Mohamed A.A. Orabi

Hydrolyzable tannins of tamaricaceous plants. III.1 Hellinoyl-and macrocyclic-type ellagitannins from Tamarix nilotica

Three new hellinoyl-type ellagitannins, nilotinins M4 (7), D7 (8), and D8 (9), and a new macrocyclic-type, nilotinin D9 (10), together with eight known tannins, hirtellins B (2), C (11), and F (12), isohirtellin C (13), tamarixinin A (3), tellimagrandins I and II, and 1,2,6-tri-O-galloyl-beta-d-glucose (14), were isolated from an aqueous acetone extract of Tamarix nilotica dried leaves. Nilotinin M4 (7) is a monomeric tannin possessing a hellinoyl moiety. The structure of 8 demonstrated replacement of one of the HHDP groups at the glucose core O-4/O-6 in ordinary dimeric tannins with a galloyl moiety at O-6. This is a new structural feature among the tamaricaceous ellagitannins. On the basis of the results, reported spectroscopic assignments for 2, 3, and the macrocyclic tannins 11-13 were revised. Unusual shifts in the NMR spectra of these macrocyclic tannins are also discussed in relation to their conformations. Several tannins isolated from T. nilotica were assessed for possible cytotoxic activity against four human tumor cell lines, and nilotinin D8 (9) and hirtellin A (1) showed high cytotoxic effects.

Monomeric and dimeric hydrolysable tannins of Tamarix nilotica

An ellagitannin monomer, nilotinin M1 (1), and three dimers, nilotinins D1 (2), D2 (3), and D3 (4), were isolated from leaves of Tamarix nilotica (Ehrenb.) Bunge. Structures were elucidated based on analysis of spectroscopic data and chemical correlations with known compounds. In addition, six known tannins, hirtellin A (5) (dimer), remurin A (6), remurin B (7), 1,3-di-O-galloyl-4,6-O-(S)-hexahydroxydiphenoyl-beta-D-glucose (8), gemin D (9), and hippomanin A (10) (monomers), were isolated for the first time from this plant species. The reported (13)C NMR assignments of the dehydrodigalloyl moiety and glucose cores of 5 are revised, and the (13)C NMR spectroscopic data for 6 and 7 are also reported for the first time.

Hydrolyzable Tannins of Tamaricaceous Plants. V. Structures of Monomeric–Trimeric Tannins and Cytotoxicity of Macrocyclic-Type Tannins Isolated from Tamarix nilotica(1)

Three new ellagitannin monomers, nilotinins M5-M7 (1-3), a dimer, nilotinin D10 (4), and a trimer, nilotinin T1 (5), together with three known dimers, hirtellin D (7) and tamarixinins B (8) and C (9), and a trimer, hirtellin T2 (6), were isolated from Tamarix nilotica dried leaves. The structures of the tannins were elucidated by intensive spectroscopic methods and chemical conversions into known tannins. The new trimer (5) is a unique macrocyclic type whose monomeric units are linked together by an isodehydrodigalloyl and two dehydrodigalloyl moieties. Additionally, dimeric and trimeric macrocyclic-type tannins isolated from T. nilotica in this study were assessed for possible cytotoxic activity against four human tumor cell lines. Tumor-selective cytotoxicities of the tested compounds were higher than those of synthetic and natural potent cytotoxic compounds, including polyphenols, and comparable with those of 5-fluorouracil and melphalan.

Structures of two new flavonoids and effects of licorice phenolics on vancomycin-resistant Enterococcus species.

Since our previous study revealed that several licorice phenolics have antibacterial effects on methicillin-resistant Staphylococcus aureus (MRSA), and suppressive effects on the oxacillin resistance of MRSA, we further investigated effectiveness of licorice constituents on vancomycin-resistant Enterococcus (VRE) bacteria, and purified 32 phenolic compounds. Two flavonoids among them were characterized structurally, and identified their structures as demethylglycyrol (31) and 5,7-di-O-methylluteone (32), respectively. Examination of antibacterial effects of licorice phenolics showed that 3-arylcoumarins such as licoarylcoumarin (9) and glycycoumarin (26), and 2-arylcoumarones such as gancaonin I (17), have moderate to potent antibacterial effects on the VRE strains used in this study.

Ellagitannins, gallotannins, and gallo-ellagitannins from the galls of Tamarix aphylla.

