Lyngbyabellins K–N from Two Palmyra Atoll Collections of the Marine Cyanobacterium <i>Moorea bouillonii</i>

Abstract

Five lipopeptides of the lyngbyabellin structure class, four cyclic (<b>1-3</b>, and <b>5</b>) and one linear (<b>4</b>), were isolated from the extracts of two collections of filamentous marine cyanobacteria obtained from Palmyra Atoll in the Central Pacific Ocean. Their planar structures and absolute configurations were elucidated by combined spectroscopic and chromatographic analyses as well as chemical synthesis of fragments. In addition to structural features typical of the lyngbyabellins, such as two thiazole rings and a chlorinated 2-methyloctanoate residue, these new compounds possess several unique aspects. Of note, metabolites <b>2</b> and <b>3</b> possessed rare mono-chlorination on the 3-acyloxy-2-methyloctanoate residue while lyngbyabellin N (<b>5</b>) had an unusual <i>N,N</i>-dimethylvaline terminus. Lyngbyabellin N also possessed a leucine statine residue, and showed strong cytotoxic activity against HCT116 colon cancer cell line (IC₅₀ = 40.9 ± 3.3 nM).