Stereoselective pharmacokinetics of BOF-4272 racemate after oral administration to rats and dogs

The stereoselective pharmacokinetics of BOF-4272 enantiomers in rats and dogs was investigated by simultaneously measuring concentrations in arterial, portal, and venous plasma, the liver, and the kidney at 2 h after the oral administration of the racemic drug. The concentrations of BOF-4272 enantiomers were measured using high-performance liquid chromatography. The concentrations of the S(-) enantiomer in arterial, portal, and venous plasma were higher than those of the R(+) enantiomer in rats, but the opposite was found in dogs. In rats, absorption from the intestinal tract into the portal system was almost the same for the two enantiomers, whereas the hepatic uptake of the R(+) enantiomer was greater than that of the S(-) enantiomer. In dogs, absorption from the intestinal tract into the portal system was greater for the R(+) enantiomer than for the S(-) enantiomer, whereas hepatic uptake was comparable for the two enantiomers. The stereoselectivity of the renal uptake of BOF-4272 enantiomers had little effect on the stereoselectivity of enantiomers in the systemic circulation in both rats and dogs. The stereoselectivity in the systemic circulation of BOF-4272 enantiomers is therefore related to hepatic uptake in rats, and to absorption from the intestinal tract into the portal system in dogs.     

In vitro and in vivo studies on the stereoselective pharmacokinetics and biotransformation of an (S)-(–)- and (R)-(+)-pyrazolotriazine sulfoxide in the male rat

1. BOF-4272 (a pyrazolotriazine sulfoxide) is a new drug for the treatment of hyperuricemia. The pharmacokinetics and biotransformation of both BOF-4272 enantiomers were investigated in rat. 2. Plasma concentrations after intravenous or oral administration of racemic BOF-4272 to rat were significantly higher for (S) - than for (R) -BOF-4272. 3. The concentration of (S) -BOF-4272 in hepatocyte culture medium 24 h after the addition of racemic BOF-4272 was higher than that of (R) -BOF-4272. 4. Liver concentrations after oral adminstration of racemic BOF-4272 to rat were significantly higher for (R) - than for (S) -BOF-4272. Kidney concentrations were significantly higher for (S) - than for (R) -BOF-4272. 5. Hepatic biotransformation from BOF-4272 to unknown metabolites, possibly conjugates, is stereoselective. Biotransformation of both enantiomers to the sulfone metabolite by cytochrome P450 in rat liver may also be stereoselective. 6. Biotransformation of the sulfide metabolite of BOF-4272 to BOF-4272 may be stereoselective, possibly due to the stereospecificity of flavin-containing mono-oxidase and/or cyrochrome P450. 7. The stereoselectivity of plasma concentrations of racemic BOF-4272 after intravenous or oral administration appears to be due to differences in the hepatic uptake of the two enantiomers as well as the stereoselective biotransformation of the sulfide metabolite to BOF-4272 in rat liver. Biotransformation of BOF-4272 in rat liver may also be stereoselective.     

In vitro and in vivo studies on the stereoselective pharmacokinetics and biotransformation of an (S)-(-)- and (R)-(+)-pyrazolotriazine sulfoxide in the male rat

1. BOF-4272 (a pyrazolotriazine sulfoxide) is a new drug for the treatment of hyperuricemia. The pharmacokinetics and biotransformation of both BOF-4272 enantiomers were investigated in rat. 2. Plasma concentrations after intravenous or oral administration of racemic BOF-4272 to rat were significantly higher for (S)- than for (R)-BOF-4272. 3. The concentration of (S)-BOF-4272 in hepatocyte culture medium 24 h after the addition of racemic BOF-4272 was higher than that of (R)-BOF-4272. 4. Liver concentrations after oral adminstration of racemic BOF-4272 to rat were significantly higher for (R)- than for (S)-BOF-4272. Kidney concentrations were significantly higher for (S)- than for (R)-BOF-4272. 5. Hepatic biotransformation from BOF-4272 to unknown metabolites, possibly conjugates, is stereoselective. Biotransformation of both enantiomers to the sulfone metabolite by cytochrome P450 in rat liver may also be stereoselective. 6. Biotransformation of the sulfide metabolite of BOF-4272 to BOF-4272 may be stereoselective, possibly due to the stereospecificity of flavin-containing mono-oxidase and/or cyrochrome P450. 7. The stereoselectivity of plasma concentrations of racemic BOF-4272 after intravenous or oral administration appears to be due to differences in the hepatic uptake of the two enantiomers as well as the stereoselective biotransformation of the sulfide metabolite to BOF-4272 in rat liver. Biotransformation of BOF-4272 in rat liver may also be stereoselective.     

