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Biomedical subjects

A Marston

Publications and source records attributed to A Marston.

116 records · Page 7Linked to original sources
PubMedDate not supplied

NMR and LC-MSn characterisation of two minor saponins from Ilex paraguariensis.

Two minor saponins obtained from the methanolic extract of the leaves of Ilex paraguariensis have been characterised by 13C-NMR, 1H-NMR, API-MS and chemical hydrolysis as oleanolic acid-3-O-(beta-D-glucopyranosyl-(1-->3)-alpha-L-arabinopyranosyl)-(28-->1)- beta-D-glucopyranosyl ester (guaiacin B) and oleanolic acid-3-O-(beta-D-glucopyranosyl-(1-->3)-(alpha-L-rhamnopyranosyl- (1-->2))-alpha-L-arabinopyranosyl)-(28-->1)-beta-D-glucopyranosyl ester (nudicaucin C). Both are isomeric forms of the known matesaponins 1 (MSP 1) and 2 (MSP 2) and differ only by the nature of the aglycone: they have oleanolic acid instead of ursolic acid, as found in the matesaponins. These minor saponins have not been fully separated from their major isomers MSP 1 and 2 and were characterised by in-mixture NMR analysis, LC-MS and LC-MSn experiments.

Base Sequence↗
PubMedDate not supplied

A rapid TLC bioautographic method for the detection of acetylcholinesterase and butyrylcholinesterase inhibitors in plants.

A simple and rapid bioautographic enzyme assay on TLC plates has been developed for the screening of acetylcholinesterase and butyrylcholinesterase inhibition by plant extracts. Enzyme activity was detected by the conversion of naphthyl acetate into naphthol and the formation of the corresponding purple-coloured diazonium dye with Fast Blue B salt. Inhibitors of cholinesterases produced white spots on the dye-coloured background of the TLC plates. The alkaloids galanthamine and physostigmine, which are known inhibitors of acetylcholinesterase, were used to determine the sensitivity of the assay. Various plant extracts were tested using the bioassay.

Acetylcholinesterase↗
PubMedDate not supplied

On-line identification of unstable catalpol derivatives from Jamesbrittenia fodina by LC-mS and LC-NMR.

LC-UV-MS analysis of the methanol extract of Jamesbrittenia fodina O. M. Hilliard (Scrophulariaceae) revealed the presence of cinnamic ester derivatives. Two isomeric pairs of these constituents were detected, but could not be isolated. In order to identify these unstable compounds, LC-1H-NMR spectra were obtained for each individual isomer and standard NMR measurements were performed in-mixture. The spectra clearly demonstrated that the fractions consisted of mixtures of cis and trans cinnamoyl catalpol glycoside esters.

Chromatography, Liquid↗
PubMedDate not supplied

On-line identification of unstable iridoids from Jamesbrittenia fodina by HPLC-MS and HPLC-NMR.

HPLC-UV-MS analysis of the methanol extract of Jamesbrittenia fodina (Wild) O. M. Hilliard (Scrophulariaceae) revealed the presence of different iridoid cinnamic esters; however, isolation of these constituents was prevented by instability problems. HPLC-UV-MS and HPLC-NMR analysis of the mixtures obtained after a tentative isolation indicated that, in the first instance, instability was due to a light-induced cis/trans isomerisation of the cinnamic moieties. Further investigation of related compounds showed an additional instability problem linked to other chemical transformations. A detailed HPLC-NMR-MS study of these fractions demonstrated that the modifications occurred on the rhamnose moiety of these iridoids. It could be concluded that the second type of instability was attributable to transesterification of the cinnamic moiety on the rhamnose unit. The recording of stop-flow HPLC-NMR spectra for specific HPLC peaks permitted the direct monitoring of these transformations. Based on these on-line data, six new unstable aucubin derivatives were efficiently characterised.

Chromatography, High Pressure Liquid↗
PubMedDate not supplied

The determination of huperzine A in European Lycopodiaceae species by HPLC-UV-MS.

A rapid qualitative HPLC-UV-MS method was developed for the detection of huperzine A in Lycopodiaceae species. HPLC coupled with mass spectrometry experiments allowed the identification of the alkaloid and enabled targeted analysis of complex matrices such as herbal extracts. Huperzine A was detected by single ion monitoring of the pseudomolecular ion [M + H]+ at m/z 243.2. The alkaloid was also detected on TLC in a bioautographic enzyme assay with acetylcholinesterase to show the activity of the compound. Four Lycopodiaceae species collected in Switzerland were tested by these methods and Huperzia selago (L.) Bernh. ex Schrank et Martius was the only species found to contain huperzine A.

Alkaloids↗