2—（4—氨酰基—2—噻唑基）—1,4—脱水—L—木糖醇及其氟代衍 …

用计算机分析模拟方法研究了２－（４－氨酰基－２－噻唑基）－１，４－脱水－Ｌ－木糖醇及其氟代衍生物的糖基构象，计算结果显示，６个碳核苷类似物的糖基构象均为Ｓ型。核磁共振谱和晶体Ｘ射线衍射结果与计算结果相吻合。     

反式-1,2-双[5-取代苯基(口恶)唑-2-基]-乙烯的构象

合成了反式-1,2-双[5-(2,4,6-三甲基苯基)(口恶)唑-2-基]乙烯(1_a),并用分子力学法(MMX程序)计算了标题化合物(POEOP,2,5-二甲基-POEOP及2,4,6-三甲基POEOP).POEOP的结构、构象与X衍射结果颇吻合,分子中2个(口恶)唑环呈稳定的反向排布.比同向排布稳定4.6kJ/mol,旋转能垒约16.8～20.9 kJ/mol.还讨论了标题系列化合物的构象对其紫外光谱的影响.     

N-[2-(2-吡啶)乙基]苯胺及其CoCl2配合物的晶体结构及配体的构象研究

本文制备了二氯[N-(2-吡啶乙基)苯胺]钴配合物, 并用X射线衍射法测定了配合物及配体的晶体结构。结合EHMO和DPCILO计算, 从能量角度, 跟踪配体从构象1(配体的晶态构象)变至构象2(配体在配合物中的晶态构象)的变化过程。     

N-[2-(2-吡啶)乙基]苯胺及其COCl_2配合物的晶体结构及配体的构象研究

本文制备了二氯[N-(2-吡啶乙基)苯胺]钴配合物,并用 X 射线衍射法测定了配合物及配体的晶体结构。结合 EHMO 和 DPCILO 计算,从能量角度,跟踪配体从构象1(配体的晶态构象)变至构象2(配体在配合物中的晶态构象)的变化过程。     

区域选择性合成2-取代磺酰基亚肼基-3-全乙酰糖基-2,3-二氢噻唑及其表征、生物活性研究

以取代磺酰肼和糖基异硫氰酸酯反应,生成8种1-取代磺酰基-4-全乙酰糖基氨基硫脲,然后在ClCH2CHO/CH3COONa/DMF条件下关环,区域选择性地合成了一系列新型2-取代磺酰基亚肼基-3-全乙酰糖基-2,3-二氢噻唑.化合物3e的1H-13CHMBC谱图表明1-取代磺酰基-4-全乙酰糖基氨基硫脲与氯乙醛的缩合反应关环位置为氨基硫脲的N-4,而非N-2.所有新化合物的结构均经过1HNMR,13CNMR和元素分析确证,生物活性初步测定结果表明该类二氢噻唑化合物具有一定的除草活性.     

N-糖基-2-取代-氨基硫脲及N-糖基-N''''-取代-联二硫脲类化合物的合成

芳香酸经酯化、肼解,合环后再引入肼基,得2-肼基-5-芳基-1,3,4-噁二唑(2),芳基硫脲经环化、肼解得2-肼基-4/6-取代-苯并噻唑(3).糖基异硫氰酸酯(1)分别与2,3及N-取代氨基硫脲(4)发生亲核加成反应,制得系列新的N-糖基-2-取代-氨基硫脲衍生物5,6及N-糖基-N'-取代-联二硫脲类化合物7.所有化合物的结构均经IR,1H NMR,MS谱和元素分析证实.IR谱中900cm-1附近的吸收及1H NMR谱中偶合常数JCl-H=9～10 Hz,证明产物为β-构型.     

α，α-二取代环十二酮的构象

利用分子力学计算，1~H NMR和单晶X射线衍射分析技术研究了α，α-二取代 环十二酮的构象．结果势构象骨架仍是[3333]-2-酮，在晶体和溶液中，它们的优 势构象均为α-角顺、α-角反-二取代[3333于α-角反位，后上基团处于α-角顺位.     

