Recognition Mechanism of a Novel Gabapentinoid Drug, Mirogabalin, for Recombinant Human α2δ1, a Voltage-Gated Calcium Channel Subunit.

Mirogabalin is a novel gabapentinoid drug with a hydrophobic bicyclo substituent on the γ-aminobutyric acid moiety that targets the voltage-gated calcium channel subunit α2δ1. Here, to reveal the mirogabalin recognition mechanisms of α2δ1, we present structures of recombinant human α2δ1 with and without mirogabalin analyzed by cryo-electron microscopy. These structures show the binding of mirogabalin to the previously reported gabapentinoid binding site, which is the extracellular dCache_1 domain containing a conserved amino acid binding motif. A slight conformational change occurs around the residues positioned close to the hydrophobic group of mirogabalin. Mutagenesis binding assays identified that residues in the hydrophobic interaction region, in addition to several amino acid binding motif residues around the amino and carboxyl groups of mirogabalin, are critical for mirogabalin binding. The A215L mutation introduced to decrease the hydrophobic pocket volume predictably suppressed mirogabalin binding and promoted the binding of another ligand, L-Leu, with a smaller hydrophobic substituent than mirogabalin. Alterations of residues in the hydrophobic interaction region of α2δ1 to those of the α2δ2, α2δ3, and α2δ4 isoforms, of which α2δ3 and α2δ4 are gabapentin-insensitive, suppressed the binding of mirogabalin. These results support the importance of hydrophobic interactions in α2δ1 ligand recognition.

A novel [5.2.1]bicyclic amine is a potent analgesic without µ opioid activity.

We identified (5R)-6-methyl-5-phenyl-1,3,4,5,6,7-hexahydro-2,5-methano-2,6-benzodiazonine (DS21980956: 4-(R)) as a novel [5.2.1]bicyclic basic compound. The scaffold was inspired by fentanyl or pethidine, which possess potent analgesic activities. DS21980956 had potent analgesic activity in the mouse acetic acid writhing test or tail flick test without agonistic activity at the µ opioid receptor (MOR). The mechanism of analgesic action of DS21980956 was considered to differ from a biased ligand, for example, TRV-130 (3, oliceridine).

Discovery of DS34942424: An orally potent analgesic without mu opioid receptor agonist activity.

We identified (5'S)-10'-fluoro-6'-methyl-5',6'-dihydro-3'H-spiro[cyclopropane-1,4'-[2,6]diaza[2,5]methano[2,6]benzodiazonin]-7'(1'H)-one, 22b (DS34942424) with a unique and original bicyclic skeleton. 22b showed an orally potent analgesic in the acetic acid-induced writhing test and formalin test in ddY mice without sedation. Moreover, 22b did not exhibit mu opioid receptor agonist activity.

Discovery of a novel bicyclic compound, DS54360155, as an orally potent analgesic without mu-opioid receptor agonist activity.

We synthesized derivatives of a natural alkaloid, conolidine, and evaluated these derivatives in the acetic acid-induced writhing test and formalin test in ddY mice after oral administration. As a result, we identified (5S)-6-methyl-1,3,4,5,6,8-hexahydro-7H-2,5-methano[1,5]diazonino[7,8-b]indol-7-one sulfate salt, 15a (DS54360155), with a unique and original bicyclic skeleton, as an analgesic more potent than conolidine. Moreover, 15a did not exhibit mu-opioid receptor agonist activity.

Discovery of novel PTHR1 antagonists: Design, synthesis, and structure activity relationships.

The discovery and optimization of a novel series of PTHR1 antagonists are described. Starting from known PTHR1 antagonists, we identified more potent 1,4-benzodiazepin-2-one derivatives by means of a scaffold-hopping approach. The representative compound 23 (DS08210767) exhibited nanomolar-level PTHR1 antagonist activity and potential oral bioavailability in a pharmacokinetic study.

Discovery of conolidine derivative DS39201083 as a potent novel analgesic without mu opioid agonist activity.

We discovered a novel compound, 5-methyl-1,4,5,7-tetrahydro-2,5-ethanoazocino[4,3-b]indol-6(3H)-one sulfuric acid salt (DS39201083), which was formed by derivatization of a natural product, conolidine. DS39201083 had a unique bicyclic skeleton and was a more potent analgesic than conolidine, as revealed in the acetic acid-induced writhing test and formalin test in ddY mice. The compound showed no agonist activity at the mu opioid receptor.

