Oludotun A. Phillips

Synthesis and antibacterial activity of 5-substituted oxazolidinones.

A series of 5-substituted oxazolidinones with varying substitution at the 5-position of the oxazolidinone ring were synthesized and their in vitro antibacterial activity was evaluated. The compounds demonstrated potent to weak antibacterial activity. A novel compound (PH-027) demonstrated potent antibacterial activity, which is comparable to or better than those of linezolid and vancomycin against antibiotic-susceptible standard and clinically isolated resistant strains of gram-positive bacteria. Although the presence of the C-5-acetamidomethyl functionality at the C-5 position of the oxazolidinones has been widely claimed and reported as a structural requirement for optimal antimicrobial activity in the oxazolidinone class of compounds, our results from this work identified the C-5 triazole substitution as a new structural alternative for potent antibacterial activity in the oxazolidinone class.

Synthesis and antibacterial activity of novel 5-(4-methyl-1H-1,2,3-triazole) methyl oxazolidinones.

A series of 5-(4-methyl-1,2,3-triazole)methyl oxazolidinones were synthesized and tested for their antibacterial activity against a panel of Gram-positive and Gram-negative clinical isolates in comparison with linezolid and vancomycin. Most of the compounds demonstrated strong to moderate in vitro antibacterial activity against susceptible and resistant Gram-positive pathogenic bacteria. Antibacterial activity varied with substitutions at the phenyl C4 position with bulky alkylcarbonyl and alkoxycarbonyl substitutions on the piperazine N4 being detrimental to antibacterial activity. Whereas the presence of the 4-methyl-1,2,3-triazole moiety in the acyl-piperazine containing analogs resulted in increased protein binding, and decreased antibacterial activity particularly against Streptococcus pneumoniae strains.

Determination of linezolid in human plasma by LC-MS-MS

A rapid, sensitive and selective LC-atmospheric pressure-chemical ionization-MS-MS method for the determination of the new antimicrobial agent, linezolid, in human plasma using selected reaction monitoring (SRM) was developed. Linezolid and the internal standard were extracted from the biological samples by solid phase extraction (SPE) and analyzed on a reversed-phase Shim Pack CLC-CN, C18 column with the mobile phase of acetonitrile and 20 mM ammonium acetate solution (4 + 1 v/v). Detection was accomplished using an LCQ mass spectrometer (Finnigan), which was programmed in positive MS-MS mode to permit measurement of the fragment ions of linezolid and internal standard at m/z 296.2 and 223.2, respectively. The assay run-time was less than 3.5 min. Quantitative analysis was based on peak area ratio of linezolid to the internal standard. Calibration plots were established over the concentration range of 0.1-20 micrograms ml-1 of linezolid with the lowest detection limit of 0.05 microgram ml-1 using 10 microliters sample volume. The SPE technique quantitatively recovered linezolid and the internal standard from the plasma samples at a percentage range of 89.1-93.7%. Determination of control samples of linezolid in plasma validated the LC-MS-MS-SRM method. Intra-assay and inter-assay precision were in the range of 5.1-11.4% relative standard deviation, whereas the intra- and inter-accuracy were in the range of 97.5-114.0% of the nominal concentrations of linezolid added. The data confirmed that the plasma samples of linezolid were stable at room temperature and when stored at -20 degrees C for at least 10 d. The developed LC-MS-MS-SRM method is recommended for the determination of linezolid in human plasma.

Synthesis and structure–antibacterial activity of triazolyl oxazolidinones containing long chain acyl moiety

A series of new piperazinyl 5-triazolylmethyl oxazolidinones containing long chain acyl group at the piperazine N-4-position were synthesized and evaluated against a panel of standard and clinical isolates of Gram-positive and Gram-negative bacteria. Derivatives having long chain acyl groups with nine or more number of carbon atoms showed significant decrease in antibacterial activity. Antibacterial activity correlated positively with heat of formation of the compounds, but correlated negatively with Clog P values, surface area, ovality and molecular volume. However, no significant correlation was observed between activity and E(LUMO), E(HOMO) and dipole, respectively.

