Design, synthesis, and structure-activity relationships of novel spiro-piperidines as acetyl-CoA carboxylase inhibitors.

Spiro-lactone (S)-1 is a potent acetyl-CoA carboxylase (ACC) inhibitor and was found to be metabolically liable in human hepatic microsomes. To remove one of the risk factors in human study by improving the metabolic stability, we focused on modifying the spiro-lactone ring and the benzothiophene portion of the molecule. Spiro-imide derivative 8c containing a 6-methylthieno[2,3-b]pyridine core exhibited potent ACC inhibitory activity and favorable pharmacokinetic profiles in rats.

Symmetrical approach of spiro-pyrazolidinediones as acetyl-CoA carboxylase inhibitors.

Spiro-pyrazolidinedione derivatives without quaternary chiral center were discovered by structure-based drug design and characterized as potent acetyl-CoA carboxylase (ACC) inhibitors. The high metabolic stability of the spiro-pyrazolo[1,2-a]pyridazine scaffold and enhancement of the activity by incorporation of a 7-methoxy group on the benzothiophene core successfully led to the identification of compound 4c as an orally bioavailable and highly potent ACC inhibitor. Oral administration of 4c significantly decreased the values of the respiratory quotient in rats, indicating the stimulation of fatty acid oxidation.

Design, synthesis, and structure-activity relationships of spirolactones bearing 2-ureidobenzothiophene as acetyl-CoA carboxylases inhibitors.

The co-crystal structure of the human acetyl-coenzyme A 2 (ACC2) carboxyl transferase domain and the reported compound CP-640186 (1b) suggested that two carbonyl groups are essential for potent ACC2 inhibition. By focusing on enhancing the interactions between the two carbonyl groups and the amino acid residues Gly(2162) and Glu(2230), we used ligand- and structure-based drug design to discover spirolactones bearing a 2-ureidobenzothiophene moiety.

Neurochemical properties of ramelteon (TAK-375), a selective MT1/MT2 receptor agonist.

Ramelteon (TAK-375) is a novel melatonin receptor agonist currently under investigation for the treatment of insomnia. This study describes the neurochemical and receptor binding characteristics of ramelteon in vitro. Ramelteon showed very high affinity for human MT1 (Mel1a) and MT2 (Mel1b) receptors (expressed in Chinese hamster ovary [CHO] cells), and chick forebrain melatonin receptors (consisting of Mel1a and Mel1c receptors) with Ki values of 14.0, 112, and 23.1 pM, respectively, making the affinities of ramelteon for these receptors 3-16 times higher than those of melatonin. The affinity of ramelteon for hamster brain MT3 binding sites was extremely weak (Ki: 2.65 microM) compared to melatonin's affinity for the MT3 binding site (Ki: 24.1 nM). In addition, ramelteon showed no measurable affinity for a large number of ligand binding sites (including benzodiazepine receptors, dopamine receptors, opiate receptors, ion channels, and transporters) and no effect on the activity of various enzymes. Ramelteon inhibited forskolin-stimulated cAMP production in the CHO cells that express the human MT1 or MT2 receptors. Taken together, these results indicate that ramelteon is a potent and highly selective agonist of MT1/MT2 melatonin receptors.

Synthesis of a novel series of tricyclic indan derivatives as melatonin receptor agonists.

