Endothelins (ETs) are the most ubiquitous, highly potent and unusually long-lasting peptidic constrictors of human vessels known. Elevated levels of the plasma concentration of ETs were observed in several diseases such as hypertension, acute myocardial infarction, congestive heart failure, renal failure, pulmonary hypertension, and atherosclerosis. ETs exert their activities via specific seven-transmembrane, G protein-coupled receptors. To date two receptor subtypes, endothelin A (ET(A)) and endothelin B (ET(B)), have been identified and cloned. A literature survey revealed that a number of compounds that bind ET receptors with affinity and selectivity are known, nevertheless these compounds belong only to few chemical classes. The aim of this work is the identification of an "hit compound" with novel chemical structure endowed with reasonable ET affinity and selectivity. Accordingly, new variously substituted 2-carboxamido-3-carboxythiophene derivatives (29-52) were synthesized. These compounds were tested for their ability to inhibit ETs binding in radioligand binding assay using CHO cells stably expressing human ET(A) and ET(B) receptors.