Comparative proteomic analysis of different Toxoplasma gondii genotypes by two‐dimensional fluorescence difference gel electrophoresis combined with mass spectrometry

Toxoplasma gondii is a protozoan parasite infecting almost all warm‐blooded animals and humans. There are three infective stages of T. gondii: the tachyzoites, the bradyzoites, and the oocysts. The tachyzoite is a rapidly multiplying stage and the main pathogenic factor. In North America and Europe, T. gondii is consisted of four major clonal lineages (namely Types I, II, III, and Type 12). In this study, we explored the proteomic profiles of different genotypes (Type I‐RH strain, Type II‐PRU strain, Type II‐TgQHO strain, and ToxoDB 9‐TgC7 strain) of T. gondii tachyzoites by using 2D DIGE combined with MALDI‐TOF MS. Totally, 110 differentially abundant protein spots were selected. Of these, 98 spots corresponding to 56 proteins from T. gondii were successfully identified. These included surface antigen (SAG1), heat shock protein 70 (Hsp 70), disulfide isomerase, coronin, heat shock protein 60 (Hsp 60), pyruvate kinase, receptor for activated C kinase 1, and peroxiredoxin. Gene ontology enrichment analysis revealed that most of the differentially abundant proteins were involved in biological regulation, metabolic process, response to stress, binding, antioxidant activity, and transporter activity. According to the KEGG metabolic pathway maps of T. gondii, some identified proteins were involved in the glycolytic/gluconeogenesis pathway. The present study identified differentially abundant proteins among different genotypes of T. gondii and these findings have implications for the better understanding of the phenotypic differences among the examined T. gondii genotypes, which in turn may contribute to the better control of toxoplasmosis.     

Inhibitors of the Bifunctional 2‐C‐Methyl‐d‐erythritol 4‐Phosphate Cytidylyl Transferase/2‐C‐Methyl‐d‐erythritol‐2,4‐cyclopyrophosphate Synthase (IspDF) of Helicobacter pylori

A library of over 103 thousand compounds was screened for inhibitors of the IspD domain (2‐C‐methyl‐d ‐erythritol 4‐phosphate cytidylyl transferase domain) of the bifunctional IspDF protein from Helicobacter pylori using a photometric assay. Around 300 compounds showed IC₅₀ values below 100 μm , and three compounds had IC₅₀ values below 1 μm . A few IspD inhibitors could also inhibit the IspF domain (2‐C‐Methyl‐d ‐erythritol‐2,4‐cyclopyrophosphate synthase) of the IspDF protein. The most potent IspD inhibitors were tested as growth inhibitors of H. pylori. Several compounds showed inhibition of bacterial growth with IC₅₀ in the single‐digit μm range. The most potent growth inhibitor had an IC₅₀ value of 3.4 μm . The most potent growth inhibitor without measurable effect on eukaryotic cell viability had an IC₅₀ value of 7.2 μm .     

Synthesis of a series of diaminobenzo[f]- and diaminobenzo[h]pyrimido[4,5-b]quinolines as 5-deaza tetracyclic nonclassical antifolates