Evaluation of the pharmacological actions and pharmacokinetics of BOF-4272, a xanthine oxidase inhibitor, in mouse liver

BOF-4272 (+/-)-8-(3-methoxy-4-phenylsulphinylphenyl) pyrazolo[1,5-a]-1,3,5-triazine-4-(1H)-one, a new synthetic anti-hyperuricaemic drug, which has a chiral centre and exists as racemates, is a potent inhibitor of xanthine oxidase/dehydrogenase in the purine catabolism pathways. The present studies using mice demonstrated that BOF-4272 was specifically distributed in the liver, which is the main organ of uric acid production. Therefore, a decrease in uric acid concentration in the liver, rather than the plasma, was identified as a pharmacological action of BOF-4272. The ratio of liver to plasma concentrations of BOF-4272 increased from 2.5 to 6.3 over time, up to 8 h after oral administration. The elimination half-life of BOF-4272 in the liver was 5-1-fold longer than that in the plasma. High concentrations of BOF-4272 were observed in the liver up to 8 h after oral administration. Furthermore, the influx of BOF-4272 into hepatocytes occurred in a temperature-dependent manner. The liver concentrations of uric acid from 1 h to 8 h after the oral administration of BOF-4272 (0.34-0.75 microg (g tissue)(-1)) were significantly lower than those in control animals (5.03-10.96 microg (g tissue)(-1)). BOF-4269 (the sulphide metabolite of BOF-4272) was the only metabolite detected in plasma or faeces after intravenous or oral administration. BOF-4269, which has no inhibitory action on the uric acid biosynthesis system, is generated by the metabolism of BOF-4272 in the intestinal tract. In conclusion, this work using the liver as the target organ has allowed us to identify the pharmacological actions of BOF-4272 in mice. The long-lasting effect of BOF-4272 in reducing levels of hepatic uric acid was consistent with the prolonged high BOF-4272 concentrations in the liver. These results also demonstrate that the mouse is a suitable animal species for evaluating the clinical pharmacology and pharmacokinetics of BOF-4272.     

Metabolic pathways and pharmacokinetics of BOF-4272, a sulfoxide-containing drug, in the dog: in vivo and in vitro studies

BOF-4272, (+/-)-8-(3-methoxy-4- phenylsulfinylphenyl)pyrazolo[1,5-a]-1,3,5-triazine-4(1H)-one, is a new drug intended for the treatment of hyperuricemia. This report describes the detailed metabolic pathways of BOF-4272 in the dog. The metabolic pathways were investigated using the metabolites found in plasma, urine, and feces after intravenous or oral administration of BOF-4272, as well as the metabolites found in the liver S9 incubation mixture after the addition of BOF-4272 or BOF-4269. BOF-4269 (the sulfide metabolite of BOF-4272) was the only metabolite detected in plasma and feces after the intravenous or oral administration of BOF-4272. BOF-4269 was detected in dog plasma after a lag time following the oral administration of BOF-4272, and the Cmax and AUC0-t of BOF-4269 were higher in fed dogs than in fasted dogs after the oral administration of BOF-4272. A small amount of BOF-4269 was detected in dog plasma immediately after the intravenous administration of BOF-4272. Only BOF-4276 (the sulfone metabolite of BOF-4272) was detected in the S9 incubation mixture after the addition of BOF-4272. Mainly BOF-4272 was detected and small amounts of BOF-4276 and M-1 (the hydroxy metabolite of BOF-4269) were detected in the S9 incubation mixture after the addition of BOF-4269. These findings suggest that BOF-4272 is mainly metabolized to BOF-4269 by the intestinal flora in dogs, whereas little of this drug is metabolized to BOF-4269 in the dog liver. In conclusion, this work has allowed us to formulate the proposed metabolic pathways of BOF-4272 in the dog.     

