Enzymatic Carbon−Carbon Bond Formation in Water-in-Oil Highly Concentrated Emulsions (Gel Emulsions)

Abstract

Water-in-oil (W/O) highly concentrated emulsions (gel emulsions) of water/C14E4/aliphatic hydrocarbon systems were investigated as reaction media for the aldolic condensation of dihydroxyacetone phosphate (DHAP) with acceptor aldehydes such as phenylacetaldehyde (1) and benzyloxyacetaldehyde (2), catalyzed by D-fructose-1,6-bisphosphate aldolase from rabbit muscle (RAMA). Prior to any enzymatic reaction, both the formation and stability of the W/O gel emulsions in the presence of reactants were assessed. It was found that the aldehydes improved greatly the kinetic stability of W/O gel emulsions at 25 °C by decreasing the hydrophile-lipophile balance temperature (THLB) of the water/C14E4/aliphatic hydrocarbon systems. Interestingly, the stability of RAMA in W/O gel emulsions was improved by 7-and 25-fold compared to that in aqueous medium or conventional dimethylformamide/water 1/4 v/v mixture, respectively. It was found that the equilibrium yields and enzymatic activity depended on both the aldehyde partitioning between the continuous and dispersed phases and the water-oil interfacial tension. The highest enzymatic activities were achieved in W/O gel emulsion systems with the lowest water-oil interfacial tension. The equilibrium yield depended on the water-oil interfacial tension for the hydrophobic phenylacetaldehyde, and on the partition coefficient for the hydrophilic benzyloxyacetaldehyde. Optimum equilibrium product yields (65-70%) were achieved at either the lowest water-oil interfacial tension or partition coefficient values.

Dihydroxyacetone Phosphate Aldolase Catalyzed Synthesis of Structurally Diverse Polyhydroxylated Pyrrolidine Derivatives and Evaluation of their Glycosidase Inhibitory Properties

“…Furthermore, on increasing the reactant concentration up to [DHAP] = 100 mm and [N-Cbz-aminoaldehyde] = 170 mm (see Supporting Information) conversions for RhuA-and FucA-catalyzed reactions were generally higher in emulsion than those in 1:4 DMF/H 2 O, probably because of the better solubilization properties of the former reaction medium. [37] Investigations of temperature effects: Temperature effects were also investigated for RhuA aldolization of aldehydes (R)-2 a, (R)-2 b (vide infra), (R)-2 c, (R)-2 f, and (S)-2 f. To this end, the selected reactions were conducted at 4 8C, because it has been reported that at this temperature the conversion achieved on FucA-catalyzed aldol addition of DHAP to (R)-N-Cbz-alaninal was significantly improved. [38] Interestingly, there were temperature effects on the stereoselectivity of the enzymatic reactions (vide infra), but no improvement on aldol conversions was observed for any of the selected examples, indicating that this phenomenon is not of general applicability.…”

Influence of secondary reactions on the synthetic efficiency of DHAP‐aldolases

“…Final yields and stereoselectivity are depending on the aldehyde and enzyme employed. The influence of reaction medium on the synthesis performance has also been studied (Espelt et al, 2003b). Nevertheless, the practical application of aldolase catalyzed processes in chiral synthesis requires appropriate reactor design based on a deep knowledge of reactions behavior, and improvement of the synthesis yields which are often relatively low.…”

Chemoenzymatic Synthesis and Inhibitory Activities of Hyacinthacines A1 and A2 Stereoisomers

“…[15] Emulsions and DMF/buffer (1:4 v/v) were the reaction systems of choice at both 25 8C and 4 8C. The literature precedent from enzymatic DHAP aldol addition studies demonstrated that the conversions may be influenced by the reaction media, [16] and improved at 4 8C. [17] The enzymatic reactions were incubated until constant conversion values were monitored.…”