Novel N,N-disubstituted indol-3-ylglyoxylamides (1-56), bearing different combinations of substituents R 1-R 5, were synthesized and evaluated as ligands of the translocator protein (TSPO), the 18 kDa protein representing the minimal functional unit of the "peripheral-type benzodiazepine receptor" (PBR). Most of the new compounds showed a nanomolar/subnanomolar affinity for TSPO and stimulated steroid biosynthesis in rat C6 glioma cells with a potency similar to or higher than that of classic TSPO ligands such as PK 11195. Moreover, when evaluated in vivo by means of the elevated-plus-maze (EPM) paradigm in the rat, compound 32, the best-performing derivative in terms of TSPO affinity and pregnenolone production, showed clear anxiolytic effects. The results of this study suggested that the novel N,N-disubstituted indol-3-ylglyoxylamides may represent a promising class of compounds potentially suited for the treatment of anxiety disorders.

In the framework of the continuing interest of this research group in the use of 8-aryl-8-hydroxy-8H-[1,4]thiazino[3,4-c][1,2,4]oxadiazol-3-ones (1) as calcium entry blockers, a number of acetals were synthesized and assayed "in vitro". All of them are structurally related to diltiazem and pyrrolobenzothiazines. The effect on the biological profile was measured by functional assays for a wide variety of acetal residues: saturated linear and branched chains, short and long unsaturated E and/or Z chains as well as benzyl and methylcyclohexyl residues. From selective assays on the most active derivative (5b) (EC(50) = 0.04 microM), which is 20 times more active than diltiazem (EC(50) = 0.79 microM), a muscarinic or adenosinic mechanism of action was excluded. A 3D QSAR model was obtained and validated with homologous literature data, and a virtual receptor scheme was derived for the unknown binding site. The following pharmacophoric features favorably affect the potency: one positively charged center, three lipophilic groups, and two hydrogen-bonding acceptor groups.

A multidisciplinary project has led to the discovery of novel, structurally diverse, L-type calcium entry blockers (CEBs). The absolute configuration of a recently reported CEB has been determined by vibrational circular dichroism spectroscopy, to assign the stereospecificity of the ligand-channel interaction. Thereafter, a virtual screening procedure was performed with the aim of identifying novel chemotypes for CEBs, starting from a database of purchasable compounds; 340,000 molecules were screened in silico in order to prioritize structures of interest for bioscreening. As a result, 20 compounds were tested in vitro, and functional and binding assays revealed several hits with promising behavior as CEBs.

The chiral oxadiazol-3-one 2 has recently been shown to exhibit myocardial calcium entry channel blocking activity, substantially higher than that of diltiazem. To determine the enantioselectivity of this activity, the enantiomers of 2 have been resolved using chiral chromatography. The absolute configuration (AC) of 2 has been determined by comparison of density functional theory (DFT) calculations of its vibrational circular dichroism (VCD) spectrum, electronic circular dichroism (ECD) spectrum, and optical rotation (OR) to experimental VCD, ECD, and OR data. All three chiroptical properties yield identical ACs; the AC of 2 is unambiguously determined to be S(+)/R(-).

As a continuation of our studies on 2-phenylindol-3-ylglyoxylamides as potent and selective translocator protein (TSPO) ligands, two subsets of novel derivatives, featuring hydrophilic group (OH, NH2, COOH) at the para-position of the pendent 2-phenyl ring (8-16) or different 2-aryl moieties, namely, 3-thienyl, p-biphenyl, 2-naphthyl (23-35), were synthesized and biologically evaluated, some of them showing Ki values in the subnanomolar range and the 2-naphthyl group performance being the best. The resulting SARs confirmed the key role played by interactions taking place between ligands and the lipophilic L1 pocket of the TSPO binding site. Docking simulations were performed on the most potent compound of the present series (29) exploiting the recently available 3D structures of TSPO bound to its standard ligand (PK11195). Our theoretical model was fully consistent with SARs of the newly investigated as well of the previously reported 2-phenylindol-3-ylglyoxylamide derivatives.

Adenosine induces glioma cell proliferation by means of an antiapoptotic effect, which is blocked by cotreatment with selective A(3) AR antagonists. In this study, a novel series of N(2)-substituted pyrazolo[3,4-d]pyrimidines 2a-u was developed as highly potent and selective A(3) AR antagonists. The most performing compounds were derivatives 2a (R(1) = CH(3) and R(2) = COC(6)H(5); K(i) 334, 728, and 0.60 nM at the human A(1), A(2A), and A(3) ARs, respectively) and 2b (R(1) = CH(3) and R(2) = COC(6)H(4)-4-OCH(3); K(i) 1037, 3179, and 0.18 nM at the human A(1), A(2A), and A(3) ARs, respectively), which counteracted the effect of the A(3) AR agonists Cl-IB-MECA and IB-MECA on human glioma U87MG cell proliferation. This effect was concentration-dependent, with IC(50) values comparable to A(3) AR binding affinity values of 2a and 2b, thereby suggesting that their effects were receptor-mediated. Furthermore, the antiproliferative activity of the new compounds was demonstrated to be mediated by the block of A(3) AR agonist activation of intracellular kinases ERK 1/2.

Fluorescent ligands for the peripheral-type benzodiazepine receptor (PBR) featuring the 7-nitrobenz-2-oxa-1,3-diazol-4-yl moiety were synthesized, based on N,N-dialkyl-2-phenylindol-3-ylglyoxylamides, a potent, selective class of PBR ligands previously described by us. All the new ligands are moderately to highly potent at the PBR, with a complete selectivity over the central benzodiazepine receptor. Results from fluorescence microscopy showed that these probes specifically labeled the PBR at the mitochondrial level in C6 glioma cells.

As an extension of previous investigations (Tetrahedron 1999, 55, 5433-5440; J. Heterocycl. Chem. 2000, 37, 875-878), a series of 21 [1,4]thiazino[3,4-c][1,2,4]oxadiazolones, which has already been synthesized (except for compounds 5a, 5b, 6), was evaluated as calcium entry blockers by functional studies, namely, in isolated guinea-pig left and right atria and K(+)-depolarized aortic strips. With the aim of investigating the effect of a condensed benzene ring on the molecular structure and the influence of substituents on the 8-phenyl ring of 4a, ab initio computations (RHF/3-21G) were performed on compounds 3, 4a-d, 4f, and 4k. The results obtained show that many of the compounds studied are potent and selective negative inotropic agents; in particular, compounds 4e and 4f are about 3- and 2-fold more potent than diltiazem, respectively.