美丽红豆杉二萜的研究——Ⅱ.一个新的紫杉烷二萜的结构

在前文[1]中,我们报道了从美丽红豆杉茎皮中分离得到的三个非紫杉烷二萜型的新的二萜化合物1、2和3.本文报道从美丽红豆杉茎皮中分到的两个紫杉烷二萜化合物:经高分辩~1H NMR 和 COSY 测定其结构为红豆杉素 J(taxinine J,4)和2-去乙酰氧基-红豆杉素J(2-deacetoxy-taxinine J,5)4是已知的,5是新化合物.初步药理结果表明:4和5对肝癌细胞具不同程度的抑制作用.     

美丽红豆杉二萜的研究 I: 美丽红豆杉素A,B和C的结构测定

从美丽红豆杉(Taxus mairei)的茎皮中分离得三个新的二萜化合物, 其中美丽红豆杉素A(taxamairin A, 1)和美丽红豆杉素B(taxamairin B, 2)是含有 酮的三环二萜,它们的骨架尚未见文献报道; 美丽红豆杉素C(taxamairin C, 3)是含有半缩酮的四环二萜. 结构鉴定应用了高分辨的^1H NMR, ^1^3C NMR ^1H-^1H COSY和DFNOE等方法. 美丽红豆杉素A的结构还通过X射线单晶衍射予以证实.     

美丽红豆杉二萜的研究 Ⅰ.美丽红豆杉素A,B和C的结构测定

从美丽红豆杉(Taxus mairei)的茎皮中分离得三个新的二萜化合物,其中美丽红豆杉素A(taxamairin A,1)和美丽红豆杉素B(taxamairin B,2)是含有(艹卓)酮的三环二萜,它们的骨架尚未见文献报道;美丽红豆杉素C(taxamairin C,3)是含有半缩酮的四环二萜.结构鉴定应用了高分辨的~1H NMR,~(13)C NMR ~1H-~1H COSY和DFNOE等方法.美丽红豆杉素A的结构还通过X射线单晶衍射予以证实.     

美丽红豆杉素B的全合成研究

美丽红豆杉素Ｂ的全合成研究王学超，张驰，潘鑫复，陈耀祖（兰州大学化学系，应用有机化学国家重点实验室，兰州，７３００００）关键词美丽红豆杉素Ｂ，全合成，Ｆｒｉｅｄｅｌ－Ｃｒａｆｔｓ成环反应，选择性氧化化合物９（１０→２０）重排松香烷化合物是近年来被人们...     

紫杉烷二萜研究IV

从红豆杉(taxus chinensis)枝叶中分到五个微量紫杉烷类二萜, 其中四个为新二萜, 分别为: 1β, 5α, 13α-trihydroxy-9α,10β-diacetate-2α-benzoatetaxa-4(20), 11-diene(1), 1β,13α-dihydroxy-9α,10β-diacetate-2α-benzoate-5α-cinnamatetaxa-4(20), 11-diene(2), 1β,5α-dihydroxy-9α,10β,13α-triacetate-2α-benzoatetaxa-4(20), 11-diene(3)和1β,2α,5α,9α,10β,13α-hexahydroxytaxa-4(20), 11-diene(4), 另外一个为已知二萜19-hydroxybaccatin III(5)。     

紫杉烷二萜研究IV

从红豆杉(taxus chinensis)枝叶中分到五个微量紫杉烷类二萜, 其中四个为新二萜, 分别为: 1β, 5α, 13α-trihydroxy-9α,10β-diacetate-2α-benzoatetaxa-4(20), 11-diene(1), 1β,13α-dihydroxy-9α,10β-diacetate-2α-benzoate-5α-cinnamatetaxa-4(20), 11-diene(2), 1β,5α-dihydroxy-9α,10β,13α-triacetate-2α-benzoatetaxa-4(20), 11-diene(3)和1β,2α,5α,9α,10β,13α-hexahydroxytaxa-4(20), 11-diene(4), 另外一个为已知二萜19-hydroxybaccatin III(5)。     

