Abstract
Graded alkaline hydrolysis of the monoacid
tertiary bases kopsiflorine (C23H28O5N2),
kopsilongine (C24H30O6N2), and
kopsamine (C24H28O7N2) shows that
they contain two methoxycarbonyl groups. All but one of the residual oxygen
atoms are accounted for as aromatic ether linkages. One of the methoxycarbonyl
groups is responsible for the deactivation of the other nitrogen atom (N(a))
present, since anew basic centre is generated by partial hydrolysis and
subsequent decarboxylation of the acid produced. The alkaloids are tentatively
formulated as blocked indoline bases containing a urethane grouping at N(a).
The fourth alkaloid, kopsinine (C21H26O2N2)
is similarly formulated, but in this case N(a) is weakly basic, the urethane
methoxycarbonyl group and the additional oxygen atom being absent.
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