氢化阿托酸在大鼠体内时间药代动力学参数的立体选择性

研究了氢化阿托酸在大鼠体内的立体选择药代动力学参数,结果表明,在标准明暗周期下,T_1/2α和CL具有立体择性,而反相明暗周期下,有立体选择性的药代动力学参数为T_1/2β,AUC,CL,Vc和MRT。比较两种明暗周期各相应参数,除极少数几个参数外,都无显著差异。     

维拉帕米对映体在人体的药代动力学

目的： 考察维拉帕米(VPM)和去甲维拉帕米(NVPM)对映体的药代动力学特性。 方法： 8名汉族男性健康志愿者分别po外消旋VPM 80 mg和静滴5 mg,以三甲基-β-环糊精为手性选择剂,毛细管电泳法同时测定VPM和NVPM对映体的血浆浓度,用二房室开放模型拟合药-时曲线。结果： po VPM的R/S(AUC),R/S(CL)和R/S(C_max)比率分别为3.66±1.86,0.3±0.053和4.82±0.58;NVPM的R/S(C_max)和R/S(AUC)比率为2.58和2.36。iv VPM的R/S(AUC),R/S(CL)和R/S(C_max)比率分别为1.04±0.29,1.01±0.3和1.36±0.12。R-(+)-VPM和S-(-)-VPM的绝对生物利用度为30.3±19和9.8±5.9。结论： VPM有较大的对映体特异性首过代谢,选择优对映体S-(-)-VPM为监测对象有利于临床合理使用外消旋VPM。     

β阻滞剂及其对映体拮抗TNFα诱发的心肌细胞信号转导异常

目的：观察β阻滞剂及其对映异构体对TNFα诱发的心肌细胞信号转导异常的拮抗作用。方法：用体外培养的乳鼠心肌细胞进行β受体密度、G蛋白、AC活性及PKA活性测定。结果：TNFα下调β受体密度;下调Gs蛋白,上调Gi蛋白,降低Gs/Gi比值;细胞内cAMP水平升高;激活PKA,总PKA水平升高。此作用能被β阻滞剂的R(+)型对映体而不是S(-)型对映体所拮抗。结论：β阻滞剂的R(+)型对映体有较好的拮抗TNFα介导的细胞毒作用,可能有利于对心衰的治疗。     

合霉素及其前体消旋-反式-1-对硝基苯-2-氨基-1,3-丙二醇的拆开

合霉素(消旋-I_a)可利用由D(-)-扁桃酸制成的α-乙酰氧基苯乙酰氯作为拆开剂拆开.L(+)-I_a的D(-)-α一乙酰氧基苯乙酸酯在乙醇中首先析出.合霉素前体(消旋-II)于应用(+)-酒石酸单甲酯为拆开剂时,获得L(+)-II的酒石酸单甲酯盐,从母液中分得不纯的D(-)-II.     

苯丙哌林在健康人体内的对映体选择性药物动力学研究

目的　研究苯丙哌林在健康人体内的对映体选择性动力学过程。方法　以非手性HPLC法测定不同时刻血浆样品中苯丙哌林的浓度,再用手性HPLC法测定两对映体的浓度比值,计算得到血浆中(R)-和(S)-苯丙哌林的浓度。结果　6名受试者血浆中S体浓度始终高于R体,S体的AUC_0-t和C_max的均值分别为R体的2.12倍和2.18倍,但二者的T_1/2无显著性差异。服药后0.5 h血浆中S/R对映体浓度比值高达3.8,此后迅速下降,2 h后约为2.2,基本保持恒定到24 h。结论　口服(±)-苯丙哌林后, 两对映体在人体内的药物动力学过程具有显著的立体选择性。     

