Total synthesis of the thiopeptide promothiocin A

The thiopeptide (or thiostrepton) antibiotics are a class of sulfur-containing highly modified cyclic peptides with interesting biological activity. Described herein is the total synthesis of the thiopeptide antibiotic promothiocin A, which utilizes a modified Bohlmann-Rahtz pyridine synthesis to establish the oxazolyl-thiazole-pyridine heterocyclic centerpiece of the antibiotic. The oxazole building blocks were obtained by a dirhodium(II)-catalyzed chemoselective carbenoid N-H insertion reaction followed by cyclodehydration, and the thiazoles by the Hantzsch reaction. Two different strategies for macrocyclization were successfully employed, with the dehydroalanine side chain of the natural product being introduced in the last steps of the synthesis.