Individual Optical Isomers Research Articles

Investigation of the Optical Isomers of Methcathinone, and Two Achiral Analogs, at Monoamine Transporters and in Intracranial Self-Stimulation Studies in Rats.

Methcathinone (MCAT; 1), the progenitor of numerous and widely abused "synthetic cathinone" central stimulants, exists as a pair of optical isomers. Although S(-)MCAT is several-fold more potent than R(+)MCAT in rodent locomotor stimulation and in stimulus generalization studies in rat drug discrimination assays, the individual optical isomers of MCAT have never been directly compared for their actions at monoamine transporters that seem to underlie their actions and have never been examined for their relative abuse potential. Here, we found that the isomers of MCAT are nearly equieffective at dopamine and norepinephrine transporters (DAT and NET, respectively) as transporter substrates (i.e., as releasing agents) and are ≥63-fold less potent at the serotonin transporter (SERT). In intracranial self-stimulation (ICSS) studies to evaluate abuse-related drug effects in rats, S(-)MCAT was approximately twice as potent as its R-enantiomer. Achiral analogs, α-methyl MCAT (3) and α-des-methyl MCAT (4), also were DAT/NET substrates and also produced abuse-related ICSS effects, indicating that they retain abuse potential and that they might be useful for the further study of the stereochemistry of synthetic cathinone analogs with chiral β- (or other) substituents.

Effects of N-Alkyl-4-Methylamphetamine Optical Isomers on Plasma Membrane Monoamine Transporters and Abuse-Related Behavior.

4-Methylamphetamine (4-MA) is an emerging drug of abuse that acts as a substrate at plasma membrane transporters for dopamine (DAT), norepinephrine (NET), and serotonin (SERT), thereby causing nonexocytotic release of monoamine transmitters via reverse transport. Prior studies by us showed that increasing the N-alkyl chain length of N-substituted 4-MA analogues converts 4-MA from a transportable substrate (i.e., releaser) at DAT and NET to a nontransported blocker at these sites. Here, we studied the effects of the individual optical isomers of N-methyl-, N-ethyl-, and N- n-propyl 4-MA on monoamine transporters and abuse-related behavior in rats because action/function might be related to stereochemistry. Uptake inhibition and release assays were conducted in rat brain synaptosomes whereas electrophysiological assessments of drug-transporter interactions were examined using cell-based biosensors. Intracranial-self-stimulation in rats was employed to assess abuse potential in vivo. The experimental evidence demonstrates that S(+) N-methyl 4-MA is a potent and efficacious releaser at DAT, NET, and SERT with the highest abuse potential among the test drugs, whereas R(-) N-methyl 4-MA is a less potent releaser with reduced abuse potential. The S(+)ethyl analogue has decreased efficacy as a releaser at DAT but retains full release activity at NET and SERT with a reduction in abuse-related effects; the R(-)ethyl analogue has a similar profile but is less potent. S(+) N-Propyl 4-MA is a nontransported blocker at DAT and NET but an efficacious releaser at SERT, whereas the R enantiomer is almost inactive. In conclusion, the S enantiomers of the N-alkyl 4-MA analogues are most potent. Lengthening the N-alkyl chain converts compounds from potent nonselective releasers showing abuse-related effects to more selective SERT releasers with no apparent abuse potential.

In vitro analysis of itraconazole cis-diastereoisomers inhibition of nine cytochrome P450 enzymes: stereoselective inhibition of CYP3A

1. Itraconazole (ITZ), an antifungal azole derivate is a chiral drug that consists of four cis-diastereoisomers ((+)-2R,4S,2′R-ITZ-A; (+)-2R,4S,2′S-ITZ-B; (–)-2S,4R,2′S-ITZ-C and (–)-2S,4R,2′R-ITZ-D) which may differ in their pharmacokinetics and pharmacodynamics.2. As ITZ is known as a CYP3A4 inhibitor causing severe drug–drug interaction, the inhibitory potencies of its individual optical isomers towards nine drug-metabolising cytochrome P450 (including CYP3A, CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6 and CYP2E1), were investigated.3. All ITZ diastereoisomers dose-dependently inhibited CYP3A activity in both used assays, midazolam and testosterone hydroxylation. The Ki values were assessed: for testosterone ITZ-A/0.085 µM; ITZ-B/0.91 µM, ITZ-C/0.20 µM and ITZ-D/0.022 µM; for midazolam ITZ-A/0.44 µM; ITZ-B/0.48 µM, ITZ-C/1.56 µM and ITZ-D/3.48 µM. The enzyme activity of CYP2C19 was moderately inhibited (IC50 30–53 µM), but in this case without large differences between the individual optical isomers.4. The significant differences between diastereoisomers were presented. Antifungal potency of ITZ stereoisomers also differs so the potential enantiopure preparations of ITZ was not of interest.

