Preparation and photochemistry of o-aminocinnamates

A series of 2-aminocinnamic acid esters and amides was prepared and the photochemistry of these compounds was studied. The compounds undergo trans–cis photoisomerization followed by cyclization with expulsion of alcohol or amine. The o-amino compounds generally have longer wavelength absorption than the corresponding o-hydroxycinnamates, and alkyl substitution on the amino group generally shifts the absorption to longer wavelength. On the other hand, substitution on the amino group reduces the cyclization rate constants (kc), as compared to the unsubstituted parent. A solvent effect on lactamization was found for these compounds, as increasing Tris buffer content accelerates the cyclization process. These compounds are suitable for use as protecting groups for alcohols and amines and they also serve as models for new photo-labile serine protease inhibitors. A biotinylated derivative has been prepared which extends their use as photo-cleavable linkers for proteins and avidin via the biotin–avidin complex. This permits binding and photorelease of thrombin and other serine protease enzymes to avidin affinity columns.