外消旋普罗帕酮在经诱导的大鼠肝微粒体中N-去丙基化的立体选择性

采用对照及β-萘黄酮(β-NF)或地塞米松(Dex)诱导的大鼠肝微粒体,应用GITC柱前衍生化,反相高效液相色谱法研究了消旋普罗帕酮〔(R/S)-PPF〕体外代谢的立体选择性. 实验结果表明,在Dex,β-NF诱导的微粒体中有N-去丙基普罗帕酮生成。在β-NF,Dex预处理组,(R/S)-PPF低浓度时的经肝微粒体代谢具有立体选择性,R(-)对映体的清除大于S(+)对映体,高浓度时的代谢无立体选择性. R(-)对映体的K_m值显著低于S(+)对映体,而V_max值无显著性差异. 在Dex预处理组中的立体选择性大于β-NF组. 在对照组中代谢无立体选择性,且K_m,V_max值均小于β-NF,Dex预 处理组。结果提示,CYP1A,CYP3A4亚族对普罗帕酮(PPF)的N-去丙基化有贡献. (R/S)-PPF的N-去丙基化具有浓度依赖性的立体选择性.     

酞丁安对映体合成及其抗单纯疱疹病毒活性评价

酞丁安(3-酞酰亚胺-2-氧-正丁醛双缩氨硫脲,TDA)是药物研究所创制的抗病毒新药。为了研究其对映异构体(R),(S)-TDA对病毒活性及毒性是否有差异,并与消旋酞丁安(RS)-TDA的抗病毒活性及毒性进行比较,本文分别用已知构型的(R)-与(S)-丙氨酸为原料,通过缩合等6步反应,得到光学活性的(R)-,(S)-TDA,并与外消旋酞丁安比较其抗病毒活性及毒性。三者的抗单纯疱疹病毒活性与对细胞的毒性差别不大,说明消旋酞丁安临床使用是安全有效的。     

多沙唑嗪对映体对兔四种血管α受体的作用

多沙唑嗪(doxazosin，DOX)作为高选择性α₁受体阻断药，是临床上治疗良性前列腺增生(benign prostatic hyperplasia, BPH)的一线药物，但同时引起心血管系统的不良反应。本研究采用兔离体动脉环张力实验及电场刺激兔离体隐动脉诱发交感嘌呤能血管收缩实验观察R-多沙唑嗪(R-doxazosin，R-DOX)和S-多沙唑嗪(S-doxazosin，S-DOX)对兔耳动脉、肠系膜动脉和肺动脉血管平滑肌α₁受体的作用，以及较高浓度R-DOX和S-DOX对兔隐动脉交感神经突触前膜α₂受体的作用。结果表明，在兔耳动脉、肠系膜动脉和肺动脉，R-DOX和S-DOX竞争性拮抗去甲肾上腺素(noradrenaline，NA)诱发的血管收缩反应；其pA₂值分别为7.91±0.03和7.53±0.05，7.80±0.05和7.29±0.07以及8.32±0.06和7.97±0.07；且S-DOX的pA₂值均明显小于R-DOX的pA₂值(P<0.01)。R-DOX和S-DOX(0.1～10 μmol·L^-1)对电刺激诱发的血管收缩反应无明显影响；R-DOX或S-DOX(100 μmol·L^-1)显著抑制电刺激诱发的血管收缩反应，完全抑制外源性NA诱发的血管收缩反应，但对1 mmol·L^-1腺苷三磷酸诱发的血管收缩反应无明显影响。上述结果提示，R-DOX和S-DOX对NA诱发兔耳动脉、肠系膜动脉和肺动脉收缩反应具有竞争性拮抗作用，对上述三种血管S-DOX拮抗NA的pA₂值均明显小于R-DOX。此外，R-DOX和S-DOX的浓度升至10 μmol·L^-1时，对血管交感神经末梢突触前膜α₂受体仍无明显影响。     

HPLC和1HNMR分析确定cis-A-和cis-B-羟甲芬太尼的组成和构型

羟甲芬太尼(1)是一个强效的镇痛剂和高亲和、高选择性的阿片μ受体激动剂。通过HPLC和¹HNMR分析,cis-A-l被确定为由等量的cis-(+)-(3R,4S,2'S)-l和:cis-(—)-(3S,4R,2'R)-1组成的外消旋体,cis-B-l被确定为由等量的cis-(—)-(3R,4S,2'R)-1和cis-(+)-(3S/,4R,2'S)-1组成的外消旋体。     

