Abstract: Disclosed herein are immunoconjugates comprising an inhibitor of Eg5 linked to an antigen binding moiety such as an antibody, that are useful for treating cell proliferative disorders. Also disclosed are novel inhibitors of Eg5 that can be used either alone or as part of an immunoconjugate to treat cell proliferation disorders. The Eg5 inhibitors include compounds of this formula as described herein: The invention further provides pharmaceutical compositions comprising these compounds and immunoconjugates, and compositions comprising the immunoconjugates or compounds with a therapeutic co-agent, and methods to use these compounds, conjugates and compositions for treating cell proliferation disorders.