五味子联苯环辛烯类木脂素成分的结构与药理活性关系和药物创新

传统中药五味子具有多种药理活性。20世纪70年代以来,我国临床发现五味子能改善慢性肝炎病人的肝功能异常,在此基础上,我所化学家和药理学家对五味子分离得到的20余种联苯环辛烯类木酯素成分和其药理作用进行了大量研究。五味子的药理活性主要有:保肝,抗氧化,诱导肝药酶,增强解毒功能,促进蛋白质、糖原合成,克服肿瘤耐药性,增强对抗药癌的敏感性以及对中枢神经系统的镇静作用。在这些研究基础上,合成了保肝作用最强的五味子丙素结构类似物,相继研制出两种抗肝炎新药联苯双酯（DDB）和双环醇（bicyclol）。本文对五味子木脂素类成分的结构与药理活性关系以及两种新药的创制做一综述。     

南北五味子荧光光谱差异的原因

建立了用荧光法快速鉴别五味子和部分含五味子制剂中五味子是属于北五味子还是南五味子的方法,探明了南北五味子荧光光谱差异的主要原因。研究了五味子的五种活性成分五味子醇甲、五味子酯甲、五味子甲素、五味子乙素和安五脂素的荧光性质和五味子以及护肝片乙醇提取液的荧光光谱,并用高效液相色谱测定了供试品五种活性成分的含量。研究表明：发光效率按安五脂素、五味子乙素、五味子甲素和五味子醇甲依次减弱,五味子酯甲不具有荧光性;北五味子的主要荧光物质为五味子乙素,而南五味子的主要荧光物质是安五脂素,它们是导致南北五味子荧光光谱差异的主要原因。用荧光法鉴别南北五味子具有简单、快速和灵敏的特点     

三种五味子素荧光性质

研究了五味子甲素、五味子乙素和五味子酯甲的荧光性质,并对五味子酯甲分别在氢氧化钠和硫酸70℃条件下的水解产物用高效液相色谱法和荧光法进行了研究.试验结果表明:以250～260 nm波长的光作为激发光源,五味子甲素和五味子乙素发射光波长在350～360 nm之间,但五味子乙素的发光效率比五味子甲素强十几倍,而五味子酯甲不产生荧光,但五味子酯甲的水解产物能产生荧光,且发光效率与五味子乙素相似.     

毛细管电泳法测定五味子中五味子甲素

采用毛细管电泳法,以15 mmol·L-1磷酸氢二钠、15 mmol·L-1硼砂和20%乙醇的缓冲溶液作为运行电解质溶液,获得了五味子甲素与五味子中其余成分的有效分离,且峰形较好.测得五味子甲素线性回归方程为y=-0.72+24.9 x,相关系数为0.998;线性范围为0.03～0.37 g·L-1.测得的五味子中五味子甲素质量分数为1.18%,相对标准偏差为2.63%(n=6);平均回收率为99.6%.     

南北五味子醇提液的荧光光谱鉴别

建立了用荧光光谱法快速鉴别五味子和部分含五味子制剂中五味子药材种属的方法. 研究了五味子中的五味子醇甲、五味子酯甲、五味子甲素、五味子乙素和安五脂素5种活性成分以及南北五味子和护肝片的乙醇提取液的荧光光谱,并用高效液相色谱测定了供试品中5种活性成分的含量. 结果表明,安五脂素和五味子乙素具有强荧光性且峰形差异显著,五味子甲素和五味子醇甲的荧光性较弱,而五味子酯甲不具有荧光性;南北五味子的主要荧光物质分别为安五脂素和五味子乙素,据此可用乙醇提取液的荧光光谱快速鉴别南北五味子.     

