Bang-Hua Xie

Bio: Bang-Hua Xie is an academic researcher from Southwest University. The author has contributed to research in topics: Aldol reaction & Michael reaction. The author has an hindex of 4, co-authored 6 publications receiving 91 citations.

Promiscuous enzyme-catalyzed Michael addition: synthesis of warfarin and derivatives

Abstract: BACKGROUND: Biocatalytic promiscuity has attracted much attention from chemists and biochemists in recent years. Warfarin, one of the most effective anticoagulants, has been introduced for clinical use as a racemate for more than half a century. Although some different chemical strategies towards the synthesis of optically active warfarin have been reported, biocatalytic preparation of warfarin remains unexploited. RESULTS: Lipase from porcine pancreas (PPL) was used as a biocatalyst to catalyze the Michael addition of 4-hydroxycoumarin to α,β-unsaturated enones in organic medium in the presence of water to synthesize warfarin and derivatives. The products were obtained in moderate to high yields (up to 95%) with none or low enantioselectivities (up to 28% ee). The influence of reaction conditions including solvents, temperature and molar ratio of substrates was systematically investigated. CONCLUSION: Among the many reported lipase-catalyzed Michael additions, only a few showed enantioselectivity. Therefore, this Michael addition activity of, for example, PPL is a valuable case of enantioselective lipase catalytic promiscuity. In addition, it was the first time warfarin and derivatives were prepared using a biocatalyst. Copyright © 2012 Society of Chemical Industry

The enzymatic asymmetric aldol reaction using acidic protease from Aspergillus usamii

Abstract: AUAP (acidic protease from Aspergillus usamii) could catalyze the direct aldol reactions between aromatic aldehydes and cyclic ketones in acetonitrile (MeCN) in the presence of water. The enantioselectivities of up to 88% ee and diastereoselectivities of up to 97:3 (anti/syn) were achieved. This new activity of protease expands the application of the biocatalyst and provides a novel example of enzymatic promiscuity.

Biocatalytic Knoevenagel reaction using alkaline protease from Bacillus licheniformis

Abstract: BLAP (alkaline protease from Bacillus licheniformis) was used as a biocatalyst in the Knoevenagel condensations of aromatic, hetero-aromatic and α;β-unsaturated aldehydes with less reactive acetylacetone or ethyl acetoacetate. The reactions were performed in organic solvent in the presence of water. The functionalized trisubstituted alkenes and α,β,γ,δ-unsaturated carbonyl compounds could be obtained in moderate to good yields with E/Z selectivities up to >99:1. This biocatalytic reaction provided an alternative pathway for Knoevenagel condensation, which also demonstrates a novel case of unnatural activity of existing enzymes.

Direct asymmetric aldol reactions catalyzed by lipase from porcine pancreas.

Abstract: Porcine pancreas lipase type II (PPL II) exhibited unnatural catalytic activity in direct asymmetric aldol reactions between cyclic ketones and aromatic or heteroaromatic aldehydes in acetonitrile in the presence of phosphate buffer. A wide range of substrates was accepted by the enzyme to afford the corresponding aldol products in low to high yields (10 - 98%), with moderate to excellent enantioselectivities (53 - 94% ee, for anti-isomers) and low to moderate diastereoselectivities (48/52 - 87/13 dr, anti/syn). This methodology expands the application of PPL II, and it might be developed into a potentially valuable method for sustainable organic synthesis.

Recent advances on sources and industrial applications of lipases

Abstract: Lipases are the industrially important biocatalysts, which are envisioned to have tremendous applications in the manufacture of a wide range of products. Their unique properties such as better stability, selectivity and substrate specificity position them as the most expansively used industrial enzymes. The research on production and applications of lipases is ever growing and there exists a need to have a latest review on the research findings of lipases. The present review aims at giving the latest and broadest overall picture of research and development on lipases by including the current studies and progressions not only in the diverse industrial application fields of lipases, but also with regard to its structure, classification and sources. Also, a special emphasis has been made on the aspects such as process optimization, modeling, and design that are very critical for further scale-up and industrial implementation. The detailed tabulations provided in each section, which are prepared by the exhaustive review of current literature covering the various aspects of lipase including its production and applications along with example case studies, will serve as the comprehensive source of current advancements in lipase research. This review will be very useful for the researchers from both industry as well as academia in promoting lipolysis as the most promising approaches to intensified, greener and sustainable processes. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:5-28, 2018.

An overview of Bacillus proteases: from production to application.

Abstract: Proteases have a broad range of applications in industrial processes and products and are representative of most worldwide enzyme sales. The genus Bacillus is probably the most important bacterial source of proteases and is capable of producing high yields of neutral and alkaline proteolytic enzymes with remarkable properties, such as high stability towards extreme temperatures, pH, organic solvents, detergents and oxidizing compounds. Therefore, several strategies have been developed for the cost-effective production of Bacillus proteases, including optimization of the fermentation parameters. Moreover, there are many studies on the use of low-cost substrates for submerged and solid state fermentation. Other alternatives include genetic tools such as protein engineering in order to obtain more active and stable proteases and strain engineering to better secrete recombinant proteases from Bacillus through homologous and heterologous protein expression. There has been extensive research on proteases because of the broad number of applications for these enzymes, such as in detergent formulations for the removal of blood stains from fabrics, production of bioactive peptides, food processing, enantioselective reactions, and dehairing of skins. Moreover, many commercial proteases have been characterized and purified from different Bacillus species. Therefore, this review highlights the production, purification, characterization, and application of proteases from a number of Bacillus species.

Biocatalytic Methods for C ? C Bond Formation

Abstract: Carbon-carbon bond formation is among the most challenging transformations in the organic synthetic chemistry. Enzymes capable to perform this reaction are of great interest. The enzymes for stereoselective CC bond formations have been investigated very intensively during the last two decades. New recombinant DNA technologies have paved the way for improved catalysts and broaden the application scope of the already known enzymes and reactions. On the other side new discoveries have brought more enzyme players in the arena of CC bond formation reactions. Novel enzymatic CC bond formation reactions have been applied, implying the most important benefit of biocatalysis, namely the high selectivity.

Recent developments in enzyme promiscuity for carbon-carbon bond-forming reactions.

Abstract: Numerous enzymes have been found to catalyze additional and completely different types of reactions relative to the natural activity they evolved for. This phenomenon, called catalytic promiscuity, has proven to be a fruitful guide for the development of novel biocatalysts for organic synthesis purposes. As such, enzymes have been identified with promiscuous catalytic activity for, one or more, eminent types of carbon-carbon bond-forming reactions like aldol couplings, Michael(-type) additions, Mannich reactions, Henry reactions, and Knoevenagel condensations. This review focuses on enzymes that promiscuously catalyze these reaction types and exhibit high enantioselectivities (in case chiral products are obtained).

Engineering aldolases as biocatalysts

Abstract: Aldolases are seen as an attractive route to the production of biologically important compounds due to their ability to form carbon–carbon bonds. However, for many industrial reactions there are no naturally occurring enzymes, and so many different engineering approaches have been used to address this problem. Engineering methods have been used to alter the stability, substrate specificity and stereospecificity of aldolases to produce excellent enzymes for biocatalytic processes. Recently greater understanding of the aldolase mechanism has allowed many successes with both rational engineering approaches and computational design of aldolases. Rational engineering approaches have produced desired enzymes quickly and efficiently while combination of computational design with laboratory methods has created enzymes with activity approaching that of natural enzymes.