A series of diaminobenzo[f]- and diaminobenzo[h]pyrimido[4,5-b]quinolines 1–11 were designed as 5-deaza tetracyclic nonclassical, lipophilic antifolates. The compounds were designed as conformationally semi-rigid and rigid analogs of 2,4-diamino-6-phenyl- 12 and 2,4-diamino-7-phenylpyrido[2,3-d]pyrimidines 13 and 14 . The target compounds were synthesized by cyclocondensation of chlorovinyl aldehydes obtained from appropriately substituted 1- or 2-tetralone, with 2,4,6-friaminopyrimidine. Compounds 1–11 were evaluated as inhibitors of P. carinii and T. gondii dihydrofolate reductases. These pathogens cause fatal opportunistic infections in AIDS patients. In addition, the selectivity of these agents was evaluated using rat liver dihydrofolate reductase as the mammalian source. In general the benzo[f]pyrimido[4,5-b]quinolines 1–5 were more potent than the corresponding benzo[h]pyrimido[4,5-b]quinoline analogues 6–11 against P. carinii and rat liver dihydrofolate reductase and were equipotent against T. gondii dihydrofolate reductase. Compounds 6–11 were moderately selective towards T. gondii dihydrofolate reductase with IC₅₀S in the 10⁻⁷ M range. In contrast analogues 1–5 lacked selectivity against P. carinii or T. gondii dihydrofolate reductase and were, in general, potent inhibitors of rat liver dihydrofolate reductase with IC₅₀S in the 10⁻⁸ M range. Analogues 1 and 4 were evaluated against a series of tumor cell lines in vitro and were found to have moderate antitumor activity (IC50 10⁻⁶ M). The structure activity/selectivity relationships suggest that benzo[f]pyrimido analogues 1–5 with the phenyl ring substitution in the “upper” portion of the tetracyclic ring are better accommodated within the rat liver (mammalian) dihydrofolate reductase and P. carinii dihydrofolate reductase active sites compared to the benzo[h]pyrimido analogues 6–11 which have the phenyl ring substitution in the “lower” portion of the tetracyclic ring. In contrast T. gondii dihydrofolate reductase does not discriminate between the isomers and binds to both series of compounds with similar affinities.     

Investigation of the effect of berberines alkaloids in <Emphasis Type="Italic">Coptis chinensis</Emphasis> Franch on <Emphasis Type="Italic">Bacillus shigae</Emphasis> growthby microcalorimetry

The inhibitory effects of five berberines alkaloids (BAs) from rhizoma of Coptis chinensis Franch, a traditional Chinese medicinal (TCM) herb, on Bacillus shigae (B. shigae) growth were investigated by microcalorimetry. The power-time curves of B. shigae with and without BAs were acquired; meanwhile, the extent and duration of inhibitory effects on the metabolism were evaluated by growth rate constants (k1, k2), half inhibitory ratio (IC50), maximum heat output (Pmax), and peak time (tp). The values of k1 and k2 of B. shigae in the presence of the five BAs decreased with the increasing concentrations of BAs. Moreover, Pmax was reduced, and the value of tp increased with increasing concentrations of the five drugs. The inhibitory activity varied with different drugs. IC50 of the five BAs was respectively 75 μg/mL for berberine, 90 μg/mL for coptisine, 115 μg/mL for palmatine, 220 μg/mL for epiberberine, and 400 μg/mL for jatrorrhizine. The sequence of antimicrobial activity of the five BAs berberine ＞ coptisine ＞ palmatine ＞ epiberberine ＞ jatrorrhizine. The functional groups methylenedioxy at C2 and C3 on phenyl ring improve antimicrobial activity more strongly than methoxyl at C2 and C3 on phenyl ring. However, the effect of bacteriostasis is not significant with methylenedioxy or methoxyl at C9 and C10 on phenyl ring.     

Toxic effects of protoberberine alkaloids from <Emphasis Type="Italic">Rhizoma Coptidis</Emphasis> on <Emphasis Type="Italic">Tetrahymena thermophila</Emphasis> BF<Subscript>5</Subscript> growth based on microcalorimetry

Rhizoma Coptidis consists mainly of protoberberine alkaloids (PAs), and has been used for many years as a traditional medicine. Recent research revealed the toxicity of Rhizoma Coptidis, but studies focusing on the relationships between the structures of PAs and their toxicities are lacking. The toxic effects of four PAs from Rhizoma Coptidis on the growth of Tetrahymena thermophila BF₅ were investigated by microcalorimetry. The power-time curves of T. thermophila BF₅ with and without PAs were obtained; the extent and duration of toxic effects on the metabolism of this organism were evaluated by studying thermokinetic parameters and the half-inhibitory ratio (IC ₅₀). All the thermokinetic parameters showed regular variations with alteration of PA concentrations. The magnitude of the toxic effects of PAs was ascertained from IC ₅₀ values: palmatine > jateorhizine > berberine ≈ coptisine. The structure–function relationship of PAs indicated that the C2 and C3 positions contributed more to the toxic effect of PAs. That is, when substituted with methoxyl groups, the toxic effect would be increased.     