一测多评高效液相色谱法同时测定五味子中五味子醇甲、五味子甲素、五味子乙素

建立一测多评高效液相色谱法同时测定五味子中五味子醇甲、五味子甲素、五味子乙素含量的方法,并验证该法的可行性和准确度。通过Plackett-Burman设计考察流动相中甲醇比例、流动相流量、柱温、进样体积对五味子醇甲色谱峰分离度的影响,确定流动相中甲醇比例、柱温为关键分析参数（P<0.05）。通过中心组合设计优化关键分析参数,建立色谱分析条件：以甲醇-水（体积比为70∶30）溶液作为流动相进行洗脱,流量为1.0 mL/min,柱温为35℃,检测波长为254 nm,进样体积为10μL。以五味子醇甲为内参物,分别建立五味子甲素、五味子乙素与五味子醇甲的相对校正因子,计算各成分含量,实现一测多评。采用外标法测定五味子甲素、五味子乙素含量,比较外标法的实测值与一测多评法预测值之间的差异,以验证一测多评法的准确度及可行性。五味子中五味子醇甲与五味子甲素、五味子乙素的相对校正因子分别为1.039、1.246。五味子醇甲、五味子甲素、五味子乙素色谱峰面积与质量浓度在5～500μg/mL范围内呈良好的线性关系,相关系数均大于0.999。样品加标回收率分别为100.1%、100.6%、100.3%,...     

(S)-与(R)-五味子丙素的HPLC手性分离及质谱研究

建立了一种反相高效液相色谱法分析(S)-和(R)-五味子丙素对映异构体的方法.选用Chiralcel OD-RH手性色谱柱,以甲醇和水(体积比78 : 22、97 : 3)为流动相,流速0.5 mL/min,254 nm波长下检测,五味子丙素合成中间体噁唑啉取代联苯对映异构体2和2'的保留时间分别为22.2 min和19.9 min,分离度为2.5,五味子丙素对映异构体3'和3的保留时间分别为7.5、9.0 min,与相邻杂质峰分离度分别为3.2和2.7.经液相色谱-质谱实现了分离与鉴定.方法灵敏度高、重复性好,可用于五味子丙素对映异构体的立体选择性研究及质量控制.     

南五味子中五味子甲素的薄层扫描色谱定量分析

南五味子是2000年中国药典开始收录的中药材。南五味子与北五味子的性状完全不同,所含化学成分亦不同,功能主治各有侧重。南五味子为木兰科植物华中五味子的干燥成熟果实,性味酸、甘、温,具有收敛固涩,益气生津,补肾宁心之功效。现代研究表明,南五味子的活性成分主要包括五味子甲素和五味子酯甲等木脂素成分。五味子甲素具有显著的功效,但药典仅有五味子酯甲的含量测定,未有五味子甲素的含量测定,相关研究报道也很少,因此有必要研究建立南五味子中五味子甲素含量测定方法。     

华中五味子的研究——Ⅱ.有效成分五味子酯甲、乙、丙、丁、戊及有关化合物的结构

前已报导从华中五味子临床有效部分中分得五味子酯甲和去氧五味子素,今继从该部分中又分得四种木聚糖酯类化合物:五味子酯乙、丙、丁和戊,除五味子酯戊外,在临床上对迁延性、慢性病毒性肝炎患者的血清谷丙转氨酶升高均有降低作用,通过紫外光谱、红外光谱、质谱、核磁共振谱及化学降解等研究,推定其结构式和构象分别为II_a、II_b;III_a、III_b;IV_a、Iv_b及V_a、V_b,并将五味子酯甲及已知的类似物γ-五味子素和五味子丙素结构中的次甲二氧基位置分别改正为如I_a、VI工和VII所示。     

高效液相色谱法测定北五味子中5种木脂素含量

应用高效液相色谱法测定北五味子中五味子醇甲、五味子酯甲、五味子甲素、五味子乙素和五味子丙素等5种木脂素的含量。北五味子样品(1.000g)在70℃温度下用甲醇(20mL)微波辅助提取5min。分取部分提取液,以Hypersil ODS C18色谱柱为固定相,用乙腈和水以不同比例混合的溶液为流动相进行梯度洗脱,在检测波长225nm处进行测定。5种木脂素在一定的质量浓度范围内与其峰面积呈线性关系,方法的检出限(3S/N)在0.029 2~0.050 7mg·L-1之间。以样品为基体,在3个浓度水平加入混合标准溶液进行回收试验,测得回收率在95.3%~101%之间,测定值的相对标准偏差(n=6)在1.1%~2.4%之间。     

