The synthesis and pharmacological activity of a new series of 1-arylpyrazoles as potent σ(1) receptor (σ(1)R) antagonists are reported. The new compounds were evaluated in vitro in human σ(1)R and guinea pig σ(2) receptor (σ(2)R) binding assays. The nature of the pyrazole substituents was crucial for activity, and a basic amine was shown to be necessary, in accordance with known receptor pharmacophores. A wide variety of amines and spacer lengths between the amino and pyrazole groups were tolerated, but only the ethylenoxy spacer and small cyclic amines provided compounds with sufficient selectivity for σ(1)R vs σ(2)R. The most selective compounds were further profiled, and compound 28, 4-{2-[5-methyl-1-(naphthalen-2-yl)-1H-pyrazol-3-yloxy]ethyl}morpholine (S1RA, E-52862), which showed high activity in the mouse capsaicin model of neurogenic pain, emerged as the most interesting candidate. In addition, compound 28 exerted dose-dependent antinociceptive effects in several neuropathic pain models. This, together with its good physicochemical, safety, and ADME properties, led compound 28 to be selected as clinical candidate.

The synthesis and pharmacological activity of a series of bicyclic pyrazolo[1,5-a]pyrimidines as potent and selective cyclooxygenase-2 (COX-2) inhibitors are described. The new compounds were evaluated both in vitro (COX-1 and COX-2 inhibition in human whole blood) and in vivo (carrageenan-induced paw edema and air-pouch model). Modification of the pyrimidine substituents showed that 6,7-disubstitution provided the best activity and led to the identification of 3-(4-fluorophenyl)-6,7-dimethyl-2-(4-methylsulfonylphenyl)pyrazolo[1,5-a]pyrimidine (10f) as one of the most potent and selective COX-2 inhibitor in this series.

We have identified a co-crystal of tramadol hydrochloride−celecoxib (ctc; E-58425/MR308), a novel active pharmaceutical ingredient (API)−API co-crystal formed by an intrinsic 1:1 molecular ratio of rac-tramadol•HCl and celecoxib, which displays favorable physicochemical and dissolution profiles. Adequate treatment of pain represents an unmet medical need that is often addressed via combination therapy. API−API co-crystals represent a new approach with potential to improve physicochemical properties, bioavailability, stability, or formulation capacity, which may translate into optimized pharmacokinetic profiles and clinical benefits compared with individual APIs or their combination. ctc showed a well-defined differential scanning calorimetry profile, and its single-crystal X-ray diffraction structure demonstrated a supramolecular 3D network in which the two active enantiomers of tramadol and celecoxib are linked via hydrogen bonding and chloride ions. Oversaturation studies indicated that the saturation effect for highly insoluble celecoxib occurred at a higher concentration in ctc than in celecoxib alone. Comparative intrinsic dissolution rate studies showed that the release of celecoxib was faster, and the release of tramadol was slower, from ctc than from the individual APIs, predicting an improved pharmacokinetic behavior for ctc. Together with findings from preclinical studies, these data support the clinical development of ctc for the treatment of pain.

The synthesis and the pharmacological activity of a series of 1,5-diarylimidazoles developed as potent and selective cyclooxygenase-2 (COX-2) inhibitors are described. The new compounds were evaluated both in vitro (COX-1 and COX-2 inhibition in human whole blood) and in vivo (carrageenan-induced paw edema, air-pouch, and hyperalgesia tests). Modification of all the positions of two regioisomeric imidazole cores led to the identification of 4-[4-chloro-5-(3-fluoro-4-methoxyphenyl)imidazol-1-yl]benzenesulfonamide (UR-8880, 51f) as the best candidate, which is now undergoing Phase I clinical trials.

The mechanism of binding of different nonsteroidal anti-inflammatory drugs to the cyclooxygenase active site of cyclooxygenase-2 (COX-2) has been studied by means of a wide range of theoretical techniques including molecular dynamics and free energy calculations. It is found that theoretical methods predict accurately the binding of different drugs based on different scaffolds. Calculations allow us to describe in detail the key recognition sites and to analyze how these recognition sites change depending on the scaffold of the drug. It is concluded that the recognition site of COX-2 is very flexible and can adapt its structure to very subtle structural changes in the drug.