Piero Angeli

1,3-Dioxolane-Based Ligands as Rigid Analogues of Naftopidil: Structure–Affinity/Activity Relationships at α1 and 5-HT1A Receptors

Conformational restriction of naftopidil led to the discovery of a new class of ligands with a 1,3‐dioxolane (1,3‐oxathiolane, 1,3‐dithiolane) structure that bind to α1 adrenoceptor subtypes and 5‐HT1A receptors. Adequate structural modifications address the selectivity toward one or the other receptor system.

Doxazosin-related alpha1-adrenoceptor antagonists with prostate antitumor activity.

Doxazosin analogues 1-3 and 1a were synthesized and investigated at alpha1-adrenoceptors and PC-3, DU-145, and LNCaP human prostate cancer cells. Compound 1 (cyclodoxazosin) was a potent alpha(1B)-adrenoceptor antagonist displaying antiproliferative activity higher than that of doxazosin in cancer cells in vitro and in vivo, respectively. Because of its antitumor efficacy at low concentrations, lower apoptotic activity in NHDF vs tumor cells, and antiangiogenetic effect, 1 showed a better therapeutic profile relative to doxazosin.

Structure-activity relationships of acetylcholinesterase noncovalent inhibitors based on a polyamine backbone. 2. Role of the substituents on the phenyl ring and nitrogen atoms of caproctamine

Continuing our studies on polyamine-based compounds of potential interest in the field of Alzheimers disease therapeutics, we investigated the structure-activity relationships (SAR) of a lead compound (caproctamine, 3) identified in a previous work. In particular, we varied the substituents on the phenyl ring and on the nitrogen functions (both the amine and the amide), and studied the effects of such modifications on the inhibitory potency against isolated acetyl- and butyryl-cholinesterase (AChE and BChE). Moreover, the ability of selected compounds to reverse the d-tubocurarine-induced neuromuscular blockade and their antagonism toward muscarinic M(2) receptors in guinea pig left atrium were assayed. The most interesting SAR result was the identification of a relationship between the electronic characteristics of 2-substituents (measured by pK(a)) and the AChE inhibitory potency (pIC(50)) of tertiary amine compounds 6-12, which was confirmed by the invariance of the pIC(50) values of the corresponding methiodide derivatives 14-20. With regard to the biological profile, the most interesting compound was the N-ethyl-analogue of caproctamine (9), that showed pIC(50) values of 7.73 (+/-0.02) and 5.65 (+/-0.03) against AChE and BChE, respectively. The ability to increase the acetylcholine level was maintained in the functional assay (pAI(50) for reversing the neuromuscular blockade was 6.45 (+/-0.07)), as well as the ability to antagonize the M(2) receptors (pK(b) = 5.65 (+/-0.06)). Moreover, 9 showed a long duration of action as AChE inhibitor, an useful property in view of a possible development of this compound as a therapeutic agent.

Stereoselective Increase in Cholinergic Transmission by R-(+)-hyoscyamine

R-(+)-hyoscyamine, the dextro enantiomer of atropine, has been shown to amplify cholinergic transmission. R-(+)-hyoscyamine, unlike S-(-)-hyoscyamine, was able to increase acetylcholine release both in vitro and in vivo at a range of concentrations (10(-14) to 10(-12) M) and doses (5 microg/kg i.p.) which were inadequate for blocking muscarinic receptors. The increase over control values in ACh release was 15.9 +/- 2.1% in in vitro experiments performed in rat phrenic nerve-hemidiaphragm preparations (n = 6), and 63.3 + 16.3% in cortical microdialysis performed in free-moving rats (n = 5). The maximum ACh release was reached 60 min after R-(+)-hyoscyamine administration in in vivo experiments. At the same doses and concentrations, R-(+)-hyoscyamine was also able to elicit: antinociception of a cholinergic type (55.6-112.7% depending on the test used); complete prevention of scopolamine- and dicyclomine-induced amnesia; potentiation of muscular contractions electrically evoked in isolated guinea-pig ileum (16.7 +/- 3.6%) and in rat phrenic nerve-hemidiaphragm (19.9 +/- 3.2%) preparations. Antinociception was performed using the hot-plate and acetic acid abdominal constriction tests in mice, and the paw pressure test in rats, while prevention of induced amnesia was evaluated in mice using the passive-avoidance test. The respective affinities (pA2) for R-(+)- and S-(-)-hyoscyamine vs M1 (rabbit vas deferens), M2 (rat atrium) and M3 (rat ileum) receptor subtypes were as follows: 7.05 +/- 0.05/9.33 +/- 0.03 for M1; 7.25 +/- 0.04/8.95 +/- 0.01 for M2; 6.88 +/- 0.05/9.04 +/- 0.03 for M3. The respective pKi values for R-(+)- and S-(-)-hyoscyamine vs the five human muscarinic receptor subtypes expressed in Chinese hamster oocytes (CHO-K1) were as follows: 8.21 +/- 0.07/9.48 +/- 0.18 for m1; 7.89 +/- 0.06/9.45 +/- 0.31 for m2; 8.06 +/- 0.18/9.30 +/- 0.19 for m3; 8.35 +/- 0.11/9.55 +/- 0.13 for m4; 8.17 +/- 0.08/9.24 +/- 0.30 for m5.