Optical Isomers of Atorvastatin, Rosuvastatin and Fluvastatin Enantiospecifically Activate Pregnane X Receptor PXR and Induce CYP2A6, CYP2B6 and CYP3A4 in Human Hepatocytes.

Atorvastatin, fluvastatin and rosuvastatin are drugs used for treatment of hypercholesterolemia. They cause numerous drug-drug interactions by inhibiting and inducing drug-metabolizing cytochromes P450. These three statins exist in four optical forms, but they are currently used as enantiopure drugs, i.e., only one single enantiomer. There are numerous evidences that efficacy, adverse effects and toxicity of drugs may be enantiospecific. Therefore, we investigated the effects of optical isomers of atorvastatin, fluvastatin and rosuvastatin on the expression of drug-metabolizing P450s in primary human hepatocytes, using western blots and RT-PCR for measurement of proteins and mRNAs, respectively. The activity of P450 transcriptional regulators, including pregnane X receptor (PXR), aryl hydrocarbon receptor (AhR) and glucocorticoid receptor (GR), was assessed by gene reporter assays and EMSA. Transcriptional activity of AhR was not influenced by any statin tested. Basal transcriptional activity of GR was not affected by tested statins, but dexamethasone-inducible activity of GR was dose-dependently and enantioselectively inhibited by fluvastatin. Basal and ligand-inducible transcriptional activity of PXR was dose-dependently influenced by all tested statins, and the potency and efficacy between individual optical isomers varied depending on statin and optical isomer. The expression of CYP1A1 and CYP1A2 in human hepatocytes was not influenced by tested statins. All statins induced CYP2A6, CYP2B6 and CYP3A4, and the effects on CYP2C9 were rather modulatory. The effects varied between statins and enantiomers and induction potency decreased in order: atorvastatin (RR>RS = SR>SS) > fluvastatin (SR>RS = SS>RR) >> rosuvastatin (only RS active). The data presented here might be of toxicological and clinical importance.

Stereoselective Actions of Methylenedioxypyrovalerone (MDPV) To Inhibit Dopamine and Norepinephrine Transporters and Facilitate Intracranial Self-Stimulation in Rats.

The designer stimulant methylenedioxypyrovalerone (MDPV) is a potent reuptake inhibitor at transporters for dopamine (DAT) and norepinephrine (NET) that produces a constellation of abuse-related behavioral effects. MDPV possesses a chiral center, and the abused formulation of the drug is a racemic mixture, but no data are available on the pharmacology of its isomers. Here, the individual optical isomers of MDPV were prepared and examined with respect to their neurochemical actions on neurotransmitter reuptake and behavioral effects in an assay of intracranial self-stimulation (ICSS) in rats. In assays of DAT uptake inhibition, S(+)MDPV (EC50 = 2.13 nM) was more potent than either (±)MDPV (EC50 = 4.85 nM) or R(-)MDPV (EC50 = 382.80 nM); the three drugs were less potent at NET uptake inhibition, with the same rank order of potency. Neither racemic MDPV nor its optical isomers inhibited the reuptake of serotonin at concentrations up to 10 μM. S(+)MDPV produced an abuse-related and dose-dependent facilitation of ICSS, and the potency of S(+)MDPV (significant facilitation at doses ≥ 0.1 mg/kg) was greater than that of the racemate (significant facilitation at doses ≥ 0.32 mg/kg). R(-)MDPV failed to alter ICSS at doses up to 100 times greater than the lowest effective dose of S(+)MDPV. The results indicate that abuse-related neurochemical and behavioral effects of racemic MDPV reside primarily with its S(+) isomer.

