Axinellin C, a proline-rich cyclic octapeptide isolated from the Fijian marine sponge Stylotella aurantium

The structure of a new cyclic octapeptide, axinellin C, (cyclo[Thr1-Val2-Pro3-Trp4-Pro5-Phe6-Pro7-Leu8]), with all-trans peptide bond geometry, was elucidated by a combination of 2D NMR methods and tandem mass spectrometry. The solution state conformation was determined by ROE restrained molecular dynamics calculations. The structural features were found to be similar to those of the crystal structure of the cyclic decapeptide, phakellistatin 8, despite differing peptide sequences.