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PubMed2004

Experimental and theoretical investigations of structural trends for selenium(IV) imides and oxides: X-ray structure of Se3(NAd)2.

The thermal decomposition of Se(NAd)(2) (Ad = 1-adamantyl) in THF was monitored by (77)Se NMR and shown to give the novel cyclic selenium imide Se(3)(NAd)(2) as one of the products. An X-ray structural determination showed that Se(3)(NAd)(2) is a puckered five-membered ring with d(Se-Se) = 2.404(1) A and |d(Se-N)| = 1.873(4) A. On the basis of (77)Se NMR data, other decomposition products include the six-membered ring Se(3)(NAd)(3), and the four-membered rings AdNSe(micro-NAd)(2)SeO and OSe(micro-NAd)(2)SeO. The energies for the cyclodimerization of E(NR)(2) and RNEO (E = S, Se; R = H, Me, (t)Bu, SiMe(3)), and the cycloaddition reactions of RNSeO with E(NR)(2), RNSO(2) with Se(NR)(2), and S(NR)(2) with Se(NR)(2) have been calculated at MP2, CCSD, and CCSD(T) levels of theory using the cc-pVDZ basis sets and B3PW91/6-31G* optimized geometries. Sulfur(IV) and selenium(IV) diimide monomers are predicted to be stable, the sole exception being Se(NSiMe(3))(2) that shows a tendency toward cyclodimerization. The cyclodimerization energy for RNSeO and the cycloaddition reaction energies of RNSeO with Se(NR)(2) as well as that of RNSO(2) with Se(NR)(2) are negative, consistent with the observed formation of OSe(micro-N(t)Bu)(2)SeO, OSe(micro-N(t)Bu)(2)SeN(t)Bu, and O(2)S(micro-N(t)Bu)(2)SeN(t)Bu, respectively. Cycloaddition is unlikely when one of the reactants is a sulfur(IV) diimide.

Journal Article↗
PubMed2006

Aryl isocyanate, carbodiimide, and isocyanide prepared from carbon dioxide. A metathetical group-transfer tale involving a titanium-imide zwitterion.

Carbon dioxide can be readily converted quantitatively and under mild conditions into the aryl isocyanate and symmetrical carbodiimide via a metathetical reaction involving a zwitterionic titanium imide (nacnac)Ti=NAr(CH(3)B(C(6)F(5))(3)) (nacnac(-) = [ArNC((t)Bu)](2)CH, Ar = 2,6-(i)Pr(2)C(6)H(3)). The metathetical process to generate isocyanates allows also for facile formation of sterically demanding aryl isocyanide, by a deoxygenation route. Labeling studies using enriched (13)CO(2) are also described.

Journal Article↗
PubMed2002

Novel radical alkylation of carboxylic imides.

Although alkylation is one of the most important and fundamental organic reactions, radical-mediated alkylations of carboxylic acid derivatives have not been well studied. The first successful radical alkylation of carboxylic imides is achieved by the addition of an alkyl radical to a ketene O,N-acetal and the subsequent cleavage of N-O bond. It is noteworthy that alkyl halides activated with an electron-withdrawing group undergo alkylations under tin-free conditions due to 1,2-phenyl transfer from silyl to oxygen.

Journal Article↗
PubMed2003

Synthesis and characterization of the monomeric imides Ar'MNAr' ' (M = Ga or In; Ar' or Ar' ' = terphenyl ligands) with two-coordinate gallium and indium.

Reaction of Ar'MMAr' (M = Ga or In) with N3Ar' ' (Ar' = C6H3-2,6-Dipp2, Dipp = C6H3-2,6-Pri2, Ar' ' = C6H3-2,6(Xyl-4-But)2) afforded the first monomeric imides of heavier group 13 elements with two-coordinate metals. Planar, trans-bent structures with short M-N bond distances were observed, which are consistent with lone pair character at both M and N and a bond order less than the formally expected triple one.

Journal Article↗
PubMed2004

Hydrogenolysis of [PhBP3]Fe[triple bond]N-p-tolyl: probing the reactivity of an iron imide with H2.

