Greening pigments produced reaction of ethyl caffeate with methylamine

Little is known about the greening reaction of chlorogenic acid with amino acid in alkaline conditions. The isolation and characterization of the pigment were attempted by using ethyl caffeate and methylamine instead of chlorogenic acid and amino acid. The green compounds were purified by using Sephadex G-10 and thin layer chromatography, and were analyzed by ESR and C-13 MNR. The ESR spectrum of F3 (corresponding to purified pigment) in a liquid state showed that the structure of the C-OH moiety seemed to give either the quinone type or its polymerized form. The ESR spectrum of F3 in a solid state showed that the g-value of this fraction was 2.003. On the basis of the C-13 NMR spectrum, the signals assigned to two carbons (C1" and C-2") of the alcohol moiety of ethyl caffeate were observed clearly in F3. Considering the chemical shift of C-1 in ethyl caffeate, the C-1 in F3 could exist as -C=N-CH3. F3 seemed to be a precursor of the greening compound.