Shigeto Hirayama

Design and synthesis of KNT-127, a δ-opioid receptor agonist effective by systemic administration.

We have reported previously the novel δ-opioid agonist, SN-28, which was more potent in in vitro assays than the prototype δ-agonists, TAN-67 and SNC-80. However, when administered by subcutaneous injection, this compound showed no analgesic effect at dosages greater than 30mg/kg in the acetic acid writhing test. We speculated that SN-28 was not effective in the test because the presence of the charged ammonium groups prevented its penetration through the blood-brain barrier. On the basis of our proposal, we designed the novel δ-agonist, KNT-127, which was effective with systemic administration.

Usefulness of olanzapine as an adjunct to opioid treatment and for the treatment of neuropathic pain.

Background: The use of opioids for pain management is often associated with nausea and vomiting. Although conventional antipsychotics are often used to counter emesis, they can be associated with extrapyramidal symptoms. However, chronic pain can induce sleep disturbance. The authors investigated the effects of the atypical antipsychotic olanzapine on morphine-induced emesis and the sleep dysregulation associated with chronic pain. Methods: A receptor binding assay was performed using mouse whole brain tissue. The emetic response in ferrets was evaluated by counting retching and vomiting behaviors. Catalepsy in mice was evaluated by placing both of their forepaws over a horizontal bar. Released dopamine was measured by an in vivo microdialysis study. Sleep disturbance in mice in a neuropathic pain-like state was assayed by electroencephalogram and electromyogram recordings. Results: Olanzapine showed high affinity for muscarinic M1 receptor in brain tissue. Olanzapine decreased morphine-induced nausea and vomiting in a dose-dependent manner. However, olanzapine at a dose that had an antiemetic effect (0.03 mg/kg) did not induce catalepsy or hyperglycemia. In addition, olanzapine at this dose had no effect on the morphine-induced release of dopamine or inhibition of gastrointestinal transit. Finally, olanzapine inhibited thermal hyperalgesia and completely alleviated the sleep disturbance induced by sciatic nerve ligation. Conclusion: These findings suggest that olanzapine may be useful for the treatment of morphine-induced emesis and as an adjunct for the treatment of neuropathic pain associated with sleep disturbance.

Synthesis of quinolinomorphinan-4-ol derivatives as δ opioid receptor agonists

The previously reported morphinan derivative SN-28 showed high selectivity and agonist activity for the δ opioid receptor. In the course of examining the structure-activity relationship of SN-28 derivatives, the derivatives with the 4-hydroxy group (SN-24, 26, 27) showed higher selectivities for the δ receptor over the μ receptor than the corresponding SN-28 derivatives with the 3-hydroxy group (SN-11, 23, 28). Derivatives with the 4-hydroxy group showed potent agonist activities for the δ receptor in the [(35)S]GTPγS binding assay. Although the 17-cyclopropylmethyl derivative (SN-11) with a 3-hydroxy group showed the lowest selectivity for the δ receptor among the morphinan derivatives, the agonist activity toward the δ receptor was the most potent for candidates with the 3-hydroxy group.

Essential structure of opioid κ receptor agonist nalfurafine for binding to the κ receptor 2: synthesis of decahydro(iminoethano)phenanthrene derivatives and their pharmacologies.

To clarify the essential structures of an opioid κ receptor selective agonist, nalfurafine, for binding to the κ receptor, we designed and synthesized some nalfurafine derivatives and the decahydro(iminoethano)phenanthrene derivatives with a cyclohexene moiety as a surrogate for the phenol ring. In addition to the 6-amide side chain and the 17-nitrogen substituted by a cyclopropylmethyl group, the 4,5-epoxy ring, phenolic hydroxy group, and angular hydroxy group played important roles in eliciting the binding properties of nalfurafine but these three moieties were not indispensable for binding to the κ receptor. Moreover, the phenol ring was also not essential for the binding to the κ receptor, and the cyclohexene moiety would play an important role in fixing the conformation of decahydro(iminoethano)phenanthrene derivatives to effectively raise the amide side chain, rendering a conformation that resembled the active one of nalfurafine.

Synthesis of (−)-Homogalanthamine from Naltrexone

Acetylcholinesterase inhibitor (-)-homogalanthamine 3 was synthesized from μ opioid antagonist naltrexone (2) in 16% total yield. The synthesis features Grob fragmentation as a key reaction, which was especially accelerated in the presence of 15-crown-5.