冬凌草中的新对映-贝壳杉烷二萜化合物

对河南省济源地区产冬凌草[Isodon rubescens(Hemsl.)Hara]再次进行了深入 的研究，从其叶的乙酸乙酯提取物中分离得到了16个化合物，其中1和2为两个新的 7，20-环氧-对映-贝壳杉烷类二萜化合物，其结构通过波谱分析确定为16（S）-羟 甲基-1α，6β，7β，11β-甲羟基-7α，20-环氧-对映-贝壳杉烷-15-酮（1）和 16（R）-羟甲基-1α，6β，7β，14β-四羟基-7α，20-环氧-对映-贝壳杉烷-15- 酮（2），分别命名为冬凌草已素（1）和庚素（2）；其余的已知化合物分别鉴定 为lasiodonin（3），冬凌草甲素（oridonin，4），乙素（ponicidin），丙素（ rubescensin C），丁素（rubescensin D），牛尾草丙素（rabdoternin C），荛 花香茶菜乙素（wikstroemioidin B），enmenol-1α-O-β-D-glucoside， enmenol，胡麻素（pedalitin），水杨酸，乌索酸，β-谷甾醇和胡萝卜甙。     

大理紫乌头的二萜生物碱成分研究

为了研究大理紫乌头的二萜生物碱成分,采用硅胶柱层析进行化合物的分离纯化,通过NMR方法对其化合物结构进行鉴定。结果表明大理紫乌头含6个二萜生物碱成分,包括5个C_(19)-乌头碱型:塔拉萨敏(1)、14-乙酰塔拉萨敏(2)、黄草乌碱丙(3)、8-去乙酰滇乌碱(4)、印乌碱(5)和1个C_(20)-海替定型宽乌宁(6)。其中化合物3～6为首次从该物种分离得到。     

内南五味子化学成分的研究

从内南五味子的茎藤中分得七个化合物, 经波谱和X衍射分析, 其中五广系一类新型的螺环衍生物木脂素, 分别定名为内南五味子素(3), 内南五味子素乙(4), 丙(5),J(6)及异内南五味子素(7), 另外两个已知化合物为南五味子素和β-谷甾醇。     

HPLC法对5种红豆杉属植物中紫杉烷类化合物成分的分析

采用快速真空液相层析法(VLC)富集红豆杉属植物中5种主要紫衫烷类化合物,回收率在95%以上.5种红豆杉植物中紫杉烷类化合物含量测定结果显示:加拿大红豆杉(树皮)中10-DABⅢ和9-羟基-13-乙酰基巴卡亭Ⅲ含量较高;东北红豆杉(树皮)中7-木糖紫杉醇和三尖杉宁碱含量较高;而紫杉醇含量在东北红豆杉(树皮)中最高,曼地亚(枝叶,搁置一年)次之;本文首次发现矮紫杉中含有4种紫杉烷类化合物.     

FCl:PCX complexes: old and new types of halogen bonds

MP2/aug'-cc-pVTZ calculations have been performed to investigate the halogen-bonded complexes FCl:PCX, for X = NC, CN, F, H, CCH, CCF, CH(3), Li, and Na. Although stable complexes with a F-Cl···P halogen bond exist that form through the lone pair at P (configuration I), except for FCl:PCCN, the more stable complexes are those in which FCl interacts with the C≡P triple bond through a perturbed π system (configuration II). In complexes I, the nature of the halogen bond changes from traditional to chlorine-shared and the interaction energies increase, as the electron-donating ability of X increases. The anionic complex FCl:PC(-) has a chlorine-transferred halogen bond. SAPT analyses indicate that configuration I complexes with traditional halogen bonds are stabilized primarily by the dispersion interaction. The electrostatic interaction is the most important for configuration I complexes with chlorine-shared halogen bonds and for configuration II complexes except for FCl:PCNa for which the induction term is most important. The F-Cl stretching frequency is red-shifted upon complexation. EOM-CCSD/(qzp,qz2p) spin-spin coupling constants have been obtained for all FCl:PCX complexes with configuration I. (1)J(F-Cl) decreases upon complexation. (2X)J(F-P) values are quadratically dependent upon the F-P distance and are very sensitive to halogen-bond type. (1X)J(Cl-P) tends to increase as the Cl-P distance decreases but then decreases dramatically in the chlorine-transferred complex FCl:PC(-) as the Cl-P interaction approaches that of a covalent Cl-P bond. Values of (1)J(F-Cl) for configuration II are reduced relative to configuration I, reflecting the longer F-Cl distances in II compared to those of the neutral complexes of I. Although the F-P and Cl-P distances in configuration II complexes are shorter than these distances in the corresponding configuration I complexes, (2X)J(F-P) and (1X)J(Cl-P) values are significantly reduced, indicating that coupling through the perturbed C-P π bond is less efficient. The nature of F-P coupling for configuration II is also significantly different, as evidenced by the relative importance of PSO, FC, and SD components.     