Synthesis, FTIR, FT-Raman, UV-visible, ab initio and DFT studies on benzohydrazide

A systematic vibrational spectroscopic assignment and analysis of benzohydrazide (BH) has been carried out by using FTIR and FT-Raman spectral data. The vibrational analysis were aided by electronic structure calculations--ab initio (RHF) and hybrid density functional methods (B3LYP and B3PW91) performed with 6-31G(d,p) and 6-311++G(d,p) basis sets. Molecular equilibrium geometries, electronic energies, IR intensities, harmonic vibrational frequencies, depolarization ratios and Raman activities have been computed. Potential energy distribution (PED) and normal mode analysis have also been performed. The assignments proposed based on the experimental IR and Raman spectra have been reviewed and complete assignment of the observed spectra have been proposed. UV-visible spectrum of the compound was also recorded and the electronic properties, such as HOMO and LUMO energies and λ(max) were determined by time-dependent DFT (TD-DFT) method. The geometrical, thermodynamical parameters and absorption wavelengths were compared with the experimental data. The interactions of carbonyl and hydrazide groups on the benzene ring skeletal modes were investigated.     

Structures, energetics and vibrational frequency shifts of hydrated pyrimidine

More than 70 unique micro-hydrated structures of pyrimidine, ranging in size from 1 to 7 water molecules, have been characterized with the B3LYP density functional and the 6-311++G(2df,2pd) triple-ζ split-valence basis set. Explicitly correlated MP2-F12 single-point computations were performed on each structure with a correlation consistent triple-ζ basis set to estimate the relative and dissociation energies at the MP2 complete basis set (CBS) limit. Many of these new structures have significantly lower energies than those previously reported (by as much as 12.66 kcal?mol(-1)). For clusters with 1 and 2 water molecules, the MP2-F12 relative and dissociation energies are virtually identical to the corresponding CCSD(T)-F12 values. As the number of hydrating waters increases, the structures in which the water molecules are clustered together at one of the N atoms have lower energies than those where the water molecules are more distributed around the pyrimidine ring. Micro-hydrated structures that effectively extend the low-energy hydrogen-bonding motifs to both sides of the ring, as would be expected in the bulk phase, reproduce the experimentally observed vibrational frequency shifts of ν(1) and ν(8b) in very dilute aqueous pyrimidine solutions to within 1 cm(-1) . Micro-hydrated structures of pyrimidine in which water molecules are clustered together have lower energies than structures in which the water molecules are more evenly spread around the pyrimidine ring.     

Ring strain in [n]ladderanes

The ring strain energies in a series of [ n]ladderanes (n = 3-8) have been calculated by using high-level ab initio method (G3MP2//B3LYP-6-31G*) and the series of isodesmic, homodesmotic, and protobranching compensated reactions. The results show that various four-member rings incorporated into the ladderane chain have different strain energies and that the total strain in a ladderane molecule is smaller than the corresponding sum of strain energies of the cyclobutane rings.     

