Search

A series of new 1-aryl-4-propylpiperazines containing the modified terminal amide fragment 9, 15-19, 21, 23 and 25 were synthesized and their 5-HT1A and 5-HT2A receptor affinities were determined. All the compound were highly potent 5-HT1A receptor ligands with a diverse 5-HT2A receptor affinity. It was found that the 5-HT2A receptor affinity depends on the dipole moment and lipophilicity of amide moiety. Compound 9b was found to be a 5-HT2A receptor antagonist and a weak 5-HT1A receptor agonist.

Two series of new MP 3022 analogs, i.e. 1-(o-methoxyphenyl)-4-n-propylpiperazines (3, 4a, 4b, 6-9, and 12-13) and 2-(n-propyl)-1,2,3,4-tetrahydroisoquinolines (5a, 5b, 11a, and 11b) containing a terminal heteroaromatic system with a different number of nitrogen atoms, were synthesized and their 5-HT1A/5-HT2A and alpha 1 receptor affinity was assayed. The majority of investigated piperazines may be classified as non-selective 5-HT1A/5-HT2A/alpha 1 receptor ligands. Compounds 3, 4a, 4b, 7-9a with the highest affinity for 5-HT1A receptors (Ki = 4-54 nM) were tested in vivo. Their functional activity was differentiated; while 3, 8, and 9a behaved like weak antagonists of postsynaptic 5-HT1A receptors, 4b and 7 may be classified as potential partial 5-HT1A receptors, agonists. Isomer 4a has characteristic features of a potential weak postsynaptic 5-HT1A receptor agonist.

A series of new 3-(omega-aminoalkyl)-5,5-disubstituted hydantoins, containing 1-phenylpiperazine, 1-(o-methoxyphenyl)piperazine or 1,2,3,4-tetrahydroisoquinoline fragments, were synthesized by standard alkylation procedures and their 5-HT1A and 5-HT2A receptor affinities were determined. It has been shown that the investigated derivatives are recognized by 5-HT1A and 5-HT2A receptors due to the presence of a 1-arylpiperazine fragment however, the terminal hydantoin moiety plays an important role in stabilization of the receptor-ligand complex. It has also been found that the two 1-phenylpiperazine derivatives 32 and 36 are new selective 5-HT2A receptor ligands (Ki = 34 and 37 nM, respectively), whereas the derivative of 1-(o-methoxyphenyl)piperazine (38) is a new, highly potent 5-HT1A receptor ligand (Ki = 0.51 nM) with a moderate affinity for 5-HT2A receptors (Ki = 213 nM).

A new analog of buspirone (1), i.e., 8-[4-[2-(1,2,3,4-tetrahydroisoquinolinyl)]butyl]-8-azaspiro- [4.5]decane-7,9-dione (6a), was synthesized. In was demonstrated that buspirone and its analog 6a were equipotent 5-HT(1A) ligands. Several behavioral models showed that 6a had essentially the same functional profile at 5-HT(1A) receptors as buspirone. The obtained results permit a conclusion that the basic nitrogen atom and terminal, bulky cycloimide moiety, but not the 2-pyrimidinyl group, of buspirone are directly involved in the formation of the bioactive complex with 5-Ht1A receptors.

A series of new N-substituted derivatives of 3-[4-(2-methoxyphenyl)-1-piperazinyl]-2-phenylpropanamide, 6-10, were synthesized and their 5-HT1A, 5-HT2A, and alpha 1 receptor affinities were determined. All the compounds were highly potent 5-HT1A ligands with a moderate or low 5-HT2A and alpha 1 affinity. It was shown that the 5-HT2A affinity of 1 and 6-10 depended crucially on the volume of amide substituents. None of the investigated racemic mixtures 1 and 6-8 antagonized the 8-OH-DPAT-induced lower lip retraction in rats, whereas (+/-)-7 behaved like a weak agonist of 5-HT1A receptors in the model used.

The 5-HT1A receptor affinities and ionization constants of a set of 1-arylpiperazine (4) 1,2,3,4-tetrahydroisoquinoline (6), and -quinoline (7) containing N-(omega-arylalkyl) or N-(E)-cinnamyl substituents as well as two morpholine derivatives (8a, 8b) were determined. It was shown that some tetrahydroisoquinoline (6c, 6d) and morpholine (8a) derivatives were 5-HT1A ligands equipotentto 1-phenylpiperazine (4a) and 1,2,3,4,4a,5-hexahydropyrazino [1,2-a]indole (5). On the basis of molecular modelling studies it was also demonstrated that 6c, 6d and 8a mimicked very well the reference structures of 4a and its rigid analog 5. Another, more complex 1,2,3,4-tetrahydroisoquinoline derivative 3, which served as a model compound to confirm the previously reported 5-HT1A binding mode of derivatives 1a-d and 2, had the highest 5-HT1A affinity (Ki = 6.7 +/- 0.5 nM) of all the investigated compounds.

