Bis-4-aminobenzamidines: Versatile, Fluorogenic A/T-Selective dsDNA Binders

N(1),N(3)-Bis(4-amidinophenyl)propane-1,3-diamine (BAPPA, R = H) is a bisaminobenzamidine fluorogenic derivative that displays a large increase in its emission fluorescence when bound to the minor groove of specific A/T DNA sites (K(d) for an AATT site approximately 79 +/- 6 nM). Moreover, the structural characteristics of BAPPA allow the easy introduction of functional groups that protrude out of the DNA surface.