Formation of a Novel Cage Compound with a Pentacyclo

Abnormally long C-C single bonds are found in the polycyclic caged diol with a pentacyclo[6.3.0.1(4,11).0(2,6).0(5,10)]dodecane skeleton formed by photolysis (see scheme). This skeleton resembles the structure of diamantane, but instead of having six cyclohexane rings in a chair conformation it contains only two cyclohexane rings in a distorted chair conformation and four cyclopentane rings, which makes it more highly strained than diamantane.     

Crystal and molecular structure of the diterpene alkaloid talatisine

As a result of x-ray studies, the spatial structure and conformation of the talatisine molecule have been determined. The mean bond lengths are C-C 1.539(6) Å, N-C 1.493 (5) Å, HO-C(sp³) 1.429(5) Å. The six-membered rings A and B have the chair conformation, and rings C and D have distorted boat conformations. The five-membered rings E, F, and G have the envelope conformation.     

Azolium-linked cyclophanes: effects of structure, solvent, and counteranions on solution conformation behavior

This paper describes the synthesis, structural characterization, and solution behavior of some xylyl-linked imidazolium and benzimidazolium cyclophanes decorated with alkyl or alkoxy groups. The addition of alkyl/alkoxy chains to the cyclophanes allows for studies in chlorinated solvents, whereas previous solution studies of azolium cyclophanes have generally required highly polar solvents. The azolium cyclophanes may exist in a syn/syn conformation (azolium rings mutually syn, arene rings mutually syn) or a syn/anti conformation (azolium rings mutually syn, arene rings mutually anti). The preferred conformation is significantly affected by (i) binding of bromide (ion pairing) to the protons on the imidazolium or benzimidazolium rings, which occurs in solutions of bromide salts of the cyclophanes in chlorinated solvents, and (ii) the addition of alkoxy groups to the benzimidazolium cyclophanes. These structural modifications have also led to cyclophanes that adopt conformations not previously identified for similar azolium cyclophane analogues. Detailed (1)H NMR studies for one cyclophane identified binding of bromide at two independent sites within the cyclophane.     

The use of squaric acid as a scaffold for cofacial phenyl rings

[structure: see text] To examine the possibility of using squaric acid as a scaffold for organizing phenyl rings in a cofacial orientation, we undertook an investigation of the conformational preferences of secondary and tertiary N-phenylsquaramides. In secondary squaramides, the extended ZZ conformation is preferred, while in the N-methyl derivative, the folded EE conformation with cofacial phenyl rings is preferred. This conformational switch is likely driven by a combination of steric and electronic factors.     

Synthesis of Calix[6]arene-Porphyrin Receptors and Study on their Catalytic Performance in Epoxidation of Styrene

The artificial receptors with multiple recognition site had been synthesized by linking two unsymmetrical monofunctionalized porphyrin to p-tert-butyl calix[6]-arene via two flexible chain, followed by inserting metal ion into the porphyrin species.The structures (see Fig 1) of these calix[6]arene-diporphyrins and their metal complexes were confirmed by UV-vis spectra, IR spectra, mass spectra, ¹NMR spectra(600 MHz) and/or ¹³C NMR. Their conformations were investigated preliminarily by UV-vis spectra and computer simulation. In constrast with the correspounding porphyrin monomer, the soret bond of calix[6]arene-diporphyrins in UV-vis spectra showed hypsochromic shift. This phenomenon suggested that two porphyrin rings maintain a face to face parallel conformation, as confirmed by computer simulation that showed the conformation energy is the lowest as two porphyrin rings hold such a conformation. Besides, simplicity of the ¹NMR spectra indicates that the conformation of calix[6]arene-diporphyrin possesses high symmetry. Therefore,the calix[6]arene must be cone conformation.     

Structural and stereochemical factors in the mass spectrometry of mono- and dimethylbicyclo[3.3.1]nonanes

The mass spectra of mono- and dimethylbicyclo[3,3,1]nonanes have been studied. In addition to the fragmentation of the bicyclic form of the molecular ion, the latter appears to dissociate from its monocyclic form. Structural isomers and stereoisomers with essential differences in thermodynamic stability may be identified by the quantitative differences in their mass spectra. Stereoisomers with a ‘boat’ conformation of one of the cyclohexane rings have been shown to differ from the stereoisomers with a ‘chair’ conformation of both rings by virtue of higher intensity of odd-electron ions for the former.     

