Fig 1.
CVT6975 (1) and the pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine derivative 2 as potent A2B and A3 AR antagonists, respectively.
Fig 2.
Rational for the design of the target compounds 3–7.
Fig 3.
Synthesis of desired compounds 3–7.
Reagents: i: NH2NH2.H2O, EtOH, reflux, 3 days; ii: Ph2O, 260°C, 2.5 h; iii: NH2CN, pTsOH, 160°C, 4 h; iv: PhNCO, dioxane, reflux; v: RCOCl, Et3N, dioxane, reflux.
Fig 4.
Structures and binding profile of reference (1,2,33,36) and synthesized compounds (3–7).
aDisplacement of specific [3H]-CCPA binding at hA1 ARs expressed in CHO cells, (n = 3–6). bDisplacement of specific [3H]-NECA binding at hA2A ARs expressed in CHO cells. cKi values of the inhibition of NECA-stimulated adenylyl cyclase activity in CHO cells expressing hA2B ARs. dDisplacement of specific [3H]-HEMADO binding at hA3 ARs expressed in CHO cells. Data are expressed as geometric means, with 95% confidence limits. edata from ref. [22]. fdata from ref. [32].
Fig 5.
Binding mode of xanthine-based compounds at the four AR subtypes.
Compound 36, in dark green, was selected as reference to show the proposed binding mode at the four AR subtypes. The crystallographic coordinates of caffeine, in magenta, bound to hA2A AR are reported superimposed to the binding mode of compound 36. The xanthine core of compound 36 is oriented in a similar manner to the crystallographic data. Residues particularly important in the binding are reported as light grey sticks.
Fig 6.
Binding mode of compound 6 at the hA3 AR.
(A) (B) Hypothetical binding mode A and B of newly synthetized compounds to hA3 AR. The most potent derivative, 6, was selected as example and is represented as orange stick. Subsets of hA3 AR residues, involved in the binding, are coloured in light grey. (C) The electrostatic and hydrophobic contributes to interaction energy calculated for the residue mostly involved in the binding are reported compound 6 in the conformation reported in panel A (in red) and B (in blue). Electrostatic energy values are expressed in kcal mol–1, whereas hydrophobic scores are expressed in arbitrary hydrophobic units.