Discovery of 2,9-diaryl-6-carbamoylpurines as a novel class of antitubercular agents

A series of novel 9-alkyl/aryl-2-aryl-6-carbamoylpurines were synthesized, and their activity against Mycobacterium tuberculosis strain H₃₇Rv was assessed. The SAR analysis on the first set of derivatives, with an alkyl or aryl unit at N-9 and a phenolic unit at C-2, showed that the activity depends on the purine ring substituents at N-9 and C-2. A phenyl group at N-9 combined with a 3-hydroxyphenyl or 4-hydroxyphenyl at C-2 improve the activity. The most active compound of this set has a phenyl group at N-9 and a 4-hydroxyphenyl group at C-2, displaying an IC₉₀ = 1.2 μg/mL and a selectivity index higher than 25.5. This compound served as a Hit to design the second set of derivatives. A phenyl group at N-9 was maintained, and the group at C-2 was diversified. The SAR analysis showed that the aryl unit at C-2 must have an oxygen or nitrogen atom bonded in the para position. A proton, a small alkyl or a substituted aryl group may also be bonded to the oxygen. The compound with the 4-methoxyphenyl group at C-2, 1Bd, exhibits the highest activity with an IC₉₀ < 0.19 μg/mL. This compound is highly potent against M. tuberculosis strain H₃₇Rv and non-toxic for VERO mammalian cells with an SI > 153.8. Compound 1Bd was also non-cytotoxic against primary macrophage cultures at IC₉₀, 2xIC_90, and 10xIC₉₀ and significantly reduced the bacterial load in M. tuberculosis-infected macrophages at the same concentrations. Compound 1Bd showed a favorable pharmacokinetic profile when administered orally, with major lung and liver accumulation. In vivo antimycobacterial efficacy of 1Bd was tested at 25 mg/kg. At the tested regimen, a decrease in bacterial burden was observed in the liver. Optimization of the treatment regimen should be performed to fully potentiate the in vivo efficacy of our lead molecule, particularly in the lung, the main target organ of M. tuberculosis.