Microdesmis keayana LÉONARD (Pandaceae) is a tropical shrub, the leaves of which are used in the Ivory Coast against malaria and some other parasites. Its antiplasmodial, 1,2) antitrypanosomal 3) and anthelmintic 4) activities have already been tested. Its roots are also used by traditional healers as a remedy for sexual dysfunction. An aqueous extract of these roots, recently tested, exhibited vasorelaxing properties, explained by an increase in nitric oxide (NO) in the vascular bed, via antioxidant properties and stimulation of endothelial nitric oxide synthase (eNOS) mRNA expression.5) In a previous paper three new tris(4-hydroxycinnamoyl)spermidines have been reported. 6) Continuing investigations on the roots of M. keayana have now led to the isolation and structural elucidation of two other new compounds, one quinoline derivative xanthoquininamide 1 and one tris(4-hydroxycinnamoyl)spermine keayanine 2.
Results and DiscussionXanthoquininamide (1) was obtained as a pale yellow powder soluble in methanol. It showed an [MϩH] ϩ peak at m/z 189 in the ESI-MS data. The 1 H-NMR spectrum in MeOD was very simple and all chemical shifts and couplings which were observed between d H 7.3 and d H 8.8, including a not-so-common Jϭ4.5 Hz between H-2 and H-3, 7) were consistent for a quinoline derivative which was substituted on C-6 or C-7 (because of the ABX system) and on C-4. Mono-( 1 H and 13 C) and bidimensional (COSY, HMQC, HMBC) NMR experiments, as well as comparison with data of previously described quinine-like alkaloids, 8) made it possible to establish the structure of 1 as 6-hydroxyquinoline-4-carboxamide.1 H-and 13 C-NMR chemical shifts are given in Table 1. To our knowledge, this is the first report of both the natural occurrence of 1 and of its complete spectroscopic data, although it has already been synthesised from xanthoquininic acid by amidification.
9)Compound 2 was characterized both by ESI-MS and NMR data. In the electrospray mass spectrum, a [MϩH] ϩ peak was observed at m/z 701. Typical fragments were observed on ESI-MS spectrum at m/z 147 and m/z 177, corresponding to one coumaroyl and two feruloyl residues respectively, according to the relative heights of both signals. The subtraction of these three elements from the molecular mass of the compound (m/z 700) gave a mass of 199, compatible with a tri-substituted spermine. The positions of all three acyl moieties were determined by ESI-MS (see Fig. 2 Purification of a Microdesmis keayana hydromethanolic root extract led to the isolation of two new natural compounds, xanthoquininamide (6-hydroxyquinoline-4-carboxamide) and tris(4-hydroxycinnamoyl)spermine (N 5 -(p-coumaroyl)-N 1 ,N 14 -diferuloylspermine) which was named keayanine. Their structures were determined using spectroscopic analyses (ESI-MS, 1D-and 2D-NMR).