New 1-phenyl- and 1-(3-chlorophenyl)piperazines containing a 4-[3-(heterocyclic)propyl] fragment were synthesized. It was found that of all the investigated compounds 11b (Ki = 13 +/- 2 nM) and 8b (Ki = 38 +/- 2 nM) were the most active 5-HT1A and 5-HT2A ligands, respectively. Several derivatives (3a, 4a, 8b, 11b, 12b, 13a, and 13b) were selected as good candidates for new, potential antidepressants on the basis of their 5-HT1A/5-HT2A receptor binding profiles.

Spiro[piperidine-4',1-(1,2,3,4-tetrahydro-beta-carboline)] (10), its derivatives 11-15 and its analogs 16 and 17 were examined as ligands of serotonin 5-HT1A receptors. It was shown that compounds 12 and 14 had essentially the same 5-HT1A affinity as 1-phenylpiperazine and its rigid analog 7, whereas there were substantial differences in the steric arrangement of their crucial pharmacophores, i.e. aromatic and protonation centers. On the basis of the existing models and using the (+)-LSD structure as a template, a new, extended three-point topographic model of 5-HT1A receptors has been proposed.

The 5-HT1A and 5-HT2 receptor affinity of a set of 44 N-alkylated 1-aryl-piperazines and their analogs has been analyzed: the n-hexyl derivatives were the most potent and the most selective 5-HT1A ligands of all the investigated N-alkyl homologues. The alkyl chain may stabilize the 5-HT1A receptor-ligand complex by hydrophobic forces. A set of the alkyl substituent contributions (CHT1A) for prediction of the 5-HT1A affinity of N-alkyl derivatives of 1-arylpiperazines and related compounds have been defined on the basis of the Free-Wilson analysis.

The 5-HT1A and 5-HT2A receptor affinity of model 1-(2-pyrimidinyl)-piperazine derivatives 15-21 and 23-32 has been determined. 2-(N-Methylpiperazino)-4,6-di(2-thienyl)pyrimidine 26 is a new, highly active and selective 5-HT2A receptor ligand. The topography of a molecule and the stereoelectronic effects of the thiophene rings are the major factors responsible for the high affinity and selectivity of 26 towards 5-HT2A sites.

A new set of 4-alkyl-1-(o-methoxyphenyl)piperazines containing a terminal benzotriazole fragment were synthesized, and their 5-HT1A and 5-HT2 affinity was determined. It was shown that the benzotriazole moiety contributes to both the 5-HT1A and 5-HT2 receptor affinity. It was demonstrated in several behavioral models that 4-[3-(benzotriazol-1- yl)propyl]-1-(2-methoxyphenyl)piperazine (11) is a new, potent presynaptic and postsynaptic 5-HT1A receptor antagonist. However, it is not selective for 5-HT1A versus alpha 1 receptors.

The synthesis and 5-HT1A and 5-HT2 receptor affinities of 1-aryl-2-[3-(4-aryl-1-piperazinyl)propyl]-1,4-dihydro-3(2H)- isoquinolinones 7-28 are reported. The two derivatives 7 and 13 were the most potent 5-HT1A ligands (Ki 1.72 +/- 0.07 and 2.75 +/- 0.59 nM, respectively) of all the investigated compounds. It has been found that the effect of the substituent in the 1-arylpiperazine portion is opposite to the observed in simple 1-arylpiperazine. The molecular modelling results indicate that the investigated derivatives may interact with 5-HT1A sites in two different ways: as ordinary 4-substituted 1-arylpiperazines, or in such a manner that the aryl substituent at position 1 of the 3(2H)-isoquinolinone moiety and N-4 piperazine atom mimics remarkably well the bioactive conformation of simple 1-arylpiperazines.

The synthesis of three 1-[4-(4-aryl-1-piperazinyl)butyl]-3,4-dihydro-2(1H)-quinolinones (5-7) was described and the receptor binding profile (5-HT1A, 5-HT2, alpha 1, D1, D2) was determined. It was found that m-chloro (5) and o-methoxy (6) derivatives are potent antagonists of the 5-HT1A, 5-HT2 and D2 receptors. It was shown that compound 6 resembles very well some atypical antipsychotics and may be considered as a novel agent of this class of drugs.

