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11.
Aubrey L. Burrows Brian F.G. Johnson Jack Lewis David G. Parker 《Journal of organometallic chemistry》1977,127(1):C22-C24
A shift reagent has been employed to demonstrate the sterically-hindered environment of the methoxy group in tricarbonyl(5-endo-methoxycyclohexa-1,-diene)iron relative to that of the methoxy group in the 5-exo analogue. 相似文献
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5-Ethoxy-3-(trichloromethyl)-1, 2, 4-oxadiazole (V) was synthesized to elucidate the chemistry involved in the preparation of the hitherto unreported alkoxy-1, 2, 4-oxadiazoles and to determine the effect of the isosteric replacement of sulfur by oxygen on antifungal activity. Heating the “amino-oxime” tautomer II of trichloroacetamidoxime with ethyl chloroformate furnished exclusively the O-acylated product III. The trans configuration of III accounts for its resistance to cyclize under a variety of conditions, in contrast to the general behaviour of acylated amidoximes. Pyrolysis of III at 160° yielded IV which exists in the keto form. Refluxing IV with ethyl iodide in the presence of silver oxide gave an isomeric mixture which was separated by v.p.c. to give V and VI. Compound V retained 60% of the overall activity of the corresponding sulfur analog. 相似文献
15.
The conformation of the amino acid residues, glycine, alanine, proline, and phenylalanine have been predicted from molecular orbital calculations of appropriate model compounds. Using the current main chain rotation convention (, ) the principle conformations were found to be glycine (0, 0), alanine (240, 240), proline (120, 330) and phenylalanine (30, 330). Several secondary conformations were also found for glycine. A comparison of the predicted conformations is in good agreement with experimental data on comparable residues or model compounds.Supported by National Institutes of Health Grants No. FR 5409-07 and GM 16312-01.Recipient of a Public Health Service Research Career Development Award AM 1159-01. 相似文献
16.
[reaction: see text] A study toward a possible biomimetic hetero Diels-Alder reaction is reported between humulene and a novel tropolone ortho-quinone methide. A suitable tropolone ortho-quinone methide precursor has been prepared from 3-methyl-2-furoate. Heating the ortho-quinone methide precursor gave a tropolone ortho-quinone methide, which in the presence of humulene underwent a hetero Diels-Alder reaction to give a deoxy analogue of epolone B. 相似文献
17.
Gérard Hopfgartner Claude Piguet Jack D. Henion 《Journal of the American Society for Mass Spectrometry》1994,5(8):748-756
Double-helical [M2L2] n+, triple-helical [M2L3] n+, and toroidal [M3L3] n+ (M = Cu, Co, Fe, Ni, La, Eu, Gd, Tb, or Lu) supramolecular complexes have been fully characterized by ion spray mass spectrometry (IS-MS). The IS-MS spectra from pure acetonitrile solutions reflect the nature of the cations present in solution with conservation of the charge state and allow an efficient qualitative speciation of the compounds. The mass spectrometry results can be correlated with other powerful techniques (nuclear magnetic resonance and electronic spectroscopy) for the characterization of supramolecular complexes in solution, Structural information is obtained by collision-induced dissociation, which strongly depends on the metal ions used in the supramolecular complexes and on the various connectivities and topologies of the ligands. When the ligand contains 3,5dimethoxybenzyl groups bound to the benzimidazole rings, the partial fragmentation of the complexes is associated with a decrease of the total charge of the complexes and the appearance of the characteristic fragment at m/z 151 that corresponds to the 3,5-dimethoxybenzyl cation. A detailed analysis of the fragmentation pathways of these supramolecular complexes suggests that the metal-nitrogen coordination bonds are very strong in the gas phase. 相似文献
18.
The oxidation of [PtCl3(C2H4)]- by Cl2 in aqueous solution, to yield CH2ClCH2OH and [PtCl4]2-, has been shown to proceed through the following sequence of steps: [PtCl3(C2H4)] Cl2Cl [PtCl5(CH2CH2Cl)]2- [PtCl5(CH2CH2OH)]2- → [PtCl42- + CH2ClCH2OHEach of the steps and intermediates in this mechanistic sequence has been identified and characterized. 相似文献
19.
Jack Huet 《Tetrahedron》1978,34(16):2473-2479
The measure of relative stabilities of β-alcoxystyrene isomers I: C6H5-CHCH-OR shows that the trans compound is the most stable when RCH3 and C2H5 and the cis compound is the most stable when Ri-C3H7 and t-C4H9. The orientation of the OR group can be determined by RMN 13C. The stabilities of these molecules are discussed in terms of non bounded attractive interactions. This interpretation is confirmed by the measure of relative stabilities of α-methyl β-alcoxy (and acetoxy)-styrene isomers II: C6H5-C(CH3)CH-OR. (RCH3, C2H5 et COCH3). 相似文献
20.
[3-3H]-valine was efficiently synthesised from sodium α-ketoisovalerate. With a β-lactam negative mutant of C. acremonium, l-[1-14C-3-3H]-valine and dl-[1-14C-3-3H]-valine were independently incorporated into the Arnstein tripeptide dimer, i.e. Bis-δ-(l-α-aminodipyl)-l-cystinyl-bis-d-valine, with full retention of trieium at C-3 of the d-valine residue. This result strongly suggested retention of configuration at C-3 of valine when the tripeptide was biosynthesised, and further limited the number of possible mechanisms for the biosynthesis of penicillins. 相似文献