The aniline R group was extensively
The aniline R2 group was extensively explored and a large variety of substitution was tolerated at several positions on the aryl ring (). Notably, substitution at the 3-position often gave increased potency. Increasing lipophilic bulk at this position gave increasing potency within an ether series (compounds –) and again attempts to introduce polarity generally resulted in a loss of potency, for example compounds and . Introduction of a carboxylic Guanethidine Sulfate was not well tolerated in compound . The bis-amide sub-series afforded the opportunity to achieve higher solubility by means of an ionisable centre. The pKa of such compounds was typically in the range 5–7, depending on other substituents and resulted in solubilities generally greater than 10μM. Modest DGAT -1 potency improvements could be made but were generally accompanied with increased lipophilicity and decreased LLE (). High metabolic clearance, particularly in rat (e.g., showed 62% liver blood flow and 3% bioavailability), led us to discontinue work in this series. Introduction of an ionisable centre, particularly a carboxylic acid remained a key goal to obtain acceptable solubility and high LLE. Disclosure of a potent acidic series in the patent literature encouraged us to continue to explore the incorporation of an acid group into the R1 side chain (). Modestly potent butanoate indicated that this would be possible and biphenyl containing acids – maintained potency relative to the biphenyl non-acid . Saturation of either ring resulted in decreased potency in but significantly increased potency in relative to the non-acid . Subsequent to this work, the acid fragment R in has been reported as a privileged structure contained within several DGAT-1 inhibitors., , , Des-homologue was also potent but the phenyl--hexyl-ethanoate group gave a clear potency and LLE advantage. Our previous R2 aniline SAR could be mapped onto a new acid-containing sub-series and was quickly identified as having a good overall balance of properties, most notably achieving our key aims of high potency and LLE (). Excellent potency in inhibiting triacylglycerol (TAG) synthesis in human HuTu 80 cells, relevant to the gut as a target organ, was determined. showed no significant activity against DGAT-2, the hERG encoded potassium channel (>30μM), and cytochrome P450 enzymes CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4 (all >30μM). Aqueous solubility of crystalline is lower than ideal but is counterbalanced by good cellular permeability, resulting in good pharmacokinetic profiles determined in vivo in three pre-clinical species: mouse, rat and dog (). Oral exposure was substantial in all species. The rat and mouse pharmacokinetic profiles were characterised by high oral bioavailability and low clearance while more moderate bioavailability was observed in dog. In an oral lipid tolerance test (OLTT), fasted rats were administered compound at a range of doses 2h prior to a bolus dose of corn oil and plasma TAG levels were measured 1.5h later. shows that was highly efficacious in reducing plasma TAG excursion in this model, exhibiting 40%, 66% and 73% inhibition at doses of 0.03, 0.1 and 0.2mg/kg respectively. shows the relationship between plasma TAG and free compound levels in plasma for in the rat OLTT assay. A direct response PK/PD model ( sigmoidal model) was used to successfully fit the PK/PD data showing a clear correlation between compound levels in plasma and an effect in the OLTT. PK/PD parameters for the model fit are shown in . The fact that the in vivo IC (0.00005μM) is 10-fold lower than the in vitro IC (0.0005μM) is compatible with the idea that local inhibition of DGAT-1 in the gut (and not the systemic exposure) could be the main driver for efficacy in the OLTT assay. Compound also showed good effects on adipose TAG synthesis (expressed as TAG:DAG ratio in adipose tissue) giving 33%, 65%, 78% and 78% decrease in the TAG:DAG ratio in adipose tissue at 0.1, 0.3, 1 and 3mg/kg, respectively (). shows the relationship between adipose TAG synthesis and free compound levels in plasma for in the rat. A direct response PK/PD model ( sigmoidal model) was used to succesfully fit the PK/PD data showing a clear correlation between free compound levels in plasma and an effect in the adipose TAG:DAG ratio. PK/PD parameters for the model fit are shown on .