二甲基精氨酸二甲胺水解酶-1的理论研究

运用分子对接和分子动力学方法研究二甲基精氨酸二甲胺水解酶-1(DDAH-1)与其抑制剂亚胺基烯丁基-L-鸟氨酸(L-VNIO)和亚胺基丙基-L-鸟氨酸(Me-L-NIO)的相互作用和结合模式,并根据实验得到的结论设计了亚胺基苯乙基-L-鸟氨酸(Ph-L-NIO)抑制剂.结果表明:L-VNIO比Me-L-NIO对DDAH-1的抑制效果更强,这个结果与实验测得L-VNIO和Me-L-NIO对DDAH-1的半抑制浓度IC50值大小一致.Phe75、Asp78、His172、Ser175和Asp268这五个氨基酸残基在三种抑制剂形成的复合物中起到非常重要的作用,从计算结果推断在这三个抑制剂中我们设计得到的Ph-L-NIO对DDAH-1的抑制效果最好.     

非对称二甲基精氨酸二甲胺水解酶-2的理论研究

利用同源模建的方法,构建了DDAH-2的三位结构.并与L-瓜氨酸、L-高半胱氨酸分别进行对接研究.其中,Asp77,Gly269,Glu27和Arg96是与L-瓜氨酸相互作用较强的残基,Asp77,His171,Asp125和Ala270是与-L高半胱氨酸相互作用较强的残基.尤其Asp77是在两种复合物中同时起重要作用的氨基酸,并且它与抑制剂之间都形成了氢键.     

Determinants of the Inhibition of DprE1 and CYP2C9 by Antitubercular Thiophenes

Mycobacterium tuberculosis (Mtb) DprE1, an essential isomerase for the biosynthesis of the mycobacterial cell wall, is a validated target for tuberculosis (TB) drug development. Here we report the X‐ray crystal structures of DprE1 and the DprE1 resistant mutant (Y314C) in complexes with TCA1 derivatives to elucidate the molecular basis of their inhibitory activities and an unconventional resistance mechanism, which enabled us to optimize the potency of the analogs. The selected lead compound showed excellent in vitro and in vivo activities, and low risk of toxicity profile except for the inhibition of CYP2C9. A crystal structure of CYP2C9 in complex with a TCA1 analog revealed the similar interaction patterns to the DprE1–TCA1 complex. Guided by the structures, an optimized molecule was generated with differential inhibitory activities against DprE1 and CYP2C9, which provides insights for development of a clinical candidate to treat TB.     

Enantioselective Total Synthesis of Pseudopteroxazole and Ileabethoxazole

Enantioselective total syntheses of pseudopteroxazole ( 1 ) and ileabethoxazole ( 2 ) are presented. The two original stereocenters were constructed in excellent enantioselectivity and good diastereoselectivity through Carreira's asymmetric dual catalytic allylation, which shows potential for accessing diastereoisomers at C2 and C3 of 1 and 2 . Cationic cyclizations of 13 and 24 demonstrated an effective pathway for the construction of the opposite configurations at C1 in 1 and 2 . Additionally, an approach for the introduction of methyl at C4 is a feasible solution for structural modifications at C4 in 1 and 2 .     

Ethylene tetramerization: a new route to produce 1-octene in exceptionally high selectivities

Linear alpha-olefins, such as 1-hexene and 1-octene, are important comonomers in the production of linear low-density polyethylene (LLDPE). The conventional method of producing 1-hexene and 1-octene is by oligomerization of ethylene, which yields a wide spectrum of linear alpha-olefins (LAOs). While there exists several processes for producing 1-hexene via ethylene trimerization, a similar route for the selective production of 1-octene has so far been elusive. We now, for the first time, report an unprecedented ethylene tetramerization reaction that produces 1-octene in selectivities exceeding 70%, using an aluminoxane-activated chromium/((R2)2P)2NR1 catalyst system.     