Anti-fungal effect of berberine on <Emphasis Type="Italic">Candida albicans</Emphasis> by microcalorimetry with correspondence analysis

Using a LKB-2277 bioactivity monitor, stop-flow mode, the power–time curves of Candida albicans growth at 37 °C affected by berberine were measured. The check experiments were studied based on agar cup method to observe the inhibitory diameter and serial dilution method to determine the minimal inhibitory concentration (MIC) of berberine on C. albicans growth. By analyzing the quantitative thermogenic parameters taken from the power–time curves using correspondence analysis (CA), we could find that berberine at a low concentration (5.0 μg mL⁻¹) began to inhibit the growth of C. albicans and at a high concentration (75.0 μg mL⁻¹) completely inhibited C. albicans growth. The anti-fungal activity of berberine could also be expressed as half-inhibitory concentration IC₅₀, i.e., 50% effective in this inhibition. The value of IC₅₀ of berberine on C. albicans was 34.52 μg mL⁻¹. The inhibitory diameters all exceeded 10 mm in test range and the MIC was 500 μg mL⁻¹. Berberine had strong anti-fungal effect on C. albicans growth. This work provided an important idea of the combination of microcalorimetry and CA for the study on anti-fungal effect of berberine and other compounds. Compared with the agar cup method and serial dilution method, microcalorimetry not only offered a useful way for evaluating the bioactivity of drugs, but also provides more information about the microbial growth and all this information was significant for the synthesis and searching of antibiotics.     

Computational study on the reaction of CH<Subscript>3</Subscript>SCH<Subscript>2</Subscript>CH<Subscript>3</Subscript> with OH radical: mechanism and enthalpy of formation

The reaction mechanism of CH₃SCH₂CH₃ with OH radical is studied at the CCSD(T)/6-311+G(3df,p)//MP2/6-31+G(2d,p) level of theory. Three hydrogen abstraction channels, one substitution process and five addition–elimination channels are identified in the title reaction. The result shows hydrogen abstraction is dominant. Substitution process and addition–elimination reactions may be negligible because of the high barrier heights. Enthalpies of formation [ \Updelta_f H_{(298.15\textK)}^o \Updelta_{f} H_{(298.15{\text{K}})}^{o} ] of the reactants and products are evaluated at the CBS-QB3, G3 and G3MP2 levels of theory, respectively. It is found that the calculated enthalpies of formation by the aforementioned three methods are in consistent with the available experimental data. Rate constants and branching ratios are estimated by means of the conventional transition state theory with the Wigner tunneling correction over the temperature range of 200–900 K. The calculation shows that the formations of P1 (CH₂SCH₂CH₃ + H₂O) and P2 (CH₃SCHCH₃ + H₂O) are major products during 200–900 K. The three-parameter expressions for the total rate constant is fitted to be k_\texttotal = 1.45 ×10 ^{- 21} T^3.24 exp( - 1384.54/T) k_{\text{total}} = 1.45 \times 10^{ - 21} T^{3.24} \exp ( - 1384.54/T) cm³ molecule⁻¹ s⁻¹ from 200 to 900 K.     

Antioxidant,antimicrobial, and tyrosinase inhibition activities of acetone extract of <Emphasis Type="Italic">Ascophyllum nodosum</Emphasis>

The search for new antioxidants of natural origin derived from plants and seaweeds is still very important at present. In our study, the acetone extract of A. nodosum was investigated for its potential use as a natural antioxidant, natural feed additive with antibacterial activity and as a tyrosinase inhibitor. This study could be useful in the context of improved utilization of the A. nodosum extract in the food and cosmetics industry, being not only economically advantageous but also environmentally friendly. Extracts showed antioxidant activity with application of different methodologies: 1,1-diphenyl-2-picrilhydracil DPPH· radicals scavenging (39 %, 4 mg of freeze-dried sample), β-carotene-linoleic acid antioxidant assay (11 %, 4 mg of freeze-dried sample), O₂· radicals scavenging activity (IC₅₀ 0.43 mg mL⁻¹), OH· radicals scavenging activity (IC₅₀ 1.55 mg mL⁻¹), and iron chelation ability (IC₅₀ 0.56 mg mL⁻¹). The extract showed considerable antibacterial activity being more effective against gram-positive bacteria (Micrococcus luteus, Staphylococcus aureus) than against gram-negative bacteria (Escherichia coli, Enterococcus aerogenes). Results of tyrosinase assay for the acetone extract of Ascophyllum nodosum presented 65.6 % inhibition of tyrosinase activity at the IC₅₀ value of 0.1 mg mL⁻¹. The outcomes of our study support potential utilization of this brown seaweed as a source of natural antioxidants. Antioxidant activity of the studied seaweed can be apparently explained by the free radicals scavenging activity, particularly related to the mechanisms of O₂⁻· radicals scavenging activity, OH· radicals inactivation, and iron chelation ability.     

