In vivo phenotypic screening for treating chronic neuropathic pain: modification of C2-arylethynyl group of conformationally constrained A3 adenosine receptor agonists

J Med Chem. 2014 Dec 11;57(23):9901-14. doi: 10.1021/jm501021n. Epub 2014 Nov 25.


(N)-Methanocarba adenosine 5'-methyluronamides containing 2-arylethynyl groups were synthesized as A3 adenosine receptor (AR) agonists and screened in vivo (po) for reduction of neuropathic pain. A small N(6)-methyl group maintained binding affinity, with human > mouse A3AR and MW < 500 and other favorable physicochemical properties. Emax (maximal efficacy in a mouse chronic constriction injury pain model) of previously characterized A3AR agonist, 2-(3,4-difluorophenylethynyl)-N(6)-(3-chlorobenzyl) derivative 6a, MRS5698, was surpassed. More efficacious analogues (in vivo) contained the following C2-arylethynyl groups: pyrazin-2-yl 23 (binding Ki, hA3AR, nM 1.8), fur-2-yl 27 (0.6), thien-2-yl 32 (0.6) and its 5-chloro 33, MRS5980 (0.7) and 5-bromo 34 (0.4) equivalents, and physiologically unstable ferrocene 36, MRS5979 (2.7). 33 and 36 displayed particularly long in vivo duration (>3 h). Selected analogues were docked to an A3AR homology model to explore the environment of receptor-bound C2 and N(6) groups. Various analogues bound with μM affinity at off-target biogenic amine (M2, 5HT2A, β3, 5HT2B, 5HT2C, and α2C) or other receptors. Thus, we have expanded the structural range of orally active A3AR agonists for chronic pain treatment.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, N.I.H., Intramural

MeSH terms

  • Adenosine A3 Receptor Agonists / chemical synthesis*
  • Adenosine A3 Receptor Agonists / pharmacology
  • Animals
  • CHO Cells
  • Cricetulus
  • Humans
  • Mice
  • Neuralgia / drug therapy*
  • Structure-Activity Relationship


  • Adenosine A3 Receptor Agonists