Effects of mirtazapine on sleep disturbance under neuropathic pain-like state

Sleep disturbance has been reported to be one of the most frequent symptoms in patients suffered from severe pain. Benzodiazepines are effective and reduce anxiety in the hours after use, but the induced sleep tends to be less than ideal in quality, with increased Stages I–II and reduces Stages III–IV sleep. In the present study, we investigated sleep disturbance under a neuropathic pain‐like state in mice using electroencephalogram (EEG)/electromyogram (EMG). In a model of neuropathic pain, sciatic nerve ligation caused a marked decrease in the latency of paw withdrawal in response to a thermal stimulus only on the ipsilateral side. Under this condition, sciatic nerve‐ligated animals showed a statistically significant increase in wakefulness and a decrease in non‐rapid eye movement (NREM) sleep during the light phase. Mirtazapine (MTZ) is an antidepressant, which is considered to enhance noradrenergic and serotonergic neurotransmission via antagonistic action at central α2‐adrenergic autoreceptors and heteroreceptors. In the present binding study, MTZ showed higher affinity for histamine H1 and serotonin 5‐HT2A/2C receptors than other receptors, including α2‐adrenergic receptor, in the mouse brain tissue. The thermal hyperalgesia and sleep disturbance following nerve ligation were almost completely alleviated by MTZ. These findings suggest that MTZ may improve the quality of sleep as well as control pain in patients with neuropathic pain mainly through histamine H1‐ and serotonin 5‐HT2‐receptor antagonistic actions. Synapse, 2012.

Synthesis and Pharmacology of a Novel κ Opioid Receptor (KOR) Agonist with a 1,3,5-Trioxazatriquinane Skeleton

We designed and synthesized the 1,3,5-trioxazatriquinane derivatives with m-hydroxyphenyl groups. These compounds include the phenethylamine structure within them, which is a common structure observed in morphinan derivatives like morphine. Among the synthesized compounds, (-)-8c with two m-hydroxyphenyl groups selectively bound and exerted full agonist activity toward the κ opioid receptor (KOR). Subcutaneously administered (-)-8c exhibited significant antinociceptive effects via the KOR in a dose-dependent manner. These results suggest the emergence of a novel class of KOR agonist.

Essential structure of opioid κ receptor agonist nalfurafine for binding to the κ receptor 3: synthesis of decahydro(iminoethano)phenanthrene derivatives with an oxygen functionality at the 3-position and their pharmacologies.

To clarify the essential structures of an opioid κ receptor selective agonist, nalfurafine, for binding to the κ receptor, we designed and synthesized the decahydro(iminoethano)phenanthrene derivatives with an oxygen functionality at the 3-position. The introduction of a hydroxy group to the derivatives increased the affinity and selectivity to the κ receptor regardless of the configuration at the 3-position. However, their affinities were lower than those of nalfurafine with the phenolic hydroxy group. The results suggested that the acidity of the hydroxy group would play an important role in the interaction with the opioid receptor. The low affinities of the 3-keto derivatives indicated that the 3-hydroxy group may participate in the hydrogen bonding with the receptor site not as a hydrogen acceptor but as a hydrogen donor. This is the first experimental evidence for a role as a hydrogen donor for the 3-hydroxy group in morphinans. Furthermore, the κ selectivities in these derivatives with the 6α-amide side chain were affected by the the 3-hydroxy group. The obtained structure-activity relationship information is expected to be useful for the design of more selective ligands for the κ receptor.

Synthesis of novel triplet drugs with 1,3,5-trioxazatriquinane skeletons and their pharmacologies. Part 2: Synthesis of novel triplet drugs with the epoxymethano structure (capped homotriplet).

An improved synthetic method for triplet drugs with the 1,3,5-trioxazatriquinane skeleton was developed that used p-toluenesulfonylmethyl isocyanide (TosMIC) instead of 1,3-dithiane. Using the improved method, we synthesized compounds with two identical pharmacophore units and an epoxymethano group, that is, capped homotriplets. Among the synthesized capped homotriplets, KNT-123 showed high selectivity for the μ receptor over the κ receptor, and the μ selectivity was the highest among the reported μ selective nonpeptide ligands. KNT-123 administered subcutaneously induced a dose-dependent analgesic effect in the acetic acid writhing assay, and its potency was 11-fold more potent than that of morphine. KNT-123 may serve as a useful tool for the study of the pharmacological actions mediated specifically via the μ receptor.

Design and Synthesis of Potent and Highly Selective Orexin 1 Receptor Antagonists with a Morphinan Skeleton and Their Pharmacologies

Nalfurafine, a κ-selective opioid receptor agonist, unexpectedly showed a selective antagonist activity toward the orexin 1 receptor (OX1R) (Ki = 250 nM). Modification of the 17-amino side chain of the opioid ligand to an arylsulfonyl group and the 6-furan acrylamide chain to 2-pyridyl acrylamide led to compound 71 with improvement of the antagonist activity (OX1R, Ki = 1.36 nM; OX2R, not active) without any detectable affinity for the opioid receptor. The dihydrosulfate salt of 71, freely soluble in water, attenuated the physical dependence of morphine. Furthermore, all of the active nalfurafine derivatives in this study had almost no activity for OX2R, which led to high OX1R selectivity. These results suggest that nalfurafine derivatives could be a useful series of lead compounds to develop highly selective OX1R antagonists.