Abstract: The invention on hand refers to diseases associated with abnormal protein structures, including Alzheimer's disease, Creutzfeldt-Jakob's disease, BSE and other prion-associated diseases. It is the task of the invention on hand to provide new active agents preventing the formation of amyloid plaques and to dissolve existing plaques, such agents being convenient for therapy, diagnosis and prophylaxis of diseases that are associated with abnormal protein structures. This task is performed in terms of the current invention by heterocyclic or aromatic agents with a rigid structure and a donor-acceptor-donor pattern (DAD), the latter being formed by donors and acceptors of hydrogen bridge linkages which comply with the ?-sheet structure of the peptide or protein and thus fit as binding partners. The heterocyclic or aromatic agents are available at least as dimers. They recognise peptides and proteins with a ?-sheet structure, form stable complexes with them and inhibit their aggregation to ?-amyloid plaques.