α-Selective Ribofuranosylation of Alcohols with Ribofuranosyl Iodides and Triphenylphosphine Oxide

Synthesis and Glycosidation of Anomeric Halides: Evolution from Early Studies to Modern Methods of the 21st Century

Advances in synthetic carbohydrate chemistry have dramatically improved access to common glycans. However, many novel methods still fail to adequately address challenges associated with chemical glycosylation and glycan synthesis. Since a challenge of glycosylation has remained, scientists have been frequently returning to the traditional glycosyl donors. This review is dedicated to glycosyl halides that have played crucial roles in shaping the field of glycosciences and continue to pave the way toward our understanding of chemical glycosylation.

Reading ADP-ribosylation signaling using chemical biology and interaction proteomics

ADP-ribose (ADPr) readers are essential components of ADP-ribosylation signaling, which regulates genome maintenance and immunity. The identification and discrimination between monoADPr (MAR) and polyADPr (PAR) readers is difficult because of a lack of suitable affinity-enrichment reagents. We synthesized well-defined ADPr probes and used these for affinity purifications combined with relative and absolute quantitative mass spectrometry to generate proteome-wide MAR and PAR interactomes, including determination of apparent binding affinities. Among the main findings, MAR and PAR readers regulate various common and distinct processes, such as the DNA-damage response, cellular metabolism, RNA trafficking, and transcription. We monitored the dynamics of PAR interactions upon induction of oxidative DNA damage and uncovered the mechanistic connections between ubiquitin signaling and ADP-ribosylation. Taken together, chemical biology enables exploration of MAR and PAR readers using interaction proteomics. Furthermore, the generated MAR and PAR interaction maps significantly expand our current understanding of ADPr signaling.

Reagent Controlled Glycosylations for the Assembly of Well-Defined Pel Oligosaccharides

A new additive, methyl(phenyl)formamide (MPF), is introduced for the glycosylation of 2-azido-2-deoxyglucose building blocks. A linear α-(1,4)-glucosamine tetrasaccharide was assembled to prove the utility of MPF. Next, a hexasaccharide fragment of the Pseudomonas aeruginosa exopolysaccharide Pel was assembled using a [2 + 2 + 2] strategy modulated by MPF. The used [galactosazide-α-(1,4)-glucosazide] disaccharide building blocks were synthesized using a 4,6-O-DTBS protected galactosyl azide donor.

Hydrogen-Bonding-Assisted Exogenous Nucleophilic Reagent Effect for β-Selective Glycosylation of Rare 3-Amino Sugars

Challenges for stereoselective glycosylation of deoxy sugars are notorious in carbohydrate chemistry. We herein report a novel strategy for the construction of the less investigated β-glycosidic bonds of 3,5- trans-3-amino-2,3,6-trideoxy sugars (3,5- trans-3-ADSs), which constitute the core structure of several biologically important antibiotics. Current protocol leverages a C-3 axial sulfonamide group in 3,5- trans-3-ADSs as a hydrogen-bond (H-bond) donor and repurposes substoichiometric phosphine oxide as an exogenous nucleophilic reagent (exNu) to establish an intramolecular H-bond between the former and the derived α-oxyphosphonium ion. This pivotal interaction stabilizes the α-face-covered intermediate to inhibit the formation of the more reactive β-intermediate, thereby yielding reversed β-selectivity, which is unconventional for an exNu-mediated glycosylation system. A wide range of substrates was accommodated, and good to excellent β-selectivities were ensured by this H-bonding-assisted exNu effect. The robustness of the current strategy was further attested by the architectural modification of natural products and drugs containing 3,5- trans-3-ADSs, as well as the synthesis of a trisaccharide unit in avidinorubicin.

Pre-activation Based Stereoselective Glycosylations

Due to the wide presence of carbohydrates in nature and their crucial roles in numerous important biological processes, oligosaccharides have attracted a lot of attention in synthetic organic chemistry community. Many innovative synthetic methods have been developed for oligosaccharide synthesis, among which the pre-activation based glycosylation is particularly noteworthy. Traditionally, glycosylation reactions are carried out when the glycosyl donor and the acceptor are both present when the promoter is added. In comparison, the pre-activation based glycosylation is unique, where the glycosyl donor is activated by the promoter in the absence of the acceptor. Upon complete donor activation, the acceptor is added to the reaction mixture enabling glycosylation. The key step in any oligosaccharide synthesis is the stereoselective formation of the glycosidic bond. As donor activation and acceptor glycosylation are temporally separated, pre-activation based glycosylation can bestow unique stereochemical control. This review systematically discusses factors impacting the stereochemical outcome of a pre-activation based glycosylation reaction including substituents on the glycosyl donor, reaction solvent, and additives. Applications of pre-activation based stereoselective glycosylation in assembly of complex oligosaccharides are also discussed.

Dehydrative glycosylation with cyclic phosphonium anhydrides

Cyclic phosphonium anhydrides generated from bis-phosphine oxides and trifluoromethanesulfonic anhydride are shown as general coupling reagents in a dehydrative glycosylation reaction of C1-hemiacetals. This reaction protocol is characterized by a broad substrate scope and high yields, including reactions of O-, C-, N-, and S-based nucleophiles with furanose, pyranose, and deoxysugar donors.

Total synthesis of amphidinins E, F and epi-amphidinin F

A unified approach leading to the total synthesis of amphidinins E, F and epi-amphidinin F of a new structural class of linear marine polyketides is described.

Eosin Y-catalyzed photooxidation of triarylphosphines under visible light irradiation and aerobic conditions

A novel method for Eosin Y-catalyzed photooxidation of triarylphosphines under visible light irradiation and aerobic conditions was reported.

TMSBr-mediated solvent- and work-up-free synthesis of α-2-deoxyglycosides from glycals

The thio-additions of glycals were efficiently promoted by a stoichiometric amount of trimethylsilyl bromide (TMSBr) to produce S-2-deoxyglycosides under solvent-free conditions in good to excellent yields. In addition, with triphenylphosphine oxide as an additive, the TMSBr-mediated direct glycosylations of glycals with a large range of alcohols were highly α-selective.