Convergent and short-step syntheses of dl-Cypridina luciferin and its analogues based on Pd-mediated cross couplings

dl-Cypridina luciferin and its analogues were synthesized from 2-aminopyrazine by an eight-step method that included two regio-selective Pd-mediated cross couplings, and their chemi- and bioluminescent activities were compared. Analogues having a 3-benzofuranyl or a 3-benzothienyl group in the place of a 3-indolyl group showed luciferase affinities similar to Cypridina luciferase but with a lower luminescent efficiency, suggesting that the NH group is unimportant for molecular recognition whereas the indolyl group is crucial for efficient luminescence.