title: Deciphering the influence of column chemistry and mass spectrometry settings for the analyses of geometrical isomers of L-chicoric acid.
abstract: Resolving the chemo-diversity of plant extract samples is an essential step for in-depth analyses of natural products which often exhibit promising biological activities. One of the challenges in this endeavor has been the confident differentiation of geometrical isomers. In this study, we investigated these aspects in chromatography (column chemistry and mobile phase composition) and mass spectrometry settings with regards to better differentiation of geometrical isomers. A standard of a hydroxycinnamic acid (HCA) derivative, L-chicoric acid (L-CA) - a di-acylated caffeoyltartaric acid ester found in a number of plant families - was used. Geometrical isomers of L-CA were formed by exposing the compound to ultraviolet (UV) radiation, to mimic the natural environment. The high performance liquid chromatography photo-diode array (HPLC-PDA) and ultra-high performance liquid chromatography mass spectrometry (UHPLC-MS) platforms were used to analyze the trans and cis geometrical isomers of L-CA. The HPLC-PDA results confirmed the generation of two cis geometrical isomers following UV exposure of the authentic trans-L-CA standard. Furthermore, the HPLC-PDA analyses demonstrated that the changes in both column chemistry (reverse-phase: C18, biphenyl, phenyl-hexyl and pentafluorophenyl propyl) and mobile phase composition (aqueous acetonitrile and aqueous methanol) affect the chromatographic elution profiles of the L-CA isomers. The MS results, on the other hand, revealed undisputed fragmentation differences between the geometrical isomers of L-CA. Thus, this study demonstrates that the identification of the L-CA isomers can be achieved more efficiently and confidently with good chromatography coupled to well-optimized mass spectrometry conditions, a requirement which has been proven impossible with other types of HCA derivatives. Moreover, differences in the binding modes of L-CA geometrical isomers to the HIV type 1 integrase enzyme were observed, suggesting a synergistic anti-HIV-1 activity of these isomers.
authors.affiliation: Department of Biochemistry, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, South Africa.
authors.forename: Keabetswe
authors.initials: K
authors.lastname: Masike
authors.affiliation: Department of Biochemistry, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, South Africa.
authors.forename: Fidele
authors.initials: F
authors.lastname: Tugizimana
authors.affiliation: Department of Biochemistry, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, South Africa.
authors.forename: Nombuso
authors.initials: N
authors.lastname: Ndlovu
authors.affiliation: Department of Chemistry, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, South Africa.
authors.forename: Elize
authors.initials: E
authors.lastname: Smit
authors.affiliation: Department of Microbiology, Biochemistry and Food Biotechnology, University of the Free State, Bloemfontein, South Africa.
authors.forename: Louis
authors.initials: L
authors.lastname: du Preez
authors.affiliation: Department of Biochemistry, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, South Africa.
authors.forename: Ian
authors.initials: I
authors.lastname: Dubery
authors.affiliation: Department of Biochemistry, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, South Africa. Electronic address: emadala@uj.ac.za.
authors.forename: Edwin
authors.initials: E
authors.lastname: Madala
mesh_terms: D002109:Caffeic Acids / Q000737:chemistry* / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D015658:HIV Infections / Q000188:drug therapy / Q000821:virology; D019427:HIV Integrase / Q000378:metabolism; D019428:HIV Integrase Inhibitors / Q000737:chemistry* / Q000494:pharmacology; D015497:HIV-1 / Q000201:enzymology; D006801:Humans; D007536:Isomerism; D013058:Mass Spectrometry / Q000379:methods*; D062105:Molecular Docking Simulation; D013386:Succinates / Q000737:chemistry* / Q000494:pharmacology
chemical_list: D002109:Caffeic Acids; D019428:HIV Integrase Inhibitors; D013386:Succinates; D019427:HIV Integrase; C100435:chicoric acid
keywords: Chicoric acid (di-caffeoyltartaric acid); Fragmentation; Geometrical isomers; Mass spectrometry; Photochemical reaction; Ultra-violet (UV) light; cis/trans isomerization