High lipophilicity of seems to cause poor PK

High lipophilicity of seems to cause poor PK profiles. First we replaced the phenyl ring of compound with various hetero aromatic rings to reduce lipophilicity, (). The synthesis of pyridine derivative was shown in . (2′,6′-Dimethylbiphenyl-3-yl)methanol () was reacted with 2,5-dibromopyridine in the presence of NaH. The corresponding bromopyridine and ethyl acrylate were coupled under the microwave-assisted Heck coupling condition. Olefin moiety of compound was reduced with NaBH using NiCl as a catalyst. Saponification of ethyl ester in compound gave pyridine derivative . Other compounds in were synthesized in the similar manner as in . Pyridine derivative showed similar GPR40 agonistic activity to compound . In contrast, pyridine derivative was found to be a weaker agonist than compound . Five-membered hetero aromatic rings were not tolerant (compound , ). Next we introduced another nitrogen atom to compound to lower its hydrophobicity (compound –). Only a pyrazine derivative kept strong activity with a lowered log value, while its solubility became worse. Methyl scanning of compound (compound –) resulted in less potent agonists. We assessed PK profiles of compound in rats. Bioavailability of compound (=24%) was improved compared to compound (=0.9%) probably due to lower lipophilicity of (). These results encouraged us to take further optimization of compound in order to adjust the PK profiles better. It is well known that fatty acids are metabolized via β-oxidation in the mitochondria, hence compound which contains propanoic Triflusal moiety could be metabolized. Therefore we introduced substituents on the carbon chain of the propanoic acid to block the oxidation (). The fluoro, methyl and alkoxy substituents were introduced on the α-position (compound –). Only the fluoro group kept activity. The acidity of carboxylic acid has changed by the electronic effect of these substituents. Electron donating substituent (compound , ) could decrease the ionic interaction of the carboxylic acid. On the other hand, these substituents on the β-position were tolerant (compound –). Among them, the alkoxy substituent (compound ) was promising in terms of strong agonistic activity and preserved lipophilicity. Conformationally restricted derivative did not increase its agonistic activity. To determine cytotoxicity of a series of compounds, we evaluated the inhibition of mitochondrial respiratory chain complex 1, which blocks electron transportation and leads to the cell toxicity., , Unfortunately these derivatives including compound have strong inhibition of complex 1. It was reported that the number of aromatic rings correlated with successful transition of compounds from discovery through clinical trials., We hypothesized that the biphenyl moiety which was the common structure of these compounds was crucial for cytotoxicity. Compound was synthesized to remove the biphenyl structure. As we expected, the function of the respiratory chain could keep working normally. However its GPR40 agonistic activity has significantly diminished. According to its log value of 0.7, hydrophobic interaction between the receptor and the ligand might be too weak. In order to restore the binding affinity, the central pyridine ring was changed back to the phenyl ring. As a result, compound recovered strong GPR40 agonistic activity (EC=20nM) and moreover the inhibition of mitochondrial function by was found to be weak. It is reported that small nonpolar substituents at -position were favored over or -position on the benzyl moiety of propanoic acid series. In contrast, the methyl substituent introduced at - or -position was acceptable in the β-ethoxy-propanoic acid series (compound –). Compound was synthesized via . Benzyl moiety was introduced by the reaction of 4-hydroxybenzaldehyde () and 2-methylbenzyl bromide in the presence of CsCO. β-Hydroxyl ester was obtained by aldol reaction of aldehyde and ethyl acetate with the base of LHMDS. The alkylation of hydroxyl substituent at β-position of by iodoethane with excess amount of AgO in toluene reflux gave the ethoxy product in moderate yield. Hydrolysis of ethyl ester in methanol at room temperature gave .