Fourier transform pulsed-gradient spin-echo studies of molecular diffusion

Azadirachtin: an update

Over the course of the past half century, the structural elucidation of unknown natural products has undergone a tremendous revolution Before World War II, a chemist would have relied almost exclusively on the art of chemical synthesis, primarily in the form of degradation and derivatization reactions, to develop and test structural hypotheses in a process that often took years to complete when grams of material were available Today, a battery of advanced spectroscopic methods, such as multidimensional NMR spectroscopy and high-resolution mass spectrometry, not to mention X-ray crystallography, exist for the expeditious assignment of structures to highly complex molecules isolated from nature in milligram or sub-milligram quantities In fact, it could be argued that the characterization of natural products has become a routine task, one which no longer even requires a reaction flask! This Review makes the case that imaginative detective work and chemical synthesis still have important roles to play in the process of solving nature's most intriguing molecular puzzles

https://onlinelibrary.wiley.com/doi/pdf/10.1002/anie.200590046

Chasing molecules that were never there: misassigned natural products and the role of chemical synthesis in modern structure elucidation.

The neem tree has long been recognized for its unique properties both against insects and in improving human health. It is grown in most tropical and sub-tropical areas of the world for shade, reforestation and for the production of row material for natural insecticides and medicines. Azadirachtin, a complex tetranortriterpenoid limonoid from the neem seeds, is the main component responsible for the toxic effects in insects. Six international conferences on neem and a vast scientific literature report both the antifeedant and physiological effects of neem. This article reviews the behavioral and physiological properties of azadirachtin, including effects on insect reproduction, direct and "secondary" antifeedancy, and the physiological effects measured as growth reduction, increased mortality and abnormal and delayed moults. These effects are here categorized in two ways: direct effects on cells and tissues and indirect effects exerted via the endocrine system. It also describes the work carried out to date to identify the mode of action of azadirachtin at the cellular level. The differential effects between animal phyla and over non-target organisms are discussed and point to its potential success as a safe insecticide.

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Azadirachtin from the neem tree Azadirachta indica: its action against insects

The activation of small molecules by dinuclear complexes of copper and other metals

An NMR spectroscopic study of azadirachtin and its trimethyl ether

Multipulse NMR in liquids

Syntheses and spectral properties of tropocoronands, a new class of versatile metal-complexing macrocycles derived from aminotropone imines

13C n.m.r. chemical shifts and carbon-proton coupling constants of 2-substituted pyrimidines are reported. The carbon chemical shifts are correlated with π-electron densities. Substituents which cause deshielding at the directly bound carbon (e.g. NH2, OCH3 and F) exert a more powerful effect in the benzene series than in the pyridine or pyrimidine series. The carbon-proton coupling constants do not correlate with the electronegativity of the substituents. Carbon-proton coupling constants and proton-proton coupling constants over the same number of bonds do not obey the Karabatsos relationship. The changes in the carbon-proton coupling constants in 2(1H)-pyrimidinone and 2(1H)-pyrimidinethione which accompany anion and cation formation are reported.

Christopher J. Turner

Papers

An NMR spectroscopic study of azadirachtin and its trimethyl ether

Multipulse NMR in liquids

Syntheses and spectral properties of tropocoronands, a new class of versatile metal-complexing macrocycles derived from aminotropone imines

13C n.m.r. spectra of 2-substituted pyrimidines

One- and two-dimensional 31P spin-echo studies of myocardial ATP and phosphocreatine☆