Contact chemoreceptive mate recognition in Cerambyx welensii Küster (Coleoptera: Cerambycidae)

1. Cerambyx welensii Küster (Coleoptera: Cerambycidae) is a wood-borer responsible for the decline of Mediterranean oaks in open woodlands.
2. To establish that contact pheromones are involved in mate recognition of C. welensii, we extracted the cuticular hydrocarbons by solid phase microextraction at pre-reproductive, beginning and ending of the reproductive period, and by solvent extraction of prothorax and elytra. The extracts were analysed by GC–MS under electron impact and chemical ionization conditions. Cuticular hydrocarbon profiles varied according to the reproductive period, although differences between sexes were not significant. Two compounds, 11/13-methylheptacosane and 11-methylnonacosane were more abundant in females at the beginning and ending of the reproductive periods. Compound 11/13-methylheptacosane was also more representative in female prothorax than in males, and 2-methyloctacosane was richer in male elytra than in females.
3. We also studied the role of cuticular hydrocarbons in mate recognition in arena bioassays. Treatment of solvent-washed dead females and glass dummies with one female equivalent (FE) of cuticular extract elicited mating responses in males, especially at the beginning of the reproductive period, with copulation attempts reaching 61.9% on solvent-washed dead females and 23.8% on dummies. The successive treatment with synthetic compounds approaching a male cuticular profile inhibited male response.
4. Our results confirm that contact pheromones mediate mate recognition in C. welensii. Knowledge of the precise role played by the major compounds 11/13-methylheptacosane and 11-methylnonacosane and other minor compounds representative in female prothorax may contribute to the development of novel management strategies against C. welensii.

     

The influence of aging on the stereoselective pharmacokinetics of propranolol in the rat.

The influence of aging on the pharmacokinetics and the tissue distribution of (R)- and of (S)-propranolol was studied in 3-, 12-, and 24-month-old rats. After both iv and oral administration of rac-propranolol, the plasma concentrations were higher for the (R)- than for the (S)-enantiomer. For the tissue concentrations, the reverse was true. The free fraction of (S)-propranolol in plasma was about 4 times larger than that of (R)-propranolol, and this is the main factor responsible for the differences in kinetics between the two enantiomers. There was a suggestion for a difference in tissue binding between the two enantiomers. With aging, the plasma and tissue concentrations of both enantiomers increase, probably due to a decrease in blood clearance. Tissue binding did not change much with aging. Notwithstanding the marked differences between the kinetics of the propranolol enantiomers, the changes which occur with aging affect both enantiomers to the same degree.     

Stereoselectivity of the Inhibition of [3H]Hemicholinium-3 Binding to the Sodium-Dependent High-Affinity Choline Transporter by the Enantiomers of a- and β-Methylcholine

Abstract: In a previous report, we showed that the enantiomers of α- and β-methylcholine inhibited choline uptake with Stereoselectivity, but that their transport by the choline carrier of nerve terminals showed stereospecificity. The present experiments used the same choline analogues to determine if either of the above characteristics pertains to their ability to interact with the [³H]-hemicholinium-3 binding site present on striatal membranes and synaptosomes. [³H]Hemicholinium-3 binding to striatal membranes could be inhibited stereoselectively by the enantiomers of β-methylcholine, but R (+)-α-methyl-choline was little better than its enantiomer in this test. However, [³H]hemicholinium-3 binding to striatal synaptosomes was inhibited stereoselectively by the enantiomers of both α- and β-methylcholine. This difference between the properties of [³H]hemicholinium-3 binding to membranes or to synaptosomes appears related to the presence of two ligand binding states. The [³H]hemicholinium-3 binding site could be shifted to a low-affinity state by ATP treatment and to a high-affinity state by EDTA washing. When the [³H]hemicholinium-3 binding site existed in its low-affinity state, binding was inhibited stereoselectively by the enantiomers of both a- and β-methylcholine, but when shifted to its high-affinity state, it was inhibited stereoselectively only by the enantiomers of β–methylcholine. We conclude that hemicholinium-3 interacts with the substrate recognition site of the high-affinity choline transporter, but that the Stereoselectivity of this site changes depending on its affinity state.     

