Absolute Minimal Sampling of Homonuclear 2D NMR TOCSY Spectra for High‐Throughput Applications of Complex Mixtures

Abstract

Modern applications of 2D NMR spectroscopy to diagnostic screening, metabolomics, quality control, and other high-throughput applications are often limited by the time-consuming sampling requirements along the indirect time domain t1. 2D Total Correlation Spectroscopy (TOCSY) provides unique spin-connectivity information for the analysis of a large number of compounds in complex mixtures, but standard methods typically require >100 t1-increments for an accurate spectral reconstruction, rendering these experiments ineffective for high-throughput applications. Here, we demonstrate for a complex metabolite mixture how absolute minimal sampling (AMS), based on direct fitting of resonance frequencies and amplitudes in the time domain, yields an accurate spectral reconstruction of TOCSY spectra using as few as 16 t1-points. This permits the rapid collection of homonuclear 2D NMR experiments at high resolution with measurement times that previously were the realm of 1D experiments only.

Practical aspects of the simultaneous collection of COSY and TOCSY spectra

“…All these MFA methods do not require any special software or hardware requirement and can be run in automation mode as performed with the regular COSY and TOCSY experiments. The proposed experiments can also take advantage of other options, namely, equivalent sequences to provide phase‐sensitive data, the use of non‐uniform sampling to reduce experimental times or to improve digital resolution along the F1 dimension, as reported in conventional COSY and TOCSY experiments . We are convinced that the ideas and results presented here will be useful for future developments of time‐efficient MFA supersequences.…”

Non‐Uniform and Absolute Minimal Sampling for High‐Throughput Multidimensional NMR Applications

“…AMS also has useful applicability for homonuclear 2D experiments, such as 2D TOCSY,o fc omplexm ixtures as encountered in metabolomics. [54] As ah omonucleare xperiment, it has significantly higher sensitivity than the 2D 13 CÀ 1 HH SQC experiment (when at 13 Cn atural abundance). Therefore, many TOCSY for protein resonance assignments.T he 4p anels belongt o2differentr esidues of AK as indicated in the figures.T he solid black linescorrespond to 1D cross-section along the w 1 (CO) dimension of aregular 3D FT spectrum with 44 complex t 1 points, whereas the red bars correspond to the AMS-derived frequencies and amplitudes obtained with only 4 t 1 points (Panels A, B) or 6 t 1 points (Panels C, D).…”

“…AMS also has useful applicability for homonuclear 2D experiments, such as 2D TOCSY, of complex mixtures as encountered in metabolomics . As a homonuclear experiment, it has significantly higher sensitivity than the 2D 13 C− 1 H HSQC experiment (when at 13 C natural abundance).…”

“…peak volumes), the TOCSY cross‐peak intensities can display a large dynamic range, which makes the solution to the optimization problem of Equation (5) more challenging and susceptible to noise, especially for low intensity peaks. In order to overcome these challenges, we find a moderately conservative NUS schedule most effective when paired with an extensive search for the global minimum of Equation (5) . For the NUS schedule, linear sampling for the initial increments followed by triangular sampling works particularly well with a total of about 16 increments .…”

“…In order to overcome these challenges, we find a moderately conservative NUS schedule most effective when paired with an extensive search for the global minimum of Equation (5) . For the NUS schedule, linear sampling for the initial increments followed by triangular sampling works particularly well with a total of about 16 increments . For triangular sampling, the spacing between adjacent t 1 points is linearly increased, which amounts to a quadratic distribution of t 1 points.…”