Biomimetic synthesis and HPLC–ECD analysis of the isomers of dracocephins A and B

Abstract

Starting from racemic naringenin ((±)-<b>1</b>), a mixture of dracocephin A stereoisomers 6-(2"-pyrrolidinone-5"-yl)naringenin (±)-<b>2a-d</b> and its regioisomer, dracocephin B 8-(2"-pyrrolidinone-5"-yl)naringenin (±)-<b>3a-d</b> originally isolated from <i>Dracocephalum rupestre</i>, have been synthesized in a one-pot reaction. The separation of <b>2a-d</b> and <b>3a-d</b> was achieved by preparative HPLC. The four stereoisomers of each natural product were separated by analytical chiral HPLC and their absolute configuration was studied by the combination of HPLC-ECD measurements and TDDFT-ECD calculations. The synthesized flavonoid alkaloids were further characterized by physicochemical and in vitro pharmacological studies.