Sorption and Separation of Optical Isomers of 2-Butanol by Chiral Porous Coordination Polymers

It was shown that porous coordination polymers (PCPs) of 3d metals containing chiral centers in fragments of deprotonated (S)-lactic and (R)-aspartic acid or trimesoyl-(S)-alanine are characterized by different values of sorption capacity with respect to the individual optical isomers of 2-butanol upon sorption of such substrates from the gas phase. The difference between the sorption capacity values with respect to the (R) and (S) isomers of 2-butanol correlates with the value of the enantiomeric excess achieved upon separation of the alcohol racemate on the respective PCP by column chromatography.

Enantioselective effects of alpha-hexachlorocyclohexane (HCH) isomers on androgen receptor activity in vitro

Alpha-hexachlorocyclohexane (alpha-HCH), a part of the HCH pesticide mixture, is one of the most widespread persistent organic pollutants. Interestingly, only limited number of studies addressed the toxicity of alpha-HCH and the effects of its individual optical isomers have not been investigated in detail. In the present study we separated two alpha-HCH enantiomers by preparative HPLC and studied their activities towards androgen receptor (AR) using the MDA-kb2 cell line stably transfected with the luciferase reporter gene under the control of AR. There was no direct effect of alpha-HCH on AR but both isomers significantly suppressed the activity of AR in co-exposure with the natural ligand dihydrotestosterone in a concentration-dependent manner. One of the enantiomers appeared to be more active at lower concentration, which was also supported by the molecular modeling calculations with AR that showed a slight difference in estimated free energy of binding and inhibition constant between two enantiomers. Although studies with other pesticides demonstrated strong enantioselective differences in toxicity, the present research shows rather minor differences in modulations of AR by both alpha-HCH enantiomers. For the first time, enantioselective effects of alpha-HCH were demonstrated and the results suggest interaction with multiple regulatory events controlling the AR activity. Full elucidation of the toxicity mechanism will require further research.

Luminescence and crystal-field fitting of two optical isomeric complexes of europium

FT-IR and Raman vibrational spectra and electronic emission spectra have been recorded for enantiomers of europium complexes with DBM: dibenzoylmethanate 1, 2, and TTFA: 2-thenoyltrifluoroacetonate 3, 4, employing the chiral ligands L SS (+)- and L RR (-)-4,5-pinene bipyridine. Contrary to the previously published X-ray data, where geometrical differences were stated to occur for particular enantiomers, the vibrational (and the emission) spectra of the individual optical isomers of a complex are not distinguishable. Using excitation into the Eu 3+ 5D 2 multiplet term, the emission intensity is weak from 5D 1, whereas a complex structure is observed for the 5D 0→ 7F J transitions. Features in the vibronic sidebands exhibit similar derived vibrational energies to those observed in the Raman spectra. Fittings of 25 4f 6 crystal-field energy levels of 2 and 4 have been attempted with some approximations concerning the local Eu 3+ environments. The 5D 0 emission lifetimes are monoexponential and are 0.5 ( 1, 2) and 0.9 ms ( 3, 4) at room temperature.

Synthesis and Pharmacological Characterization of Nicotinic Acetylcholine Receptor Properties of (+)- and (−)-Pyrido-[3,4-b]homotropanes

(+/-)-Pyrido[3,4-b]homotropane [(+/-)-1] is a conformationally rigid analogue of nicotine (2) or nornicotine (3) that showed high affinity for nicotinic acetylcholine receptors. Even though the synthesis and potent activity of this highly interesting compound was originally reported in 1986 (Kanne, D. B.; Ashworth, D. J.; Cheng, M. T.; Mutter, L. C.; Abood, L. G. Synthesis of the first highly potent bridged nicotinoid. 9-Azabicylo[4.2.l]nona[2,3-c]pyridine (pyrido[3,4-b]homotropane). J. Am. Chem. Soc. 1986, 108, 7864-7865), the individual optical isomers have not been prepared and studied. In this study, we report the synthesis of (+)- and (-)-1 and show that (+)-1 has Ki = 1.29 nM at the alpha4beta2* nAChR and has over 260 times higher affinity than (-)-1. Single-crystal X-ray analysis of an intermediate used to prepare the isomers established the absolute stereochemistry as (1S,6S)-(+)-1 and (1R,6R)-(-)-1. Surprisingly, both isomers failed to produce antinociception in the mouse tail-flick and hot-plate assays, engender nicotine-like responding in rat drug discrimination, or alter current amplitude in alpha4beta2- and alpha3beta4-containing cells. However, (-)-1 antagonized nicotine-induced antinociception with an ED50 of 0.07 microg/kg in the tail-flick assay. The reason for this unusual pharmacology is unknown, but it is possible that (-)-1 is acting at a non-epibatidine-sensitive receptor subtype to antagonize nicotine's effects in the tail-flick assay.

