Yegao Chen

Isolation of α-glucosidase inhibitors including a new flavonol glycoside from Dendrobium devonianum

From the whole plant of Dendrobium devonianum, a new flavonol glycoside, 5-hydroxy-3-methoxy-flavone-7-O-[β-d-apiosyl-(1 → 6)]-β-d-glucoside, as well as 13 known compounds, was isolated. Their structures were identified based on extensive spectroscopic studies including HR-EI-MS, 1H, 13C NMR, DEPT, H–H COSY, HSQC, HMBC and NOESY spectra. The new compound and gigantol were evaluated for their α-glucosidase inhibitory activity, and both displayed more potent α-glucosidase inhibitory activity than acarbose, one of the most potent α-glucosidase inhibitor drugs, with the inhibition rate of 43.4% and 36.7%, respectively, in the concentration of 437.5 μmol/L.

A new 9,10-dihydrophenanthrene from Dendrobium moniliforme

A new 9,10-dihydrophenanthrene,1,5-dihydroxy-3,4,7-trimethoxy-9,10-dihydrophenanthrene (1) was isolated and identified from the whole plants of Dendrobium moniliforme, as well as 24 known compounds including hircinol (2), (2R*,3S*)-3-hydroxymethyl-9-methoxy-2-(4′-hydroxy-3′,5′-dimethoxyphenyl)-2,3,6,7-tetrahydro-phenanthro[4,3-b]furan-5,11-diol (3), diospyrosin (4), aloifol I (5), moscatilin (6), 3,4′-dihydroxy-3′,4,5-trimethoxybibenzyl (7), gigantol (8), 3,3′-dihydroxy-4,5-dimethoxybibenzyl (9), longicornuol A (10), N-trans-cinnamoyltyramine (11), paprazine (12), N-trans-feruloyl 3′-O-methyldopamine (13), moupinamide (14), dihydroconiferyl dihydro-p-coumarate (15), dihydrosinapyl dihydro-p-coumarate (16), 3-isopropyl-5-acetoxycyclohexene-2-one-1 (17), p-hydroxybenzaldehyde (18), vanillin (19), p-hydroxyphenylpropionic acid (20), vanillic acid (21), protocatechuic acid (22), (+)-syringaresinol (23), β-sitosterol (24) and daucosterol (25). Compounds 3, 4, 13, 16, 17 and 20 were isolated from the Dendrobium genus for the first time, and compounds 2, 5, 7, 9–12, 14, 15, 18, 21 and 22 were originally obtained from D. moniliforme.

Two new biphenanthrenes with cytotoxic activity from Bulbophyllum odoratissimum

Two new dimeric phenanthrenes, bulbophythrins A (1) and B (2), were isolated from Bulbophyllum odoratissimum. Their structures were elucidated by HR-ESI-MS, 1D and 2DNMR spectroscopy. They were evaluated in vitro for their inhibitory ability against the growth of human leukemia cell lines K562 and HL-60, human lung adenocarcinoma A549, human hepatoma BEL-7402 and human stomach cancer SGC-7901. Both compounds showed significant cytotoxicity against the tested cell lines. Compound 1 exhibited some selectivity against HL-60 and BEL-7402 with IC(50) values of 1.27 x 10(-3) and 1.22 x 10(-3) micromol/ml respectively, whereas 2 was most active against A549 with IC(50) value of 1.18 x 10(-3) micromol/ml.

1,4,5-Trihydroxy-7-methoxy-9H-fluoren-9-one, a new cytotoxic compound from Dendrobium chrysotoxum

A new compound, 1,4,5-trihydroxy-7-methoxy-9H-fluoren-9-one, has been isolated together with two known fluorenones, dendroflorin and denchrysan A, from the whole plant of Dendrobium chrysotoxum, a plant of Dendrobium genus, used as a health-food. The structure of the fluorenones has been determined on the basis of spectroscopic studies. The isolated compounds were evaluated in vitro for their inhibitory ability against the growth of human leukaemia cell lines K562 and HL-60, human lung adenocarcinoma A549, human hepatoma BEL-7402 and human stomach cancer SGC-7901. All three fluorenones displayed selective cytotoxicity against BEL-7402 with IC50 values of 1.49, 0.97 and 1.38μg/ml, respectively.

