Baker’s yeast (Saccharomyces cerevisiae) catalyzed synthesis of bioactive heterocycles and some stereoselective reactions

Saccharomyces cerevisiae, commonly known as baker’s yeast, has gained significant importance as a mild, low-cost, environmentally benign biocatalyst. Initially it was mostly employed as an efficient catalyst for the enantioselective reduction of carbonyl compounds. Over the last decade, baker’s yeast has found versatile catalytic applications in various organic transformations. Many multicomponent reactions were also catalyzed by baker’s yeast. Various heterocyclic scaffolds with immense biological activities were synthesized by employing baker’s yeast as catalyst at room temperature. In this communication, we have summarized baker’s yeast catalyzed various organic transformations focusing primarily on heterocyclic synthesis.

Fungal biotransformation of limonene and pinene as a biotechnological approach for production of aroma compounds

The number of aroma compounds obtained by biotechnological process has increased tremendously in recent years and, as a result, are now being extensively employed in order to make products more attractive for consumers. In the present review, we inten to assess the wide range of reactions are catalyzed by fungal strains in regards to biotransformation of limonene and pinene for the aroma compounds production, their production rates/maximum concentrations and their biological potential. We comprehensively summarized in this review available data (2000–2021) regarding fungal biotransformation of limonene and pinene as biotechnological processes. Over the past years, has been paid to the biotransformation processes due to mild and environmentally friendly conditions applied. This review has shown that reports on the application of the fungi as a promising source of biocatalysts, mainly for stereoselective reactions such as hydroxylation and epoxidation. Studies have demonstrated the existence of promising monoterpenes used as substrates, which could be important from an industrial standpoint since this increases their importance as starting materials for obtaining aromatic molecules new. Moreover, biological (e.g.,antioxidant, anticancer) activities attributed to some monoterpene biotransformation products are increasingly being reported, indicating that their applications may transcend food, cosmetic and pharmaceutical industry.

Light-Mediated Cross-Coupling of Anomeric Trifluoroborates

Stereoselective reactions at the anomeric carbon constitute the cornerstone of preparative carbohydrate chemistry. Here, we report the synthesis of axial C1 trifluoroborates and stereoselective C-arylation and etherification reactions under photoredox conditions. These reactions are characterized by high anomeric selectivities for 2-deoxysugars and broad substrate scope (24 examples), including disaccharides and trifluoroborates with free hydroxyl groups. Computational studies show that high axial selectivities for these reactions originate from a combination of kinetic anomeric effect of the intermediate C1 radical and stereoelectronic stabilization of Ni(III) through the metallo-anomeric effect. Taken together, this new class of carbohydrate reagents adds the palette of anomeric nucleophile reagents suitable for efficient installation C-C and Cheteroatom bonds.

Light-Mediated Cross-Coupling of Anomeric Trifluoroborates

Stereoselective reactions at the anomeric carbon constitute the cornerstone of preparative carbohydrate chemistry. Here, we report the synthesis of axial C1 trifluoroborates and stereoselective C-arylation and etherification reactions under photoredox conditions. These reactions are characterized by high anomeric selectivities for 2-deoxysugars and broad substrate scope (24 examples), including disaccharides and trifluoroborates with free hydroxyl groups. Computational studies show that high axial selectivities for these reactions originate from a combination of kinetic anomeric effect of the intermediate C1 radical and stereoelectronic stabilization of Ni(III) through the metallo-anomeric effect. Taken together, this new class of carbohydrate reagents adds the palette of anomeric nucleophile reagents suitable for efficient installation C-C and Cheteroatom bonds.

Stereoselective organocatalysis and flow chemistry

Organic synthesis has traditionally been performed in batch. Continuous-flow chemistry was recently rediscovered as an enabling technology to be applied to the synthesis of organic molecules. Organocatalysis is a well-established methodology, especially for the preparation of enantioenriched compounds. In this chapter we discuss the use of chiral organocatalysts in continuous flow. After the classification of the different types of catalytic reactors, in Section 2, each class will be discussed with the most recent and significant examples reported in the literature. In Section 3 we discuss homogeneous stereoselective reactions in flow, with a look at the stereoselective organophotoredox transformations in flow. This research topic is emerging as one of the most powerful method to prepare enantioenriched products with structures that would otherwise be challenging to make. Section 4 describes the use of supported organocatalysts in flow chemistry. Part of the discussion will be devoted to the choice of the support. Examples of packed-bed, monolithic and inner-wall functionalized reactors will be introduced and discussed. We hope to give an overview of the potentialities of the combination of (supported) chiral organocatalysts and flow chemistry.

