Cinnamic acid derivatives from welsh onion (Allium fistulosum) and their antibacterial and cytotoxic activities

Abstract

Introduction Cinnamic acids are a class of compounds based on phenyl propanoid backbone (C6-C3) isolated from plants and microorganisms, exhibiting interesting biological activities. Objective To characterise cinnamic acids through the phytochemical study of welsh onion, Allium fistulosum, and to evaluate their antibacterial and cytotoxic properties. Material and methods The phytochemical study of A. fistulosum was performed through chromatographic techniques, including reversed phase medium-pressure liquid chromatography (MPLC) and high-pressure liquid chromatography (HPLC). Preliminary analysis of crude chromatographic fractions from the organic extracts was carried out by proton nuclear magnetic resonance (H-1-NMR) in order to prioritise the study of those having phenyl propanoid skeleton. The structural identification of the isolated compounds was performed through analysis of spectroscopic data, mainly one-dimensional (1D) and two-dimensional (2D) NMR. The antibacterial activity was assessed against gram negative (Escherichia coli) and gram positive (Staphylococcus aureus) bacteria while the cytotoxic property was evaluated on breast cancer cell line (MCF-7). Results The H-1-NMR study of crude fractions and application of a straightforward method to purify the phenyl propanoid compounds by reversed phase MPLC and HPLC, allowed the effortless isolation of several cinnamic acids, including two new rare phenolic imidates (1 and 2). The use of an entirely NMR approach for structural elucidation of the isolated metabolites allowed the isolated material to be kept for further pharmacological tests. Conclusion These results corroborate the importance of the use of 1D and 2D NMR to the identification of new phenyl propanoids, potential lead compounds against bacteria and cancer cells.