A novel class of adenosine A3 receptor ligands. 1. 3-(2-Pyridinyl)isoquinoline derivatives

J Med Chem. 1998 Oct 8;41(21):3987-93. doi: 10.1021/jm980036q.


A series of 3-(2-pyridinyl)isoquinoline derivatives was synthesized as potential antagonists for the human adenosine A3 receptor by substitution of the 1-position. The compounds were obtained by various synthetic routes from 1-amino-3-(2-pyridinyl)isoquinoline. The affinity was determined in radioligand binding assays for rat brain A1 and A2A receptors and for the cloned human A3 receptor. A structure-activity relationship analysis indicated that a phenyl group when coupled by a spacer allowing conjugation on position 1 of the isoquinoline ring increased the adenosine A3 receptor affinity. In contrast, such a phenyl group directly bound to position 1 of the isoquinoline ring decreased affinity. Since the combination of a phenyl group together with a spacer raised adenosine A3 receptor affinity, various spacers were investigated. VUF8501 (N-[3-(2-pyridinyl)isoquinolin-1-yl]benzamidine (15) showed an affinity at the human adenosine A3 receptor of 740 nM. Substituent effects on the phenyl group were investigated by in vitro evaluation of a series of substituted benzamidines. Electron-donating groups at the para position of the benzamidine ring increased adenosine A3 receptor affinity. These investigations led to VUF8505 (4-methoxy-N-[3-(2-pyridinyl)isoquinolin-1-yl]benzamidine(22)), which is a moderately potent and selective ligand for the human adenosine A3 receptor with an affinity of 310 nM in our test system having negligible affinity for rat A1 and A2A receptors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Benzamidines / chemical synthesis*
  • Benzamidines / chemistry
  • Benzamidines / metabolism
  • Benzamidines / pharmacology
  • CHO Cells
  • Cell Line
  • Cerebral Cortex / metabolism
  • Corpus Striatum / metabolism
  • Cricetinae
  • Humans
  • In Vitro Techniques
  • Isoquinolines / chemical synthesis*
  • Isoquinolines / chemistry
  • Isoquinolines / metabolism
  • Isoquinolines / pharmacology
  • Ligands
  • Purinergic P1 Receptor Antagonists
  • Rats
  • Receptor, Adenosine A2A
  • Receptor, Adenosine A3
  • Receptors, Purinergic P1 / biosynthesis
  • Receptors, Purinergic P1 / metabolism*
  • Structure-Activity Relationship


  • Benzamidines
  • Isoquinolines
  • Ligands
  • N-(3-(2-pyridinyl)isoquinolin-1-yl)benzamidine
  • Purinergic P1 Receptor Antagonists
  • Receptor, Adenosine A2A
  • Receptor, Adenosine A3
  • Receptors, Purinergic P1