To develop a new therapeutic agent for sleep disorders, we synthesized a novel series of tricyclic indan derivatives and evaluated them for their binding affinity to melatonin receptors. In our previous paper, we proposed a conformation of the methoxy group favorable for the binding of the MT(1) receptor. To fix the methoxy group in an active conformation, we decided to synthesize conformationally restricted tricyclic indan analogues with the oxygen atom in the 6-position incorporated into a furan, 1,3-dioxane, oxazole, pyran, morpholine, or 1,4-dioxane ring system. Among these compounds, indeno[5,4-b]furan analogues were found to be the most potent and selective MT(1) receptor ligands and to have superior metabolic stability. The optimization of substituents led to (S)-(-)-22b, which showed very strong affinity for human MT(1) (K(i) = 0.014 nM), but no significant affinity for hamster MT(3)() (K(i) = 2600 nM) or other neurotransmitter receptors. The pharmacological effects of (S)-(-)-22b were studied in experimental animals, and it was found that a dose of 0.1 mg/kg, po promoted a sleep in freely moving cats, as demonstrated by a decrease in wakefulness and increases in slow wave sleep and rapid eye movement sleep, which lasted for 6 h after administration. Melatonin (1 mg/kg, po) also had a sleep-promoting effect, though it lasted only 2 h. A new chiral method for the synthesis of (S)-(-)-22b starting from 60, which was prepared from 59 employing asymmetric hydrogenation with the (S)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl-Ru complex, was developed. (S)-(-)-22b (TAK-375) is currently under clinical trial for the treatment of insomnia and circadian rhythm disorders.

Synthesis of a novel series of benzocycloalkene derivatives as melatonin receptor agonists.

We synthesized a novel series of benzocycloalkene derivatives and evaluated their binding affinities to melatonin receptors. To control the spatial position of the amide group, one of the important pharmacophores, we incorporated an endo double bond, an exo double bond (E- and Z-configurations), and a chiral center (R- and S-configurations) at position 1. The indan derivatives with the S-configuration at position 1 were the most promising in terms of potency and selectivity for the human melatonin receptor (MT(1) site), while compounds with the R-configuration showed little potential. Our next attempt was to investigate the most favorable conformation of the methoxy group, the other important pharmacophore for binding to the MT(1) receptor. The introduction of a methyl group at position 5 of the indene ring conserved affinity; however, at position 7, it caused a decrease in affinity. These results suggested that the substitution at position 7 forced the methoxy group to adopt an unfavorable orientation. The optimization of the condensed ring size and substituents led to (S)-8d [(S)-N-[2-(2,3-dihydro-6-methoxy-1H-inden-1-yl)ethyl]propionamide], which had high affinity for the human MT(1) receptor (K(i) = 0.041 nM) but no significant affinity for the hamster MT(3)receptor (K(i) = 3570 nM). In addition, a practical synthetic method of chiral N-[2-(2,3-dihydro-1H-inden-1-yl)ethyl]alkanamides employing asymmetric hydrogenation with (S)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl-Ru has been established.

Design, synthesis, and biological activity of potent and orally available G protein-coupled receptor 40 agonists.

G protein-coupled receptor 40 (GPR40) is being recently considered to be a new potential drug target for the treatment of type 2 diabetes because of its role in the enhancement of free fatty acid-regulated glucose-stimulated insulin secretion in pancreatic ß-cells. We initially identified benzyloxyphenylpropanoic acid (1b) (EC(50) = 510 nM), which was designed based on the structure of free fatty acids, as a promising lead compound with GPR40 agonist activity. Chemical modification of compound 1b led to the discovery of 3-{4-[(2',6'-dimethylbiphenyl-3-yl)methoxy]-2-fluorophenyl}propanoic acid (4p) as a potent GPR40 agonist (EC(50) = 5.7 nM). Compound 4p exhibited acceptable pharmacokinetic profiles and significant glucose-lowering effects during an oral glucose tolerance test in diabetic rats. Moreover, no hypoglycemic event was observed even after administration of a high dose of compound 4p to normal fasted rats. These pharmacological results suggest that GPR40 agonists might be novel glucose-dependent insulin secretagogues with little or no risk of hypoglycemia.

Kinetic resolutions of indan derivatives using bacteria.

Racemic indan derivatives have been resolved by the hydrolysis of amide bonds using Corynebacterium ammoniagenes IFO12612 to produce (S)-amine and (R)-amides. In the kinetic resolution of 1 (N-12-(6-methoxy-indan-1-yl)ethyl]acetamide), it was possible to run the reaction to 44% conversion on a 10-g scale, obtaining (S)-amine 4 ((S)-2-(6-methoxy-indan-1-yl)ethylamine) at >99% enantiomeric excess (ee) and (R)-1 at 98% ee.