Methylsulfonylethoxycarbonyl (Msc) and fluorous propylsulfonylethoxycarbonyl (FPsc) as hydroxy-protecting groups in carbohydrate chemistry

Mild and General Protocol for Selective Deacetylation of Acetyl/Benzoyl-Protected Carbohydrates

Herein, we report a mild and general protocol for chemoselective deacetylation of mixed acetyl- and benzoyl-protected carbohydrates under mild acidic conditions. The protocol allows quick access to partially protected carbohydrates, which serve as versatile synthetic intermediates during the total synthesis of various mono- and oligosaccharide targets. The applicability of the developed protocol was successfully demonstrated on a range of carbohydrate substrates of various configurations and substitution patterns featuring functionalized aliphatic and aromatic aglycones. The protocol has shown excellent compatibility with the widely used O-anomeric protecting groups, prespacer aglycones, and thioglycoside glycosyl donors.

Semisynthesis of Aminomethyl-Insulin: An Atom-Economic Strategy to Increase the Affinity and Selectivity of a Protein for Recognition by a Synthetic Receptor

Advancements in the molecular recognition of insulin by nonantibody-based means would facilitate the development of methodology for the continuous detection of insulin for the management of diabetes mellitus. Herein, we report a novel insulin derivative that binds to the synthetic receptor cucurbit[7]uril (Q7) at a single site and with high nanomolar affinity. The insulin derivative was prepared by a four-step protein semisynthetic method to present a 4-aminomethyl group on the side chain of the Phe^B1 position. The resulting aminomethyl insulin binds to Q7 with an equilibrium dissociation constant value of 99 nM in neutral phosphate buffer, as determined by isothermal titration calorimetry. This 6.8-fold enhancement in affinity versus native insulin was gained by an atom-economical modification (-CH₂NH₂). To the best of our knowledge, this is the highest reported binding affinity for an insulin derivative by a synthetic receptor. This strategy for engineering protein affinity tags induces minimal change to the protein structure while increasing affinity and selectivity for a synthetic receptor.

Photolabile 2-(2-Nitrophenyl)-propyloxycarbonyl (NPPOC) for Stereoselective Glycosylation and Its Application in Consecutive Assembly of Oligosaccharides

A photolabile protecting group (PPG) 2-(2-nitrophenyl)-propyloxycarbonyl (NPPOC) was explored in glycosylation and applied in the consecutive synthesis of oligosaccharides. NPPOC displays a strong neighboring group participation (NGP) effect to facilitate the construction of 1,2-trans glycosides in excellent yield. Notably, NPPOC could be efficiently removed by photolysis, and the deprotection conditions are friendly to typical protecting groups. A branched and asymmetric oligomannose Man6 was rapidly prepared, and the consecutive assembly of oligosaccharides without intermediate purification was further investigated owing to the compatibility conditions between NPPPOC's photolysis and glycosylation.

Synthetic Carbohydrate Chemistry and Translational Medicine

The importance of post-translational glycosylation in protein structure and function has gained significant clinical relevance recently. The latest developments in glycobiology, glycochemistry, and glycoproteomics have made the field more manageable and relevant to disease progression and immune-response signaling. Here, we summarize the current progress in glycoscience, including the new methodologies that have led to the introduction of programmable and automatic as well as large-scale enzymatic synthesis, and the development of glycan array, glycosylation probes, and inhibitors of carbohydrate-associated enzymes or receptors. These novel methodologies and tools have facilitated our understanding of the significance of glycosylation and development of carbohydrate-derived medicines that bring the field to the next level of scientific and medical significance.

