Synthesis and Anti-Renal Fibrosis Activity of Conformationally Locked Truncated 2-Hexynyl-N⁶-Substituted-(N)-Methanocarba-nucleosides as A₃ Adenosine Receptor Antagonists and Partial Agonists

Abstract

Truncated N6-substituted-(N)-methanocarba-adenosine derivatives with 2-hexynyl substitution were synthesized to examine parallels with corresponding 4′-thioadenosines. Hydrophobic N6 and/or C2 substituents were tolerated in A3AR binding, but only an unsubstituted 6-amino group with a C2-hexynyl group promoted high hA2AAR affinity. A small hydrophobic alkyl (4b and 4c) or N6-cycloalkyl group (4d) showed excellent binding affinity at the hA3AR and was better than an unsubstituted free amino group (4a). A3AR affinities of 3-halobenzylamine derivatives 4f–4i did not differ significantly, with Ki values of 7.8–16.0 nM. N6-Methyl derivative 4b (Ki = 4.9 nM) was a highly selective, low efficacy partial A3AR agonist. All compounds were screened for renoprotective effects in human TGF-β1-stimulated mProx tubular cells, a kidney fibrosis model. Most compounds strongly inhibited TGF-β1-induced collagen I upregulation, and their A3AR binding affinities were proportional to antifibrotic effects; 4b was most potent (IC50 = 0.83 μM), indicating its potential as a good therapeutic candidate for treating renal fibrosis.

The A3Adenosine Receptor: History and Perspectives

“…Moreover, a very recent study has obtained a novel series of A 3 AR partial agonists and antagonists as truncated 2-hexynyl-N 6 -substituted-(N)-methanocarba nucleosides, with K i values of 7.8216.0 nM (Nayak et al, 2014). These compounds were screened for renoprotective effects in a human kidney fibrosis model.…”

“…In addition to inflammatory mediator modulation, A 3 AR may be involved in human ventricular remodeling by stimulating MMP-9 production, relevant for revascularization, supporting the use of A 3 AR agonists during the remodeling phase (Velot et al, 2008). Although most studies indicate a role for A 3 AR agonists as inhibitors of inflammation, a recent novel application of A 3 AR antagonists was discovered for a novel series of truncated nucleosides, i.e., that of inhibiting TGF-b1-induced collagen I upregulation, making them appear as good therapeutic 88 candidates for treating renal fibrosis (Nayak et al, 2014).…”

Exploring the Role of N6-Substituents in Potent Dual Acting 5′-C-Ethyltetrazolyladenosine Derivatives: Synthesis, Binding, Functional Assays, and Antinociceptive Effects in Mice

“…In general, all compounds showed weaker binding affinities at rA 3 AR than at hA 3 AR as previously reported also by Jacobson et al in a series of truncated N 6 -substituted-( N )-methanocarbaadenosine derivatives. 20 Surprisingly, at rA 3 AR all tested compounds switched from antagonists to full agonists. It is interesting to note that 3-halobenzyl derivatives 9 , 11 , 13 , 15 , and 26 emerged as the most potent compounds at rA 3 AR, whereas compounds 1 and 3 were 76- and 114-fold less potent at rA 3 AR than at hA 3 AR (rA 3 AR K i = 66.0 and 65.2 nM, respectively; hA 3 AR K i = 0.87 and 0.57 nM, respectively).…”

“…The same results were reported by Jacobson et al in the 4′-truncated N 6 -substituted-( N )-methanocarbaadenosine derivatives. 20 It is surprising to note that the corresponding 2-chloro derivatives (compounds 10 , 12 , 14 , and 26 , 7 respectively) were less active at hA 1 AR ( K i = 2.71–6.04 nM), while at hA 3 AR their affinities remained in the subnanomolar range ( K i = 0.34–0.58 nM) and marginally increased for the 3-fluorobenzyl-2-chloroadenosine derivative 10 ( K i = 0.81 nM). It should be underlined that except for 3-fluorobenzyladenosine derivative 9 , all N 6 -cycloalkyl and N 6 -3-halobenzyl derivatives (compounds 1 – 4 and 9 – 15 , respectively) showed subnanomolar affinity at hA 3 AR.…”

N6-Substituted 5′-N-Methylcarbamoyl-4′-selenoadenosines as Potent and Selective A3 Adenosine Receptor Agonists with Unusual Sugar Puckering and Nucleobase Orientation

“…26 The hA 1 AR or hA 3 AR was expressed in Chinese hamster ovary (CHO) cells, and the hA 2A AR was expressed in human embryonic kidney (HEK)-293 cells. [ 125 I] N 6 -(3-Iodo-4-aminobenzyl)-5′- N -methylcarboxamidoadenosine (I-AB-MECA) was used to measure the binding affinity at the hA 3 AR, while [ 3 H](-)- N 6 -2-phenylisopropyl adenosine (R-PIA) and [ 3 H]2-[ p -(2-carboxyethyl)phenylethylamino]-5′- N -ethylcarboxamidoadenosine) (CGS21680) were used for the hA 1 AR and hA 2A AR, respectively.…”