One-pot Glycosylation Strategy Research Articles

Donor Preactivation-Based Glycan Assembly: from Manual to Automated Synthesis.

Carbohydrates are called the third chain of life. Carbohydrates participate in many important biochemical functions in living species, and the biological information carried by them is several orders of magnitude larger than that of nucleic acids and proteins. However, due to the intrinsic complexity and heterogeneity of carbohydrate structures, furnishing pure and structurally well-defined glycans for functional studies is a formidable task, especially for homogeneous large-size glycans. To address this issue, we have developed a donor preactivation-based one-pot glycosylation strategy enabling multiple sequential glycosylations in a single reaction vessel.The donor preactivation-based one-pot glycosylation refers to the strategy in which the glycosyl donor is activated in the absence of a glycosyl acceptor to generate a reactive intermediate. Subsequently, the glycosyl acceptor with the same anomeric leaving group is added, leading to a glycosyl coupling reaction, which is then iterated to rapidly achieve the desired glycan in the same reactor. The advantages of this strategy include the following: (1) unique chemoselectivity is obtained after preactivation; (2) it is independent of the reactivity of glycosyl donors; (3) multiple-step glycosylations are enabled without the need for intermediate purification; (4) only stoichiometric building blocks are required without complex protecting group manipulations. Using this protocol, a range of glycans including tumor-associated carbohydrate antigens, various glycosaminoglycans, complex N-glycans, and diverse bacterial glycans have been synthesized manually. Gratifyingly, the synthesis of mycobacterial arabinogalactan containing 92 monosaccharide units has been achieved, which created a precedent in the field of polysaccharide synthesis. Recently, the synthesis of a highly branched arabinogalactan from traditional Chinese medicine featuring 140 monosaccharide units has been also accomplished to evaluate its anti-pancreatic-cancer activity. In the spirit of green and sustainable chemistry, this strategy can also be applied to light-driven glycosylation reactions, where either UV or visible light can be used for the activation of glycosyl donors.Automated synthesis is an advanced approach to the construction of complex glycans. Based on the two preactivation modes (general promoter activation mode and light-induced activation mode), a universal and highly efficient automated solution-phase synthesizer was further developed to drive glycan assembly from manual to automated synthesis. Using this synthesizer, a library of oligosaccharides covering various glycoforms and glycosidic linkages was assembled rapidly, either in a general promoter-activation mode or in a light-induced-activation mode. The automated synthesis of a fully protected fondaparinux pentasaccharide was realized on a gram scale. Furthermore, the automated synthesis of large-size polysaccharides was performed, allowing the assembly of arabinans up to an astonishing 1080-mer using the automated multiplicative synthesis strategy, taking glycan synthesis to a new height far beyond the synthesis of nucleic acids (up to 200-mer) and proteins (up to 472-mer).

One-Pot Assembly of Mannose-Capped Lipoarabinomannan Motifs up to 101-Mer from the Mycobacterium tuberculosis Cell Wall.

Lipoarabinomannan (LAM) from the Mycobacterium tuberculosis cell envelope represents important targets for the development of new therapeutic agents against tuberculosis, which is a deadly disease that has plagued mankind for a long time. However, the accessibility of long, branched, and complex lipoarabinomannan over 100-mer remains a long-standing challenge. Herein, we report the modular synthesis of mannose-capped lipoarabinomannan 101-mer from the M. tuberculosis cell wall using a one-pot assembly strategy on the basis of glycosyl ortho-(1-phenylvinyl)benzoates (PVB), which not only accelerates the modular synthesis but also precludes the potential problems associated with one-pot glycosylation with thioglycosides. Shorter sequences including 18-mer, 19-mer, and 27-mer are also synthesized for in-depth structure-activity relationship biological studies. Current synthetic routes also highlight the following features: (1) streamlined synthesis of various linear and branched glycans using one-pot orthogonal glycosylation on the combination of glycosyl N-phenyltrifluoroacetimidates, glycosyl ortho-alkynylbenzoates, and glycosyl PVB; (2) highly stereoselective construction of 10 1,2-cis-arabinofuranosyl linkages using 5-O-(2-quinolinecarbonyl)-directing 1,2-cis-arabinofuranosylation via a hydrogen-bond-mediated aglycone delivery strategy; and (3) convergent [(18 + 19) × 2 + 27] one-pot synthesis of the 101-mer LAM polysaccharide. The present work demonstrates that this orthogonal one-pot glycosylation strategy can highly streamline the chemical synthesis of long, branched, and complex polysaccharides.

