Approaches to the synthesis of heterocyclic C-nucleosides

This review is focused on the synthetic strategies to heterocyclic C-nucleosides and covers the literature from 2011 to 2021. The main attention is paid to the following three approaches: the direct C-C coupling of a carbohydrate moiety with a preformed aglycon unit, the construction of a (pseudo)sugar residue on a pre-formed aglycon, and the construction of an aglycon on a pre-formed (pseudo)sugar. In each Section, the literature data are categorized in terms of the size of aglycon from simple to complex, the advantages and drawbacks of the reviewed approaches are discussed.

Convenient and General Synthesis of C-3-Substituted Het(aryl)indole C-Nucleoside Analogues from Sugar Alkynes

The synthesis of C-3-substituted het(aryl)indole C-nucleoside analogues bearing structurally diverse sugar moieties has been achieved by Sonogashira coupling of terminal sugar alkynes with het(aryl) iodides followed by heteroannulation of the corresponding sugar/het(aryl) alkynes with substituted 2-iodoanilines. This method is simple and general and is suitable for structurally diverse sugars and various het(aryl) iodides. The terminal sugar alkynes include furanosides, pyranosides, and acyclic sugars with sensitive groups and bulky substituents. The het(aryl) iodides involve iodobenzene, iodothiophene, iodobenzothiophene, and iodobenzofuran. Thirty-one examples are presented and the corresponding 2-het(aryl)indole C-nucleoside analogues are obtained in moderate to excellent yields.

Efficient synthesis of novel indolizine C-nucleoside analogues via coupling of sugar alkynes, pyridines and α-bromo carbonyl compounds in one pot

The synthesis of novel indolizine C-nucleoside analogues has been achieved by the three-component coupling reaction of sugar alkynes, pyridines and α-bromo carbonyl compounds in one pot. The corresponding products are obtained in good to excellent yields. 49 examples have been given. The synthetic method is convenient, practical and efficient. It is suitable for various substrates including structurally diversified sugar alkynes with sensitive groups. The sugar alkynes include pyranosides, furanosides, and acyclic sugars. A plausible mechanism for the formation of indolizine C-nucleoside analogues has been elucidated.

A new and informative [a,b,c,d] nomenclature for one-pot multistep transformations: a simple tool to measure synthetic efficiency

Domino, cascade and tandem reactions constitute the most efficient and creative chemical transformations with a huge domain of synthetic utility and applications. A number of reactions may be achieved in a single pot, accompanied by the formation of new rings and new bonds, leading towards higher molecular complexity. A lack of one unified, yet informative descriptor often understates the synthetic ingenuity of certain highly creative transformations. In this review, we propose a new tetra-coordinated [a,b,c,d] nomenclature which takes into account and displays the basic parameters which generally indicate the level of efficiency of a chemical transformation. An almost exhaustive set of one-pot multistep reactions may be described by this system and this review is an attempt to display the one-pot multistep transformations reported from our group and to classify them based on our proposed descriptor.

Efficient synthesis of fluorescent alkynyl C-nucleosides via Sonogashira coupling for the preparation of DNA-based polyfluorophores

A facile and general procedure for the preparation of alkynyl C-nucleosides with varied fluorophores is presented. Sonogashira coupling was used as a key reaction to conjugate the dyes to an easily accessible ethynyl functionalized deoxyribose derivative. The new C-nucleosides were used for the preparation of DNA-based polyfluorophores.

Cross-metathesis reaction of α- and β-vinyl C-glycosides with alkenes

Cross-metathesis of α- and β-vinyl C-deoxyribosides and α-vinyl C-galactoside with various terminal alkenes under different conditions was studied. The cross-metathesis of the former proceeded with good yields of the corresponding products in ClCH2CH2Cl the latter required the presence of CuI in CH2Cl2 to achieve good yields of the products. A simple method for the preparation of α- and β-vinyl C-deoxyribosides was also developed. In addition, feasibility of deprotection and further transformations were briefly explored.