Takako Kimura

Discovery of CS-2100, a potent, orally active and S1P3-sparing S1P1 agonist

S1P(3)-sparing S1P(1) agonists have attracted attention as a suppressant of autoimmunity with reduced side effects. Our synthetic efforts and extensive SAR studies led to the discovery of 10b named CS-2100 with the EC(50) value of 4.0 nM for human S1P(1) and over 5000-fold selectivity against S1P(3). The in vivo immunosuppressive efficacy was evaluated in rats on host versus graft reaction and the ID(50) value was determined at 0.407mg/kg. The docking studies of CS-2100 with the homology model of S1P(1) and S1P(3) showed that the ethyl group on the thiophene ring of CS-2100 was sterically hindered by Phe263 in S1P(3), not in the case of Leu276 in S1P(1). This observation gives an explanation for the excellent S1P(3)-sparing characteristic of CS-2100.

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.

Optimization of 3-aryl-3-ethoxypropanoic acids and discovery of the potent GPR40 agonist DS-1558

GPR40 agonists stimulate insulin secretion only under the presence of high glucose concentration. Based on this mechanism, GPR40 agonists are believed to be promising novel insulin secretagogues with low risk of hypoglycemia. The optimizations of 3-aryl-3-ethoxypropanoic acids were performed to improve in vitro activity. We discovered compound 29r (DS-1558), (3S)-3-ethoxy-3-(4-{[(1R)-4-(trifluoromethyl)-2,3-dihydro-1H-inden-1-yl]oxy}phenyl)propanoic acid, which was confirmed to have an enhancing effect on glucose-dependent insulin secretion after intravenous glucose injection in SD rats.

Design, synthesis, and pharmacological evaluation of a novel series of hormone sensitive lipase inhibitor

HSL inhibition is a promising approach to the treatment of dyslipidemia. As a result of re-optimization of lead compound 2, we identified novel compound 25a exhibiting potent inhibitory activity against HSL enzyme and cell with high selectivity for cholinesterases (AChE and BuChE). Reflecting its potent in vitro activity, compound 25a exhibited antilipolytic effect in rats at 1mg/kg p.o., which indicated that this novel compound is the most potent orally active HSL inhibitor. Moreover, compound 25a did not show bioactivation liability.

Synthesis and SAR studies of benzyl ether derivatives as potent orally active S1P1 agonists

We report herein the synthesis and structure-activity relationships (SAR) of a series of benzyl ether compounds as an S1P₁ receptor modulator. From our SAR studies, the installation of substituents onto the central benzene ring of 2a was revealed to potently influence the S1P₁ and S1P₃ agonistic activities, in particular, an ethyl group on the 2-position afforded satisfactory S1P₁/S1P₃ selectivity. These changes of the S1P₁ and S1P₃ agonistic activities caused by the alteration of substituents on the 2-position were reasonably explained by a docking study using an S1P₁ X-ray crystal structure and S1P₃ homology modeling. We found that compounds 2b and 2e had a potent in vivo immunosuppressive efficacy along with acceptable S1P₁/S1P₃ selectivity, and confirmed that these compounds had less in vivo bradycardia risk through the evaluation of heart rate change after oral administration of the compounds (30 mg/kg, p.o.) in rats.

Analysis of Mechanism-Based Inhibition of CYP 3A4 by a Series of Fluoroquinolone Antibacterial Agents