Synthesis, antibacterial and anticonvulsant evaluations of some cyclic enaminones.

Several cyclic enaminone esters were synthesized, characterized, and evaluated for anticonvulsant and antibacterial activities using standardized tests. A series of enaminones were mainly phenyl analogs of anticonvulsant enaminones, while a second series comprised of compounds bearing the oxazolidinone pharmacophoric moiety found in the synthetic antibacterial linezolid. The enaminone ester bearing an unsubstituted anilino analog showed class 2 anticonvulsant activity. This represents a first report of an unsubstituted anilino enaminone with anticonvulsant activity. The enaminone esters gave interesting UV data, and four analogs displayed potent anticonvulsant activities, while another four compounds showed moderate anticonvulsant activities. Surprisingly, none of the enaminone esters had any significant antibacterial activity.

LC-MS/MS determination of Synercid® injections

Synercid is a combination of two semisynthetic pristinamycin derivatives, quinupristin and dalfopristin in 30:70 (w/w) ratio. A rapid and specific high-performance liquid chromatography-mass spectrometry was developed for the determination of quinupristin and dalfopristin using positive electrospray tandem mass spectrometry (+ESI-MS/MS). Multiple reaction monitoring transitions at 1023.05>134.34 and 691.87>166.26 were selected for the quantitation of quinupristin and dalfopristin, respectively. The assay run cycle-time was approximately 2.0 min injection-to-injection. The assay was linear up to concentration of 4000 ng x ml(-1) quinupristin and 1920 ng x ml(-1) dalfopristin. The lowest limits of quantitation of quinupristin and dalfopristin were found to be 1000 and 480 ng x ml(-1), respectively. Quantitation was based on peak area measurement of quinupristin and dalfopristin using weighed linear regression. Linear relationships with correlation coefficients (r>0.99) were automatically computed for both constituents by MASSLYNX quantify program. The ratio of the slopes of the calibration curves of quinupristin and dalfopristin was found to be 0.425, which matches the nominal ratio composition of the antimicrobial compounds in Synercid. The %RSD ranges were 2.3-4.0% for dalfopristin and 1.3-4.2% for quinupristin, whereas the %DEV ranges were (-7.5+3.7) and (-1.2+9.1%), respectively, indicating appropriate precision and accuracy. Recoveries of 99.5-103.8% and 97.8-99.0% of quinupristin and dalfopristin, respectively, were computed from Synercid injection. The described method is recommended for rapid determination of the contents and for tracking the stability and compatibility of quinupristin and dalfopristin in Synercid injection.

Pleuromutilin antibacterial agents: patent review 2001 - 2006

Derivatives of the naturally occurring pleuromutilin, of which certain analogs were successfully developed in veterinary medicine, have regained interest in the past few years as promising antibacterial agents with potential for human use. This review provides an overview of patents related to pleuromutilin derivatives during 2001 – 2006. Representative compounds along with their antibacterial activities are selected for this purpose, and a section focuses on pleuromutilins in clinical development and practice, in particular retapamulin. Most of the patents reveal the usefulness of different analogs as antibacterial agents effective against multi-drug-resistant organisms, whereas one patent disclosed the in vitro effectiveness of pleuromutilins against Helicobacter pylori. Few patents disclosed novel formulations, methods of preparation in order to improve efficacy, delivery, stability upon storage and synthesis of pleuromutilins.

