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.

A number of derivatives of 4-amino-6-hydroxy-2-mercaptopyrimidine ( 5) were synthesized and biologically evaluated as A 3 adenosine receptor (A 3 AR) antagonists. The new compounds were designed as open chain analogues of a triazolopyrimidinone derivative displaying submicromolar affinity for the A 3 AR, which had been previously identified using a 3D database search. Substituents R, R', and R'' attached to the parent compound 5 were chosen according to factorial design and stepwise lead optimization approaches, taking into account the essentially hydrophobic nature of the A 3 AR binding site. As a result, 5m (R = n-C 3H 7, R' = 4-ClC 6H 4CH 2, R'' = CH 3) was identified among the pyrimidine derivatives as the ligand featuring the best combination of potency and selectivity for the target receptor. This compound binds to the A 3 AR with a K i of 3.5 nM and is devoid of appreciable affinity for the A 1, A 2A, and A 2B ARs.

The 18 kDa translocator protein (TSPO) is a mitochondrial protein whose basal density is altered in several diseases, with the result that the evaluation of its expression levels by means of molecular imaging techniques represents a promising diagnostic approach. Experimental procedures using a labeled ligand often cause loss of the bound probe, and consequently high affinity ligands covalently binding the receptor protein are needed to overcome this problem. We have previously described a series of N,N-dialkyl-(2-phenylindol-3-yl)glyoxylamides as potent and selective TSPO ligands. Starting from these derivatives, we designed novel TSPO irreversible ligands bearing an electrophilic isothiocyanato group (7, 8), together with an irreversible NBD-fluorescent probe (18). The TSPO affinity of the new irreversible ligands was measured on rat tissue homogenates by [(3)H]Ro 5-4864 radiobinding kinetic assays, all compounds showing high affinities for the target protein. Further biological characterization of the fluorescent irreversible TSPO probe 18 was carried out by using fluorescent spectroscopy in human glioma cells.

The A(3) adenosine receptors (A(3) ARs), belonging to the adenosine receptor family of G-protein-coupled receptors (GPCRs), are ubiquitously expressed in a wide variety of tissues in human body, with high levels in peripheral organs and low levels in the brain. The A(3) ARs are involved in a variety of important patho-physiological processes, including modulation of cerebral and cardiac ischemic damage, inflammation, modulation of intraocular pressure, regulation of normal and tumor cell growth, and immunosuppression. Consequently, A(3) AR selective ligands may represent important pharmacological tools in the treatment of a variety of diseases. Indeed, the development of potent and selective A(3) AR ligands has been the subject of medicinal chemistry research for more than two decades. Although to date a considerable number of selective A(3) AR agonists and antagonists have been discovered, much is still to be learned about the exact function of this subtype, due to its enigmatic role in several physiological processes. In the last two decades, numerous medicinal chemistry groups have made intense efforts in searching for ideal ligands for the A(3) AR subtype. The purpose of this review is to summarize the most recent developments made in the field of selective A(3) AR ligands, which have been subdivided on the basis of their main chemical structural features. For each chemical class, attention has been focused on the SARs which determine ligand affinity and selectivity for the target subtype, and on eventually available preclinical data.