Kazumi Kondo

7-Chloro-5-hydroxy-1-[2-methyl-4-(2-methylbenzoyl-amino)benzoyl ]-2,3,4,5-tetrahydro-1H-1-benzazepine (OPC-41061): a potent, orally active nonpeptide arginine vasopressin V2 receptor antagonist.

We previously reported a series of benzazepine derivatives as orally active nonpeptide arginine vasopressin (AVP) V2 receptor antagonists. After the lead structure OPC-31260 was structurally evaluated and optimized, the introduction of the 7-Cl moiety on the benzazepine and 2-CH3 on the aminobenzoyl moiety enhanced its oral activity. The new AVP-V2 selective antagonist OPC-41061 was determined to be a potent and orally active agent.

Phosphorylation of cytohesin-1 by Fyn is required for initiation of myelination and the extent of myelination during development.

Transgenic and knockout mice reveal a pathway that controls the extent of myelination by Schwann cells. Promoting Myelination Through Phosphorylation In response to signals from axons in the peripheral nervous system, Schwann cells remodel their plasma membrane and wrap it around the length of the axon to produce myelin, which increases the efficiency with which axons conduct action potentials. Yamauchi et al. investigated signaling within Schwann cells and found that the guanine nucleotide exchange factor cytohesin-1 was required for efficient myelination. The tyrosine kinase Fyn phosphorylated and activated cytohesin-1, leading to activation of the guanosine triphosphatase Arf6 and changes in cellular morphology. Mice expressing a mutant cytohesin-1 devoid of the Fyn target site in Schwann cells had axons with decreased myelin thickness compared to those in their wild-type counterparts. This work identifies critical steps in the pathway leading from signals produced by neurons to myelination by Schwann cells, which could have implications for demyelinating diseases. Schwann cells respond to cues from axons by transforming their cellular morphology and forming myelin. We demonstrated that the guanine nucleotide exchange factor (GEF) cytohesin-1 promoted myelination by activating the small guanosine triphosphatase (GTPase) Arf6. In mice, ablating cytohesin-1 delayed myelination and diminished the amount of myelin produced. We determined that the Src-family kinase Fyn phosphorylated tyrosine 382 (Y382) of cytohesin-1, and we generated transgenic mice that expressed a Schwann cell–specific phosphorylation mutant of cytohesin-1 (Y382F) that could not be targeted by Fyn. During development, these transgenic mice displayed delayed myelination compared to that of wild-type mice, as well as a decrease in the amount of myelin produced, similar to that observed in cytohesin-1−/− mice. These findings demonstrate that phosphorylation of cytohesin-1 by Fyn is required for full myelination and suggest that tyrosine phosphorylation of GEFs may be a mechanism to activate small GTPases engaged in cell morphogenesis.

Characterization of a novel nonpeptide vasopressin V2‐agonist, OPC‐51803, in cells transfected human vasopressin receptor subtypes

We discovered the first nonpeptide arginine‐vasopressin (AVP) V2‐receptor agonist, OPC‐51803. Pharmacological properties of OPC‐51803 were elucidated using HeLa cells expressing human AVP receptor subtypes (V2, V1a and V1b) and compared with those of 1‐desamino‐8‐D‐arginine vasopressin (dDAVP), a peptide V2‐receptor agonist. OPC‐51803 and dDAVP displaced [3H]‐AVP binding to human V2‐ and V1a‐receptors with Ki values of 91.9±10.8 nM (n=6) and 3.12±0.38 nM (n=6) for V2‐receptors, and 819±39 nM (n=6) and 41.5±9.9 nM (n=6) for V1a‐receptors, indicating that OPC‐51803 was about nine times more selective for V2‐receptors, similar to the selectivity of dDAVP. OPC‐51803 scarcely displaced [3H]‐AVP binding to human V1b‐receptors even at 10−4 M, while dDAVP showed potent affinity to human V1b‐receptors with the Ki value of 13.7±3.2 nM (n=4). OPC‐51803 concentration‐dependently increased cyclic adenosine 3′, 5′‐monophosphate (cyclic AMP) production in HeLa cells expressing human V2‐receptors with an EC50 value of 189±14 nM (n=6). The concentration‐response curve for cyclic AMP production induced by OPC‐51803 was shifted to the right in the presence of a V2‐antagonist, OPC‐31260. At 10−5 M, OPC‐51803 did not increase the intracellular Ca2+ concentration ([Ca2+]i) in HeLa cells expressing human V1a‐receptors. On the other hand, dDAVP increased [Ca2+]i in HeLa cells expressing human V1a‐ and V1b‐receptors in a concentration‐dependent fashion. From these results, OPC‐51803 has been confirmed to be the first nonpeptide agonist for human AVP V2‐receptors without agonistic activities for V1a‐ and V1b‐receptors. OPC‐51803 may be useful for the treatment of AVP‐deficient pathophysiological states and as a tool for AVP researches.

