N-pentenyl Glycosides Research Articles

Glycosylation of n-pentenyl glycosides using bromodiethylsulfonium salt as an activator: interception of the glycosyl intermediate by chloride ion transfer.

Utilization of n-pentenyl glycosides (NPGs) in modern carbohydrate synthesis may be hindered by their sluggish activation, which results from reversible halogenation and cyclization processes. Bromodiethylsulfonium bromopentachloroantimonate (BDSB) has been previously shown to be a powerful brominating agent for the cation-π polyene cyclization of less reactive and electron-poor polyenes. This study demonstrates the activation of NPGs using BDSB as a powerful brominating agent. BDSB effectively activates the terminal olefins of NPGs and the reaction proceeds through 5-exo-tet cyclization, offering a rapid and mild approach for glycosylation with a wide range of glycosyl donors, including n-pentenyl mannoside, n-pentenyl galactoside, and n-pentenyl glucoside. The success of this approach derives from the chloride ion transfer from the nonnucleophilic SbCl5Br anion to the glycosyl intermediate, which disrupts the equilibrium and produces a glycosyl chloride intermediate that is smoothly converted to 22 coupling products, with yields ranging from moderate to excellent (49-100%). The β-selective glycosylation is accomplished when employing NPGs equipped with a neighboring participating group. The practicality of the BDSB-activated glycosylation is demonstrated by a gram-scale synthesis. This study showcases BDSB as a potent activator for NPG glycosylation through the interception of a glycosyl intermediate that diminishes the equilibration during halogenation and 5-exo-tet cyclization.

α/β-Stereo- and diastereoselective glycosylation with n-pentenyl glycoside donors, promoted by N-iodosuccinimide and catalyzed by chiral Brønsted acid.

A method involving stereoselective glycosylation catalyzed by (+)-isomenthol ester of pentacarbomethoxycyclopentadiene as a chiral Brønsted acid, with n-pentenyl glycosides in the presence of N-iodosuccinimide as the promoter is described; this method offered a chiral recognition of racemic substrates.

Access to n-pentenyl tetra- and pentasaccharide analogues of the antitumor drug PI-88 based on 1,2-methyl orthoester glycosyl donors

Convergent synthetic routes to PI-88 tetra- and pentasaccharide-component analogues, have been developed featuring regioselective glycosylations of mannose-polyol n-pentenyl glycosides (NPG) acceptors with 1,2-methyl orthoesters (MeOE) glycosyl donors.

Efficient synthesis of oligosaccharyl 1,2-O-orthoesters from n-pentenyl glycosides and application to the pentaarabinofuranoside of the mycobacterial cell surface.

Complex oligosaccharide syntheses employ the use of more than one glycosyl donor and hence, methods for the interconversion of glycosyl donors are highly valuable for the overall synthesis plan. Herein, n-pentenyl glycosides are efficiently converted to glycosyl 1,2-O-orthoesters in the presence of both acid and base sensitive functional groups. The identified protocol was found to be suitable for the synthesis of trisaccharyl and tetrasaccharyl 1,2-O-orthoester as well. Furthermore, an iterative synthesis of pentaarabinofuranoside present on the Mycobacterium tuberculosis cell surface was accomplished using this method.

Glycosyl fluorides from n-pentenyl-related glycosyl donors — Application to glycosylation strategies

n-Pentenyl glycosides (NPGs) and n-pentenyl orthoesters (NPOEs) have been transformed into glycosyl fluorides by a variety of methods. In the case of NPGs, Barluenga’s reagent, bis(pyridinium)iodonium(I)tetrafluoroborate (IPy2BF4), gives good yields of glycosyl fluorides when HF–pyridine complex is used as an additional fluoride source. NPOEs can be activated either by a combination of electrophilic iodonium (Barluenga’s reagent) and HBF4 or by the action of HF–pyridine complex. The ensuing glycosyl fluorides form a semiorthogonal pair of glycosyl donors when confronted with NPGs.

ChemInform Abstract: Armed—Disarmed Effects in Carbohydrate Chemistry: History, Synthetic and Mechanistic Studies

AbstractReview: 109 refs.

