首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The biomimetic reactions of epoxygermacrene-D (1) with basic alumina afforded three new interesting compounds (4, 5, and 6), two of which (4 and 6) have the same carbon skeleton as that of periplanone-A (3), a sexual stimulant for the American cockroach. The remaining one (5) is a bicyclo[3.1.0]hexane derivative, from whch an axisonitrile-3 type compound (14) has been produced. Finally, preisocalamendiol (2) was also converted into 6.  相似文献   

2.
3.
The rate constants, kCR, of ortho- into para-positronium (o-Ps→p-Ps) spin conversion reactions, CR, caused by the high-spin [CoIIsep]2+, [CoIIdinosar]2+ and [CoIIdiamsar]2+ macrocyclic complexes and also by high-spin [CoII sen]2+ tripod complex were measured at several temperatures. The delocalizations, β, of CoII unpaired electrons, promoted by the mentioned ligands, were determined by using the previously established correlations between kCR and the electron delocalization β of unpaired metal electrons. β is given by the ratio between the Racah inter-electronic repulsion parameters of complexes, B, and that of the free ions, B0. The β values are compared with those of the CoII complexes with en (1,2-ethanediamine), pn (1,2 propanediamine) and dien (2,2′ diamino diethylamine) ligands. The kCR rate constants are also compared with those of the Ps oxidation reactions, OR, promoted by the corresponding CoIII complexes. It is concluded that, unlike OR's, the CR's do not occur by formation of hepta-coordinate adducts with Ps atoms.  相似文献   

4.
Barile E  Lanzotti V 《Organic letters》2007,9(18):3603-3606
A new tricyclic diterpenoid, named pre-segetanin (1), and two new diterpenes, named segetanin A and B (2 and 3), the latter based on the rare segetane skeleton, have been identified from the whole plant of sea spurge along with four known segetane diterpenes (4-7). Among them, pre-segetanin (1) has an unprecedented carbon skeleton, whose isolation provides a first insight into the biosynthesis of diterpenoids with a segetane skeleton. The stereostructure elucidation of the isolated metabolites was determined by extensive spectroscopic analysis, including 1D and 2D NMR (COSY, TOCSY, HSQC, HMBC, and ROESY) and HRFABMS experiments.  相似文献   

5.
The hybridization in several cyclic polyacetylene compounds has been calculated by the maximum overlap method, assuming planar and non-planar geometries of the molecules. In the planar configuration the hybrids describing the molecular skeleton deviate from the corresponding bond directions. We have a few “bent” bonds, but in contrast to the situation in small rings, here the deviation angles are negative, i.e., the hybrids point toward the inside of the ring. Non-planar structures in which acetylene groups are kept in a plane and CCH2 or CH2 groups are displaced out of the plane show less deviation from the bond directions of bent bonds. Furthermore, the deviation angles decrease with an increase in the out-of-plane displacement of methylene groups. Finally, when the angle of bending of the molecules approaches 50°, the deviation vanishes, predicting a puckered conformation for the molecules. Correlation between CC stretching vibration frequencies and the corresponding CC bond overlap is discussed.  相似文献   

6.
New forms have been observed for oscillatory Briggs-Rauscher reactions catalyzed by macrocyclic nickel complexes. The number of oscillations in the reaction increases in the presence of cobalt complexes. Suggestions are made on how the catalysts act in these systems.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 3, pp. 167–171, May–June, 1994.  相似文献   

7.
The reaction of 4,6-dimethoxyindoles with stannic chloride results in an oxidative biaryl coupling, producing a series of 2,7′-biindolyls. Reactions of representatives of these biindolyls with p-benzoquinone gave the novel tetraindolyls.  相似文献   

