Enzyme-catalyzed synthesis of bioactive heterocycles

Enzymes are proteins that functions as biological catalyst. It is now a known fact that enzyme can catalyze many synthetic operations better than the conventional reagents. Not only in the synthesis of natural products, they can also be applied for construction of varieties of unnatural compounds. In this chapter, Pariyar and Ghosh have discussed in brief synthesis of various biologically active heterocyclic compounds using different enzymes as catalysts. Among various enzymes, laccases, trypsin, α-amylase and Bakers’ yeast are few that are easily available and have been extensively explored for various synthetic strategies. This chapter will definitely serve as valuable source of information to the readers in the field of enzyme-catalyzed reactions.

In vitro biosynthesis of ATP from adenosine and polyphosphate

Adenosine triphosphate (ATP) acts as a crucial energy currency in vivo, and it is a widely used energy and/or phosphate donor for enzyme-catalyzed reactions in vitro. In this study, we established an in vitro multi-enzyme cascade system for ATP production. Using adenosine and inorganic polyphosphate (polyP) as key substrates, we combined adenosine kinase and two functionally distinct polyphosphate kinases (PPKs) in a one-pot reaction to achieve chain-like ATP regeneration and production. Several sources of PPK were screened and characterized, and two suitable PPKs were selected to achieve high rates of ATP production. Among these, Sulfurovum lithotrophicum PPK (SlPPK) exhibited excellent activity over a wide pH range (pH 4.0–9.0) and synthesized ATP from ADP using short-chain polyP. Furthermore, it had a half-life > 155.6 h at 45 °C. After optimizing the reaction conditions, we finally carried out the coupling-catalyzed reaction with different initial adenosine concentrations of 10, 20, and 30 mM. The highest yields of ATP were 76.0, 70.5, and 61.3%, respectively. Graphical Abstract

Recent Advance in Organocatalyzed Asymmetric Reduction of Prochiral Ketones: An Update

Chiral alcohols are important synthetic intermediates or building blocks for the diverse synthesis of drugs, agrochemicals, and natural products. Asymmetric reduction of prochiral ketones has been the most popularly investigated method for accessing chiral alcohols. In this regard, the organocatalyzed asymmetric reduction as a complementary of transition-metal- and enzyme-catalyzed reactions have attracted tremendous interest in the past decades due to the nature of metal-free and easy operation, as well as, principly, the ease of recovery and reuse of catalysts. Following up a comprehensive overview on organocatalyzed asymmetric reduction of prochiral ketones in early 2018, this short review is intended to summarize the recent progress in this area from the beginning of the year 2018 to the end of Aug. 2021.

An In Vivo Biocatalytic Cascade Featuring an Artificial Enzyme Catalyzed New-to-Nature Reaction

Artificial enzymes utilizing the genetically encoded non-proteinogenic amino acid p-aminophenylalanine (pAF) as catalytic residue are able to react with carbonyl compounds through an iminium ion mechanism, making reactions possible that have no equivalent in nature. Here, we report an in vivo biocatalytic cascade that is augmented with such an artificial enzyme catalyzed new-to-nature reaction. The artificial enzyme in this study is a pAF containing evolved variant of the Lactococcal multidrug resistance Regulator, designated LmrR_V15pAF_RMH, which efficiently converts in vivo produced benzaldehyde derivatives into the corresponding hydrazone products inside E. coli cells. These in vivo biocatalytic cascades comprising an artificial enzyme catalyzed reactions are an important step towards achieving a hybrid metabolism.

An on-demand, drop-on-drop method for studying enzyme catalysis by serial crystallography

Serial femtosecond crystallography has opened up many new opportunities in structural biology. In recent years, several approaches employing light-inducible systems have emerged to enable time-resolved experiments that reveal protein dynamics at high atomic and temporal resolutions. However, very few enzymes are light-dependent, whereas macromolecules requiring ligand diffusion into an active site are ubiquitous. In this work we present a drop-on-drop sample delivery system that enables the study of enzyme-catalyzed reactions in microcrystal slurries. The system delivers ligand solutions in bursts of multiple picoliter-sized drops on top of a larger crystal-containing drop inducing turbulent mixing and transports the mixture to the X-ray interaction region with temporal resolution. We demonstrate mixing using fluorescent dyes, numerical simulations and time-resolved serial femtosecond crystallography, which show rapid ligand diffusion through microdroplets. The drop-on-drop method has the potential to be widely applicable to serial crystallography studies, particularly of enzyme reactions with small molecule substrates.

Interaction of Melanin with Metal Ions Modulates Their Cytotoxic Potential

Melanin is one the most common biological pigments. In humans, specialized cells called melanocytes synthesize the pigment from tyrosine and 3,4-dihydroxyphenylalanine via enzyme-catalyzed reactions and spontaneous processes. The formed melanin granule consists of nanoaggregates of oligomers containing different monomers. Although the main biological function of melanin is protection against damage from solar radiation, melanin may also be involved in protection against oxidative stress. In the latter function, sequestration of redox-active metal ions and scavenging of reactive oxygen species are of importance. The paper reviews basic physicochemical properties of melanin responsible for binding of metal ions and discusses specific conditions that may induce cytotoxicity of metal ions such as iron and copper by facilitating their redox activation and release from melanin. While the value of EPR spectroscopy and other EPR-related techniques for the study of melanin is emphasized, the concomitant use of other physicochemical methods is the most efficient approach.

Enzymes as Biocatalysts: Review on Investigations on Synthesis, Mechanism, Kinetics, Applications and Potential

Sustainable development is becoming the goal of many investigations carried out in chemistry and chemical engineering. Because of the waste generated by chemical reactions, there is a shift from traditional thinking about the catalyst's yield, selectivity, efficiency, and effectiveness. Mild, low temperature, highly selective alternative was found in biological reactions. Biocatalyst application fulfills the two important requirements. It does not deplete natural resources and does not have any significant environmental footprints. Modeling of biological reactions is a very important area of investigation on enzyme-catalyzed reactions. Monod and Moser growth kinetics can be applied to cell growth and substrate utilization. The discovery of new enzymes and optimization of the synthesis and application methods for biocatalysts are being investigated widely for better and industrially applicable technologies.