Identification of Tetrahydropyrido[4,3-d]pyrimidine Amides as a New Class of Orally Bioavailable TGR5 Agonists

Abstract

Takeda G-protein-coupled receptor 5 (TGR5) represents an exciting biological target for the potential treatment of diabetes and metabolic syndrome. A new class of high-throughput screening (HTS)-derived tetrahydropyrido[4,3-d]pyrimidine amide TGR5 agonists is disclosed. We describe our effort to identify an orally available agonist suitable for assessment of systemic TGR5 agonism. This effort resulted in identification of 16, which had acceptable potency and pharmacokinetic properties to allow for in vivo assessment in dog. A key aspect of this work was the calibration of human and dog in vitro assay systems that could be linked with data from a human ex vivo peripheral blood monocyte assay that expresses receptor at endogenous levels. Potency from the human in vitro assay was also found to correlate with data from an ex vivo human whole blood assay. This calibration exercise provided confidence that 16 could be used to drive plasma exposures sufficient to test the effects of systemic activation of TGR5.

Keywords: GLP-1; GPCR; TGR5; agonist; diabetes.

Figure 1

Previously disclosed TGR5 agonists.

Scheme 1. Synthesis of Tetrahydropyrido[4,3-d]pyrimidine Core(s)

Reagents and conditions: PG = Boc or Cbz. (a) Morpholine, toluene, 110 °C. (b) Ethyl oxalyl chloride, Et₃N, CH₂Cl₂. (c) R¹-amidine, 2-methyl-isothiourea or urea, Et₃N, EtOH, reflux. (d) Ammonia, MeOH. (e) Conversion of R¹ = SMe into R¹ = EtNH: (1) 3-chloroperoxybenzoic acid, CH₂Cl₂; (2) EtNH₂, THF. (f) Conversion of R¹ = OH into R¹ = Cl: POCl₃, acetone. (g) Conversion of R¹ = Cl into R¹ = cPr: cPrZnBr, PEPPSI^TM-IPr, THF. (h) Conversion of R¹ = Cl into R¹ = OEt: NaH/EtOH. (i) 4 N HCl, dioxane. (j) Pd/C, H₂, MeOH.

Scheme 2. Synthesis of Phenpropanamides

Reagents and conditions: (a) Aldehyde, base. (b) Et₃SiH, EtOH, cat. 5% Pd/C. (c) Aryl halide, (tBu₃P)₂Pd, dioxane, 95 °C.

Figure 2

Inhibition of TNF-α secretion, ex vivo whole blood LPS challenge. Data based on an average of three donors. Normalized to maximum TNF-α secreted.