Crystal and molecular structure of the diterpene alkaloid talatisine

As a result of x-ray studies, the spatial structure and conformation of the talatisine molecule have been determined. The mean bond lengths are C-C 1.539(6) Å, N-C 1.493 (5) Å, HO-C(sp³) 1.429(5) Å. The six-membered rings A and B have the chair conformation, and rings C and D have distorted boat conformations. The five-membered rings E, F, and G have the envelope conformation.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 335–341, May–June, 1981.     

Conformation and stereodynamics of 2,2'-disubstituted N,N'-diaryl ureas

Except in the most hindered of cases, N,N'-diaryl N,N'-dimethyl ureas adopt a conformation with the two aryl rings disposed cis to one another. Variable temperature NMR studies reveal the rate at which the Ar-N bonds rotate as well as the conformational preference of ortho disubstituted ureas in which more than one cis orientation is possible. In general, a conformation in which the aryl rings lie close in space but with their most bulky 2-substituents aligned anti is preferred, but with particularly bulky 2-substituents, conformations in which one of the aryl rings points away from the other may also be populated.     

Chair to boat interconversion and face to face interactions in isomeric aryl-substituted perhydrocyclopentaquinolizines

The structure and the conformation of the two isomeric 3,5-di(4-methoxyphenyl)perhydrocyclopenta[ij]quinolizines 1 and 2 have been determined by a combination of NOE experiments, analysis of vicinal J coupling constants, and DFT computations. The two aryl rings were found to exhibit a face to face disposition, and variable-temperature NMR spectra allowed the determination of the corresponding rotation barriers, as well as chair to boat and nitrogen inversion processes of the quinolizine rings. The structure and the conformation of the two corresponding ammonium salts 1-H+ and 2-H+ were also obtained in solution by the same techniques: in addition, their solid-state structures were determined by X-ray diffraction.     

Triterpenoide. XX. 3β‐Acetoxy‐12‐oxo‐18β‐olean‐ und 3β‐Acetoxy‐12,19‐dioxo‐9(11),13(18)‐oleandien‐28‐säure‐methyl­ester

The structures of methyl 3β‐acetoxy‐12‐oxo‐18β‐olean‐28‐oate [C₃₃H₅₂O₅, (I)] and methyl 3β‐acetoxy‐12,19‐dioxoolean‐9(11),13(18)‐dien‐28‐oate [C₃₃H₄₆O₆, (II)] are described. In (I), all rings are in the chair conformation, rings D and E are cis and the other rings trans‐fused. In compound (II), only rings A and E are in the chair conformation, ring B has a distorted chair conformation, ring C a distorted half‐boat and ring D an insignificantly distorted half‐chair conformation.     

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

ＣｒｙｓｔａｌａｎｄＭｏｌｅｃｕｌａｒＳｔｒｕｃｔｕｒｅｏｆ５，６，７，８，９，１０－Ｈｅｘａｈｙｄｒｏ－３－（４－ｍｅｔｈｙｌｐｈｅｎｙｌａｍｉｎｏ）－２－ｔｈｉｏｘｏｑｕｉｎｏｘａｌｉｎｅＳｕｎＤａ－Ｑｉｎｇ；ＬａｎｇＪｉａｎ－Ｐｉｎｇ；ＬｕＺｈ...     

A pharmacophore model for NK2 antagonist comprising compounds from several structurally diverse classes

A neurokinin 2 (NK2) antagonist pharmacophore model has been developed on the basis of five non-peptide antagonists from several structurally diverse classes. To evaluate the pharmacophore model, another 20 antagonists were fitted to the model. By use of exhaustive conformational analysis (MMFFs force field and the GB/SA hydration model) and least-squares molecular superimposition studies, 23 of the 25 antagonists were fitted to the model in a low energy conformation with a low RMS value. The pharmacophore model is described by four pharmacophore elements: Three hydrophobic groups and a hydrogen bond donor represented as a vector. The hydrophobic groups are generally aromatic rings, but this is not a requirement. The antagonists bind in an extended conformation with two aromatic rings in a parallel displaced and tilted conformation. The model was able to explain the enantioselectivity of SR48968 and GR159897.     

