Bivalent linkers and conjugates therof

A compound of the formula

• wherein
• n is an integer from 1 to about 4;
• Ra and Rb are each independently selected from the group consisting of hydrogen and alkyl, including lower alkyl such as C1-C4 alkyl that are optionally branched;
• or Ra and Rb are taken together with the attached carbon atom to form a carbocyclic ring;
• and
• X1 and X2 are each independently selected leaving groups, where each of said leaving groups is displaceable by an independently selected nucleophile.