ChemInform Abstract: Iodonium-Promoted Reactions of Disarmed Thioglycosides.

Abstract N-Iodosuccinimide/trifluoromethanesulfonic acid, which had been shown to promote the solvolysis of disarmed n-pentenyl glycosides, has been found to induce the same reactivity with disarmed thioglycosides as substrates.

ChemInform Abstract: Use of n-Pentenyl Glycosides as Precursors to Various Spacer Functionalities.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Orthogonal Activation of Propargyl and n-Pentenyl Glycosides and 1,2-Orthoesters

An orthogonal activation strategy with propargyl and n-pentenyl glycosides has been identified. According to this methodology, n-pentenyl glycosides can be selectively activated with NIS/TMSOTf in the presence of either armed or disarmed propargyl O-glycosides. In addition, we report herein that propargyl 1,2-orthoesters can be selectively activated with AuBr(3) in CH(2)Cl(2) at room temperature in the presence of n-pentenyl glycosides. Similarly, pentenyl 1,2-orthoesters can be selectively activated with NIS/Yb(OTf)(3) in the presence of propargyl glycosides.

Silver(I) tetrafluoroborate as a potent promoter for chemical glycosylation

We have identified silver tetrafluoroborate (AgBF 4) as an excellent promoter for the activation of various glycosyl donors including glycosyl halides, trichloroacetimidates, and thioimidates. Easy handling and no requirement for azeotropic dehydration prior to application makes AgBF 4 especially beneficial in comparison to the commonly used AgOTf. Selective activation of glycosyl halides or thioimidates over thioglycosides or n-pentenyl glycosides, including simple sequential one-pot syntheses, has also been demonstrated. Versatility of glycosyl thioimidates was further explored by converting these intermediates into a variety of other classes of glycosyl donors.

IPy2BF4/HF-Pyridine: A New Combination of Reagents for the Transformation of Partially Unprotected Thioglycosides and n-Pentenyl Glycosides to Glycosyl Fluorides

The combination of bis(pyridinium)iodonium (I) tetrafluoroborate (IPy2BF4), and hydrogen fluoride pyridine (HF-py) forms an iodine monofluoride (IF) synthetic equivalent that can be used in the preparation of partially unprotected glycosyl fluorides from partially unprotected n-pentenyl glycosides and thioglycosides, thus avoiding the need for the protection/deprotection steps normally required in that transformation.

Regioselective Strategies Mediated by Lanthanide Triflates for Efficient Assembly of Oligomannans

Readily prepared mannosyl n-pentenylorthoesters (NPOEs) serve as donors in themselves and as convenient intermediates for other glycosyl donors, such as n-pentenyl glycosides (NPGs), thioglycosides, and trichloroacetimidates. These various donors are activated by different reagents, and are therefore amenable to versatile, discriminate use. Scandium and ytterbium triflates respond very differently to these donors, with the result that chemoselective discrimination between NPOEs, NPGs, trichloroacetimidates as well as ethyl and phenyl thioglycosides can be achieved. Appropriate NPOEs are also able to provide 2,6 and 3,6 diol acceptors via rearrangement or glycoside formation, and these can be used for one-pot, sequential glycosidations based on orthogonal donors, and in situ double differential glycosidations. Thus NPOEs activated by iodonium ion, specifically generated from ytterbium triflate/N-iodosuccinimide, can be used to monoglycosidate the diols rapidly, with exquisite regio, and sometimes chemo, selectivity. The residual NPOE is converted into disarmed NPG, which is refractory to the reaction conditions, and so poses no threat to the free-OH of the monoglycosidation product. Further glycosidation of the latter can then achieved by direct addition of a trichloroacetimidate or ethyl thioglycoside. This basic strategy has been used to prepare a branched chain pentadecamannan. The success is an example of the efficiency of donor/acceptor MATCH concept for regioselective glycosylation.

IPy2BF4-Mediated Transformation of n-Pentenyl Glycosides to Glycosyl Fluorides: A New Pair of Semiorthogonal Glycosyl Donors

Bis(pyridinium) iodonium(I) tetrafluoroborate (IPy2BF4), a solid and stable reagent, can be used to transform n-pentenyl orthoesters (NPOEs) and n-pentenyl glycosides (NPGs) into glycosyl fluorides. The latter pair constitutes a new set of semiorthogonal glycosyl donors that can be used in glycosylation strategies, alone or in combination with NPOEs.