This paper describes the reductive hydrogenolysis of a low-spin (S = 1/2) iron(III) imide. Pseudotetrahedral [PhBP3]FeIIIN-p-tolyl is reduced by hydrogen at ambient temperature and pressure in benzene solution. The reduction appears to proceed in a stepwise fashion. An intermediate S = 2 iron(II) anilide, [PhBP3]Fe(N(H)-p-tolyl), is observed and has been independently generated and structurally characterized. Prolonged hydrogenolysis in benzene results in the complete hydrogenolysis of the Fe-N linkage to release H2N-p-tolyl. The major iron-containing product formed from this step is the diamagnetic cyclohexadienyl complex, [PhBP3]Fe(eta5-cyclohexadienyl), which has also been independently prepared and structurally characterized. Evidence is presented to suggest that the final [PhBP3]Fe(eta5-cyclohexadienyl) product is formed via benzene insertion into a reactive [PhBP3]FeII-H intermediate.

Journal Article↗
PubMed1986

Buspirone analogues. 2. Structure-activity relationships of aromatic imide derivatives.

Several analogues of the novel anxiolytic buspirone were synthesized and evaluated in vivo for tranquilizing activity and their ability to reverse neuroleptic-induced catalepsy. The in vitro binding affinities of these compounds were also examined for both the alpha 1 and dopamine D2 receptor systems. The general structure-activity relationships of this series highlight compounds 17, 21, and 32 as having anticonflict activity. Each of these structures contains the 1-(2-pyrimidinyl)piperazine moiety linked by a tetramethylene chain to a variable cyclic imide moiety. Compound 32 (4,4-dimethyl-1-[4-[4-(2-pyrimidinyl)-1-piperazinyl]butyl]-2,6- piperidinedione) was found to be equipotent with buspirone in its anxiolytic activity and was therefore selected for extensive preclinical characterization. The pharmacology of buspirone and 32 is contrasted, and the potent serotonin agonist properties of 32 are discussed with reference to its potential contribution to the anxioselective mechanism of this compound.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1983

Synthesis of aminomethyl-substituted cyclic imide derivatives for evaluation as anticonvulsants.

A series of aminomethyl-substituted cyclic imides (II) based on the 2,5-pyrrolidinedione (X = CH2, succinimide) and 2,4-imidazolidinedione (X = NH, hydantoin) ring systems have been prepared. The compounds were designed on the basis of a potential interaction in the gamma-aminobutyric acid (GABA) neurotransmitter system and evaluated for anticonvulsant activity. The 3-(aminomethyl)-2,5-pyrrolidinediones were prepared by a dehydration procedure beginning with N-benzyl-2-(aminomethyl)succinic acid, whereas the 3-(aminomethyl)-3-methyl-2,3-pyrrolidinediones were best obtained by fusion of the amine salts of 2-(aminomethyl)-2-methylsuccinic acid. The hydantoin derivative, 5-(aminomethyl)-5-methyl-2,4-imidazolidinedione, was obtained by standard procedures. Although none of the compounds tested showed significant activity against convulsions induced by pentylenetetrazole (PTZ), some showed significant activity against maximal electroshock seizures in mice. Possible reasons for the lack of anti-PTZ activity and directions for further testing are discussed.

Animals↗
PubMed1999

2-Amino-3-substituted-6-[(E)-1-phenyl-2-(N-methylcarbamoyl)vinyl]imid azo[1,2-a]pyridines as a novel class of inhibitors of human rhinovirus: stereospecific synthesis and antiviral activity.