An efficient synthesis of the anti-asthmatic agent T-440: a selective N-alkylation of 2-pyridone

6,7-Diethoxy-1-[1-(2-methoxyethyl)-2-oxo-1,2-dihydropyridin- 4-yl]naphthalene-2,3-dimethanol [T-440, (1)] is a potential anti-asthmatic agent based on selective phosphodiesterase 4 inhibition. It was necessary for the further evaluation of 1 to develop an efficient synthetic route for 1, especially the construction of the 1-(2-methoxyethyl)-2-pyridone moiety. We examined an N-selective alkylation of pyridone derivative (2) in basic media. 2-Methoxyethylation of 2 with 2-methoxyethyl iodide utilizing LiH as the base gave predominantly an N-alkyl pyridone derivative (3a) in 82% yield (N/O-alkylation=92/8), which is compatible with an ab initio calculation of transition-state structures for the methylation of 2-pyridone. Single crystallization of a crude mixture of 3a and 4a furnished pure 3a, which is a key synthetic intermediate of 1.     

Identification of caerulomycin A gene cluster implicates a tailoring amidohydrolase

The biosynthetic gene cluster for caerulomycin A (1) was cloned and characterized from the marine actinomycete Actinoalloteichus cyanogriseus WH1-2216-6, which revealed an unusual hybrid polyketide synthase (PKS)/nonribosomal peptide synthetase (NRPS) system. The crmL disruption mutant accumulated caerulomycin L (2) with an extended L-leucine at C-7, implicating an amidohydrolase activity for CrmL. The leucine-removing activity was confirmed for crude CrmL enzymes. Heterologous expression of the 1 gene cluster led to 1 production in Streptomyces coelicolor.     

An improved asymmetric synthesis of malyngamide U and its 2'-epimer

An accelerated and improved asymmetric synthesis of malyngamide U (1) and its 2'-epimer (2'-epi-1) was accomplished from readily available n-hexanal, ethanolamine and (R)-(-)-carvone. The key steps involved a Johnson-Claisen rearrangement in the synthesis of an unsaturated carboxylic acid 4 and an aldol reaction in the construction of the skeleton of 1 and 2'-epi-1. There are 13 steps in the synthesis, with a 2.7% overall yield for 1 and a 0.4% yield for 2'-epi-1.     

Benzothiazinones are suicide inhibitors of mycobacterial decaprenylphosphoryl-β-D-ribofuranose 2'-oxidase DprE1

Benzothiazinones (BTZs) are antituberculosis drug candidates with nanomolar bactericidal activity against tubercle bacilli. Here we demonstrate that BTZs are suicide substrates of the FAD-dependent decaprenylphosphoryl-β-D-ribofuranose 2'-oxidase DprE1, an enzyme involved in cell-wall biogenesis. BTZs are reduced by DprE1 to an electrophile, which then reacts in a near-quantitative manner with an active-site cysteine of DprE1, thus providing a rationale for the extraordinary potency of BTZs. Mutant DprE1 enzymes from BTZ-resistant strains reduce BTZs to inert metabolites while avoiding covalent inactivation. Our results explain the basis for drug sensitivity and resistance to an exceptionally potent class of antituberculosis agents.     

Development of an electrochemical immunosensor for the detection of HbA1c in serum

