Studies On Structural Diversity And Biological Activities Of Marine Cyanotoxins Aplysiatoxins

Cyanobacteria,also known as blue-green algae,is the oldest,most widely distributed and most diverse oxygen-containing photoautotrophic microbial community on the earth.The particularity of marine environment results in the diversity of chemical structures and biological activities of secondary metabolites of marine cyanobacteria.Cyanobacteria toxin is an important component of its secondary metabolites,and studies have found that marine cyanobacteria can produce natural toxins,including microcystins、saxitoxins、kalkitoxin、antillatoxin and amylotoxins(ATXs).Among them,marine cyanobacterial toxins have attracted extensive attention in the research and development of new marine drugs due to their novel structure,antitumor activity,neurotoxicity and cytotoxicity.Based on the previous research on cyanobacterium Lyngbya sp,and in order to obtain more cyanobacterial toxins with novel structure and biological activity,this work was focused on study the chemical structural diversity and biological activity of the derivatives of apsiatoxins from cyanobacterium Lyngbya sp.collected from Hainan.Study on the chemical constituents of aplysiatoxins from the cyanobacterium Lyngbya sp.Cyanobacteria samples were extracted by ultrasonic with organic reagents.Four kinds of crude components with different polarity were obtained by liquid-liquid extraction,including petroleum ether layer,dichloromethane layer,ethyl acetate layer and methanol layer.The crude components with better activity and more compounds were selected by Artemia Toxicity Test and Thin Layer Chromatography,Then the single compound was purified by Vacuum Liquid Chromatography,Octadecylsilyl Silica and High Performance Liquid Chromatography.Finally,two novel structural aplysiatoxin derivatives were obtained from Fr.D11 and Fr.D 17,neodebromoaplysiataoxin G(1)with bridged ring structure firstly and neodebromoaplysiataoxin H(2)with 5/6 dioxin spiro ring systems.Meanwhile,debromoaplysiatoxin(3),anhydrodebromoaplysiatoxin(4),3methoxydebromoaplysiatoxin(5),4-hydroperoxyoscillatoxin B(6),oscillatoxin F(7),neo-debromoaplysiatoxin A(8),neo-debromoaplysiatoxin C(9)and 30methyloscillatoxin D(10)also were got from the same collection.They were elucidated by 1D-NMR,2D-NMR,HRESIMS,optical rotation comparison,GIAO NMR chemical shift calculation combined with DP4+statistical probability analysis,biosynthesis pathway and auxiliary reference comparison.The bioactivities of aplysiatoxin derivatives were tested.The influence of Kv1.5 ion channel on two new compounds was studied,and the results showed that compounds 1 and 2 showed inhibitory activity of Kvl.5 ion channel(IC50=1.79 ± 0.22μM and 1.46 ± 0.14 μM,respectively).The brine shrimp toxicity of the aplysiatoxin derivatives representing differential structural classifications indicated that the traditional ABC tricyclic structural aplysiatoxin derivatives were all lethal to Artemia at 10 μM,while the monospiro structural and the new skeleton structural aplysiatoxin derivatives had no obvious effect at even 30 μM.Meanwhile,the experimental results also showed that the debromoaplysiatoxin was the most toxic compound(IC50 value=0.34 ± 0.036 μM).The antitumor activity of these traditional aplysiatoxins with obvious brine shrimp toxicity was further tested,and the results showed that they all showed inhibition on the growth of tumor cells and debromoaplysiatoxin had most significant effect.As the mechanism of action of aplysiatoxins derivatives with different bioactivities has not been clearly studied,therefore,it is speculated that different structural types of aplysiatoxin derivatives have different biological activity regulation mechanisms,and the specific mechanism of action needs to be further studied.