A series of 2-amino-3-substituted-6-[(E)-1-phenyl-2-(N-methylcarbamoyl)vinyl]+ ++imid azo[1,2-a]pyridines 1a-i, structurally related to Enviroxime and its analogous benzimidazoles, was designed and prepared for testing as antirhinovirus agents. The imidazo ring in this class of compounds was constructed starting from the aminopyridine after tosylation and subsequent treatment with the appropriate acetamides. The key steps in the synthesis include the development and use of a new Horner-Emmons reagent for the direct incorporation of methyl vinylcarboxamide. The reaction was stereospecific in the substrates 5a-f leading exclusively to the desired E-isomer and avoiding the use of reverse-phase preparative HPLC for the separation of both possible isomers before antiviral activity evaluation. The isopropylsulfonyl group, known as the best substituent at the 1-position in the benzimidazole SAR in terms of activity, was introduced in this new series of imidazo[1,2-a]pyridines via halogen-metal exchange and subsequent treatment with isopropyl isopropanethiolsulfonate. Compounds 1a-i were evaluated in plaque reduction assay and in a cytopathic effect assay. Compounds 1b-d,h exhibited a strong antirhinovirus activity, and no apparent cellular toxicity was visible. The substitution at the 3-position was required for activity. Surprisingly the isopropylsulfonyl in this family of compounds did not enhance the activity as in the case of benzimidazoles. Instead, compound 1i was 4 times less active than its phenyl and sulfide partners. The chemistry as well as the biological evaluation are discussed.

Antiviral Agents↗
PubMed1999

Substitution at the F-ring N-imide of the indolocarbazole antitumor drug NB-506 increases the cytotoxicity, DNA binding, and topoisomerase I inhibition activities.

The antitumor drug NB-506, which is currently undergoing phase I/II clinical trials, contains a DNA-intercalating indolocarbazole chromophore substituted with a glucose residue. In addition to interacting with DNA, the drug stabilizes the topoisomerase I-DNA covalent complex. To reinforce the DNA binding and anti-topoisomerase I activities of NB-506, an analogue containing a new substituent on the naphthalimide ring F was synthesized. The N-formylamino group of NB-506 has been replaced with a more hydrophilic group, N-bis(hydroxymethyl)methylamino. In this study we show that the incorporation of a longer substituent on the N6 position effectively reinforces both the interaction with DNA and the capacity of the drug to maintain the integrity of the topoisomerase I-DNA covalent complexes. The strength and the mode of binding of the drugs to DNA were studied by complementary biophysical techniques including absorption, fluorescence, and circular and linear dichroism. Various biochemical procedures were applied to investigate the effects on human topoisomerase I using plasmid DNA as well as restriction fragments. The drug binding sites and the positions of the topoisomerase I-mediated cleavage sites were mapped with nucleotide resolution using footprinting and sequencing techniques. Cytotoxicity measurements performed with various human cancer cell lines (HCT-116, DLD-1, MKN-45) indicate that the newly designed drug is 3 to 4 times more toxic to colon and gastric cancer cells than NB-506. Therefore, the results suggest that the antitumor activity of indolocarbazole-based drugs can be enhanced by incorporating DNA and/or topoisomerase I reactive groups. They also support the hypothesis that the substituent on the imide nitrogen on the F ring of NB-506 has direct interaction with the molecular target. The study helps to define the structure-activity relationships in the indolocarbazole series of antitumor agents targeting topoisomerase I.

Animals↗
PubMed2002

Nucleophilicity in ionic liquids. 2.(1) Cation effects on halide nucleophilicity in a series of bis(trifluoromethylsulfonyl)imide ionic liquids.

In this work, the nucleophilicities of chloride, bromide, and iodide have been determined in the ionic liquids [bmim][N(Tf)(2)], [bm(2)im][N(Tf)(2)], and [bmpy][N(Tf)(2)] (where bmim = 1-butyl-3-methylimidazolium, bm(2)im = 1-butyl-2,3-dimethylimidazolium, bmpy = 1-butyl-1-methylpyrrolidinium, and N(Tf)(2) = bis(trifluoromethylsulfonyl)imide). It was found that in the [bmim](+) ionic liquid, chloride was the least nucleophilic halide, but that changing the cation of the ionic liquid affected the relative nucleophilicities of the halides. The activation parameters DeltaH(), DeltaS(), and DeltaG() have been estimated for the reaction of chloride in each ionic liquid, and compared to a similar reaction in dichloromethane, where these parameters were found for reaction by both the free ion and the ion pair.

