– GR-127935 is a potent and selective 5-HT1B/1D receptor antagonist with pKi of 8.5 for both guinea pig 5-HT1D and rat 5-HT1B receptor; displays >100-fold selectivity over 5HT1A, 5-HT2A, 5-HT2C receptors and other receptor types; blocks porcine carotid vascular response to sumatriptan in vivo; orally bioavailable and centrally active.