Discriminative stimulus properties of α-ethyltryptamine optical isomers

α-Ethyltryptamine (α-ET) possesses central stimulant and hallucinogenic activity. Also, in tests of stimulus generalization using rats trained to discriminate the controlled substance analog (i.e., designer drug) N-methyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane (MDMA) from vehicle, α-ET substituted for MDMA. These previous studies employed racemic α-ET. Because psychoactive phenylalkylamines with abuse potential can produce one or more of three distinct stimulus effects (i.e., amphetamine-, DOM- and/or PMMA-like effects) in animals trained to discriminate either the stimulant (+)amphetamine, the hallucinogen 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM), or N-methyl-1-(4-methoxyphenyl)-2-aminopropane (PMMA) from vehicle, and because these effects can be stereoselective, the individual optical isomers of α-ET were examined in groups of animals trained to discriminate (+)amphetamine, DOM, PMMA and MDMA from saline vehicle. (−)α-ET (ED 50=7.8 mg/kg), but not (+)α-ET (maximum of 53% drug-appropriate responding), substituted for (+)amphetamine, whereas (+)α-ET (ED 50=2.7 mg/kg), but not (−)α-ET (maximum of 33% drug-appropriate responding), substituted for DOM. Both optical isomers of α-ET substituted for PMMA and MDMA with ED 50 values of 1.6 and 1.4 mg/kg (PMMA-trained animals) and 1.3 and 2.0 mg/kg (MDMA-trained animals) for (−)α-ET and (+)α-ET, respectively. The results of this investigation suggest that both optical isomers of α-ET are capable of producing an MDMA/PMMA-like effect at nearly comparable doses, and that the stimulant or amphetamine-like nature of α-ET resides primarily with its (−)isomer whereas hallucinogenic or DOM-like character resides primarily with the (+)enantiomer.

Clinical pharmacology and safety profile of esomeprazole, the first enantiomerically pure proton pump inhibitor.

Awareness of important differences in the pharmacological profile of individual optical isomers of chiral drugs led to the development of esomeprazole, the S-isomer of omeprazole, a new pharmacological entity designed to improve the clinical outcome of available proton pump inhibitors in the management of acid-related disorders. The superior acid control achieved by esomeprazole is mainly due to an advantageous metabolism compared with racemate omeprazole, leading to improved bioavailability and to enhanced delivery of the drug to the gastric proton pump.

An examination of isomeric phenylpropanolamines in (−)ephedrine-trained rats

A total of eight isomeric phenylpropanolamines are possible when the terminal amine is either an N-monomethylamine or a primary amine: (−)ephedrine, (+)ephedrine, (+)pseudoephedrine, (−)pseudoephedrine, (−)norephedrine, (+)norephedrine, (+)cathine, and (−)cathine. Few previous studies have examined the individual optical isomers of these phenylpropanolamines and, with the exception of one report on locomotor effects, no comparative behavioral data have been published on this series of agents. Using rats trained to discriminate 4 mg/kg of (−)ephedrine (i.p.) from saline vehicle using standard operant conditioning with a VI 15-s schedule of reinforcement, all eight agents were examined in tests of stimulus generalization. The (−)ephedrine stimulus (ED 50=0.90 mg/kg) generalized to (+)ephedrine (ED 50=2.64 mg/kg), (+)pseudoephedrine (ED 50=6.58 mg/kg), (−)norephedrine (ED 50=1.86 mg/kg), (+)norephedrine (ED 50=5.75 mg/kg), and (+)cathine (ED 50=4.87 mg/kg). The (−)ephedrine stimulus failed to generalize to either (−)pseudoephedrine or (−)cathine; the latter agents produced a maximum of 29 and 31% (−)ephedrine-appropriate responding, respectively. Thus, (a) six of the eight phenylpropanolamines produced ephedrine-like stimulus effects, (b) (−)ephedrine was the most potent of the examined agents, and (c) where stimulus generalization occurred, ED 50 values spanned less than a tenfold range.