光学活性益康唑和咪康唑的对映体选择性合成及其抗真菌活性

首次用对映体选择性合成法制备了光学活性的益康唑和咪康唑。初步体外抗真菌活性试验结果表明,(R)-(—)-益康唑和(R)-(—)-咪康唑的抗真菌活性高于相应的(S)-异构体和外消旋体。     

Stereoselective drug distribution and anticoagulant potency of the enantiomers of phenprocoumon in rats

The elimination, distribution and anticoagulant activity of S(—)-, R(+)-, and R,S(±)-phenprocoumon were determined in male Wistar-Lewis rats after intravenous injection of a single dose of 0·6 mg kg^?1. From the plasma concentrations which elicited the same anticoagulant effect, S(—)-phenprocoumon was 4 to 5 times more potent than R(+)-phenprocoumon. The potency of the racemate was between those of the enantiomers. The mean biologic half-life of the S(—)-enantiomer was shorter (12·5 h) than that of R(+)-phenprocoumon (17·8 h). No differences were observed in the apparent volume of distribution. However, the mean liver: plasma concentration ratio was higher for the S(—)-(6·9) than for the R(+)-enantiomer (5·2). At a total concentration of 16·8 μg ml^?1 the percentage of unbound drug in rat serum was significantly higher for the S(—)- (1·13%) than that for the R(+)-enantiomer (0·76%). Values obtained for the racemate were always between those of the enantiomers. It is concluded that stereoselective differences in the distribution between plasma and liver, and consequently in the rate of elimination are most likely due to stereoselective differences in serum protein binding. The greater anticoagulant potency of the S(—)- over the R(+)-enantiomer, cannot be explained primarily by the observed pharmacokinetic differences.     

The Metabolism of Amphetamine in vitro by Rabbit Liver Preparations: A Comparison of R(−) and S(+) Enantiomers

1. Incubation of R(?), S(+) and RS(±) amphetamines with rabbit liver 9000 g supernatant indicated that R(?) was metabolized at a faster rate than S(+), but that racemic amphetamine was metabolized at the same rate as S(+) during one hour incubations.

2. N-Hydroxyamphetamine and 1-phenyl-2-propanol were the major compounds detected in both R(?) and S(+) amphetamine incubations.

3. Phenylacetone oxime was detected in significant quantities after 3?h incubations of R(?) amphetamine, but only in minor quantities from S(+).

4. A fall in the amount of N-hydroxyamphetamine present in R(?) amphetamine incubations after a 3?h period as compared to a 1?h incubation, paralleled by a rise in the amount of phenylacetone oxime during 3?h suggested that the oxime was derived as a secondary metabolite from N-hydroxyamphetamine.

5. R(?) and S(+) N-hydroxyamphetamines were both metabolized to phenylacetone oxime by rabbit liver 9000 g supernatant, but the R(?) enantiomer was converted at a faster rate than S(+).     

S(−)Propranolol as a discriminative stimulus and its comparison to the stimulus effects of cocaine in rats

