Salvianolic acids are a group of polyphenolic acids consisting on several combinations of caffeic acid and danshensu (salvianic acid) through ester and enol bonds. Salvianolic acids are water-soluble components produced by many species of the genus Salvia, mainly extracted from Salvia miltiorrhiza.
More than 10 distinct salvianolic acids (Sal), identified by letters from A to J, have been recognized. Notably, Sal-A and Sal-B are the most abundant forms. The combination of danshensu and a caffeic acid derivative or caffeic acid dimer produces several kinds of skeletons. Sal-A is formed by a molecule of danshensu and a dimer of caffeic acid. Sal-B, on the other hand, is constituted by three molecules of danshensu and one molecule of caffeic acid. Sal-C results from the combination of two molecules of danshensu, while Sal-D is characterized as a dimer of caffeic acid.[1]
The formation of salvianolic acids is closely linked to that of rosmarinic acid. They are primarily synthesized through the phenylpropanoid and tyrosine-derived branches of the phenolic acid biosynthetic pathway. Rosmarinic acid undergoes a not well-understood oxidative reaction to convert into Salvianolic acid B.[2] This reaction involves laccases, which are widely spread in many genera such as Arabidopsis, poplars, sorghum, etc., but appears to be highly expressed in Salvia miltiorrhiza and Salvia bowleyana.[3]