An investigation for alkaloids in Charpentiera obovata Gaud

Typescript.Thesis (Ph. D.)--University of Hawaii, 1965.Bibliography: leaves 51-55.ii, 55 l illusThe genus Charpentiera belongs to the plant family Amaranthaceae and is endemic to the Hawaiian Islands. The Hawaiian name of the several members of the genus is papala. An investigation for alkaloids in the species Charpentiera obovata Gaud. was undertaken for several reasons. There is a reference to the general use of various species of this family against skin diseases. This is an example of the general phenomenon that physiological activity is frequently linked to the presence of alkaloids. Secondly, no structural work has been reported in the literature on alkaloids from the plant family Amaranthaceae. Thirdly, the plant family Amaranthaceae is one of several families referred to as the Centrospermae plants. A common characteristic of eight of these families is the unusual occurrence of nitrogenous pigments called betacyanins, structurally different from the other well-known class of pigments, anthocyanins. It was therefore felt that an investigation of the alkaloidal constituents of the species Charpentiera obovata might show whether a structural relationship exists between the alkaloids and the betacyanins. Surprisingly, only one alkaloid could be isolated, and that in a very small yield of ca. 0.0005%, by solvent extraction and column chromatography. The alkaloid crystallized as pale yellow needles from an ethanol-acetone-hexane mixture, but could be sublimed to a white feathery substance, m.p. 220-221°. The molecular formula of C15H10N2O2 was supported by combustion analysis and by mass spectrum. The compound possesses one methoxyl group, one olefinic proton and six aromatic protons as shown by proton magnetic resonance spectrum. This information coupled with the ultraviolet spectrum in methanol sufficed to suggest that the alkaloid was probably 4-methoxycanthin-6-one, the structure of which is shown below. Final confirmation was provided by a synthesis of 4-methoxycanthin-6-one along lines described previously and by comparison of ultraviolet and infrared spectra and of Rf-values (thin-layer chromatogram) and by mixed melting point determination which showed no depression. This is the first instance that this alkaloid, 4-methoxycanthin- 6-one has been isolated from natural sources. The significance of this finding to chemotaxonomic study is discussed. Infrared spectra of some of the synthetic intermediates, e.g. harman, benzalharman, β-carboline-l-carboxylic acid, 4-hydroxycanthin- 6-one have been determined