Synthesis and Crystal Structure of Monocarbonyl Analogs of Curcumin

Two monocarbonyl analogs of curcumin containing bis(2,6-difluorobenzyl) were synthesized,and their molecular structures were characterized by 1H NMR,ESI-MS,and X-ray crystallography.In this paper,the crystal structures of these two analogs(A75 and C75) are described and compared with their bis(2-fluorobenzyl) analogues as well as with the available data of curcumin.The cyclopentane rings in A75 have an envelope conformation,while the cyclohexane ring in C75 has a chair conformation.The compounds are symmetrical and the central structure of A75 and C75 connects with two benzylidene rings through E,E-oriented double bonding.     

Synthesis and structure of macrocyclic bis(hydroxynaphthoic amide)s connected by an achiral or chiral diamine

Macrocyclic bis(hydroxynaphthoic amide)s 6, connected by an achiral or chiral diamine, were synthesized by the tandem Claisen rearrangement. CD spectra, X-ray crystallographic analyses, and variable-temperature NMR measurements of the chiral bis(hydroxynaphthoic amide)s revealed that the two hydroxynaphthalene rings in these macrocycles adopt a twisted conformation both in solution and in the crystalline state because of the steric hindrance between the two hydroxynaphthalene rings and that the chirality of the twisted conformation is generated by that of the chiral linker. Theoretical calculations revealed that the chiral linker works effectively to favor energetically one conformer of the diastereomers, although a flipping process was possible and can be observed to occur on the NMR time scale in variable-temperature experiments.     

Oleana‐12(13),15(16)‐diene‐3α,28‐diyl di­acetate

The title compound, C₃₄H₅₂O₄, consists of five six‐membered rings. Barring the two rings, with double bonds, all other rings are in chair conformations. Mean‐plane and ring‐puckering calculations indicate these two rings to be in distorted‐chair conformations, with distortion towards the boat conformation. There are no strong hydrogen bonds and the structure is stabilized by van der Waals interactions only. The structure is compared with those reported for other triterpenes.     

Structure of the P-diastereomer of 1,2;3,4;5,6-tris-O-(diethyl-amidothionephosphate)galactite,C18H38N3O6P3S3

Conclusions An x-ray diffraction structural analysis showed that the P-diastereomer of 1,2;3,4;5,6-tris-O-(diethylamidothionephosphate)galactite (C₁₈H₃₈N₃O₆P₃S₁₈) with melting point 178.5-179C has terminal dioxaphospholane rings in a cis arrangement. One of these rings has planar conformation, while the other has twist conformation. These rings also differ in the configuration of the phosphorus atom. The central ring has twist conformation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1408–1410, June, 1988.     

Polyfuryl(aryl)alkanes and their derivatives. 13. Molecular structure of bis(5-methyl-2-furyl)(4-methoxyphenyl)methane and tris(5-methyl-2furyl)methane

4-Methoxyphenylbis(5-methyl-2-furyl)methane (I) and tris(5-methyl-2-furyl)methane (II) were investigated by x-ray crystallographic analysis. It was established that the molecules of (I) have a propeller conformation with C_s symmetry, and the furan rings are turned with the oxygen atoms towards the methine hydrogen atom. The molecule of (II) has a different conformation with C_2v symmetry; one of the furan rings and the methine C-H bond lie ideally in one plane, and the other two furan rings are arranged symmetrically with the oxygen atoms in relation to this bond and incline toward eclipsing of the exocyclic C-C bond.For Communication 12, see [1].Kubansk State Technological University, Krasnodar. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 648–653, May, 1996.     

5,5'-双(4-甲基苯)-2,2-联恶唑的晶体结构及构象

本文报道5,5'-双(4-甲基苯基)-2,2'-联恶唑(POOP)的晶体结构,并辅以分子力学法(MM-X程序)计算,探讨了POOP分子的基态构象.     

Spirane—III 3,3′-spirobi[benzo-[2H.4H]-[1.5]-dioxepin]

The conformation of the mentioned new spiran system has been determined by NMR spectroscopy. It contains two heterocyclic rings in the chair form, is chiral and shows a twofold axis of symmetry.     

A model for describing the conformations of flexible 6-membered rings—I : The non-chair conformations

An empirical model for calculating the torsional angles for flexible 6-membered rings is presented in terms of three independent parameters, two geometrical and one pseudorotation angle. The rings are classified according to four estimators, the fit of the model depending upon their values. Equations are given for defining any conformation by a point in a 2-dimensional pathway. Some examples have been examined in the light of this model.