Cyclosporin A: Regioselective Ring Opening and Fragmentation Reactions via Thioamides. A Route to Semisynthetic Cyclosporins
Cyclosporin A (1a) served as the starting material for the semisynthetic preparation of a variety of novel cyclosporins.Acetylcyclosporin A (2) was treated with Lawesson's reagent.From the reaction mixture, three novel acetylated thioamides were isolated: