Yanhusanines A–F, Isoquinoline-Derived Alkaloid Enantiomers from Corydalis yanhusuo and Their Biological Activity

Six new pairs of isoquinoline alkaloid enantiomers, designated as yanhusanines A-F (1-6), were isolated from an aqueous extract of Corydalis yanhusuo tubers. The structures of these enantiomers were elucidated via physicochemical analysis and a variety of spectroscopic methods. All compounds were resolved into their enantiomers via chiral-phase HPLC, and their configurations were determined by DP4+ NMR calculation methods, specific rotations, and comparison of experimental and calculated ECD spectra. Compounds 1-6 bear a rare 9-methyl moiety, and compound 1 possesses a rare 1-oxa-6-azaspiro[4.5]decane core containing an N-CHO group. Compounds (+)-2, (-)-2, (+)-4, (-)-4, (+)-5, (-)-5, (+)-6, and (-)-6 exhibited selective inhibitory activities against human carboxylesterase (hCE2), in the IC₅₀ value range of 2.0-13.2 μM.