RU26988 is a highly specific glucocorticoid receptor agonist with a very low affinity for salocorticoid receptors[1].
References
[1] Gomez-Sanchez CE, et al. RU-26988--a new tool for the study of the mineralocorticoid receptor. Endocrinology. 1983 Sep;113(3):1004-9. DOI:10.1210/endo-113-3-1004
