Synthesis of Heterocycle-Bridged Peptidic Macrocycles through 1,3-Diyne Transformations

Macrocyclic tetrapeptide analogues containing a 1,3-diyne moiety were synthesized by a Glaser-Hay-type macrocyclization. The obtained 1,3-diyne was evaluated as a handle to introduce heterocycles into the macrocyclic structure. It was shown that the macrocyclic 1,3-diynes were successfully transformed into various heterocycles by nucleophilic attack of (bis)nucleophiles to the diyne moiety. Treatment with NaHS or H2O as nucleophiles gave rise to 2,5-bridged thiophenes or furans, whereas the use of hydrazines and hydroxylamine gave rise to the corresponding pyrazole- and isoxazole-containing macrocycles. In addition, a thermoreversible Diels-Alder cycloaddition of a cyclopeptidic bridged furan was demonstrated.