Preparative biotransformations

Enzymatic reactions in supercritical CO2: carboxylation, asymmetric reduction and esterification

“…In our case, very high enantioselectivities (>99% ee) were obtained for the reduction with the majority of the substrates tested, while slightly lower enantioselectivities (96, 97% ee) were observed for a few of them. The enantioselectivities obtained in this system are superior to or at least equal to those for most other biocatalytic and chemical systems [62][63][64][65][66][81][82][83]. The immobilized resting cell of G. candidum was also used as a catalyst for the reduction of ketones in a semi-continuous flow process using supercritical CO 2 [51].…”

“…An increasing number of chemical CO 2 fixation reactions [54 -61] has been reported, especially using supercritical CO 2 , such as the synthesis of urethane [54], dimethyl carbonate [55], styrene carbonate [56], and methyl ethanoate [57]. On the other hand, biocatalysis is now one of the most powerful and indispensable tools for organic synthesis due to its environmental friendliness and excellent enantio-, regioand chemoselectivities [62][63][64][65][66]. Some enzymatic CO 2 fixation reactions have also been reported including the central CO 2 fixation reaction in photosynthetic organisms catalyzed by ribulose-1,5-diphosphate carboxylases [67], the reduction of CO 2 to formic acid or methanol by dehydrogenases [68][69][70][71][72], the reductive CO 2 fixation on 2-oxoglutarate and pyruvate by isocitrate [73] or malate [74] dehydroge- nases, and the CO 2 fixation on pyrrole and phenolic compounds (phenol and catechol) by decarboxylases from Bacillus megaterium [75][76][77][78] or Clostridium hydroxybenzoicum [79,80], respectively.…”

Peptide synthesis: chemical or enzymatic

“…Besides the hydrolysis and formation of peptide bonds between amino acids, proteases can catalyze other types of reactions as well, such as esterification and transesterification in the resolution of racemic alcohols and carboxylic acids and the stereoselective acylation of meso and prochiral diols (Broos et al 1995;Khmelnitsky et al 1997;Liu and Tam, 2001), the synthesis of glycoconjugates (Wong et al 1993;Bordusa, 2002) and the kinetic resolution of racemic mixtures, even though in this case lipases and esterases are more useful for the resolution of non amino acidic derivatives (Kirchner et al 1985;Bornscheuer and Kazlauskas, 1999;Pogorevc and Faber, 2000;Roberts, 2001). On the other hand, non-proteolytic enzymes can also be used in connection with peptides, as illustrated by the kinetic resolution of N-phenylacetyl-DLtert-leucine in the production of the non-proteinogenic chiral amino acid L-tert-leucine recently reported with penicillin G acylase from Kluyvera citrophila (Liu et al 2006).…”

Green chemistry: the emergence of a transformative framework

“…Challenges for successful biocatalytic systems include achieving high activity toward xenobiotic substrates and avoiding inhibition by substrate or products (36). Nevertheless, numerous biotransformations have been reported for production of organic chemicals (37). One-pot ''cascade'' reactions have been developed, based purely on enzymatic processes, or with enzymatic and chemical reactions working in concert.…”