8′,8′-Difluoro- and 8′,8′,8′-trifluoroabscisic acids as highly potent, long-lasting analogues of abscisic acid

Racemic 8′,8′-difluoroabscisic acid (difluoro-ABA) and 8′,8′,8′-trifluoroabscisic acid (trifluoro-ABA) were synthesized as highly potent, long-lasting analogues of abscisic acid (ABA). The individual optical isomers were obtained by optical resolution of the racemic mixture by HPLC with a chiral column. (+)-8′,8′-Difluoro-ABA and (+)-8′,8′,8′-trifluoro-ABA inhibited the elongation of rice seedlings six and 30 times more strongly, respectively, than (+)-ABA. These analogues also showed double the (+)-ABA-induced inhibition of lettuce seed germination. In causing stomatal closure and inhibiting the induction of α-amylase by gibberellin A 3, these analogues were equally as effective as (+)-ABA. The high activity in the assays over a long period suggested that the metabolism of difluoro- and trifluoro-ABAs was delayed. (−)-Enantiomers were equal to, or weaker than (−)-ABA in the assays.

Effect of Abscisic Acid Optical Isomers, Alone or in Combination with Gibberellic Acid, on Barley Malt Quality

The effect of racemic abscisic acid (ABA) and the individual optical isomers, (+)ABA and (−)ABA, alone or in combination with gibberellic acid (GA3), on the malting quality of Bonanza barley was de...

Effect of the optical isomers of YM-12617 on increased intra-urethral pressure induced by phenylephrine in anaesthetized dogs.

1. Effects of the individual optical isomers of YM-12617 (R, S 5-[2-[[2-(o-ethoxyphenoxy)ethyl]-amino]propyl]-2- methoxybenzenesulphonamide HCl, (+/-)-YM), a potent selective alpha 1-adrenoceptor antagonist, on the increase in intraurethral pressure (IUP) and diastolic blood pressure (DBP) induced by phenylephrine were evaluated in pentobarbital-anaesthetized female dogs. 2. Phenylephrine (0.1-30 micrograms kg-1 i.v.), an alpha 1-adrenoceptor agonist, dose-dependently increased IUP and DBP. 3. alpha-adrenoceptor antagonists (i.v.) dose-dependently antagonized the increase in IUP and DBP induced by phenylephrine, with a potency ranking of R(-)-YM greater than (+/-)-YM greater than prazosin greater than phentolamine greater than S(+)-YM greater than yohimbine. 4. These results suggest that the alpha 1-adrenoceptor mediates the increase in IUP as well as DBP in anaesthetized dogs, and that alpha 1-adrenoceptors in the urethra and arteries show a stereochemical preference for R(-)-YM.

Synthesis, resolution and biological activity of 7′,7′-difluoroabscisic acid

7′,7′-Difluoroabscisic acid was synthesized in seven steps from the known ketoaldehyde 4,4-ethylenedioxy-2-formal-6,6-dimethylcyclohex-2-en-1-one. Fluorination with diethylaminosulphur trifluoride afforded the key intermediate 2-difluoromethyl-4,4-ethylenedioxy-6,6-dimethyleyclohex-2-en-1-one which was further transformed to 7′,7′-difluoroabscisic acid. The racemic mixture and the individual optical isomers, obtained by resolution of the methyl esters by HPLC, displayed activity similar to the optical isomers of ABA in assays for germination in cress and freezing tolerance in bromegrass cell suspension culture.

