Computer-Aided ¹³C NMR Chemical Profiling of Crude Natural Extracts without Fractionation

Abstract

A computer-aided, C NMR-based dereplication method is presented for the chemical profiling of natural extracts without any fractionation. An algorithm was developed in order to compare theC NMR chemical shifts obtained from a single routine spectrum with a set of predicted NMR data stored in a natural metabolite database. The algorithm evaluates the quality of the matching between experimental and predicted data by calculating a score function and returns the list of metabolites that are most likely to be present in the studied extract. The proof of principle of the method is demonstrated on a crude alkaloid extract obtained from the leaves of Peumus boldus, resulting in the identification of eight alkaloids, including isocorydine, rogersine, boldine, reticuline, coclaurine, laurotetanine, N-methylcoclaurine, and norisocorydine, as well as three monoterpenes, namely, p-cymene, eucalyptol, and α-terpinene. The results were compared to those obtained with other methods, either involving a fractionation step before the chemical profiling process or using mass spectrometry detection in the infusion mode or coupled to gas chromatography.

Green Extraction of Alkaloids and Polyphenols from Peumus boldus Leaves with Natural Deep Eutectic Solvents and Profiling by HPLC-PDA-IT-MS/MS and HPLC-QTOF-MS/MS

“…, which correspond to the loss of NH 3 and CH 3 NH 2 , respectively. These data agrees with the fragmentation patterns of coclaurine and N-methylcoclaurine [29][30][31]. In addition to this fragmentation pattern, these compounds suffer neutral loss of CH 3 OH, which explain the fragment ion at m/z 237.…”

“…For compounds corresponding to peaks 9 and 10 in positive ionization mode, the molecular formulas of ions at m/z , generated by the sequential loss of two methyl radicals and 28 Da from -CO loss, respectively. These data and the comparison of elution order for standards in C-18 columns suggest that the identity of peaks 9 and 10 could unambiguously be assigned to isoboldine and boldine [29,31,33,34]. For compound corresponding to peak 15 in positive ionization mode, the molecular formula of ion at m/z 329.16323 was predicted as C 19 H 23 NO 4 .…”

1H and 13C NMR for the Profiling of Natural Product Extracts: Theory and Applications

“…This approach is being enhanced by availability of 13C NMR databases and predictive software which list compounds that are most likely to be present in the extract. These results have been found to be comparable to those obtained using LC-MS and GC-MS, which require fractionation and sample preparation [62].…”

Analytical Methods of Isolation and Identification

“…13 C-NMR spectra can provide structural information of organic compounds, including the number, types, and chemical environment of carbon atoms [27]. It is one of the important means for the structural identification of organic compounds.…”