The biosynthesis of the herbicide cornexistin in the fungus Paecilomyces variotii was investigated by full sequencing of its genome, knockout of key genes within its biosynthetic gene cluster and isolation and identification of intermediate compounds. The general biosynthetic pathway resembles that of byssochlamic acid and other nonadrides in the early stages, but differs in requiring fewer enzymes in the key nonadride dimerisation step, and in the removal of one maleic anhydride moiety.

Quantitative NMR spectroscopy (qNMR) is an essential tool in organic chemistry, with applications including reaction monitoring, mechanistic analysis, and purity determination. Establishing the correct acquisition rate for consecutive qNMR scans requires knowledge of the longitudinal relaxation time constants (T 1 ) for all of the nuclei being monitored. We report a simple method that is about 10-fold faster than the conventional inversion recovery technique for the estimation of T 1 .

We present a signal enhancement strategy for benchtop NMR that produces SNR increases on the order of 10 to 30 fold by collapsing the target resonance into an extremely narrow...

The accuracy and practicality of measuring heteronuclear scalar coupling constants, J, from modern NMR experimental methods is examined, based on F1 or F2 evolution of J in HSQMBC (including EXSIDE) and HMBC experiments. The results from these methods are compared to both robust experimental data (derived from coupled C spectra), computed (Density Functional Theory) and literature values where available. We report on the accuracy, ease of use and time efficiency of these multi-dimensional methods and highlight their extent and limitations.

Benchtop NMR spectrometers provide a promising alternative to high-field NMR for applications that are limited by instrument size and/or cost. 19 F benchtop NMR is attractive due to the larger chemical shift range of 19 F relative to 1 H and the lack of background signal in most applications. However, practical applications of benchtop 19 F NMR are limited by its low sensitivity due to the relatively weak field strengths of benchtop NMR spectrometers. Here we present a sensitivity-enhancement strategy that combines SABRE (Signal Amplification By Reversible Exchange) hyperpolarization with the multiplet refocusing method SHARPER (Sensitive, Homogeneous, And Resolved PEaks in Real time). When applied to a range of fluoropyridines, SABRE-SHARPER achieves overall signal enhancements of up to 5700-fold through the combined effects of hyperpolarization and linenarrowing. This approach can be generalized to the analysis of mixtures through the use of a selective variant of the SHARPER sequence, selSHARPER. The ability of SABRE-selSHARPER to simultaneously boost sensitivity and discriminate between two components of a mixture is demonstrated, where selectivity is achieved through a combination of selective excitation and the choice of polarization transfer field during the SABRE step.

We extend the SHARPER NMR method designed to accommodate challenging reaction conditions to monitor simultaneously multiple resonances such as those of a reactant (2,6-difluoro-4-methoxyphenylboronic acid) and product (3,5-difluoroanisole).

Since its discovery in mid-20th century, the sensitivity of Nuclear Magnetic Resonance (NMR) has increased steadily, in part due to the design of new, sophisticated NMR experiments. Here we report on a liquid-state NMR methodology that significantly increases the sensitivity of diffusion coefficient measurements of pure compounds, allowing to estimate their sizes using a much reduced amount of material. In this method, the diffusion coefficients are being measured by analysing narrow and intense singlets, which are invariant to magnetic field inhomogeneities. The singlets are obtained through signal acquisition embedded in short (<0.5 ms) spin-echo intervals separated by non-selective 180° or 90° pulses, suppressing the chemical shift evolution of resonances and their splitting due to J couplings. The achieved 10−100 sensitivity enhancement results in a 100−10000-fold time saving. Using high field cryoprobe NMR spectrometers, this makes it possible to measure a diffusion coefficient of a medium-size organic molecule in a matter of minutes with as little as a few hundred nanograms of material.

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