Chromatographic separation of an aqueous acetone extract of the galls from Tamarix aphylla using gels resulted in isolation of an ellagitannin, phyllagallin M1 (13), a gallo-ellagitannin, phyllagallin D1 (14), and four gallotannins, phyllagallin M2 (15) and phyllagallins D2-D4 (16-18), in addition to four known ellagitannins and three phenolics of lower molecular weight structurally related to hydrolyzable tannins. The structures of the six new tannins were elucidated based on spectroscopic and chemical data. Among the phenolics, flavogallonic acid dilactone (8), which is presumed to be biogenetically produced by C-C oxidative coupling of an ellagic acid unit with a galloyl residue, shows an exceptional oxidative pattern of gallic acid residues in plants of the family Tamaricaceae. Although the ellagitannin tamarixellagic acid (4) was reported to be a constituent of the galls of T. aphylla, such compounds with anomalous location of the DHDG moiety at O-3 on the glucopyranose core have not been observed among the tannins of tamaricaceous plants.

Hydrolyzable tannins of tamaricaceous plants. IV: Micropropagation and ellagitannin production in shoot cultures of Tamarix tetrandra.

Shoot cultures of Tamarix tetrandra on Linsmaier-Skoog (LS) agar medium with 30 g l(-1) sucrose, 2.13 mg l(-1) indoleacetic acid and 2.25 mg l(-1) benzyl adenine produced ellagitannins found in intact plants of the Tamaricaceae. This was demonstrated by the isolation of 14 monomeric-tetrameric ellagitannins from the aq. Me2CO extract of the cultured tissues. This is the first report on the production of ellagitannin tetramers by plant tissue culture. The effects of light and certain medium constituents on tissue growth and ellagitannin production were examined. The contents of representative tannins of different types [i.e., tellimagrandin II (monomer), hirtellin A (linear GOG-type dimer), hirtellin B (hellinoyl-type dimer), hirtellin C (macrocyclic-type dimer), and hirtellin T1 (linear GOG-type trimer)] in the resultant tissues in response to these factors were estimated by HPLC, and the optimal condition for production of these tannins were established. Shoots cultured on LS hormone-free medium promoted root development, and regenerated plants could adapt to ordinary soil and climate. Acclimatized and intact T. tetrandra plants that were collected in November and May, respectively, demonstrated seasonal differences in individual ellagitannin contents. HPLC comparison of individual ellagitannin contents in different plant materials (i.e., leaves, stems, and roots) of intact T. tetrandra plants is also reported. The results are discussed with respect to cellular deposition and biosynthetic relationship of tannins.

New monomeric and dimeric hydrolyzable tannins from Tamarix nilotica

Two new ellagitannin monomers, nilotinins M2 (4) and M3 (5), two new dimers, nilotinins D4 (6), D5 (7), and a known dimer (8), were isolated from an aqueous acetone extract of dried leaves of Tamarix nilotica (Ehrenb.) Bunge. Structures of 4-7 were determined based on spectral data and chemical correlations with known tannins. The known dimer 8 was isolated from a plant extract for the first time; its 1 H and 13 C assignments are also reported here.

Hydrolyzable Tannins of Tamaricaceous Plants. 7.1 Structures and Cytotoxic Properties of Oligomeric Ellagitannins from Leaves of Tamarix nilotica and Cultured Tissues of Tamarix tetrandra

Partially unacylated new oligomeric hydrolyzable tannins, nilotinin T2 (1, trimer) and nilotinin Q1 (2, tetramer), together with four known trimers, nilotinin T1 (3) and hirtellins T1-T3 (4-6), and a dimer, tamarixinin B (7), were isolated from the aqueous acetone extracts of leaves of Tamarix nilotica. Among them, the new trimer 1 and the known trimers 4 and 6, in addition to the partially unacylated new trimer nilotinin T3 (8), the known dimers nilotinin D3 (9) and tamarixinin C (10), and the monomer tellimagrandin I (11), were isolated from the cultured shoots of Tamarix tetrandra. The structures of the new hydrolyzable tannins were established by chromatographic analyses and extensive 1D and 2D NMR, HRESI-TOFMS, and ECD spectroscopic experiments. Among the new oligomeric tannins, the particular unacylated position of a glucose core is attributed to a possible biosynthetic route. Isolation of the same oligomeric tannins from cultured shoots of T. tetrandra emphasizes the unique biogenetic ability of the obtained cultures on production of the structurally and biologically characteristic tamaricaceous tannins commonly produced by the intact Tamarix plants. Additionally, tannins obtained in the present study together with gemin D (12) and 1,3-di-O-galloyl-4,6-O-(aS)-hexahydroxydiphenoyl-β-d-glucose (13), from our previous investigation of the leaves of T. nilotica, exhibited variable tumor-specific cytotoxic effects. The ellagitannin trimers 4, 6, and 8 and the dimer 9 exerted predominant tumor-selective cytotoxic effects with high specificity toward human promyelocytic leukemia cells.