Youcai Hu

New vernocuminosides from the stem barks of Vernonia cumingiana Benth.

Seven new stigmastane-type steroidal glycosides, vernocuminosides A-G (1-7), have been isolated from the stem barks of Vernonia cumingiana Benth. The structural elucidation and stereochemistry determination were achieved by spectroscopic and chemical methods including 1D and 2D NMR ((1)H-(1)H COSY, HSQC, HMBC, and NOE) experiments, especially the employment of Snatzkes method expressed by the induced circular dichroism spectra. Anti-inflammatory activities and cytotoxicities of compounds 1-7 were evaluated.

Prenylated C6–C3 compounds with molecular diversity from the roots of Illicium oligandrum

Eleven prenylated C(6)-C(3) compounds, illioliganpyranone A (1), illioliganfunone A-D (2-5), and illioliganone D-I (6-11), together with five known prenylated C(6)-C(3) compounds (12-16), were isolated from roots of Illicium oligandrum. The structures of 1-11 were elucidated by spectroscopic methods including 1D and 2D NMR, HRESIMS, and CD experiments. Possible biosynthetic pathways to compounds 1-16 derived from a common precursor of 5-allylbenzene-1,2,4-triol were postulated. All compounds were evaluated for cytotoxic activities against five human cancer cell lines (HCT-8, Bel-7402, BGC-823, A549 and A2780). Compound 15 exhibited significant cytotoxicity against HCT-8, BGC-823, A549, and A2780 cell lines with IC(50) values of 0.30-2.57 μM. Compound 16 showed moderate selective cytotoxicity against sensitive A2780 cells with IC(50) value of 1.38 μM.

Lysidicins F−H, Three New Phloroglucinols from Lysidice rhodostegia

Three new phloroglucinols, named lysidicins F-H (1-3), were isolated from the roots of Lysidice rhodostegia. These compounds have a unprecedented benzyl benzo[b]furo[3,2-d]furan skeleton, and lysidicin F (1) is the first example of natural product with trans-fused furan rings. Their structures were established on the basis of extensive spectroscopic analysis, and the absolute configurations of them were determined by computational methods. A possible biosynthetic pathway for 1-3 was also postulated.

Targeted Isolation and Structure Elucidation of Stilbene Glycosides from the Bark of Lysidice brevicalyx Wei Guided by Biological and Chemical Screening

An efficient procedure based on biological and chemical screening has been performed to investigate the antioxidant constituents of the bark of Lysidice brevicalyx Wei. The procedure allowed the rapid identification of known compounds and tentative characterization of unknown compounds by online LC/UV/ESIMS(n) analyses of the antioxidant fraction. Targeted isolation of the unknown compounds has led to the discovery of seven new stilbene glycosides, named lysidisides L-R (1-7), together with a known stilbene glycoside, (E)-resveratrol 3-O-rutinoside (8). The structures of these compounds were further determined on the basis of spectroscopic and chemical evidence. The antioxidant activities of compounds 1-8 and two related compounds, (E)-polydatin (9) and lysidiside E (11), were evaluated. The known compound (E)-polydatin (9) showed antioxidant activity at concentrations of 10(-4) and 10(-5) mol/L.

Cytotoxic cardenolides from the stems of Periploca forrestii.

Six new cardenolides, periforosides D-E (1-2), periforgenin C (3) and periforosides F-H (4-6), as well as 10 previously identified cardenolides (7-16) were isolated from the ethanol extract of the stems of Periploca forrestii. The structures of the new compounds were determined using extensive spectroscopic analyses including HRESI-MS, 1D and 2D NMR data. Evaluation of the cytotoxic activity of all the isolated compounds in five different human cancer cell lines indicated that compounds 2-6, 8, 9 and 12-16 have potent activity.

Structural characterization of constituents with molecular diversity in fractions from Lysidice brevicalyx by liquid chromatography/diode-array detection/electrospray ionization tandem mass spectrometry and liquid chromatography/nuclear magnetic resonance.