Discovery of DS-6930, a potent selective PPARγ modulator. Part II: Lead optimization.

Attempts were made to reduce the lipophilicity of previously synthesized compound (II) for the avoidance of hepatotoxicity. The replacement of the left-hand side benzene with 2-pyridine resulted in the substantial loss of potency. Because poor membrane permeability was responsible for poor potency in vitro, the adjustment of lipophilicity was examined, which resulted in the discovery of dimethyl pyridine derivative (I, DS-6930). In preclinical studies, DS-6930 demonstrated high PPARγ agonist potency with robust plasma glucose reduction. DS-6930 maintained diminished PPARγ-related adverse effects upon toxicological evaluation in vivo, and demonstrated no hepatotoxicity. Cofactor recruitment assay showed that several cofactors, such as RIP140 and PGC1, were significantly recruited, whereas several canonical factors was not affected. This selective cofactor recruitment was caused due to the distinct binding mode of DS-6930. The calcium salt, DS-6930b, which is expected to be an effective inducer of insulin sensitization without edema, could be evaluated clinically in T2DM patients.

Discovery of DS-6930, a potent selective PPARγ modulator. Part I: Lead identification.

The lead identification of a novel potent selective PPARγ agonist, DS-6930 is reported. To avoid PPARγ-related adverse effects, a partial agonist was designed to prevent the direct interaction with helix 12 of PPARγ-LBD. Because the TZD group is known to interact with helix 12, the TZD in efatutazone (CS-7017) was replaced to discover novel PPARγ intermediate partial agonist 8i. The optimization of 8i yielded 13ac with high potency in vitro. Compound 13ac exhibited robust plasma glucose lowering effects comparable to those of rosiglitazone (3 mg/kg) in Zucker diabetic fatty rats. Upon toxicological evaluation, compound 13ac (300 mg/kg) induced hemodilution to a lower extent than rosiglitazone; however, 13ac elevated liver enzyme activities. X-ray crystallography revealed no direct interaction of 13ac with helix 12, and the additional lipophilic interactions are also suggested to be related to the maximum transcriptional activity of 13ac.

Alkylsulfanyl analogs as potent α2δ ligands.

We identified novel (3R, 5S)-3-aminomethyl-5-methanesulfanyl hexanoic acid (5a: DS75091588) and (3R, 5S)-3-aminomethyl-5-ethanesulfanyl hexanoic acid (6a: DS18430756) as sulfur-containing γ-amino acid derivatives that were useful for the treatment of neuropathic pain. These two compounds exhibited a potent analgesic effect in animal models of both type I diabetes and type II diabetes, and good pharmacokinetics.

Synthesis and biological evaluation of novel imidazol-1-ylacetic acid derivatives as non-brain penetrant bombesin receptor subtype-3 (BRS-3) agonists.

Novel compounds based on 1a were synthesized with the focus of obtaining agonists acting upon peripheral BRS-3. To identify potent anti-obesity compounds without adverse effects on the central nervous system (CNS), a carboxylic acid moiety and a labile carboxylic ester with an antedrug functionality were introduced. Through the extensive synthetic exploration and the pharmacokinetic studies of intravenous administration in mice, the ester 2b was selected owing to its most suitable pharmacological profile. In the evaluation of food intake suppression in C57BL/6N mice, 2b showed significant in vivo efficacy and no clear adverse effects on blood pressure change in dogs administered the compound by intravenous infusion.

Synthesis and biological evaluation of novel chiral diazepine derivatives as bombesin receptor subtype-3 (BRS-3) agonists incorporating an antedrug approach.

Novel compounds based on the lead BRS-3 agonists from our HTS compounds 2a and 2b have been synthesized with the focus on obtaining peripheral BRS-3 agonists. To identify potent anti-obesity compounds without adverse effects on the central nerve system, a labile carboxylic ester with an antedrug functionality was introduced onto the terminal position. Through the extensive synthetic exploration and the pharmacokinetic studies of oral administration in mice, the phenol ester 17c was selected due to the most suitable pharmacological profile. In the evaluation of food intake suppression in B6 mice, 17c showed significant in vivo efficacy and no clear adverse effect on heart rate and blood pressure change in dog iv infusion. Our study paved the way for development of anti-diabetes and obesity drugs with a safer profile.

Discovery of novel chiral diazepines as bombesin receptor subtype-3 (BRS-3) agonists with low brain penetration.