Ab initio calculation of bowl, cage, and ring isomers of C20 and C20-

High-level ab initio calculations have been carried out to reexamine relative stability of bowl, cage, and ring isomers of C(20) and C(20)(-). The total electronic energies of the three isomers show different energy orderings, strongly depending on the hybrid functionals selected. It is found that among three popular hybrid density-functional (DF) methods B3LYP, B3PW91, PBE1PBE, and a new hybrid-meta-DF method TPSSKCIS, only the PBE1PBE method (with cc-pVTZ basis set) gives qualitatively correct energy ordering as that predicted from ab initio CCSD(T)/cc-pVDZ [CCSD(T)-coupled-cluster method including singles, doubles, and noniterative perturbative triples; cc-pVDZ-correlation consistent polarized valence double zeta] as well as from MP4(SDQ)/cc-pVTZ [MP4-fourth-order Moller-Plesset; cc-pVTZ-correlation consistent polarized valence triple zeta] calculations. Both CCSD(T) and MP4 calculations indicate that the bowl is most likely the global minimum of neutral C(20) isomers, followed by the fullerene cage and ring. For the anionic counterparts, the PBE1PBE calculation also agrees with MP4/cc-pVTZ calculation, both predicting that the bowl is still the lowest-energy structure of C(20)(-) at T=0 K, followed by the ring and the cage. In contrast, both B3LYP/cc-pVTZ and B3PW91/cc-pVTZ calculations predict that the ring is the lowest-energy structure of C(20)(-). Apparently, this good reliability in predicting the energy ordering renders the hybrid PBE method a leading choice for predicting relative stability among large-sized carbon clusters and other carbon nanostructures (e.g., finite-size carbon nanotubes, nano-onions, or nanohorns). The relative stabilities derived from total energy with Gibbs free-energy corrections demonstrate a changing ordering in which ring becomes more favorable for both C(20) and C(20)(-) at high temperatures. Finally, photoelectron spectra (PES) for the anionic C(20)(-) isomers have been computed. With binding energies up to 7 eV, the simulated PES show ample spectral features to distinguish the three competitive C(20)(-) isomers.     

Ring strain energies: substituted rings, norbornanes, norbornenes and norbornadienes

Ring strain energies (RSEs) are predicted using homodesmotic reactions at the B3LYP/6-31G^* level of theory. Substituents are conserved in the acyclic reference and any difference in energy between the ring and the acyclic reference corresponds exclusively to RSE. Small rings are stabilized by alkyl substituents and this stabilization decreases as the size of the ring increases. There is a destabilization of medium sized rings. Greater stabilization is found upon alkyl substitution at a double bond in an unsaturated ring and this stabilization decreases as ring size increases. The effects of cis-1,2-disubstitution on RSEs have been evaluated and indicate stabilization for both small and medium sized rings. RSEs of saturated and unsaturated polycyclic systems agree well with the RSEs derived from experimental thermochemical data. RSEs are reported for substituted norbornanes, norbornenes, and norbornadienes to complement experimental studies.     

From Furan to Molecular Stairs: Syntheses,Structural Properties,and Theoretical Investigations of Oligocyclic Oligoacetals

The synthesis of oligocyclic oligoacetals using five‐membered rings as repetitive unit is described. Furan was used as the starting material, which is converted by a three‐step procedure consisting of twofold cyclopropanation, reduction, and oxidative ring enlargement into a tricyclic bis(enol ether). A repetition of this synthetic procedure leads to the formation of extended oligoacetal systems. Insights into the structures were gained by X‐ray crystallographic investigations and revealed helical arrangements of the subunits in the solid‐state. DFT (B3LYP) calculations have been carried out to elucidate the transition state of the ring enlargement and the flexibility of the annelated oligocyclic systems. Strain energies and topologies of potential cyclically condensed oligoacetals are predicted.     

1, 4-Pyrone Effects on O-H Bond Dissociation Energies of Catechols in Flavonoids: A Density Functional Theory Study

In recent years, there has been growing interest in selecting efficient antioxidants with low toxicity to reduce the damage of free radicals. Among these antioxidants, flavonoids have been paid much attention, owing to their excellent antioxidative and pharmacological activities1. Up to now, many efforts have been given to summarize the structure-activity relationships (SAR) for flavonoids. It has been widely accepted that two structural factors are critical for flavonoids to enhance the…     

Base-catalyzed reactions of environmentally relevant N-chloro-piperidines. A quantum-chemical study

