Complex sentence: Tesmilifene is a diphenylmethane derivative that is structurally related to the triphenylethylene derivative tamoxifen but lacks the stilbene bridge and third phenyl ring necessary for binding to the estrogen receptor (ER), and as such, it is not a selective estrogen receptor modulator (SERM).
Split into simpler sentences: Tesmilifene is a diphenylmethane derivative that is structurally related to tamoxifen but lacks the stilbene bridge and third phenyl ring necessary for binding to the estrogen receptor (ER). As such, unlike tamoxifen, tesmilifene is not a selective estrogen receptor modulator (SERM).