Compounds and compositions are disclosed in which a Drug unit (D) is linked to a Ligand unit (L). In an exemplary embodiment, the compound is of the formula LAa-Ww-Yy-D).sub.p Ia or a pharmaceutically acceptable salt thereof, where A is a stretcher unit, W is an amino acid unit, Y is a spacer unit, D is of the formula ##STR00001## and a, w, y, p and R.sup.2-R.sup.10 are as disclosed in the specification. Methods for treating cancer, autoimmune disease, and infectious disease using the compounds and compositions of the invention are also disclosed.