Abstract
The extensive chemical investigation on the branches and leaves of Terminalia chebula var. tomentella (Combretaceae) led to the isolation of two new lignan glucosides with a furofuran skeleton, termitomenins F (1) and G (2). In addition, 19 known compounds including five lignan glucosides (3–7), six hydrolyzable tannins (8–13) and eight simple phenolics (14–21) were also identified. Their structures were determined by comprehensive spectroscopic analyses. It is noted that 8 and 9 were C-glycosidic hydrolyzable tannins with one hexahydroxydiphenoyl and one gallagyl group linked to an open-chain glucosyl C-1/O-2/O-3 and O-4/O-6, respectively, which were rarely found in plants. Nine known compounds, 6–9, 13, and 18–21, were procured from the titled plant for the first time, while 3–5, 10–12 and 14–17 were also found in the fruits. Notably, the known hydrolyzable tannins 8–13 exhibited stronger α-glucosidase inhibitory activities with IC50 values ranging from 0.10 to 3.12 μM, than the positive control, quercetin (IC50 = 9.38 ± 0.33 μM).Graphic abstract
Highlights
Terminalia Linn, the second largest genus in the family Combretaceae, is distributed globally in the tropical and subtropical areas
(7) [6], six hydrolyzable tannins, punicacortein C (8) [7], punicacortein D (9) [7], punicalagin (10) [8], 1,3,6-triO-galloyl-β-d-glucopyranose (11) [9], 1,2,3,4,6-pentaO-galloyl-β-d-glucopyranose (12) [9], and corilagin (13) [10], and six simple phenolics, shikimic acid (14) [11], (−)-5-O-galloylshikimic acid (15) [12], chebulic acid (16) [13], gallic acid (16) [14], 2,5-dihydroxybenzoic acid (18) [15], propyl gallate (19) [16], brevifolincarboxylic acid (20) [17], and glycerol-1-gallate (21) [18], respectively, on account of comparison of their NMR and High-resolution electrospray ionization mass (HRESIMS) data with those recorded in the literatures (Fig. 1)
Compounds 8–9 were C-glycosidic hydrolyzable tannins with one hexahydroxydiphenoyl (HHDP) and one gallagyl group linked to an open-chain glucosyl C-1/O-2/O-3 and O-4/O-6, rarely found to exist in plants
Summary
Terminalia Linn, the second largest genus in the family Combretaceae, is distributed globally in the tropical and subtropical areas. The fruits have been recorded as Chebulae Fructus in the Chinese Pharmacopoeia, together with those of its original species, T. chebula, for the treatment of diarrhea, hemorrhoids, cough, and sore throat [2] They have been used traditionally in Tibetan medicines for the treatments of diabetic, tumor, and microbial infection. As a part of our efforts to search for unique structural constituents from the genus Terminalia, two new lignan glucosides termitomenins F and G (1–2), were isolated from the branches and leaves of T. chebula var. Tomentella, along with five known lignan glucosides (3–7), six known hydrolyzable tannins (8–13) and eight simple phenolics (14–21) Their structures were determined by spectroscopic analyses and comparison of 1D/2D NMR, IR, UV, HRESIMS and calculated ECD analysis. We describe the isolation, structural elucidation, and α-glucosidase inhibitory activities of these compounds
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