The corrected structure of depressoside, an antioxidative iridoid glucoside extracted from the flowers of Gentiana urnula Harry Sm.

All three compounds exhibited excellent DPPH radical scavenging activities (IC 50 : 10–20 μmol L −1 ) comparable to that of ascorbic acid and Trolox. However, examination of the NMR data revealed that the reported chemical structure of depressoside, previously isolated from the leaves of G. depressa , needed correcting due to incorrect elucidation around C-7 of the iridane skeleton, and was corrected to 6-β-(2,3-dihydroxyphenyl)-d-glucosyl 7- O -(2,3-dihydroxybenzoyl)-loganate.

Depressoside exhibited a much higher scavenging activity against superoxide radicals (IC 50 : 45.5 μmol L −1 ) than the other two extracted compounds (IC 50 : more than 900 μmol L −1 ) due to the crucial presence of a pyrogallyl unit.