The present invention provides novel tubulysin analogues, methods of making and methods of using such analogues and conjugates thereof. The essential features for the potent cytotoxicity of tubulysin D have been established for the first time by the synthesis and evaluation of a series of analogues. By identifying functionality that surprisingly is not necessary for activity, highly potent cell-growth inhibitors have been developed that are smaller and considerably more stable than tubulysin D.
