Pyridinylpiperazines, a new class of selective alpha 2-adrenoceptor antagonists

Direct C(3)5-H Polyfluoroarylation of 2-Amino/alkoxy Pyridines Enabled by a Transient and Electron-deficient Palladium Intermediate

Herein, we present an unprecedented azine-limited C5-H polyfluoroarylation of 2-aminopyridines enabled by a transient and electron-deficient perfluoroaryl-Pd species via C-H/C-H coupling. The protocol further allows C3(5)-H polyfluoroarylation of 2-alkoxypyridines guided by sterics and electronics for the first time. The late-stage C-H functionalization of drugs, drug derivatives, and natural product derivatives and synthesis of C5-aryl drug derivatives further demonstrated the method's utility. The preliminary mechanistic studies reveal that the synergistic combination of the bulky yet electrophilic perfluoroaryl-Pd species and the partial nucleophilicity of the C5-position of 2-amino/alkoxy-pyridines is the origin of reactivity and selectivity. Importantly, the first experimental evidence for the role of diisopropyl sulfide is provided.

Synthesis and anti-HIV-1 activity of new delavirdine analogues carrying arylpyrrole moieties

In our search for novel anti-human immunodeficiency virus (HIV)-1 agents, 14 delavirdine analogues were synthesized and evaluated as potential anti-HIV-1 agents in cell-based assays. Compound 1Aa exhibited potent and selective anti-HIV-1 activity in acutely infected MT4 cells, with effective concentration (EC50) values in the submicromolar range.

Potential multifunctional inhibitors of HIV-1 reverse transcriptase. Novel [AZT]-[TSAO-T] and [d4T]-[TSAO-T] heterodimers modified in the linker and in the dideoxynucleoside region

In an attempt to combine the anti-HIV-inhibitory capacity of nucleoside reverse transcriptase (RT) inhibitors (NRTI) and non-nucleoside RT inhibitors (NNRTI), several heterodimer analogues of the previously reported [AZT]-(CH(2))(3)-[TSAO-T] prototype have been prepared. In these novel series, other NRTIs, an expanded range of linkers with different conformational freedom and other attachment sites for these linkers on the base part of the NRTI analogue have been explored. Moreover, in order to circumvent the dependence of the NRTI moiety of the heterodimer on activation by cellular nucleoside kinases, novel heterodimers in which the NRTI is bearing a masked monophosphate group at the 5'-position are described. Among the novel heterodimers, several derivatives show a potent anti-HIV-1 activity, which proved comparable, or even superior, to that of the AZT heterodimer prototype. The nature of the NRTI was important for the eventual anti-HIV-1 activity. In particular, the d4T heterodimer derivative containing a propyl linker between the N-3 positions of the base of TSAO-T and d4T was approximately 5- to 10-fold more inhibitory to HIV-1 than the corresponding AZT heterodimer prototype.

Hybridized and isosteric analogues of N1-acetyl-N4-dimethyl-piperazinium iodide (ADMP) and N1-phenyl-N4-dimethyl-piperazinium iodide (DMPP) with central nicotinic action

A series of piperazine derivatives, obtained by hybridization of N1-acetyl-N4-dimethyl-piperazinium iodide (1, ADMP) and N1-phenyl-N4-dimethyl-piperazinium iodide (3, DMPP) or of the corresponding tertiary bases (2, 4) with arecoline (5) and arecolone (6) or by isosteric substitution of the phenyl ring of DMPP, has been synthesized. Hybridization afforded compounds that, both as tertiary bases and as iodomethylates, have no affinity for the nicotinic receptor. On the contrary, isosteric substitution gave compounds that maintain affinity for the receptor; among them, two tertiary bases (37, 38), show affinity in the nanomolar range for the nicotinic receptor. The pharmacological profile of these isomeric compounds is quite interesting as they present differences in their peripheral and central effects, suggesting that they interact with different subtypes of the nicotinic receptor.

