Investigation of cyclic depsipeptides by fast atom bombardment-mass spectrometry.

In recent years, the synthetic analogue elcatonin has been used successfully in the treatment of osteoporosis. During an investigation of synthetic strategies for the production of elcatonin, a number of peptide products were generated. These could be purified by liquid chromatography and were shown to have identical amino acid compositions. Investigation by fast atom bombardment-mass spectrometry revealed three of the peptides to have a common pseudomolecular ion but notably dissimilar fragmentation patterns. Further studies involving chemical modification, mass spectrometry and chromatographic separation showed these products to be novel depsipeptides, cyclized with an ester bond between either the serine or the threonine residue and the side chain of aminosuberic acid.