Years of cumulative research can result in the development of a clinically useful drug, providing either a cure for a particular disease or symptomatic relief from a physiological disorder. A lead compound with a desired pharmacological activity may have associated with it undesirable side effects, characteristics that limit its bioavailability, or structural features which adversely influence its metabolism and excretion from the body. Bioisosterism represents one approach used by the medicinal chemist for the rational modification of lead compounds into safer and more clinically effective agents. The concept of bioisosterism is often considered to be qualitative and intuitive.1 The prevalence of the use of bioisosteric replacements in drug design need not be emphasized. This topic has been reviewed in previous years.2-5 The objective of this review is to provide an overview of bioisosteres that incorporates sufficient detail to enable the reader to understand the concepts being delineated. While a few popular examples of the successful use of bioisosteres have been included, the George Patani graduated with a B.Pharm. in 1992 from the College of Pharmaceutical Sciences, Mangalore University at Manipal, India. In 1996, he received his M.S. in Pharmaceutical Science at Rutgers University under the direction of Professor Edmond J. LaVoie. He is presently pursuing graduate studies in pharmaceutics. His current research interests are focused on drug design and controlled drug delivery.

https://www.mch.estranky.sk/file/228/1996chemrev96-3147-76_bioisosterism.pdf

Bioisosterism: A Rational Approach in Drug Design.

The mouse light/dark box test.

The neurobiology and control of anxious states

In recent years, there has been an ever-increasing need for rapid reactions that meet the three main criteria of an ideal synthesis: efficiency, versatility, and selectivity. Such reactions would allow medicinal chemistry to keep pace with the multitude of information derived from modern biological screening techniques. The present review describes one of these reactions, the 1,3-dipolar cycloaddition ("click-reaction") between azides and alkynes catalyzed by copper (I) salts. The simplicity of this reaction and the ease of purification of the resulting products have opened new opportunities in generating vast arrays of compounds with biological potential. The present review will outline the accomplishments of this strategy achieved so far and outline some of medicinal chemistry applications in which click-chemistry might be relevant in the future.

Click chemistry reactions in medicinal chemistry: applications of the 1,3-dipolar cycloaddition between azides and alkynes.

Do Novel Antipsychotics Have Similar Pharmacological Characteristics? A Review of the Evidence

The behavioral profiles of five clinically used selective serotonin reuptake inhibitors (SSRIs) citalopram, paroxetine, sertraline, fluvoxamine and fluoxetine, have been compared in animal models of antidepressant (mouse forced swim test), anxiolytic (exploration of black and white test box and foot-shock-induced ultrasonic vocalization in the rat) and antiaggressive (isolation-induced aggressive behavior in the mouse) activity the results are discussed in relation to receptor binding data from the literature Furthermore, affinities for the sigma 1 and sigma 2 binding sites are presented Citalopram reversed the immobility induced by forced swimming with a potency similar to that of imipramine Paroxetine, fluvoxamine and fluoxetine reversed swim-induced immobility less potently and with a maximum of 40-50% reversal Citalopram produced a mixed anxiogenic-/anxiolytic-like response in rats tested in the two-compartment black and white box Paroxetine induced an anxiogenic-like response at low doses and the other SSRIs were without major effects Citalopram and paroxetine inhibited footshock-induced ultrasonic vocalization with high potencies The dose-response curve was biphasic for citalopram with a maximum of 64% inhibition Sertraline and fluvoxamine inhibited the vocalization less potently, and fluoxetine induced a weak inhibitory effect corresponding to a maximum of 32% Sertraline, fluvoxamine and fluoxetine inhibited isolation-induced aggressive behavior, whereas citalopram and paroxetine were inactive Both 5-HT1 and 5-HT2 receptors are involved, and there was a functional interaction between 5-HT1A and 5-HT2A or 5-HT2C receptors, as ritanserin potentiated the antiaggressive effect of 1,5-HTP as well as that of 8-OH-DPAT

Behavioral profiles of SSRIs in animal models of depression, anxiety and aggression. Are they all alike?