2-苯甲酰噻吩的晶体结构

2-苯甲酰噻吩分子的构象已有报道,但用不同方法所得结果似有不同。Martin等人根据核磁共振化学位移的研究和Traynard等人根据偶极矩的计算认为,噻吩环平面和苯环平面对于羰基三角形的扭角     

2',3'-二脱氧-2',3'-二去氢鸟嘌呤核苷构象稳定性的理论研究

采用密度泛函方法在B3LYP/6-31＋G**水平上研究了2',3'-二脱氧-2',3'-二去氢鸟嘌呤核苷分子(D4G)的构象. 分别研究在气相中的孤立分子和一水合物异构体的相对稳定性和异构体之间的相互转变过程, 分析了水分子的参与对D4G异构体的相对稳定性和几何结构参数以及自然电荷的影响. 结果表明, 孤立的D4G分子在气相中存在8种稳定构象, 其中构象d4g-2是所有构象中最稳定的, 气相中D4G主要以d4g-2存在. 气相中各构象的相对稳定性为: d4g-2＞d4g-1＞d4g-5＞d4g-3＞d4g-6＞d4g-4＞d4g-8＞d4g-7. 计算得到的各构象键长和键角数据与实验值接近. 一个水分子的加入对D4G分子的构型参数有所影响, 基本不改变D4G分子各构象的稳定性顺序, 但构象转变的能垒有所提高. 氢键在分子构象中发挥了重要作用.     

2',3'-二脱氧-2',3'-二去氢鸟嘌呤核苷构象稳定性的理论研究

采用密度泛函方法在B3LYP/6-31＋G**水平上研究了2',3'-二脱氧-2',3'-二去氢鸟嘌呤核苷分子(D4G)的构象. 分别研究在气相中的孤立分子和一水合物异构体的相对稳定性和异构体之间的相互转变过程, 分析了水分子的参与对D4G异构体的相对稳定性和几何结构参数以及自然电荷的影响. 结果表明, 孤立的D4G分子在气相中存在8种稳定构象, 其中构象d4g-2是所有构象中最稳定的, 气相中D4G主要以d4g-2存在. 气相中各构象的相对稳定性为: d4g-2＞d4g-1＞d4g-5＞d4g-3＞d4g-6＞d4g-4＞d4g-8＞d4g-7. 计算得到的各构象键长和键角数据与实验值接近. 一个水分子的加入对D4G分子的构型参数有所影响, 基本不改变D4G分子各构象的稳定性顺序, 但构象转变的能垒有所提高. 氢键在分子构象中发挥了重要作用.     

Conformational studies on the four stereoisomers of the novel anticholinergic 4-(dimethylamino)-2-phenyl-2-(2-pyridyl)pentanamide

Summary To interpret differences in the anticholinergic activity among the four steroisomers of 4-(dimethylamino)-2-phenyl-2-(2-pyridyl)pentanamide (1–4), we performed conformational studies using the semiempirical molecular orbital method. The structures of the global minimum-energy conformations obtained for 1–4, however, could not explain the different activities, particularly in terms of distances between the essential pharmacophores. We thus implemented superimposition studies, using the energetically stable conformations of the most active stereoisomer, 1(2S,4R), as a template. The energy penalties for a conformation change of the less active stereoisomers 2–4 from their global minimum-energy structure to a new conformation, fitting onto the global minimum-energy conformation of 1, appear to account for the differences in the pharmacological potency better than using the other conformations of 1 as a template. We thus presume that the global minimum-energy conformation of 1 is closely related to the bioactive conformation for these anticholinergics, and also that the pharmacological potency is linked to how readily these substances can change their conformations to fit the muscarinic receptor.     