Ultraviolet spectroscopy of anticonvulsant enaminones

The ultraviolet (UV) spectra of selected enaminones were determined in acidic, alkaline and neutral media and compared to their anticonvulsant activities. The wavelength of maximum absorption and molar absorptivity were compared with the anticonvulsant activity of the selected secondary and tertiary enaminones, and general inferences were made. The UV spectra of the enaminones had hypsochromic shifts in acidic media in comparison with neutral media. Generally, a small hypsochromic shift occurred in alkaline media when compared to the neutral solutions of the enaminones. The tertiary enaminones absorbed UV light at longer wavelength than the secondary enaminones in acidic, neutral and alkaline media. In particular, the tertiary enaminones displayed absorption at the higher end and secondary enaminones towards the lower end of the UV wavelength range 292-315nm in aqueous media. Tertiary enaminones (30-33) which were devoid of the NH proton were found to be uniformly inactive in a mouse model of electroshock seizures, while some secondary enaminones (1, 5-8, 12, 16, 18, 20, 23-25, 28 and 29) had anticonvulsant activity. Thus the NH group of secondary enaminones is very important for anticonvulsant activity, and this agrees with an already established trend in proton NMR spectroscopy. In addition, the para-substitution on the phenyl group in some enaminones result in higher molar absorptivity (epsilon) values that enhance anticonvulsant activity. These results indicate that the anticonvulsant activity of enaminones is not due to electronic effect alone, but is probably due to a combination of factors including electronic and steric effects, lipophilicity, and hydrogen bonding.

LC–MS/MS Determination of Carbamazepine, Pindolol, and Theophylline in Human Serum

Abstract A rapid, sensitive, and specific LC–MS/MS method for the determination of carbamazepine (CAZ), pindolol (PIND), and theophylline (THEO) in human serum is presented. The investigated drugs were separated from serum by deproteinization with acetonitrile and were analyzed on an XTerraTM MS, C18, 2.5 µm (2.1 mm × 30 mm) column. Carbamazepine and PIND were eluted with 65% aqueous acetonitrile containing 2 mM ammonium acetate and 0.1% formic acid, whereas THEO was eluted with 65% aqueous acetonitrile containing 2 mM ammonium acetate at flow rate 0.4 mL min−1. The analytes were detected by a triple quadrupole mass spectrometer (Quattro LC, Micromass) using positive (CAZ, PIND) and negative (THEO) electrospray ionization modes. Multiple reaction monitoring (MRM) transitions at 237 > 194, 249 > 116, and 179 > 164 were selected for quantification of CAZ, PIND, and THEO, respectively. Calibration plots were constructed over the concentration ranges 5–50 ng mL−1 (CAZ), 10–50 ng mL−1 (PIND), and 50–1000 ng mL−1 (THEO). The run cycle‐time was ∼2 min, injection to injection. The assay procedure was highly selective, as no interference either from biological constituents or co‐administered drugs was observed. Analysis of control samples of the examined drugs validated the LC–MS/MS method. The overall intra‐ and inter‐assay %CV were in the range 0.9–5.6%, whereas the overall intra‐ and inter‐assay %DEVs ranged −13.6/+7.4%. The protein precipitation method quantitatively recovered the analytes in mixtures from human serum samples in the range of 94.0–104.3%. The data suggest the utility of the developed LC–MS/MS for monitoring serum levels of CAZ, PIND, and THEO in clinical studies.

Synthesis, neuronal activity and mechanisms of action of halogenated enaminones

Due to the excellent anticonvulsant activity of previously synthesized halogenated enaminones, more disubstituted analogs were synthesized and evaluated in vitro. The new enaminones either had no effect, depressed, or enhanced population spike (PS) amplitude in the rat hippocampus in a concentration-dependent manner. Structure-activity relationship (SAR) analysis indicated that compounds 21 and 25 (with dibromo substituents) were equipotent, and more potent than compound 2 (with dichloro substituents), with compound 25 being the most efficacious of all tested compounds. Both diiodo derivatives 30 and 31 tested produced no significant effect on PS. For PS depression, phenyl substitution on the cyclohexenone ring produced the most efficacious compound 25. PS depressing analogues also depressed evoked excitatory postsynaptic current (EPSC) and action potential firing frequency. Removal of phenyl or methyl group from position 6 on the cyclohexenone ring of enaminone esters produced compound 28 which exhibited pro-convulsant effects. There was no direct correlation between C log P values and anticonvulsant activity of the halogenated enaminones. The mechanisms of anticonvulsant activity were the indirect suppression of excitatory synaptic transmission by enhancing extracellular GABA, and the direct suppression of action potential firing of the neurons.