Electronic structure methods have been applied to calculate the gas and aqueous phase reaction energies for base-induced rearrangements of N-chloropiperidine, N-chloro-3-(hydroxymethyl)piperidine, and N-chloro-4-(4-fluorophenyl)-3-(hydroxymethyl)piperidine. These derivatives have been selected as representative models for studying the chemical fate of environmentally relevant chloramines. The performance of different computational methods (MP2, MP4, QCISD, B3LYP and B2PLYP) for calculating the thermochemistry of rearrangement reactions was assessed. The latter method produces energies similar to those obtained at G3B3(+) level, which themselves have been tested against experimental results. Experimental energy barriers and enthalpies for ring inversion, nitrogen inversion and dehydrochlorination reactions in N-chloropiperidine have been accurately reproduced when solvent effects have been included. It was also found that the combined use of continuum solvation models (e.g. CPCM) and explicit consideration of a single water molecule is sufficient to properly describe the water-assisted rearrangement of N-chlorinated compounds in basic media. In the case of N-chloro-4-(4-fluorophenyl)-3-(hydroxymethyl)piperidine, which represents the chlorinated metabolite of the antidepressant paroxetine, several different reactions (intramolecular addition, substitution, and elimination reactions) have been investigated. Transition state structures for these processes have been located together with minimum energy structures of conceivable products. Imine 4A is predicted to be the most stable reaction product, closely followed by imine 4B and oxazinane 8, while formation of isoxazolidine 7 is much less favourable. Calculated reaction barriers in aqueous solution are quite similar for all four processes, the lowest barrier being predicted for the formation of imine 4A.     

Mechanistic insights into triterpene synthesis from quantum mechanical calculations. Detection of systematic errors in B3LYP cyclization energies

Most quantum mechanical studies of triterpene synthesis have been done on small models. We calculated mPW1PW91/6-311+G(2d,p)//B3LYP/6-31G* energies for many C30H51O+ intermediates to establish the first comprehensive energy profiles for the cationic cyclization of oxidosqualene to lanosterol, lupeol, and hopen-3beta-ol. Differences among these 3 profiles were attributed to ring strain, steric effects, and proton affinity. Modest activation energy barriers and the ample exothermicity of most annulations indicated that the cationic intermediates rarely need enzymatic stabilization. The course of reaction is guided by hyperconjugation of the carbocationic 2p orbital with parallel C-C and C-H bonds. Hyperconjugation for cations with a horizontal 2p orbital (in the plane of the ABCD ring system) leads to annulation and ring expansion. If the 2p orbital becomes vertical, hyperconjugation fosters 1,2-methyl and hydride shifts. Transition states leading to rings D and E were bridged cyclopropane/carbonium ions, which allow ring expansion/annulation to bypass formation of undesirable anti-Markovnikov cations. Similar bridged species are also involved in many cation rearrangements. Our calculations revealed systematic errors in DFT cyclization energies. A spectacular example was the B3LYP/6-311+G(2d,p)//B3LYP/6-31G* prediction of endothermicity for the strongly exothermic cyclization of squalene to hopene. DFT cyclization energies for the 6-311+G(2d,p) basis set ranged from reasonable accuracy (mPW1PW91, TPSSh with 25% HF exchange) to underestimation (B3LYP, HCTH, TPSS, O3LYP) or overestimation (MP2, MPW1K, PBE1PBE). Despite minor inaccuracies, B3LYP/6-31G* geometries usually gave credible mPW1PW91 single-point energies. Nevertheless, DFT energies should be used cautiously until broadly reliable methods are established.     

Ring conserved isodesmic reactions: A new method for estimating the heats of formation of aromatics and PAHs

Density functional theory (DFT) has been used along with isodesmic reaction schemes to estimate heats of formation for aromatics and polynuclear aromatic hydrocarbons (PAHs). Calculations have been performed for 42 molecules, 12 of which have uncertain or unknown experimental values, using the B3-LYP functional with the small 6-31G(d) basis set. Heats of formation for the group of test molecules were estimated using both conventional bond separation (BS) isodesmic reactions as well as a new technique of ring conserved (RC) isodesmic reactions which is able to correct systematic errors in B3-LYP calculations. When a ring conserved isodesmic reaction based on delocalization energies is used, the estimated heat of formation is more accurate than that obtained by the bond separation technique. The methodology for creating and using appropriate ring conserved isodesmic reactions is discussed. The present scheme also compares favorably against a recently developed bond centered group additivity scheme that was tested against a large number of PAH molecules.