Indole Alkaloids. XX. Isolation and Structural Elucidation of Four Minor Alkaloids from Voacanga Chalotiana Pierre Ex Stapf

Abstract

A further study of Voacanga chalotiana Pierre ex Stapf has led to the isolation of two known indole alkaloids: polyneuridine

Indole Alkaloids XXV: The Oxidation of Voachalotine with Potassium Dichromate

“…The structural determination of these compounds was reported previously [3,4]. It is noteworthy that the transformation of (1) into (2) and (3) confirms the assigned structures, including the absolute configuration and the geometric configuration of the ethylidene side-chain.…”

“…spectra of this compound and that of the corresponding hydrochloride leads to the conclusion that the configuration is that represented in figure 3B. If dehydropolyneuridine pseudoindoxyl were represented by the C, epimeric structure A, one would expect-as in the case of voachalotine oxindole (3) [4]-a bathochromic shift of the vc = band of the ammonium salt as compared with the free base. Examination of models suggests that intramolecular hydrogen bonding of the NTH with the pseudoindoxyl carbonyl group is to be expected in A.…”

“…4) in the mass spectrum further suggests that the primary alcoholic group was involved in a cyclisation leading to a tetrahydrofuran ring as in dehydrovoachalotine. The M-103 ion is a characteristic feature of the mass spectra of (1) and (3) [4]. It is known to correspond to the loss of the radical CH,OH-CH-COOCH,.…”

“…In previous communications the occurrence of several oxidation products of (l), namely dehydrovoachalotine (2) [3], voachalotine oxindole (3) [4] and 21 (? )-hydroxyvoachalotine (4) [4] was reported in the same species. This observation prompted us to undertake an investigation of the action of potassium dichromate on (1).…”

Chemistry and biology of the genusVoacanga

“…Iboluteine (63), voaluteine (64), and decarbomethoxyvoacamine (65) were all found and identified to be present in the crude extract from the bark of V. thouarsii, var obtuse (Goldblatt et al, 1970). Chemical investigation of V. chalotiana resulted in the isolation of (-)-polyneuridine (66), 21-hydroxy-voachalotine (67), voachalotine oxindole (68) and N-acetylvoamonine (69) (Braekman et al, 1969). The ethanol extract of the leaves of V. africana yielded the interesting epoxyalkaloid named conoflorine (70) (Kunesch et al, 1968) (Figure 6).…”