Reagent controlled stereoselective synthesis of teichoic acid α-(1,2)-glucans

The stereoselective construction of 1,2-cis-glycosidic linkages is key in the assembly of biologically relevant glycans, but remains a synthetic challenge. Reagent-controlled glycosylation methodologies, in which external nucleophiles are employed to modulate the reactivity of the glycosylation system, have become powerful means for the construction of 1,2-cis-glycosidic linkages. Here we establish that nucleophilic additives can support the construction of α-1,2-glucans, and apply our findings in the construction of a d-alanine kojibiose functionalized glycerol phosphate teichoic acid fragment. This latter molecule can be found in the cell wall of the opportunistic Gram-positive bacterium, Enterococcus faecalis and represents a structural element that can possibly be used in the development of therapeutic vaccines and diagnostic tools.

The 2,2-Dimethyl-2-(ortho-nitrophenyl)acetyl (DMNPA) Group: A Novel Protecting Group in Carbohydrate Chemistry

The 2,2-dimethyl-2-(ortho-nitrophenyl)acetyl (DMNPA) group was introduced to synthetic carbohydrate chemistry as a protecting group (PG) for the first time. Benefiting from a unique chemical structure and novel deprotection conditions, the DMNPA group can be cleaved rapidly and mutually orthogonal to other PGs. Orchestrated application of the DMNPA group with other PGs led to the highly efficient synthesis of the glycan of thornasterside A.

2-O-Benzyloxycarbonyl protected glycosyl donors: a revival of carbonate-mediated anchimeric assistance for diastereoselective glycosylation

Benzyloxycarbonyl can be used as participating group for the diastereoselective glycosylation of base-labile products and the synthesis of glycosyl esters.

Chemical Glucosylation of Labile Natural Products Using a (2-Nitrophenyl)acetyl-Protected Glucosyl Acetimidate Donor

The synthesis of (2-nitrophenyl)acetyl (NPAc)-protected glucosyl donors is described that were designed for the neighboring-group assisted glucosylation of base-labile natural products also being sensitive to hydrogenolysis. Glycosylation conditions were optimized using a trichloroacetimidate glucosyl donor, and cyclohexylmethanol and (+)-menthol as model acceptors. The approach was then extended to a one-pot procedure for the synthesis of 1,2-trans-glycosides. This method was finally applied for improved synthesis of the masked mycotoxin T2-O-β,d-glucoside.

An Efficient Synthesis of Milnacipran Hydrochloride via Reductive Amination of Aldehyde

An efficient synthesis of milnacipran hydrochloride has been accomplished. The important application of this paper is the reductive amination of aldehyde to primary amine with water soluble reagents. This method provides a high yield of primary amine as the major product, reduces the number of steps, and discourages by-products.

Teichoic acids: synthesis and applications

This review describes synthetic strategies to assemble well-defined teichoic acids and their use in unraveling their biological mode of action.

Protecting groups in carbohydrate chemistry: influence on stereoselectivity of glycosylations

Saccharides are polyhydroxy compounds, and their synthesis requires complex protecting group manipulations. Protecting groups are usually used to temporarily mask a functional group which may interfere with a certain reaction, but protecting groups in carbohydrate chemistry do more than protecting groups usually do. Particularly, protecting groups can participate in reactions directly or indirectly, thus affecting the stereochemical outcomes, which is important for synthesis of oligosaccharides. Herein we present an overview of recent advances in protecting groups influencing stereoselectivity in glycosylation reactions, including participating protecting groups, and conformation-constraining protecting groups in general.

Synthesis and application of a 2-[(4-fluorophenyl)-sulfonyl]ethoxy carbonyl(Fsec) protected glycosyl donor in carbohydrate chemistry

The 2-[(4-fluorophenyl)sulfonyl]ethoxy carbonyl (Fsec) group for protection of hydroxyl groups has been designed, synthesized, and evaluated. Fsec-Cl was readily prepared in 91% yield over three steps and subsequently used to protect 4-fluorobenzyl alcohol in high yield. The Fsec group was cleaved from the resulting model compound under mild basic conditions e.g., 20% piperidine in DMF and was stable under acidic conditions, e.g., neat acetic acid. The Fsec group was used to protect the unreactive 4-OH in a galactose building block that was later used in the synthesis of 6-aminohexyl galabioside.