The 2‐N,N‐Dibenzylamino Group as a Participating Group in the Synthesis of β‐Glycosides

The novel glycosyl donor 2‐N,N‐dibenzylaminothioglycoside 1 reacts with glycopyranoside alcohols 2 , presumably via intermediate 3 , to provide 1,2‐trans‐linked disaccharides 4 in high yield (78–86 %) and with high stereoselectivity. The N‐benzyl protecting groups are readily cleaved under normal hydrogenolysis conditions, facilitating the synthesis of oligosaccharides with free amino groups.     

Highly Regio- and Stereoselective Synthesis of Mannose-Containing Oligosaccharides with Acetobromo Sugars as the Donors and Partially Protected Mannose Derivatives as the Acceptors via Sugar Orthoester Intermediates

An orthoester formation/rearrangement sequence , in which 1,2-O-ethylidenated mannose or partially protected mannosides function as the glycosyl acceptors and simple acetobromo sugars as the glycosyl donors (see reaction scheme), provides an efficient and highly regio- and stereoselective route to mannose-containing 1→6, 1→3, and 3,6-branched oligosaccharides with exclusive 1,2-trans linkage.     

A New Intramolecular Reaction for the Regioselective Debenzylation or Protection of Alcohols

Strained benzylidene acetals such as 1 can be prepared with a new intramolecular reaction that allows the selective removal of benzyl protecting groups neighboring free OH groups, without attacking other benzyl groups. The mechanism of this reaction, which is useful for carbohydrate synthesis, probably proceeds via ionic intermediates with neighboring group participation.     

Solid-Phase Supported Synthesis of the Branched Pentasaccharide Moiety That Occurs in Most Complex Type N-Glycan Chains

Repetitive glycosylation on a sulfanylalkyl-functionalized Merrifield resin leads to the branched, complex pentasaccharide 1 in 20% overall yield in ten steps when appropriately protected O-glycosyl trichloroacetimidates are used as glycosyl donors. A decisive factor here was the tuning of the reaction conditions for the solid-phase glycosylation and the conditions for selective removal of the protecting groups and for cleavage of the samples from the resin for characterization. The subsequent cleavage of the product was achieved with a thiophilic reagent that does not attack the O-glycosidic linkages.     

Amidoglycosylation of Polymer-Bound Glycals: A Complete Solid-Phase Synthesis of the Oligosaccharide Domain of the Lewisb Blood Group Determinant

A new general method for the preparation of N-acetylglucosamine glycosidic linkages has been developed for solid-phase synthesis. The complete pentasaccharide domain of the Lewis^b blood group antigen, which is a mediator in the formation of ulcers and gastric cancer, has now been synthesized on solid support (see 1 ; the shaded circle is the polystyrene support; TIPS=triisopropylsilyl).     

Solid-Phase Synthesis of Oligosaccharides: Construction of a Dodecasaccharide

Complicated oligosaccharides such as dodecasaccharide 1 can be constructed by a new solid-phase strategy. The attachment to the polymeric support (gray sphere) is through a photolabile linker (structure I ), and thioglycosides serve as carbohydrate donors. Bn=benzyl, Bz=benzoyl.     

Selectively protected galactose derivatives for the synthesis of branched oligosaccharides

Synthesis and characterization of several new anomerically pure galactose derivatives, based on simple and effective protective group manipulations of benzyl β-d-galactopyranoside, are reported. The monosaccharides described contain selectively protected/deprotected hydroxyl functionalities at their 1,2,3,4- and 6-positions rendering them useful as building blocks for construction of branched oligosaccharides.     

Synthesis of β-Mannosides via Prearranged Glycosides

The choice of activator is decisive for whether the α-(1→4)-linked disaccharide 2 α or the anomeric compound 2 β is formed from the prearranged glycoside 1 . Other β-mannosylsaccharides can also be synthesized selectively by intramolecular glycosylation. Bn=benzyl, Bz=benzoyl, MeOTf= methyl trifluoromethanesulfonate, NIS=N-iodosuccinimide.     

Synthesis and antitumor activities of glucan derivatives

A highly efficient and practical method for the preparation of β-d-Glc-(1→6)-[β-d-Glc-(1→3)]-β-d-Glc-(1→6)-β-d-Glc-(1→6)-[β-d-Glc-(1→3)]-d-Glc-OMe was described. A dendritic nonasaccharide was also synthesized. The antitumor activities of hexasaccharide, the dendrimer, their sulfated derivatives, together with the natural glucan-protein and the corresponding polysaccharide isolated from barmy mycelium of Grifola frondosa, were preliminarily investigated based on Sarcoma-180 studies in mice tests. Our results suggest that the sulfated branching oligosaccharide and natural glycoprotein have better antitumor activities comparing to the parent sugar residue (oligosaccharide or polysaccharide).     

Controlling the Assembly of Cellulose-Based Oligosaccharides through Sequence Modifications

Peptides and nucleic acids with programmable sequences are widely explored for the production of tunable, self-assembling functional materials. Herein we demonstrate that the primary sequence of oligosaccharides can be designed to access materials with tunable shapes and properties. Synthetic cellulose-based oligomers were assembled into 2D or 3D rod-like crystallites. Sequence modifications within the oligosaccharide core influenced the molecular packing and led to the formation of square-like assemblies based on the rare cellulose IV_II allomorph. In contrast, modifications at the termini generated elongated aggregates with tunable surfaces, resulting in self-healing supramolecular hydrogels.     