Orthogonal Glycosylation with Phosphate Acceptors for Expeditious Synthesis of Bacterial Inner Core Oligosaccharides.

We report a practical one-pot glycosylation strategy for synthesis of bacterial inner core oligosaccharides that composed of unavailable L-glycero-D-manno and D-glycero-D-manno-heptopyranose components. The glycosylation method features a new orthogonal glycosylation procedure; whereby a phosphate acceptor is coupled with a thioglycosyl donor producing a disaccharide phosphate, which can be engaged in another orthogonal glycosylation procedure to couple with a thioglycosyl acceptor. The phosphate acceptors used in above one-pot procedure are directly prepared from thioglycosyl acceptors via the in-situ phosphorylation. Such phosphate acceptor preparation protocol eliminates the traditional protection and deprotection procedures. Based on the new one-pot glycosylation strategy, two partial inner core structures of Yersinia pestis lipopolysaccharide and Haemophilus ducreyi lipooligosaccharide were acquired.

Total Synthesis of Phellinus ribis Glycans with Immunostimulating Activities by an Orthogonal One-Pot Glycosylation Strategy

AbstractA total synthesis of nonasaccharide repeating units and shorter sequences from Phellinus ribis glycans with strong immunostimulating activities was achieved by an orthogonal one-pot glycosylation strategy based on an N-phenyltrifluoroacetimidate glycosylation, a Yu glycosylation, and an ortho-(1-phenylvinyl)benzoate glycosylation. The issues inherent to thioglycosides-based orthogonal one-pot glycosylations, such as aglycone transfer, are eliminated by this one-pot glycosylation strategy, which streamlines the chemical synthesis of glycans.

Total Synthesis of Cordyceps militaris Glycans via Stereoselective Orthogonal One-Pot Glycosylation and α-Glycosylation Strategies.

Cordyceps militaris glycans with potent antioxidant activities have been efficiently and collectively synthesized. The synthetic approach features the following: (1) a stereoselective orthogonal one-pot glycosylation strategy for both 1,2-trans- and 1,2-cis-glycosidic linkages; (2) a merged reagent modulation and remote anchimeric assistance (RMRAA) α-glucosylation strategy; (3) DMF-modulated α-glucosylation; (4) convergent [3 + 4 + 6] orthogonal one-pot assembly of the target tridecasaccharide.

One-Pot Glycosylation Strategy Assisted by Ion Mobility-Mass Spectrometry Analysis toward the Synthesis of N-Linked Oligosaccharides.

N-Glycans are major constituents of several cellular glycoproteins. One-pot strategies for the synthesis of N-glycans are crucial for the rapid generation of pure samples to determine their biological functions. Herein, we describe a double one-pot strategy for the synthesis of N-glycans assisted by an IM-MS analysis approach for rapid screening of optimized glycosylation reaction conditions. This research includes triflate-mediated direct β-mannosylation and tandem glycosylation in a one-pot strategy for the synthesis of the challenging N-linked trisaccharide core β-5. Furthermore, a one-pot sequential glycosylation of the N-linked trisaccharide core 7 furnishes diverse high-mannose type N-glycans with excellent stereo- and regioselectivities. In particular, ion mobility-mass spectrometry-based quantitative analysis is applied to identify the stereo- and regioselective outcomes of the crude reaction mixtures to develop a highly efficient one-pot protocol.