The 5-HT1A and 5-HT2 receptor affinity of 2- and 3-substituted 1,2,3,4-tetrahydro-beta-carbolines 1-8, 10 and 12-15 has been determined. It has been found that the specific 5-HT1A affinity of the protonated form (KiAH+) 2-n-hexyl derivatives 4, 8, 14 and (+)-LSD is of the same order. It has been shown by means of molecular modelling methods that pharmacophores of all the active compounds can adopt a common position at the 5-HT1A receptor model. The model also offers an explanation for the observed stereoselectivity chiral compounds.

We have performed a quantitative analysis of the interaction with DNA of several unfused aromatic compounds synthesized in our laboratory and substituted with one or two short cationic chains. These and similar literature compounds, for which DNA binding data are available, bind with DNA by partial intercalation of the aromatic system, groove interaction of the linker chain, and groove electrostatic interactions of the terminal cationic group. Several independent quantitative and qualitative approaches show consistently that the strength of the interaction of the aromatic unit of the molecule with DNA binding sites depends on the direction and magnitude of polarity of the aromatic system. The phenomenon is explained in terms of the greatest negative potential in the DNA grooves, a concept extensively elaborated by Pullman and Pullman [cf. Lavery, R. and Pullman, B. [(1985) J. Biomol. Struct. Dyn. 2, 1021-1032] and references therein]. Classical, fused-ring planar intercalators do not follow the polarity-DNA affinity correlation, presumably because the intercalative forces depend more strongly on polarizability than on polarity of the aromatic system.

The effect of a steric hindrance around the protonation center of the model 4-substituted 1-(3-chlorophenyl)-piperazines 1-9 and 11-14 on their affinity for 5-HT1A and 5-HT2 receptor sites was investigated. Additional evidence for hydrophobic interactions between the N-4 hydrocarbon substituents and 5-HT1A receptors has been presented. However, the hydrophobic forces play a minor role in stabilization of the bioactive complex with 5-HT2 receptors. It has also been found that even bulky substituents around the protonation center of 1-aryl-piperazines are well tolerated at both 5-HT1A and 5-HT2 sites.

The synthesis and the 5-HT1A and 5-HT2 receptor affinity of 2-substituted 1-[3-(4-aryl-1-piperazinyl)propyl]-imidazoles (1-8) has been described. It has been shown that both the N-3 imidazole atom and the N-1 piperazine one should be considered as possible protonation centers under physiological conditions. It has been found that the folded conformations of 1-8 exist predominantly in solution. Moreover, three different modes of interaction of the analyzed compounds with 5-HT1A and 5-HT2 receptor sites have been proposed.

The effect of the hydrocarbon chain of the model 4-substituted 1-(3-chlorophenyl)piperazines 12-31 on their affinity for 5-HT1A receptor sites was investigated. It was found that elongation of the 4-n-alkyl chain strongly increases the 5-HT1A affinity of the investigated compounds. The affinity reaches the maximum (Ki = 2.67 nM) for the n-hexyl derivative 20. It was shown that hydrophobic interactions of N-4 substituents of 1-arylpiperazines significantly contribute to their 5-HT1A affinity. The specific binding constant was defined as the receptor affinity of the protonated species of compounds under physiological conditions. The range of Ki(AH+) = 1 - 3 x 10(-11) M is a specific affinity limit of the investigated class of compounds at the 5-HT1A receptor sites.

Seven derivatives of 1,2,3,4-tetrahydro-beta-carbolin-1-one have been prepared. Three of them showed significant central anti-serotonin activity, comparable with that of trazodone or etoperidone. Some structural features were found to be important for the central antiserotonin activity of the investigated class of compounds.

Quantitative structure-activity relationships (QSAR) were analyzed for 5-HT1 and 5-HT1A affinity data of two series of 1-arylpiperazines. A conformational analysis of the investigated derivatives was performed using CNDO/2 method. It was shown that some 1-arylpiperazines adopt the bioactive conformations, while the others, like 1-(2-alkylphenyl)-piperazines, should exist in the twisted conformations at the receptor sites.

Thirty-eight 2-(aryl or heteroaryl)quinolin-4-amines, N,N-disubstituted, N-monosubstituted, and without a substituent at the amino group have been synthesized with use of novel chemistries developed by us recently. Some of these derivatives show anti-HIV-1 activity at a concentration level of 1 microM and low cell toxicity in vitro. The most active and least toxic compounds are derivatives of 2-(3-pyridyl)quinoline. The results of the quantitative structure-activity relationship analyses, including several classical, linear regression correlations and a Free-Wilson approach of de novo model, provide guidelines for the design of new active compounds of this class.

