A study of the antimicrobial activity of selected synthetic and naturally occurring quinolines.

The antimicrobial activities of 60 naturally occurring and synthetic quinolines were studied. The quinolines were organised into seven structural subgroups and, using an in-house microtitre assay, were tested against a range of gram-positive and gram-negative bacteria, including a hospital isolate of meticillin-resistant Staphylococcus aureus (MRSA). The quinolines exhibiting good bioactivity [i.e. low minimum inhibitory concentration (MIC)] against two S. aureus strains were then assessed for their antimicrobial activity against a range of eight clinically isolated MRSA strains. The study showed that 30 of the tested compounds displayed antimicrobial activity, mostly against gram-positive bacteria. The effects of substituent groups on the bioactivity of these quinolines have also been discussed. The quinoline 4-hydroxy-3-iodo-quinol-2-one (11) exhibited significant antimicrobial activity, being active against the MRSA clinical isolates with MIC values comparable with the antibiotic vancomycin used in the treatment of MRSA infections. In particular, 4-hydroxy-3-iodo-quinol-2-one (11) showed MIC values of 0.097 microg/mL against an Irish hospital MRSA-1 strain and 0.049 microg/mL against a distinct MRSA strain as well as a non-typeable MRSA strain.

A study of the antimicrobial activity of selected naturally occurring and synthetic coumarins.

The antimicrobial activities of 43 naturally occurring and synthetic coumarins were studied. Using a microtitre assay developed in-house, a range of Gram-positive and Gram-negative bacteria, including a hospital isolate of methicillin-resistant Staphylococcus aureus (MRSA),were utilised. The coumarins exhibiting good bioactivity (i.e. a low minimum inhibitory concentration) against two S. aureus strains were then assessed for their antimicrobial activities against a range of eight clinically isolated MRSA strains. The study showed that nearly one-half of the tested compounds displayed antimicrobial activity. Sixteen of these coumarins also possessed resistance-modifying activity, which reversed the resistance mechanism in MRSA allowing the antimicrobial oxacillin to exert an enhanced effect against an MRSA hospital strain. When tested in combination with oxacillin, 8-iodo-5,7-dihydroxycoumarin (32) had a similar activity to vancomycin, which is the current drug of choice for the treatment of MRSA infections.

An investigation of bioactive phytochemicals in the leaves of Melicope vitiflora by electrospray ionisation ion trap mass spectrometry.

The ethyl acetate extract of the leaves of Melicope vitiflora was separated by column chromatography and the resulting fractions tested for their bioactivity towards methicillin-resistant-Staphylococcus aureus (MRSA) and Micrococcus luteus (ML). The bioactive column chromatography fractions were further separated by preparative TLC and dereplication was carried out on them by first subjecting them to electrospray ionisation-ion trap mass spectrometry (ESI-MS(n)). The resulting molecular masses, their fragmentation patterns in addition to the chemnet database (www.chemnetbase.com) were used to aid in the structural elucidation of some of the compounds by permitting comparison with known structures of natural origin. Some molecular masses and the corresponding fragmentations were found that did not correlate with any known compounds thus revealing potentially novel natural products that could be investigated on a larger scale and could ultimately find application as new drugs against MRSA and other multi drug resistant microorganisms. Structures are also proposed for known compounds that have not been previously reported for M. vitiflora.

Characterisation of nicotine and related compounds using electrospray ionisation with ion trap mass spectrometry and with quadrupole time-of-flight mass spectrometry and their detection by liquid chromatography/electrospray ionisation mass spectrometry.

Electrospray ionisation ion trap mass spectrometry (ESI-MS(n)) has been used to study the fragmentation patterns of nicotine and nine of its related compounds. From this study certain characteristic fragmentations are apparent with generally the pyrrolidine or piperidine ring being subject to chemical modifications. The structures of the product ions proposed for the ESI-MS(n) study have been supported by results from electrospray ionisation quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS). Compounds with pyrrolidine and piperidine rings that possess an unsubstituted N atom have been shown to lose NH(3) at the MS(2) stage. Those compounds with N-methyl groups lose CH(3)NH(2) at the MS(2) stage. The loss of NH(3) or CH(3)NH(2) leaves the corresponding rings opened and this is followed by ring closure at the pyridine-2 carbon atom. Mono-N-oxides fragment in a similar way but the di-N-oxide can also fragment by cleavage of the bond between the pyridine and pyrrolidine rings. Cotinine also can undergo cleavage of this bond between the rings. This data therefore provides useful information on how substituents and the nature of the non-pyridine ring can affect the fragmentation patterns of nicotine and its related compounds. This information can be used in the characterisation of these compounds by liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) which results in the separation of nicotine and its related compounds with limits of detection (LODs) ranging from 15 to 105 ng/mL. The use of LC/ESI-MS to study nicotine-containing samples resulted in the simultaneous and unambiguous identification of seven of the compounds discussed in this paper: cotinine identified at retention time 12.5 min (with its [M+H](+) ion at m/z 177), nornicotine 16.0 min (m/z 149), anatabine 18.0 min (m/z 161), myosmine 18.5 min (m/z 147), anabasine 20.4 min (m/z 163), nicotine 22.2 min (m/z 163), and nicotyrine 31.4 min (m/z 159). For quality control of nicotine replacement therapy products, these nicotine impurities can be readily identified and determined at levels up to 0.3% for single impurities and up to 1.0% for total impurities.