One-Pot Glycosylation Strategy for Rapid Access of Oligosaccharides with Wide Range of Molecular Diversity

: In carbohydrate chemistry, the synthesis of complex saccharides with well-defined structures is the most formidable process as it is quite strenuous to isolate carbohydrates in acceptable purity and amounts from natural sources. Therefore, complex saccharides with well-defined structures are often most conveniently accessed through chemical syntheses. This review mainly focuses on the methodologies for one-pot glycosylation into the complex glycans from the non-reducing end to reducing end and vice versa, orthogonal, preactivation based, photochemical as well as hybrid one-pot glycosylation. The main goal of this review in the carbohydrate community was to rapidly synthesize biologically relevant glycans that can be implemented for research in carbohydrate-based vaccine development, diagnostics, as well as drug discovery.

A One-Pot Synthesis of Glycans and Nucleosides Based on ortho-(1-Phenylvinyl)benzyl Glycosides.

One-pot synthesis of both glycans and nucleosides remains rare and challenging. Herein, we report a one-pot glycosylation strategy for glycans and nucleosides synthesis based on ortho-(1-phenylvinyl)benzyl glycosides, which has several advantages, including no aglycon transfers, no undesired interference of departing species, no unpleasant odor, and up to the construction of four different glycosidic linkages.

Merging Reagent Modulation and Remote Anchimeric Assistance for Glycosylation: Highly Stereoselective Synthesis of α-Glycans up to a 30-mer.

The efficient synthesis of long, branched, and complex carbohydrates containing multiple 1,2-cis glycosidic linkages is a long-standing challenge. Here, we report a merging reagent modulation and 6-O-levulinoyl remote anchimeric assistance glycosylation strategy, which is successfully applied to the first highly stereoselective synthesis of the branched Dendrobium Huoshanense glycans and the linear Longan glycans containing up to 30 contiguous 1,2-cis glucosidic bonds. DFT calculations shed light on the origin of the much higher stereoselectivities of 1,2-cis glucosylation with 6-O-levulinoyl group than 6-O-acetyl or 6-O-benzoyl groups. Orthogonal one-pot glycosylation strategy based on glycosyl ortho-alkynylbenzoates and ortho-(1-phenylvinyl)benzoates has been demonstrated in the efficient synthesis of complex glycans, precluding such issues as aglycon transfer inherent to orthogonal one-pot synthesis based on thioglycosides.

An orthogonal and reactivity-based one-pot glycosylation strategy for both glycan and nucleoside synthesis: access to TMG-chitotriomycin, lipochitooligosaccharides and capuramycin.

Both glycans (O-glycosides) and nucleosides (N-glycosides) play important roles in numerous biological processes. Chemical synthesis is a reliable and effective means to solve the attainability issues of these essential biomolecules. However, due to the stereo- and regiochemical issues during glycan assembly, together with problems including the poor solubility and nucleophilicity of nucleobases in nucleoside synthesis, the development of one-pot glycosylation strategies toward efficient synthesis of both glycans and nucleosides remains poor and challenging. Here, we report the first orthogonal and reactivity-based one-pot glycosylation strategy suitable for both glycan and nucleoside synthesis on the basis of glycosyl ortho-(1-phenylvinyl)benzoates. This one-pot glycosylation strategy not only inherits the advantages including no aglycon transfers, no undesired interference of departing species, and no unpleasant odors associated with the previously developed orthogonal one-pot glycosylation strategy based on glycosyl ortho-alkynylbenzoates, but also highly expands the scope (glycans and nucleosides) and increases the number of leaving groups that could be employed for the multistep one-pot synthesis (up to the formation of four different glycosidic bonds). In particular, the current one-pot glycosylation strategy is successfully applied to the total synthesis of a promising tuberculosis drug lead capuramycin and the divergent and formal synthesis of TMG-chitotriomycin with potent and specific inhibition activities toward β-N-acetylglucosaminidases and important endosymbiotic lipochitooligosaccharides including the Nod factor and the Myc factor, which represents one of the most efficient and straightforward synthetic routes toward these biologically salient molecules.

