Transdermal administration of aqueous pregabalin solution as a potential treatment option for patients with neuropathic pain to avoid central nervous system-mediated side effects.

Pregabalin, (S)-3-isobutyl-γ-aminobutyric acid (GABA), is a widely used adjuvant therapy for patients with neuropathic pain, which is defined as chronic pain caused by lesions or diseases of the somatosensory nervous system. However, dizziness and somnolence (sleepiness) are common dose-limiting side effects, probably due to excessive sedative effects on higher centers of the central nervous system (CNS) which are involved in the anticonvulsant and analgesic actions of pregabalin. We speculated that transdermal delivery would minimize centrally mediated side effects. To test this idea, we evaluated the analgesic effects of pregabalin delivered through the transdermal route in animal models of neuropathic pain. Transdermally administered pregabalin increased the pain thresholds in response to mechanical stimuli in a partial sciatic nerve ligation model in rats and a spinal nerve ligation model in mice, and surprisingly also in normal animals. It is noteworthy that simple transdermal application of an aqueous solution of pregabalin is effective. This could be a useful treatment option to avoid or minimize the CNS-mediated side effects of orally administered pregabalin.

Functionalized oxatriquinanes and their structural equilibrium in protic solvent.

We synthesized oxatriquinane hexafluorophosphate bearing an ethoxycarbonylmethyl group 7 or a 2-oxopropyl group 11. Both of these organic oxonium cation compounds were obtained as stable solids. However, (1)H-NMR analysis showed that oxatriquinane 7 was present as the oxonium cation in aprotic solvent CD3CN, but was in rapid equilibrium with ring-opened bicyclic compound 8 in protic solvent CD3OD. The oxatriquinane 11 also showed similar behavior in protic solvent. Phenyl-substituted oxatriquinanes 12 and 14 were also obtained as stable solids, and showed similar properties to 7 and 11.

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.

Synthesis of Am80 (tamibarotene) prodrug candidates, congeners and metabolites.

Compound 1 (IT-M-07000) was previously reported as a candidate prodrug of Am80 (Tamibarotene; used to treat acute promyelocytic leukemia), and shown to be efficiently metabolized to Am80 via ß-oxidation. Here, we describe in detail the synthesis of 1, together with another tetradeuterated candidate prodrug, IT-YA-00616 (2), as well as two congeners, and several metabolic intermediates of 1 previously detected in mouse plasma.

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.

Design, synthesis and evaluation of retinoids with novel bulky hydrophobic partial structures.

Many synthetic retinoids contain an aromatic structure with a bulky hydrophobic fragment. In order to obtain retinoids with therapeutic potential that do not bind to or activate retinoic acid X receptors (RXRs), we focused on the introduction of novel hydrophobic moieties, that is, metacyclophane, phenalene and benzoheptalene derivatives. The designed compounds were synthesized and their agonistic activities towards RARs and RXRs were evaluated. Most of the active compounds showed selectivity for RARα and RARß over RARγ, and higher RARß transactivating activity seemed to correlate with higher cell differentiation-inducing activity towards promyelocytic leukemia cell line HL-60. These compounds showed no agonistic activity towards RXRs.

(R)- and (S)-4-Amino-3-(trimethylsilyl)methylbutanoic acids ameliorate neuropathic pain without central nervous system-related side effects.

Neuropathic pain is a chronic pain condition resulting from neuronal damage, and is usually treated with pregabalin or gabapentin, which are structurally related to γ-aminobutyric acid (GABA) and are originally developed as anticonvulsant drugs. Here, we report the synthesis and pharmacology of (R)- and (S)-4-amino-3-(trimethylsilyl)methylbutanoic acids (1a and 1b), which showed analgesic activity as potent as that of pregabalin in the Chung spinal nerve ligation model. However, unlike pregabalin, 1a and 1b do not have antiepileptic effects, and they are therefore promising candidates for selective therapeutic agents to treat neuropathic pain without central nervous system-related side effects.

Novel synthesis of ureas: application of t-butylureas.

Otherwise inaccessible tropolonylureas were prepared by reaction of t-butylurea with appropriate amines, with elimination of t-butylamine. This method is also generally applicable for urea synthesis.

Disposition of a new tamibarotene prodrug in mice.

Recently, a new compound IT-M-07000 was designed as a prodrug of tamibarotene, one of the therapeutic agents for acute promyelocytic leukemia. In the present study, IT-M-07000 was administered to mice to investigate whether it is actually metabolized to tamibarotene. Its metabolic pathway and the utility as a tamibarotene prodrug were also evaluated. After oral administration of IT-M-07000, IT-M-07000, tamibarotene and two compounds that were supposed to be metabolic intermediates in a beta-oxidation pathway of IT-M-07000 to tamibarotene were detected in mouse plasma. It was thus shown that IT-M-07000 is probably beta-oxidized to tamibarotene in mice. Comparison of tamibarotene concentration profiles after oral administration of IT-M-07000 or tamibarotene showed that the plasma tamibarotene concentration increased slower and was retained stable, and the area under the plasma concentration-time curve (AUC) of tamibarotene was larger in mice administered IT-M-07000 than tamibarotene. These results indicate that IT-M-07000 is possibly useful as a prodrug of tamibarotene.

On the structure of "5-nitrosotropolone".

It has long been discussed whether "5-nitrosotropolone" 1 takes the nitroso structure 1A or the tautomeric oxime structure 1B. Analysis of NMR and UV spectra data in this study indicates that the tropoquinone-5-monoxime 1B is preferred. The UV absorption shift to longer wavelength at dilute solutions is attributable to the dissociated form 3.