Design, synthesis, structure and properties of an α-helix cap template derived from N-[(2S)-2-chloropropionyl]-(2S)-Pro-(2R)-Ala-(2S,4S)-4-thioPro-OMe which initiates α-helical structures

A strategy based upon removing the requirement for all of the carbonyl dipoles to align at the same time in the transition state leading to the cyclisation of N-[(2S)-2-chloropropionyl]-(2S)-Pro-(2R)-Ala-(2S,4S)-4-thioPro-OMe to a Zimm-Bragg type α-helix peptide intitator template was successful. Each amide bond of the 12-membered macrocyclic template existed in the trans-rotomeric form. Derivatives of the template were prepared by extending the C-terminus and these were characterised by NMR spectroscopy and restrained simulated annealing. In deuterochloroform solution at low temperature, separate sets of NMR signals were observed for two rapidly interconverting helical conformational isomers of the thioether macrocycle which possessed an appended trialkylammonium ion. A similar time-averaged conformation was also observed in aqueous solution. At −80 °C in d₂-dichloromethane the rate of conformational exchange was slowed sufficiently to obtain resonance assignments and NOE data separately for each isomer. In the minor isomer (40%), the four carbonyl oxygen hydrogen-bond acceptors of the template are aligned in an α-helical conformation and in the major conformer the Pro² carbonyl dipole was anti-aligned with the other three dipoles. Thus, the conformers differ in the orientation of one carbonyl group. Molecular modelling calculations showed that the minor isomer was stabilised by coulombic interactions between the trialkylammonium salt and the carbonyl group dipole moments.     

Crystal and Molecular Structure of 5，6，7，8，9，10－Hexahydro－3－（4－methylphenylamino）－2－thioxoquinoxaline

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Assignment of the photoelectron spectra of FeS3(-) by density functional theory, CASPT2, and RCCSD(T) calculations

The geometric structures of FeS(3) and FeS(3)(-) with spin multiplicities ranging from singlet to octet were optimized at the B3LYP level, allowing two low-lying conformations for these clusters to be identified. The planar D(3h) conformation contains three S(2-) atomic ligands (S(3)Fe(0/-)), whereas the C(2v) structure contains, in addition to an atomic S(2-) ligand, also a S(2)(2-) ligand that is side-on-bound to the iron cation: an η(2)-S(2)FeS conformation. Subsequently, energy differences between the various states of these conformations were estimated by carrying out geometry optimizations at the multireference CASPT2 level. Several competing structures for the ground state of the anionic cluster were recognized at this level. Relative stabilities were also estimated by performing single-point RCSSD(T) calculations on the B3LYP geometries. The ground state of the neutral complex was unambiguously found to be (5)B(2). The ground state of the anion is considerably less certain. The 1(4)B(2), 2(4)B(2), (4)B(1), and (6)A(1) states were all found as low-lying η(2)-S(2)FeS(-) states. Also, (4)B(2) of S(3)Fe(-) has a comparable CASPT2 energy. In contrast, B3LYP and RCCSD(T) mutually agree that the S(3)Fe(-) state is at a much higher energy. Energetically, the bands of the photoelectron spectra of FeS(3)(-) are reproduced at the CASPT2 level as ionizations from either the (4)B(2) or (6)A(1) state of η(2)-S(2)FeS. However, the Franck-Condon factors obtained from a harmonic vibrational analysis at the B3LYP level show that only the (4)B(2)-to-(5)B(2) ionization, which preserves the η(2)-S(2)Fe-S conformation, provides the best vibrational progression match with the X band of the experimental photoelectron spectra.     

Preparation of single-enantiomer 2-methyl-4-heptanol, a pheromone of Metamasius hemipterus, using (S)-2-methoxy-2-(1-naphthyl)propionic acid

To investigate the resolution of secondary alcohols using 2-methoxy-2-(1-naphthyl)propionic acid (MalphaNP acid), 2-methyl-4-heptanol, one of the aggregation pheromones of Metamasius hemipterus, was resolved using (S)-MalphaNP acid. As a chiral-resolving agent, MalphaNP acid is superior to 3,3,3-trifluoro-2-methoxy-2-phenylpropionic acid (MTPA) in terms of HPLC separation and NMR shielding. A better separation of diastereomeric MalphaNP esters was observed when n-hexane-THF was used as the eluent for silica gel HPLC. The solvolysis of the diastereomeric MalphaNP esters gave (R)-2-methyl-4-heptanol and its enantiomer; enantiopure (S)-MalphaNP acid was also recovered. In addition, the preferred conformation of the MalphaNP ester was confirmed using methyl (R)-3-hydroxyvalerate as an authentic compound.     

