PHASIC SYSTEMS WATER - ORGANIC

Fig. 11. Priniciple of stereospecific reduction of carbonyl compounds coupled with cofacter regeneration (a) and outline of the stereospecific reduction of ethyl 4-chloroacetoacetate (CAAE) by Sporobolomyces aldehyde reductase (AR) with glucose dehydrogenase (GDH) as a cofactor regenerator in a water-organic solvent two-phasic system (b). CHBE, ethyl 4-chloro-3-hydroxybutanoate...

Shimizu, S. and Yamasa, H. (1990) Stereospecific reduction of 3-keto acid esters by a novel aldehyde reductase of Sporobolomyces salmonkolor in a water-organic solvent two-phasic system. Ann. N.Y. Acad. Sci., 613, 628-632. 

What about when the substrate and product are water soluble The problem of catalyst recovery in this case can be solved by employing inverse aqueous bi-phasic catalysis. An example is the hydroformylation of N-allylacetamide in an aqueous biphasic system in which the catalyst is dissolved in the organic phase and the substrate and product remain in the water phase. This formed the basis for an elegant synthesis of the natural product, melatonin, in which the aqueous solution of the hydroformylation product was used in the next step without work-up (Fig. 7.6) [32]. 

In this chapter, latest advancements in solvent engineering in bioreductions and greener needs for bioreaction media have been discussed in depth with recent examples. Solvents for bioreductions may be categorized as (i) aqueous (ii) water/water-miscible (monophasic aqueous-organic system) (iii) water/ water-immiscible (biphasic aqueous-organic system) (iv) nonaqueous (mono-phasic organic system, including solvent-free system) and (v) nonconventional media (e.g., ionic liquids, supercritical fluids, gas-phase media, and reverse micelles). 

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