The effects of a range of dopamine (DA) agonists on stereotyped behaviour in rats were analysed and compared both with the affinity of the compounds for D1 and D2 receptor binding sites in vitro and their ability to stimulate the adenylate cyclase activity in rat striatal homogenates. Full and partial agonists at the D1 receptor coupled toadenylate cyclase do not induce stereotypies when given alone, whereas full D2 agonists (e.g. quinpirole) induce hyperactivity but not oral stereotypies. Partial D2 agonists (e.g. (—)-3-PPP) only induce sedation. Mixed D1/D2 agonists (e.g. apomorphine) induce both hyperactivity and oral stereotypies. Maximum stereotypies were induced by combination of SK & F 38393 and a series of D2 agonists, including full agonists and the partial D2 agonist B-HT 920, whereas partial agonists with low intrinsic activity (e.g. (-)-3-PPP, EMD 23448) did not induce stereotypies when given together with SK & F 38393. However, these partial agonists reduced the maximum effect of apomorphine, whereas the full agonists (e.g. quinpirole, (—)-NPA) and B-HT 920 had no apomorphine antagonistic activity. The mixed D1/D2 agonists apomorphine and N,N-dipropyl-5,6-ADTN were only weakly influenced by SK & F 38393, or not at all. D1 agonists with central effects, including SK & F 38393, SK & F 81297 (with relatively high efficacies), and the partial agonist SK & F 75670 with low efficacy, changed the hyperactivity induced by quinpirole into maximum oral stereotypy, whereas the peripheral D1 agonist fenoldopam had no such effect. Inhibition of DA and NA synthesis with α-methyl-p-tyrosine depleted striatal DA levels by 72 per cent and antagonized the hyperactivity induced by the D2 agonists quinpirole and (—)-NPA, but not that of apomorphine. Combination of SK & F 38393 and quinpirole induced maximum stereotypy in DA-depleted animals. These results suggest that D1 receptor tonus is a necessary prerequisite for the expression of a DA agonist's effect. The hyperactivity induced by full D2 agonists appears to be mediated by D1 tonus provided by endogenous DA activity, but stronger D1 stimulation is necessary to induce oral stereotypy. A high degree of D1 receptor activation increases the ability of partial D2 agonists to induce hyperactivity or oral stereotypies since treatment with both SK & F 38393 and B-HT 920 had marked effects while B-HT 920 was ineffective. The behavioural stimulation induced by a particular DA agonist thus depends on relative D1/D2 receptor affinity and also on the intrinsic activity at D2 receptors, while intrinsic activity at D1 receptors appears to be less important. The relative importance of D1 and D2 receptors for expression of different stereotypy patterns is useful for in vivo evaluation of the selectivity ratios of DA agonists.

Relative dopamine D1 and D2 receptor affinity and efficacy determine whether dopamine agonists induce hyperactivity or oral stereotypy in rats.

A series of 4-(1H-indol-3-yl)-1-butyl-substituted 4-phenylpiperidines, 4-phenyl-1,2,3,6-tetrahydropyridines, and 4-phenylpiperazines was synthesized. The phenyl group was optionally substituted with 4-fluoro or 2-methoxy substituents. High affinity for both sigma 1 and sigma 2 binding sites was achieved with these compounds. Additionally, these compounds had relatively high affinity for serotonin 5-HT1A and 5-HT2A, dopamine D2, and adrenergic alpha 1 receptors. Introduction of a 4-fluorophenyl substituent at the indole nitrogen atom rendered very selective sigma 2 ligands with subnanomolar affinity for the sigma 2 binding site. The prototype of such a compound was 1-(4-fluorophenyl)-3-[4-[4-(4-fluorophenyl)-1-piperidinyl]-1-butyl]-1H- indole, 11a (code no. Lu 29-253). This compound had the following binding affinities: IC50 (sigma 1) = 16 nM, IC50 (sigma 2) = 0.27 nM, IC50 (5-HT1A) = 22,000 nM, IC50 (5-HT2A) = 270 nM, IC50 (D2) = 4200 nM, IC50 (alpha 1) = 220 nM. Spiro-joining of the phenyl and the piperidine rings into a spiro[isobenzofuran-1(3H),4'-piperdine] ring system resulted in even more selective compounds. Variations of the 1-substituent at the indole and of the chain length of the alkylene spacer group were studied. The optimal compound was the spiro analogue of compound 11a. This compound is 1'-[4-[1-(4-fluorophenyl)-1H-indol-3-yl]-1-butyl]spiro[isobenzofuran- 1(3H),4'-piperidine], 14f (code no. Lu 28-179), with the binding affinities: IC50 (sigma 1) = 17 nM, IC50 (sigma 2) = 0.12 nM, IC50 (5-HT1A) = 21,000 nM, IC50 (5-HT2A) = 2000 nM, IC50 (D2) = 800 nM, IC50 (alpha 1) = 330 nM. However, the most selective sigma 2 versus sigma 1 ligand was the tropane derivative 1-(4-fluorophenyl)-3-[4-[3-(4-fluorophenyl)-8-azabicyclo[3.2.1]oct-2- en-8-yl]-1-butyl]-1H-indole, 15a. This compound had the following binding affinities: IC50 (sigma 1) = 1200 nM, IC50 (sigma 2) = 2.5 nM. Potent anxiolytic activity in the black/white box exploration test in rats was found with the two most prominent sigma 2 ligands Lu 29-253 and Lu 28-179. Good penetration into the CNS was documented both after subcutaneous and peroral administration of Lu 28-179 by ex vivo binding studies. Long duration of action was demonstrated both in ex vivo binding (T1/2 approximately 20 h) and in the black/white box exploration test.