Synthesis of the four components of the female sex pheromone of the painted apple moth,Teia anartoides

Four pheromone components of the female painted apple moth (Teia anartoides), an Australian insect pest, were synthesized. These were (Z)-6-henicosen-11-one (1), (6Z, 8E)-6,8-henicosadien-11-one (2), (Z)-cis-9,10-epoxy-6-henicosene (3), and (Z)-cis-9,10-epoxy-6-icosene (4). 2-Dodecanone was converted to 1 and 2, and both the enantiomers of 3 and 4 were synthesized from the enantiomers of 4-tert-butyldimethylsilyloxy-cis-2,3-epoxy-1-butanol.     

Identification of rat cytochrome P450 forms involved in the metabolism of clausenamide enantiomers

To identify which cytochrome P450 (CYP) isoform(s) are responsible for the metabolism of clausenamide (CLA) enantiomers in rats, effects of various CYP isoform inducers and inhibitors on the formation of CLA metabolites were investigated in liver microsomes. In incubations with rat liver microsomes, CLA enantiomers were mainly converted to 4-hydroxy, 5-hydroxy, and 7-hydroxy-metabolites. 4-OH-CLA was the major metabolite of (+)-3R, 4S, 5S, 6R-CLA [(+)-CLA], while 7-OH-CLA was the major one of (-)-3S, 4R, 5R, 6S-CLA [(-)-CLA]. In induction studies, enzymatic parameters were used to assess the role of different CYP forms in CLA hydroxylation reactions. A marked increase in the rate of metabolism of CLA enantiomers was observed in microsomes of dexamethasone treated rats, V(max)/K(m) values for 4-OH-(+)-CLA, 7-OH-, 5-OH-, and 4-OH-(-)-CLA were 5.3, 6.5, 3.0, and 5.9 times higher than those in control microsomes, respectively. Rifampicin treatment caused corresponding 1.7-, 2.6-, 3.1-, and 2.8-fold increases. Dex and Rif also increased in the amount of (+)-5- and (+)-7-OH-CLA that were not detectable in the control group. These results suggested that inducible CYP3A1 was involved in the hydroxylation of CLA enantiomers. In inhibition studies, ketoconazone (6.25 microM) completely inhibited the production of main metabolites of (-)-CLA (100%) and (+)-CLA (97%). Triacetyloleandomycin (12.5 microM) strongly inhibited the corresponding metabolites by 34-85%. These findings also indicated that institutive CYP3A2 shared a major role in the hydroxylation of CLA enantiomers with CYP3A1 in untreated rats. Together, the data suggested that CYP3A was the predominant isoform responsible for the metabolism of CLA enantiomers.     

Stereospecificity of the in vitro and in vivo blockade of beta-receptors by FM 24, a slowly reversible ligand

Exo FM 24 (1-(2-exo-bicyclo[2,2,1]hept-2-ylphenoxy)-3[(1-methylethyl) amino]-2-propanol hydrocloride, a long lasting β-blocker is a mixture of four enantiomers. Exo FM 24 and its endo derivative were 5 to 8 times more potent after preincubation on [³H]DHA binding to rat brain membranes. Similar results were obtained with the four enantiomers, the order of potency being (αS,2S) > (αR,2S) > (αS,2R) > (αR,2R). These four enantiomers behave as competitive antagonists when no preincubation is performed but blocked β-receptors in a non competitive manner after preincubation. Under conditions in which the effect of (S,R) propranolol was completely reversed (7 cycles of washing), the effect of the two 2 S enantiomers was not reversed whereas the effect of the two 2R enantiomers was partially reversed. The potency and duration of blockade of β-receptors, as measured by the in vivo binding of [¹²⁵I] hydroxybenzylpindolol to mouse brain, heart and lung, correlated very well with the in vitro results. The potency and duration of exo FM 24 appeared to be the mean of its four enantiomers. It is proposed that the exo FM 24 formed a reversible complex with β-receptors which is slowly transformed to a non competitive slowly reversible complex which corresponds to the two 2R enantiomers, and to a non competitive irreversible complex which corresponds to the two 2S enantiomers.     

Evaluation of chiral discrimination of highly negatively charged enantiomers by quaternary ammonium beta-cyclodextrin using 1H NMR

The positively charged quaternary ammonium cyclodextrin, QA-beta-CD, was previously used as a chiral selector to achieve baseline resolution of two of the dianionic enantiomers of disodium 3-(p-isothiocyanatophenoxy)-3-(p-isothiocyanatophenyl)propane-1,2-disulfate by capillary electrophoresis. The basis of the chiral discrimination between QA-beta-CD and the enantiomers was investigated by (1)H NMR spectroscopy. COSY and NOESY spectra were used to infer the role that molecular interactions and the stereocenters have upon association of QA-beta-CD with the enantiomers. A parallel two-step complexation model is used to rationalize the NMR and the chiral discrimination observed during separation of the enantiomers.     

