Recognition of Lost Glycosidic Linkages by Reverse HMBC Experiments in Milk Oligoglycoside/Oligosaccharide.

Position of glycosidic linkages in oligosaccharide was confirmed by alditol acetate. methylation/acid hydrolysis in traditional studies. Later. core units and structure reporter group theory along with comparison of chemical shifts of natural and acetylated oligosaccharides were used for confirming the position of glycosidic linkages. These methods were. however. inappropriate and imperfect in certain cases. In recent times. 2D heteronuclear multiple bond correlation (HMBC) NMR experiments are being used for this purpose. making it possible to fix the position of glycosidic linkages unequivocally. In this experiment the multiple bond correlation of anomeric carbon of next monosaccharide gives a cross peak with the methine proton of the previous monosaccharide in an oligosaccharide chain. It becomes more complicated when the oligosaccharide is comprised of long or branched chains. but due to some proximal and steric hindrances this correlation is often not observed restricting the process of sequencing in milk oligosaccharides. In these circumstances. an alternative experiment. Reverse HMBC is used and is explained for the first time. meaning thereby. we observe the cross peak between methine carbon of the monosaccharide under observation with the anomeric proton of the next monosaccharide. In the present paper. Reverse HMBC technique for structure elucidation of novel heptaglycoside named Arkaroside from Tharparkar cow milk has been used. [ABSTRACT FROM AUTHOR]