N6-Ethyl-2-alkynyl NECAs, selective human A3 adenosine receptor agonists

A series of N6-ethyl-2-alkynyl NECA (5′-N-ethylcarboxamidoadenosine) analogs were synthesized and their binding affinity with the four human adenosine receptors was evaluated. One of the compounds ZR1121 shows high affinity with hA3 receptor and its selectivity over hA1 receptor is 1–2 log orders greater than IB-MECA or Cl-IB-MECA, the currently employed selective A3 agonists.