Studies on the stereoselective effects of a novel 5-HT2 receptor antagonist on contractile responses of rat aorta

The effect of the enantiomers of a novel 5-HT2 receptor antagonist, (+/-)-(1R,3S)-1-[2-[4-[3-(p-fluorophenyl)-1-indanyl]-piperazinyl] ethyl]-2-imidazolidinone, was studied on serotonin (5-HT), noradrenaline (NA), potassium (K+), and calcium (Ca2+)-induced contractions in isolated rat thoracic aorta. The enantiomers shifted the 5-HT, NA, K+, and Ca2+ concentration-response curves to the right in a concentration-dependent manner and depressed the maximal contractile responses. The (+)-enantiomer was a far more potent inhibitor of 5-HT-induced contractions than the (-)-enantiomer. The (+)-enantiomer and phentolamine, both at 10(-6) M, had equal inhibitory effects on NA-evoked contractions. The (+)-enantiomer was again more potent inhibiting NA-induced contractions than the (-)-enantiomer. Both enantiomers had an equieffective inhibitory effect on K+ and Ca2(+)-induced contractions. The results show that the 5-HT and alpha-adrenoceptor antagonism of the two enantiomers is stereoselective, the (+)-enantiomer being more potent than the (-)-enantiomer. In contrast the enantiomers had equal, nonstereoselective inhibitory effects on K+ and Ca2(+)-evoked contractions.     

Resolution of racemic carbovir and selective inhibition of human immunodeficiency virus by the (-) enantiomer

(+-) Carbocyclic 2',3'-didehydro-2',3'-dideoxyguanosine (Carbovir; NSC 614846) is an antiretroviral agent which is undergoing preclinical evaluation for the treatment of AIDS. Racemic carbovir was separated into its D and L enantiomers by the action of adenosine deaminase on the 2,6-diaminopurine precursor. Subsequent evaluation of the enantiomers against human immunodeficiency virus type 1 revealed that the antiviral activity of carbovir resides in the (-) isomer that is analogous to the nucleoside, beta-D-2',3'-didehydro-2',3'-dideoxyguanosine.     

Resolution and stability of oxazepam enantiomers

A solvent mixture containing dioxane, acetonitrile, and hexane was found to be suitable as a mobile phase to resolve oxazepam enantiomers by chiral stationary phase high performance liquid chromatography using covalent Pirkle columns. The resolved oxazepam enantiomers in this solvent mixture had a racemization half-life greater than 3 days at 23°C. When desiccated at 0°C as dried residue, OX enantiomers were stable for at least 50 days with less than 2% racemization. The conditions which stabilized OX enantiomers significantly facilitated the determination of racemization half-lives of OX enantiomers in a variety of aqueous and nonaqueous solvents and at different temperatures. © 1992 Wiley-Liss, Inc.     

Enantiomeric separation of malathion and malaoxon and the chiral residue analysis in food and environmental matrix

Malathion is a widely used chiral phosphorus insecticide, which has a more toxic chiral metabolite malaoxon. In this work, the enantiomers of malathion and malaoxon were separated by high-performance liquid chromatography-mass/mass (HPLC-MS/MS) with chiral columns using acetonitrile/water or methanol/water as mobile phase, and the chromatographic conditions were optimized. Based on the chiral separation, the chiral residue analysis methods for the enantiomers in soil, fruit, and vegetables were set up. Two pairs of the enantiomers were better separated on CHIRALPAK IC chiral column, and baseline simultaneous separations of malathion and malaoxon enantiomers were achieved with acetonitrile/water (40/60, v/v) as mobile phase at a flow rate of 0.5 mL/min. The elution orders were −/+ for both malathion and malaoxon measured by an optical rotation detector. The chiral residue analysis in soil, fruit, and vegetables was validated by linearity, recovery, precision, limit of detection (LOD), and limit of quantification (LOQ). The LODs and LOQs for the enantiomers of malathion were 1 μg/kg and 3–5 μg/kg and 0.08 μg/kg and 0.20–0.25 μg/kg for malaoxon enantiomers. Good linear calibration curves for each enantiomer in the matrices were obtained within the concentration range of 0.02–12 mg/L. The mean recoveries of the enantiomers of malathion and malaoxon ranged from 82.26% to 109.04%, with RSDs of 0.71–8.63%.The results confirmed that this method was capable of simultaneously determining the residue of malathion and malaoxon in food and environmental matrix on an enantiomeric level.     

