Thionation of segetalins A and B, cyclic peptides with estrogen-like activity from seeds of Vaccaria segetalis Original Research Article

Thionation of estrogen-like active cyclic peptides, segetalins A (1) and B (2), with Lawessonʹs reagent provided each two thiosegetalins; thiosegetalin A1 [Gly-1-ψ(CS-NH)-Val-2; Trp-5-ψ(CS-NH)-Ala-6]segetalin A, thiosegetalin A2 [Gly-1-ψ(CS-NH)-Val-2; Ala-6-ψ(CS-NH)-Gly-1]segetalin A, thiosegetalin B1 [Gly-1-ψ(CS-NH)-Val-2; Ala-3-ψ(CS-NH)-Trp-4]segetalin B, and thiosegetalin B2 [Gly-1-ψ(CS-NH)-Val-2; Trp-4-ψ(CS-NH)-Ala-1]segetalin B. Thiosegetalin A2 only showed estrogen-like activity against ovariectomized rats. On the basis of their conformations analysed by NMR experiments, the backbone conformation was considered to play an important role in estrogen-like activity for segetalins.