The Synthesis Of Novel Cyclic Peptide Compounds

Cyclic peptides showed significant bioactivities and illustrated a good prospect of application. Cyclic peptides exist extensively, but the low contents and complicated separation have been big stumbling blocks to the development and application. Therefore, the exploration of cyclic peptides synthesis methods is very important.Characterized by high yield, high regioselectivity, independent of metal ion templates and high dilution, photo-induced single electron transfer cyclization reaction is used widely recently. In this study, four novel donor and accept electronic systems were synthesized, using amidosilane terminated polyproline peptide as electronic donor and phthalimido group as electronic acceptor. As a result, nitrogen heterocyclic proline peptide was obtained efficiently and selectively in photo-reaction with methanol as solvent. Single electron transfer happened between carbonyl chromophore from photo-induced-excited state phthalimide and nitrogen from o-amide to form ion pair free radical. In this process, intrachain SET (ISET) transmitted among electron donors and an equilibrium of resonant appeared. Because trimethylsilane was away due to the assistant function of methanol, resonant equilibrium moved to positive radicals of terminal nitrogen. Finally, terminalα-carbon radical intermediate of proline peptide precursor formed with absolute advantages, and radicals conjugated to generate nitrogen heterocyclic proline peptide. All of the new end products and intermediates were structurally identified by 1H-NMR,13C-NMR and Mass spectrometry.