The present disclosure provides compounds of formula (I) or (II) or a pharmaceutically acceptable salt or stereoisomer thereof, wherein Rx-R8 are defined herein. Also provided are compositions comprising a compound described herein and a pharmaceutically effective excipient, methods of stabilizing microtubules in a patient comprising administering to the patient a microtubule-stabilizing amount of a compound described herein, methods of treating cancer in a patient comprising administering to the patient a therapeutically effective amount of a compound described herein, and methods of treating a neurodegenerative disease in a patient comprising administering to the patient a therapeutically effective amount of a compound described herein.