Roles of electrolytes on charge recombination in dye-sensitized TiO(2) solar cells (2): the case of solar cells using cobalt complex redox couples

Dye-sensitized solar cells (DSC) were prepared from nanoporous TiO(2) electrodes with two different cobalt complex redox couples, propylene-1,2-bis(o-iminobenzylideneaminato)cobalt(II) {Co(II)(abpn)} and tris(4,4'-di-tert-buthyl-2,2'-bipyridine)cobalt(II) diperchlorate {Co(II)(dtb-bpy)(3)(ClO(4))(2)}. The performances of the DSCs were examined with varying the concentrations of the redox couples and Li cations in methoxyacetonitrile. Under 1 sun conditions, short-circuit currents (J(sc)) increased with the increase of the redox couple concentration, and the maximum J(sc) was found at the Li(+) concentration of 100 mM. To rationalize the observed trends of J(sc), electron diffusion coefficients and lifetimes in the DSCs were measured. Electron diffusion coefficients in the DSCs using cobalt complexes were comparable to the previously reported values of nanoporous TiO(2). Electron lifetime was independent of the concentration of the redox couples when the concentration ratio of Co(II)(L) and Co(III)(L) was fixed. With the increase of Li(+) concentration, the electron lifetime increased. These results were interpreted as due to their slow charge-transfer kinetics and the cationic nature of Co complex redox couples, in contrast to the anionic redox couple of I(-)/I(3)(-). The increase of the lifetimes with Li(+) was interpreted with the decrease of the local concentration of Co(III) near the surface of TiO(2). The addition of 4-tert-butylpyridine (tBP) with the presence of Li(+) increased J(sc) significantly. The observed increase of the electron lifetime by tBP could not explain the large increase of J(sc), implying that tBP facilitates the charge transfer from Co(II)(L) to dye cation, with the association of the change of the reorganization energy between Co(II) and Co(III).     

Structure and phase transitions in poly[bis-(2,2,3,3-tetrafluoropropoxy) phosphazene]

The structure and phase transitions in poly[bis-(2,2,3,3-tetrafluoropropoxy)phosphazene] have been studied by differential scanning calorimetry (DSC) and x-ray diffraction. Two crystalline phases and one mesomorphic phase are found, denoted I, II, and III, respectively. These phases convert reversibly one into the other on heating and cooling. The Phase I–Phase II transition occurs in a temperature range from 5 to 30°C whereas the Phase II mesophase (Phase III) transition proceeds above 80°C. Heats of transitions are measured to be about 29.0 J/g and 3.6 J/g, respectively. Crystalline Phase I is characterized by a monoclinic unit cell with the parameters: α = 24.4 Å, b = 9.96 Å, c = 4.96 Å, γ = 123°. The axes of both chains, traversing the unit cell, are directed along the “c” axis, the main chains having cis-trans conformation. Phase I is the common crystalline structure for the main chain and side chains. The structure of Phase II is controlled mainly by packing of the side chains. Transition of Phase II into mesomorphic Phase III is accompanied with distortion of packing of the side chains. Only regular packing of the main chains of macromolecules in the plane perpendicular to their axes exists in Phase III. Mesomorphic phase III is stable up to the degradation temperature of the polymer. A significant effect of stress on the Phase II–III transition in oriented samples was found.     

Proton reduction and dihydrogen oxidation on models of the [2Fe]H cluster of [Fe] hydrogenases. A density functional theory investigation

