page_title: Selective estrogen receptor modulator
section_title: Second-generation benzothiophenes
hierarchical_section_title: Selective estrogen receptor modulator / Structure and function / Binding modes / Second-generation benzothiophenes
caption_attribution_description: English: "A ring" (A) and "D ring" (D) marked in Raloxifene.
context_page_description: Selective estrogen receptor modulators are a class of drugs that act on the estrogen receptor. A characteristic that distinguishes these substances from pure ER agonists and antagonists is that their action is different in various tissues, thereby granting the possibility to selectively inhibit or stimulate estrogen-like action in various tissues.
context_section_description: Raloxifene, like 4-hydroxytamoxifen, binds to ERα with the hydroxyl group of its phenolic "A ring" (see figure 15) through hydrogen bonds with Arg-394 and Glu-353. In addition to these bonds, raloxifene forms a second hydrogen bond to ER through the side group of His-524 because of the presence of a second hydroxyl group in the “D ring” (see figure 15). This hydrogen bond is also unlike that between 17β-estradiol and His-524, as the imidazole ring of His-524 is rotated to counteract the difference of the oxygen position in raloxifene and in 17β-estradiol. Just like in 4-hydroxytamoxifen, the bulky side chain of raloxifene displaces helix 12.
caption: Figure 15: "A ring" (A) and "D ring" (D) marked in raloxifene.
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