Variations in the Glycosidic Pattern of Anthocyanins

Abstract

THE distribution tests devised by the Robinsons1 have long been in use for determining the glycosidic nature of anthocyanin plant pigments. While employing paper chromatographic methods2 for the same purpose, it has now been observed that the variation in the number and nature of the sugars present in anthocyanins is greater than was originally thought1. Anthocyanins have been found which do not fit into any of the glycoside classes described by the Robinsons. One of these was a pelargonidin derivative present as the major pigment in red tubers of cultivated diploid potatoes. Results already reported3,4 showed that this pigment occurred in association with an acyl group, p-coumaric acid and two sugars, arabinose and glucose. The deacylated pigment on the basis of distribution tests and chromatography in n-butanol-2 N-hydrochloric acid (1 : 1, top layer) and comparison with authentic pelargonin (pelargonidin-3 : 5-diglucoside) was described as a 3 : 5-dimonoside. However, when chromatographed in 1 per cent aqueous hydrochloric acid it travelled farther than the pelargonin marker, suggesting that it had one more sugar residue present in the molecule than pelargonin. This was borne out by later experiments, in which four simpler glycosides were produced from it by controlled acid hydrolysis. From this data, it has been possible to assign the deacylated pigment a provisional structure, namely, the 3-arabinoglucoside, 5-arabinoside of pelargonidin. It is assumed that similar anthocyanin pigments, derived from peonidin, petunidin and delphinidin, which are also present in diploid potatoes are of the same type. Such a glycosidation pattern with two sugars in the 3-position and one in the 5-position has not been described before, but it may be expected to occur in other plants, especially where 3-pentoseglycosides and 3 : 5-dimonosides are known to occur together. In the cultivated diploid potato this glycoside is dominant to a 3-pentoseglycoside (the 3-arabinoglucoside), just as true 3 : 5-dimonosides and 3-monosides have a dominant-recessive relationship in some other plants5.