A Highly Convergent Chemical Synthesis of Conformational Epitopes of Rhamnogalacturonan II

Abstract

Recent estimates indicate that more than 2000 genes encode proteins involved in the biosynthesis and remodeling of the polysaccharide-rich primary cell wall of plants.[1] The functions of only a handful of these gene products are known. [2,3] Furthermore, there is data to support the hypothesis that carbohydrate epitopes change during plant development; however, detailed knowledge about these processes is lacking. It is critical that these deficiencies in knowledge be addressed urgently because advances in plant sciences and genetics will provide researchers with tools to develop the next generation of agroenergy and agromaterial crops, which will be higheryielding and tailored for modern biorefinery operations. [4] Monoclonal antibodies are attractive tools for monitoring changes in the composition and organization of the primary plant wall at the cellular and subcellular level.[5] To date, only a small number of such monoclonal antibodies have been generated for which the binding specificities have been characterized. Synthetic chemistry can provide well-defined plant-derived oligosaccharides, [6][7][8] which can be employed for the production of monoclonal antibodies. In particular, the highly complex pectins are prime targets for this purpose. For example, rhamnogalacturonan II (RGII) is a structurally highly complex pectic oligosaccharide of the primary cell wall of higher plants [9] and is composed of four structurally different oligosaccharides referred to as side chains A-D, which are attached to a linear a(1!4)-linked d-GalpA polysaccharide backbone. These polysaccharides are crosslinked covalently through borate diesters (1:2) between two apiofuranosyl residues of the A side chain. The resulting three-dimensional pectic network contributes to the mechanical properties of the primary cell wall and is required for normal plant growth and development. Indeed, changes in cell-wall properties that decrease the borate cross-linking of pectin lead to symptoms such as dwarfism.[10]

Synthesis of Human Cancer Associated Globo-H (MBr1) Glycosylamino Acid: Some Mechanistic and Conformational Reinvestigations

“…However, when the l -fucose moiety was appended to the disaccharide ( 6 ), an interesting ring flip took place on the d -galactose moiety of the resultant trisaccharide ( 8 ) (Scheme 2). The small coupling constant observed between the vicinal hydrogen atoms of the d -galactose moiety of 8 (E ring, J H1,H2 = 4.8 Hz) is in agreement with a distorted 1 C 4 conformation (see 8′ ) xx. This ring flip may be attributed to the steric congestion of the E-ring, which presents a β- d -Galactal, an α- d -Fucose (1→2), a 3, 4-cyclic carbonate and a 6- O -TIPS ether.…”

Synthetic avenues towards a tetrasaccharide related to Streptococcus pneumonia of serotype 6A

“…The disaccharides ( 3a / 3b ) can be synthesized from their parent monomeric units 6a/6b/6c and 5 [ 27 ]. To ensure high α-selection during the formation of the central gluco-rhamno disaccharide the benzylidene protected glucosyl donor ( Fig.…”

“…This was next benzoylated almost quantitatively to give 16 . Finally DDQ-mediated deprotection of the naphthylmethyl group gave the acceptor 5 [ 27 ] in 83% yield ( Scheme 2 ).…”

Towards a Synthetic Strategy for the Ten Canonical Carrageenan Oligosaccharides – Synthesis of a Protected γ‐Carrageenan Tetrasaccharide

“…In order to increase understanding of plant cell wall biology and physiology, well‐defined plant cell wall oligosaccharides have been used as model compounds to represent domains from larger, more complex polysaccharides. Therefore, synthetic chemists have devoted attention to developing efficient strategies for the chemical synthesis of such oligosaccharide fragments . However, as outlined by a recent review summarizing all plant and algal cell wall oligosaccharides synthesized to date, there are relatively few examples of synthetic fragments representative of marine polysaccharides.…”

“…Therefore, synthetic chemists have devoted attention to developing efficient strategies for the chemical synthesis of such oligosaccharide fragments. [1][2][3][4][5][6][7][8] However, as outlined by a recent review summarizing all plant and algal cell wall oligosaccharides synthesized to date, [9] there are relatively few examples of synthetic fragments representative of marine polysaccharides. Therefore, we are interested in the synthesis of carrageenans, which are sulfated polysaccharides found in red algae seaweed.…”