Rationale  Racemic propranolol (PRO), a β-adrenoceptor antagonist, has been evaluated as a test agent but not as a discriminative stimulus. Its S(−) stereoisomer is thought to subserve the effects of (±)PRO. Materials and methods  Rats were trained to discriminate S(−)PRO (5 mg/kg) from saline in a two-lever food-reinforced operant conditioning task. Results  The S(−)PRO stimulus was shown to be centrally mediated, dose-related, time dependent, and stereoselective: S(−)PRO (ED₅₀ = 2.2 mg/kg) was twice as potent as (±)PRO and approximately four times as potent as R(+)PRO. The S(−)PRO stimulus generalized fully to the β-adrenoceptor agent pindolol, the α₁-adrenoceptor agonist methoxamine, cocaine, and the serotonergic agents TFMPP and RU 24969; partial generalization occurred to (−)ephedrine and nisoxetine but not to fenfluramine or 5-OMe DMT. The S(−)PRO stimulus was blocked completely (and competitively) when prazosin, an α₁-adrenoceptor antagonist, was given in combination with the training dose of S(−)PRO. Moreover, prazosin exerted antagonism of the S(−)PRO-like effect of (±)PRO or R(+)PRO but produced only partial antagonism of the S(−)PRO-like effect of cocaine. In a second study, rats were trained to discriminate 8 mg/kg of cocaine from saline. The cocaine stimulus generalized to S(−)PRO, (±)PRO, and R(+)PRO. Prazosin partially attenuated the stimulus effect of cocaine (8 mg/kg) but completely blocked the cocaine-like effects of (±), S(−), and R(+)PRO. Conclusions  PRO and cocaine exhibited cross-substitution, but their stimulus effects were antagonized differentially by prazosin. PRO (and its optical isomers) can exert a stimulus effect that is based, at least in part, on increased α₁-adrenoceptor activity. PRO might be better characterized as an adrenoceptor partial agonist. This study was supported, in part, by the National Institute on Drug Abuse (NIDA) grant DA-01642.     

Antagonistic actions of S(−)-Bay K 8644 on cyclic nucleotide-induced inhibition of voltage-dependent Ba2+ currents in guinea pig gastric antrum

(±)-Bay K 8644, a conventional racemic mixture of Bay K 8644, is widely used as an L-type Ca²⁺ channel agonist. Although interactions between Bay K 8644 and cyclic nucleotide have been described, they have not been properly characterized. We have investigated whether two optical isomers of Bay K 8644 (i.e., R(+)- and S(−)-Bay K 8644) modify cyclic nucleotide (cAMP and cGMP)-induced inhibitory effects on nifedipine-sensitive voltage-dependent Ba²⁺ currents (I _Ba) recorded from guinea pig gastric myocytes. Conventional whole-cell recordings were used to compare the effects of R(+)-Bay K 8644 and S(−)-Bay K 8644 on I _Ba. S(−)-Bay K 8644 enhanced the peak amplitude of I _Ba evoked by depolarizing pulses to +10 mV from a holding potential of −70 mV in a concentration-dependent manner (EC₅₀ = 32 nM), while R(+)-Bay K 8644 inhibited I _Ba (IC₅₀ = 975 nM). When R(+)-Bay K 8644 (0.5 μM) was applied, I _Ba was suppressed to 71 ± 10% of control. In the presence of R(+)-Bay K 8644 (0.5 μM), additional application of forskolin and sodium nitroprusside (SNP) further inhibited I _Ba. Conversely, in the presence of S(−)-Bay K 8644 (0.5 μM), subsequent application of forskolin and SNP did not affect I _Ba. Similarly, in the presence of 0.5 μM S(−)-Bay K 8644, db-cAMP and 8-Br-cGMP had no effect on I _Ba. These results indicate that S(−)-Bay K 8644, but not R(+)-Bay K 8644, can prevent the inhibitory actions of two distinct cyclic nucleotide pathways on I _Ba in gastric myocytes of the guinea pig antrum.     

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.     

Effects of nornicotine enantiomers on intravenous <Emphasis Type="Italic">S</Emphasis>(−)-nicotine self-administration and cardiovascular function in rats