Discovery of a new series of 5-HT1A receptor agonists

Starting from compounds previously identified as alpha(1)-adrenoceptor antagonists that were also found to bind to the 5-HT(1A) receptor, in an attempt to separate the two activities, a new series of 5-HT(1A) receptor agonists was identified and shown to have high potency and/or high selectivity. Of these, compound 13, which combines high selectivity (5-HT(1A)/alpha(1)=151) and good agonist potency (pD(2)=7.82; E(max)=76), was found to be the most interesting.

Synthesis and Antimuscarinic Activity of Derivatives of 2-Substituted-1,3-Dioxolanes

Geometric cis, trans isomers, derivatives of 2-substituted-1,3-dioxolanes and 2-substituted-1,3-dioxanes were designed and studied as antimuscarinic agents. The synthesized compounds were evaluated as perchlorides and methiodides by functional tests with rabit vas deferens (putatvie M1), guinea-pig heart (M2) and guinea-pig ileum (M3). The effect of the replacement of a trimethylammonium group with a dimethylsulfonium in the two rings was also evalutated. Pharmacological results indicate that the 1,3-dioxane nucleus shows the highest stereoselective values on the studied receptors.

Chiral muscarinic agonists possessing a 1,3-oxathiolane nucleus: enantio- and tissue-selectivity on isolated preparations of guinea-pig ileum and atria and of rat urinary bladder

SummaryRacemate and corresponding enantiomers of muscarinic agonists carrying a 1,3-oxathiolane nucleus were studied on isolated preparations of guinea-pig ileum and atria and of rat urinary bladder. The efficacy of these agonists were determined according to the method of Furchgott and Bursztyn (1967) and enantio-selectivity and tissue-selectivity were investigated.The enantio-selectivities of the most potent compounds studied (expressed as the ratio of potencies or affinities of the enantiomers) vary significantly from tissue to tissue, supporting the view that M2 receptors are not homogeneous.In particular, the data all indicate that the ileal receptors are different to the atrial and bladder ones.

α1-Adrenoreceptor antagonists bearing a quinazoline or a benzodioxane moiety

Publisher Summary This chapter focuses on α 1 -adrenoreceptor antagonists bearing a quinazoline or a benzodioxane moiety. Prazosin, the prototype of quinazoline-bearing compounds, is a selective α 1 -adrenoreceptor antagonist widely used as a pharmacological tool for α-adrenoreceptor subtypes characterization and as an effective agent in the management of hypertension. For these reasons, prazosin represents a valid tool to explore α1-adrenoreceptor binding site topography and a lead compound in developing new therapeutically useful agents. The role of piperazine ring of prazosin has been investigated through its replacement by an α,ω-alkanediamine chain. Benzodioxanes represent one of the oldest and best known classes of α-adrenoreceptor antagonists, whose chemical structure incorporates a 1,4-benzodioxan-2-yl moiety as the main feature. WB 4101 is the prototype of α1-adrenoreceptor antagonists bearing a benzodioxane moiety. Several investigations have been devoted to improving both affinity and selectivity.

Pentatomic cyclic antagonists and muscarinic receptors: a 30-year review☆

This work is a sequel to and completes the review, that recently appeared in this journal, of pentatomic cyclic muscarinic agonists. It reports the results of structure-activity relationship (SAR) studies of pentatomic cyclic antagonists on muscarinic receptors and compares these results with some recent advances in molecular biology and quantitative structure-activity relationship (QSAR) studies.

Determination of muscarinic agonist potencies at M1 and M2 muscarinic receptors in a modified pithed rat preparation.

SummaryThe agonistic potencies of (±)muscarine, (±)cis - 2 - methyl - 5 - [(dimethylamino)methyl] - 1,3 -oxathiolane methiodide (cis-oxathiolane) and its two enantiomers were determined at muscarinic M1 and M2 receptors in the pithed rat. In non-pretreated animals, i.v. administration of these agents produced bradycardic effects mediated by cardiac M2 receptors followed by increases in heart rate mediated by M1 receptors in sympathetic ganglia. As these responses have been shown to partly overlap, “true” M1 and M2 potencies were determined after selective blockade of M1 and M2 receptors by pirenzepine and methoctramine, respectively. A similar rank order of agonist potencies was obtained at M1 and M2 receptors: (+)cis-oxathiolane > (±)cis-oxathiolane > (±)muscarine > (-)cis-oxathiolane. At both receptor subtypes, (+)cis-oxathiolane was considerably more potent (ca. 30-fold) than its corresponding (−) enantiomer indicating that the agonist binding sites of the two receptor subtypes may have similar stereochemical properties. While (±)muscarine showed similar potencies at M1 and M2 receptors, racemic cis-oxathiolane and its two enantiomers showed a slight selectivity (3–7 fold) for M1 receptors indicating the potential usefulness of these compounds in the development of selective M1 receptor agonists.