α-Chymotrypsin catalyzed oligomerization of the "dipeptide lego" KL-ethyl ester (OEt) in aqueous media triggers a rapid sol-gel transition due to formation of alternating (KL)x. Resulting mixed chain oligomers, at alkaline pH, self-assemble into β-sheets. Thereafter, intermolecular backbone hydrogen bonding between peptides causes formation of physically entangled nanofibrillar networks.

A unique route to perfectly alternating oligopeptides is described. First, AG-OEt was prepared by standard chemical coupling. Then, AG-OEt was converted by papain-catalysis in 30 s to (AG)(x) (80%-yield, x = 9.4 ± 0.3). Extension of this strategy to other alternating peptide compositions as well as the importance of selecting a protease and reaction conditions that avoid competing transamidation and hydrolysis reactions is discussed.

Some quinoline-containing c-Met kinase inhibitors are aldehyde oxidase (AO) substrates. 3-Substituted quinoline triazolopyridine analogs were synthesized to understand the electron-donating and steric hindrance effects on AO-mediated metabolism. Metabolic stability studies for these quinoline analogs were carried out in liver cytosol from mice, rats, cynomolgus monkeys, and humans. Several 3-N-substituted analogs were found to be unstable in monkey liver cytosolic incubations (half-life, <10 minutes), and five of them (63, 53, 51, 11, and 71) were chosen for additional mechanistic studies. Mono-oxygenation on the quinoline ring was identified by liquid chromatography tandem mass spectrometry. Metabolite formation was inhibited by the AO inhibitors menadione and raloxifene, but not by the xanthine oxidase inhibitor allopurinol. It was found that small electron-donating groups at the 3-quinoline moiety made the analogs more susceptible to AO metabolism, whereas large 3-substituents could reverse the trend. Although species differences were observed, this trend was applicable to all species tested. Small electron-donating substituents at the 3-quinoline moiety increased both affinity (decreased Michaelis constant) and maximum velocity toward AO in kinetic studies, whereas large substituents decreased both parameters probably as a result of steric hindrance. Based on our analysis, a common structural feature with high AO liability was proposed. Our finding could provide useful information for chemists to minimize potential AO liability when designing quinoline analogs.