Search results for "reo"
showing 10 items of 7464 documents
Pyrazolo[3,4-d][1,2,3]triazolo[1,5-a]pyrimidine: a new ring system through Dimroth rearrangement
2008
Abstract Derivatives of the new ring system pyrazolo[3,4- d ][1,2,3]triazolo[1,5- a ]pyrimidine were synthesized from the corresponding angular isomers, through a Dimroth rearrangement, in quantitative yields. Preliminary computational studies demonstrated that this class of compounds could be a good candidate as DNA intercalating agents.
Can copper(II) mediate Hoogsteen base-pairing in a left-handed DNA duplex? A pulse EPR study
2010
Pulse EPR spectroscopy is sued to investigate possible structural features of the copper(II) ion coordinated to poly(dG-dC) poly(dG-dC) in a frozen aqueous solution, and the structural change of the polynucleotide induced by the presence of the metal ion. Two different copper species were identified and their geometry explained by a molecular model. According to this model, one species is exclusively coordinated to a single guanine with the N7 nitrogen atom forming a coordinative bond with the copper. In the other species, a guanine and a cytosine form a ternary complex together with the copper ion. A copper crosslink between the N7 of guanine and N3 of cytosine is proposed as the most prob…
Crystal and solution structures of di-n-butyltin(IV) complexes of 5-[(E)-2-(4-methoxyphenyl)-1-diazenyl]quinolin-8-ol and benzoic acid derivatives: E…
2009
Abstract Reactions of nBu2SnCl(L1) (1), where L1 = acid residue of 5-[(E)-2-(4-methoxyphenyl)-1-diazenyl]quinolin-8-ol, with various substituted benzoic acids in refluxing toluene, in the presence of triethylamine, yielded dimeric mixed ligand di-n-butyltin(IV) complexes of composition [nBu2Sn(L1)(L2–6)]2 where L2 = benzene carboxylate (2), L3 = 2-[(E)-2-(2-hydroxy-5-methylphenyl)-1-diazenyl]benzoate (3), L4 = 5-[(E)-2-(4-methylphenyl)-1-diazenyl]-2-hydroxybenzoate (4), L5 = 2-{(E)-4-hydroxy-3-[(E)-4-chlorophenyliminomethyl]-phenyldiazenyl}benzoate (5) and L6 = 2-[(E)-(3-formyl-4-hydroxyphenyl)-diazenyl]benzoate (6). All complexes (1–6) have been characterized by elemental analyses, IR, 1H,…
Desulfurization and ring opening of thiirane induced by tantalocene trihydride complexes: Synthesis, reactivity and X-ray structure of Cp′2Ta(=S)(S-i…
1999
The reaction of the tantalocene trihydride complexes Cp′ 2 TaH 3 1 (Cp′= η 5 -C 5 H 4 t Bu) or Cp″CpTaH 3 1′ (Cp″= η 5 -C 5 H 2 -1,2-Me 2 -4- t Bu) with propylene sulfide was found to proceed via an unprecedented sulfur transfer and regioselective ring opening reaction at once to yield sulfido-thiolato tantalocene complexes Cp′ 2 Ta(S)(S- i Pr) 2a whose structure has been determined by X-ray crystallography or Cp″CpTa(S)(S- i Pr) 2′a . Complex 1 reacts with ethylene sulfide to give Cp′ 2 Ta(S)(S–Et) 2b . The reactivity of 2a towards a variety of electrophilic moities has been investigated: protonation (with HBF 4 ) and alkylation (with MeI) reactions occur at the terminal sulfur ligand, …
Synthesis and stereochemical studies of 2-substituted thiazolidine-4-carboxamide derivatives
2000
A series of new 2-substituted thiazolidine-4-carboxamide derivatives which have potentially useful immunological properties, have been synthesized in a stereoselective manner by coupling 2-subsituted thiazolidine-4-carboxylic acids with amines or amino esters. The structure of these compounds was established by combination of NMR methods and by X-ray analysis.
Intermolecular oxidative dehydrogenative 3,3′-coupling of benzo[b]furans and benzo[b]thiophenes promoted by DDQ/H+: total synthesis of shandougenine B
2016
With an excess of a strong acid, 2,3-dichloro-5,6-dicyano-1,4-quinone (DDQ) is shown to promote metal-free intermolecular oxidative dehydrogenative (ODH) 3,3'-coupling of 2-aryl-benzo[b]furans and 2-aryl-benzo[b]thiophenes up to 92% yield as demonstrated with 9 substrates. Based on the analysis of oxidation potentials and molecular orbitals combined with EPR, NMR and UV-Vis observations, the studied reaction is initiated by a DDQ-substrate charge transfer complex and presumably proceeds via oxidation of the substrate into an electrophilic radical cation that further reacts with another molecule of a neutral substrate. The coupling reactivity can easily be predicted from the oxidation potent…
Stereochemical features of the hydrolysis of 9,10-epoxystearic acid catalysed by plant and mammalian epoxide hydrolases
2002
cis-9,10-Epoxystearic acid was used as a tool to probe the active sites of epoxide hydrolases (EHs) of mammalian and plant origin. We have compared the stereochemical features of the hydrolysis of this substrate catalysed by soluble and membrane-bound rat liver EHs, by soluble EH (purified to apparent homogeneity) obtained from maize seedlings or celeriac roots, and by recombinant soybean EH expressed in yeast. Plant EHs were found to differ in their enantioselectivity, i.e. their ability to discriminate between the two enantiomers of 9,10-epoxystearic acid. For example, while the maize enzyme hydrated both enantiomers at the same rate, the EH from soybean exhibited very high enantioselecti…
1,3-Dipolar Cycloaddition Reactions of Indan-1-one Enamines across Arylnitrile Oxides Leading to Novel Cyclic Isoxazoline Derivatives
2013
Synthesis of a series of cyclic fused-isoxazolines has been accomplished by regioselective and diastereoselective 1,3-dipolar cycloaddition of 3-methylindan-1-one enamines (1a, 1b, 1c) and 3-phenylindan-1-one enamines (2a, 2b, 2c) to arylnitrile oxides (3d, 3e, 3f, 3g, 3h). The structure of the cycloadducts was elucidated by 1H and 13C NMR spectroscopy. The proposed regio- and stereochemistry of fused-compounds (4) and (5) has also been corroborated by two single-crystal X-ray diffraction studies carried out on 4-methyl-8b-morpholinyl-3-(p-tolyl)-4H-3a,8b-dihydroindeno[2,3-d]isoxazoline (4be) and 3-(p-anisyl)-4-phenyl-8b-pyrrolidinyl-4H-3a,8b-dihydroindeno[2,3-d]isoxazoline (5af) and by mea…
Il caracol quadrato in Sicilia (XVI secolo)
2022
Square spiral staircases appear in Sicily during the 16th century in different contexts and for different purposes. This contribution focuses on two case studies at the “opposite poles” of a casuistry that shares the common characteristics of suspended ramps revolving within a square masonry box around a central void. By analysing these cases we find a probable link with models from Spain. At the same time, they demonstrate a common descent from a constructive culture rooted in the Spanish and Mediterranean stereotomic experience of the early modern age.