During
a research program to identify new cholinesterase inhibitors
of natural origin, two new 7,8-didehydroprotoberberine alkaloids (
1
and
2
) and nine known compounds (
3
–
11
) were isolated from the capsules of the common
ornamental poppy,
Papaver setiferum
(previously
P. pseudo-orientale
). Despite their reported instability,
the 7,8-didehydroprotoberberines isolated herein appeared relatively
stable, particularly as their trifluoroacetic acid salts. The spatial
distributions of the isolated alkaloids were also analyzed using desorption
electrospray ionization imaging mass spectrometry. The alkaloids were
localized predominantly within the walls and vascular bundles of the
capsules, with the highest relative abundances occurring in the lower
half of the capsules toward the peduncle. The relative abundances
of the alkaloids were also compared across plant development stages.
Although most alkaloids did not show clear patterns in their concentration
across development stages, the concentration of suspected oxidation
products clearly spiked upon plant death. Finally, all isolated natural
products were screened for inhibitory activities against a panel of
cholinesterases, from both human and animal sources. These studies
identified several competitive inhibitors of cholinesterases with
potency in the low micromolar range (
1
–
4
,
6
,
7
), offering new lead compounds for
the development of cholinesterase inhibitory drugs.