Structure of the Tomato Glycoalkaloid Tomatidenol-3-β-lycotetraose (Dehydrotomatine)

Experiments were carried out to establish the structure of the monosaccharides comprising the carbohydrate side chain of the tomato glycoalkaloid dehydrotomatine. This was accomplished by (a) isolating dehydrotomatine and α-tomatine from commercial tomatine, (b) derivatizing the monosaccharides formed on acid hydrolysis of commercial tomatine, dehydrotomatine, and α-tomatine to alditol acetates and methylated alditol acetates, and (c) determining the structures of the galactose, glucose, and xylose derivatives by gas chromatography−mass spectrometry. Both dehydrotomatine and α-tomatine have the same tetrasaccharide side chain. They differ only by the presence in dehydrotomatine of a double bond at carbon atoms 5 and 6 of ring B and its absence in α-tomatine. Dehydrotomatine, or tomatidenol-3β-lycotetraose, appears to represent a new class of glycoalkaloids in which a lycotetraose carbohydrate side chain is attached to an aglycon containing a double bond. Biosynthetic pathways leading to the formation of dehydrotomatine and α-tomatine and the significance of the results to host-plant resistance and the diet are discussed.