Structures of ß-glycosidase LXYL-P1-2 reveals the product binding state of GH3 family and a specific pocket for Taxol recognition.

LXYL-P1-2 is one of the few xylosidases that efficiently catalyze the reaction from 7-ß-xylosyl-10-deacetyltaxol (XDT) to 10-deacetyltaxol (DT), and is a potential enzyme used in Taxol industrial production. Here we report the crystal structure of LXYL-P1-2 and its XDT binding complex. These structures reveal an enzyme/product complex with the sugar conformation different from the enzyme/substrate complex reported previously in GH3 enzymes, even in the whole glycohydrolases family. In addition, the DT binding pocket is identified as the structural basis for the substrate specificity. Further structure analysis reveals common features in LXYL-P1-2 and Taxol binding protein tubulin, which might provide useful information for designing new Taxol carrier proteins for drug delivery.

Chiroptical properties of ajugol investigated by quantum chemical calculation using time-dependent density functional theory.

The chiroptical properties of an iridoid glycoside ajugol were fully investigated by quantum chemical calculations of specific optical rotation at the sodium D line ([α]D value), optical rotatory dispersion (ORD), and electronic circular dichroism (ECD) using time-dependent density functional theory (TDDFT). TDDFT calculations of the [α]D value and ORD of ajugol over the range of 365-633 nm were in good agreement with the experimental data. The predicted ECD spectrum of ajugol was also consistent with the experiment, showing a strong negative Cotton effect (CE) at around 190 nm and a weak positive CE at around 220 nm. Our results unambiguously determined the absolute configuration (AC) of the aglycone part of ajugol as (1S, 5R, 6R, 8S, 9S) and supported the generally accepted AC assignments of iridoid glycosides. Semi-empirical rule for the enol ether chromophore, basis set selection, and effect of glucose group on ECD spectra were also discussed in the case of ajugol.

Prenylated C6-C3 compounds from the roots of Illicium henryi.

Eleven prenylated C(6)-C(3) compounds, illihenryifunones A, B (1, 2), illihenryifunol A (3), illihenryipyranol A (4), illihenryiones A-G (5-11), and three known prenylated C(6)-C(3) compounds (12-14), were isolated from the roots of Illicium henryi. Structures of 1-11 were elucidated by spectroscopic methods including NMR, HRESIMS, and CD. The absolute configuration of the 11,12-diol moiety in 5 was determined by observing its induced circular dichroism after addition of Mo(2)(OAc)(4) in DMSO. The absolute configuration of C-11 in 4 was determined as S based on the Rh(2)(OCOCF(3))(4)-induced CD data; the absolute configuration of 3 was determined as R by comparison of its experimental and calculated electronic circular dichroism (ECD). The antioxidant activities of compounds 1-14 were also evaluated. Compound 4 exhibited strong antioxidant activity with an IC(50) value of 2.97±1.30 µM, whereas compounds 3 and 8 showed antioxidant activities with IC(50) values of 44.36±0.30 and 48.00±2.01 µM, respectively.

Study on the absolute configurations of 3-alkylphthalides using TDDFT calculations of chiroptical properties.

Absolute configurations (ACs) of 3-alkylphthalides including natural products (-)-3-n-butylphthalide ((-)-1) and fuscinarin have been studied using chiroptical properties and quantum chemical calculation. Electronic circular dichroism and optical rotatory dispersion spectra of (S)-1 predicted adopting time-dependent density functional theory and hybrid functionals coincide very well with the experimental and literature data of (-)-1, leading unambiguously to AC assignment as S for levorotatory isomer. The relationship between structures and chiroptical properties of 3-alkylphthalides were also studied using theoretical calculation. It is found that when the alkyl group is adjacent to the single chiral center in the molecule, both the length of the alkyl side chain and the polarity of solvent may exert significant effect on electronic circular dichroism spectra. On the basis of these observations, it is recommended that the long-chain alkyl group may be replaced by at least propyl instead of methyl group in such compounds. The present work shows that combination of chiroptical properties and ab initio calculations can provide a feasible and reliable way to the AC establishment of novel 3-alkylphthalide derivatives with a high degree of confidence.

Bioactive sesquiterpenoids from the rhizomes of Acorus calamus.

Eight new sesquiterpenes (1-8) and one new norsesquiterpene (9) named calamusins A-I were isolated from the ethanol extract of Acorus calamus rhizomes. The absolute configuration of compound 8 was determined by comparing its experimental and calculated ECD spectra. The absolute configurations of the other compounds were determined from their CD spectra. Furthermore, in in vitro assays, compounds 3, 4, 7, and 9 (10 µM) exhibited weak hepatoprotective activities against APAP-induced HepG2 cell damage.

Neolignans and sesquiterpenes from cell cultures of Stellera chamaejasme.