Stereoselective [4+2] Cycloaddition of Singlet Oxygen to Naphthalenes Controlled by Carbohydrates

Stereoselective reactions of singlet oxygen are of current interest. Since enantioselective photooxygenations have not been realized efficiently, auxiliary control is an attractive alternative. However, the obtained peroxides are often too labile for isolation or further transformations into enantiomerically pure products. Herein, we describe the oxidation of naphthalenes by singlet oxygen, where the face selectivity is controlled by carbohydrates for the first time. The synthesis of the precursors is easily achieved starting from naphthoquinone and a protected glucose derivative in only two steps. Photooxygenations proceed smoothly at low temperature, and we detected the corresponding endoperoxides as sole products by NMR. They are labile and can thermally react back to the parent naphthalenes and singlet oxygen. However, we could isolate and characterize two enantiomerically pure peroxides, which are sufficiently stable at room temperature. An interesting influence of substituents on the stereoselectivities of the photooxygenations has been found, ranging from 51:49 to up to 91:9 dr (diastereomeric ratio). We explain this by a hindered rotation of the carbohydrate substituents, substantiated by a combination of NOESY measurements and theoretical calculations. Finally, we could transfer the chiral information from a pure endoperoxide to an epoxide, which was isolated after cleavage of the sugar chiral auxiliary in enantiomerically pure form.

Face-selective adsorption of a prochiral compound on the chiral pore-surface of a metal–macrocycle framework (MMF) directed towards stereoselective reactions

The chiral pore-surface of a porous metal–macrocycle framework face-selectively adsorbs a prochiral molecule with the aid of a supramolecular chiral auxiliary.

Fungal Biotransformation: An Efficient Approach for Stereoselective Chemical Reactions

Abstract:: There is great interest in developing chemical technologies to achieve regioselective and stereoselective reactions since only one enantiomer is required for producing the chiral leads for drug development. These selective reactions are provided by traditional chemical synthetic methods, even under expensive catalysts and long reaction times. Filamentous fungi are efficient biocatalysts capable of catalyzing a wide variety of reactions with significant contributions to the development of clean and selective processes. Although some enzymes have already been employed in isolated forms or as crude protein extracts as catalysts for conducting selective reactions, the use of whole-cell provides advantages regarding cofactor regenerations. It is also possible to carry out conversions at chemically unreactive positions and to perform racemic resolution through microbial transformation. The current literature contains several reports on the biotransformation of different compounds by fungi, which generated chemical analogs with high selectivity, using mild and eco-friendly conditions. Prompted by the enormous pharmacological interest in the development of stereoselective chemical technologies, this review covers the biotransformations catalyzed by fungi that yielded chiral products with enantiomeric excesses published over the period 2010-2020. This work highlights new approaches for the achievement of a variety of bioactive chiral building blocks, which can be a good starting point for the synthesis of new compounds combining biotransformation and synthetic organic chemistry.

Transfer learning enables the molecular transformer to predict regio- and stereoselective reactions on carbohydrates

Organic synthesis methodology enables the synthesis of complex molecules and materials used in all fields of science and technology and represents a vast body of accumulated knowledge optimally suited for deep learning. While most organic reactions involve distinct functional groups and can readily be learned by deep learning models and chemists alike, regio- and stereoselective transformations are more challenging because their outcome also depends on functional group surroundings. Here, we challenge the Molecular Transformer model to predict reactions on carbohydrates where regio- and stereoselectivity are notoriously difficult to predict. We show that transfer learning of the general patent reaction model with a small set of carbohydrate reactions produces a specialized model returning predictions for carbohydrate reactions with remarkable accuracy. We validate these predictions experimentally with the synthesis of a lipid-linked oligosaccharide involving regioselective protections and stereoselective glycosylations. The transfer learning approach should be applicable to any reaction class of interest.

Taming Nitrene Reactivity with Silver Catalysts

Nitrene transfer (NT) is a convenient strategy to directly transform C–H bonds into more valuable C–N bonds and exciting advances have been made to improve selectivity. Our work in silver-based NT has shown the unique ability of this metal to enable tunable chemo-, site-, and stereoselective reactions using simple N-dentate ligand scaffolds. Manipulation of the coordination environment and noncovalent interactions around the silver center furnish unprecedented catalyst control in selective NT and provide insights for further improvements in the field.1 Introduction1.1 Strategies for Nitrene Transfer1.2 Brief Summary of Chemocatalyzed Nitrene Transfer1.3 Focus of this Account2 Challenges in Chemocatalyzed Nitrene Transfer2.1 Reactivity Challenges2.2 Selectivity Challenges2.3 Chemoselective Nitrene Transfer2.4 Site-Selective Nitrene Transfer2.5 Enantioselective Nitrene Transfer3 Summary and Perspective3.1 Future Opportunities and Challenges3.2 Conclusion