Studies On Isolation And Planar Structure Identification Of The New Marine Super-Carbon-Chain Compound AKZT-1

Microalgae are the most biodiverse marine plants in the marine ecosystem.Among them,dinoflagellates,a phylum of microalgae,are an important part of the lower marine plant community.Dinoflagellates are not only widely distributed,but also highly adaptable to the environment.From tropical to polar,from hyposaline to hypersaline environments,from planktonic to benthic,they are all present.Marine dinoflagellates have large and specialized genomes that produce structurally diverse secondary metabolites,such as Super-Carbon-Chain Compounds(SCCCs).SCCCs are a unique type of marine natural product.Their structural backbone is a long chain of highly oxidized,end-to-end carbon-carbon links.Typically,these compounds contain numerous hydroxyl groups and dozens of chiral centers along the long carbon-chain backbones,and their molecular weights exceed 1000 daltons.Polyol-Polyene Compounds(PPCs)and Ladder-Frame Polyethers(LFPs)are two classic families.Among them,PPCs are mainly derived from marine dinoflagellates such as Amphidinium,Karlodinium,Ostreopsis and Prorocentrum.In this paper,we isolated,purified and structurally characterized the SCCCs produced by the marine dinoflagellates Amphidinium sp.collected from the South China Sea.A novel super-carbon-chain compound,named AKZT-1,was isolated by macroporous adsorption resin column chromatography,positive/reverse phase silica gel column chromatography and high performance liquid chromatography.The planar structure of AKZT-1 was elucidated by high/low resolution electrospray ionization mass spectrometry,nuclear magnetic resonance spectroscopy,deuterated solvent isotope shift experiment,ketone carbonyl oxime reaction and periodate degradation of the 1,2-diol groups.Meanwhile,Mosher’s MTPA ester method was applied to determine the absolute configuration of a sodium periodate degradation fragment,AKZT-1-NaIO4-C.AKZT-1 is a novel super-carbon-chain compound containing 32 chiral carbons and 23 hydroxyl groups.Among the hydroxyl substituents are 1,2-diol,1,3-diol,1,6-diol,1,2,3-triol and 1,3,5,7,9-pentanol groups.In addition,the molecule contains one tetrahydropyran ring and two spiro moieties,namely one each of 6,6spiroketal motif and 5,6-spiroketal motif.