The effect of food or sucralfate on the bioavailability of S(+) and R(-) enantiomers of ibuprofen.

This randomized, multiple cross-over pharmacokinetic study was undertaken to determine if food or sucralfate alter the bioavailability of the active S(+) enantiomer of ibuprofen. Eleven healthy adult male volunteers were given three single 600-mg doses of ibuprofen (separated by 1 week) administered either in a fasting state, after a standardized breakfast, or with sucralfate 1 g. The main outcome measures were area under the concentration (AUC), maximum peak plasma concentration (Cmax), and time to reach peak concentration (tmax) for total, S(+), and R(-) enantiomer serum ibuprofen levels, drawn up to 10 hours after dosing. The AUC for R(-) ibuprofen was significantly lower than S(+) ibuprofen in all three treatment groups. The treatments had no different effects on AUC for S(+), R(+), or total ibuprofen. There was no difference in the ratio of S(+):R(-) enantiomers across different treatment groups, but the intersubject variability was significant (P < .05). The S(+) ibuprofen Cmax was greater than the R(-) ibuprofen Cmax for all treatment groups (P < .05). Sucralfate reduced the peak concentration of both S(+) and R(-) enantiomers when compared with fasting (P < .05). There was a slight but nonsignificant increase in the mean time to achieve peak concentration of both S(+) and R(-) enantiomers. Neither food nor sucralfate has a significant effect on ibuprofen enantiomer pharmacokinetics, but interindividual variability contributes significantly to the variability of enantiomer bioavailability.     

Octoclothepin enantiomers. A reinvestigation of their biochemical and pharmacological activity in relation to a new receptor-interaction model for dopamine D-2 receptor antagonists.

Octoclothepin (1) was resolved into its R and S enantiomers via the diastereomeric tartaric acid salts. The enantiomers were shown to be of high optical purity by 1H NMR with use of the chiral shift reagent (R)-(-)-2,2,2-trifluoro-1-(9-anthryl)ethanol. Pharmacological and biochemical testing confirmed that (S)-1 is the more potent dopamine (DA) D-2 antagonist both in vitro and in vivo, although the R enantiomer still has significant D-2 antagonistic activity. In contrast, both enantiomers were equally active in test models detecting activity at D-1 receptors, serotonin-2 (5-HT2) receptors and alpha 1 adrenoceptors. Contrary to a previous prediction, it was found that norepinephrine (NE) uptake inhibition was confined solely to the S enantiomer. Overall, (S)-1 has a "classical" neuroleptic profile, while the R enantiomer has a more "atypical" profile. These pharmacological profiles seem to be in agreement with the reported clinical profiles of the two enantiomers. A previous conformational study was revised in light of the biochemical test results with enantiomers of known optical purity. Their relative D-2 receptor affinity corresponded well with the calculated conformational energy difference between their "active conformations" deduced from a previously reported new D-2 receptor model. Also the high enantioselectivity of (S)-1 at the NE uptake site could be explained after a detailed conformational analysis showing strict requirements for the orientation of the piperazine lone-pair direction at the NE uptake site.     

Stereoselective pharmacokinetics of a novel uricosuric antihypertensive diuretic in rats: pharmacokinetic interaction between enantiomers.

