H S Isbell

Bio: H S Isbell is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 32 citations.

Mechanism of chemical O-glycosylation: from early studies to recent discoveries.

Abstract: The main focus of this perspective lies in the discussion of the recent mechanistic theories and supporting experimental evidences that have been put forth in an attempt to advance our understanding of the factors affecting chemical glycosylation.

Synthesis of a 28-mer oligosaccharide core of Mycobacterial lipoarabinomannan (LAM) requires only two n-pentenyl orthoester progenitors

Abstract: Regioselective glycosidation of acceptor polyols greatly reduces the number of orthogonal protecting groups that are normally required for conventional syntheses of highly branched oligosaccharides. The MATCH between a donor and one of the many-OHs is the basis of a simple, ready synthesis of the 28-mer oligosaccharide described in this manuscript. The strategy relies heavily upon the unique interplay between n-pentenyl orthoesters (NPOEs), n-pentenyl glycosides, ytterbium triflate, and N-iodosuccinimide which allows exquisite, high-yielding regio- and chemoselective glycosylations. The NPOEs, effective as mannose or arabinose donors, are the sole sources of all saccharide components of the lipoarabinomannan oligosaccharide. Once considerable systematic research had been invested, the 12-mer mannan, 92, and 16-mer capped arabinan, 91, domains can be rapidly assembled in 300 mg and 1 g quantities, respectively, using conventional laboratory equipment. The 28-mer, 93 (MW = 11122.54) is, as far as we are aware of, the largest hetero-oligosaccharide that has been synthesized.

Zusammensetzung und Konformation von Zuckern in Lösung

Abstract: Die Konformation der Aldosen in Losung und die Zusammensetzung der Gleichgewichtsmischungen, die sich beim Losen dieser Zucker in Wasser bilden, sind NMR-spektroskopisch bestimmt worden. Berechnungen auf der Basis nichtbindender Wechselwirkungen und des anomeren Effekts gestatten eine Erklarung der beobachteten Konformationen und eine approximative Vorhersage des α/β-Verhaltnisses der Pyranosen im Gleichgewicht sowie des Ausmases der Anhydridbildung bei Zuckern in saurer Losung. In manchen Fallen sind die Furanose- bestandiger als die Pyranoseformen.

Some implications in carbohydrate chemistry of theories relating to the mechanisms of replacement reactions.

Abstract: Publisher Summary This chapter discusses some implications of the theories relating to the mechanisms of replacement reactions in the carbohydrate chemistry. It discusses the significance of new concepts from the field of theoretical organic chemistry and thus helps to stimulate the advance. The chapter focuses on the reactions of O -acyl derivatives of sugars, glycosides, and glycosyl halides because these substances play the central role in carbohydrate chemistry. The chapter presents the correlation of both stability and reactivity with structure. This requires the complete structure of each compound considered to be established unequivocally. Several experiments carried out by different scientists are discussed. The chapter reviews the nature and activating effect of neighboring-group participation in reactions at the lactol carbon atom. General considerations of anomerization are presented. Acetylated aldoses, O -acetylglycosyl halides, and acetylated alkyl glycosides are reviewed in detail in the chapter.

Synthetic N- and O- Glycosyl Derivatives of L-Asparagine, L-Serine, and L-Threonine

Abstract: Publisher Summary This chapter describes the synthetic N - and O -glycosyl derivatives of l -asparagine, l -serine, and l -threonine. Glycoproteins' are macromolecules containing one carbohydrate chain covalently linked to a protein backbone. They include proteoglycans, N -glycoproteins, O -glycoproteins, and collagen or basal-membrane proteins. The chapter presents the method of forming an amide bond between the 4-carboxyl group of l -aspartic acid and a glycosylamine in the presence of dicyclohexylcarbodiirnide. A series of derivatives of l -alanine, l -glutamic acid, glycine, l -serine, and l -valine, required for determining the specificity of amidohydrolase enzymes, as well as for testing the growth-inhibitory activity, was synthesized by coupling amine 8 with protected amino acids. The synthesis of glycopeptides of l -asparagine by the solid-phase procedure required a derivative protected, for example, by the acid-labile N -( tert -butoxycarbonyl) group. The reaction of a glycosyl bromide with the sodium salt of a phenol was the first procedure for the preparation of an O -glycosyl derivative of an amino acid. It is found that the glycoproteins of animal origin have glycoside linkages involving the hydroxyl groups of l -serine and l -threonine, as treatment with alkali releases the sugar component simultaneously with the loss of an equimolecular amount of hydroxyamino acid.