Chemical constituents of Dendrobium chrysotoxum

The stems of several Dendrobium species (Orchidaceae) are used in traditional Chinese medicine as a tonic to nourish the stomach, promote the production of body fluid, and reduce fever [1]. D. chrysotoxum Lindl. is distributed in India, Nepal, Thailand, Laos, Vietnam, and Yunnan of southwestern China [2]. Previous investigations on the constituents from D. chrysotoxum have isolated a series of aromatic compounds such as bibenzyls, phenanthrenes, 9,10-dihydrophenanthrenes, fluorenones, and simple aromatic acids and esters [3–10]. The EtOH extract and some of the compounds such as erianin, chrysotoxine, and confusarin were found to possess antitumor activity [11–15]. To find of further antitumor principles from D. chrysotoxum, we investigated the plant. Dendrobium chrysotoxum was collected from Simao County of Yunnan, China in February, 2005. The air-dried whole plants (0.5 kg) were chopped and exhaustively extracted with 95% EtOH. The EtOH extract (22 g) was applied to a silica gel column, eluting with petroleum ether containing increasing amounts of EtOAc to offer five fractions (A–E). Fraction B (5 g) was subjected to repeated column chromatography (silica gel, petroleum ether–EtOAc 4:1; then Sephadex LH-20, MeOH–H2O 9:1) to afford 1 (15 mg), 3 (9 mg), 4 (4 mg), 5 (5 mg), 6 (4 mg), 8 (7 mg), and 10 (25 mg). Fraction C (5 g) was chromatographed over silica gel (CHCl3–Me2CO 20:1) and then purified by chromatography over Sephadex LH-20 (MeOH–H2O 9:1) to furnish 7 (3 mg) and 11 (6 mg). Fraction D (4 g) was separated on silica gel chromatography (CHCl3–MeOH 15:1) and then purified by chromatography over Sephadex LH-20 (MeOH–H2O 9:1) to yield 2 (8 mg) and 9 (6 mg).

Isolation of a new carboline alkaloid from Trigonostemon lii

A new carboline alkaloid, 1-(7-methoxy-quinolinyl-4′-yl)-3,4-dihydro-β-carboline (1), was isolated from the leaves and twigs of Trigonostemon lii Y.T. Chang, together with three known ones, trigonostemonines C and D (2 and 3), and trigonoliimine A (4). Their structures were elucidated by spectroscopic analyses, including 2D-NMR techniques.

