Characterization of di- and trimethoxybenzaldehydes by analysis of deshielding gradients obtained with Eu(fod)3 shift reagent

Eu(fod)₃ shift reagent was used to simplify PMR spectra from isomeric mono-, di and trimethoxybenzaldehydes. Deshielding gradients, obtained by plotting induced shift vs. molar ratio of [Eu(fod)₃]/[substrate] made it possible to assign methoxyl proton signals to the correct positional substituent in polymethoxylated benzaldehydes. Anomalous upfield shifts for the aldehydic protons of 2,6-dimethoxy- and 2,4,6-trimethoxybenzaldehyde were observed with Eu(fod)₃ Various instances of long-range (⁵J) proton coupling between the aldehydic proton and a meta-proton provide insight to the geometry of the substrate in the complexed state with Eu(fod)₃. Di- and trimethoxybenzaldehydes are important precursors for the synthesis of the correspondingly methoxylated amphetamines which are of pharmacological and forensic interest because of abuse and illicit manufacture.     

Quasiquadrupolar echoes in solids containing spins-12 triads undergoing hindered reorientation

The spin echo responses to resonant 90⁰-τ-β_φ⁰ rf pulse sequences in solids containing spin-$\text{1}\text{2}$ triads undergoing hindered rotations, are shown to be predicted by a model of dipolar coupled quasiparticles of spin-$\text{3}\text{2}$.     

Addition of sulphenic acids to unactivated alkynes to give alkenyl sulphoxides

Sulphenic acids, conveniently generated by thermolysis of readily available β-cyanosulphoxides, added regiospecifically in good yield to 1-alkynes to provide syntheticall useful alkenyl sulphoxides.     

Mass spectrometric studies of some novel sulfonamides

A recent paper described the overall 5-endo cyclisation of homoallylic sulfonamides to give pyrrolidines. This reaction was also used to prepare polycyclic systems. Mass spectrometric analysis using classical electron ionisation spectra and accurate mass measurement played a vital role in confirming the proposed structures for the products. These materials were not amenable to newer mass spectrometric methods and this study shows the continuing importance of older techniques.     

D/H amide isotope effect in model alpha-helical peptides

The contribution of amide related hydrogen bonds to protein stability has recently been evaluated using the "Cm experiment", which measures the D/H amide isotope effect in proteins. We show here using isolated alpha-helical peptides that there is a significant effect of denaturant concentration on the measured D/H isotope effect, and that valid comparison of different proteins requires correcting for differences in denaturant (GdmHCl) concentration. Finally our results suggest that H-bonds in an isolated alpha-helix may contribute more to helix stability because of less strain compared to those in helical proteins and that the buried helical H-bonds in helical proteins are not necessarily energetically more favorable than solvent exposed H-bonds in isolated helices.