Quantitative Monitoring of Solid-Phase Synthesis Using Gated Decoupling 13C NMR Spectroscopy with a 13C-Enriched Protecting Group and an Internal Standard in the Synthesis of Sialyl LewisX Tetrasaccharide

Just tagging along. For the nondestructive quantitative monitoring of solid-phase oligosaccharide synthesis a ¹³C-enriched tag (*) was incorporated in the linker and a ¹³C-enriched protecting group (⧫) was included in the growing molecule. By integration of the signals in a gated decoupling ¹³C NMR experiment the reaction progress can be monitored. This method was demonstrated with the synthesis of sialyl Lewis^x tetrasaccharide on a Tentagel support ((P)). Bn=benzyl, PEG=poly(ethylene glycol).     

New Protecting Group Strategies for the Solid-Phase Synthesis and Modification of Peptides,Oligonucleotides, and Oligosaccharides

Blocking and activation can be achieved with protecting groups such as the ortho-nitrobenzenesulfonyl group (see picture). In solid-phase peptide synthesis, this group can be used for temporary protection (path A) as well as the activation and selective N-alkylation (path B) of an amino group.     

Selective cleavage of acetals with ZnBr2 in dichloromethane

A selective cleavage of acetals of 1,2- and 1,3-diols has been achieved under mild conditions using ZnBr₂ in dichloromethane at room temperature. Acetal types cleavable by this procedure include benzylidene, isopropylidene and cyclohexylidene acetals. This method is compatible with several other types of hydroxyl protecting groups such as Bn, Bz, TBDPS, TIPS and TBDMS.     

The Total Synthesis of Eleutherobin: A Surprise Ending

An “sp ² –sp ³ Stille coupling” of the vinyl triflate 1 and the stannyl compound 2 is a key step toward the completion of the total synthesis of eleutherobin, a natural product exhibiting taxol-like cytotoxic activity.     

Selective Synthesis of Oligosaccharides by Mechanochemical Hydrolysis of Chitin over a Carbon-Based Catalyst

Oligosaccharides possess fascinating functions that are applicable in a variety of fields, such as agriculture. However, the selective synthesis of oligosaccharides, especially chitin-oligosaccharides, has remained a challenge. Chitin-oligosaccharides activate the plant immune system, enabling crops to withstand pathogens without harmful agrichemicals. Here, we demonstrate the conversion of chitin to chitin-oligosaccharides using a carbon catalyst with weak acid sites and mechanical milling. The catalyst produces chitin-oligosaccharides with up to 94 % selectivity in good yields. Monte-Carlo simulations indicate that our system preferentially hydrolyzes larger chitin molecules over oligomers, thus providing the desired high selectivity. This unique kinetics is in contrast to the fact that typical catalytic systems rapidly hydrolyze oligomers to monomers. Unlike other materials carbons more strongly adsorb large polysaccharides than small oligomers, which is suitable for the selective synthesis of small oligosaccharides.     

Rapid Separation on Activated Charcoal of High Oligosaccharides in Honey

A novel, simple and rapid stability-indicating high-performance liquid chromatographic (HPLC) method for pravastatin sodium (PRA) was successfully developed and validated for the assay of in tablets. Chromatographic separation was achieved isocratically on a C₁₈ column (150 mm × 4.6 mm) utilizing a mobile phase of methanol-phosphate buffer (pH 7; 0.02 M) (57:43, v/v) at a flow rate of 1.0 mL min⁻¹ with UV detection at 238 nm. A linear response (r = 0.9999) was observed in the range of 1–5 μg mL⁻¹. The method showed good recoveries (100.50%) and the relative standard deviation of intra and inter-day were 1.40%. The method can be used for both quality control assay of pravastatin in tablets and for stability studies as the method separates pravastatin from its degradation products and tablet excipients.An erratum to this article can be found at     

糖苷和寡糖的立体选择性合成研究进展

精苷、寡糖的立体选择性合成是一个十分重要的课题. 本文结合作者的研究工作介绍了糖苷、寡糖的立体选择合成的方法学进展,主要涉及近年来合成寡糖的新方法,并对这些方法的优势及不足进行了评述.     

Exploratory N-Protecting Group Manipulation for the Total Synthesis of Zwitterionic Shigella sonnei Oligosaccharides

Shigella sonnei surface polysaccharides are well-established protective antigens against this major cause of diarrhoeal disease. They also qualify as unique zwitterionic polysaccharides (ZPSs) featuring a disaccharide repeating unit made of two 1,2-trans linked rare aminodeoxy sugars, a 2-acetamido-2-deoxy-l -altruronic acid (l -AltpNAcA) and a 2-acetamido-4-amino-2,4,6-trideoxy-d -galactopyranose (AAT). Herein, the stereoselective synthesis of S. sonnei oligosaccharides comprising two, three and four repeating units is reported for the first time. Several sets of up to seven protecting groups were explored, shedding light on the singular conformational behavior of protected altrosamine and altruronic residues. A disaccharide building block equipped with three distinct N-protecting groups and featuring the uronate moiety already in place was designed to accomplish the iterative high yielding glycosylation at the axial 4-OH of the altruronate component and achieve the challenging full deprotection step. Key to the successful route was the use of a diacetyl strategy whereby the N-acetamido group of the l -AltpNAcA is masked in the form of an imide.     

Inositolphosphoglycan Mediators: An Effective Synthesis of the Conserved Linear GPI Anchor Structure*

An effective new preparative synthesis of the conserved linear pseudopentasaccharide structure of the GPI anchors and of the full GPI structure has been carried out that has permitted obtaining both molecules in sufficient quantities as to perform further structural and biologic studies. The synthesis involves a 3+2 block synthesis strategy in which a conveniently protected Man α(1→4) GlcN₃ α(1→6) myo‐Ins building block, previously used in the synthesis of inositolphosphoglycan (IPG) mediators, is glycosylated with a protected Man α(1→2) Man trichloroacetimidate.