Green synthesis of triazolo-nucleoside conjugates via azide–alkyne C–N bond formation

Modified nucleosides are the core precursors for the synthesis of artificial nucleic acids, and are important in the field of synthetic and medicinal chemistry. In order to synthesize various triazolo-compounds, copper and ruthenium catalysed azide–alkyne 1,3-dipolar cycloaddition reactions also known as click reaction have emerged as a facile and efficient tool due to its simplicity and convenient conditions. Introduction of a triazole ring in nucleosides enhances their therapeutic value and various photophysical properties. This review primarily focuses on the plethora of synthetic methodologies being employed to synthesize sugar modified triazolyl nucleosides, their therapeutic importance and various other applications.

Graphene Oxide Catalyzed Synthesis of Fused Chromeno Spiro Pyrrolidine Oxindoles via Tandem Decarboxylation and 1,3-Dipolar Cycloaddition

A short and efficient multicomponent sequence for synthesizing fused novel polyheterocyclic chromeno spiro-pyrrolidine oxindoles via 1,3-dipolar cycloaddition reaction mediated by reactive azomethine ylides catalyzed by the Graphene Oxide (GO) is reported herein. This approach was utilized for synthesizing fused polyheterocyclic spiro-pyrrolothiazole and spiro-pyrrole oxindoles with yields ranging from good to excellent. A heterogeneous GO catalyst with an ultra-low catalytic loading of 0.05 wt% could proficiently catalyze the reaction without the formation of any side products and can also be visualized by the formation of solid mass in the reaction flask. The methodology is green in nature and the products were isolated by simple filtration without the use of any chromatographic techniques.

Azomethine Ylide Cycloaddition of 1,3- dienyl esters: Highly regio- and diastereoselective synthesis of functionalized pyrrolidinochromenes

An efficient protocol for the synthesis of tricyclic pyrolidinochromenes has been developed via an intramolecular 1,3-dipolar cycloaddition of azomethine ylides generated in situ from 1,3- dienyl ester tethered O-hydroxyarylaldehyde and...

8 Sydnone-Based Cycloadditions in Click Chemistry

The 1,3-dipolar cycloaddition of sydnones (1,2,3-oxadiazolium-5-olates) with dipolarophiles, such as alkynes, has recently emerged as a versatile click reaction, with applications ranging from the mild and regioselective preparation of polysubstituted pyrazoles for drug discovery to the metal-free bioorthogonal ligation of biomacromolecules in living cells. This chapter reviews the importance of metal catalysis for controlling the regioselectivity of the copper-mediated reaction (CuSAC), as well as the development of fluorogenic probes, the click and release strategy, and photo-triggered ligations based on strain-promoted sydnone–alkyne cycloadditions (SPSAC).

From α-Keto Acids to Nitrile Oxides Enabled by Copper Nitrate: A Facile Access to Fused Isoxazolines

α-Keto acids were unprecedentedly employed as novel precursors of nitrile oxides on treatment with copper nitrate, which reacted with maleimides via [3+2] dipolar cycloaddition leading to pharmacologically interesting fused isoxazolines....

2.5 CuAAC and Metal-Free 1,3-Dipolar Huisgen Cycloadditions in Drug Discovery

Proclaimed by Sharpless in 2001, the manifesto of click chemistry philosophy shifted the focus from target-oriented to drug-like-oriented synthesis, and has enormously accelerated the drug-discovery process over the last two decades. Copper(I)-catalyzed and metal-free versions of the Huisgen 1,3-dipolar cycloaddition of azides and alkynes have become the reference click chemistry synthetic tools. These processes are adaptable to various drug-design modes such as kinetic target guided synthesis (in situ click chemistry assembling; KTGS), combinatorial chemistry/high-throughput-screening approaches, or structure-based rational projecting. Moreover, the facile click chemistry derivatization of natural or synthetic products, linking molecules or improving the stability of leads by installation of 1,2,3-triazoles, is another important stream of bioactivities. This review is intended to provide a general overview of click-chemistry-powered drug design, with dozens of successful examples resulting in the discovery of nanomolar-active 1,2,3-triazoles in every stage of drug development.

Revealing the unknown aspects of initial steps of prenylated flavin mononucleotide biosynthesis – the role of Lys129 in PaUbiX

Background Prenylated flavin mononucleotide (prFMN) is a recently discovered, heavily modified flavin compound. It is the only known cofactor that enables enzymatic 1,3-dipolar cycloaddition reactions. It is produced by enzymes from UbiX family, from flavin mononucleotide and either dimethylallyl mono- or diphosphate. prFMN biosynthesis is currently reported to be initiated by a protonation of the substrate by Glu140. Methods Computational chemistry methods are applied herein - mostly different flavors of molecular dynamics MD, such as Constant pH MD, hybrid Quantum-Mechanical / Molecular Mechanical MD, and classical MD. Results Glu140 competes for a single proton with Lys129 but it is the latter that adopted a protonated state throughout most of the simulation time. Lys129 plays a key role in the positioning of the DMAP’s phosphate group within the PaUbiX active site. DMAP’s breakdown into a phosphate and a prenyl group can be decoupled from the protona-tion of the DMAP’s phosphate group. Conclusions The role of Lys129 in functioning of PaUbiX is reported for the first time. The severity of interactions between Glu140, Lys129, and DMAP’s phosphate group enables an unusual decoupling of phosphate’s protonation from DMAP’s breakdown. Those findings are most likely conserved throughout the UbiX family to the structural re-semblence of active sites of those proteins. Significance Mechanistic insights into a crucial biochemical process, biosynthesis of prFMN, are provided. This study, alt-hough purely computational, extends and perfectly complements the knowledge obtained in classical laboratory experiments.

Highly Efficient and Diastereoselective Construction of Substituted Pyrrolidines Bearing A Quaternary Carbon Center via 1,3-Dipolar [3 + 2] Cycloaddition

A general approach to substituted pyrrolidines via [3 + 2] 1,3-dipolar cycloaddition between nonstabilized azomethine ylides and cyanosulfones was developed. The efficient method provides a series of substituted pyrrolidines bearing a quaternary carbon center in high yields (up to 98%) excellent diastereoselectivities (up to >25:1 dr) under ambient reaction conditions.