Determination of the enantiomers of a novel 20,21-dinoreburnamenine derivative in rat plasma and brain by high-performance liquid chromatography using a chiral stationary phase

A high-performance liquid chromatographic method with solid-phase extraction was developed for the assay of the enantiomers of a novel 20,21-dinoreburnamenine derivative (RU 49041) in rat plasma and brain using a chiral stationary phase (Nucleosil Chiral 2) and ultraviolet detection. The limit of detection was 10 ng/ml (or ng/g) in both tissues and the intra-assay precision was satisfactory (plasma, ca. 5%; brain, ca. 1%). The pharmacokinetic profiles of the two enantiomers were determined following oral administration of the racemate (10 mg/kg). The results show that their pharmacokinetics are very different: whereas both enantiomers appear in the brain, only the 3α,16β-enantiomer is detected in plasma.     

The effect of the diameter of cyclic peptide nanotube on its chirality discrimination

In this work, the transport behaviors of the enantiomers of lactic acid (LA) in two cyclic peptide nanotubes (CPNTs) with different diameters were studied using steered molecular dynamic (SMD) simulation to investigate the effect of the diameter of CPNT on the discrimination of the enantiomers of LA. For this purpose, two cyclic peptides with two different sizes ([Ala-_D-Ala-_L]₅ and [Ala-_D-Ala-_L]₄) were used for constructing two CPNTs so that each CPNT was composed of eight cyclic peptide units. The docking calculations were performed to obtain the appropriate position of each enantiomer at the lumen of each CPNT. The variation of the pulling force versus time, exerted on the enantiomers moving in the CPNTs was calculated using the SMD simulations with two different strategies (positional and directional).The obtained results showed that the diameter of CPNT has considerable effect on the discrimination of the LA enantiomers so that the increase of the diameter of CPNT, increased the velocity difference between two enantiomers and improved the performance of CPNT for the chirality discrimination. The SMD simulations indicated that the velocity of S-enantiomer became more than R-enantiomer and its motion became more comfortable than R-enantiomer when the diameter of CNPT increased. The RDFs of the H and O atoms of the LA enantiomers relative to the O atoms of CPNT were calculated and it was found that the increase of the diameter of CPNT creates the significant changes in the RDFs of H1, H2 and H3 atoms of the enantiomers.     

Synthesis and evaluation of the antidepressant activity of the enantiomers of bupropion

The synthesis of the enantiomers of bupropion, (rac)-2-tert-butylamino-3′-chloropropiophenone 1 (Wellbutrin®) is described. The enantiomers were compared with the racemate in both the tetrabenazine-induced sedation model and the inhibition of uptake of biogenic amine assay. No significant differences were found in their potencies to reverse tetrabenazine-induced sedation in mice or in their IC₅₀ values as inhibitors of biogenic amine uptake into nerve endings obtained from mouse brain. © 1993 Wiley-Liss, Inc.     

Assay of tocainide enantiomers in plasma by solid-phase extraction and indirect chiral high-performance liquid chromatography after derivatization with (−)-menthyl chloroformate

A fast high-performance liquid chromatographic (HPLC) assay was developed for determination of tocainide enantiomers in plasma. Subsequent to solid-phase extraction of tocainide from plasma, homochiral derivatization with ()-menthyl chloroformate enabled separation of the enantiomers by a conventional reversed-phase HPLC system. The detection was performed by UV absorption at 262 nm. An enantiomeric resolution of 1.0 was obtained. Linearity of the method was investigated and found to be good in the range from 1.0 to 20.0 μg/ml tocainide enantiomer and the limit of quantitation was 1.0 μg/ml. The method was applied to a study of the distribution and elimination pharmacokinetics of tocainide enantiomers in the rabbit. No difference in distribution or elimination between the enantiomers was found nor did the enantiomers affect the disposition of one another when administered together as the racemate.     

