Optimization of Oligosaccharide Synthesis from Cellobiose by Dextransucrase

There is a growing market for oligosaccharides as sweeteners, prebiotics, anticariogenic compounds, and immunostimulating agents in both food and pharmaceutical industries. Interest in novel carbohydrate-based products has grown because of their reduced toxicity and low immune response. Cellobiose is potentially valuable as a nondigestible sugar. The reaction of cellobiose, as an acceptor with a sucrose as a donor, catalyzed by a dextransucrase from Leuconostoc mesenteroides B-512FMCM, produced a series of cellobio-oligosaccharides. This production system was optimized using a Box–Behnken experimental design for 289 mM of sucrose and 250 mM of cellobiose and 54 U of the enzyme at pH 5.2 and 30 °C, to produce maximum yields of oligosaccharide.     

Synthesis of Oligosaccharide Fragments of the Lipoarabinomannan from Rhodococcus ruber *

The synthesis of two oligosaccharide fragments (1 and 2) of the lipoarabinomannan from Rhodococcus ruber is reported. Thioglycoside donors were used to assemble these glycans, which were prepared as their 8‐(methoxycarbonyl)octyl glycosides for potential incorporation into neoglycoconjugates.     

Reviews on Oligosaccharide Synthesis

Abstract

A list of the titles, authors, and references for significant review articles on oligosaccharide synthesis, published since 1980, is provided below. These articles are divided into three categories: (a) general reviews, (b) reviews limited in terms of subject matter covered, and (c) reviews limited to specific time periods. Within each group, articles are listed in chronological order. The purpose in establishing this list is to gather in a single place references to those review articles which contain a significant amount of information related to oligosaccharide synthesis. In addition to the title, authors, and other essential information, the number of references found in each article also is included to provide an indication of the potential of the article to direct the reader to the original literature. Finally, if a review was not written in English, the language used has been noted.     

Fluorous-Assisted One-Pot Oligosaccharide Synthesis

A new method for oligosaccharide assembly that combines the advantages of one-pot synthesis and fluorous separation is described. After one-pot glycosylations are completed, a fluorous tag is introduced into the reaction mixture to selectively "catch" the desired oligosaccharide, which is rapidly separated from non-fluorous impurities by fluorous solid-phase extraction (F-SPE). Subsequent "release" of the fluo rous tag and F-SPE achieved the purification of the desired oligosaccharide without the use of time- and solvent-consuming silica gel chromatography. Linear and branched oligosaccharides have been synthesized with this approach in just a few hours (for the overall oligosaccharide assembly and purification process).     

寡糖合成中的“预活化”策略

寡糖及其缀合物因其重要的生物学功能而日益受到人们的关注,由于糖链结构的复杂性与多样性,寡糖的化学合成具有很大的挑战性。为了减少合成及分离步骤,提高寡糖合成的效率,糖基化策略十分重要。"一釜合成法"由于进行多个连续的糖基化反应但不需分离中间体而具有很大优势,但传统"一釜法"在设计单糖模块时需要进行精细复杂的保护基操作和离去基调整而影响其合成效率。"预活化"寡糖合成策略不依赖于糖基供体与糖基受体的活性差异,无需复杂的保护基操作,所有偶联反应在同一条件下一釜完成,实现了寡糖的高效、快速合成。本文在简要介绍传统"一釜合成法"的基础上,对"预活化"策略的研究进展进行综述,重点介绍"预活化"策略的基本原理,发展过程及其在生物活性寡糖合成上的应用。     

Photoinactivation of Moraxella catarrhalis Using 405-nm Blue Light: Implications for the Treatment of Otitis Media

Moraxella catarrhalis is one of the major otopathogens of otitis media (OM) in childhood. M. catarrhalis tends to form biofilm, which contributes to the chronicity and recurrence of infections, as well as resistance to antibiotic treatment. In this study, we aimed to investigate the effectiveness of antimicrobial blue light (aBL; 405 nm), an innovative nonpharmacological approach, for the inactivation of M. catarrhalis OM. M. catarrhalis either in planktonic suspensions or 24-h old biofilms were exposed to aBL at the irradiance of 60 mW cm⁻². Under an aBL exposure of 216 J cm⁻², a >4-log₁₀ colony-forming units (CFU) reduction in planktonic suspensions and a >3-log₁₀ CFU reduction in biofilms were observed. Both transmission electron microscopy and scanning electron microscopy revealed aBL-induced morphological damage in M. catarrhalis. Ultraperformance liquid chromatography results indicated that protoporphyrin IX and coproporphyrin were the two most abundant species of endogenous photosensitizing porphyrins. No statistically significant reduction in the viability of HaCaT cells was observed after an aBL exposure of up to 216 J cm⁻². Collectively, our results suggest that aBL is potentially an effective and safe alternative therapy for OM caused by M. catarrhalis. Further in vivo studies are warranted before this optical approach can be moved to the clinics.     

