14C-labeled and large-scale synthesis of the angiotensin-(1-7)-receptor agonist AVE 0991 by cross-coupling reactions

The synthesis of C-14-labeled AVE 0991 (C-14-1a) and large-scale synthesis of AVE 0991 (1a) are described. In the key step of the synthesis, the C-C coupling reaction of the imidazole (2) and thiophene (3) building blocks was studied under Suzuki and Stille reaction conditions, respectively. Suzuki reaction gave only moderate yields, whereas the best results were obtained under Stille reaction conditions with up to 64% yield.