8.
New chiral perazamacrocycles containing four pyrrole rings have been synthesized by the [2+2] condensation of (R,R)-diaminocyclohexane and 5,5'-(alkane-2,2-diyl)bis(1H-pyrrole-2-carbaldehydes). These macrocycles, differing for the alkyl/aryl meso-substituents, were used as ligands in the copper-catalyzed Henry reactions of aromatic and aliphatic aldehydes with nitroalkanes. In the optimized experimental conditions, the condensations of nitromethane and aromatic and aliphatic aldehydes in the presence of catalytic amounts of copper diacetate and methyl-substituted macrocyclic ligand (2:1 ratio) in ethanol at room temperature provided products often with high enantiomeric excesses (up to 95% ee). The positive influence of the macrocyclic structure on the efficiency/enantioselectivity of the catalytic system was demonstrated by comparison with the outcomes of Henry reactions performed using analogous macrocyclic ligands (trianglamines) and open-chain ligands derived from (R,R)-diaminocyclohexane.  相似文献   

9.
A series of macrocyclic ether-esters has been prepared by treating various glycols with adipoyl chloride and various substituted malonyl, succinyl and glutaryl chlorides. The prepared compounds include: 15-ethyl- and 15-phenyl-1,4,7,10,13-pentaoxacyclohexadecane-14,16-dione (5 and 6); 15-methyl-, 15-phenyl-, cis-cyclohexo-[o]-and benzo-[o]-1,4,7,10,13-pentaoxacycloheptadecane-14,17-dione (7–10); trans,trans-1,4,7,10,13,18,21,24,27,30-de-caoxacyclotetratriacontane-15, 32-diene-14,17,31,34-tetraone (11); 1,4,7,10,13-pentaoxacyclooctadecane-14,18-dione (12); 15,15,16,16,17,17-hexafluoro- and 16-methyl-1,4,7,10,13-pentaoxacyclooctadecane-14,18-dione (13 and 14); 1,4,7,10-tetraoxacyclohexadecane-11,16-dione (15); and 1,4,7,10,13-pentaoxacyclononadecane-14,19-dione (16).  相似文献   

10.
The conformation of macrocycles consisting of the uracil and two thiopyrimidine moieties linked by polymethylene spacers depends on the spacer length, intramolecular hydrogen bonds, and the solvent nature. In CDCl3 the intramolecular hydrogen bond (NH) appreciably stabilizes the “skew” conformation but only for the macrocycles with methylene spacers consisting of five carbon atoms. Protonation leads to the cleavage of intramolecular hydrogen bonds, destabilization of the “skew” conformation, and self-association due to the strong intermolecular hydrogen bond involving the acid counterion, and the intermolecular bond is cleaved in a polar solvent.  相似文献   

11.
Multidrug resistance related to the increased expression of P-glycoprotein (P-gp) by cancer cells is the major contributor for the failure of chemotherapeutic treatments. Starting from pharmacophores and data already published and in macrocyclic diterpenes isolated from Euphorbia species, a comprehensive study of pharmacophore definitions of features was performed in order to obtain a new improved four-point pharmacophore able to detect literature and in-house modulators and simultaneously specific enough to avoid the detection of most nonactive molecules in a universe of 152 (literature), 74 (in-house), and 46 (inactive) molecules. This pharmacophore detects 84.2% of the molecules described in the literature, along with 100% detection of in-house isolated compounds and 19.5% of false positives. The importance of the hydrophobic and electron acceptor moieties as essential features for recognition of different molecules by the P-gp drug-binding site is clarified. The best combination of acceptor, donor, hydrophobic, and aromatic characteristics that contribute for the increased selectivity shown by the described pharmacophore is evaluated, and the protonation state of the molecules is also addressed.  相似文献   