Asymmetric synthesis and biological evaluation of the enantiomeric isomers of the immunosuppressive FTY720-phosphate

A practical asymmetric synthesis of both enantiomers of the immunosuppressive FTY720-phosphate (2) was accomplished, and the enantiomers were pharmacologically evaluated. Several lipases showed considerable activity and enantioselectivity for O-acylation of N-acetyl FTY720 (3) or N-benzyloxycarbonyl FTY720 (7) in combination with vinyl acetate or benzyl vinyl carbonate as the acyl donors. The synthesis using the lipase-catalyzed acylation as the key step produced the enantiomerically pure (>99.5% ee) enantiomers of 2 in multigram quantities. (S)-Isomer of 2 had more potent binding affinities to S1P(1,3,4,5) and inhibitory activity on lymphocyte migration toward S1P than (R)-2, suggesting that (S)-isomer of 2 is responsible for the immunosuppressive activity after administration of 1. Severe bradycardia was observed in anesthetized rats when (S)-2 was administered intravenously, while (R)-2 had no clear effect on heart rate up to 0.3 mg/kg.     

Stereoselectivity toward VX is determined by interactions with residues of the acyl pocket as well as of the peripheral anionic site of AChE

The origins of human acetylcholinesterase (HuAChE) reactivity toward the lethal chemical warfare agent O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX) and its stereoselectivity toward the P(S)-VX enantiomer (VX(S)) were investigated by examining the reactivity of HuAChE and its mutant derivatives toward purified enantiomers of VX and its noncharged isostere O-ethyl S-(3-isopropyl-4-methylpentyl) methylphosphonothioate (nc-VX) as well as echothiophate and its noncharged analogue. Reactivity of wild-type HuAChE toward VX(S) was 115-fold higher than that toward VX(R), with bimolecular rate constants of 1.4 x 10(8) and 1.2 x 10(6) min(-1) M(-1). HuAChE was also 12500-fold more reactive toward VX(S) than toward nc-VX(S). Substitution of the cation binding subsite residue Trp86 with alanine resulted in a 3 order of magnitude decrease in HuAChE reactivity toward both VX enantiomers, while this replacement had an only marginal effect on the reactivity toward the enantiomers of nc-VX and the noncharged echothiophate. These results attest to the critical role played by Trp86 in accommodating the charged moieties of both VX enantiomers. A marked decrease in stereoselectivity toward VX(S) was observed following replacements of Phe295 at the acyl pocket (F295A and F295A/F297A). Replacement of the peripheral anionic site (PAS) residue Asp74 with asparagine (D74N) practically abolished stereoselectivity toward VX(S) (130-fold decrease), while a substitution which retains the negative charge at position 74 (D74E) had no effect. The results from kinetic studies and molecular simulations suggest that the differential reactivity toward the VX enantiomers is mainly a result of a different interaction of the charged leaving group with Asp74.     

Synthesis, characterization and antiproliferative studies of the enantiomers of cis-[(1,2-camphordiamine)dichloro]platinum(II) complexes

The platinum(II) complex cis-[(1S,2R,3S)-1,7,7-trimethylbicyclo[2.2.1]heptane-2,3-diamine]dichloroplatinum(II) (1) and its enantiomer (2) have been synthesized and physically and spectroscopically characterized. To obtain the enantiopure complexes the chiral pool approach was applied. The synthetic pathway has four steps, starting from (+/-)-diphenylethylenediamine (DPEDA) (3) and the natural products (1S)-camphorquinone or (1R)-camphorquinone to obtain enantiomers 1 and 2, respectively. The interaction of the Pt(II) complexes with DNA was studied by several techniques: circular dichroism, electrophoresis on agarose gel and atomic force microscopy (AFM). These studies showed differences in the degree of interaction between both enantiomers and DNA (calf thymus DNA and plasmid pBR322 DNA). The cytotoxicity of enantiomers 1 and 2 against the HL-60 cell line was studied by in vitro tests of antiproliferative activity, incubating during both 24 h and 72 h. An important difference of activity was found between both enantiomers regarding the IC50 data at 24 h of incubation. Thus, complex 1 showed to be much more active than its enantiomer 2.     

Synthetic racemate and enantiomers of cytosporone E, a metabolite of an endophytic fungus, show indistinguishably weak antimicrobial activity

The racemate and the enantiomers of cytosporone E [3-heptyl-4,5,6-trihydroxyphthalide (1)], a metabolite of the endophytic fungus, CR200 (Cytospora sp.), were synthesized. The key steps were (i) Sharpless asymmetric dihydroxylation of an alkene (8) and (ii) HPLC separation of the enantiomers of tert-butyldimethylsilyl ether (12) on a chiral stationary phase. The racemate and enantiomers of cytosporone E showed only weak antimicrobial activity with no difference among them.