Structural analysis of human glutamine:fructose-6-phosphate amidotransferase, a key regulator in type 2 diabetes

Glutamine:fructose‐6‐phosphate amidotransferase (GFAT) is a rate‐limiting enzyme in the hexoamine biosynthetic pathway and plays an important role in type 2 diabetes. We now report the first structures of the isomerase domain of the human GFAT in the presence of cyclic glucose‐6‐phosphate and linear glucosamine‐6‐phosphate. The C‐terminal tail including the active site displays a rigid conformation, similar to the corresponding Escherichia coli enzyme. The diversity of the CF helix near the active site suggests the helix is a major target for drug design. Our study provides insights into the development of therapeutic drugs for type 2 diabetes.

An amino acid residue whose change by mutation affects drug binding to the HERG channel

We did the experiments to search for amino acids that affect quinidine binding to the HERG channel, and have identified an amino acid whose change by mutation affects the binding of various drugs. The residue is located at position 647 in the S6 and is not involved in the recently identified methanesulfonanilide binding pocket. The homology model of the HERG channel indicated that the residue faces toward the outside of the channel pore. We conclude that the residue at position 647 does not interact directly with drug molecules but plays an important role in keeping the binding sites high affinity for drugs.

Recent discovery and development of non-peptide vasopressin V2 receptor agonists

Desmopressin, 1-desamino-8-D-arginine vasopressin (DDAVP), is a peptide analogue of arginine vasopressin (AVP), which is an agonist of the AVP V2 receptor. It is used for the treatment of central diabetes insipidus, the control of nocturnal enuresis and may also be of use for controlling nocturia. However, DDAVP is a peptide analogue with variable bioavailability, even via an intranasal route or in oral formulation. Therefore, the discovery and the development of an orally effective non-peptide V2 agonist may be particularly useful in all respects. The continuous filing of patents since 1995 evidences the importance of this field.

Practical stereoselective synthesis of (2,3,4,5-tetrahydro-1H-benzo[b]azepin-5-yl)acetic acid

Highly enantioselective asymmetric hydrogenation of readily accessible olefins, (E)- and (Z)-[1-(toluene-4-sulfonyl)-1,2,3, 4-tetrahydro-1H-benzo[b]azepin-5-ylidene]acetic acid (4a and 4b, respectively) and [1-(toluene-4-sulfonyl)-2, 3-dihydro-1H-benzo[b]azepin-5-yl]acetic acid (4c), is presented as an efficient and straightforward route to (R)-[1-(toluene-4-sulfonyl)-2,3,4, 5-tetrahydro-1H-benzo[b]azepin-5-yl]acetic acid [(R)-1] which is a key intermediate for the synthesis of non-peptide AVP V2-agonist. Hydrogenation of carboxylic acid 4c gave (R)-1 in quantitative yield and 85% ee using Ru(OAc)2[(S)-H8-BINAP], a Ru(II) complex of a partially hydrogenated BINAP (H8-BINAP), as a catalyst. When (R)-1 of 76% ee was transformed into the corresponding isopropylamide 6, pure enantiomer (R)-6 was obtained in 75% yield by recrystallization from MeOH.