Identification of novel polyphenol oxidase inhibitors by enzymatic one-pot synthesis and deconvolution of combinatorial libraries

Phenylpropanoid Derivatives from the Tuber of Asparagus cochinchinensis with Anti-Inflammatory Activities

Three undescribed phenylpropanoid derivatives, including two new bibenzyl constituents (1-2), one new stilbene constituent (3), together with five known compounds stilbostemin F (4), dihydropinosylvin (5), 2-(4-hydroxyphenyl)ethyl benzoate (6), 1-(4-hydroxybenzoyl)ethanone (7), and 4-hydroxy-3-prenylbenzoic acid (8), were isolated from the tuber of Asparagus cochinchinensis. The structures of 1-8 were elucidated according to UV, IR, HRMS, 1D and 2D-NMR methods together with the published literature. All of the isolated compounds were assessed for anti-inflammatory activity by acting on lipopolysaccharide (LPS)-induced RAW 264.7 macrophage cells in vitro. The results showed that compounds 2 and 5 were found to inhibit the production of nitric oxide (NO) with the IC₅₀ value of 21.7 and 35.8 µM, respectively. In addition, further studies found that compound 2 demonstrated concentration-dependent suppression of the protein expression of iNOS and exerted anti-inflammatory activity via the NF-κB signalling pathway. The present data suggest that phenylpropanoid derivatives from the tuber of A. cochinchinensis might be used as a potential source of natural anti-inflammatory agents.

Furan metabolites from the sponge-derived yeast Pichia membranifaciens

Five new compounds, pichiafurans A-C (1-3) and pichiacins A and B (4 and 5), along with five known compounds (6-10), have been isolated from the yeast Pichia membranifaciens derived from a marine sponge Petrosia sp. Their structures were elucidated by 1D and 2D NMR and mass spectrometry techniques. Pichiafurans are rare examples of monofurano metabolites isolated from yeast.

Assembly of a three-dimensional array of glycoconjugates by combinatorial biocatalysis in nonaqueous media

Glycoconjugates can be artificially synthesized by combinatorial biocatalysis. An example is given in this paper describing the construction of glycoconjugates array by using glycosidase and lipase in nonaqueous media. This array was started from glucose, with three aryl alcohols as the aglycone moiety of glycosides and five acids or esters as acyl donors for combinatorial acylation of glycosides, affording a three-dimensional array containing about 30 members with diverse structures. The array would be more abundant if more aglycones and acyl donors with other structures were filled in. Indeed, diverse classes of carbohydrates besides glucose can also be employed for generating diverse glycoconjugates due to their different roles in numerous physiological responses. The composition and distribution of the demonstration glycoconjugates array was detected and evaluated by HPLC-MS with electrospray ionization. And also, the distribution of the artificial array can be adjusted by changing the molar ratio of the auxiliary materials.

Preparation of biosensors by immobilization of polyphenol oxidase in conducting copolymers and their use in determination of phenolic compounds in red wine

Electrochemically produced graft copolymers of thiophene capped polytetrahydofuran (TPTHF1 and TPTHF2) and pyrrole were achieved by constant potential electrolysis using sodium dodecylsulfate (SDS) as the supporting electrolyte. Characterizations were based on Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Electrical conductivities were measured by the four-probe technique. Novel biosensors for phenolic compounds were constructed by immobilizing polyphenol oxidase (PPO) into conducting copolymers prepared by electropolymerization of pyrrole with thiophene capped polytetrahydrofuran. Kinetic parameters, maximum reaction rate (V(max)) and Michaelis-Menten constant (K(m)) and optimum conditions regarding temperature and pH were determined for the immobilized enzyme. Operational stability and shelf-life of the enzyme electrodes were investigated. Enzyme electrodes of polyphenol oxidase were used to determine the amount of phenolic compounds in two brands of Turkish red wines and found very useful owing to their high kinetic parameters and wide pH working range.

Preventing inhibition of tyrosinase with modified electrodes

Wines, especially red wines, contain numerous biologically active compounds, the most important of which are polyphenols, whose nutritional importance is attributed to their antioxidant power. Because of this, the detection of the amount of phenolic compounds in red wines becomes extremely important. However, using free enzyme in the determination of phenolic compounds in wines cannot reflect the actual values since there are also naturally found inhibitors in red wines. In this study, benzoic acid, cinnamic acid, and sorbic acid were utilized to understand the behavior of immobilized polyphenol oxidase in the conducting polymer matrices toward inhibition. Cinnamic acid was found to be the most powerful inhibitor for both free and immobilized enzyme in copolymer matrix of poly(terephthalic acid bis-(2-thiophen-3-yl-ethyl) ester) (PTATE) with polypyrrole (PPy). In the case of immobilized enzyme in PPy matrix, it was observed that sorbic acid is a stronger inhibitor than cinnamic acid. The inhibitory effects of these inhibitors on PPO were compared with respect to both the structural differences of inhibitors and conducting polymer matrices.

Applying combinatorial chemistry and biology to food research

In the past decade combinatorial chemistry has become a major focus of research activity in the pharmaceutical industry for accelerating the development of novel therapeutic compounds. The same combinatorial strategies could be applied to a broad spectrum of areas in agricultural and food research, including food safety and nutrition, development of product ingredients, and processing and conversion of natural products. In contrast to "rational design", the combinatorial approach relies on molecular diversity and high-throughput screening. The capability of exploring the structural and functional limits of a vast population of diverse chemical and biochemical molecules makes it possible to expedite the creation and isolation of compounds of desirable and useful properties. Several studies in recent years have demonstrated the utility of combinatorial methods for food research. These include the discovery of synthetic antimicrobial, antioxidative, and aflatoxin-binding peptides, the identification and analysis of unique flavor compounds, the generation of new enzyme inhibitors, the development of therapeutic antibodies for botulinum neurotoxins, the synthesis of unnatural polyketides and carotenoids, and the modification of food enzymes with novel properties. The results of such activities could open a large area of applications with potential benefits to the food industry. This review describes the current techniques of combinatorial chemistry and their applications, with emphasis on examples in food science research.

Combinatorial biocatalysis

The published applications of combinatorial biocatalysis have continued to expand at a growing rate. This is exemplified by the variety of enzyme catalysts and whole-cell catalysts used for the creation of libraries through a wide range of biocatalytic reactions, including acylation, glycosylation, halogenation, oxidation and reduction. These biocatalytic methods add the capability to perform unique chemistries or selective reactions with complex or labile reagents when integrated with classical combinatorial synthesis methods. Thus, applications towards the production of libraries de novo, the expansion of chemically derived combinatorial libraries, and the generation of novel combinatorial reagents for library synthesis can be achieved. Theoretically, these results illustrate what is already evident from nature: that complex, biologically active, structurally diverse compound libraries can be generated through the application of biocatalysis alone or in combination with classical organic synthesis approaches.