An electrochemical immuno-biosensor for detecting glycosylated haemoglobin (HbA1c) is reported based on glassy carbon (GC) electrodes with a mixed layer of an oligo(phenylethynylene) molecular wire (MW) and an oligo(ethylene glycol) (OEG). The mixed layer is formed from in situ-generated aryl diazonium cations. To the distal end of the MW, a redox probe 1,1'-di(aminomethyl)ferrocene (FDMA) was attached followed by the covalent attachment of an epitope N-glycosylated pentapeptide (GPP), an analogon to HbA1c, to which an anti-HbA1c monocolonal antibody IgG can selectively bind. HbA1c was detected by a competitive inhibition assay based on the competition for binding to anti-HbA1c IgG antibodies between the analyte in solution, HbA1c, and the surface bound epitope GPP. Exposure of the GPP modified sensing interface to the mixture of anti-HbA1c IgG antibody and HbA1c results in the attenuation of ferrocene electrochemistry due to free antibody binding to the interface. Higher concentrations of analyte led to higher Faradaic currents as less anti-HbA1c IgG is available to bind to the electrode surface. It was observed that there is a good linear relationship between the relative Faradaic current of FDMA and the concentration of HbA1c from 4.5% to 15.1% of total haemoglobin in serum without the need for washing or rinsing steps.     

Efficient excitation energy transfer in long meso-meso linked Zn(II) porphyrin arrays bearing a 5,15-bisphenylethynylated Zn(II) porphyrin acceptor

Electronically coupled porphyrin arrays are suitable for artificial light harvesting antenna in light of a large absorption cross-section and fast excitation energy transfer (EET). Along this line, an artificial energy transfer model system has been synthesized, comprising of an energy donating meso-meso linked Zn(II) porphyrin array and an energy accepting 5,15-bisphenylethynylated Zn(II) porphyrin linked via a 1,4-phenylene spacer. This includes an increasing number of porphyrins in the meso-meso linked Zn(II) porphyrin array, 1, 2, 3, 6, 12, and 24 (Z1A, Z2A, Z3A, Z6A, Z12A, and Z24A). The intramolecular singlet-singlet EET processes have been examined by means of the steady-state and time-resolved spectroscopic techniques. The steady-state fluorescence comes only from the acceptor moiety in Z1A-Z12A, indicating nearly the quantitative EET. In Z24A that has a molecular length of ca. 217 A, the fluorescence comes largely from the acceptor moiety but partly from the long donor array, indicating that the intramolecular EET is not quantitative. The transient absorption spectroscopy has provided the EET rates in real time scale: (2.5 ps)(-1) for Z1A, (3.3 ps)(-1) for Z2A, (5.5 ps)(-1) for Z3A, (21 ps)(-1) for Z6A, (63 ps)(-1) for Z12A, and (108 ps)(-1) for Z24A. These results have been well explained by a revised F?rster equation (Sumi formula), which takes into account an exciton extending coherently over several porphyrin pigments in the donor array, whose length is not much shorter than the average donor-acceptor distance. Advantages of such strongly coupled porphyrin arrays in light harvesting and transmission are emphasized in terms of fast EET and a large absorption cross-section for incident light.     

抗肿瘤氟喹诺酮C3等排衍生物——噁二唑曼尼希碱衍生物的合成和抗肿瘤活性

用噁二唑硫酮杂环作为培氟沙星(1)的C3羧基电子等排体,得中间体C3噁二唑硫酮4(5),再将其与仲胺或取代苯胺及甲醛通过氨甲基化反应形成系列氟喹诺酮C3噁二唑硫酮曼尼希碱(6a~6j)目标化合物。 用元素分析、1H NMR和MS测试技术确证了目标化合物的组成和结构。 采用MTT法评价了目标化合物对体外培养人肝癌Hep-3B细胞生长的抑制活性。 结果表明,10种目标化合物活性均显著高于对照化合物1的活性,并且脂肪胺曼尼希碱的活性高于芳香胺曼尼希碱的活性。     

Synthesis of new Galβ1→4Fuc segments useful for biological investigations

Useful segments (1, 2) for chemical probes embedded in a Galβ1→4Fuc unit were designed and prepared for characterizing sugar-binding proteins in Caenorhabditis elegans. Segment 1 with an amino group terminus was used as a recognition unit in affinity chromatography. It was revealed that some proteins (annexins and galectins) in C. elegans have an affinity for Galβ1→4Fuc.     

Growth hormone abuse in the horse: preliminary assessment of a mass spectrometric procedure for IGF-1 identification and quantitation.

