Revision of the Structure of Escholidine

Abstract

The structure of the quaternary tetrahydroprotoberberine alkaloid escholidine is revised on the basis of 2D NMR spectroscopy and X-ray diffraction. In contrast to the originally reported constitution, escholidine bears an -OH group at C-9 and an -OCH3 group at C-10. The 1H and 13C NMR data and long-range 1H-13C and NOE interactions of escholidine are compared with those of thalifendine and tetrahydroberberrubine. The 15N NMR data of escholidine obtained by using long-range 1H-15N correlation experiments at natural abundance are also reported.