Synthesis of three carbon atom bridged 2,4‐diaminopyrrolo[2,3‐d]‐pyrimidines as nonclassical dihydrofolate reductase inhibitors

A series of seven nonclassical three carbon atom bridged 2,4‐diamino‐5‐substituted‐pyrrolo[2,3‐d]‐pyrirnidines 1a‐g were synthesized as potential inhibitors of dihydrofolate reductase. Selective oxidation of diols 7a‐g affords α‐hydroxy ketones 8a‐g. Subsequent condensation with malononitrile gave the requisite 2‐amino‐3‐cyano‐4‐substituted furan precursors 9a‐g. Cyclocondensation with guanidine in refluxing ethanol in one step affords the three carbon atom bridged 2,4‐diamino‐5‐substituted‐pyrrolo[2,3‐d]‐pyrimidines 1a‐g. Preliminary biological results indicated that these compounds showed moderate inhibitory activities against dihydrofolate reductases from Pneumocystis carinii, Toxoplasma gondii, Mycobacterium avium and rat liver with IC₅₀ values in the 0.66 μM ‐ 70.1 μM range and some compounds had marginal selectivity for T. gondii dihydrofolate reductase.     

Synthesis of 2‐amino‐4‐oxo‐5‐substitutedbenzylthiopyrrolo[2,3‐d]‐pyrimidines as potential inhibitors of thymidylate synthase

A series of ten novel 2‐amino‐4‐oxo‐5‐[(substitutedbenzyl)thio]pyrrolo[2,3‐d]pyrimidines 2‐11 were synthesized as potential inhibitors of thymidylate synthase and as antitumor agents. The analogues contain various electron withdrawing and electron donating substituents on the benzylsulfanyl ring of the side chains and were synthesized from the key intermediate 2‐amino‐4‐oxo‐6‐methylpyrrolo[2,3‐d]pyrimidine, 14 . Appropriately substituted benzyl mercaptans were appended to the 5‐position of 14 via an oxidative addition reaction using iodine, ethanol and water. The compounds were evaluated against human, Escherichia coli and Toxoplasma gondii thymidylate synthase and against human, Escherichia coli and Toxoplasma gondii dihydrofolate reductase. The most potent inhibitor, ( 6 ) which has a 4′‐methoxy substituent on the side chain, has an IC₅₀=25 μM against human thymidylate synthase. Contrary to analogues of general structure 1 , electron donating or electron withdrawing substituents on the side chain of 2‐11 had little or no influence on the human thymidylate synthase inhibitory activity.     

Microcalorimetric investigation of the growth of the <Emphasis Type="Italic">Escherichia coli</Emphasis> DH5α in different antibiotics

The effects of Amoxicillin Sodium and Cefuroxime Sodium on the growth of E. coli DH5α were investigated by microcalorimetry. The metabolic power-time curves of E. coli DH5α growth were determined by using a TAM air isothermal microcalorimeter at 37°C. By evaluation of the obtained parameters, such as growth rate constants (k), inhibitory ratio (I), the maximum heat power (P _m) and the time of the maximum heat power (t _m), one found that the inhibitory activity of Amoxicillin Sodium vs. E. coli DH5α is enhanced with the increasing of the Amoxicillin Sodium concentration, and the Cefuroxime Sodium has a stimulatory effect on the E. coli DH5α growth when the concentration is about 1 μg mL⁻¹. The IC₅₀ for the Amoxicillin Sodium and the Cefuroxime Sodium are 1.6 and 2.0 μg mL⁻¹, respectively, it implicates that the E. coli DH5α is more sensitive to Amoxicillin Sodium than Cefuroxime Sodium.     

