Absolute Configuration and Body Part Distribution of the Alkaloid 6-epi-Monanchorin from the Marine Polychaete Chaetopterus variopedatus

Abstract

As a result of the first study on secondary metabolites from the cosmopolitan bioluminescent marine tube polychaete Chaetopterus variopedatus, a new bicyclic guanidine alkaloid, 6-epi-monanchorin (1), along with the previously known monanchorin (2) were isolated. The structure of 1 was elucidated by spectroscopic and chemical methods, including a cleavage of the C 1-O 7 bond to obtain a secondary alcohol (3), which was used to determine the absolute configurations by Mosher's method. It was found that 1 and 2 were mainly accumulated in a secreted mucus special organ of the worm (food net), where green and blue-green microalgae were detected. A biosynthetic pathway to 6-epi-monanchorin and monanchorin from dietary polyenic fatty acid precursors was proposed.

Marine Bacterium Vibrio sp. CB1-14 Produces Guanidine Alkaloid 6-epi-Monanchorin, Previously Isolated from Marine Polychaete and Sponges

“…The 6- epi -monanchorin ( 2 , Figure 1) was isolated from the EtOAc extracts of both cells and lyophilized culture broth using reverse-phase HPLC. The structure was exactly identified on the basis of 1 H NMR and HRESIMS data by comparison with authentic sample [4]. As a result, it was found that the CB1-14 strain biosynthesizes 6- epi -monanchorin ( 2 ).…”

“…Most of the marine guanidine alkaloids found in marine sponges are polycyclic, and two bicyclic representatives of this group, namely monanchorin ( 1 ) and 6- epi -monanchorin ( 2 ), are known. These compounds were isolated from representatives of two phylogenetically distant taxa, namely marine sponges Monanchora ungiculata and Halichondria panicea (phylum Porifera) [2,3], and marine polychaete Chaetopterus variopedatus (phylum Annelida) [4]. Previously it has been reported that the compound 1 shows weak cytotoxic activity against IC2 murine mast cells [2], while compounds 1 and 2 (Figure 1) are able to inhibit the migration and colony formation of cisplatin-resistant cancer NCCIT-R cells [4].…”

“…Recently, we compared levels of these alkaloid content in different body parts of the polychaete C. variopedatus [5,6]. Both alkaloids were predominant into the food net parts of the animals and the content of 6-epi-monanchorin ( 2 ) was very high (5.0% of dry weight) [4]. These findings prompted us to undertake the present study.…”

Application of Oxidative and Reductive Transformations in the Structure Determination of Marine Natural Products

“…Subsequent application of Mosher’s procedure resulted in the esters 180a , b , which allowed determination of the absolute configurations of all of the stereogenic centers of 178 (Scheme ). The same configurations with the exception of the C-6 stereogenic center had earlier been established in the related monanchorin and confirmed by stereoselective syntheses. , …”