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  • As disclosed in our preceding paper medicinal chemistry

    2022-05-17

    As disclosed in our preceding paper, medicinal chemistry SAR optimization of an HTS hit led to the discovery of , a potent and selective GPR119 agonist. This scaffold differs significantly from the ‘classical’ GPR119 pharmacophore, exemplified by the examples and (). Notably, ML 221 lacks an essential ‘headgroup’ (arylsulfone or heterocycle), as well as a piperidine-derived ‘tail group’. Compound showed good in vitro activity toward raising cAMP levels via GPR119 human and murine receptors, and demonstrated the ability to secrete GLP-1 and insulin in the respective cell lines. Although it acutely elevated levels of active GLP-1 in vivo inC57Bl/6 mice, it was only marginally active in an acute rat OGTT study. We hypothesized that the low efficacy may be due to three main factors: (1) partial agonism (⩽80%) on the receptor, (2) high plasma protein binding and (3) poor exposure due to low solubility and low metabolic stability. Hence we sought to improve the physicochemical properties of the scaffold while also enhancing its agonistic efficacy on the receptor. First we expanded the existing SAR of by substituting positions of the pyrrolopyrimidine core not previously investigated. The results depicted in suggest that substitution is tolerated in positions 2 and 6 (entries , and , respectively), but not in position 5 (entry ). It is noteworthy that in both positions only small substituents such as methyl and halogen groups were tolerated, whereas larger substituents led to loss of GPR119 activity. However, both potency and efficacy were not improved. We observed a significant drop of activity, especially on the rodent receptor (e.g. compound ). Not surprisingly, these compounds did not significantly elevate GLP-1 levels in rodents (data not shown). In order to gain agonist efficacy on the receptor, we intended to find if there was a preferred ‘active’ conformation of the scaffold ameliorating the binding and activation of both the human and mouse receptor. One way to sample some of the potential conformations is to reduce the degree of rotational freedom and rigidify the scaffold into a productive, pharmacologically relevant conformation. Hence a number of tricyclic compounds were synthesized, using the 6-position of the scaffold as an anchoring point for cyclizations. The cyclizations involved each of the three substituents of the quaternary carbon next to position 7 of the core (e.g. the ester, methyl or benzyl group), thereby allowing to ‘freeze’ three distinct conformations of this particular substituent. Cyclizing the ester or the benzylic position with the 6-Me group led to inactive compounds (results not shown), but tying both methyl groups into a ring led to the more restricted analog . Analogs such as consistently displayed high potency with increased agonist efficacy on both human and rodent receptors (). This increase in receptor activity of compound came at the price of a decrease in exposures compared to the lead compound (). Whereas log values and permeabilities did not change dramatically, we noticed a further drop in the already poor solubility (generally <5μM), the extent of which was difficult to pick up in our solubility assay. However, in several organic and aqueous media, there was significantly more precipitation observed for compounds and compared to . The in vitro hepatic clearance (depicted as a range of microsomal extraction ratio in human, mouse and rat liver microsomes) had a clear trend to increase dramatically in the tricyclic system . Concomitantly, oral exposure in mice significantly decreased from to (in vivo hepatic clearance not measured). We hypothesized that the gains in receptor potency and ML 221 efficacy for the tricyclic analogs would allow us to implement changes to the scaffold previously not tolerated in the bicyclic series, thereby leading to increased exposures via more favorable physicochemical properties, while keeping activities in the acceptable range required for in vivo efficacy. An SAR summary (human and mouse GPR119 receptor activity, physicochemical properties, metabolic stability) for analogs – is depicted in .