The Discovery of Tadalafil: A Novel and Highly Selective PDE5 Inhibitor. 1: 5,6,11,11a-Tetrahydro-1H-imidazopyridoindole-1,3(2H)-dione Analogues
Alain Daugan, Pascal Grondin, Cecile Ruault, Anne-Charlotte Le Monnier de Gouville, Herve Coste, Jorge Kirilovsky, François Hyafil, and Richard Labaudiniere
J. Med. Chem.; 2003; 46(21) pp 4525 - 4532;