Mono-aromatic constituents of Dendrobium longicornu

The stems of several Dendrobium species (Orchidaceae) are used in traditional Chinese medicine as a tonic to nourish the stomach, promote the production of body fluid, and reduce fever [1]. The products prepared from the dried stems of Dendrobium plants are also used as precious health foods and nutrients [2]. Earlier work on the genus led to the isolation of a series of compounds such as alkaloids, fluorenones, sesquiterpenoids, bibenzyls, and phenanthrenes with antioxidant, antitumor, antimutagenic, and other activities [3–6]. D. longicornu Lindl is distributed in Nepal, Sikkim, Bhutan, India, Vietnam, and the southwestern part of China [7]. Previously, there have been no reports on its chemical constituents. In the course of our search for new bioactive natural products from medicinal plants in Yunnan of China, we investigated the plant. D. longicornu was collected from Lianghe County of Yunnan Province, China in September, 2004. The air-dried whole plants (3.4 kg) were chopped and extracted with 95% EtOH five times (each 20 L) at room temperature. The EtOH extract (115 g) was diluted with H2O (1 L) and then extracted with petroleum ether, EtOAc, and n-BuOH (each 0.5 L, five times) successively. Evaporation of the respective solvents gave the petroleum ether (30 g), EtOAc (26 g), and n-BuOH (52 g) extracts. The EtOAc extract (26 g) was applied to a silica gel column (200–300 mesh, 100 cm × 10 cm), eluting with petroleum ether containing increasing amounts of acetone to obtain six fractions monitored by TLC tests. Spots on the plate were observed under UV light and visualized by spraying with 15% H2SO4 in ethanol followed by heating. Fraction 1 (2 g) was further purified on column chromatography (silica gel, 200–300 mesh, 60 cm × 4 cm, petroleum ether–acetone 30:1) to afford five subfractions. The second and third subfractions were isolated on preparative TLC (20 cm × 20 cm, petroleum ether–benzene 1:1) to afford 1 (40 mg) and 2 (35 mg), respectively. The fourth subfraction was purified by recrystallization from acetone to obtain 8 (100 mg); Fr. 2 (4.5 g) was separated on column chromatography (silica gel, 200–300 mesh, 60 cm × 5 cm, CHCl3–acetone 15:1) to yield five subfractions. The second subfraction was isolated on a Sephadex LH-20 column (120 cm × 3 cm, MeOH) to obtain 5 (15 mg). The third subfraction was purified on a preparative TLC plate (20 cm × 20 cm, petroleum ether– EtOAc 9:1) to afford 7 (8 mg). The fourth subfraction was separated on a preparative TLC plate (20 cm × 20 cm, CHCl3–acetone 15:1) to afford 6 (6 mg); Fr. 5 (9 g) was purified on column chromatography (silica gel, 200–300 mesh, 60 cm × 4 cm, CHCl3–acetone 10:1) to afford two subfractions. The second subfraction (3 g) was subjected to repeated column chromatography similarly, first on Sephadex LH-20 (MeOH), and then on preparative TLC (20 cm × 20 cm, petroleum ether– EtOAc 2:1, CHCl3–MeOH 15:1) to isolate 3 (11 mg) and 4 (20 mg).

New Chalcone and Dimeric Chalcones with 1,4-p-Benzoquinone Residue from Combretum yunnanense

New chalcone and dimeric chalcones with 1,4- P-benzoquinone residue, combrequinone A (1), combrequinone B (2), and combrequinone C (3), along with three known compounds (4-6), were isolated from the ethanolic extract of the stems and leaves of Combretum yunnanense, and their structures were determined by spectroscopic analysis. Compounds 1-3 were evaluated for in vitro cytotoxicity against five human cancer cell lines: HL-60, SMMC-7721, A-549, MCF-7, and SW480. Compounds 1, 2 and 3 were found to be most potent against HL-60 acute leukemia cells, with IC₅₀ values of 4.63, 4.07, and 1.26 µM, respectively.

Chemical composition of the essential oil of Senecio scandens flowers

The genus Senecio (Compositae) is composed of about 1000 species widely distributed in the world except in Antarctica. In China, there are 63 species grown mainly in southwestern area [1]. A great deal of interest in phytochemical studies on plants of the Senecio genus has yielded various types of compounds such as pyrrolizidine alkaloids, sesquiterpenoids, diterpenoids, and flavonoids, with hepatotoxic, carcinogenic, insecticidal, antimicrobial, antitumor, antivirus, antiulcer, and immunosupressing activities [2–6]. Pyrrolizidine alkaloids and sesquiterpenoids have been proved to be the potent constituents of Senecio species and are known to be hepatic toxins and carcinogens [7]. S. scandens was used in traditional Chinese medicine to treat ophthalmic diseases, inflammation, and leptospirosis [8]. Its extracts and compounds were reported to possess significant antimicrobial and antiinflammatory activities [2, 9–10], but there are no references about the oil content and chemical composition of its fresh flower. We report here the results of our studies on the composition of oil from the fresh flowers of S. scandens.

Isolation of 5-hydroxypyrrolidin-2-one and other constituents from the young fronds of Pteridium aquilinum

Abstract5-Hydroxypyrrolidin-2-one, along with (2R)-pterosin B, shikimic acid, kaempferol-3-O-β-D-glucopyranoside, transtiliroside, β-sitosterol, daucosterol, glycerol 1-stearate and benzoic acid, were isolated from the young fronds of the bracken fern Pteridium aquilinum. 5-Hydroxypyrrolidin-2-one, shikimic acid and glycerol 1-stearate were isolated from the plant for the first time.