Mass spectrometry of 3,4-dihydroquinazolin-4-ones of pharmaceutical interest. Part 3 . Electron ionization mass spectra of 2-substituted-3-(5′-pyrazolyl)-4(3H)-quinazolinones

The fragmentation reactions induced by electron impact of eighteen title compounds has been investigated with the aid of low beam energy spectra (14 eV, nom. value), metastable ion detection, high resolution measurements and labelling experiments. The loss of the 4-carbonyl oxygen together with the 3-substituent, which constitutes a characteristic fragmentation route of 3-aryl and 3-heteroaromatic substituted-4(3H)-quinazolinones, is again observed, but the presence of a carboxyethyl group at the 4′-position of the pyrazole ring is responsible of an anomalous loss of 47 daltons from the molecular ion. Lastly, a comparison with the previously described behaviour of 3-(5′-isoxazolyl) derivatives was carried out.     

1H-NMR,Ultraviolet and infrared spectra of some (Z)-α-(phenyl)-β-(2-furyl), -(2-pyrrolyl) and -(N-methyl-2-pyrrolyl)acrylonitriles

The ¹H-nmr data of some (Z)-α-(p-substituted-phenyl)-β-(2-furyl), -(2-pyrrolyl), and -(N-methyl-2-pyrrolyl)-acrylonitriles have been investigated to indicate the preferred conformation and to establish the conformational preferences of the β-heterocyclic ring. The ultraviolet spectra have been discussed in order to obtain information about the chromophores responsible for the absorption. The infrared spectra have been analyzed for the identification of the main absorption frequencies of cyano and ethylenic groups and to assign the characteristic absorption bands to specific normal vibrations of the heteroaromatic nuclei.     

Copper(II) complexes of N-terminal protected tri- and tetra-peptides containing histidine residues

Copper(II) complexes of peptides containing two or three histidyl residues (Ac-HisGlyHis-OH, Ac-HisGlyHis-NHMe, Ac-HisHisGlyHis-OH and Ac-HisHisGlyHis-NHMe) have been studied by potentiometric, UV-Vis, EPR and CD spectroscopic measurements. The imidazole nitrogen atoms are described as the primary metal binding sites of all ligands resulting in the formation of various macrochelates in the pH range 4 to 7. The (Nim, N-, Nim)-co-ordinated [CuH-1L]0+ complexes were mainly detected in samples containing free carboxylates at the C-termini, whilst the [CuH-2L]-(0) complexes were the predominant species in slightly alkaline solution and their binding modes were described via 4N-co-ordination (Nim, N-, N-, Nim) in (7,5,6)-membered fused chelate rings. Deprotonation and co-ordination of the third amide nitrogens were detected above pH approximately 9 in all cases.     

High resolution electrospray and electrospray tandem mass spectra of rotenone and its isoxazoline cycloadducts

An evaluation of the gas-phase ion chemistry of rotenone (1) by electrospray ionisation (ESI) mass spectrometry (MS) and tandem mass spectrometry (MS2) is presented, aiming at providing tools for its determination in natural and biological matrices. The behaviour of its cycloadducts with benzonitrile-N-oxide (2) and 2,4,6-trimethylbenzonitrile-N-oxide (3) was also evaluated and the MS data thus obtained have provided evidence into the mechanism of formation of the key product ion at m/z 192 which can be considered a marker in the MS and MS2 spectra of rotenone and its derivatives.     

NMR stereospecific long-range coupling and preferred conformations in some (E)- and (Z)-α-phenyl-β-[2-(N-methyl)nitropyrrolyl] acrylic acids

NMR data have been used to assign the stereochemistry to some new (E)- and (Z)-α-phenyl-β-[2-(N-methyl)nitropyrrolyl]acrylic acids. The (E)-molecules are biased in the s-cis conformation showing NMR spectroscopic features strictly depending on the conformation.The analysis of the NMR spectra reveals that the (Z)-isomers exist also in the s-cis conformation.     

Wavy graphene sheets from electrochemical sewing of corannulene

The presence of non-hexagonal rings in the honeycomb carbon arrangement of graphene produces rippled graphene layers with valuable chemical and physical properties. In principle, a bottom-up approach to introducing distortion from planarity of a graphene sheet can be achieved by careful insertion of curved polyaromatic hydrocarbons during the growth of the lattice. Corannulene, the archetype of such non-planar polyaromatic hydrocarbons, can act as an ideal wrinkling motif in 2D carbon nanostructures. Herein we report an electrochemical bottom-up method to obtain egg-box shaped nanographene structures through a polycondensation of corannulene that produces a new conducting layered material. Characterization of this new polymeric material by electrochemistry, spectroscopy, electron microscopy (SEM and TEM), scanning probe microscopy, and laser desorption-ionization time of flight mass spectrometry provides strong evidence that the anodic polymerization of corannulene, combined with electrochemically induced oxidative cyclodehydrogenations (Scholl reactions), leads to polycorannulene with a wavy graphene-like structure.

A bottom-up synthesis of wavy graphene structures obtained through an anodic polymerization process, combined with an electrochemically triggered oxidative cyclodehydrogenation, of the bowl-shaped polyaromatic hydrocarbon corannulene.     

Crystal structure and reactivity of 2-chloro-3,5-dinitrothiophene and of 2-phenylsulphonyl-3,5-dinitrothiophene with nucleophiles

The geometry obtained by a crystal structure determination of the title compounds, as compared with that of the analogous benzene derivatives, along with results of ab initio calculations, is used to interpret the different S_NAr reactivities in some thiophene and benzene compounds. The smaller rotation of the nitro groups with respect to the aromatic rings observed in thiophene derivatives should be considered a relevant factor in the higher reactivity in the thiophene series.     

Synthesis and characterization of 4-hydroxy-3-phenylprolines

4-Hydroxy-3-phenylprolines were synthesized via 1-acetyl-2,2-diethoxycarbonyl-2,3-dihydro-3-phenyl-1H-pyrrole. Reversed phase hplc resulted in the isolation of the products which were characterized by ¹H and ¹³C nmr spectroscopy.     

Solvent effects in the reaction of 2-thiophenesulfonyl chloride with aniline

The second order rate constants k₂ and the activation parameters for the reaction of 2-thiophenesulfonyl chloride with aniline together with solution enthalpies of the reactants have been measured in methanol, ethanol, 2-propanol, acetonitrile and acetone. The reaction rates are slower in dipolar aprotic solvents than in protic ones due to a remarkable activation negative entropy. The rate constants k₂ are correlated with empirical solvent polarity parameters. The data seem in accord with a S_AN reaction mechanism.