Iridoid glucosides with free radical scavenging properties from Fagraea blumei

Four new iridoid glucosides 1-4, named blumeosides A-D, were isolated From the methanolic stem-bark extract of Fagraea blumei G. DON. (Loganiaceae). They were accompanied by the benzyl-alcohol derivative di-O-methylcrenatin (5) and the flavone C-glucoside swertisin (6). The structures of 1-4 were established by spectroscopic methods, including FAB-MS, and H-1- and C-13-NMR, and by alkaline hydrolysis. Blumeosides A (1) and C (3) are 10-O-(2,5-dihydroxyterephthalo)adoxosidic acid and 10-O-(2-hydroxyterephthalo)adoxosidic acid, respectively. In blumeosides B (4) and D (2), both carboxylic groups of the terephthalic-acid moiety are esterified by adoxosidic-acid units. Blumeosides A-D (1-4) inhibited bleaching of crocin induced by alkoxyl radicals. Blumeosides A(1) and D(2) also demonstrated scavenging properties towards the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical in TLC autographic and spectrophotometric assays.