Structure of dilignol,β-O-4-[1-(4-hydroxyphenyl)-2-(2-methoxyphenoxy)-1-ethanol] in crystal and in solution

The structure of dilignol, 1-(4-hydroxyphenyl)-2-(2-methoxyphenoxy)-1-ethanol was studied by x-ray diffraction structural analysis and¹H PMR spectroscopy. The dilignol molecules crystallize in an extended conformation with trans-Ar-C-C-O and trans-C-C-O-Ar structures: the angle between the plane of the aromatic systems was 74.0°. This conformation was stabilized by intermolecular hydrogen bonds, which linked the molecules into chains. Weak Y-shaped hydrogen bonds were found between molecules of adjacent chains. These results were compared with the literature data on the crystal structure of -O-4 dilignols. A similar conformation of dilignol stabilized by an intramolecular hydrogen bond, whose existence was indicated by IR spectroscopy, was found to predominate in acetone and chloroform solutions. A conclusion was drawn concerning the conformational mobility of -O-4 dilignols and the factors determining the conformational composition of dilignols in solution were discussed.S. M. Kirov Leningrad Forest Technology Institute, Institute of Wood Chemistry, Academy of Sciences of the Latvian SSR. Institute of Organic Synthesis, Academy of Sciences of the Latvian SSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 5, pp. 135–141, September–October, 1989.     

Synthesis of oligomers of trans-(4S,5R)-4-carboxybenzyl 5-methyl oxazolidin-2-one: an approach to new foldamers.

The synthesis of two oligomers containing three and four residues, respectively, of trans-(4S,5R)-4-carboxy 5-methyloxazolidin-2-ones is described. The monomer is obtained by starting from benzyl-N-Boc-(3R)-aminobutanoate, by cyclization into the corresponding trans-(2S,3R)-2-carboxybenzyl-3-methyl-N-Boc-aziridine and rearrangement of the product to trans-(4S,5R)-4-carboxybenzyl-5- methyloxazolidin-2-one, catalyzed by Sn(OTf)2. The oligomers are synthesized by activating the carboxy group as its pentaflourophenyl ester. The trimer and the tetramer are obtained in good yield, and their 1H NMR spectra suggest that these molecules fold in ordered structures, where the C-4 hydrogen of a ring is always close to the carbonyl of the next ring. This result shows that the 4-carboxy-5-substituted-oxazolidin-2-ones are a new class of pseudoprolines which fully control the formation of a Xaai-1-Proi peptide bond in the trans conformation and are complementary to the pseudoprolines obtained from cyclocondensation of cysteine, serine, or threonine and aldehydes or ketones, which strongly favor the Xaai-1-Proi peptide bond in the cis conformation.     

Analysis of vibrational circular dichroism spectra of (s)-(+)-2-butanol by rotational strengths expressed in local symmetry coordinates

The vibrational circular dichroism (VCD) spectra of (S)-(+)-2-butanol have been observed in dilute CS(2) solutions. Two strong VCD bands are assigned mainly to the OH bending modes with the aid of quantum chemical calculations. The calculated VCD spectra corresponding to these bands are shown to depend on the conformation of the OH group. To understand this feature, we have calculated the contribution of each local vibrational mode to the rotational strengths and concluded that the coupling of the group vibrations between the in-plane and out-of-plane modes about the locally assumed symmetry planes play a significant role in VCD. This finding has provided a new scope of VCD in relation to molecular vibrations.     

Conformational analysis of some (E)-α-phenyl-β-(2-thienyl)- and -(2-furyl_acrylic acids

NMR spectral data of some (E)-α-phenyl-β-(2-thienyl) acrylic acids indicate that these compounds exist in the preferred s-trans conformation. In the case of (E)-α-phenyl-β-(2-furyl)acrylic acids and their methyl esters the presence of only s-cis rotamer has been established.     

Δ-2 thiazoline et alkyl-2 Δ-2 thiazolines: etude vibrationnelle infrarouge et Raman.conformation

Raman spectra (liquid state) and infrared spectra of 2-Δ thiazoline and its 2-alkyl derivatives (vapor, liquid, solution and solid states) have been analysed between 4000 and 200 cm⁻¹. The assignments proposed for the fundamental vibrations of these heterocycles agree with a planar or a very little distorted conformation of the cycle.