Total synthesis and modification of proline-rich cyclopeptides Phakellistatins 17 and 18 isolated from marine sponge

The Phakellistatins 17 and 18, two naturally occurring cyclic proline-rich peptides from marine sponge, were synthesized by utilizing a two-step solid-phase/solution synthesis strategy for the first time. Phakellistatin 18 exhibited a weak inhibitory activity against human lung carcinoma cell (A549) and human hepatoma (BEL-7042). In order to improve the activity of Phakellistatin 18, two of its analogues which contain sulfonyl fluoride group (P18-1) and arginine substituted derivative (P18-2) were also synthesized respectively. The spectral data of Phakellistatins 17 and 18 were identical to that reported for the natural products. Analogues P18-1 and P18-2 were identified by means of HR-QTOF-MS, H-1 NMR and C-13 NMR. More importantly, analogue P18-1 exhibited significantly enhanced cytotoxicity against BEL-7042 cancer cells compared with Phakellistatin 18, suggesting that the sulfonyl fluoride group in the parent peptide may contribute to the improvement of antitumor activity. This strategy provides a reference method for improving the activity of natural peptides. reserved. (C) 2018 Published by Elsevier Ltd.