A study was undertaken to prepare inhibitors of the lymphocyte protein-tyrosine kinase p56lCk. Using the known p561ck inhibitor 3, 4-dihydroxy-a-cyanocinnamamide (4) as a lead compound, bicyclic analogues were designed as conformationally constrained mimetics in which the phenyl ring and vinyl side chain of the cinnamamide are locked into a coplanar orientation. Such planarity was rationalized to be an important determinant for binding ...