Determination of Polyphenolic Phytochemicals using Highly Deshielded -OH 1H-NMR Signals

Introduction - Quantitative analysis of plant extracts is a tedious and time consuming process requiring chromatographic techniques and/or the use of specilised hyphenated spectroscopic methods. Thus, investigation of a rapidmethod capable for the determination of bioactive constituents is of major importance. Objective - To employ high resolution H-1-NMR spectroscopy of the - OH spectral region, as a rapid method for the simultaneous determination and quantification of polyphenolic phytochemicals in crude oregano and olive leaf extracts without any prior isolation step. Methodology - A critical overview of experimental parameters that influence the resolution of the - OH groups is provided with emphasis on the nature of the extraction solvent, effects of dilution, pH, temperature and nature of the NMR solvent. The compounds were assigned with the use of H-1-NMR, 2D H-1-C-13 HMBC NMR and spiking experiments with model compounds. Results - The method was applied for the NMR analysis of natural product extracts and the results were found to be in good agreement with those obtained with the use of the time consuming HPLC-DAD, preparative LC and LC-SPE-NMR. Conclusion - The method is rapid, selective, with very good analytical performance characteristics, which support the efficiency of the suggested methodology. Copyright (C) 2016 John Wiley & Sons, Ltd.