Mutarotation and ring structure of mannuronic lactone

Abstract

The numerous commercial applications of algin, a polysaccharide derived from certain marine plants, makes important the study of its principal constituent, D-mannuronic lactone. In 'this paper it is shown that by oxidation with bromine mannosaccharic dilactone of known structure is formed directly from mannuronic lactone without change in ring structure, and hence the latter SUbstance, like mannosaccharic dilactone, has a bicyclic structure consisting of two butylene oxide rings. The initial rapid mutarotation reaction of the substance is show n to consist of a conversion of the beta furanose modification to an equilibrium mixture containing the alpha furanose, and a detectable amount of the aldehyde modification. There is a small but measurable displacement of equilibrium with change in temperature. The mutarotation is exceptionslly sensitive to basic catalysts and for this reason the point of minimum rate lies in the acid region at pH 3.1.