Selective oxidation of penicillin G with hydrogen peroxide and with enzymatically generated peroxyoctanoic acid

Predicting Autoxidation of Sulfides in Drug-like Molecules Using Quantum Mechanical/Density Functional Theory Methods

Autoxidation of drugs and drug-like molecules is a major concern in the development of safe and effective therapeutics. Because active pharmaceutical ingredients (APIs) that contain sulfur atoms can form sulfoxides under oxidative stress, predicting oxidative susceptibilities within an organic molecule can have a major impact in accelerating the compound's stability assessment. For investigation of a sulfur atom's oxidative stability, density functional theory (DFT) methods were applied to accurately predict S-O estimated bond dissociation enthalpies (BDEs) of sulfoxides. Our process employed B3LYP/6-31+G(d) for geometry optimization and frequency calculation, and we employed B3P86/6-311++G(2df,2p) to obtain electronic energies from single-point energy calculations. A total of 84 drug-like molecules containing 50 different sulfide scaffolds were used to develop a risk scale. Our results showed that when S-O BDE is less than 69 kcal/mol, the sulfur atom has low oxidative susceptibility. High oxidation risk occurs when the S-O BDE is greater than 75 kcal/mol. The risk scale was successful in predicting the relative propensities of sulfide oxidation among the small organic molecules and commercial drugs examined.

Switching catalysis from hydrolysis to perhydrolysis in Pseudomonas fluorescens esterase

Many serine hydrolases catalyze perhydrolysis, the reversible formation of peracids from carboxylic acids and hydrogen peroxide. Recently, we showed that a single amino acid substitution in the alcohol binding pocket, L29P, in Pseudomonas fluorescens (SIK WI) aryl esterase (PFE) increased the specificity constant of PFE for peracetic acid formation >100-fold [Bernhardt et al. (2005) Angew. Chem., Int. Ed. 44, 2742]. In this paper, we extend this work to address the three following questions. First, what is the molecular basis of the increase in perhydrolysis activity? We previously proposed that the L29P substitution creates a hydrogen bond between the enzyme and hydrogen peroxide in the transition state. Here we report two X-ray structures of L29P PFE that support this proposal. Both structures show a main chain carbonyl oxygen closer to the active site serine as expected. One structure further shows acetate in the active site in an orientation consistent with reaction by an acyl-enzyme mechanism. We also detected an acyl-enzyme intermediate in the hydrolysis of epsilon-caprolactone by mass spectrometry. Second, can we further increase perhydrolysis activity? We discovered that the reverse reaction, hydrolysis of peracetic acid to acetic acid and hydrogen peroxide, occurs at nearly the diffusion limited rate. Since the reverse reaction cannot increase further, neither can the forward reaction. Consistent with this prediction, two variants with additional amino acid substitutions showed 2-fold higher k(cat), but K(m) also increased so the specificity constant, k(cat)/K(m), remained similar. Third, how does the L29P substitution change the esterase activity? Ester hydrolysis decreased for most esters (75-fold for ethyl acetate) but not for methyl esters. In contrast, L29P PFE catalyzed hydrolysis of epsilon-caprolactone five times more efficiently than wild-type PFE. Molecular modeling suggests that moving the carbonyl group closer to the active site blocks access for larger alcohol moieties but binds epsilon-caprolactone more tightly. These results are consistent with the natural function of perhydrolases being either hydrolysis of peroxycarboxylic acids or hydrolysis of lactones.

Hydrolase-catalysed synthesis of peroxycarboxylic acids: Biocatalytic promiscuity for practical applications

The enzymatic promiscuity concept involves the possibility that one active site of an enzyme can catalyse several different chemical transformations. A rational understanding of the mechanistic reasons for this catalytic performance could lead to new practical applications. The capability of certain hydrolases to perform the perhydrolysis was described more than a decade ago, and recently its molecular basis has been elucidated. Remarkably, a similarity between perhydrolases (cofactor-free haloperoxidases) and serine hydrolases was found, with both groups of enzymes sharing a common catalytic triad, which suggests an evolution from a common ancestor. On the other hand, several biotechnological applications derived from the capability of hydrolases to catalyse the synthesis of peracids have been reported: the use of hydrolases as bleaching agents via in situ generation of peracids; (self)-epoxidation of unsaturated fatty acids, olefins, or plant oils, via Prileshajev epoxidation; Baeyer-Villiger reactions. In the present review, the molecular basis for this promiscuous hydrolase capability, as well as identified applications are reviewed and described in detail.

Effect of mutations in Candida antarctica B lipase

Three variants of the Candida antarctica B lipase have been constructed and characterized. The variant containing the T103G mutation, which introduces the consensus sequence G-X-S-X-G found in most other known lipases, shows an increased thermostability but retains only half the specific activity of the native enzyme. Also in ester synthesis the activity is lowered but the specificity and enantioselectivity remains unchanged. The W104H mutant, in which more space is introduced into the active site, has more dramatically changed properties. Both the thermostability and the specific activity are slightly reduced but the activity and specificity in ester synthesis is highly different from the native enzyme. In general, the activity is very low and the enantioselectivity is, furthermore, highly reduced. Finally, the mutation M72L was introduced to increase the oxidation stability of the enzyme. This variant did exhibit an increased resistance towards oxidation but the thermostability was, unfortunately, also reduced.