Two new neolignans (1, 2) and six sesquiterpenes (3- 8) were isolated from the cell cultures of Stellera chamaejasme. Their structures and absolute configurations were elucidated by extensive spectroscopic and computational methods. Compound 4 exhibited significant protective effects against CCl (4)-induced hepatotoxicity in HepG2 cells, reducing aspartate aminotransferase release by 29.49 % at 10 µM. These compounds have not been isolated from plant material, which implies that in vitro plant cell cultures may offer alternative and effective sources of bioactive natural compounds.

Carbazole alkaloids from the stems of Clausena lansium.

Ten new carbazole alkaloids, claulansines A-J (1-10), and seven known analogues (11-17) were isolated from the stems of Clausena lansium. Their structures were established on the basis of extensive spectroscopic analyses, and their absolute configurations were determined by CD experiments and computational methods. Screening results indicated that compounds 1, 6, 8-10, 13, 14, and 17 showed selective neuroprotective effects at the concentration of 10 µM.

Two new terpenoids from endophytic fungus Periconia sp. F-31.

Two new terpenoids, (+)-(3S,6S,7R,8S)-periconone A (1) and (-)-(1R,4R,6S,7S)-2-caren-4,8-olide (2), have been isolated from an endophytic fungus Periconia sp., which was collected from the plant Annona muricata. Their structures were elucidated on the basis of extensive spectroscopic analyses. In the in vitro assays, the two compounds showed low cytotoxic activities against six human tumor cell lines (HCT-8, Bel-7402, BGC-823, A549, A2780 and MCF-7) with IC(50)>10(-5) M.

Indole alkaloids and quassinoids from the stems of Brucea mollis.

Seven new indole alkaloids, bruceollines H-N (1-7), three new quassinoids, yadanziolides T-V (10-12), and four known analogues, bruceolline E (8), bruceolline F (9), bruceine D (13), and yadanziolide B (14), were isolated from an ethanol extract of the stems of Brucea mollis. The absolute configurations of compounds 2 and 5 were determined by comparison of their experimental and calculated ECD spectra. The absolute configuration of the known compound 9 was determined by using Mo2(OAc)4-induced CD analysis for the first time. Compounds 10, 13, and 14 exhibited cytotoxic activities with IC50 values of 3.00-5.81 µM.

Study on the absolute configuration of levetiracetam via density functional theory calculations of electronic circular dichroism and optical rotatory dispersion.

Theoretical calculation of chiroptical properties has been a powerful tool for the absolute configuration assignment of chiral compounds including synthetic drugs and natural products. In the present work, time-dependent density functional theory (TDDFT) calculations of electronic circular dichroism (ECD) and optical rotatory dispersion (ORD) were employed to investigate the absolute configuration of levetiracetam, which is a widely used anticonvulsant drug. Nine conformers were generated by conformation search using the MMFF94 molecular mechanics force field, and the geometries were then optimized using the Becke 3-Lee-Yang-Parr (B3LYP) exchange-correlation functional. The population-averaged ECD spectrum was obtained by adding ECD spectrum of each conformer using Boltzmann statistics. The predicted ECD spectrum is in excellent agreement with the measured ECD spectrum of levetiracetam. Theoretical ORD spectra show the same tendency as the experimental data of levetiracetam, further confirming the absolute configuration derived from the ECD spectra. Our results demonstrated that the only chiral carbon atom of levetiracetam is unambiguously to be S configuration.

Anticancer effect and neurotoxicity of S-(+)-deoxytylophorinidine, a new phenanthroindolizidine alkaloid that interacts with nucleic acids.

Phenanthroindolizidine alkaloids are a family of plant-derived compounds with significant antineoplastic activity as well as other effects like antiamebicidal, antiviral, and anti-inflammatory activities. The specific biomolecular targets of these compounds have not yet been clearly identified. S-(+)-Deoxytylophorinidine (CAT) is a new phenanthroindolizidine alkaloid, originally extracted from the roots of Tylophora atrofolliculata and Tylophora ovata. Potent anticancer activity was observed in vitro and in vivo. Neurotoxicity of CAT was also studied and it was far less serious than that of vinblastine. Interactions between this compound and DNA had been studied in detail in our laboratory previously, and we further studied its interactions with RNA.

Three new indole alkaloids from Trigonostemon lii.

Three unprecedented indole alkaloids, trigonoliimines A-C (1-3) with a unique polycyclic system, were isolated from the leaves of Trigonostemon lii Y. T. Chang. The structures of 1-3 were determined by the spectroscopic, computational, and CD exciton chirality approaches. Trigonoliimine A showed modest anti-HIV-1 activity (EC(50) = 0.95 microg/mL, TI = 7.9).

Neolignans and glycosides from the stem bark of Illicium difengpi.

