Two xanthones and two rotameric (3⟶8) biflavonoids from the Cameroonian medicinal plant Allanblackia floribunda Oliv. (Guttiferae)

Abstract

Two xanthones, 2-(3-hydroxy-3,3-dimethyldihydroallyl)-dihydro-6-deoxyisojacareubin (1) and dihydro-6-deoxyjacareubin (2), and two 3⟶8 rotameric biflavonoids, (2R,3S)volkensiflavone-7-O--acetylglucopyranoside (3) and (2S,3S)-morelloflavone-7-O-acetylglucopyranoside (4), together with fifteen known compounds, were isolated from a dichloromethane/methanol (1/1, v/v) extract of the bark of the plant Allanblackia floribunda. The structures of the new compounds were elucidated by NMR spectroscopy and mass spectroscopic techniques and those of the known ones were deduced by comparison with data reported in the literature. The isolated biflavonoids were obtained as mixtures of conformers exhibiting duplicate NMR signals in solution at 25 °C and their respective absolute configurations were assigned using circular dichroism spectroscopy. Some of the isolated compounds were assessed for their antibacterial and antioxidant properties.

Catalyst-free regioselective acetylation of primary hydroxy groups in partially protected and unprotected thioglycosides with acetic acid

“…Acetylation at O-6 is common for carbohydrate low-molecular weight metabolites in plants. [43][44][45][46][47] Bacterial polysaccharides oen contain 6-O-acetyl groups, which play a complex role in the functional immune response. [48][49][50][51] Hence, the development of ways for selective acetylation of unprotected and partially protected carbohydrates would contribute greatly to the study of naturally occurring carbohydrate molecules.…”

New Polyprenylated Acylphloroglucinol Derivatives and Xanthones From Hypericum wilsonii

“…The 13 C NMR and DEPT data (Table 3) indicated that compound 5 possessed 23 carbons comprising ten quaternary carbons, one carbonyl, six methines, two methylenes, and four methyl groups. Comparing with the data in the literature (Mountessou et al, 2018) the 2,2-dimethyldihydropyran moiety was inferred from the signals at δ H 2.98 (dd,J 16.3,5.1 Hz) and 2.44 (dd,J 16.3,9.3 Hz), δ H 1.86 (1H, m) and δ H 1.48 and 1.27 (3H each, s) which was also confirmed by the signals at δ C 79.9, 40.8, 27.6, 21.9, and 21.4 in the 13 C NMR spectrum. The 2,2-dimethyldihydropyran group was attached at C-3 and C-4 of the xanthone skeleton of compound 5 as illustrated by HMBC correlations observed between the methylene protons at H-1' (δ H 2.98 and 2.44) 2).…”

Pachypodostyflavone, a New 3-methoxy Flavone and Other Constituents with Antifilarial Activities from the Stem Bark of Duguetia staudtii

“…The spectrometer operated in positive mode (mass range: 100-1500, with a scan rate of 1.00 Hz) with automatic gain control to provide high-accuracy mass measurements within 0.40 ppm deviation using Na Formate as calibrant. The 1 H and 13 C NMR spectra were recorded at 500 and 125 MHz, respectively, on Bruker DRX 500 NMR spectrometers (Bruker Corporation) in CDCl 3 or CD 3 OD. Chemical shifts (δ) were reported in ppm using tetramethylsilane (TMS) (Sigma-Aldrich) as an internal standard, while coupling constants (J) were measured in Hertz (Hz).…”

“…Concerning our previous chemotaxonomic studies on this plant species, we also reported that lignans and flavonoids could be considered as chemotaxonomic markers for the genus. In continuation of our search for bioactive compounds from Cameroonian medicinal plants [13][14][15], we have investigated the bark of D. staudtii for its minor secondary metabolites. Herein, we report the bioassay-guided fractionation, as well as the structural elucidation of a new flavone and the antifilarial activities of the selected isolated compounds.…”