Substituted pyrazoles as novel selective ligands for the human dopamine D4 receptor

Two novel series of 3-(heterocyclylmethyl)pyrazoles have been synthesised and evaluated as ligands for the human dopamine D4 receptor. Compounds in series I (exemplified by 8k) have a phenyl ring joined to the 4-position of the pyrazole while those in series II (exemplified by 15j) have a 5-phenyl ring linked by a saturated chain to the 4-position of the pyrazole. Both series supplied compounds with excellent affinity for the human D4 and good selectivity over other dopamine receptors. Excellent selectivity over calcium, sodium, and potassium ion channels was also achieved.

Antidepressant-like activity of ipsapirone, buspirone and gepirone in the forced swimming test in rats pretreated with proadifen

The antidepressant-like activity of ipsapirone, buspirone and gepirone was studied in rats in the forced swimming test (behavioural despair test). lpsapirone and buspirone administered in single doses (5-20 mg/kg) did not affect the immobility time in this test. When administered in the same doses in a three-injection course in 24 h, buspirone was also inactive, while ipsapirone slightly but significantly reduced the immobility time only after a dose of 5 mg/kg. On the other hand, gepirone administered both in single doses (2.5-20 mg/kg) and in a three-injection course (5-20 mg/kg) potently and dose-dependently shortened the immobility time. 1-(2-Pyrimidinyl)-piperazine (1-PP; 5-20 mg/kg), a common metabolite of all the three drugs, administered in single doses or in a three-injection course, was inactive in the forced swimming test. In rats pretreated with proadifen (50 mg/kg), a non-selective drug metabolism inhibitor, both ipsapirone and buspirone administered in single doses (5-20 mg/kg) reduced the immobility time in a dose-dependent manner. Proadifen also potentiated the anti-immobility effect of gepirone (5 and 10 mg/kg). The anti-immobility effect of single doses (20 mg/kg) of ipsapirone, buspirone and gepirone in proadifen-pretreated animals was completely abolished by 1-PP (4 mg/kg). These results indicate that the antidepressant-like activity of the examined drugs in the behavioural despairtest is masked (ipsapirone, buspirone) or attenuated (gepirone) by their metabolite 1-PP.

Anticonflict effect of ipsapirone, buspirone and gepirone is not mediated by their common metabolite 1-(2-pyrimidinyl)piperazine

Pyrimidinylpiperazine anxiolytic drugs-ipsapirone, buspirone and gepirone-dose- dependently increased punished responding in an anticonflict (shock-induced suppression of drinking) paradigm in rats. Similar effect was also produced by their common metabolite 1- (2-pyrimidinyl)piperazine (1-PP). Anticonflict effects of ipsapirone, buspirone and gepirone, administered in maximal doses, were considerably stronger when tested 30 min than 120 min after their administration. Furthermore, anticonflict effects of these drugs, given in subthres hold or medium effective doses, were significantly potentiated by the non-selective drug metabolism inhibitor proadifen. Comparison of these results with literature pharmacokinetic data indicate that the pharmacological effect of ipsapirone, buspirone and gepirone parallels better cerebral concentrations of the parent drugs than 1-PP. Therefore anticonflict activity of the investigated drugs does not seem to be mediated by their common metabolite 1-PP.

Blockade of alpha 2-adrenoceptors by 1-(2-pyrimidinyl)-piperazine (PmP) in vivo and its relation to the activity of buspirone

The effect of 1-(2-pyrimidinyl)-piperazine (PmP) and the parent drug, buspirone in counteracting the behavioral and biochemical effects of clonidine were evaluated in the rat. Intraperitoneal or oral administration of PmP, buspirone and yohimbine, but not of prazosin, antagonized the slowing of gastrointestinal motility induced by subcutaneous clonidine (0.1 mg/kg). The doses that inhibited the effect of clonidine on the transit time by 50% were 0.5 mg/kg i.p. and 0.7 mg/kg p.o. for PmP, 7 mg/kg i.p. and 9 mg/kg p.o. for buspirone and 0.5 mg/kg i.p. for yohimbine. PmP (0.5 mg/kg) did not block the antitransit effect of clonidine when administered by intracerebroventricular injection. The antitransit effect of a low dose of morphine (0.05 mg/kg i.p.) was not blocked by PmP (2 mg/kg i.p.). The prolongation of the hexobarbital-induced loss of the righting reflex that occurs after clonidine (0.25 mg/kg i.p.) administration was inhibited by pretreatment with PmP (0.1-2 mg/kg p.o.) or yohimbine (1 mg/kg i.p.) but not by pretreatment with prazosin (2 mg/kg i.p.). Buspirone (1-20 mg/kg) also reduced the effect of clonidine after oral administration, with a maximal effect at 5 mg/kg, whereas the same dose administered i.v. had less effect. PmP (2 mg/kg) and buspirone (15 mg/kg) raised the levels of total 3-methoxy-4-hydroxyphenylgycol (MHPG) in rat cerebral cortex, and prevented the decrease in MHPG induced by clonidine. These findings show that buspirone, in doses at which it is active as an anxiolytic, suppresses the central and peripheral effects of clonidine. This action occurs through alpha 2-adrenoceptors and is mediated primarily by the metabolite, PmP.