Density functional theory was used to compare reaction pathways for H2 formation and H+ reduction catalyzed by models of the binuclear cluster found in the active site of [Fe] hydrogenases. Terminal H+ binding to an Fe(I)-Fe(I) form, followed by monoelectron reduction and protonation of the di(thiomethyl)amine ligand, can conveniently lead to H2 formation and release, suggesting that this mechanism could be operative within the enzyme active site. However, a pathway that implies the initial formation of Fe(II)-Fe(II) mu-H species and release of H2 from an Fe(II)-Fe(I) form is characterized by only slightly less favored energy profiles. In both cases, H2 formation becomes less favored when taking into account the competition between CN and amine groups for H+ binding, an observation that can be relevant for the design of novel synthetic catalysts. H2 cleavage can take place on Fe(II)-Fe(II) redox species, in agreement with previous proposals [Fan, H.-J.; Hall, M. B. J. Am. Chem. Soc. 2001, 123, 3828] and, in complexes characterized by terminal CO groups, does not need the involvement of an external base. The step in H2 oxidation characterized by larger energy barriers corresponds to the second H+ extraction from the cluster, both considering Fe(II)-Fe(II) and Fe(II)-Fe(III) species. A comparison of the different reaction pathways reveals that H2 formation could involve only Fe(I)-Fe(I), Fe(II)-Fe(I), and Fe(II)-Fe(II) species, whereas Fe(III)-Fe(II) species might be relevant in H2 cleavage.     

Mercerized cellulose biocomposites: a study of influence of mercerization on cellulose supramolecular structure, water retention value and tensile properties

In this study the effect of the mercerization degree on the water retention value (WRV) and tensile properties of compression molded sulphite dissolving pulp was evaluated. The pulp was treated with 9, 10, or 11 % aqueous NaOH solution for 1 h before compression molding. To study the time dependence of mercerization the pulp was treated with 12 wt% aqueous NaOH for 1, 6 or 48 h. The cellulose I and II contents of the biocomposites were determined by solid state cross polarization/magic angle spinning carbon 13 nuclear magnetic resonance (CP/MAS ¹³C NMR) spectroscopy. By spectral fitting of the C6 and C1 region the cellulose I and II content, respectively, could be determined. Mercerization decreased the total crystallinity (sum of cellulose I and cellulose II content) and it was not possible to convert all cellulose I to cellulose II in the NaOH range investigated. Neither increased the conversion significantly with 12 wt% NaOH at longer treatment times. The slowdown of the cellulose I conversion was suggested as being the result from the formation of cellulose II as a consequence of coalescence of anti-parallel surfaces of neighboring fibrils (Blackwell et al. in Tappi 61:71–72, 1978; Revol and Goring in J Appl Polym Sci 26:1275–1282, 1981; Okano and Sarko in J Appl Polym Sci 30:325–332, 1985). Compression molding of the partially mercerized dissolving pulps yielded biocomposites with tensile properties that could be correlated to the decrease in cellulose I content in the pulps. Mercerization introduces cellulose II and disordered cellulose and lowered the total crystallinity reflected as higher water sensitivity (higher WRV values) and poorer stiffness of the mercerized biocomposites.     

南中国海海藻叶托马尾藻的化学成分研究

采自南中国海的海藻叶托马尾藻用乙醇提取、乙酸乙酯－水分配后,乙酸乙酯相中的提取物经硅胶减压柱色谱分离得到甾醇和脂肪酸两大组分。用ＧＣ／ＭＳ联用技术对它们进行了分离和鉴定。通过硅胶快速柱色谱,从混合甾醇中分离出一个主成分,经波谱分析鉴定为岩藻甾醇。     

Conformational analysis of mixed oxathia crown ethers and their complexational ability towards Ag(I) and Pd(II)-an experimental solution NMR and theoretical molecular modelling study

Both the conformation and flexibility of four mixed oxathia crown ethers and their Ag(I) and Pd(II) complexes were studied by (1)H NMR (delta, J, NOE, T(1)), (13)C NMR, dynamic (1)H NMR spectroscopy and molecular modelling. The stoichiometry and stability constants of the complexes were determined from corresponding Job's plots in the case of Ag(I) complexes as the interchange between free and complexed states was fast on the NMR timescale; interchange for the Pd(II) complexes was sufficiently slow such that distinct sub-spectra were observable for the free and complexed states. In all cases where complexation was observed, 1 : 1 complexes were formed. Global minima structures determined from the modelling studies were analysed with respect to the barriers to ring interconversion, the flexibility of the species in solution and the preferred complexation of Ag(I) and Pd(II) to the sulfur atoms of the crown ethers.     