Five new neolignans (1-4 and 9), two pairs of neolignan epimers (5-8), and two new aromatic glycosides (10 and 11) have been isolated from the stem bark of Illicium difengpi. Their structures were determined by spectroscopic methods, including 1D and 2D NMR, HRESIMS, CD experiments, and chemical methods. The absolute configurations of the 3,4-diol moiety in 1 and 1,3-diol moiety in 2 were confirmed by Snatzke's method, observing the induced circular dichroism after addition of dimolybdenum tetraacetate in DMSO. Compounds 3, 4, and 11 exhibited moderate anti-inflammatory activities with IC(50) values ranging from 1.62 to 24.4 microM, while compound 3 displayed antioxidant activity with an IC(50) value of 42.3 microM.

[Application of circular dichroism to the study of interactions between small molecular compounds and DNA].

Circular dichroism (CD) is an useful technique for monitoring DNA conformation changes resulting from changes in environmental conditions, such as temperature, ionic strength, and pH, and also for the study of the interaction between DNA and ligands (including small molecules and proteins). CD spectroscopy of DNA arises from the asymmetric backbone sugars and by the helical structures often adopted by nucleic acids. By the interpretation of induced circular dichroism (ICD) of ligand signals resulting from the coupling of electric transition moments of the ligand, DNA bases within the asymmetric DNA environment, ligand-DNA interactions, as well as the DNA-binding mode can be assessed. A number of important conclusions have been reported that related to the observed ICD signals resulting from the interactions between intercalators and groove binders with DNA. If short oligonucleotide sequences are used in the study, sequences-specific of binding also can be deduced. CD determination requires smaller amounts of sample, and not limited by the molecular weight or size and can be performed rapidly; though CD is of low resolution, but it's a complement to NMR and X-ray diffraction methods. This review will introduce the characters of the CD spectra of DNA, and its application to the studies of DNA with small molecules; some progress of the studies in our laboratory will also be discussed. CD is expected to be used as a screening method in seeking more DNA-targeted drugs, such as, antineoplastic, antimicrobial and antiviral drugs.

[Studies on chemical constituents in herb from Artemisia rupestris].

OBJECTIVE: To study the chemical constituents of Artemisia rupestris. METHOD: The chemical constituents were isolated by column chromatography on silical gel and sephadex LH - 20. Their structures were elucidated on the basis of spectral analysis. RESULT: 8 compounds have isolated from this plant, and the structures of them have identified as rupestonic acid (1), chrysosplenetin B (2), artemetin (3), herniarin (4), isokaempferide (5), vanillic acid (6), kaempferol 3, 3', 4'-trimethyl ether (7) and ermanine (8). CONCLUSION: Compounds 2-8 have been isolated from this plant for the first time.

[Xanthones from Tibetan medicine Halenia elliptica and their antioxidant activity].

OBJECTIVE: To investigate the xanthones from Tibetan medicine Halenia elliptica and their antioxidant activity. METHODS: Column chromatography over normal phase silica gel, reversed phase silica gel, Sephadex LH-20, and recrystallization techniques were used to isolate and purify constituents from Halenia elliptica. Infrared spectrometry, mass spectrometry, and nuclear magnetic resonance spectrometry were used to identify the structure of compounds. The antioxidant activity was evaluated by measuring the content of malondialdehyde product in mice liver cell microsomal induced by ferrous-cysteine. RESULTS: Eight xanthones (compound I-VIII) were isolated and identified from the ethyl acetate extract of Halenia elliptica, among which 1,7-dihydroxy-2,3,5-trimethoxyxanthone was a novel compound. Compound I, III at 10 microg/ml and 100 microg/ml could inhibit the production of malondialdehyde in mouse liver microsomes in vitro. CONCLUSION: Eight xanthones were isolated and they have certain antioxidant activity.

[Studies on chemical constituents of Halenia elliptica guided by in vivo absorption and distribution of the constituents].

AIM: To investigate the chemical constituents of the Tibetan herbal medicine Halenia elliptica by guidance of in vivo absorption and distribution of the constituents. METHODS: HPLC with a diode array detector (DAD) and HPLC-MS were used for detecting the constituents of extracts of Halenia elliptica and animal samples. Several kinds of column chromatography were used for the isolation and purification of the main in vivo absorbed and distributed compounds from the extract of Halenia elliptica. RESULTS: Six main components detected in the extracts of the animal samples were isolated from the ethanolic extract of Halenia elliptica. CONCLUSION: After rats were treated with different extracts of Halenia elliplica, low polar components xanthone aglycon of Halenia elliptica were clearly observed in the extracts of liver, lipid, blood, hidney, heart and brain tissue of rats, while the polar components xanthone glycosides were detected in very small amounts in the animal samples. The xanthone glycosides can be decomposed into xanthone aglycons during the digestion, absorption and metabolism procedure. Therefore, the in vivo activity of the xanthone glycosides might be exhibited by their decomposed products. It is an accessibly valuable method to investigate chemical components of herbal medicines under the guidance by detecting in vivo absorption and distribution of chemical components of the herbal medicine extract.