Annalisa Tait

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.

1,3-Dioxolane-based ligands incorporating a lactam or imide moiety: Structure–affinity/activity relationship at α1-adrenoceptor subtypes and at 5-HT1A receptors

A series of 1,3-dioxolane-based compounds incorporating a lactam (2-4) or imide (5-7) moiety was synthesized and the pharmacological profile at alpha(1)-adrenoceptor subtypes and 5-HT(1A) receptor was assessed through binding and functional experiments. Starting from the 2,2-diphenyl-1,3-dioxolane derivative 1, previously shown to be a selective alpha(1a(A))/alpha(1d(D))-adrenoceptor subtype antagonist, over alpha(1b(B)) subtype and 5-HT(1A) receptor, and replacing one phenyl ring with lactam or imide moiety a reduction of alpha(1)/5-HT(1A) selectivity is observed, mainly due to the increase in 5-HT(1A) affinity. In functional experiments lactam derivatives seems to favour 5-HT(1A) receptor antagonism (pKb = 7.20-7.80) and alpha(1B)-adrenoceptor antagonist selectivity (alpha(1B)/alpha(1A) and alpha(1B)/alpha(1D) of about 10-fold). The most interesting of the various imide derivatives is compound 7t, which is a selective alpha(1D)-adrenoceptor antagonist (pKb = 8.1 and alpha(1D)/alpha(1A) and alpha(1D)/alpha(1B) selectivity ratios of 16 and 11 respectively) whereas at 5-HT(1A) receptor it is a potent partial agonist (pD2 = 7.98, E(max) = 60%).]. Given that cis and trans diastereomer pairs for 2-7 are possible, a computational strategy based on molecular docking studies was used to elucidate the atomic details of the 5HT(1A)/agonist and 5HT(1A)/antagonist interaction.

Studies of enantiomerization of chiral 3,4-dihydro-1,2,4-benzothiadiazine 1,1-dioxide type compounds.

An on-column HPLC procedure using a chiral stationary phase (CSP) was developed for the determination of rate constants and free energy barriers of enantiomerization of (+/-)IDRA21. Subsequently, the HPLC method was applied for investigation of two structurally related chiral compounds. The individual enantiomers of the studied compounds were isolated in parallel by preparative HPLC and rate constants and free energy barriers of enantiomerization were determined in different solvents. The on-column enantiomerization data revealed that CSP induces different rate constants for the two enantiomers. The results generated off-line were used to determine the influence of solvents on the racemization of (+) and (-) IDRA21 and to gain further insight into the enantiomerization mechanism of chiral 3,4-dihydro-1,2,4-benzothiadiazine 1,1-dioxide type compounds.

Synthesis and free radical scavenging activity of 4-(2H-1,2,4-benzothiadiazine-1,1-dioxide-3-yl)-2,6-bis(1,1-dimethylethyl)phenols

Abstract 4-(2H-1,2,4-benzothiadiazine-1,1-dioxide-3-yl)-2,6-bis(1,1-dimethylethyl)phenols ( 1–11 ) were prepared by cyclization of the corresponding 3,5-bis(1,1-dimethylethyl)-4-hydroxy-N-2-(sulphamoylphenyl)benzamides ( 12–22 ). Compounds 1–22 were tested as free radical scavengers by reaction with DPPH using UV and ESR spectrometry and the formation of stable phenoxy radicals by their oxidation with lead tetraacetate was also studied.

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.

High-performance liquid chromatographic method for the quantification of anthranilic and 3-hydroxyanthranilic acid in rat brain dialysate

Anthranilic acid (ANA) and 3-hydroxyanthranilic acid (3-HANA) have attracted considerable attention as two of the L-tryptophan kynurenine pathway metabolites in the central nervous system. In this study, a highly sensitive and accurate method for the quantification of ANA and 3-HANA has been developed using reversed-phase high performance liquid chromatography (HPLC) with fluorimetric detection. The HPLC assay was carried out using a C(18) column (5 microm, 250 x 4.6 mm i.d.). The mobile phase consisted of a mixture of 25 mM sodium/acetic acid buffer (pH 5.5) and methanol (90:10 v/v). Fluorimetric detection at lambda(ex)=316 nm and lambda(em)=420 nm was used. The assay was applied to the measurement of ANA and 3-HANA acid in rat brain dialysate following administration of L-tryptophan or L-kynurenine. 3-HANA and ANA levels were progressively increased during 90 min following administration of L-tryptophan, then decreased progressively to basal levels. 3-HANA levels were significantly higher than ANA levels after L-kynurenine administration. These findings suggest that the assay developed should provide an improved means for investigation of neurobiology of kynurenine pathway.

