Stereoselective total synthesis of dodecagalacturonic acid, a phytoalexin elicitor of soybean

Progress and challenges in the synthesis of sequence controlled polysaccharides

The sequence, length and substitution of a polysaccharide influence its physical and biological properties. Thus, sequence controlled polysaccharides are important targets to establish structure-properties correlations. Polymerization techniques and enzymatic methods have been optimized to obtain samples with well-defined substitution patterns and narrow molecular weight distribution. Chemical synthesis has granted access to polysaccharides with full control over the length. Here, we review the progress towards the synthesis of well-defined polysaccharides. For each class of polysaccharides, we discuss the available synthetic approaches and their current limitations.

Automated Glycan Assembly of Plant Cell Wall Oligosaccharides

Synthetic cell wall oligosaccharides are promising molecular tools for investigating the structure and function of plant cell walls. Their well-defined structure and high purity prevents misinterpretations of experimental data, and the possibility to introduce chemical handles provides means for easier localization and detection. Automated glycan assembly as emerged has a powerful new method for the efficient preparation of oligosaccharide libraries. We recently made use of this technology to prepare a collection of plant cell wall glycans for cell wall research. In this chapter, detailed experimental procedures for the automated synthesis of oligosaccharides that are ready for use in biological assays are described.

Synthesis of oligosaccharide fragments of the rhamnogalacturonan of Nerium indicum

Three trisaccharides, one pentasaccharide, and one heptasaccharide, namely α-D-GalA-(1→2)-α-L-Rha-(1→4)-β-D-GalA-OC3H7 (1), α-L-Rha-(1→4)-α-D-GalA-(1→4)-β-D-GalA-OC3H7 (2), α-D-GalA-(1→4)-α-D-GalA-(1→2)-α-L-Rha-OC3H7 (3), α-D-GalA-(1→2)-α-L-Rha-(1→4)-α-D-GalA-(1→2)-α-L-Rha-(1→4)-β-D-GalA-OC3H7 (4), and α-D-GalA-(1→2)-α-L-Rha-(1→4)-α-D-GalA-(1→2)-α-L-Rha-(1→4)-α-D-GalA-(1→2)-α-L-Rha-(1→4)-β-D-GalA-OC3H7 (5), which are relevant to the fragments of the rhamnogalacturonan of Nerium indicum, were concisely synthesized. The syntheses feature highly stereoselective formation of the α-D-GalA-linkage with GalA N-phenyltrifluoroacetimidates as donors.

Carbohydrate microarrays in plant science

Almost all plant cells are surrounded by glycan-rich cell walls, which form much of the plant body and collectively are the largest source of biomass on earth. Plants use polysaccharides for support, defense, signaling, cell adhesion, and as energy storage, and many plant glycans are also important industrially and nutritionally. Understanding the biological roles of plant glycans and the effective exploitation of their useful properties requires a detailed understanding of their structures, occurrence, and molecular interactions. Microarray technology has revolutionized the massively high-throughput analysis of nucleotides, proteins, and increasingly carbohydrates. Using microarrays, the abundance of and interactions between hundreds and thousands of molecules can be assessed simultaneously using very small amounts of analytes. Here we show that carbohydrate microarrays are multifunctional tools for plant research and can be used to map glycan populations across large numbers of samples to screen antibodies, carbohydrate binding proteins, and carbohydrate binding modules and to investigate enzyme activities.

Tansley Review No. 86 Accumulation of phytoalexins: defence mechanism and stimulus response system

Phytoalexin synthesis is a defence-response- that is characterized by a requirement for a number of distinct elements, all of which must be present for the response to be expressed fully. These same elements: a signal, a cellular receptor, a signal transduction system and a responsive metabolic system, are also used to describe a stimulus-response system. A number of molecular species can function as signal molecules or elicitors of phytoalexin synthesis, including poly- and oligosaccharides, proteins and polypeptides, and fatty acids. Few receptors for elicitors have been identified but those that have been are proteins located on the plasma membrane of the plant. Induction of phytoalexin synthesis involves selective and co-ordinated activation of specific defence response genes, including those encoding the enzymes of phytoalexin synthesis, and these genes constitute the responsive metabolic system. The separate, and distant, locations of the receptor and the responsive genes means that the event in which the signal is perceived by the receptor must be relayed to the genes by means of a second messenger system. Several second messengers are candidates for such a coupling- or signal transduction-system, including udenosine-3',5'-cyclic monophosphate, Ca²⁺ , diacylglycerol and inositol 1,4,5-trisphosphate, active oxygen species and jasmonic acid. Each has been examined as a possible component of the signal transduction system mediating between the elicitor receptor interaction and the phytoalexin synthesis it induces. Analysis of the signalling events is made complex by the simultaneous solicitation by the invading micro-organism of several defence responses, each of which might involve elements of a different signal system. The same complexity is evident which the role of phytoalexin accumulation in resistance is analysed. Evaluation of the contribution made by phytoalexin accumulation towards resistance has been attempted by the use of various inhibitors and enhancers of the process. Transgenic and mutant plants with specific alterations in one or more ot those elements necessary for the plant to respond to the signals for phytoalexin synthesis and other defence responses, are beginning to aid resolution of the complex pattern ot signalling events and the respective roles of the inducible defence mechanisms in resistance. CONTENTS Summary 1 I. Introduction 2 II. Chemistry of phytoalexins 3 III. Phytoalexin accumulation as a determinant of resistance 6 IV. Elicitation of phytoalexin accumulation 11 References 34.

Synthesis of the tetrasaccharide repeating unit of the antigen from Klebsiella type 2

The disaccharide ethyl 2,4,6-tri-O-acetyl-3-O-(2,3,4,6-tetra-O-benzyl-alpha- D-glucopyranosyl)-1-thio-beta-D-glucopyranoside (6) and methyl 2,6-di-O-benzyl-3-O-(methyl 2,3,4-tri-O-benzyl-alpha-D- glucopyranosyluronate)-beta-D-mannopyranoside (21) have been synthesized and condensed in the presence of methyl triflate to afford a tetrasaccharide derivative. Removal of protecting groups gave methyl 3-O-(methyl alpha-D-glucopyranosyluronate)-4-O-(3-O-alpha-D- glucopyranosyl-beta-D-glucopyranosyl)-beta-D-mannopyranoside (23), the repeating unit of the antigen from Klebsiella type 2, in the form of its methyl ester methyl glycoside.