Previous studies have shown that insulin-like growth factor 1 (IGF-1) is a promising marker for the detection of growth hormone (GH) abuse in the horse. The significant increases observed with GH administration in comparison to natural levels imply the possibility of setting a threshold level for IGF-1 that would be indicative of GH abuse. Although an immunoradiometric assay (IRMA) has been identified as a reliable screening method, a more specific IGF-1 quantification method needs to be developed for the prosecution of GH abuse by horseracing authorities. This study describes such an HPLC electrospray mass spectrometry (LC/ESI-MS) method that was developed and then assessed for the specific analysis of IGF-1 at the low levels encountered in serum. The structural identity of IGF-1 was confirmed by endoproteinase Asp-N digestion followed by LC/MS and LC/MS/MS characterisation. This was followed by quantification of IGF-1 as the intact molecule against an internal standard.     

Total synthesis and proof of relative stereochemistry of (-)-aureonitol

Two trisubstituted epimeric tetrahydrofurans, 1 and 2, have been synthesized in order to confirm the relative stereochemistry in the natural product aureonitol. The key step in the synthesis of 1 and 2 involved a stereoselective intramolecular allylation of an allylsilane with an aldehyde, which introduced the stereotriad in the five-membered ring. The major tetrahydrofuran diastereoisomer 18 from this cyclization reaction was subsequently elaborated to tetrahydrofuran 1. Its 3-epimer (2) was then prepared from 1 via an oxidation-reduction sequence. Compound 1 exhibits identical (1)H NMR data to those reported for aureonitol, which was isolated from Helichrysum aureonitons by Bohlmann in 1979, whereas the (1)H NMR data for 2 are markedly different. The (1)H NMR data (in CDCl3, CD3OD, and C6D6) and (13)C NMR data (in CDCl3) for 1 are also identical with those reported for a natural product isolated from various Chaetomium sp. by Abraham, Seto, and Teuscher. These findings support Abraham's conclusion that the structure of aureonitol should be revised from 2 to 1. The enantioselective synthesis of 1 has also confirmed that (-)-aureonitol isolated by Abraham contains the (2S,3R,4S) absolute configuration of stereocenters on the tetrahydrofuran ring.     

Sensitive determination of traces of boron in waters,fertilizers na geological and biological materials by isotope-dilution mass spectrometry

A method is described for determining traces of boron in water, fertilizers, geological and biological (reference) materials by isotope-dilution mass spectrometry after separation on an Amberlite IRA-743 borate-selective ion-exchange column. Boron (–250 ng g^?1) in water can be determined with an accuracy of 5–20% (computed on a 2s basis). After correction for weighing errors and for moisture, content, which varied from 0 to 8% for the samples tested, 1–35 μg g^?1 boron in “dry” fertilizer, biological or geological sample can be assayed with an accuracy of 5–30% (2s). In an IAEA interlaboratory program on a simulated fresh water, the method yielded a value of 24.3 +? 2 μg l^?1, compared to the make-up value of 25 μg l^?1.     

Nonlinear analysis of dynamic binding in affinity capillary electrophoresis demonstrated for inclusion complexes of beta-cyclodextrin

The stability of the molecular host-guest inclusion complexes of beta-cyclodextrin with benzoate and four different hydroxybenzoates is investigated. For the measurement of the binding constants an experimental method is devised that is based on affinity capillary electrophoresis (ACE) with indirect UV absorbance detection. We derive an explicit equation for effective mobilities in ACE experiments without violation of rigorous mass balance. This equation is employed in the nonlinear least-squares analyses of the experimental data yielding binding constants of 48+/-2 M(-1) for benzoate, 299+/-38 M(-1) for 2-hydroxybenzoate, 37+/-1 M(-1) for 3-hydroxybenzoate, 228+/-9 M(-1) for 4-hydroxybenzoate, and 895+/-110 M(-1) in the case of 2,4-dihydroxybenzoate.     