Scouting new sigma receptor ligands: Synthesis, pharmacological evaluation and molecular modeling of 1,3-dioxolane-based structures and derivatives.

Herein we report the synthesis and biological activity of new sigma receptor (σR) ligands obtained by combining different substituted five-membered heterocyclic rings with appropriate σR pharmacophoric amines. Radioligand binding assay, performed on guinea pig brain membranes, identified 25b (1-(1,4-dioxaspiro[4.5]decan-2-ylmethyl)-4-benzylpiperazine) as the most interesting compound of the series, displaying high affinity and selectivity for σ1R (pKiσ1 = 9.13; σ1/σ2 = 47). The ability of 25b to modulate the analgesic effect of the κ agonist (-)-U-50,488H and μ agonist morphine was evaluated in vivo by radiant heat tail-flick test. It exhibited anti-opioid effects on both κ and μ receptor-mediated analgesia, suggesting an agonistic behavior at σ1R. Docking studies were performed on the theoretical σ1R homology model. The present work represents a new starting point for the design of more potent and selective σ1R ligands.

Profiling of Flavonol Derivatives for the Development of Antitrypanosomatidic Drugs

Flavonoids represent a potential source of new antitrypanosomatidic leads. Starting from a library of natural products, we combined target-based screening on pteridine reductase 1 with phenotypic screening on Trypanosoma brucei for hit identification. Flavonols were identified as hits, and a library of 16 derivatives was synthesized. Twelve compounds showed EC50 values against T. brucei below 10 μM. Four X-ray crystal structures and docking studies explained the observed structure-activity relationships. Compound 2 (3,6-dihydroxy-2-(3-hydroxyphenyl)-4H-chromen-4-one) was selected for pharmacokinetic studies. Encapsulation of compound 2 in PLGA nanoparticles or cyclodextrins resulted in lower in vitro toxicity when compared to the free compound. Combination studies with methotrexate revealed that compound 13 (3-hydroxy-6-methoxy-2-(4-methoxyphenyl)-4H-chromen-4-one) has the highest synergistic effect at concentration of 1.3 μM, 11.7-fold dose reduction index and no toxicity toward host cells. Our results provide the basis for further chemical modifications aimed at identifying novel antitrypanosomatidic agents showing higher potency toward PTR1 and increased metabolic stability.

Structure-affinity/activity relationships of 1,4-dioxa-spiro[4.5]decane based ligands at α 1 and 5-HT1A receptors.

Recently, 1-(1,4-dioxaspiro[4,5]dec-2-ylmethyl)-4-(2-methoxyphenyl)piperazine (1) was reported as a highly selective and potent 5-HT1AR ligand. In the present work we adopted an in-parallel synthetic strategy to rapidly explore a new set of arylpiperazine (7-32) that is structurally related to 1. The compounds were tested for binding affinity and functional activity at 5-HT1AR and α1-adrenoceptor subtypes and SAR studies were drawn. In particular, compounds 9, 27 and 30 emerged as promising α1 receptor antagonists, while compound 10 behaves as the most potent and efficacious 5-HT1AR agonist. All the compounds were docked into the 5HT1AR theoretical model and the results were in agreement with the biological experimental data. These findings may represent a new starting point for developing more selective α1 or 5-HT1AR ligands.

(2,2‐Diphenyl‐[1,3]oxathiolan‐5‐ylmethyl)‐(3‐phenyl‐propyl)‐amine: a Potent and Selective 5‐HT1A Receptor Agonist

A selective 5‐HT1A receptor agonist: A new series of ligands acting at 5‐HT1A serotonin receptor were identified. Among them (2,2‐diphenyl‐[1,3]oxathiolan‐5‐yl‐methyl)‐(3‐phenyl‐propyl)amine (shown) possesses outstanding activity (pKi=8.72, pD2=7.67, Emax=85) and selectivity (5‐HT1A/α1D>150), and represents a new 5‐HT1A agonist chemotype.