Cyanobiphenyl-group alignment observed by a scanning tunneling microscope

The geometry of a nematic liquid crystal (LC), 4-n-octyl-4'-cyanobiphenyl (8CB) on the (0002) surface of graphite is studied by scanning tunneling microscopy. The tilting of cyanobiphenyl-groups on a substrate is observed. Molecular orbital calculations confirm that the molecular orbitals of neighboring molecules interact with each other. It is confirmed by the calculation between two molecules that a cyanobenzene configuration normal to the graphite surface is energetically favorable. This shows that the LC molecule alignment is determined not only by the interaction between molecules but also by its interaction with the substrate. This may provide a means of making individual molecule optical isomers.

Stereospecific recognition of inositol 1,4,5-trisphosphate analogs by the phosphatase, kinase, and binding proteins.

A series of DL-inositol 1,4,5-trisphosphate (IP3) analogs, with a bulky substitutent on the 2nd carbon of the inositol ring, has been synthesized. These compounds exert biological activities with only minor reduction in potency, in several assay systems (Hirata, M., Watanabe, Y., Ishimatsu, T., Ikebe, T., Kimura, Y., Yamaguchi, K., Ozaki, S., and Koga, T. (1989) J. Biol. Chem. 264, 20303-20308). Two analogs with aminocyclohexanecarbonyl (designated as analog 206) or aminobenzoyl group (analog 209) were separated into individual optical isomers and examined for stereospecificity in recognition by IP3-5-phosphatase, IP3-3-kinase and IP3 binding activity. IP3-5-phosphatase activity of erythrocyte ghosts was competitively inhibited by L-209 with a lower Ki value than D-IP3, but with a higher Ki value by L-206. D-Isomers of both analogs at 100 microM failed to inhibit the hydrolysis of D-[3H]IP3. On the other hand, D-isomers but not L-isomers of both analogs were as potent as D-IP3 in the recognition by IP3-3-kinase of rat brain cytosol and only the D-isomer of analog 206 could serve as substrate for the kinase. Also D-isomers of both analogs were equipotent to D-IP3 in displacing [3H]IP3 binding to rat cerebellum microsomes. These observations suggest that the IP3 analogs we synthesized are stereospecifically recognized by three IP3-recognizable proteins, but the phosphatase recognizes opposite isomers. Such being the case, the second hydroxyl group of D-IP3 may be involved in the recognition by IP3-5-phosphatase, but not by IP3-3-kinase and binding sites.

Stimulus properties of a new designer drug: 4-methylaminorex (“U4Euh”)

Like other phenylisopropylamine derivatives, 4-methylaminorex is a central stimulant. The cis isomer of 4-methylaminorex (“U4Euh”; “ICE”) has appeared on the clandestine market as a novel designer drug and was recently classified as a Schedule I substance. In the present investigation, the stimulus properties of racemic cis, racemic trans, and all four individual optical isomers of 4-methylaminorex were examined in rats trained to discriminate 1 mg/kg of S(+)amphetamine sulfate from saline. The S(+)amphetamine stimulus generalized to all of the agents investigated and the relative potencies of the optical isomers (followed by ED 50 values) were as follows: trans(4 S,5 S) (0.25 mg/kg) > cis(4 S,5 R) (1.2 mg/kg) = cis(4 R,5 S) (1.5 mg/kg) > trans(4 R, 5 R). The trans(4 R,5 R) isomer did not completely substitute for S(+)amphetamine unless a longer (i.e., 60-min) presession injection interval was used, suggesting that it has a longer duration of onset that the other isomers of 4-methylaminorex. The results, which are consistent with established structure-activity relationships, suggest that the trans(4 S,5 S) isomer (which has not been scheduled) is similar in potency to (+)amphetamine (ED 50=0.4 mg/kg) and is more potent than either of the cis isomers.

Diastereomeric resolution of carotenoids : IV. Carotenoids with a 4-hydroxy-β-end group

A method is described for the diastereomeric resolution of carotenoids with a 4-hydroxy-β-end group, viz., β-isocryptoxanthin (β,β-caroten-4-ol), isozeaxanthin (β,β-carotene-4,4′-diol) and 4′-hydroxyechinenone (4′-hydroxy-β,β-caroten-4-one). The separation of each carotenoid into individual optical isomers was achieved by high-performance liquid chromatography using a Chiralcel OD [cellulose tris(3,5-dimethylphenylcarbamate) coated on silica gel] chiral resolution column after conversion to the corresponding benzoates.