Here, we report suvanine, a marine sponge sesterterpene, as an antagonist of the mammalian bile acid sensor farnesoid-X-receptor (FXR). Using suvanine as a template, we shed light on the molecular bases of FXR antagonism identifying the essential conformational changes responsible for the transition from the agonist to the antagonist form. Molecular characterization of the nuclear co-repressor NCoR and co-activator Src-1 revealed that receptor conformational changes are associated with a specific dynamic of recruitment of these cofactors to the promoter of OSTα, a FXR regulated gene. Using suvanine as a novel hit, a library of semi-synthetic derivatives has been designed and prepared, leading to pharmacological profiles ranging from agonism to antagonism towards FXR. Deep pharmacological evaluation demonstrated that derivative 19 represents a new chemotype of FXR modulator whereas alcohol 6, with a simplified molecular scaffold, exhibits excellent antagonistic activity.