Electronically unsaturated three-coordinate chloride and methyl complexes of iron,cobalt, and nickel

Three-coordinate organometallic complexes are rare, especially with the prototypical methyl ligand. Using a hindered, rigid bidentate ligand (L), it is possible to create 12-electron methyliron(II) and 13-electron methylcobalt(II) complexes. These complexes are thermally stable, and (1)H NMR spectra suggest that the low coordination number is maintained in solution. Attempts to create the 14-electron LNiCH(3) led instead to the three-coordinate nickel(I) complex LNi(THF). Single crystals of LMCH(3) are isomorphous with the new three-coordinate chloride complexes LNiCl and LCoCl. Along with the recently reported LFeCl (Smith, J. M.; Lachicotte, R. J.; Holland, P. L. Chem. Commun. 2001, 1542), these are the only examples of three-coordinate iron(II), cobalt(II), and nickel(II) complexes with terminal chloride ligands, enabling the systematic evaluation of the effect of coordination number and metal identity on M-Cl bond lengths. Electronic structure calculations predict the ground states of the trigonal complexes.     

Wide compositional and structural diversity in the system Tl/Bi/P/Q (Q=S, Se) and observation of vicinal P-Tl J coupling in the solid state

The compounds alpha-TlBiP2Se6 (I), beta-TlBiP2Se6 (II), TlBiP2S6 (III), Tl3Bi3(PS4)4 (IV), TlBiP2S7 (V), and Tl3Bi(PS4)2 (VI) were synthesized, and the structures of I-V were determined by single-crystal X-ray diffraction analysis. The structure of I features infinite chains. Those of compounds II, III, and V are layered. The structure of IV features a three-dimensional framework. Tl4Bi2(PS4)2(P2S6) (VII) was also prepared for comparison to the title compounds. The band gaps of each compound are 1.23, 1.27, 1.81, 1.88, 2.06, 1.98, and 1.97 eV for I-VII, respectively. Compounds I, III, IV, and VI melt congruently at 544, 595, 495, and 563 degrees C, respectively, and compounds II, V, and VII melt incongruently at 544, 509, and 600 degrees C, respectively. Solid-state 31P NMR spectroscopy of the reported compounds demonstrates chemical shifts and chemical shift anisotropies in line with related chalcophosphate materials. Evidence for two-bond P-Tl J coupling was observed in 31P NMR spectra (J=481-1781 Hz), and to the best of our knowledge, this is the first example of two-bond P-Tl J coupling and the first example of P-Tl coupling in the solid state. It was possible to assign chemical shifts of inequivalent 31P atoms from the same [PxQy]z- anion type based on different modes of metal ion coordination to the chalcogen. These assignments provide information about the vicinal metal ion contribution to the 31P chemical shift.     

Copper chemistry of beta-diketiminate ligands: monomer/dimer equilibria and a new class of bis(mu-oxo)dicopper compounds

A series of Cu(I) and Cu(II) complexes of a variety of beta-diketiminate ligands (L(-)) with a range of substitution patterns were prepared and characterized by spectroscopic, electrochemical, and, in several cases, X-ray crystallographic methods. Specifically, complexes of the general formula [LCuCl](2) were structurally characterized and their magnetic properties assessed through EPR spectroscopy of solutions and, in one instance, by variable-temperature SQUID magnetization measurements on a powder sample. UV-vis spectra indicated reversible dissociation to 3-coordinate monomers LCuCl in solution at temperatures above -55 degrees C. The Cu(I) complexes LCu(MeCN) exhibited reversible Cu(I)/Cu(II) redox couples with E(1/2) values between +300 and +520 mV versus NHE (cyclic voltammetry, MeCN solutions). These complexes were highly reactive with O(2), yielding intermediates that were identified as rare examples of neutral bis(mu-oxo)dicopper complexes on the basis of their EPR silence, diagnostic UV-vis absorption data, and O-isotope-sensitive resonance Raman spectroscopic features. The structural features of the compounds [LCuCl](2) and LCu(MeCN) as well as the proclivity to form bis(mu-oxo)dicopper products upon oxygenation of the Cu(I) complexes are compared to data previously reported for complexes of more sterically hindered beta-diketiminate ligands (Aboelella, N. W.; Lewis, E. A.; Reynolds, A. M.; Brennessel, W. W.; Cramer, C. J.; Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 10600. Spencer, D. J. E.; Aboelella, N. W.; Reynolds, A. M.; Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 2108. Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 1999, 121, 7270). The observed structural and reactivity differences are rationalized by considering the steric influences of both the substituents on the flanking aromatic rings and those present on the beta-diketiminate backbone.