A combination of electrospray ionization tandem mass spectrometry with high-performance liquid chromatography (HPLC/ESI-MSn), and hyphenation of liquid chromatography to nuclear magnetic resonance spectroscopy (HPLC/NMR), have been extensively utilized for on-line analysis of natural products, analyzing metabolite and drug impurity. In our last paper, we reported an on-line analytical method for structural identification of trace alkaloids in the same class. However, the structural types of the constituents in plants were various, such as flavanoids, terpenoids and steroids. It is important to establish an effective analytical method for on-line structural identification of constituents with molecular diversity in extracts of plants. So, in the present study, the fragmentation patterns of some isolated stilbenes, phloroglucinols and flavanoids from Lysidice rhodostegia were investigated by ESI-MSn. Their fragmentation rules and UV characteristics are summarized, and the relationship between the spectral characteristics, rules and the structures is described. According to the fragmentation rules, NMR and UV spectral characteristics, 24 constituents of different types in the fractions from L. brevicalyx of the same genus were structurally characterized on the basis of HPLC/HRMS, HPLC-UV/ESI-MSn, HPLC/1H NMR and HPLC/1H-1H COSY rapidly. Of these, six (10, 13, 14, 16, 17 and 23) are new compounds and all of them are reported from L. brevicalyx for the first time. The aim is to develop an effective analytical method for on-line structural identification of natural products with molecular diversity in plants, and to guide the rapid and direct isolation of novel compounds by chemical screening.

Seven new steroidal glycosides from the roots of Cynanchum forrestii.

Seven new steroidal glycosides, cynaforrosides K (1), L (2), M (3), N (4), and Q (7), based on a 13,14:14,15-disecopregnane-type aglycone, and cynaforrosides O (5) and P (6) with a 14,15-secopregnane-type aglycone, were isolated from the 95% ethanol extract of the roots of Cynanchum forrestii Schlechter. The structures of new compounds were determined on the basis of spectroscopic and chemical evidence. The sugar units of cynaforrosides K-P contained two moieties of glucoses with the mode of 1-->4 linkage and those of cynaforrosides K-O contained six moieties of sugars.

Cytotoxic oxygenated triterpenoid saponins from Symplocos chinensis.

A n-butanol-soluble fraction of an ethanolic extract from the roots of Symplocos chinensis showed cytotoxic activity against several cancer cell lines. Bioassay-guided purification led to the isolation and characterization of eight new triterpenoid saponins, symplocososides L-S (1-8). The structures of 1-8 were elucidated as glycosides based on oxygenated aglycons by spectroscopic and chemical methods. These compounds and their hydrolytic products, along with some additional analogues obtained earlier from S. chinensis roots, were evaluated for cytotoxicity in a small cancer cell panel.

Rapid structural determination of modified pregnane glycosides from Cynanchum forrestii by liquid chromatography-diode-array detection/electrospray ionization multi-stage tandem mass spectrometry.

The fragmentation behaviors of the two types of modified pregnane glycosides from Cynanchum forrestii were investigated by positive ion electrospray ionization multi-stage tandem mass spectrometry equipped with an ion trap analyzer. The spectral data further illuminated the predominance of ESI-MS(n) technique on the identification of pregnane glycosides, especially of two sorts of modified pregnane glycosides with aglycone skeletons of 13,14:14,15-disecopregnane-type and 14,15-secopregnane-type, which differed in the presence of the characteristic [M-46+Na]+ ion. For sugar residues, the fragment ions were analyzed and some possible fragmentation pathways were proposed, especially for 3-demethyl-2-deoxythevetose, the glycosidic cleavage reaction was easier to occur than those of other sugar units in its moiety. The natures and differences of the pregnane cores, and the types and linked sequences of sugar residues were illustrated. According to these conclusions, eight new pregnane glycosides in the fraction of Cynanchum forrestii were structurally elucidated by HPLC/HRMS and HPLC-DAD/ESI-MS(n) techniques. Results of the present studies can benefit the rapid identification and structural determination of analogous constituents in crude plant extracts.

Two new compounds from the roots of Lysidice rhodostegia.

Two new compounds, lysidicin D (1) and lysidicin E (2), were isolated from the roots of Lysidice rhodostegia. Their structures were elucidated by means of spectroscopic methods. Among them compound 1 showed potent anti-oxidant activity on in vitro.