One-Pot Synthesis of Spirooxazino Derivatives via Enzyme- Initiated Multicomponent Reactions

Recent developments in the total synthesis of natural products using the Ugi multicomponent reactions as the key strategy

The total syntheses of selected natural products using different versions of the Ugi multicomponent reaction is reviewed on a case-by-case basis. The revision covers the period 2008-2023 and includes detailed descriptions of the synthetic sequences, the use of state-of-the-art chemical reagents and strategies, as well as the advantages and limitations of the transformation and some remedial solutions. Relevant data on the isolation and bioactivity of the different natural targets are also briefly provided. The examples clearly evidence the strategic importance of this transformation and its key role in the modern natural products synthetic chemistry toolbox. This methodology proved to be a valuable means for easily building molecular complexity and efficiently delivering step-economic syntheses even of intricate structures, with a promising future.

Recent developments in promiscuous enzymatic reactions for carbon-nitrogen bond formation

Biocatalytic promiscuity is a new field of enzyme application in biochemistry, which has received much attention and has developed rapidly in recent years. The promiscuous biocatalysis has been promoted as a useful supplement to traditional strategy for the formation of C-heteroatom bonds. The generation of carbon-nitrogen (CN) bonds is an important issue in synthetic chemistry and is indispensable for the manufacturing of various pharmaceuticals and agrochemicals. Therefore, numerous efficient and reliable synthetic methods for the formation of CN bonds have been developed in recent years. Enzymatic CN bond forming reactions catalyzed by lipases, cytochrome P450 monooxygenases, glycosyltransferases, amine dehydrogenases, proteases, acylases, amylases and halohydrin dehalogenases are well established for synthetic purposes. This review introduces the recent progress in the construction of CN bonds using promiscuous enzymes.

Stereoselective Promiscuous Reactions Catalyzed by Lipases

The ability of lipases to display activity beyond their physiological reactions, so-called "catalytic promiscuity", has gained increasing interest in the last two decades as an important tool for expanding the application of these enzymes in organic synthesis. Some lipases have been shown to be effective in catalyzing a variety of C-C bond formation reactions and most of the investigations have been directed to the optimization of the products yield through a careful tuning of the experimental parameters. Despite the fact that new stereogenic carbons are formed in many of the tested reactions, the target products have been often obtained in racemic form and examples of an efficient asymmetric induction by the used lipases are quite limited. The aim of this review, mainly focused on those lipase-catalyzed promiscuous reactions in which optically active products have been obtained, is to offer a current state of art together with a perspective in this field of asymmetric synthesis.

Four-Component Reaction Access to Nitrile-Substituted All-Carbon Quaternary Centers

A four-component reaction strategy for access to acyclic nitrile-substituted all-carbon quaternary centers is disclosed. In the presence of a DABCO-based ionic liquid catalyst, the reactions proceed smoothly with a wide range of substrates efficiently to deliver nitrile-substituted all-carbon quaternary centers under mild reaction conditions. This protocol is further demonstrated as an efficient method for the construction of contiguous all-carbon quaternary centers. All the reactions are easily operated in a green manner, producing water as the only byproduct. Some of the products show excellent activity against specific fungi.

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.

Different strategies for the lipase immobilization on the chitosan based supports and their applications

Immobilized enzymes have received incredible interests in industry, pharmaceuticals, chemistry and biochemistry sectors due to their various advantages such as ease of separation, multiple reusability, non-toxicity, biocompatibility, high activity and resistant to environmental changes. This review in between various immobilized enzymes focuses on lipase as one of the most practical enzyme and chitosan as a preferred biosupport for lipase immobilization and provides a broad range of studies of recent decade. We highlight several aspects of lipase immobilization on the surface of chitosan support containing various types of lipase and immobilization techniques from physical adsorption to covalent bonding and cross-linking with their benefits and drawbacks. The recent advances and future perspectives that can improve the present problems with lipase and chitosan such as high-price of lipase and low mechanical resistance of chitosan are also discussed. According to the literature, optimization of immobilization methods, combination of these methods with other techniques, physical and chemical modifications of chitosan, co-immobilization and protein engineering can be useful as a solution to overcome the mentioned limitations.

Enzyme-catalysed one-pot synthesis of 4H-pyrimido[2,1-b] benzothiazoles and their application in subcellular imaging

Enzymes, which provide more efficient and eco-friendly strategies for various functional molecules' construction than traditional chemo-catalysts, were utilized for the synthesis of 4H-pyrimido[2,1-b] benzothiazole derivatives. Reported herein is a trypsin-catalysed three- component Biginelli reaction of aldehyde, β-ketoester and 2-amino benzothiazole in one pot, affording a streamlined pathway to diverse ring-fused pyrimidines. In addition to using commercially available aromatic aldehydes as substrates, acetaldehyde, the chemical liquid with rather low boiling point and difficult to handle above room temperature, is utilized to further extend the range of substrates. It was verified that most of the tested substrates exhibited satisfactory reactivity. In addition, several substrates indicated AIE (Aggregation-Induced Emission) property and have been investigated as potential biomarkers.

