Guanidine marine invertebrates

Owing to their intrinsic basicity, marine invertebrate guanidine alkaloids have a rather polar behavior and their isolation from complex mixtures may be difficult. Isolation procedures frequently include chromatography on lipophilic Sephadex LH20, on reversed phase silica gel (such as Cig bonded, aminopropyl bonded, or cyanopropyl bonded), or even on ion-exchange resins. HPLC purification using acidic (TFA) or buffered eluents have frequently been employed. 

Several guanidine-modified tetrapeptides have been isolated from marine invertebrates, in particular marine sponges. Nazumamide A (39) has been isolated from the sponge Theondla sp. and identified by analysis of spectroscopic data [60] as well as by X-ray diffraction analysis of a nazumamide A-human thrombin complex [61[. Nazumamide A has been synthesized by conventional peptide synthesis [62[. A series of nazumamide derivatives have been prepared via combinatorial synthesis [63[. 

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