Cascade In Situ Phosphorylation and One-Pot Glycosylation for Rapid Synthesis of Heptose-Containing Oligosaccharides.

We report a one-pot glycosylation strategy for achieving rapid syntheses of heptose (Hep)-containing oligosaccharides. The reported procedure was designed to incorporate an in situ phosphorylation step into an orthogonal one-pot glycosylation. Hep-containing oligosaccharides were assembled directly from building blocks with minimal effort expended on manipulation of protecting and aglycone leaving groups. The utility of our one-pot procedure was illustrated by synthesizing partial core oligosaccharide structure present in the lipopolysaccharide of Ralstonia solanacearum.

Modular Synthesis of Nona-Decasaccharide Motif from Psidium guajava Polysaccharides: Orthogonal One-Pot Glycosylation Strategy.

The synthesis of long, branched, and complex carbohydrate sequences remains a challenging task in chemical synthesis. Reported here is an efficient and modular one-pot synthesis of a nona-decasaccharide and shorter sequences from Psidium guajava polysaccharides, which have the potent α-glucosidase inhibitory activity. The synthetic strategy features: 1) several one-pot glycosylation reactions on the basis of N-phenyltrifluoroacetimidate (PTFAI) and Yu glycosylation to streamline the chemical synthesis of oligosaccharides, 2) the successful and efficient assembly sequences (first O3', second O5', final O2') toward the challenging 2,3,5-branched Araf motif, 3) the stereoselective 1,2-cis-glucosylation by reagent control, and 4) the convergent [6+6+7] one-pot coupling reaction for the final assembly of the target nona-decasaccharide. This orthogonal one-pot glycosylation strategy can streamline the chemical synthesis of long, branched, and complicated carbohydrate chains.

One-Pot Synthesis of the Repeating Unit of Type VII Group B Streptococcus Polysaccharide and the Dimer.

The first synthesis of the hexasaccharide repeating unit of type VII group B Streptococcus capsular polysaccharide was achieved by a one-pot glycosylation strategy. The dimer of this repeating unit was also synthesized by one-pot glycosylation to achieve the backbone hexasaccharide first followed by one-pot dual glycosylations with the side-chain trisaccharide donor. All glycosylation reactions gave excellent stereoselectivity, which took advantage of a new stereospecific α-glucosylation method and the neighboring group participation effect for 1,2- trans glycosylations.

Chemical synthesis of glycans and applications in carbohydrate-based vaccines

Carbohydrates play important roles in many biological processes. However, the lack of resources of structurally-defined carbohydrates and their weak immunogenicity have always restricted the development of chemical glycobiology especially carbohydrate-based vaccines. The progress in chemical synthesis of carbohydrates and glycoconjugates has greatly promoted the development of carbohydrate-based vaccines including antibacterial vaccines, anti-tumor vaccines and anti-HIV vaccines. The use of one-pot glycosylation strategy and solid-phase glycosylation strategy is able to synthesize oligosaccharides and even polysaccharides more effectively than before. Glycoconjugates produced by combining the carbohydrate antigens and proper protein carriers improve the immunogenicity of carbohydrates. This review covers the general methods and strategies of carbohydrate chemical synthesis, and the recent development of carbohydrate-based vaccines, and also summarizes related work of our group, hoping to offer readers better understanding of chemical glycobiology especially carbohydrate-based vaccines.

O-(p-Methoxyphenylethynyl)phenyl Glycosides: Versatile New Glycosylation Donors for the Highly Efficient Construction of Glycosidic Linkages.

