NEO-AMYLOPECTINYL MODELS SYNTHESIS OF COMPLEX BETA-BRANCHED MALTO-OLIGOSACCHARIDES IN SOLUBLE AND SOLID PHASE
Résumé
Starch is the ubiquitous glucidic reserve compound in nature. Synthesized by most plants from solar energy it is easily produced in very large scale cultures (cereals, tubers, legumes…). Besides its irreplaceable position in the food chain Starch is also a widely used commodity for its non-alimentary properties (paper, textile industry, adhesive, gels…) in almost all human activities. Though the polysaccharidic nature and the basic structure : poly-alpha(1,4) glucopyrannose of its minor constituent Amylose, and alpha-1,6) branched alpha-1,4-polyglucopyrannose of the major amylopectin has long been known, to date, the fine primary structure of the former still remains to be described ! The branching pattern found in amylopectin can reach extreme complexity. The determination of amylopectins' primary structures from various botanical origins families can be a real challenge. Moreover, though the enzymes involved in starch synthesis have been well-described, no satisfactory in-vitro synthesis has been achieved to date, one of the reasons invoked being the lack of proper primer substrate. In this paper we present an investigation of such structural diversity by rebuilding well-defined branched malto-oligosaccharidic model structures through chemical hemisynthesis, in order to obtain such substrates. Several isoamylase resistant, beta-branched neo-amylopectinyl oligosaccharides having degrees of polymerisation (DP) 4 to 8, with well-defined structures, were obtained. The construction of these models was performed using chemically modified malto-oligosaccharides in solution. All structures were confirmed by long distance heteronuclear NMR spectroscopy. Using activated Wang resin, solid-phase supported oligosaccharides were synthesised and the structures analysed by HR-MAS NMR.
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