Efficient synthesis of bisulfide-bridged bicyclopeptides by intramolecular photoinduced electron transfer cycloreaction

A facile methodology for the synthesis of bicyclopeptides containing isoindolone was developed by an intramolecularly photo-induced electron transfer cyclo-reaction (IPETC) with high yield and stereoselectivity. Nine bisulfide-bridged bisisodindolone-cyclopeptides were successfully prepared based on the construction of an intramolecular bis-(donor-acceptor) electron system using l-cystine as the linker. The stereostructures of the bicyclopeptides were determined by ECD and C-13-NMR spectra combined with quantum chemistry calculations. The research provided a possible solution for the preparation of multi-cyclopeptides with complex and rigid cyclic structures by introducing cysteine moieties into linear peptides.