Compounds effective as IP receptor modulators, particularly IP receptor antagonists, that are of the formula I: ##STR1##

wherein A, R¹, R², R³ and R⁴ are as defined in the specification; and individual isomers, racemic or non-racemic mixtures of isomers, and pharmaceutically acceptable salts or solvates thereof. Also disclosed are pharmaceutical compositions containing such compounds and methods for their use as therapeutic agents.