Structure and activity of largazole, a potent antiproliferative agent from the Floridian marine cyanobacterium Symploca sp.

The identification of new pharmacophores is of paramount biomedical importance and natural products have recently been regaining attention for this endeavor.1 This renaissance is closely tied to the successful exploitation of the marine environment which harbors unmatched biodiversity that is presumably concomitant with chemical diversity.2 In particular, marine cyanobacteria are prolific producers of bioactive secondary metabolites,3 many of which are modified peptides or peptide-polyketide hybrids with promising antitumor activities, such as dolastatin 10,4 curacin A,5 and apratoxin A.6 As a result of our ongoing investigations to identify new drug leads from cyanobacteria in Florida, we report here the structure determination and preliminary biological characterization of a marine cyanobacterial metabolite with novel chemical scaffold and nanomolar antiproliferative activity from a cyanobacterium of the genus Symploca. Symploca species have scarcely been investigated compared to the more prevalent Lyngbya spp., yet a Palauan Symploca sp. previously yielded the clinical trial compound dolastatin 10,4 prompting us to target this genus. A sample of Symploca sp. was collected from Key Largo, Florida Keys, and extracted with organic solvents. The resulting cytotoxic crude extract was subjected to bioassay-guided fractionation by solvent partition, silica gel chromatography, and reversed-phase HPLC to yield largazole (1) as a colorless, amorphous solid {[R]D +22 (c 0.1, MeOH)}.