Pharmacological profile of a new potent and specific alpha 2-adrenoceptor antagonist, L-657,743

L-657,743,(2S,12bS)1',3'-dimethylspiro(1,3,4,5',6,6',7,12 b-octahydro-2H- benzo[b]furo[2,3-a]quinolizine)-2,4'-pyrimidin-2'-one, was tested in several in vitro and in vivo models for alpha 2-adrenoceptor antagonism. L-657,743 exhibited a high affinity (less than or equal to 1 nM) for alpha 2-adrenoceptors labelled by [3H] rauwolscine or [3H]clonidine with a 240-fold selectivity versus alpha 1-adrenoceptors labelled by [3H]prazosin. L-657,743 was a potent, selective, and competitive alpha 2-adrenoceptor antagonist in the rat isolated vas deferens (pA2 = 9.3 vs. clonidine; pA2 = 7.1 vs methoxamine). In vivo, L-657,743 potently blocked clonidine-induced mydriasis in the rat and stimulated cerebrocortical norepinephrine synthesis, two indices of central alpha 2-adrenoceptor antagonism. L-657,743 exhibited a comparatively low affinity for several monoamine receptor subtypes (D1, D2, 5-HT1, 5-HT2) in radioligand binding assays in vitro and a comparatively low potency to alter the synthesis of brain DA and 5-HT in vivo indicating a marked alpha 2-specificity versus other monoamine receptor mechanisms. Compared to yohimbine, L-657,743 had considerably higher alpha 2-antagonist potency and alpha 2/alpha 1 selectivity and was significantly more alpha 2-specific (i.e., vs. DA, 5-HT receptors).

Lipophilicity and disposition of 1-aryl-piperazines in the rat

The disposition of eight 1-aryl-piperazines was investigated in rats after i.v. administration. The concentration of 1-aryl-piperazine in body fluids and tissues was determined by h.p.l.c. or electron-capture g.l.c. Correlations of kinetics and physiological parameters with the lipophilicity of each 1-aryl-piperazine, determined by h.p.l.c. retention on a reverse-phase C18 column at neutral pH, were investigated. Binding to rat plasma proteins varied within the series, increasing with lipophilicity. For the majority of the derivatives the blood-to-plasma ratio was close to unity, implying an almost equal distribution between erythrocytes and plasma. The most lipophilic 1-aryl-piperazine of the series partitioned more into erythrocytes. The eight compounds differed widely in Vss and total Cl values and as a general trend both values increased with lipophilicity. The percentage of the dose excreted unchanged in the urine decreased progressively with increasing lipophilicity. 1-Aryl-piperazines were distributed extensively in all the tissues examined, concentrating particularly in the eliminating organs and lung. They easily entered the rat brain, Cmax values generally being reached within five minutes of parenteral injection. 1-Aryl-piperazine brain uptake increased with lipophilicity.

Ionization constants and partition coefficients of 1-arylpiperazine derivatives

The ionization constant (pKa) and liposolubilities (log P) of fourteen 1-arylpiperazines were determined by n-octanol/buffer partition. pKa varied little across the entire series. Log P values ranged from less than 1 to about 2 for the highly lipophilic derivatives of the preset series. The results are discussed in relation to the extent to which these derivatives, known to be centrally active, may enter the brain.