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.