Verbascose methylated

Fig. 1.—Molecular-rotation relationships of several raffinose-type oligosaccharides. Me, methyl a-D-galactopy ranoside Gl, D-glucose Mb, melibiose Mt, manninotriose Vt, verbascotetraose S, D-glucitol M, melibiitol Ml, manninotriitol Su, sucrose K, raffinose St, stachyose V, verbascose Gb, gentiobiose Ge, gentianose.

Methylation of verbascose, and hydrolysis, gave21 2,3,4,6-tetra-O-methyl-D-galactose (identified as the crystalline anilide), 2,3,4-tri-O-methyl-D-galactose (crystalline, identified by converting it into the 6-0-trityl derivative), 1,3,4,6-tetra-O-methyl-D-fructose (identified by analytical data and by its optical rotation), and a tri-O-methyl-D-glucose which, on further methylation, was converted into 2,3,4,6-tetra-O-methyl-D-glucose (identified through the crystalline anilide). 

To the present author, it seems more probable that the partially methylated D-gluconic acid obtained by Murakami was the 2,3,4,5-isomer, but it is obviously desirable to bring more experimental information into this area, so that the constitution of verbascose can be clarified. 

Structure. Cryoscopic molecular weight values indicate that verbascose is a pentasaccharide 169). From methylation studies, Murakami concluded that verbascose was a D-galactosyl-substituted stachyose (at C-6 of the terminal D-galactose unit of stachyose). Hot dilute acetic acid removes the D-fructose unit from verbascose to give a tetrasaccharide verbascotetraose (m.p. 240°C. [a] +191.4 (water)). This tetrose has been partially hydrolyzed, with removal of D-glucose, to give the crystalline trisaccharide galactotriose 164)-... 

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