Salvianolic acid L, a potent phenolic antioxidant from Salvia officinalis

Salvianolic acid L, a rosmarinic acid dimer, was isolated from Salvia officinalis and identified as 7,8-dihydroxy-2-(3,4-dihydroxyphenyl)-1,2-dihydronaphthalene-1,3-dicarboxylic acid di(1-carboxy-2-(3,4-dihydroxyphenyl))ethyl ester. Two novel hydrolytic products 7,8-dihydroxy-2-(3,4-dihydroxyphenyl)-1,2-dihydronaphthalene-1,3-dicarboxylic acid and the corresponding 3-monoester were also isolated and characterized. Salvianolic acid L showed strong free radical scavenging activities for DPPH and superoxide anion radicals.