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Betulinic acid is a natural product possessing abundant and favourable biological activity, including anti-cancer, anti-malarial, anti-inflammatory and anti-HIV properties, while causing minimal toxicity to unaffected cells. The full biological potency of betulinic acid cannot be fully unlocked, however, for a number of reasons, a primary one being its limited solubility in aqueous and biologically pertinent organic media. Aiming to improve the water solubility of betulinic acid without disrupting its structurally related bioactivity, we have prepared different ionic derivatives of betulinic acid. Inhibition bioassays on HIV-1 protease-catalysed peptide hydrolysis indicate significantly improved performance resulting from converting the betulinic acid to organic salt form. Indeed, for one particular cholinium-based derivative, its water solubility is improved more than 100 times and the half maximal inhibitory concentration (IC50) value (22 μg mL−1) was one-third that of wide-type betulinic acid (60 μg mL−1). These encouraging results advise that additional studies of ionic betulinic acid derivatives as a therapeutic solution against HIV-1 infection are warranted. [ABSTRACT FROM AUTHOR]

Abstract: The commercial form of immobilized Candida antarctica lipase B (CALB), known as Novozym® 435, is a catalyst routinely used in enzymatic reactions. However, we observed a number of compounds migrated from this enzyme preparation into organic solvents and ionic liquids (ILs). These compounds were further identified by GC–MS analysis as a mixture of 17 substances, including 5 major components: glycerol, benzoic acid, 2-hydroxyethyl benzoate, 2-hydroxyethyl sorbate, and sorbic acid. The importance of this discovery is that all five major compounds are reactive in the presence of CALB, especially the last four compounds are potential acyl donors in enzymatic (trans)esterification reactions. We then quantified the migration of these acyl donors into various aqueous solutions, organic solvents and ILs, and observed that the migration into polar organic solvents and ILs was rapid (10–30min). We also measured the reactivities of these acyl donors with 1-propanol in Novozym® 435-catalyzed (trans)esterifications. Our data suggest that the initial reaction rates of sorbic acid and sorbate ester were very fast; although the initial rates of benzoic acid and benzoate were much slower, their conversions into propyl benzoate were significant within 24h period. The presence of these compounds in Novozym® 435 may not have considerable impact on fast reactions involving high substrate concentrations, however, it is important to realize that these trace compounds may affect the enzyme activity, and may cause confusion during the analysis of enzymatic reactions. [Copyright &y& Elsevier]

Abstract: Ionic liquids (ILs) as neoteric solvents and microwave irradiation as alternative energy source are becoming two important tools for many enzymatic reactions. However, it is not well understood what properties of ILs govern the enzyme stabilization, and whether the microwave irradiation could activate enzymes in ILs. To tackle these two important issues, the synthetic activities of immobilized Candida antarctica lipase B (Novozyme 435) were examined in more than twenty ILs through microwave heating. Under microwave irradiation, enhanced enzyme activities were observed when the enzyme was surrounded by a layer of water molecules. However, such enhancement diminished when the reaction system was dried. To understand the effect of IL properties, the enzyme activities under microwave irradiation were correlated with the viscosity, polarity and hydrophobicity (log P) of ILs, respectively. The initial reaction rates bear no direct relationship with the viscosity and polarity (in terms of dielectric constant and ) of ILs, but have a loose correlation (a bell curve) with log P values. The enzyme stabilization by ILs was explained from aspects of hydrogen-bond basicity of anions, dissolution of the enzyme, ionic association strength of anions, and substrate ground-state stabilization by ILs. [Copyright &y& Elsevier]

Abstract: This paper examined the effect of several pyridinium and imidazolium-based ionic liquids (ILs) on the protease stability in aqueous solutions. In general, the enzyme was found quite active at low concentrations of hydrophilic ILs. In aqueous environment, the enzyme was stabilized by the kosmotropic anions (such as CF3COO− and CH3COO−) and chaotropic cations (such as [BuPy]+ and [EMIM]+), but was destabilized by chaotropic anions (such as tosylate and BF4 −) and kosmotropic cations (such as [BMIM]+). [Copyright &y& Elsevier]