Coupling of two diazotized 3‐aminothieno[3,4‐c]coumarins with aromatic amines

The coupling reactions of two diazotized 3‐aminothieno[3,4‐c]coumarins were investigated. Compounds 1a , 1b both react with sodium nitrite in concentrated sulphuric acid at 0–5°C to give the diazotized intermediates 2 and 3 , the latter resulting from the acid ‐catalyzed hydrolysis of the lactonic ring of 2 . The in situ formed diazonium salts react with aromatic amines ( 4 ) to afford a series of arylazothiophenes dyes in the form of their ammonium sulfate salts. With diazotized aniline, besides the normally expected phenylazothiophene 10 from the reaction with compound 1a , the corresponding product of acid hydrolysis 11 was also isolated. In at least one of the cases, the thienyl diazonium salt 2 undergoes a Gomberg–Bachmann arylation reaction with p‐nitroaniline to give the 2‐arylthiophene 9 . The direct hydrolysis of compounds 1a , 1b by concentrated sulphuric acid and subsequent oxidative dimerization of the primary product of acid hydrolysis led to compound 12 . J. Heterocyclic Chem., (2011).     

Application of the Floquet theory to multiple quantum NMR of dipolar-coupled multi-spin systems under magic angle spinning

A new analytical Liouville-space representation of the time-propagator under magic angle spinning (MAS) is introduced using the formalized quantum Floquet theory. This approach has the advantage that it is applicable to the analysis of any type of NMR experiment where MAS is combined with multiple-pulse excitation. General relationships describing the spectral parameters in multiple-quantum (MQ) MAS spectra are derived in this representation. Their use is illustrated with an application to double-quantum (DQ) NMR spectra of dipolar-coupled multi-spin systems. Corresponding to the separation of the MAS time-propagator into a rotor modulated and a dephasing component, two distinct mechanisms for DQ excitation are identified. One of them exploits the rotor-modulated component to excite DQ coherences through dipolar-recoupling techniques, which are familiar for spin pairs. Analytical expressions of the integral intensities and linewidths in the resulting DQ sideband pattern are derived in the form of power series expansions of the inverse rotor frequency, of which coefficients depend on structural parameters. In a multi-spin system they can most reliably be extracted in the fast spinning regime. The other mechanism exploits the dephasing component, which is characteristic to multi-spin systems only. This is shown to give rise to DQ coherences by free evolution at full rotor periods. The possibility to exploit it for selective excitation of higher order MQ coherences is discussed. In either case, the dephasing component also leads to residual broadening. The main results of the theoretical developments are demonstrated experimentally on adamantane.     

A mathematical model of aging-related and cortisol induced hippocampal dysfunction

Background  

The hippocampus is essential for declarative memory synthesis and is a core pathological substrate for Alzheimer's disease (AD), the most common aging-related dementing disease. Acute increases in plasma cortisol are associated with transient hippocampal inhibition and retrograde amnesia, while chronic cortisol elevation is associated with hippocampal atrophy. Thus, cortisol levels could be monitored and managed in older people, to decrease their risk of AD type hippocampal dysfunction. We generated an in silicomodel of the chronic effects of elevated plasma cortisol on hippocampal activity and atrophy, using the systems biology mark-up language (SBML). We further challenged the model with biologically based interventions to ascertain if cortisol associated hippocampal dysfunction could be abrogated.     

The structure of veprisinium salt

The structure of a new quaternary dihydrofuroquinoline alkaloid, veprisinium salt, isolated from $\text{Vepris louisii}$ and possessing antibacterial activity, has been determined from spectroscopic and chemical data and confirmed by partial synthesis.     

Veprisine and N-methylpreskimmianine: Novel 2-quinolones from Vepris louisii

The structures of two new 2-quinolone alkaloids, N-methylpreskimmianine and veprisine (7,8-dimethoxy-N-methylflindersine) have been deduced from their spectra and confirmed by partial synthesis from known compounds.     

Cecropiacic acid, a new pentacyclic A-ring seco triterpenoid from .

From the methylated polar extract of stem bark of (Cecropiaceae) a novel triterpenic A-ring seco derivative has been obtained and the structure elucidated by spectroscopic methods.     

Carapolides d,e and f,novel tetranortriterpenoids from the seeds of carapagrandiflora (meliaceae)

Carapolides d and e, two new ring b cleaved tetranortriterpenoids, and carapolide f, a novel tetranortriterpenoid spirolactone, have been isolated from the seeds of $\text{carapa grandiflora}$ and have been assigned structures (1), (3) and (6) on the basis of their ¹H and ¹³C spectroscopic properties.     

The use of two-dimensional long-range δC/δH correlation in conjunction with the one-dimensional proton-coupled 13C NMR spectrum in the structural elucidation of ekeberginine,a new carbazole alkaloid from ekebergia senegalensis (meliaceae)

A new strategy involving the use of 2D long-range δ_C/δ_H correlation in conjunction with the 1D proton-coupled ¹³C NMR spectrum has been applied to the structural elucidation of ekeberginine, a new carbazole alkaloid from the stem bark of $\text{Ekebergia senegalensis}$ (Meliaceae).