NMR and HRMS/MS studies of acetophenone derivatives isolated from Acronychia pedunculata (L.) Miq.-Rutaceae
Phenylated acetophenone derivatives constitute a characteristic chemical group of constituents of Acronychia pedunculata (L.) Miq. . In continuation of a previous study, seven acetophenone dimmers were isolated among them five structural isomers [2,3]. Such acetophenones exhibit particular structural characteristics as fully substituted and polyhydroxylated aromatic rings. The presence of inter- and intra-molecular hydrogen bonds and their conformational behavior due to the occurrence of rotamers complicates their structure elucidation. In the present study, NMR spectroscopy was used in order to determine the structures and the different rotamers of all isolated acetophenones. The developed methodology included variation of different solvents (DMSO-d 6, CDCl3, C6D6) as well as acquisition of NMR spectra in a broad range of temperatures (0 to 47oC) where acrovestone was used as a model compound. Two principal rotamers of acrovestone are the most populated in CDCl3 solution at 0oC, while at 47oC their representative NMR signals are not resolved due to fast inter-conversion between the rotamers. According to our study, Acronychia acetophenone rotamers' determination can be accomplished with NMR spectroscopy, by changing the polarity of solvent used as well as by altering temperature conditions of measurements. In parallel, an LC-APCI(+)-HRMS and MS/MS method was developed for the analysis of acetophenone derivatives using a LTQ-Orbitrap mass analyzer. A characteristic ion corresponding to the major fragment at m/z 319 was defined and used as diagnostic peak of the isolated phenylated acetophenone dimers. This novel developed LC-MS/MS method could be applied for the detection and identification of acrovestone-type prenylated acetophenone dimers in other substrates.
References: 1. Adsersen A et al. (2007) Biochem Syst Ecol 17: 447–453.
2. Kouloura E et al. (2008) Planta Med 74: 1051–1052.
3. Kouloura E et al. (2009) Planta Med 75: 914.