Vinyl Glycosides in Oligosaccharide Synthesis. 2. The Use of Allyl and Vinyl Glycosides in Oligosaccharide Synthesis

A novel latent-active glycosylation strategy has been described that relies on the isomerization of substituted allyl glycosides to give the corresponding vinyl glycosides, which can subsequently be used in Lewis acid-mediated glycosylations. The isomerization reaction was performed by a rhodium catalyst obtained by treating tris(triphenylphosphine)rhodium(I) chloride with n-butyllithium. This catalyst has many advantageous properties over the use of conventional Wilkinson's catalyst. The glycosylation reactions gave high yields for both primary and secondary sugar alcohols, and the anomeric selectivity could be controlled by the constitution of the glycosyl donor and reaction conditions. The new isomerization and glycosylation approach enables complex oligosaccharides of biological importance to be prepared in a highly convergent manner.     

Elucidation of the Lipopolysaccharide Core Structures of Bacteria of the Genus Providencia

Enterobacteria of the genus Providencia are opportunistic pathogens causing diarrhea in travelers and children. Lipopolysaccharide (LPS) is the major surface antigen of Providencia and the major target of the immune response. O‐polysaccharide structures have been elucidated in several Providencia O‐serogroups, but little is known about the LPS core structure. We isolated core oligosaccharides from the R‐type LPS of a number of Providencia O‐serogroups and studied them by high‐resolution mass spectrometry, including capillary skimmer dissociation technique; three selected oligosaccharides were analyzed also by NMR spectroscopy. The conserved inner core and variable outer core regions were distinguished and the full core oligosaccharide structures established in Providencia O8, O35, and O49. Providencia LPSs were found to share some structural features with Proteus LPSs.     

UCHP Method for Oligosaccharide Combinatorial Library Synthesis

A new methodology for oligosaccharide combinatorial library synthesis using a special hydroxy protecting group, the uni-chemo hydroxy protection (UCHP) group, was developed. The UCHP group was composed of oligomeric amino acid derivatives. The amino terminals of UCHP groups were protected by either Boc or Fmoc groups. By using these two types of UCHP, five kinds of trigalactoses [Galβ1-3Galβ1-3Gal, Galβ1-3(Galβ1-4)Gal, Galβ1-4Galβ1-3Gal, Galβ1-3Galβ1-4Gal, and Galβ1-4Galβ1-4Gal] were successfully synthesized on a solid support as a model of oligosaccharide combinatorial library. Each step of all reactions was also successfully monitored using a combination of two colorimetric tests, chloranil and methyl red-DIC.     

Advances in Protecting Groups for Oligosaccharide Synthesis

Carbohydrates contain numerous hydroxyl groups and sometimes amine functionalities which lead to a variety of complex structures. In order to discriminate each hydroxyl group for the synthesis of complex oligosaccharides, protecting group manipulations are essential. Although the primary role of a protecting group is to temporarily mask a particular hydroxyl/amino group, it plays a greater role in tuning the reactivity of coupling partners as well as regioselectivity and stereoselectivity of glycosylations. Several protecting groups offer anchimeric assistance in glycosylation. They also alter the solubility of substrates and thereby influence the reaction outcome. Since oligosaccharides comprise branched structures, the glycosyl donors and acceptors need to be protected with orthogonal protected groups that can be selectively removed one at a time without affecting other groups. This minireview is therefore intended to provide a discussion on new protecting groups for amino and hydroxyl groups, which have been introduced over last ten years in the field of carbohydrate synthesis. These protecting groups are also useful for synthesizing non‐carbohydrate target molecules as well.     