5-Dimethylsulfamoyl-6,7-dichloro-2,3-dihydrobenzofuran-2-carboxyli c acid (DBCA), a promising uricosuric, diuretic, and antihypertensive agent, was administered intravenously to rats. The levels of DBCA in plasma and the areas under the curve of concentration versus time (AUC values) of the S(-)-enantiomer were higher than those of the R(+)-enantiomer. Total body clearance was significantly greater for the R(+)-enantiomer. This stereoselective elimination was due to a difference in the nonrenal clearance, which seemed to reflect hepatic metabolism or biliary excretion. Hepatic metabolism seemed more likely because AUC and the amount of urinary excretion of the N-monodemethylated metabolite of DBCA were greater for the R(+)-enantiomer. The plasma had higher free fractions of the S(-)-enantiomer, a result suggesting that this enantiomer is distributed more readily to the tissues, including the liver. This result indicates that protein binding was not responsible for the stereoselective metabolism of (R)-(+)-DBCA. Although there was no difference in the renal clearances of the enantiomers, the renal clearance of free (R)-(+)-DBCA exceeded that of the S(-)-enantiomer, a result indicating the preferential excretion of the R(+)-enantiomer into the urine. Comparison of the pharmacokinetics of individual enantiomers after intravenous administration of each enantiomer or its racemate showed that the enantiomers interact with one another; dosing with racemate delayed the elimination of each enantiomer because of mutual inhibition of hepatic metabolism and renal excretion for (R)-(+)-DBCA and of renal excretion for (S)-(-)-DBCA.     

Conformational analysis and structural comparisons of (1R,3S)-(+)- and (1S,3R)-(-)-tefludazine, (S)-(+)- and (R)-(-)-octoclothepin, and (+)-dexclamol in relation to dopamine receptor antagonism and amine-uptake inhibition

Conformational analysis with molecular mechanics (MM2(85] and molecular superimposition studies of (1R,3S)-(+)- and (1S,3R)-(-)-4-[3-(4-fluorophenyl)-6-(trifluoromethyl)indan-1-yl]-1- piperazineethanol (tefludazine) and (S)-(+)- and (R)-(-)-octoclothepin have been employed to identify biologically active conformations of these compounds with respect to dopamine receptor antagonism and amine-uptake inhibition. In contrast to what is commonly assumed, these studies indicate that the conformation of (S)-(+)-octoclothepin responsible for the dopamine receptor antagonism is different from the one observed in the crystal. From least-squares molecular superimpositions with the potent and stereoselective dopamine receptor antagonist (1R,3S)-tefludazine, biologically active conformations for the two compounds on the dopamine receptor have been deduced. This analysis also rationalizes the enantioselectivity of octoclothepin on the dopamine receptor. The X-ray structure of (S)-(+)-octoclothepin is shown to correspond structurally to the 1S,3R enantiomer of tefludazine, which is an amine-uptake inhibitor. This correspondence provides a structural basis for the norepinephrine (NE) uptake blocking properties of octoclothepin. It is predicted that the enantioselectivity of the NE-uptake inhibition of octoclothepin should be low with the S-(+) enantiomer as the more active optical isomer. A comparison of the deduced biologically active conformation of (S)-(+)-octoclothepin with (+)-dexclamol is also discussed on the basis of earlier derived superimposition studies with (+)-dexclamol.     

Barbituric acid derivatives. 39. Study of the central nervous action of enantiomers of barbiturates with a basic side chain at the nitrogen atom

Derivatives of Barbituric Acid, XXXIX: Pharmacological Activity of the Enantiomers of Barbiturates with a Basic Side Chain at the Nitrogen Atom The enantiomers of the N-(aminoethyl)barbiturates 7a, 7b, 8b and 8d influence the motoric behavior when given i. v. to rats. They elicit central-nervously caused ataxia and hyperkinetic movements, which, on higher doses, change to CNS excitatoric symptoms (tonic-clonic convulsions). The dose dependence of the effect shows the R(?) enantiomer to be more active than the S(+) enantiomer. After i.p. application the enantiomers of 7a-7c and 8a-8d prolong the sleeping time of an anesthesia caused by hexobarbital. Again the R(?) enantiomer is more active than the S(+) enantiomer. Also, the effect is dose dependent, but the enantiomers of 8d prolong the sleeping time more than linearly. With a constant dose of 8d prolongation of the sleeping time is time dependent: With both enantiomers prolongation is maximal 15 min after application: 3 hours later the effect disappears completely.     