A series of fluoroquinolone compounds (compounds 1–9), which contain a common quinolone scaffold, inactivated the metabolic activity of CYP3A. The purpose of this study was to identify mechanism-based inhibition (MBI) among these fluoroquinolone compounds by metabolite profiling to elucidate the association of the substructure and MBI potential. Reversibility of MBI after incubation with potassium ferricyanide differed among the test compounds. Representative quasi-irreversible inhibitors form a metabolite-intermediate (MI) complex with the heme of CYP3A4 according to absorption analysis. Metabolite profiling identified the cyclopropane ring-opened metabolites from representative irreversible inhibitors, suggesting irreversible binding of the carbon-centered radical species with CYP3A4. On the other hand, the oxime form of representative quasi-irreversible inhibitors was identified, suggesting generation of a nitroso intermediate that could form the MI complex. Metabolites of compound 10 with a methyl group at the carbon atom at the root of the amine moiety of compound 8 include the oxime form, but compound 10 did not show quasi-irreversible inhibition. The docking study with CYP3A4 suggested that a methyl moiety introduced at the carbon atom at the root of the primary amine disrupts formation of the MI complex between the heme and the nitroso intermediate because of steric hindrance. This study identified substructures of fluoroquinolone compounds associated with the MBI mechanism; introduction of substituted groups inducing steric hindrance with the heme of P450 can prevent formation of an MI complex. Our series of experiments may be broadly applicable to prevention of MBI at the drug discovery stage.

Difference in Mechanism-Based Inhibition of Cytochrome P450 3A4 and 3A5 by a Series of Fluoroquinolone Antibacterial Agents

A series of fluoroquinolone antibacterial compounds were found to be irreversible (compounds 1–5) and quasi-irreversible (compounds 6–9) inhibitors of CYP3A4. The purpose of this study was to evaluate their mechanism-based inhibition (MBI) potency against CYP3A5. Compounds 1–5 were also irreversible inhibitors of CYP3A5, whereas compounds 6–9 showed neither irreversible nor quasi-irreversible inhibition of CYP3A5. Compounds 6 and 8 did not form a metabolite-intermediate complex with the heme of CYP3A5 during incubation. The structural analysis of the metabolites after incubation of compounds 1 and 6 with CYP3A5 revealed that their metabolites were identical to those produced by CYP3A4, including the precursors of which are speculated to account for the MBI of CYP3A4. The homology modeling of CYP3A5 suggests that four residues around the nitroso intermediate of compound 6 in the substrate-binding pocket of CYP3A4 correspond with the bulkier residues in CYP3A5—especially Phe210 in CYP3A5—which might contribute to the steric hindrance with the nitroso intermediate of compound 6. The substrate-binding pocket structure of CYP3A5 might prevent the nitroso intermediate from coordinate binding with the heme, thereby preventing quasi-irreversible inhibition. Our study may provide new insights into the observable differences between the inhibition of CYP3A4 and CYP3A5.

Alpha-Amylase Inhibitor, CS-1036 Binds to Serum Amylase in a Concentration-Dependent and Saturable Manner

(2R,3R,4R)-4-hydroxy-2-(hydroxymethyl)pyrrolidin-3-yl 4-O-(6-deoxy-β-D-glucopyranosyl)-α-D-glucopyranoside (CS-1036), which is an α-amylase inhibitor, exhibited biphasic and sustained elimination with a long t1/2 (18.4–30.0 hours) in rats and monkeys, but exhibited a short t1/2 (3.7–7.9 hours) in humans. To clarify the species differences in the t1/2, the plasma protein binding of CS-1036 was evaluated by ultrafiltration. A concentration-dependent and saturable plasma protein binding of CS-1036 was observed in rats and monkeys with the dissociation rate constant (KD) of 8.95 and 27.2 nM, and maximal binding capacity (Bmax) of 52.8 and 22.1 nM, respectively. By the assessments of the recombinant amylase and immunoprecipitation, the major binding protein of CS-1036 in rats was identified as salivary amylase (KD 5.64 nM). CS-1036 also showed concentration-dependent and saturable binding to human salivary and pancreatic amylase, with similar binding affinity in rats. However, the protein binding of CS-1036 was constant in human plasma (≤10.2%) due to the lower serum amylase level compared with rats and monkeys. From the calculation of the unbound fraction (fu) in plasma based on in vitro KD and Bmax, the dose-dependent increase in fu after oral administration is speculated to lead to a dose-dependent increase in total body clearance and a high area under the curve/dose at lower doses, such as 0.3 mg/kg in rats.