12.
Adel A. Mohamed 《Tetrahedron》2007,63(19):4000-4010
A new series of benzo-substituted macrocyclic diamides were prepared by nucleophilic reaction of the appropriate dipotassium salts with the corresponding bis(halo) compounds in refluxing DMF. Treatment of the novel macrocyclic diamides with Lawesson's reagent in refluxing toluene led to the formation of the corresponding macrocyclic dithiodiamides in good yields. Molecular orbital calculations were performed at the semi-empirical level AM1 on some of the studied macrocycles. Thermodynamic functions show that the most stable structures in gas phase that have internal amine groups are less in energy than the other ones that have internal carbonyl groups. The solvent polarity does not appreciably affect the stability trend of the three conformers of each compound due to their comparable dipole moments. A complete and thorough survey of proton affinity (PA) and proton detachment energies (PDE) on each of the possible sites has been performed.  相似文献   

13.
The electron impact mass spectrometric behaviour of five recently synthesized macrocyclic tetraesters is described and discussed in detail with the aid of exact mass measurements, linked scans and collisional activation experiments. The unusual primary loss of a dehydrogenated catecholic radical leads to a very stable cation which is the precursor of the most of the fragmentation products.  相似文献   

14.
Tandem cyclization-cycloaddition reactions of α-diazo ketones with macrocyclic olefins in the presence of rhodium(II) acetate catalyst led to the oxanorbornane fused macrocyclic di- or tetralactone ring systems in moderate yield. This forms the first example of 1,3-dipolar cycloaddition reactions with a macrocyclic olefin as a dipolarophile, affording a variety of new oxanorbornane fused macrocycles with diastereoselectivity.  相似文献   

15.
Conclusions On the basis of the results of a comparison of the mass spectra of macrocyclic pyrrolizidine alkaloids with a known configuration of the side chain (trichodesmine, monocrotaline) with the spectra of incanine, crispatine, and fulvine a hypothesis has been put forward on the relative positions of the substituents at C2 and C3 in the molecules of the three latter compounds.Order of the Red Banner of Labor Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 40–44, January–February, 1974.  相似文献   

16.
The investigation of Briggs-Rauscher reactions (BRR) with nickel complexes have shown that the range of the standard redox potentials of BRR catalysts is at least 0.7–1.7 V. An inner-sphere interaction of metal ions with hydrogen peroxide is a prerequisite of the oscillatory behavior. The unique catalytic properties of the nickel compounds are probably due to their lower redox potential.  相似文献   

17.
13C NMR data are presented for premnolal (13-formyl-11,14-dihydroxypodocarpa-8,11,13-triene), the tetraacetate of nellionol (6α,11,14,16-tetra-O-acetylabieta-8,11,13-trien-7-one), 11-ketosandaracopimar-15-en-8β-ol, sandaracopimar-15-en-1β, 8β-diol and its l-keto derivative, and sandaracopimaran-1β,8β,12β-triol, obtained from Premna latifolia Roxb.  相似文献   

18.
《Polyhedron》1988,7(24):2761-2767
Complexes of the potassium monoethyl ester of [-(4-benzeneazoanilino)-N-benzyl]phosphonic acid, [-(4-benzeneazoanilino)-N-4-hydroxybenzyl]phosphonic acid and [-(4-benzeneazoanilino)-N-4-methoxybenzyl]phosphonic acid with dibenzo- 18-crown-6 and dibenzo-24-crown-8 have been studied. The new complexes were identified and characterized on the basis of elemental and thermogravimetric analysis, conductivity measurements, and UV, IR and 1H NMR spectra. The results obtained were compared with those obtained for the corresponding sodium monoalkyl benzeneazophosphonate complexes. It has been observed that the formation of salt complexes is controlled by a combination of factors, including the metal cation size in relation to the polyether hole, size and charge density of the anion, as well as the choice of the reaction solvent.  相似文献   

19.
20.
Electron impact mass spectrometry has been used together with linked scans, exact mass measurements and mass-analysed ion kinetic energy spectrometry to study nine inacrocyclic polyether lactones in detail. The presence of abundant hydrogenated oxirane ions has been observed for all the compounds examined, and confirmed by kinetic energy release measurements.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号