Pharmacokinetics of BOF-4272, a xanthine oxidase inhibitor, after single intravenous or oral administration to male mice and rats.

BOF-4272, (+/-)-8-(3-methoxy-4-phenylsulphinylphenyl) pyrazolo [1,5-a]-1,3,5-triazine-4 (1H)-one), is a new drug intended for the treatment of hyperuricaemia. This report describes the detailed pharmacokinetics of BOF-4272 in mice and rats after intravenous or oral administration. Plasma concentrations of BOF-4272 at 2-8h after intravenous administration were significantly higher in mice than in rats. Plasma concentrations of BOF-4272 after oral administration were significantly higher in fed mice than in fasted mice, but were similar in fasted and fed rats. The elimination half-life of the distribution phase (t1/2(alpha)) was similar in mice (0.158 h) and rats (0.210 h). The elimination half-life of the terminal elimination phase (t1/2(beta)) in mice was 1.936 h, while that in rats was 0.742 h. The volume of the central compartment (V1) was almost the same in mice (415 mL kg(-1)) and rats (440 mL kg(-1)). However, the volume of the peripheral compartment (V2) in mice was 1068 mL kg(-1), while that in rats was 92 mL kg(-1). The steady-state volume of distribution (Vss) was 2.8 times larger in mice than in rats. The area under the plasma concentration-time curve (AUC) in mice was 5332 ng h mL(-1), while that in rats was 3806 ng h mL(-1). The AUC0-24 h after oral administration was 2.5 times greater in fed mice than in fasted mice, and was 1.4 times greater in fasted rats than in fed rats. The correlation coefficients of Cmax and AUC0-24 h in both mice and rats after oral administration were greater than 0.997 in the dose range 1 - 125 mg kg(-1), indicating that the linear range of absorption or elimination (or both) of BOF-4272 is very wide. The results of the present study demonstrate that the mouse is a suitable animal species for evaluating the clinical pharmacokinetics of BOF-4272.     

Disposition of the enantiomers of cromakalim in rat and cynomolgus monkey.

1. Disposition of the 3R,4S(+) and 3S,4R(-) enantiomers of the racemic antihypertensive drug cromakalim has been studied in rats and cynomolgus monkeys using the 14C-drug labelled in either the 3R,4S(+) or the 3S,4R(-) enantiomer. 2. After oral administration to rat, blood concentrations of the 3R,4S(+) enantiomer were up to fourfold higher than those of the 3S,4R(-) enantiomer. Metabolism of the former was not as extensive as that of the latter and consequently plasma and urinary radiometabolite patterns were quantitatively different. 3. In contrast to rat, there were much greater differences in the disposition of the two enantiomers following oral administration of cromakalim to the cynomolgus monkey. Plasma concentrations of the 3R,4S(+) enantiomer were approximately 100 x those of the 3S,4R(-) enantiomer and the rate of urinary 14C elimination for the 3R,4S(+) enantiomer was much faster than that for the 3S,4R(-) enantiomer. Plasma and urinary radiometabolite patterns were very different for the two isomers. Metabolic end products of the 3R,4S(+) enantiomer were predominantly phase I metabolites whereas the 3S,4R(-) enantiomer was almost entirely metabolized by glucuronidation. 4. A study of the racemic drug alone would have led to a misunderstanding of the fate of the compound in these species.     

