Axinellins A and B: New Proline‐Containing Antiproliferative Cyclopeptides from the Vanuatu Sponge Axinella carteri

Two new bioactive cyclopeptides, named axinellins A (1) and B (2) have been isolated from the marine sponge Axinella carteri. Their structure elucidation was based on two-dimensional (2D) NMR (500 MHz) as well as HRFABMS and ESMS/MS data. All amino acid residues derived from axinellins A and B were found to possess L configuration at Cα by HPLC analysis of their FDAA derivatives (Marfey's method). The amino acid sequence of 1 and 2 was established on the basis of tandem mass spectrometry data (ESMS/MS) and on 1H-1H through-space connectivities observed in NOESY and ROESY spectra. Axinellins A (1) and B (2) exhibited moderate in vitro antitumor activity against human broncopulmonary non-small-cell-lung-carcinoma lines (NSCLC-N6) with IC50 values of 3.0 and 7.3 μg/ml, respectively.