Isolation and Absolute configuration determination of Danshensu derivatives from the areial part of Clerodendranthus spicatus
Objective To further enrich the composition of Clerodendranthus spicatus(Thunb.)C.Y.Wu ex H.W.Li,the constituents in its dried aerial parts were investigated.Methods The dried aerial parts of C.spicatus were refluxed by 70% EtOH.The obtained extract was isolated by using various column chromatographies,such as silica gel,ODS column,and HPLC chromatography.And then,the structures and absolute configurations of the isolated compounds were elucidated by using circular dichroism,nuclear magnetic resonance,and mass spectra,as well as chemical reaction methods.Results Seven Danshensu derivatives were obtained from the 70% EtOH extract of C.spicatus aerial parts.They were(R)-rosmarinic acid(1),(R)-rosmarinic acid methyl ester(2),(R)-rosmarinic acid ethyl ester(3),2R-hydroxy-3-(4-hydroxyphenyl)propionic acid methyl ester(4),2R-hydroxy-3-(3,4-dihydroxyphenyl)propionic acid(5),2R-hydroxy-3-(3,4-dihydroxyphenyl)propionic acid methyl ester(6),and 2R-hydroxy-3-(3,4-dihydroxyphenyl)propionic acid ethyl ester(7),respectively.Conclusion Compound 4 is isolated from Clerodendranthus genus for the first time.In addition,it has been found that the absolute configuration of α-hydroxy carboxylic acids could not be determined by the comparison of optical rotation alone,though it is with only one chiral center.The method provided in this paper will supply a reference for the configuration study of these compounds.