Bio-Catalysis in Multicomponent Reactions

Enzyme catalysis is a very active research area in organic chemistry, because biocatalysts are compatible with and can be adjusted to many reaction conditions, as well as substrates. Their integration in multicomponent reactions (MCRs) allows for simple protocols to be implemented in the diversity-oriented synthesis of complex molecules in chemo-, regio-, stereoselective or even specific modes without the need for the protection/deprotection of functional groups. The application of bio-catalysis in MCRs is therefore a welcome and logical development and is emerging as a unique tool in drug development and discovery, as well as in combinatorial chemistry and related areas of research.

A novel substrate directed multicomponent reaction for the syntheses of tetrahydro-spiro[pyrazolo[4,3-f]quinoline]-8,5'-pyrimidines and tetrahydro-pyrazolo[4,3-f]pyrimido[4,5-b]quinolines via selective multiple C-C bond formation under metal-free conditions

A versatile and substrate oriented multicomponent reaction for the syntheses of novel highly diastereoselective tetrahydro-1'H-spiro[pyrazolo[4,3-f]quinoline-8,5'-pyrimidine]-2',4',6'(3'H)-triones (d.r. up to 20 : 1 (syn : anti)) and tetrahydro-8H-pyrazolo[4,3-f]pyrimido[4,5-b]quinoline-8,10(9H)-diones via formation of selective multiple C-C bonds under identical reaction conditions (viz. ethanol as a reaction medium and deep eutectic mixture as a catalyst) is demonstrated. Both approaches involve mild reaction conditions, use of non-hazardous solvents, and facilitate good to excellent reaction yields of the target compounds.

Microwave-assisted efficient and facile synthesis of tetramic acid derivatives via a one-pot post-Ugi cascade reaction

A facile microwave-assisted method for the synthesis of tetramic acid derivatives has been developed through an Ugi/Dieckmann cyclization strategy with DBU. This two-step one-pot procedure afforded the targeted tetramic acid analogues in good yields. With commercially available Ugi starting materials, microwave irradiation, a simple operation, excellent yields, and a broad scope, this reaction has the potential to produce a large number of tetramic acid analogues, which cannot be easily accessed by the classic synthetic methods.

Integrating biocatalysis and multicomponent reactions

While often multicomponent reactions (MCR) are used for the diversity-oriented synthesis of racemic (or achiral) molecular entities, this short review describes two alternative approaches for accessing enantiopure products exploiting the power of biocatalysis. Enzymes or microorganisms may be used for preparing enantiopure MCR inputs or for resolving racemic (or achiral) MCR adducts.

Microwave-assisted facile construction of quinoxalinone and benzimidazopyrazinone derivatives via two paths of post-Ugi cascade reaction

A facile and efficient route to synthesize quinoxalinone and benzimidazopyrazinone was developed via two paths of a post-Ugi cascade reaction. By simply alternating the order of nucleophilic substitution reactions, both heterocycles could be accessed selectively from the same Ugi adduct. Microwave-assisted synthesis protocol provided these compounds with one purification procedure for three steps. These two scaffolds with more possible spaces for further modifications provide great benefit toward combinatorial and medicinal chemistry campaigns.

PPL catalyzed four-component PASE synthesis of 5-monosubstituted barbiturates: Structure and pharmacological properties

Enzymatic four-component reactions are very rare although three-component enzymatic promiscuous reactions are widely reported. Herein, we report an efficient PASE protocol for the synthesis of potentially lipophilic zwitterionic 5-monosubstituted barbiturates by four component reaction of mixture of ethyl acetoacetate, hydrazine hydrate, aldehyde and barbituric acid in ethanol at room temperature. Seven different lipases were screened for their promiscuous activity towards the synthesis of 5-monosubstituted barbiturates and the lipase from porcine pancreas (PPL) found to give optimum efficiency. The zwitterionic 5-monosubstituted barbiturates with pyrazolyl ring showed promising pharmacological activity upon screening for antibacterial and apoptotic properties.

Recent Advances in Biocatalytic Promiscuity: Hydrolase-Catalyzed Reactions for Nonconventional Transformations

Enzymes have emerged in recent decades as ideal catalysts for synthetic transformations under mild reaction conditions. Their capacity to accelerate a myriad of biotransformations with high levels of selectivity and broad substrate specificity including excellent atom economy has led to a current full recognition. The six classes of enzymes (oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases) possess outstanding abilities to perform specific modifications in target molecules. Nevertheless, in the last fifteen years, novel examples have appeared related to nonconventional processes catalyzed by various classes of biocatalysts. Amongst these, hydrolases have received special attention since they display remarkable activities in initially unexpected reactions such as carbon-carbon and carbon-heteroatom bond-formation reactions, oxidative processes and novel hydrolytic transformations. In this review, the main findings in this area will be disclosed, highlighting the catalytic properties of hydrolases not only to catalyze single processes but also multicomponent and tandem nonconventional reactions.

Recyclable Bi2WO6-nanoparticle mediated one-pot multicomponent reactions in aqueous medium at room temperature

Room temperature multicomponent reactions (MCRs) are reported using Bi₂O₃, BiVO₄, and Bi₂WO₆ (nanoparticle) as heterogeneous catalysts. Among these, Bi₂WO₆ (5 mol%) nanoparticles showed excellent reactivity for the synthesis of functionalized dihydropyridine, polyhydroquinoline, 4H-chromene and 2-amino-4H-benzo[b]pyran derivatives in aqueous medium.