Journal Article↗
PubMed2003

Studies on quinazolines. 11. Intramolecular imidate-amide rearrangement of 2-substituted 4-(omega-chloroalkoxy)quinazoline derivatives. 1,3 -O --> N shift of chloroalkyl groups via cyclic 1,3-azaoxonium intermediates.

The omega-chloroalkylation of 2-substituted quinazolin-4(3H)-one derivatives 1 and 2 with Br-(CH(2))(n)-Cl (n = 2-4) and the intramolecular imidate-amide rearrangement of the alkylated products are described. At room temperature, the 2-phenyl substituent promoted O-alkylation, whereas the less steric 2-benzyl group led to a higher ratio of N-alkylation. The investigation of the O-alkylated products, 4-omega-chloroalkoxyquinazolines, revealed that the migration of omega-chloroethyl and omega-chloropropyl groups from oxygen to nitrogen should be intramolecular via five- and six-membered cyclic 1,3-azaoxonium intermediates, respectively. Competition between rearrangement and nucleophilic substitution results in the formation of 7a,b and 8a,b from the nucleophilic substitution of 4a,b and 6a,b, respectively.

Alkylation↗
PubMed2005

Improved imide receptors by imprinting using pyrimidine-based fluorescent reporter monomers.

[reaction: see text] Optically responsive receptors toward imides based on 6-substituted 2,4-bis(acrylamido)pyrimidines are presented. The monomers were readily prepared in good yield. Solution binding to 1-benzyluracil (BU) monitored by 1H NMR appeared lower than a previously reported pyridine-based monomer. However, as indicated by 1H NMR and IR spectral investigations, the association strength was demonstrated to be "masked" by dimerization of the pyrimidine-based monomer units. Thus, from dilution experiments, a dimerization constant of 731 M(-1) was estimated for the pyrimidine-based monomer 2,4-bis(acrylamido)-6-piperidinopyrimidine whereas for the pyridine-based monomer 2,6-bis(acrylamido)pyridine, no self-association was observed. This precluded an accurate determination of the binding constant for BU to the former monomer whereas for the latter a binding constant of 757 M(-1) was measured. Despite the strong self-association, the novel monomer was shown to lead to enhanced imprinting effects when compared to imprinted polymers prepared analogously, but using the pyridine-based monomer as the recognition element. This was attributed to a higher intrinsic binding affinity exhibited by the pyrimidine based host monomer vis a vis the guest and the existence in the former of more than one interaction site for the guest. The monomers exhibited fluorescence emission informative of the mode of monomer incorporation in the polymer and the presence of guest species. Thus, the fluorescence was rapidly and selectively quenched upon template addition, with the degree of quenching correlating with binding affinity and the amount of template bound to the polymer.

Journal Article↗
PubMed2005

Catalytic asymmetric synthesis of chiral allylic amines. Evaluation of ferrocenyloxazoline palladacycle catalysts and imidate motifs.

Palladium(II) catalysts based on a ferrocenyloxazoline palladacyclic (FOP) scaffold were synthesized and evaluated for the rearrangement of prochiral allylic N-(4-methoxyphenyl)benzimidates. When iodide-bridged dimer FOP precatalysts are activated by reaction with excess silver trifluoroacetate, the allylic rearrangement of both E and Z prochiral primary allylic N-(4-methoxyphenyl)benzimidates takes place at room temperature to give the corresponding chiral allylic N-(4-methoxyphenyl)benzamides in high yield and good ee (typically 81-95%). Several allylic imidate motifs were evaluated also. Because the corresponding enantioenriched allylic amide products can be deprotected in good yield to give enantioenriched allylic amines, allylic N-aryltrifluoroacetimidates were identified as promising substrates.

Allylamine↗
PubMed2006

Synthesis and reactivity of imide-derived bisvinyl phosphates. Reactivity of 2,6-disubstituted 1,4-dihydropyridines.