Synthesis of a 28‐mer Oligosaccharide Core of Mycobacterial lipoarabinomannan (LAM) Requires only Two n‐Pentenyl Orthoester Progenitors

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Glycosylation with Glycosyl p‐Bromophenyl Phthalates as New Efficient Glycosyl Donors.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A Strategy for Ready Preparation of Glycolipids for Multivalent Presentation

The olefinic residue of n-pentenyl glycosides serves as the trigger for regioselective construction of higher saccharides and then for elaboration in multivalent glycolipids. [reaction: see text]

Glycosylation with Glycosyl p-Bromophenyl Phthalates as New Efficient Glycosyl Donors

The development of an efficient and stereoselective glycosylation methodology has been a major concern in synthetic organic chemistry in the past a decade due to the important biological functions of complex oligosaccharides and glycoconjugates. Devising new glycosyl donors and developing new activation systems for the existing donors resulted in major advances in this area. For example, several glycosylation methodologies using the efficient glycosyl donors such as thioglycosides, glycosyl sulfoxides, glycals, glycosyl trichloroacetimidates, n-pentenyl glycosides, and glycosyl fluorides have been available. In addition, there have been recent reports regarding the development of glycosylation methods via new glycosyl donors and the application of existing glycosyl donors in novel activation systems. However, there still remains a need for more efficient and generally applicable new glycosylation methodology. In our previous endeavors, we reported a novel type of glycosyl donors, the 2’-(benzyloxycarbonyl)benzyl (BCB) glycoside and the 2’-carboxybenzyl (CB) glycoside A, as shown in Figure 1 for the stereoselective β-mannopyranosylation and the 2-deoxyglycosylation. We applied this methodology to the synthesis of a trisaccharide and tetrasaccharide. More recently, we have also reported the synthesis of the glycosyl benzyl phthalate C and its use as a new type of glycosyl donor. Although the glycosyl benzyl phthalate C proved to be the efficient glycosyl donor, there still remains a need for improvement. Thus, it is desirable to conduct the glycosylation more efficiently and at lower temperature in order to control the stereochemistry of the product and to keep acid-labile reactants or products intact under the acidic condition resulting from the use of TMSOTf. We envisaged that certain glycosyl aryl phthalates D might be more reactive than C so that the glycosylation might be conducted at lower temperature. Herein we describe the synthesis of a new type of glycosyl donors, the glycosyl aryl phthalate D and report that the glycosylation with glycosyl p-bromophenyl phthalates could be conducted under milder condition than that with glycosyl benzyl phthalates.

α-N-Acetylmannosamine (ManNAc) Synthesis via Rhodium(II)-Catalyzed Oxidative Cyclization of Glucal 3-Carbamates

[reaction: see text] Glucal 3-carbamates 1 and 7 underwent oxidative cyclization with iodobenzene diacetate or iodosobenzene in the presence of Rh2(OAc)4, providing mannosamine 2-N,3-O-oxazolidinones. With iodosobenzene, incorporation of 4-penten-1-ol provided a readily separable anomeric mixture of n-pentenyl glycosides, with the anomers exhibiting pronounced differences in reactivity as glycosyl donors. N-acylation of the sugar oxazolidinones led to alpha-selective glycosyl donors for the elaboration of various 2-mannosamine frameworks. Alternatively, the anomeric n-pentenyl glycosides of N-Cbz 2-mannosamine oxazolidinones were converted separately to oxazolidinone-opened derivatives 28alpha and 28beta. These served as stereoconvergent glycosyl donors, and the alpha-linked products were readily advanced to a variety of N-acetylmannosamine (ManNAc) frameworks, using an intramolecular O-->N acetyl transfer as the final step.

Microwave‐Assisted Saccharide Coupling with n‐Pentenyl Glycosyl Donors.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Further Insight into “Matching” of Donors and Acceptors via Reciprocal Donor Acceptor Selectivity (RDAS) Studies

AbstractFor Abstract see ChemInform Abstract in Full Text.