An efficient and cost-effective approach to kahalalide F N-terminal modifications using a nuisance algal bloom of Bryopsis pennata

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BackgroundKahalalide F (KF) and its isomer iso-kahalalide F (isoKF), both of which can be isolated from the mollusk Elysia rufescens and its diet alga Bryopsis pennata, are potent cytotoxic agents that have advanced through five clinical trials. Due to a short half-life, narrow spectrum of activity, and a modest response in patients, further efforts to modify the molecule are required to address its limitations. In addition, due to the high cost in producing KF analogues using solid phase peptide synthesis (SPPS), a degradation and reconstruction approach was employed using natural KF from a seasonal algal bloom to generate KF analogues. MethodsN-protected KF was carefully hydrolyzed at the amide linkage between l-Thr12 and d-Val13 using dilute HCl. The synthesis of the C-terminal fragment began with the formation of hexanoic succinimide ester, followed by a reaction with dipeptides. The final coupling reaction was performed between the semisynthesized Fmoc–KF hydrolysis product and the C-terminal fragment, followed by the deprotection of the Fmoc group. ResultsSix KF analogues with an addition of an amino acid residue on the N-terminal chain, d-Val14–isoKF (2), Val13–Val14–isoKF (3), d-Leu14–isoKF (4), d-Pro14–isoKF (5), d-Phe14–isoKF (6), and 3,4-2F-d-Phe14-isoKF (7) were prepared using semisynthesis at the exposed N-terminal chain. ConclusionsThe overall yield of the medication was 45%. This approach is economical, efficient and amendable to large-scale production while eliminated a nuisance algal bloom. General significanceB. pennata blooms are capable of producing KF in good yields. The semisynthesis from the natural product produced N-terminal modifications for the construction of inexpensive semisynthetic KF libraries.