Promiscuous enzyme-catalyzed cascade reaction in water: Synthesis of dicoumarol derivatives

Hydrotrope assisted green synthesis of dicoumarols and in silico and in vitro antibacterial, antioxidant and xanthine oxidase inhibition studies

Aqueous hydrotrope has been employed for the first time to synthesize heteroaryl dicoumarols by condensation of 4-hydroxycoumarin and different heterocyclic aldehydes. This method is highly efficient and green, and the same aqueous hydrotropic solution can be used up to five times without any considerable loss of yield in the product. The synthesized compounds showed good antibacterial potential against Gram-positive (Staphylococcus aureus/NTCC 0997 and B. oceanisediminis) and Gram-negative (Escherichia coli/D0157:H7 and E. coli rosetta) bacterial strains using the Resazurin microtiter plate visual method. The MIC value of 312 µg/ml for compounds 3b, 3k and 3l for S. aureus while 39 µg/ml for compounds 3a, 3b and 3k for E. coli and 625 µg/ml for 3a and 3b for B. oceanisediminis was observed. The compounds were screened via computational methods like molecular docking studies and molecular dynamic simulations with PDB Id's 2W9S and 2EX6. Antioxidant activity was assessed using DPPH and H2O2 assays. Five compounds with the best binding score in molecular docking with XO (PDB ID: 1FIQ) have been tested in an in-vitro study using an enzyme inhibition assay. Novel compound 3b gave the IC50 value of 0.28 µg/ml, comparable to the standard drug Allopurinol.Communicated by Ramaswamy H. Sarma.

Developing and enhancing promiscuous activity for NAD(P)H-dependent flavin reductase via elimination of cofactor

Promiscuous enzymes have shown their synthetic abilities in generating various organic compounds with high selectively and efficiency under mild conditions. Therefore, the design and development of conditions to raise promiscuity to the enzymes have been under the spotlight in recent years. Flavin reductase, that reduces flavins by using NADH as a cofactor, has not been studied in promiscuous reactions. In the present study, it was aimed to develop a catalytic promiscuous activity in the recombinant E.coli flavin reductase by removing its cofactor. The flavin reductase demonstrated a promiscuous activity for Knoevenagel condensation and Michael addition reactions individually. The cofactor-independent promiscuous activity of the flavin reductase was further enhanced by altering the reaction conditions to proceed a Knoevenagel-Michael addition cascade for tetraketone synthesis. Yet, the presence of the cofactor blocked the promiscuous Knoevenagel condensation, Michael addition, and therefore the cascade reaction, demonstrating that the removal of NADH was pivotal in inducing the promiscuous activity. Furthermore, molecular docking and MD simulations were performed to obtain more structural and mechanistic details of the transformation. The computational studies identified the most likely catalytic sites of the flavin reductase in the reaction. Additionally, a truncated variant of the enzyme that lacked 28 residues from the C-terminus displayed comparable activity to the wild-type enzyme, indicating the robustness of the enzyme in performing the cascade reaction. In brief, the cofactor-elimination method presented in this work could be considered as a straightforward and economical approach for inducing enzyme promiscuity in promoting organic transformations.

Green Synthesis of Spirooxindoles via Lipase-Catalyzed One-Pot Tandem Reaction in Aqueous Media

The development of non-natural enzymatic catalysis is important for multicomponent tandem organic transformations. However, the delicate acting environments of biological enzymes still present some challenges in the synthesis of spirooxindole skeleton via enzymatic catalysis. To address these issues, a lipase-catalyzed method was developed for the synthesis of spirooxindole frameworks. Using easily available isatins, cycloketones, and malononitriles as substrates, mild reaction conditions, and a reasonable reaction time, moderate to good yields (67–92%) and excellent functional group tolerance were accomplished via this protocol. The related mechanism explanation is also speculated in this paper.

Dicoumarol: from chemistry to antitumor benefits

Dicoumarol, a coumarin-like compound, is known for its anticoagulant properties associated with the ability to inhibit vitamin K, being prescribed as a drug for several decades. The pharmaceutical value of dicoumarol turned it into a focus of chemists' attention, aiming its synthesis and of dicoumarol derivatives, bringing to light new methodologies. In recent years, several other bioactive effects have been claimed for dicoumarol and its derivatives, including anti-inflammatory, antimicrobial, antifungal, and anticancer, although the mechanisms of action underlying them are mostly not disclosed and additional research is needed to unravel them. This review presents a state of the art on the chemistry of dicoumarols, and their potential anticancer characteristics, highlighting the mechanisms of action elucidated so far. In parallel, we draw attention to the lack of in vivo studies and clinical trials to assess the safety and efficacy as drugs for later application.

Progress in the Synthesis of Heterocyclic Compounds Catalyzed by Lipases

Heterocyclic compounds are representative of a larger class of organic compounds, and worthy of attention for many reasons, chief of which is the participation of heterocyclic scaffolds in the skeleton structure of many drugs. Lipases are enzymes with catalytic versatility, and play a key role in catalyzing the reaction of carbon–carbon bond formation, allowing the production of different compounds. This article reviewed the lipase-catalyzed aldol reaction, Knoevenagel reaction, Michael reaction, Mannich reaction, etc., in the synthesis of several classes of heterocyclic compounds with important physiological and pharmacological activities, and also prospected the research focus in lipase-catalyzed chemistry transformations in the future.

Efficient synthesis of cyano-containing multi-substituted indoles catalyzed by lipase

BACKGROUND

Indoles are important bioactive compounds that have been extensively studied in organic chemistry. In this work, a green and efficient process for the synthesis of Indoles from 1,3-diketones with fumaronitrile was developed.

RESULTS

Under optimal conditions (1,3-diketones (0.5 mmol), fumaronitrile (1 mmol), water (2 ml), lipase (15 mg), 30 °C, 24 h), high yields and satisfactory regioselectivity of cyano-containing multi-substituted indoles could be obtained when CRL (C. rugosa lipase) was used as the catalyst.

CONCLUSION

This enzymatic method demonstrates the great potential for the synthesis of indoles and extends the application of enzyme in organic synthesis.

Synthesis of substituted 2H-chromenes catalyzed by lipase immobilized on magnetic multiwalled carbon nanotubes

Porcine pancreas lipase (PPL) was immobilized on magnetic multiwalled carbon nanotubes successfully for the synthesis of substituted 2H-chromenes. The catalytic activity of immobilized PPL was much higher than that of free PPL. Effects of reaction medium, temperature, and enzyme dosage were also investigated. Under optimum reaction conditions (acetylacetone (1 mmol), salicylaldehyde (1 equivalent), methanol (10 equivalent), and immobilized PPL (protein content: 30 mg; 65 °C; DMF 5 mL; 5 H), the immobilized PPL showed an excellent catalytic performance on the synthesis of substituted 2H-chromenes. Moreover, the immobilized PPL exhibited satisfactory thermostability, operational simplicity, and reusability in this reaction.

Enzymatic approach to cascade synthesis of bis(indolyl)methanes in pure water

TLIM: lipase from Thermomyces lanuginosus immobilized on particle silica gel.