Purification and molecular structure of digalactosyl myo-inositol (DGMI), trigalactosyl myo-inositol (TGMI), and fagopyritol B3 from common buckwheat seeds by NMR.

Three galactosyl cyclitols, digalactosyl myo-inositol (assigned the trivial name DGMI), trigalactosyl myo-inositol (assigned the trivial name TGMI), and trigalactosyl d-chiro-inositol (fagopyritol B3), were isolated from common buckwheat (Fagopyrum esculentum Moench) seeds. Structures of the three compounds were determined by 2D NMR spectroscopy. DGMI is α-d-galactopyranosyl-(1→6)-α-d-galactopyranosyl-(1→1)-1l-myo-inositol, TGMI is α-d-galactopyranosyl-(1→6)-α-d-galactopyranosyl-(1→6)-α-d-galactopyranosyl-(1→1)-1l-myo-inositol, and fagopyritol B3 is α-d-galactopyranosyl-(1→6)-α-d-galactopyranosyl-(1→6)-α-d-galactopyranosyl-(1→2)-1d-chiro-inositol. DGMI and TGMI are higher oligomers of galactinol, a major galactosyl donor in plant seeds. Fagopyritol B3 is a higher oligomer of the fagopyritol B series and one of six fagopyritols found in buckwheat seeds and in the bran milling fraction. Samples of TGMI and fagopyritol B3 also contained the compounds N-(β-glucopyranosyl)-nicotinic acid and β-d-apiofuranosyl-(1→6)-β-d-(1-O-methyl)-glucopyranoside.