.sigma. Ligands with Subnanomolar Affinity and Preference for the .sigma.2 Binding Site. 1. 3-(.omega.-Aminoalkyl)-1H-indoles

Sertindole (5-chloro-1-(4-fluorophenyl)-3-[1-[2-(2-imidazolidinon-1-yl)ethyl]-4-Piperidyl]-1H-indole) is a new neuroleptic with a very high selectivity for dopamine (DA) neurones in the ventral tegmental area compared to DA neurones in substantis nigra pars compacta (Skarsfeldt, T., and Perregaard, J. Eur. J. Pharmacol. 182:613–614, 1990). Neurochemical and behavioural effects of sertindole have been investigated in comparison with the classical neuroleptics haloperidol and fluphenazine and the atypical neuroleptic clozapine. In vitro sertindole has high affinity for serotonin S2 (5-HT2) receptors, DA D-2 receptors, and α1-adrenoceptors, moderate affinity for DA D-1 receptors; low affinity for α2-adrenoceptors, histamine H1 receptors and sigma receptors; and no affinity for 5-HT1A, muscarine cholinergic receptors, and β-adrenoceptors. The in vivo pharmacology is atypical, i.e., a remarkably weak or no effect in acute tests for DA antagonism, and the cataleptogenic potential is very low. Sertindole shows a very potent and long-acting antagonism at central as well as peripheral 5-HT2 receptors. The antagonistic effect at peripheral α1-adrenoceptors is relatively weak in comparison with the 5-HT2 antagonistic potency in vivo and in vitro. Sertindole shows no anticholinergic effects. In conclusion the pharmacological profile suggests that sertindole is an atypical neuroleptic compound with a low potential for extrapyramidal, autonomic, and anticholinergic side effects.

Neurochemical and in vivo pharmacological profile of sertindole, a limbic-selective neuroleptic compound

A series of arecoline bioisosteres, where the ester group is replaced by a 1,2,3-triazole-4-yl or a tetrazole-5-yl group, was synthesized and evaluated in vitro for affinity and efficacy at muscarinic receptors and in vivo for cholinergic side effects. The corresponding piperidine derivatives were also studied. In the 1,2,3,6-tetrahydropyridyl-1,2,3-triazole series, only derivatives with 2-substituents in the 1,2,3-triazole ring exert muscarinic agonist activity. The same trend is seen in the corresponding tetrazole series, where only 2-substituted derivatives display muscarinic agonist activity. The methyl derivatives in both series are full agonists, whereas the derivatives with longer side chains are partial agonists. Introduction of methyl substituents in the 1,2,3,6-tetrahydropyridine ring generally lowers affinity considerably except for the 3-substituted derivatives, where some activity is retained. In both the 1,2,3-triazole and tetrazole series, derivatives without substituents at the basic nitrogen in the 1,2,3,6-tetrahydropyridine ring are unselective full agonists, whereas the methyl-substituted derivatives generally are more M1 selective compared to M2. Larger substituents than methyl abolish activity. The 4-(3-piperidyl)-1,2,3-triazole and 5-(3-piperidyl)-2H-tetrazole derivatives are generally less active than the corresponding 1,2,3,6-tetrahydropyridine derivatives, and only the 2-allyl- and 2-propargyl-1,2,3-triazole derivatives display activities comparable to the most active compounds in the 1,2,3,6-tetrahydropyridine series. The propargyl derivative is an unselective full agonist, and resolution did not reveal any stereoselectivity The allyl derivative is a partial agonist with some selectivity for the M1 receptor, and testing of the enantiomers showed that the (+)-enantiomer is an unselective partial agonist, whereas the (-)-enantiomer is a partial agonist with preference for the M1 receptor. Generally, the structure-activity relationships of the 1,2,3-triazole and tetrazole series are very similar, and two compounds, 2-ethyl-4-(1-methyl-1,2,3,6-tetrahydro-5-pyridyl)-1,2,3-triazole and 2-ethyl-5-(1-methyl-1,2,3,6-tetrahydro-5-pyridyl)-2H-tetrazole, are M1 agonists/M2 antagonists. Muscarinic compounds with this profile are of particular interest as drugs for the treatment of Alzheimer's disease.

Bioisosteres of arecoline: 1,2,3,6-tetrahydro-5-pyridyl-substituted and 3-piperidyl-substituted derivatives of tetrazoles and 1,2,3-triazoles. Synthesis and muscarinic activity.

Eddi Meier

Papers

Behavioral profiles of SSRIs in animal models of depression, anxiety and aggression. Are they all alike?

Relative dopamine D1 and D2 receptor affinity and efficacy determine whether dopamine agonists induce hyperactivity or oral stereotypy in rats.

.sigma. Ligands with Subnanomolar Affinity and Preference for the .sigma.2 Binding Site. 1. 3-(.omega.-Aminoalkyl)-1H-indoles

Neurochemical and in vivo pharmacological profile of sertindole, a limbic-selective neuroleptic compound

Bioisosteres of arecoline: 1,2,3,6-tetrahydro-5-pyridyl-substituted and 3-piperidyl-substituted derivatives of tetrazoles and 1,2,3-triazoles. Synthesis and muscarinic activity.