Besides the already described Amphibine-A (1), from the bark of Ziziphus amphibua A. Cheval. four new peptide alkaloids, Amphibine-B, -C, -D, and -E, have been isolated, and their structures were elucidated (2-5). These alkaloids belong to the cyclopeptide alkaloids with a fourteen-membered ring system. They contain trans-3-hydroxyproline, an amino acid not yet found in plant peptides to our knowledge; in addition, they differ from most of the previously known peptide alkaloids by a side chain extended by one amino acid.