A novel alkyne-activation-based glycosylation protocol using o-(p-methoxyphenylethynyl)phenyl (MPEP) glycoside was established. The glycosyl MPEP donors were shelf-stable and could be prepared efficiently via Sonogashira reaction from the corresponding o-iodophenyl (IP) glycosides. The outstanding stability of IP glycosides as well as their efficient transformations to MPEP glycosides dramatically facilitates the syntheses of MPEP glycosyl donors and IP glycosyl acceptors. Furthermore, they make the MPEP glycosylation protocol applicable to the latent-active oligosaccharide and glycoconjugate synthetic strategy, with IP glycosides as the latent form and MPEP glycosides as the active form, as illustrated by the highly efficient fabrication of Streptococcus pneumoniae type 3 trisaccharide. The phenolic glycoside nature of MPEP glycosides bestows on the new glycosyl donors enhanced stability compared to their thioglycoside counterparts toward activation conditions applied for glycosyl trichloroacetimidate (TCAI) and o-alkynylbenzoate (ABz) donor. Thus, MPEPs can also be utilized in the selective one-pot glycosylation strategy, as exemplified by the syntheses of oligosaccharides via successive glycosylations with glycosyl TCAI, ABz, and EPMP as donors. Despite sharing identical promotion conditions with thioglycoside donors, the odor-free starting material (IP), the stable departure structure of the leaving group (3-iodobenzofuran), and the decreased nucleophilicity of the o-MPEP glycoside help to eliminate the three major shortcomings of the thioglycoside donors (unpleasant odor of starting material, detrimental interference of the cleaved leaving group, and aglycon intra- or intermolecular migration) while maintaining the prominent features of the thioglycoside methodology, including the broad substrate scopes, the mild promotion conditions, the stability of glycosyl donors, and the versatile applications in existing glycoside synthesis strategies. Based on the experimental results, a mechanism for MPEP activation was proposed, which was supported by systematic mechanistic investigations, including trapping of active intermediates, design of a vital disarmed rhamnosyl donor, and isolation and characterization of the departure species of the leaving group.

One-pot synthesis of β-2,6-dideoxyglycosides via glycosyl iodide intermediates

GRAPHICAL ABSTRACT

Synthesis of a new glycosphingolipid from the marine ascidian Microcosmus sulcatus using a one-pot glycosylation strategy

A novel neutral glycosphingolipid found in Microcosmus sulcatus containing a β-d-Galp(1→4)[α-d-Fucp-(1→3)]β-d-Glcp-(1→)Cer motif was synthesized. Trisaccharide derivatives were synthesized using trimethylsilyltrifluoromethanesulfanate (TMSOTf) and N-iodosuccimide (NIS)/trifluoromethane sulfonic acid (TfOH) as the promoters. Synthesis was achieved with an efficient one-pot glycosylation strategy. This is the first report of a one-pot glycosylation strategy using the procedure of Boons et al. for the synthesis of a natural product. Coupling of trisaccharide derivative 19 and ceramide derivative 20 by TMSOTf afforded the glycosphingolipid derivative 21. The fully protected glycoside was deprotected to give the target glycosphingolipid 2.

Solvent Participation in a One-Pot Glycosylation Strategy (SPOG)

Solvent participation in a one-pot glycosylation strategy (SPOG) was developed on the basis of the low concentration β-selective glycosylation method. This strategy enables the production of a β-glycosidic bond in a one-pot oligosaccharide synthesis without or with minimal use of any C-2 participating function.

Recent progress in chemical and chemoenzymatic synthesis of carbohydrates

The important roles that carbohydrates play in biological processes and their potential application in diagnosis, therapeutics, and vaccine development have made them attractive synthetic targets. Despite ongoing challenges, tremendous progresses have been made in recent years for the synthesis of carbohydrates. The chemical glycosylation methods have become more sophisticated and the synthesis of oligosaccharides has become more predictable. Simplified one-pot glycosylation strategy and automated synthesis are increasingly used to obtain biologically important glycans. On the other hand, chemoenzymatic synthesis continues to be a powerful alternative for obtaining complex carbohydrates. This review highlights recent progress in chemical and chemoenzymatic synthesis of carbohydrates with a particular focus on the methods developed for the synthesis of oligosaccharides, polysaccharides, glycolipids, and glycosylated natural products.