Recent Advances in the Synthesis of C-linked Glycoconjugates

C-Glycopyranosyl aldehydes: emerging chiral synthons in organic synthesis

Herein, we have summarized the vast array of synthetic processes that have been developed for the synthesis of C-glycopyranosyl aldehydes and diverse C-glycoconjugates derived from them by covering the literature reported from 1979 to 2023. Notwithstanding its challenging chemistry, C-glycosides are considered stable pharmacophores and are used as important bioactive molecules. The discussed synthetic methodologies to access C-glycopyranosyl aldehydes take advantage of seven key intermediates, viz. allene, thiazole, dithiane, cyanide, alkene, and nitromethane. Furthermore, the integration of complex C-glycoconjugates derived from varied C-glycopyranosyl aldehydes involves nucleophilic addition/substitution, reduction, condensation, oxidation, cyclo condensation, coupling, and Wittig reactions. In this review, we have categorized the synthesis of C-glycopyranosyl aldehydes and C-glycoconjugates on the basis of the methodology used for their synthesis and on types of C-glycoconjugates, respectively.

Visible-Light-Promoted Stereoselective C(sp3 )-H Glycosylation for the Synthesis of C-Glycoamino Acids and C-Glycopeptides

The glycosylative modification of peptides could improve the pharmacological properties of peptide drugs and deliver them efficiently to the target sites. Compared with O-/N-glycosides, C-glycosides exhibit more metabolic stability. We here disclose the first example of visible-light-promoted and Cu-catalyzed stereoselective C-glycosylation. The mild reaction conditions are compatible with various carbohydrate substrates, as demonstrated with a series of monosaccharides and a disaccharide, and are amenable to the synthesis of a wide variety of C-glycoamino acids and C-glycopeptidomimetics with good yields and excellent stereoselectivities. The dual-functional photocatalyst formed in situ via coordination of the glycine derivative and the chiral phosphine Cu complex could not only catalyze the photoredox process but also control the stereoselectivity of the glycosylation reaction.

Synthesis of spirocyclic C-arylglycosides and -ribosides by ruthenium-catalyzed cycloaddition

Spirocyclic C-arylglycosides were synthesized from the appropriately protected delta-gluconolactones. Addition of lithium acetylide followed by glycosylation with 3-(trimethylsilyl)propargyl alcohol converted the delta-gluconolactones into silylated diynes. After desilylation, subsequent ruthenium-catalyzed cycloaddition of the resultant diynes with alkynes or chloroacetonitrile gave spirocyclic C-arylglycosides in good yields and selectivity. This strategy was also extended to the synthesis of spirocyclic C-arylribosides from the known gamma-ribonolactone derivative. Moreover, silver-catalyzed iodination of the sugar diynes followed by ruthenium-catalyzed cycloaddition with acetylene delivered spirocyclic C-iodophenylglycosides and -ribosides, which were subjected to palladium-catalyzed C-C bond-forming reactions and copper-catalyzed coupling with nitrogen heterocycles to lead to various derivatives.