Rationale Previous neurochemical evidence indicates that R(+)-nornicotine is more potent than S(−)-nornicotine in evoking dopamine release in rat nucleus accumbens slices. Objective The current study tested the hypothesis that R(+)-nornicotine is also more potent than S(−)-nornicotine in selectively decreasing intravenous S(−)-nicotine self-administration in rats. Results After acute pretreatment (1–10 mg/kg for each enantiomer), R(+)-nornicotine was more potent than S(−)-nornicotine in decreasing S(−)-nicotine self-administration; in contrast, within the same dose range, the nornicotine enantiomers were equipotent in decreasing sucrose-maintained responding. This enantioselectivity does not likely reflect a difference in bioavailability, since similar levels of nornicotine were recovered from the brain 60 min after injection (5.6 mg/kg for each enantiomer). With repeated pretreatment, tolerance did not develop to the rate-decreasing effect of either nornicotine enantiomer (3 or 5.6 mg/kg) with respect to the decrease in S(−)-nicotine self-administration, although the enantioselectivity dissipated across repeated pretreatments. While both enantiomers acutely produced a similar increase in blood pressure and heart rate, tolerance developed to the blood pressure effects of R(+)-nornicotine, but not to the effects of S(−)-nornicotine, across repeated treatments. Conclusion Both R(+)- and S(−)-nornicotine may have potential utility as a novel tobacco use cessation agent.     

Calcium Antagonism and Structure-affinity Relationships of Terfenadine,a Histamine H1 Antagonist,and Some Related Compounds

Abstract— Calcium channel affinity of terfenadine and its optical isomers was determined by the displacement of [³H]nitrendipine on rat cerebral cortex membranes. Terfenadine showed a pK_d of 6·36±0·03 whereas its R(+)-isomer (VUF4567) had a pK_d value of 6·39±0·03 and the S(–)-isomer (VUF4568) had a pK_d of 6·40 ± 0·04. The same affinity between the enantiomers suggests that the binding domain on the membrane is not sterically restricted towards the part of the molecule in which the chiral centre is present. The characteristics of terfenadine in regulating [³H]nitrendipine binding were similar to those of some other diphenyl-alkylamine type calcium antagonists. It allosterically altered the binding affinity for nitrendipine and acted at the same site linked to the calcium channel as gallopamil. A structure-affinity relationship among a group of terfenadine analogues is discussed.     

Acute and chronic effects of nornicotine on locomotor activity in rats: altered response to nicotine

Rationale: Nicotine, a tobacco alkaloid, is known to be important in the acquisition and maintenance of tobacco smoking. Nornicotine, an active nicotine metabolite, stimulates nicotinic receptors and may produce psychomotor effects similar to nicotine. Objective: The present study determined the effects of acute and repeated administration of nornicotine on locomotor activity and compared its effects with those of nicotine. Methods: R(+)-Nornicotine (0.3–10 mg/kg), S(–)-nornicotine (0.3–10 mg/kg), S(–)-nicotine (0.1–1 mg/kg) or saline was administered s.c. to rats acutely or repeatedly (eight injections at 48-h intervals). Activity was recorded for 50 min immediately after each injection. Results: S(–)-Nicotine produced transient hypoactivity, followed by dose-related hyperactivity. Repeated S(–)-nicotine administration resulted in tolerance to the hypoactivity and sensitization to the hyperactivity. Subsequent testing following a saline injection revealed evidence of conditioned hyperactivity. Acute administration of 0.3 mg/kg or 1 mg/kg R(+)- or S(–)-nornicotine produced no effect. Transient hypoactivity was observed at 3 mg/kg and 10 mg/kg R(+)-nornicotine and at 10 mg/kg S(–)-nornicotine. However, rebound hyperactivity was not observed following acute administration of either nornicotine enantiomer, suggesting that nornicotine-induced psychomotor effects differ qualitatively from those of S(–)-nicotine. Repeated R(+)-nornicotine resulted in tolerance to the transient hypoactivity, however hyperactivity was not observed. Repeated S(–)-nornicotine resulted in tolerance to the hypoactivity and the appearance of hyperactivity. Repeated administration of either nornicotine enantiomer resulted in a dose-dependent alteration in response to a 1 mg/kg S(–)-nicotine challenge, suggesting some commonalities in the mechanism of action. Conclusion: Nornicotine likely contributes to the neuropharmacological effects of nicotine and tobacco use. Received: 11 January 1999 / Final version: 25 March 1999