Biochemical Characterization of a Type III Polyketide Biosynthetic Gene Cluster from <Emphasis Type="Italic">Streptomyces toxytricini</Emphasis>

A type III polyketide biosynthetic gene cluster has been discovered in the industrially important strain Streptomyces toxytricini NRRL 15443, including four genes stp450-1, stts, stp450-2, and stmo. The stts gene encodes a putative type III polyketide synthase that is homologous to RppA, a 1,3,6,8-tetrahydroxynaphthalene (THN) synthase from Streptomyces griseus. The deduced protein product of stmo resembles the cupin-containing monooxygenase MomA from Streptomyces antibioticus that oxidizes THN into flaviolin. Two cytochrome P450s (CYPs), StP450-1 and StP450-2, are present in the gene cluster. StTS was overexpressed in Escherichia coli BL21(DE3) and identified as a THN synthase. The synthesized THN can be easily oxidized into flaviolin by air. Both CYPs were reconstituted in E. coli BL21(DE3) and can oxidize flaviolin to form oligomers. The k _cat/K _m values for StP450-1 and StP450-2 were 0.28 and 0.71 min⁻¹ mM⁻¹, respectively. UV irradiation test showed that expression of StTS in E. coli BL21(DE3) significantly protects the cells from UV radiation, and coexpression of StTS and StP450-1 provides even stronger protection.     

Synthesis of Pure <Emphasis Type="Italic">meso</Emphasis>-2,3-Butanediol from Crude Glycerol Using an Engineered Metabolic Pathway in <Emphasis Type="Italic">Escherichia coli</Emphasis>

meso-2,3-Butanediol (meso-2,3-BDO) is essential for the synthesis of various economically valuable biosynthetic products; however, the production of meso-2,3-BDO from expensive carbon sources is an obstacle for industrial applications. In this study, genes involved in the synthesis of 2,3-BDO in Klebsiella pneumoniae were identified and used to genetically modify Escherichia coli for meso-2,3-BDO production. Two 2,3-BDO biosynthesis genes—budA, encoding acetolactate, and meso-budC, encoding meso-SADH—from K. pneumoniae were cloned into the pUC18 plasmid and introduced into E. coli. In 2 l batch culture, the SGSB03 E. coli strain yielded meso-2,3-BDO at 0.31 g/g_glucose (with a maximum of 15.7 g/l_culture after 48 h) and 0.21 g/g_{crude glycerol} (with a maximum of 6.9 g/l_culture after 48 h). Batch cultures were grown under optimized conditions (aerobic, 6% carbon source, 37 °C, and initial pH 7). To find the optimal culture conditions for meso-2,3-BDO production, we evaluated the enzyme activity of meso-SADH and the whole cell conversion yield (meso-2,3-BDO/acetoin) of the E. coli SGSB02, which contains pSB02. meso-SADH showed high enzyme activity at 30–37 °C and pH 7 (30.5–41.5 U/mg of protein), and the conversion yield of SGSB02 E. coli was highest at 37–42 °C and a pH of 7 (0.25–0.28 g _meso-2,3-BDO/g_acetoin).     

Another two novel ceramides from <Emphasis Type="Italic">Zephyranthes candida</Emphasis>

From the the bulbs of Zephyranthes candida (Amaryllidaceae), another two novel ceramides have been isolated and identified. The structures of the two novel compounds were established as (2S,3S,4R,21E,2′R)2-[N-(2′-hydroxynonadecanoyl)-N-(1′′,2′′-dihydroxyethyl)amino]-21-hexacosene-1,3,4-triol, named zephyranamide C (1), and 1,3,4,5,6-pentahydroxy-2-(2′-hydroxyhexacosanoyl-amino)-18-(E)-tetracosene, named zephyranamide D (2). Their structures and stereochemistries were elucidated by spectral techniques including ¹H NMR, ¹³C NMR, as well as HSQC, HMBC, DEPT, and COSY.     