A set of 21 polyheteroaromatic compounds substituted with flexible cationic groups and of similar molecular size has been analyzed for binding with DNA and for effects of the bleomycin-mediated degradation of the DNA double helix. Increases in apparent rates of the DNA digestion were observed in all cases under the experimental conditions of noncompetitive binding of these compounds and bleomycin to DNA. Surprisingly, the quantitative structure-activity relationship analysis revealed two distinct correlations despite close structural similarities for the set of bleomycin amplifiers. These unusual results are explained in terms of the formation of two stereochemically different ternary complexes of activated bleomycin-DNA-amplifier. The relevance of this finding for the design of new bleomycin amplifiers is discussed.

It has been found that 3-alkoxycarbonyl-beta-carbolines are almost non-toxic and showed a sedative effect. The quantitative relationship between the structure of some 1,2,3,4-tetrahydro-beta-carbolines and their acute toxicity and sedative effect was found using the Free-Wilson approach.

A quantitative structure-activity relationship (QSAR) was analyzed for monoamine uptake inhibition of cis- and trans-1-alkylamino-4-aryltetralins using the Free-Wilson method. The calculated individual substituent contributions were found to be strongly correlated with the uptake inhibition activity of dopamine, 5-hydroxytryptamine and norepinephrine in the corpus striatum and hypothalamus of rats, respectively. The effect of the substituents and stereochemical factors on the monoamine uptake inhibition of the analyzed series of tetralins was discussed.

The bleomycin-mediated digestion of DNA in the presence of ferrous ion, molecular oxygen, and dithiothreitol is characterized by a fast initial reaction, which is followed by a much slower process. The fast degradation is due to the fast activation of the bleomycin-Fe(II) complex and the subsequent fast reaction of the activated complex with DNA. The rate determining step for the slow process is reactivation of the bleomycin-Fe(III) complex. The apparent rate constants for both reactions increase with increasing ionic strength. The latter, unusual results are interpreted in terms of inhibition of bleomycin turnover by binding of cationic species with DNA at low ionic strength.

The degradation of calf thymus DNA by a ferrous complex of bleomycin A2 or Blenoxane (a mixture consisting mainly of BLM-A2 and BLM-B2) is enhanced by polyamines higher than ethylenediamine. The QSAR analysis gave excellent correlation between the experimental amplification results and calculated valence molecular connectivity indices of the third order and path type for the protonated polyamines. A new amplifier of bleomycin activity has been synthesized and its interaction with DNA has been studied. This compound contains a DNA-intercalating moiety and a polyamine portion, two independent amplification systems in the same molecule. The role of the C-terminus of bleomycin as the intramolecular amplifier for the degradation of DNA is discussed.

The bleomycin amplifier 1 is sterically hindered and twisted about the torsional bond joining the two aromatic rings. The intercalation of 1 and its sterically unhindered isomer 2 with DNA has been studied using n.m.r., viscometric titrations of superhelical and linear DNA, and flow dichroism. Based on the unusually strong interaction of 1 with DNA base pairs, a non-classical intercalation model for this compound is proposed. The intrinsic twists of both the unfused biaromatic system of 1 and the hydrogen-bonded DNA base pairs are retained in the intercalator-DNA complex, and the methyl group of 1 is accommodated between the hydrogen bonded bases. The complex of 1 is the first example found to date of this type of intercalation of the methyl group with DNA. The structure-activity relationships as bleomycin amplifiers for 1, 2 and similar derivatives is discussed.

Sixteen unfused heterobiaromatic and biphenyl compounds substituted with an amino side chain (protonated in water) have been tested for (i) binding with DNA and (ii) their effect on the digestion of the DNA double helix by a bleomycin-iron complex. Only the DNA intercalating molecules amplify the digestion of DNA. One 2,2'-bipyridine derivative tested is an inhibitor of the bleomycin reaction because it removes ferrous ion from the bleomycin complex. Polarity of the intercalating unfused biaromatic system is of primary importance for effective binding of the molecule with native DNA and, at the same time, for its amplification activity. The molecules that have the biaromatic system polarized extensively in the direction of the side cationic chain, so that the intercalating sites constitutes a positive part of the dipole, show strong binding with DNA and good amplification activity. For strong intercalative forces that determine the amplification activity, it is important that both the heteroaromatic subsystems of the molecule have positive ends of their dipoles positioned away from the side chain. This work provides general guidelines for synthesis of new highly effective bleomycin amplifiers.