Mangiferin and Other Glycophenolics in Iris Species

Abstract

A YELLOW phenolic pigment, which appears on paper chromatograms under ultra-violet light as an apricot-coloured or dull-brown spot changing to a fluorescent yellow-green in ammonia, was first recognized as being present in petals of bearded iris cultivars in 1958. It is probably one of the major co-pigments in Iris flowers, producing, by interaction with the anthocyanin (a delphinidin glycoside), a range of purple, mauve and blue shades¹. In an earlier survey of leaf material, the same or a similar substance was observed on chromatograms of all species belonging to the section Pogoniris (which includes the bearded cultivars), of I. pseudacorus Fischer in the Laevigata group of the section Apogon, and of I. dichotoma Pallas in the section Pardanthopsis. This pigment differed in its spectral, chromatographic and colour properties from all the commonly occurring phenolics, such as the flavonoids, and has now been identified as the glycoxan-thone, mangiferin (2-glucosyl-1,3,6,7-tetrahydroxyxanthone) (I), by direct comparison with authentic material. Identification was by means of m.p. and mixed m.p. (268°–270°, decomp.); of the ultra-violet spectra (maxima at 242, 258, 316 and 364 mµ, undergoing characteristic bathochromic shifts in the presence of alkali, aluminium chloride, sodium acetate and sodium acetate–boric acid); of the colour reactions and of co-chromatography in eight different solvent systems. The constituent in the leaves of I. pseudacorus has been examined chromatographically and spectrophotometrically, and appears to be identical with that in the bearded iris. The constituent in I. dichotoma has not been examined in detail.