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

Starting from racemic naringenin ((±)-), a mixture of dracocephin A stereoisomers 6-(2"-pyrrolidinone-5"-yl)naringenin (±)- and its regioisomer, dracocephin B 8-(2"-pyrrolidinone-5"-yl)naringenin (±)- originally isolated from , have been synthesized in a one-pot reaction. The separation of and 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.