Ai Ito

Silicon-Containing GABA Derivatives, Silagaba Compounds, as Orally Effective Agents for Treating Neuropathic Pain without Central-Nervous-System-Related Side Effects

Neuropathic pain is a chronic condition resulting from neuronal damage. Pregabalin, the (S)-isomer of 3-isobutyl-γ-aminobutyric acid (GABA), is widely used to treat neuropathic pain, despite the occurrence of central nervous system (CNS)-related side effects such as dizziness and somnolence. Here we describe the pharmacology of novel GABA derivatives containing silicon–carbon bonds, silagaba compounds. Silagaba131, 132, and 161 showed pregabalin-like analgesic activities in animal models of neuropathic pain, but in contrast to pregabalin they did not impair neuromuscular coordination in rotarod tests. Pharmacokinetic studies showed that brain exposure to silagaba compounds was lower than that to pregabalin. Surprisingly, despite their potent analgesic action in vivo, silagaba compounds showed only weak binding to α2-δ protein. These compounds may be useful to study mechanisms of neuropathic pain. Our results also indicate that silagaba132 and 161 are candidates for orally effective treatment of neuropathic pain without CNS-related side effects.

Deprotonation equilibrium of 5-tropolonediazonium salt strongly favors 1,2,5-tropoquinone-5-diazide structure in certain solvents.

5-Tropolonediazonium salt 1 is a well-known intermediate for the preparation of 5-substituted tropolone derivatives, but 1,2,5-tropoquinone-5-diazide 2, which is expected to be formed by deprotonation of 1, has not been reported. We synthesized 2, and the structures of 1 and 2 were investigated and compared. NMR and UV spectral data indicated that 1 is easily deprotonated in water, methanol, DMSO, and DMF and exists in the form of 2 in these solvents (but not in acetone or acetonitrile) because of its strong acidity (estimated pKa -2.07). Thus, the acid-base equilibrium shows strong solvent-dependence. Compound 2 may be synthetically available as a carbene precursor.

A Novel Aromatic Carboxylic Acid Inactivates Luciferase by Acylation of an Enzymatically Active Regulatory Lysine Residue

Firefly luciferase (Luc) is widely used as a reporter enzyme in cell-based assays for gene expression. A novel aromatic carboxylic acid, F-53, reported here for the first time, substantially inhibited the enzymatic activity of Luc in a Luc reporter screening. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and tandem mass spectrometry (MS/MS) analyses showed that F-53 modifies Luc at lysine-529 via amidation of the F-53 carboxyl group. The lysine-529 residue of Luc, which plays a regulatory catalytic role, can be acetylated. Luc also has a long-chain fatty acyl-CoA synthase activity. An in vitro assay that involved both recombinant Luc and mouse liver microsomes identified F-53-CoA as the reactive form produced from F-53. However, whereas the inhibitory effect of F-53 is observed in Hela cells that transiently expressed Luc, it is not observed in an in vitro assay that involves recombinant Luc alone. Therefore, insights into the activities of certain mammalian transferases can be translated to better understand the acylation by F-53. The insights from this study about the novel inhibitory modification mechanism might help not only to avoid misinterpretation of the results of Luc-based reporter screening assays but also to explain the pharmacological and toxicological effects of carboxylic acid-containing drugs.