Chem. Rev. 2009, 109, 5288–5353 5288

Enzymatic polymer synthesis: an opportunity for green polymer chemistry.

The present article comprehensively reviews the macromolecular synthesis using enzymes as catalysts. Among the six main classes of enzymes, the three classes, oxidoreductases, transferases, and hydrolases, have been employed as catalysts for the in vitro macromolecular synthesis and modification reactions. Appropriate design of reaction including monomer and enzyme catalyst produces macromolecules with precisely controlled structure, similarly as in vivo enzymatic reactions. The reaction controls the product structure with respect to substrate selectivity, chemo-selectivity, regio-selectivity, stereoselectivity, and choro-selectivity. Oxidoreductases catalyze various oxidation polymerizations of aromatic compounds as well as vinyl polymerizations. Transferases are effective catalysts for producing polysaccharide having a variety of structure and polyesters. Hydrolases catalyzing the bond-cleaving of macromolecules in vivo, catalyze the reverse reaction for bond forming in vitro to give various polysacchar...

Enzymes as Green Catalysts for Precision Macromolecular Synthesis

The solvent dependence of enzyme specificity

Role of solvents in the control of enzyme selectivity in organic media

Substrate structure and solvent hydrophobicity control lipase catalysis and enantioselectivity in organic media

Multienzymic Synthesis of Poly(hydroquinone) for Use as a Redox Polymer

An acyl binding structural model has been developed to explain the observed catalytic efficiencies and enantioselectivities of Candida rugosa lipase-catalyzed (trans)esterification reactions involving 2-hydroxy acids and vinyl esters, respectively, and acylation reactions involving both cyclic and acyclic alcohols. A clear minimum was observed for (trans)esterification of six-carbon acyl moieties. Morever, the stereoselectivity of 2-hydroxy acid esterification in a number of hydrophilic and hydrophobic solvents was dependent on the acyl chain length: S-isomers of 2-hydroxy acids were acylated for acyl chain lengths of six or fewer, whereas the R-isomers were preferentially esterified for acyl chain lengths of eight or more

Tailoring lipase specificity by solvent and substrate chemistries

The use of partially hydrated porous silica particles has been studied as a support for cofactor-dependent enzymatic catalysis in organic solvents. At an optimal pore hydration corresponding to 70% pore volume, horse liver alcohol dehydrogenase catalyzes the oxidation and reduction of alcohols and aldehydes, respectively, with rates sixfold higher than with nonporous glass beads as the enzymatic support and with cofactor recycling numbers in excess of 105. Thus, supported aqueous-phase enzymatic catalysis makes highly effective use of the enzyme and cofactor by coimmobilization and by providing a high interfacial area for reactions in organic media.

Sanghamitra Parida

Papers

Substrate structure and solvent hydrophobicity control lipase catalysis and enantioselectivity in organic media

Multienzymic Synthesis of Poly(hydroquinone) for Use as a Redox Polymer

Tailoring lipase specificity by solvent and substrate chemistries

Supported aqueous-phase enzymatic catalysis in organic media

Use of alcohols as cosolvents in enzyme-facilitated transport of organic acids through a liquid membrane