Structure-guided fragment-based<Emphasis Type="Italic"> in silico</Emphasis> drug design of dengue protease inhibitors

An in silico fragment-based drug design approach was devised and applied towards the identification of small molecule inhibitors of the dengue virus (DENV) NS2B-NS3 protease. Currently, no DENV protease co-crystal structure with bound inhibitor and fully formed substrate binding site is available. Therefore a homology model of DENV NS2B-NS3 protease was generated employing a multiple template spatial restraints method and used for structure-based design. A library of molecular fragments was derived from the ZINC screening database with help of the retrosynthetic combinatorial analysis procedure (RECAP). 150,000 molecular fragments were docked to the DENV protease homology model and the docking poses were rescored using a target-specific scoring function. High scoring fragments were assembled to small molecule candidates by an implicit linking cascade. The cascade included substructure searching and structural filters focusing on interactions with the S1 and S2 pockets of the protease. The chemical space adjacent to the promising candidates was further explored by neighborhood searching. A total of 23 compounds were tested experimentally and two compounds were discovered to inhibit dengue protease (IC₅₀ = 7.7 μM and 37.9 μM, respectively) and the related West Nile virus protease (IC₅₀ = 6.3 μM and 39.0 μM, respectively). This study demonstrates the successful application of a structure-guided fragment-based in silico drug design approach for dengue protease inhibitors providing straightforward hit generation using a combination of homology modeling, fragment docking, chemical similarity and structural filters.     

Volumetric properties of methyl,tert-butyl, and alkoxy derivatives of tetraphenylporphyrin in benzene solution

Densities, apparent molar volumes, and partial molar volumes of benzene solutions ofmeso-tetradimethylphenyl porphyrin derivatives H₂T(i,j-CH₃)PP (where i,j = 2,3-; 2,4-; 3,4-; 2,5-; 3,5-);meso-tetra-4-alkoxyphenyl porphyrin derivatives H₂T(4-OC_nH_2n+1)PP (wheren = 2–4,6–8,10,12,16);meso-tetra-3-butoxyphenyl porphyrin H₂T(3-OC₄H₉)PP;meso-tetra-4-tert-butylphenyl porphyrin H₂T(4tBu)PP;meso-tetra-3,5-ditert-butylphenyl porphyrin H₂T(3,5-tBu)PP at 25°C and tetraphenylporphyrin, H₂TPP,H₂T(4-OC₁₀H₂₁)PP;H₂T(4-OC₁₂H₂₅)PP and H₂T(4tBu)PP at 20°C; 30°C; 40°C; 50°C were determined. The solubilities of the compounds in benzene at 25°C were measured. The solvent excluded volumes for different conformational states and the topology of dimethyl derivatives of tetraphenylporphyrin were calculated and compared with partial molar volume data. The correlation between the partial molar volumes and van der Waals volumes for the derivatives H₂TPP,n-alkanes,n-alkanols, fatty acids, cyclic compounds, and crown ethers using the equation of Terasawa was elaborated. The average increment of the methylene group for alkoxy-substituted H₂TPP was calculated as δV ₂ ^o (CH₂) = 16.6±0.4cm³-mol^-1. The volumetric expansion coefficients of benzene solutions of H₂TPP; H₂T(4-OC₁₀,H₂₁)PP; H₂T(4-OC₁₂H₂₅)PP and H₂T(4-tBu)PP were determined and discussed. The importance of packing efficiencies around the solute molecules were examined.     

Large‐scale separation of acetylcholinesterase inhibitors from Zanthoxylum nitidum by pH‐zone‐refining counter‐current chromatography target‐guided by ultrafiltration high‐performance liquid chromatography with ultraviolet and mass spectrometry screening