The enantiomeric specificity of the antihypertensive activity of 1-(phenylthio)-2-aminopropane, a synthetic substrate analogue for dopamine beta-monooxygenase

We have found that (R,S)-1-(phenylthio)-aminopropane (4a), a synthetic alternate substrate for the terminal enzyme of norepinephrine biosynthesis, dopamine beta-monooxygenase (DBM), is both an indirect sympathomimetic and a potent antihypertensive agent in spontaneously hypertensive rats. We demonstrate herein that there is a distinct enantiospecific difference in the activities of (R)-1-(phenylthio)-2-aminopropane (4b) and (S)-1-(phenylthio)-2-aminopropane (4c). We find that 4c, the more potent DBM substrate analogue, exhibits both the indirect sympathomimetic activity and the antihypertensive activity previously observed for the racemate and inhibits the active transport of catecholamines at the nerve terminal. In contrast, 4b, which is less potent as a DBM substrate or as an inhibitor of catecholamine uptake, does not exhibit an indirect sympathomimetic effect and is not an effective antihypertensive agent. These results suggest that the greater selectivity of the S enantiomer for both the catecholamine reuptake transporter and the target enzyme DBM accounts for its greater potency as an indirect-acting sympathomimetic agent as well as its activity as an antihypertensive agent. These results are also consistent with the hypothesized mechanism of action of this class of sulfur-containing DBM substrate analogues.     

Studies on the metabolism and chiral inversion of ibuprofen in isolated rat hepatocytes

The oxidative metabolism and chiral inversion of ibuprofen in freshly isolated rat hepatocytes was studied with the aid of a stereoselective GC/MS assay procedure. Hydroxylation of the isobutyl side chain at the subterminal carbon (to give hydroxyibuprofen) proved to be the major route of metabolism of both R(-)-ibuprofen and S(+)-ibuprofen, while formation of the corresponding diastereoisomeric 2-methylpropionic acid derivatives (carboxyibuprofen) was of minor quantitative importance. Both oxidative pathways were inhibited in the presence of metyrapone, a cytochrome P-450 inhibitor. R(-)-Ibuprofen underwent metabolic chiral inversion to the S(+) enantiomer, whose formation was dependent on incubation time, cell density, and substrate concentration. S(+)-Ibuprofen, on the other hand, was not converted to R(-)-ibuprofen in rat hepatocytes. When cells were incubated with a mixture of unlabeled R(-)-ibuprofen and R(-)-[3,3,3-2H3]ibuprofen, the resultant S(+) enantiomer consisted only of unlabeled and trideutero molecules (formed in the same ratio as the corresponding species of R(-)-ibuprofen), indicating that 2,3-dehydroibuprofen did not serve as the symmetrical intermediate in the chiral inversion reaction. Collectively, these results demonstrate that freshly isolated rat hepatocytes represent a convenient and reproducible in vitro model system for studies on the metabolism and chiral inversion of ibuprofen.     

Disposition of the enantiomers of cromakalim in rat and cynomolgus monkey

1. Disposition of the 3R,4S(+) and 3S,4R(-) enantiomers of the racemic antihypertensive drug cromakalim has been studied in rats and cynomolgus monkeys using the ¹⁴C-drug labelled in either the 3R,4S(+) or the 3S,4R(-) enantiomer.

2. After oral administration to rat, blood concentrations of the 3R,4S(+) enantiomer were up to fourfold higher than those of the 3S,4R(-) enantiomer. Metabolism of the former was not as extensive as that of the latter and consequently plasma and urinary radio-metabolite patterns were quantitatively different.

3. In contrast to rat, there were much greater differences in the disposition of the two enantiomers following oral administration of cromakalim to the cynomolgus monkey. Plasma concentrations of the 3R,4S(+) enantiomer were approximately 100 x those of the 3S,4R(-) enantiomer and the rate of urinary ¹⁴C elimination for the 3R,4S(+) enantiomer was much faster than that for the 3S,4R(-) enantiomer. Plasma and urinary radio-metabolite patterns were very different for the two isomers. Metabolic end products of the 3R,4S(+) enantiomer were predominantly phase I metabolites whereas the 3S,4R(-) enantiomer was almost entirely metabolized by glucuronidation.

