Tubulysin compounds of the formula (I) where R1, R2 R3a, R3b, R4, R5, W, and n are as defined herein, are anti-mitotic agents that can be used in the treatment of cancer, especially when conjugated to a targeting moiety.本發明係關於式(I)之妥布賴森(tubulysin)化合物,其中R1、R2、R3a、R3b、R4、R5、W及n係如本文中所定義,該等化合物尤其在偶聯至靶向部分時係可用於治療癌症之抗有絲分裂劑。