New Leuco-anthocyanins in Grasses

Abstract

EXAMINATION of the leaves of a series of grasses in the usual way1, which involves hydrolysing the leaves in 2 normal hydrochloric acid and extracting the hydrolysate with isoamyl alcohol, showed in four of them the presence of a component giving rise to a scarlet-coloured anthocyanidin having an Rf of 0.62 in Forestal solvent (acetic acid : concentrated hydrochloric acid : water, 30 : 3 : 10 by volume). The extract, diluted with methanol, had λmax between, 496 and 502 nm, indicating its probable identity with luteolinidin (Rf 0.62 in Forestal, λmax in, methanol 496 nm (ref. 2)). It thus seems that the four grasses contain a leucoluteolinidin. It is unlikely that such a compound could have a flavan-3,4-diol structure, but the flavan-4-ol (4,5,7,3′,4′-pentahydroxyflavan) produced by reduction of eriodictyol with sodium borohydride (unpublished results of T. Swain) and a methanolic extract of the grasses behaved identically both when boiled with 2 normal hydrochloric acid (yielding luteolinidin) and when treated with cold concentrated hydrochloric acid. In the latter case a blue colour was produced with λmax 550 nm, the product responsible being, perhaps, the carbonium ion of the ring-opened form of the flavan3. On standing, or after dilution and heating, this was partially converted into luteolinidin. It should be noted that other flavan-4-ols show similar behaviour3, but flavan-3,4-diols (for example, leucocyanidin), although giving an intermediate blue–purple component when heated in 2 normal hydrochloric acid, do not give such a colour with cold concentrated acid.