Differentiation of prototropic ions in regioisomeric caffeoyl quinic acids by electrospray ion mobility mass spectrometry.

RATIONALE: A series of dietary important regioisomeric chlorogenic acids were investigated by ion mobility mass spectrometry (IM-MS). The existence of prototropic isomers separated in the drift dimension was observed and investigated further using tandem mass spectrometry (MS/MS) and compared with suitable synthetic analogues. METHODS: Using a quadrupole ion mobility time-of-flight mass spectrometer, the IM-MS and IM-MS/MS spectra of selected chlorogenic acids were recorded in the negative ion mode and compared with synthetic analogues. RESULTS: Regioisomeric di- and monocaffeoyl quinic acids can be readily separated and investigated using IM-MS. Comparison of drift times allows assignment of the regiochemistry of precursor ions as well as for fragment ions. For 5-caffeoyl quinic acid the existence of prototropic ions was suggested and probed using synthetic analogues, unable to show this type of isomerism. These investigations suggest the presence of prototropic isomers with carboxylate and phenolate sites, respectively. CONCLUSIONS: We report on IM-MS measurements on regioisomeric mono- and dicaffeoyl quinic acids, which are important dietary natural products. Both classes of compounds can be readily separated by IM-MS in the drift time dimension and, following MS(2) experiments, fragment ion regiochemistry unambiguously determined. 5-Caffeoyl quinic acid shows two IM-MS signals, which we assign to prototropic isomers after comparison with suitable synthetic analogues, with a negative charge located at the carboxalate or phenolate functionality, respectively.

Understanding the fate of chlorogenic acids in coffee roasting using mass spectrometry based targeted and non-targeted analytical strategies.

Coffee is one of mankind's most popular beverages obtained from green coffee beans by roasting. Much effort has been expended towards the chemical characterisation of the components of the roasted coffee bean, frequently termed melanoidines, which are dominated byproducts formed from its most relevant secondary metabolites - chlorogenic acids. However, impeded by a lack of suitable authentic reference standards and analytical techniques sufficiently powerful for providing insight into an extraordinarily complex enigmatic material, unsurprisingly little structural and mechanistic information about the products of coffee roasting is available. Here we report on the characterisation of low molecular weight melanoidine fractions of roasted coffee using a conceptually novel combination of targeted and non-targeted mass spectrometrical techniques. We provide an unprecedented account of the chemical composition of roasted coffee beans. Using a targeted analytical approach we show for the first time, by comparison to authentic reference standards obtained by chemical synthesis, that chlorogenic acids follow four distinct reaction pathways including epimerization, acyl migration, lactonisation and dehydration. The analytical strategy employed in a non-targeted approach uses high resolution mass spectrometry to identify the most abundant molecular formulas present in roasted coffee samples and model roasts followed by van Krevelen and homologous series analysis. We identified the molecular formulas formed from reactions of chlorogenic acids, carbohydrates and proteins, both between classes of compounds and within same classes of compounds. Furthermore, we identified two new classes of compounds formed from chlorogenic acids during roasting, chlorogenic acid acetates and O-phenolic quinoyl and shikimoyl esters of chlorogenic acids.

Synthesis of tri-substituted biaryl based trianglimines: formation of C3-symmetrical and non-symmetrical regioisomers.

2-Functionalised aromatic monoaldehydes were synthesised in good to excellent yields by reacting 4-bromo-2-fluorobenzaldehyde with different secondary amines and phenol. The Suzuki-coupling reaction of the newly functionalised aromatic monoaldehydes with 4-formylphenylboronic acid afforded the corresponding 2-functionalised-4,4'-biphenyldialdehydes in good yields (47-85%). The [3+3]-cyclocondensation reactions of the 2-functionalised-4,4'-biphenyldialdehydes with (1R,2R)-1,2-diaminocyclohexane afforded a mixture of regioisomeric C(3)-symmetrical and non-symmetrical trianglimines. Reduction of the C(3)-symmetrical and the non-symmetrical trianglimines with NaBH(4) in a mixture of THF and MeOH afforded the corresponding trianglamines in high yields.

13-tungstoborate stabilized by an organostannoxane hexamer.

The novel dimethyltin-containing polyanion [{(CH3)2Sn}6(OH)2O2(H2BW13O46)2]12- (1) is composed of two [H2BW13O46]9- clusters linked by an unprecedented planar, hexameric [{(CH3)2Sn}6(OH)2O2]8+ organostannoxane moiety, representing the first X-ray structural characterization of a molecular hybrid organic-inorganic tungstoborate and of the elusive [HnBW13O46](11-n)- species.