Inhibition of prostaglandin biosynthesis by clidanac and related compounds: structural and conformational requirements for PG synthetase inhibition

Pharmacodynamics and chiral pharmacokinetics of carprofen in calves

The non-steroidal anti-inflammatory drug, carprofen, was administered intravenously as the racemate at a dose rate of 0.7 mg kg-1 to six Friesian bull calves aged 8-10 weeks. Anti-inflammatory properties were indicated by attenuation of temperature rise at sites of intradermal injection of the irritants, carrageenin and dextran, but responses were not statistically significant at most recording times. Carrageenin- and dextran-induced swelling were not significantly reduced by carprofen. Carprofen reduced ex vivo serum thromboxane B2 synthesis but this effect was also not significant at most sampling times. Enantioselective pharmacokinetics of carprofen was demonstrated, plasma concentrations of the R(-) enantiomer predominating at all sampling times. It is concluded that inhibition of cyclo-oxygenase is unlikely to be the sole mechanism of action of carprofen in calves.

Enantiomers in arthritic disorders

Drugs which have a center of asymmetry are often administered as an equal mixture of the two possible enantiomeric forms i.e. a racemate. However, there are frequently large pharmacodynamic and pharmacokinetic differences between enantiomers. Consequently, it is possible that while one enantiomer mediates the antiinflammatory or antirheumatic action, the other enantiomer, although adding little to the efficacy of the drug, may contribute to its adverse effects. Asymmetric drugs may also serve as sensitive pharmacological probes of the mechanisms underlying the action of drugs and the inflammatory processes which they modulate. These concepts are the focus for this review.

Isolation and stereospecific determination of the enantiomers of oxindazac by direct liquid chromatographic resolution on triacetylcellulose

The preparation of the optically pure enantiomers of the antiphlogistic trial drug oxindazac via liquid chromatographic resolution of the corresponding tert.-butyl or benzyl ester on triacetylcellulose is described. Cleavage of the optically pure enantiomeric esters to the acids proceeds without significant racemization. The methyl ester of oxindazac is also completely resolved on the same chiral phase. Whereas oxindazac racemizes easily upon derivatization to diastereomers, no racemization is observed upon methylation to the corresponding methyl ester with diazomethane. An inverse isotope dilution method has been developed to determine both enantiomers of the drug in biological fluids after administration of 14C-labelled oxindazac. The enantiomers are converted into their methyl esters and separated on triacetylcellulose. Quantitation is performed by on-line UV detection at 290 nm and off-line radiometry. In the analysis of plasma samples, endogenous compounds do not interfere. The recoveries of [14C]oxindazac from water, rat and human plasma were 99.6 +/- 1.8% for the (+/- and 96.0 +/- 1.4% for the (-)-enantiomer. The plasma concentrations and urinary excretion of the two enantiomers were determined in a human volunteer who had received 200 mg of racemic 14C-labelled oxindazac.

Depside as potent inhibitor of prostaglandin biosynthesis: a new active site model for fatty acid cyclooxygenase

Forty depsides and depsidones, the esters of phenolcarboxylic acids, were examined for their inhibitory effect against prostaglandin biosynthesis with rabbit renal microsomes. 4-0-Methylcryptochlorophaeic acid was the most active inhibitor so far tested and its IC50 value was 0.34 muM. Kinetic investigation has shown that this depside acts competitively with respect to arachidonic acid as most of the non - steroidal antiinflammatory drugs. X-Ray analysis has revealed that 4-0-methylcryptochlorophaeic acid maintains its rigid conformation by forming a strong hydrogen bond between the hydroxyl and methoxyl groups. Comparison of CPK models between 4-0-methylcryptochlorophaeic acid and non-steroidal antiinflammatory drugs revealed that the carboxyl group and the two rings of these drugs are almost superimposable to those of the depside. This finding led us to propose a new active site model based on the three dimentional structure of the depside.

Optical isomerization of R(-)-clidanac to the biologically active S(+)-isomer in guinea-pigs

Optical isomerization of clidanac (RS-6-chloro-5-cyclohexyl-1-indancarboxylic acid, I), an anti-inflammatory drug having a chiral centre in its molecule, was evaluated in guinea-pigs. After oral administration of R(-)-I, the biologically active S(+)-isomer was detectable in the plasma, in the early stages. At 3 h after dosing R(-)-I, the plasma contained above 90% of the S(+)-isomer. Little conversion of S(+)-I to R(-)-I was observed. This may account for the equivalent in vivo activities of R(-)- and S(+)-I in this species. Determination of the enantiomeric composition required derivatization of the enantiomers to their diastereomeric amides after which thin layer chromatography (t.l.c.) was used for the separation. The quantitative determination of the compounds so-separated was accomplished by in situ measurements of the u.v.-reflectance. The t.l.c.-u.v.-densitometric procedure was also used to determine the plasma concentration of I.