Sang, S., K. Lapsley, W.S. Jeong, P.A. Lachance, R.T. Rosen, C.T. Ho, 2002. Antioxidative phenolic compounds isolated from almond skin (Prunus amygdalus Batsch). J Agric Food Chem. 50:2459-63.
Nine phenolic compounds were isolated from the ethyl acetate and n-butanol fractions of almond (Prunus amygdalus) skins. On the basis of NMR data, MS data, and comparison with the literature, these compounds were identified as 3′-O-methylquercetin 3-O-beta-D-glucopyranoside (1); 3′-O-methylquercetin 3-O-beta-D-galactopyranoside (2); 3′-O-methylquercetin 3-O-alpha-L-rhamnopyranosyl-(1–>6)-beta-D-glucopyranoside (3); kaempferol 3-O-alpha-L-rhamnopyranosyl-(1–>6)-beta-D-glucopyranoside (4); naringenin 7-O-beta-D-glucopyranoside (5); catechin (6); protocatechuic acid (7); vanillic acid (8); and p-hydroxybenzoic acid (9). All of these compounds have been isolated from almond skins for the first time. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activities for compounds 1-9 were determined. Compounds 6 and 7 show very strong DPPH radical scavenging activity. Compounds 1-3, 5, 8, and 9 show strong activity, whereas compound 4 has very weak activity.