Structure of the first clinical entry, E7107 (21), which entered Phase 1 clinical trials for patients with solid tumors. The next-generation analogues 6-deoxypladienolide D (H3B-8800, 22), 17S-FD-895 (23), and cyclopropane 24 are currently being examined for clinical translation for hematologic malignancies. IND=investigational new drug application.