Separation and detection of a benzo[a]pyrene metabolite with capillary electrophoresis in the presence of DNA using laser-induced fluorescence

A novel approach was developed for the separation and detection of a benzo[a]pyrene B[a]P-DNA metabolite (tetrol I-1) in the presence of DNA using CE and laser induced fluorescence. Tetrol I-1 in the presence of DNA is intercalated and undergoes fluorescence quenching. Thus, an equilibrium is established between the intercalated tetrol I-1 and the uncomplexed tetrol I-1. It is only the uncomplexed tetrol that is fluorescent in the presence of DNA. The tetrol I-1 fluorescence intensities, at two concentrations of tetrol I-1 (0.005 and 0.01mg ml(-1)), were observed while varying the DNA concentration. Stern-Volmer plots were constructed of the fluorescence intensity of the uncomplexed tetrol I-1 versus DNA concentration. From the slopes of the Stern-Volmer plots quenching constants were determined. The quenching constants are essentially the same as an association constant for tetrol I-1 with DNA. The average value obtained for the association constant for the two concentrations of tetrol I-1 was 0.22+/-0.02 mg ml(-1). It was thus demonstrated that uncomplexed tetrol I-1 can be separated from DNA by CE and an association constant for tetrol I-1 bound to DNA can be obtained from the fluorescence quenching data.     

Calculations find that tunneling plays a major role in the reductive elimination of methane from hydridomethylbis(trimethylphosphine)platinum: how to confirm this computational prediction experimentally

DFT calculations, including the effects of small curvature tunneling, have been performed on the reductive elimination of methane from hydridomethylbis(trimethylphosphine)platinum (1d). The calculations find that at 250 K tunneling results in an increase in the rate constant for reductive elimination by a factor of 4, a lowering of Ea by 1.7 kcal/mol, and a decrease in A by a factor of nearly 10. Tunneling is also calculated to increase the primary H/D kinetic isotope effect (KIE) from k(1d)/k(1f) = 2.26 to k(1d)/k(1f) = 4.12 and to result in a large secondary KIE of k(1d)/k(1e) = 1.35. In addition, tunneling is predicted to result in a violation of the rule of the geometric mean, so that the secondary KIE for reductive elimination of methane-d1 from 1f is calculated to be k(1f)/k(1g) = 1.06, which is much smaller than the secondary KIE of k(1d)/k(1e) = 1.35 for reductive elimination of methane from 1d. Comparison of the measured values of k(1d)/k(1e) and k(1f)/k(1g) is therefore proposed as an experimental test of the prediction that tunneling plays an important role in the reductive elimination of methane from 1d.     

Spectrophotometric determination of water in organic solvents with solvatochromic dyes-II

The correlation between the absorbance of a merocyanine dye in an organic solvent and the water content of the solvent has been investigated. The merocyanine dyes investigated are 1-methyl-4-[(4-oxocyclohexa-2, 5-dienylidene)-ethylidene]-1,4-dihydropyridine (I), 1-methyl-4-[(2-oxocyclohexa-3,5-dienylidene)-ethylidene]-1, 4-dihydropyridine, 1-methyl-2-[(4-oxocyclohexa-2,5-dienylidene)-ethylidene]-1, 2-di-hydropyridine and 1-methyl-2-[(oxocyclohexa-3,5-dienylidene)-ethyl-idene]-1, 2-dihydropyridine, and the organic solvents are isopropanol, acetone, acetonitrile and pyridine. The possibility of determining a trace amount of water in an organic solvent is demonstrated, and a procedure is proposed for the determination of trace water in pyridine. The sensitivity of the method depends on the solvent, being more sensitive in an aprotic solvent than in a protic one ; for example, 0.05 or 0.27 mg of water in 1 ml of acetonitrile or of isopropanol respectively can be detected with I, by use of an ordinary spectrophotometer.