Potent and selective inhibitor of phosphodiesterase type 5 (PDE5); more selective than sildenafil (IC50 values are 0.23, 56 and > 63000 nM for T 0156 and 3.6, 29 and > 270 nM for sildenafil at PDE5, PDE6 and PDEs 1 - 4 respectively). Selective over 30 other enzymes and receptors (IC50 > 10 mM) and potentiates electrical field stimulation-induced relaxation of isolated rabbit corpus cavernosum. Active in vivo. Purity 99%. MW (observed): 620.06