Prenylated Xanthone Derivatives with Antiplasmodial Activity from Allanblackia monticola STANER L.C.

Abstract

There has been a recent increase in the research efforts on secondary metabolites of the genus Allanblackia.1-3) Our interest was stimulated by the fact that, many of the secondary metabolites from this genus such as xanthones, biflavonoids, benzophenones and pentacyclic triterpenes exhibited a wide range of biological and pharmacological activities, including cytotoxic, anti-inflammatory, antimicrobial, antifungal and HIV inhibitory activities.2,4,5) Allanblackia monticola STANER L.C., which belongs to the plant family Clusiaceae, is a large forest tree found throughout the west and south province of Cameroon, where it is used as medicinal plant to treat several diseases including, respiratory infections, diarrhoea and toothache. 6) In a previous paper, we have reported the isolation and structural elucidation of a novel polyisoprenylated xanthone, allanxanthone B, along with the known compounds: tovophyllin A, rubraxanthone, garciniafuran, lupeol and stigmasterol from the CH 2 Cl 2 -MeOH (1 : 1) extract of the stem bark of this plant. 7) In the present paper, we report the isolation and characterization of seven compounds isolated from the MeOH extract of this plant, including a new triprenylated xanthenedione, designated allanxanthone C (1), together with the known compounds norcowanin (2), 8) mangostin (3), 9) tovophyllin A (5), 10) garciniafuran (6), 11) rubraxanthone (7) 12) and stigmasterol-3-O-b-D-glucopyranoside (4).13) The structure of known compounds were identified from their spectral data and confirmed by comparison with those published in the literature. We also report on the antiplasmodial, cytotoxic and antimicrobial activities of the methanol extract and some isolated compounds.Extensive column chromatography of a methanol extract of the stem bark of A. monticola led to the isolation allanxanthone C (1).Allanxanthone C (1) was obtained as a sticky yellow oil. It reacts positively to ferric chloride test, suggesting the presence of a phenolic groups. Its molecular formula, C 28 H 32 O 6 , was deduced from the high resolution Electro Spray Ionisation-Time of Flight (ESI-TOF) mass spectrometry which showed the pseudomolecular ion [MϩH] ϩ at m/z 465.5545 (Calcd for 465.5580). The IR spectrum of 1 confirmed the presence of phenolic group (3350 cm Ϫ1 ) and suggested the presence of conjugated carbonyl group (1674 cm Ϫ1) and xanthone carbonyl group (1643 cm Ϫ1).14) The 1 H-NMR and Heteronuclear Single Quantum Coherence (HSQC) spectra of allanxanthone C (1) showed the presence of a hydrogenbonded hydroxyl at d 13.50 (1H, s, 8-OH) and two singlet protons at d 6.55 (1H, s, H-4) and d 6.45 (1H, s, H-5), d 109.5 (d, C-4) and 93.5 (d, C-5). The presence of a set of signals at d 4.74 (2H, t, Jϭ7.6 Hz, H-2Љ), 3.43 (2H, dd, Jϭ7.60, 13.6 Hz, H-1Љ), 2.73 (2H, dd, Jϭ7.6, 13.6 Hz, H-1Љ) and 1.47 (12H, s) was typical of a gem bis(3-methylbut-2-enyl) groups linked to a sp 3 carbon atom (d 56.9, C-1). Further study of the methanol extract of the stem bark of Allanblackia monticola STANER L.C. resulted in the isolati...

Oxepinochromenones, Furochromenone, and their Putative Precursors from the Endolichenic Fungus Coniochaeta sp.

“…DMAP (5.0 mg) and (S)-MTPA-Cl (10.0 µL, 0.052 mmol) were quickly added, the flask was sealed, and the mixture was stirred at room temperature for 12 h. The mixture was evaporated to dryness and purified by RP HPLC (Agilent Zorbax SB-C 18 column; 5 µm; 9.4 × 250 mm; 80% MeOH in H 2 O for 2 min, followed by 80-100% for 30 min; 2 mL/min) to afford 1a (0. In a similar fashion, a sample of 1 (1.5 mg, 0.004 mmol), CH 2 Cl 2 (3.0 mL), DMAP (5.0 mg), and (R)-MTPA-Cl (5.0 µL, 0.026 mmol) were allowed to react in a 10 mL round-bottomed flask at room temperature for 12 h, and the reaction mixture was processed as described above for 1a to afford 1b (1.2 mg): white powder; 1 Table 1; HMBC data (acetone-d 6 , 400 MHz) H-2 f C-1, 4, 9, 9a, 11; H-4 f C-1, 2, 3, 4a, 9, 9a, 11; H-5 f C-6, 7, 10a; H-6 f C-5, 7, 8; H-7 f C-6, 12; H-8 f C-6, 7, 8a, 9, 10a, 12; H 2 -11 f C-2, 3, 4; H 3 -13 f C-12; OH-1 f C-1, 2, 9a; OH-7 f C-6, 7, 8; OH-11 f C-3, 11; HRESIMS m/z 357.0578 (calcd for C 16 Table 1; HMBC data (acetone-d 6 , 400 MHz) H-2 f C-1, 4, 9, 11; H-4 f C-2, 4a, 9, 9a, 11; H-5 f C-6, 7, 10a; H-6 f C-5, 7, 8; H 3 -11 f C-2, 3, 4; H 3 -13 f C-12; OH-1 f C-1, 2, 3, 9a; OH-8 f C-8, 8a, 12; NOESY correlations (acetone-d 6 , 400 MHz) H-7 T H 3 -13; H 3 -13 T H-7; HRESIMS m/z 357.0582 (calcd for C 16 H 14 O 8 Na, 357.0581).…”

Effect of leaf extracts of Cymbopogon Citratus, Chromolaena Odorata and Newbouldia Laevis on the Dioscorea Alata rot

“…The widespread use of medicinal plants (both indigenous and alien) can be traced to the occurrence of natural products with medicinal properties in plants and their ability to synthesize a variety of chemical compounds [20][21][22][23]. The use of chemicals has helped in the control of rots but due to the identifiable problems which include: biodegradation, pollution, chemical residues, phytotoxicity, high cost, development of resistance in target organism, a times non availability and then being hazardous to man and his environment renders them either slow to adapt or farmers have totally failed to adopt them for one cultural reason or the other [24,25].…”

Investigation of efficient synthesis of 1, 8-dioxo-octahydroxanthene derivatives under solvent-free grinding method

“…strong and selective inhibition of MAO-A, antitumor activity. 10,11 For 1,8-dioxooctahydroxanthene derivatives, the inherent reactivity of pyran ring 12 makes them building block of several natural products. In literature, a number of synthetic approaches 13,14 have been developed for the preparation of 1,8-dioxo-octahydroxanthenes involving acid or base catalyzed condensation of aldehydes and 5, 5-dimethyl-1,3-cyclohexanedione (Scheme 1) in solvent-free condition, ionic liquid and aqueous medium.…”