The discovery and optimization of a novel series of BRS-3 agonists are described. We explored a potent BRS-3 agonist with low brain penetration to avoid an adverse effect derived from central nervous system exposure. Through the derivatization process, chiral diazepines 9f and 9g were identified as possessing low brain penetration as well as potent in vitro activity against human and mouse BRS-3s.

Discovery and structure-activity relationship of thienopyridine derivatives as bone anabolic agents.

A cell-based assay was performed for the discovery of novel bone anabolic agents. Alkaline phosphatase (ALPase) activity of ST2 cells was utilized as an indicator of osteoblastic differentiation, and thienopyridine derivative 1 was identified as a hit compound. 3-Aminothieno[2,3-b]pyridine-2-carboxamide was confirmed to be a necessary core structure for the enhancement of ALPase activity, and then optimization of the C4-substituent on the thienopyridine ring was carried out. Introduction of cyclic amino groups to the C4-position of the thienopyridine ring improved the activity. Especially, N-phenyl-homopiperazine derivatives were found to be strong enhancers of ALPase among this new series. Furthermore, 3-amino-4-(4-phenyl-1,4-diazepan-1-yl)thieno[2,3-b]pyridine-2-carboxamide (15k) was orally administered to ovariectomized (OVX) rats over 6 weeks for evaluating the effects on areal bone mineral density (aBMD), and statistically significant improvements in aBMD were observed from the dosage of 10 mg/kg/day.

Natural products reveal cancer cell dependence on oxysterol-binding proteins.

Cephalostatin 1, OSW-1, ritterazine B and schweinfurthin A are natural products that potently, and in some cases selectively, inhibit the growth of cultured human cancer cell lines. The cellular targets of these small molecules have yet to be identified. We have discovered that these molecules target oxysterol binding protein (OSBP) and its closest paralog, OSBP-related protein 4L (ORP4L)--proteins not known to be involved in cancer cell survival. OSBP and the ORPs constitute an evolutionarily conserved protein superfamily, members of which have been implicated in signal transduction, lipid transport and lipid metabolism. The functions of OSBP and the ORPs, however, remain largely enigmatic. Based on our findings, we have named the aforementioned natural products ORPphilins. Here we used ORPphilins to reveal new cellular activities of OSBP. The ORPphilins are powerful probes of OSBP and ORP4L that will be useful in uncovering their cellular functions and their roles in human diseases.

Potent and selective cathepsin K inhibitors.

A novel series of cathepsin K inhibitors derived from Novartis compound I is described. Optimization of the P1, P3, and P1' units led to the identification of 4-aminophenoxyacetic acid 24b with an IC(50) value of 4.8 nM, which possessed an excellent selectivity over other human cathepsins and good pharmacokinetic (PK) properties. Oral administration of compound 24b to ovariectomized (OVX) rats showed a trend toward an improvement of bone mineral density (BMD) in the femur bone.

Arylamine based cathepsin K inhibitors: investigating P3 heterocyclic substituents.

A modification of novel cathepsin K inhibitors I was carried out. The structural design was aimed at reducing the lipophilic character of compounds I for obtaining better pharmacokinetic profiles. This modification afforded several less lipophilic compounds with good inhibitory activities and pharmacokinetic profiles, although the enzyme selectivity over cathepsin S was left at issue.

4-Aminophenoxyacetic acids as a novel class of reversible cathepsin K inhibitors.

We have designed and synthesized a novel series of 3-biphenylamino acid amides as cathepsin K inhibitors based on compound I. In these inhibitors, we have discovered 4-aminophenoxyacetic acids 43 and 47 with good IC(50) values, although lipophilic groups are favorable for the hydrophobic S1' pocket.

Total synthesis of leustroducsin B.

A convergent total synthesis of leustroducsin B (1), which is known to exhibit a variety of biological activities, was successfully carried out. Notable features of our synthesis include construction of the C8 stereocenter by lipase-mediated desymmetrization of meso-diol 4 (90.2% ee) and preparation of the C9-C11 anti-diol moiety by the addition of alkynylzinc reagent 20 to the aldehyde 19. Furthermore, a new diol protecting group, p-silyloxybenzylidene, was developed for the deprotection from densely functionalized substrates under weakly acidic conditions. The protecting group was easily removed in a two-step procedure ((HF)3.Et3N; AcOH-THF-H2O).