Two cyclopeptides, the cycloheptapeptide cycloreticulin C, cyclo(Pro1 -Gly2 -Gln3 -Pro4 -Pro5 -Tyr6 -Val7 ) (1), and the cyclohexapeptide glabrin A, cyclo(Pro1 -Gly2 -Leu3 -Val4 -Ile5 -Tyr6 ) (2), have been isolated from the methanol extract of the seeds of Annona reticulata. Their structures were elucidated on the basis of the MS/MS fragmentation using a Q-TOF mass spectrometer equipped with an ESI source, chemical degradation and extensive 2D-NMR. The solution conformation of cycloreticulin C involves two b-turns, one of type II with trans-Pro1 and Gly2 at the corners, another of type VIa with trans-Pro4 and cis-Pro5 at the corners, and followed by a b-bulge at the Tyr6 -Val7 level. The solid state and solution conformations of glabrin A have been analyzed by X-ray and 2D-NMR studies, respectively, and are characterized by the presence of two b-turns, the first of type VIa and the second intermediary between types I and III at the solid state and a g-turn in solution.