A study of the analytical behaviour of selected synthetic and naturally occurring quinolines using electrospray ionisation ion trap mass spectrometry, liquid chromatography and gas chromatography and the construction of an appropriate database for quinoline characterisation.

Mass spectral fragmentation of quinoline alkaloids of significance in plants has been investigated using electrospray ionisation ion trap mass spectrometry (ESI-MS(n)) with a view to characterisation of molecules of unknown structure isolated from these natural sources. This investigation has led to the generation of an appropriate database incorporating data from ESI-MS(n) and also from gas liquid chromatography (GLC) and liquid chromatography (HPLC) for these low molecular mass quinolines. This has been put to practical application in the identification of quinoline alkaloids in a plant extract. Thus, an acid extraction of the leaves of Choisya ternata containing such tertiary alkaloids was analysed by liquid chromatography-electrospray ionisation mass spectrometry (HPLC-ESI-MS) and the resulting behaviour of the quinolines was compared with that of the quinoline alkaloids in the database.

Resolution of (RS)-proglumide using lipase from Candida cylindraceae.

Proglumide is used in the treatment of neuropathic pain. It acts by inhibiting peptide cholecystokinin (CCK). Neural injury produces an elevation in plasma CCK. Proglumide has been also shown to augment the analgesic effect of sustained release morphine in neuropathic pain. Currently proglumide is administered as a racemic mixture. In the present study, an attempt is made to separate the racemic mixture of the drug using lipase obtained from Candida cylindracea by stereoselective esterification. Enzymatic stereoselective esterification was carried out in organic solvents. The resolution was studied using a chromatographic column with a chiral support and mass spectrometry. The reaction conditions for stereoselective esterification including amount of substrate, amount of enzyme, alcohol, solvent and temperature were optimised during the present investigation. Butanol and hexanol were found to be suitable for formation of S and R esters, respectively. Hexane was the best solvent for esterification and the optimum temperature was found to be 30 degreesC.

Racemic resolution of RS-baclofen using lipase from Candida cylindracea.

Baclofen is chemically (RS)-beta-(aminomethyl)-4-chlorobenzene propanoic acid. It is used in therapy of pain and as a muscle relaxant. Baclofen produces analgesia by increasing the concentration of gamma amino butyric acid (GABA), the major rapid inhibitory transmitter. Both the isomers of baclofen have different therapeutic activity with respect to their interaction to the receptors at the site of action. Lipase from Candida cylindracea has been used as a catalyst for resolving racemic mixtures of numerous drug molecules. The present investigation deals with the racemic resolution of RS-baclofen using lipase from Candida cylindracea and a study of the factors affecting resolution.

A study of the electrospray ionisation and ion trap fragmentation of hemiterpenoid and dimeric coumarin derivatives.

The electrospray ionisation (ESI) of selected hemiterpenoid and dimeric coumarin derivatives and their subsequent fragmentation using an ion trap mass spectrometer are reported and discussed. Sequential product ion fragmentation experiments (MS(n)) were performed in order to elucidate the degradation pathways for these compounds. The results illustrate that the observed characteristic fragmentation patterns are of considerable utility in the application of ESI mass spectrometry to the characterisation of this class of compounds.

A study of the electrospray ionisation of pharmacologically significant 1,4-benzodiazepines and their subsequent fragmentation using an ion-trap mass spectrometer.

The electrospray ionisation (ESI) of sixteen pharmacologically significant 1,4-benzodiazepines and their subsequent fragmentation using an ion-trap mass spectrometer have been investigated. Sequential product ion fragmentation experiments (MSn) were performed in order to elucidate the degradation pathways for these compounds. Comparisons were also made between these ESI spectra and those obtained under electron impact (EI) conditions. The data presented in this paper provide useful information on the effect of different substituents on the ionisation/fragmentation processes and can be used in the characterisation of this important class of drugs and their metabolites.

A study of the electrospray ionisation of selected coumarin derivatives and their subsequent fragmentation using an ion trap mass spectrometer.

The electrospray ionisation (ESI) of selected coumarin derivatives and their subsequent fragmentation using an ion trap mass spectrometer have been investigated. Sequential product ion fragmentation experiments (MS(n)) were performed in order to elucidate the degradation pathways for these compounds. A comparison was also made between these ESI spectra and those obtained under electron impact (EI) conditions. The data presented in this paper provides useful information on the effect of different substituents on the ionisation/fragmentation processes and can be used in the characterisation of these compounds.