4. A study of the racemic drug alone would have led to a misunderstanding of the fate of the compound in these species.     

Comparison of norfluoxetine enantiomers as serotonin uptake inhibitors in vivo.

Norfluoxetine, the N-desmethyl metabolite of fluoxetine, has been reported to resemble fluoxetine in being a potent and selective inhibitor of the serotonin uptake carrier. The enantiomers of norfluoxetine have now been compared as serotonin uptake inhibitors in vivo, based on their antagonism of p-chloroamphetamine-induced depletion of serotonin in brain and their lowering of concentrations of the metabolite of serotonin, 5-hydroxyindoleacetic acid (5-HIAA) in brain. In rats, S-norfluoxetine (ED50 3.8 mg/kg) was more potent than R-norfluoxetine (ED50 > 20 mg/kg) in blocking the depletion of serotonin by p-chloroamphetamine after intraperitoneal administration. The S enantiomer decreased concentrations of 5-HIAA in whole brain after doses of 2.5-20 mg/kg, whereas the R enantiomer did not. The concentrations of both enantiomers in brain increased in proportion to dose and the R enantiomer disappeared from the brain at a slightly slower rate than the S enantiomer. The relative inability of the R enantiomer to block the uptake of serotonin was therefore not a result of smaller concentrations of drug in the brain. In mice, S-norfluoxetine was also more potent than R-norfluoxetine in blocking depletion of serotonin by p-chloroamphetamine (ED50 values 0.82 and 8.3 mg/kg, respectively). Thus, in contrast to the relatively similar potencies of the enantiomers of fluoxetine in blocking the uptake of serotonin, the enantiomers of norfluoxetine have markedly different potencies as inhibitors of the uptake of serotonin.     

GABA agonists and uptake inhibitors. Synthesis, absolute stereochemistry, and enantioselectivity of (R)-(-)- and (S)-(+)-homo-beta-proline

The cyclic analogue of 4-aminobutyric acid (GABA), 3-pyrrolidineacetic acid (homo-beta-proline), is a potent agonist at GABAA receptors, it interacts effectively with GABA-uptake mechanisms, and it is a moderately potent inhibitor of GABAB receptor binding. (R)-(-)- (10) and (S)-(+)-homo-beta-proline (15) were synthesized via methyl (3S)-1-[(R)-1-phenylethyl]-5-oxo-3-pyrrolidinecarboxylate (5) and its 3R diastereomer (4), respectively. The mixture 3 consisting of 4 and 5 was synthesized via addition-cyclization reactions between (R)-1-phenylethylamine and itaconic acid (1). The diastereomers 5 and 4, which were separated chromatographically, were converted into (R)- (10) and (S)-homo-beta-proline (15), respectively. The absolute stereochemistry of 10 and 15 was established on the basis of an X-ray analysis of compound 5. The enantiomers 10 and 15 were shown to bind to GABAA and GABAB receptor sites with opposite stereoselectivity. Thus, (R)-homo-beta-proline (10) proved to be more than 1 order of magnitude more potent than the S enantiomer (15) as an inhibitor of GABAA receptor binding, whereas the GABAB receptor affinity of homo-beta-proline was shown to reside exclusively in (S)-homo-beta-proline (15). In contrast to the stereoselective receptor affinities of 10 and 15, these enantiomers were approximately equieffective as inhibitors of synaptosomal GABA uptake.     