A new strategy by converging ultrafiltration high‐performance liquid chromatography with ultraviolet and mass spectrometry and pH‐zone‐refining counter‐current chromatography was developed for the rapid screening and separation of potential acetylcholinesterase inhibitors from the crude alkaloidals extract of Zanthoxylum nitidum. An optimized two‐phase solvent system composed of chloroform/methanol/water (4:3:3, v/v) was used in this study. And, in the optimal solvent system, 45 mM hydrochloric acid was added to the aqueous stationary phase as the retainer, while 5 mM triethylamine was added to the organic mobile phase as the eluter. As a result, with the purity of over 95%, five alkaloids including jatrorrhizine ( 1 , 340 mg), columbamine ( 2 , 112 mg), skimmianine ( 3 , 154 mg), palmatine ( 4 , 226 mg), and epiberberine ( 5 , 132 mg) were successfully purified in one step from 3.0 g crude alkaloidals extract. And their structures were identified by ultraviolet, mass spectrometry, ¹H and ¹³C NMR spectroscopy. Notably, compounds 2 , 4 and 5 were firstly reported in Z. nitidum. In addition, acetylcholinesterase inhibitory activities of compounds 1–5 were evaluated, and compounds 3, 4 and 5 exhibited stronger acetylcholinesterase inhibitory activity (IC₅₀ values at 8.52 ± 0.64, 14.82 ± 1.21 and 3.12 ± 0.32 μg/mL, respectively) than berberine (IC₅₀ value at 32.86 ± 2.14 μg/mL, positive control). The results indicated that the proposed method is an efficient technique to rapidly screen acetylcholinesterase inhibitors from complex samples, and could be served as a large‐scale preparative technique for separating ionizable active compounds.     

New lignans from <Emphasis Type="Italic">Syringa reticulata</Emphasis> var. <Emphasis Type="Italic">mandshurica</Emphasis>

In the search for platelet-activating-factor (PAF) antagonists, two new lignan compounds were isolated from the leaves of Syringa reticulata Hara var. mandshurica. Their structures were elucidated as (7R,8S, 8'S)-3,4,3',4'-dimethylenedioxy-8,9-dihydroxy-8.8', 7-O-9'-lignan (mandshuricol A) and (7R,8S,8'S)-3',4'methylenedioxy-4-methoxy-3,8,9-trihydroxy-8.8', 7-O-9'-lignan (mandshuricol B), Mandshuricol A and B showed antagonistic activity on PAF in the [³H] PAF receptor binding assay with IC₅₀ values of 4.8 × 10^–5 M and 3.5 × 10^–5 M, respectively.     

A novel chromone-substituted trimeric dihydroflavonol from <Emphasis Type="Italic">Anogeissus pendula</Emphasis>

A new chromone-substituted dihydrotriflavonol, (2S,3S)[6-{(3S) 3″,5″-dihydroxy-6″-methoxydihydrochromone}5,3′,4′,5′-tetrahydroxy-7-methoxy-3-O-8-dihydroflavone]₂ 3-O-8[6-{(3S) 3″,5″-dihydroxy-6″methoxydihydrochromone}3,5,3′,4′,5′-pentahydroxy-7-methoxydihydroflavonol] was isolated from the leaves of Anogeissus pendula. The structure was determined by UV, ¹H NMR, ¹³C NMR, HMBC, and CD data.     

Microcalorimetric investigation of the effect of berberine alkaloids from <Emphasis Type="Italic">Coptis chinensis</Emphasis> Franch on <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> growth

The inhibitory effects of three berberine alkaloids (BAs) from rhizome of Coptis chinensis Franch, a traditional Chinese medicinal (TCM) herb, on Staphylococcus aureus growth were investigated by microcalorimetry. The power-time curves of S. aureus with and without BAs were acquired; meanwhile the extent and duration of inhibitory effects on the metabolism were evaluated by studying the growth rate constant (k), half inhibitory ratio (IC₅₀), maximum heat-output power (P _max), peak time of maximum heat-output power (t _p) and total heat production (Q _t). The value of k of S. aureus in the presence of the three BAs decreased with the increasing concentrations of BAs. Moreover, P _max was reduced and the value of t _p increased with increasing concentrations of the three drugs. The inhibitory activity varied with different drugs. The values of IC₅₀ of the three BAs are respectively, 101.4 μg/mL for berberine, 241.0 μg/mL for palmatine and 792.3 μg/mL for jateorrhizine. The sequence of antimicrobial activity of the three BAs is: berberine > palmatine > jateorrhizine. It is suggested that the functional group methylenedioxy or methoxyl at C2 on the phenyl ring could possibly improve antimicrobial activity more strongly than hydroxyl at C2 on the phenyl ring. Supported by the National Natural Science Foundation of China (Grant No. 30625042)