Oligosaccharide Synthesis via Electrophile-Induced Activation of Glycosyl-N-Allylcarbamates 1

Abstract

Glycosyl-N-allyl carbamates, obtained by reaction of anomerically unprotected saccharides with allyl isocyanate, can be activated by an electrophile-induced cyclisation and reacted with glycosyl acceptors to form the corresponding oligosaccharides By this method the mucin core 2 trisaccharide² has successfully been synthesized. Due to the mild glycosylation conditions even 1-O-acetyl protected glycosyl acceptors can be used. This was demonstrated in the synthesis of a 1,6-linked glucosyl trisaccharide whereby a reptitious glycosylation strategy could be applied.

     

以氧化糖为原料的氨基糖衍生物的合成

首次报道了以氧化糖为原料的氨基糖衍生物的合成方法。以2位氧化糖为原料 与芳胺反应得到羰基转至3位的2位脱氧2位胺基糖，此胺基糖径NaBH_4立体选择性 还原及AcOH脱去4，6位保护基，合成了新型的D－阿洛糖胺。X射线单晶衍射分析表 明其晶体中有多种氢键，由于氢键作用，晶体呈现三维超分子结构。对2位氧化糖 与H_2NC_6H_4COOEt反应生成α，β－不饱和酮糖的机理进行了探讨。以5位氧化糖 为原料通过基转位反应合成了新型的二氢－1，4－苯并二嗪氨基糖。     

Synthesis of Selectively Protected Chitobiose and Chitotriose Derivatives from one Precursor. Versatile Building Blocks for Oligosaccharide Synthesis

Abstract

The inner core region of cell surface N-glycoproteins consists of a chitobiose substructure², containing β-(1,4)-linked disaccharides of glucosamine. Such carbohydrate structures are also found as repeating units of the bacterial cell wall peptidoglycan³ and in novel tetra- and pentasaccharide plant hormones, which are nodulation factors on legume roots.⁴ Since the first synthesis of a chitobiose derivative in 1966 by Paulsen,⁵ approaches to these compounds have relied mainly on the oxazoline method.⁶ The coupling reactions of aminosugar chlorides,⁷ bromides,⁸ acetates⁹ and trichloroacetimidates¹⁰ to suitable glycosyl acceptors have also been described. Most of these syntheses¹¹ require two completely different coupling partners; only in very few examples could the glycosyl donor and acceptor be obtained from the same starting material.¹² During our investigations into the stereocontrolled synthesis of glucosamine oligosaccharides, we required an economical synthetic route to protected derivatives of chitotriose. For the purpose of easy oligomerization, the anomeric protecting group of every building block had to be exchangeable selectively with the activating group for the next glycosylation. In this paper, we report an efficient approach to chitobiose and chitotriose from a single precursor. Furthermore, the hydroxyl groups at C-1, C-3, C-4, C-6 of these oligosaccharides are differentially protected. This protecting group scenario allows a specific access to any of these functionalities by regioselective deblocking. The N-phthalimide group was chosen out of several possible amino protecting groups to ensure β-selectivity and simultaneous activation in the coupling.¹³     

TCP Building Blocks for Oligosaccharide Synthesis: Progress Towards the Synthesis of Nodulation Factors

Abstract

The ability of tetrachlorphthaloyl (TCP) sugars to act as glycosyl acceptors as well as the viability of TCP as a global amine protecting group in the syntheis of polyglucosamine natural products such as N-methyl-N-lipid nodulation factors have been examined. Disaccharides corresponding to the reducing end segments and the core region of the target nodulation factors were assembled from n-pentenlyl glycosides. TCP acceptors were successfully coupled with a variety of pentenyl glycosyl donors to produce β-(1→4) oligosaccharides in good yields. Model coupling reactions to produce trisaccharides provided clear evidence for the disarming effect of an ester at O3 on a C4-OH in the glycosyl acceptor. Also, a unique pentenyl donor, which contained the desired N-metyl-N-lipid moiety of the non-reducing end segments of the target compounds, was synthesized and its efficacy in a coupling reaction was tested.     

Synthesis of the Tolerance-Inducing Oligosaccharide Lacto-N-Fucopentaose III Bearing an Activated Linker

A concise synthetic route to an immunomodulatory pentasaccharide, lacto-N-fucopentaose III (1) and its corresponding human serum albumin conjugate, is described. Key transformations of the strategy include two highly regio- and stereoselective glycosylations for the construction of disaccharide 10 and pentasaccharide 12, a Birch reduction for deprotection of benzyl ethers, and a UV-promoted radical addition of a thiol to an alkene for modification of the aglycone.