Biomacromolecules such as proteins are inactivated by hydrophobic ANSA derivatives of the formula: ##STR00001## wherein R.sub.1 and R.sub.2 are hydrophobic or affinity groups and R.sub.3 is selected from the group consisting of aminoacyl groups and peptidyl groups upon nitrosation. ANSA derivatives can be designed to selectively kill tumor cells and various pathogens, including bacteria, viruses, and fungi.