Resolved cis-10-hydroxy-4-n-propyl-1,2,3,4,4a,5,6,10b- octahydrobenzo[f]quinoline : central serotonin stimulating properties

cis-10-Hydroxy-4-n-propyl-1,2,3,4,4a,5,6,10b -octahydrobenzo[f]quinoline (4) is a centrally acting serotonin (5-HT) receptor agonist of moderate potency. Due to its semirigid character and the obvious similarity between (4aR,10bS)-4 and more potent, centrally acting 5-HT receptor agonist cis-(1S,2R)-8-hydroxy-1-methyl-2-(di-n-propylamino)tetralin (2), we carried out the preparation (via resolution of 6, a precursor of 4) and the pharmacological testing of the enantiomers of 4. We were able to show that the active enantiomers of 4 and 2 coincide in terms of stereochemistry, i.e., that it is the 4aR,10bS enantiomer of 4 that is the more active one. The absolute configuration was assigned on the basis of single-crystal X-ray analysis of the precursor (+)-6 of the active enantiomer (-)-4. Conformational analysis with molecular mechanics (MM2) calculations were performed on the N-methyl analogues of compounds cis-(1S,2R)-2 (cis-(1S,2R)-3) and cis-(4aR,10bS)-4 (cis-(4aR,10bS)-7). Both ammonium and free amine forms were subjected to these calculations. The results show a preference for the N-equatorial conformation, which is corroborated by the X-ray structure of (+)-6.HCl. The relatively low potency of compound cis-(4aR,10bS)-4 might be explained by unfavorable direction of the N-lone pair (or ammonium hydrogen) bond in this compound as compared to cis-(1S,2R)-2 and trans-(4aR,10bR)-5, which can be predicted to be the more active enantiomer of compound 5.     

Stereoselective disposition of ibuprofen enantiomers in man.

This study has examined the stereoselective disposition of the enantiomers of ibuprofen in four healthy male subjects following separate administration of racemic ibuprofen (800 mg) and of each enantiomer (400 mg). A mean of 63 +/- 6% of an administered dose of R(-) ibuprofen was stereospecifically inverted to the S(+) enantiomer. There were no measurable inversion of the S(+) to R(-) ibuprofen. The kinetics of the individual enantiomers were altered by concurrent administration of the respective optical antipode. It is likely that this change reflects an interaction between the enantiomers at plasma protein binding sites. It was found that formation of ester glucuronide conjugates stereoselectively favoured the S(+) enantiomer. The data have demonstrated that the pharmacokinetics of ibuprofen and other alpha-methylarylacetic acids cannot be interpreted adequately without studying the pharmacokinetics of the individual enantiomers.     

Syntheses, calcium channel agonist-antagonist modulation activities, nitric oxide release, and voltage-clamp studies of 2-nitrooxyethyl 1,4-dihydro- 2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)pyridine-5-carboxylate enantiomers

The novel (-)-(S)-2 and (+)-(R)-3 enantiomers of 2-nitrooxyethyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)pyridine-5-carboxylate were synthesized for evaluation as calcium channel modulators. Determination of their in vitro calcium-channel-modulating activities using guinea pig left atria (GPLA) and ileum longitudinal smooth muscle (GPILSM) showed that the (-)-(S)-2 enantiomer acted as a dual cardioselective calcium channel agonist (GPLA)/smooth muscle selective calcium channel antagonist (GPILSM). In contrast, the (+)-(R)-3 enantiomer exhibited calcium channel antagonist activity on both GPLA and GPILSM. The 2-nitrooxyethyl racemate is a nitric oxide (.NO) donor that released 2.7% .NO, relative to the reference drug glyceryl trinitrate (5.3% .NO release/ONO(2) moiety), in the presence of N-acetylcysteamine. Whole-cell voltage-clamp studies using isolated guinea pig ventricular myocytes indicated that both enantiomers inhibit calcium current but that the (-)-(S)-2 enantiomer is a weaker antagonist than the (+)-(R)-3 enantiomer. These results indicate that replacement of the methyl ester substituent of (-)-(S)-methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)pyridine-5-carboxylate [(-)-(S)-1] by the 2-nitrooxyethyl ester .NO donor substituent present in (-)-(S)-2 provides a useful drug design concept to abolish the contraindicated calcium channel agonist effect of (-)-(S)-1 on vascular smooth muscle. The novel (-)-(S)-2 enantiomer is a useful lead compound for drug discovery targeted toward the treatment of congestive heart failure, and it provides a useful probe to study the structure-function relationships of calcium channels.