Evoxanthine

Three new alkaloids, janetinine (1a), pleiokomenine A (2), and huncaniterine B (3a), and 13 known compounds, pleiomutinine (3b), huncaniterine A (3c), 1-carbomethoxy-β-carboline (4), evoxanthine (5), deformyltalbotine acid lactone (6), pleiocarpamine (7), N4-methyl-10-hydroxygeissoschizol (8), spegatrine (9), neosarpagine (10), aspidofractinine (11), N1-methylkopsinin (12), pleiocarpine (13), and N1-methylkopsinin- N4-oxide (14), were isolated from the stem bark of Pleiocarpa pycnantha. Janetinine (1a) is a carbazole alkaloid; in pleiokomenine A (2), two aspidofractinine-type alkaloids are bridged by a methylene unit in an unprecedented way, and huncaniterine B (3a) is a pleiocarpamine-aspidofractinine-type dimer. The structures and relative configurations of these compounds were elucidated on the basis of NMR and MS analyses. Their absolute configurations were defined by means of experimental and calculated ECD data, and additionally, the structures of 5 and 13 were determined by single crystal X-ray diffraction. Compounds 1a, 2, 3b, 4, 6, 9, and 12 displayed cancer chemopreventive properties through either quinone reductase induction ( CD = 30.7, 30.2, 29.9, 43.5, and 36.7 μM for 1a, 4, 6, 9, and 12, respectively) and/or NF-κB inhibition with IC50 values of 13.1, 8.4, 9.4, and 8.8 μM for 2, 3b, 6, and 12, respectively.

A rotameric tryptamide alkaloid (1a-1b) was isolated from the methanolic extract of the roots of Vepris lecomteana together with the known compounds anhydroevoxine (2), lecomtequinoline C (3), evoxine (4), N-methylflindersine (5), evoxanthine (6), hesperidin, lupeol, β-sitosterol and stigmasterol. The previously not reported 7-(3-anilino-2-hydroxyprenyloxy)-8-methoxydictamine (2a) was obtained by opening the epoxide of anhydroevoxine (2). The structures of above compounds were determined by comprehensive spectroscopic analyses of 1D and 2D NMR, EI-/ESI-MS, X-ray crystallography and comparison with the reported data. At room temperature, 1H and 13C NMR spectra show two rotamers (1a and 1b) with integrated intensities of 2/3, whereas at around 60 °C, only the 1b conformer was observed. Furthermore, the crystal structure of 1 was determined by the direct method of single crystal X-ray diffraction. The suggested biosynthesis for the formation of the new rotameric tryptamide alkaloid 1 is presented. Some of the isolated compounds (1, 2 and 2a) were tested in vitro against bacteria, resulting in weak for (1 and 2) to moderate activity for (2a) against Micrococcus luteus and Escherichia coli with MIC values of 15.3 and 15.3 μg/mL, respectively.

Three new prenylated furoquinoline alkaloids named lecomtequinoline A (1), B (2), and C (3), together with the known compounds anhydroevoxine (4), evoxine (5), dictamnine (6), N-methylflindersine (7), evoxanthine (8), hesperidin, lupeol, β-sitosterol, stigmasterol, β-sitosterol-3-O-β-d-glucopyranoside, stearic acid, and myristyl alcohol, were isolated by bioassay-guided fractionation of the methanolic extracts of leaves and stem of Vepris lecomteana. The structures of compounds were determined by spectroscopic methods (NMR, MS, UV, and IR) and by comparison with previously reported data. Crude extracts of leaves and stem displayed high antimicrobial activity, with Minimum Inhibitory Concentration (MIC) (values of 10.1-16.5 and 10.2-20.5 µg/mL, respectively, against Escherichia coli, Bacillus subtilis, Pseudomonas agarici, Micrococcus luteus, and Staphylococcus warneri, while compounds 1-6 showed values ranging from 11.1 to 18.7 µg/mL or were inactive, suggesting synergistic effect. The extracts may find application in crude drug preparations in Western Africa where Vepris lecomteana is endemic, subject to negative toxicity results in vivo. Keywords: Vepris lecomteana; furoquinoline alkaloids; lecomte quinoline A-C.