Enzyme-Controlled Molecular Recognition: Selective Targeting of Trypsin with a Substrate-Inhibitor Supramolecular Complex

We have synthesized and studied the host compound ( 1 ) that forms a noncovalent complex ( K = 480 ± 30 M - 1 ) with 1,4-diamidinobenzene ( 2 ) at pD 8.0 in D 2 O. Guest 2 has been shown to inhibit the proteases specific for cationic side chains ( K i values for thrombin, plasmin, and trypsin being 1.0 ± 0.4, 0.6 ± 0.1, and 0.88 ± 0.07 mM, respectively). Host 1 and the 1 · 2 complex are shown to undergo the trypsin-catalyzed cleavage that results in the increased concentration of the free form of 2 and, therefore, induces the enzyme inhibition. Plasmin and thrombin are shown to cleave 1 at a significantly lower rate than trypsin. Thus, the complex of 1 with 2 represents the first example of a selective enzyme-sensitive supramolecular system capable of enzyme targeting through a “trojan horse”-type mechanism in which a bioactive compound acts on the same molecule that provides its release from a delivery system.