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 R_f of 0.62 in Forestal solvent (acetic acid : concentrated hydrochloric acid : water, 30 : 3 : 10 by volume). The extract, diluted with methanol, had λ_max between, 496 and 502 nm, indicating its probable identity with luteolinidin (R_f 0.62 in Forestal, λ_max 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but the flavan-4-ol (4,5,7,3′,4′-pentahydroxyflavan) produced by reduction of eriodictyol with sodium borohydride (unpublished results of T. Swain) and a methanolic extract of the grasses behaved identically both when boiled with 2 normal hydrochloric acid (yielding luteolinidin) and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 λ_max 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.