Methodology for Identification of Phenolic Acids in Complex Phenolic Mixtures by High-Resolution Two-Dimensional Nuclear Magnetic Resonance. Application to Methanolic Extracts of Two Oregano Species

Abstract

Spectroscopic methodology in analyzing two-dimensional (2D) NMR spectra of a mixture of several phenolic compounds that occur in natural products is described. Particular emphasis has been given to the determination of scalar coupling connectivities by homonuclear 2D correlated spectroscopy (COSY), remote intraresidue connectivities by totally correlated spectroscopy (TOCSY), and spatially close but uncoupled 1H nuclei by homonuclear 2D nuclear Overhauser effect spectroscopy (NOESY/ROESY). Preliminary data to identify phenolic acids in the methanolic extracts from two oregano plants are also reported. Keywords: Oregano; phenolic acids; 1H NMR; COSY; TOCSY; NOESY/ROESY