Table 3. Key NMR Data of the Selected Norditerpenoid Alkaloids (δ in ppm).
Orientation label: a = axial, e = equatorial in a chair conformation, b = bowsprit, and f = flagpole in a boat conformation. Chemical shifts of overlapping signals were extracted from HSQC.
With additional two drops of DMSO-d6.
With additional drops of DCl (35% in D2O), pD ∼2.
Chemical shift of this overlapping signal was extracted from COSY.
No evidence was obtained to identify the orientation of these protons unambiguously.
With additional two drops of pyridine-d5.
With additional two drops of pyridine-d5 and two drops of NaOD solution (30% in D2O, w/w).