Symmetrical and unsymmetrical 2,6-disubstituted dihydropyridines were prepared in high yields under mild conditions using the Suzuki and Stille Pd-catalyzed coupling reactions of imide-derived bisvinyl phosphates with a range of aryl, heteroaryl, and alkenyl moieties. The alkylation reaction at C-4 easily afforded original tri- and tetrasubstituted dihydropyridines. Hydrolysis of the latter under acidic condition provided efficiently either open-chain 1,5-diketones or di- or trisubstituted pyridines.

Journal Article↗
PubMed1997

Highly Enantioselective Claisen Rearrangement of Imidates Derived from Primary Allyl Alcohols.

A highly enantioselective and diastereoselective Claisen rearrangement of N-arylimidates derived from an axially chiral binaphthylamine auxiliary is reported. Upon deprotonation of the imidates with lithium diethylamide, the resultant azaenolates rearrange at 0 degrees C to give anti alpha,beta-disubstituted, gamma,delta-unsaturated N-binaphthyl amides. A iodolactonization/zinc reduction sequence readily converts these amides into the corresponding carboxylic acids of 91-95% ee and allows an efficient recovery of the chiral auxiliary.

Journal Article↗
PubMed2005

Raman investigation of the ionic liquid N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide and its mixture with LiN(SO2CF3)2.

A preliminary Raman investigation of the ionic liquid N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR(13)TFSI) and its 2/1 complex with the lithium salt LiN(SO(2)CF(3))(2) is reported. The study was performed over a temperature range extending from -100 to +60 degrees C, i.e., with PYR(13)TFSI in the crystalline and melt states. For comparison purposes, the study was extended to PYR(13)I, which is the precursor used in the synthesis of PYR(13)TFSI.

Journal Article↗
PubMed2006

In situ STM investigation of gold reconstruction and of silicon electrodeposition on Au(111) in the room temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide.

The electrodeposition of silicon on Au(111) was investigated by cyclic voltammety (CV) and by in situ scanning tunneling microscopy (STM) in the room temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide with a SiCl(4) concentration of 0.1 mol/L. A main reduction process begins in the cyclic voltammogram at about -1800 mV versus ferrocene/ferrocinium, which is correlated to the electrodeposition of elemental semiconducting silicon. It has been found that at an electrode potential more negative than the open circuit potential (OCP), the Au(111) surface is subject to a restructuring/reconstruction both in the case of the pure ionic liquid and in the presence of SiCl(4). The first STM-probed silicon islands with 150-450 pm in height appear at about -1700 mV versus ferrocene/ferrocinium. Their lateral and vertical growth leads to the formation of a rough layer with silicon islands of up to 1 nm in height. At about -1800 mV the islands merge and form silicon agglomerates. In situ I/U tunneling spectroscopy reveals a band gap of 1.1 +/- 0.2 eV for layers of about 5 nm in height, a value that has to be expected for semiconducting silicon.

Journal Article↗
PubMed2006

Enhancement of lithium amide to lithium imide transition via mechanical activation.

The decomposition of lithium amide (LiNH2) to lithium imide (Li2NH) and ammonia (NH3) with and without high-energy ball milling is investigated to lay a foundation for identifying methods to enhance the hydrogen uptake/release of the lithium amide and lithium hydride mixture. A wide range of analytical instruments are utilized to provide unambiguous evidence of the effect of mechanical activation. It is shown that ball milling reduces the onset temperature for the decomposition of LiNH2 from 120 degrees C to room temperature. The enhanced decomposition via ball milling is attributed to mechanical activation related to the formation of nanocrystallites, the reduced particle size, the increased surface area, and the decreased activation energy. The more mechanical activation there is, then the more improvement there is in enhancing the decomposition of LiNH2. It also is found that the activation energy for the decomposition of LiNH2 without ball milling is 243.98 kJ/mol, which is reduced to 222.20 kJ/mol after ball milling at room temperature for 45 min and is further reduced to 138.05 kJ/mol after ball milling for 180 min. The rate of the isothermal decomposition at the later phase of the LiNH2 decomposition is controlled by diffusion of NH3 through the Li2NH layer.

Journal Article↗