Ircinin

A flexible entry into 2,4-disubstituted furan derivatives through condensation of the sulfur ylide derived from 20 with aldehydes, Pd-catalyzed opening of the vinyl oxirane thus formed, and a final oxidative cyclization of the furan ring was reported. Its utility was exemplified by the first total synthesis of the marine natural product ircinin-4 (21) <99SL29>. 

Thereafter, several compounds closely related to ircinins and variabilin have been isolated [5,6]. Fusetani and co-workers [34] reported the isolation of two compounds, dehydroderivative of ircinin (8) and an isomer of variabilin (9) from the Japanese sponge Cacospongia scalaris. Both compounds inhibited the cell division of fertilised starfish eggs at a concentration of 1.0 pg/ml. This assay is a variation on the test with sea urchin embryos, which can detect DNA and RNA synthesis inhibitors, microtubule assembly and protein synthesis inhibitors, the common leads... 

Three linear sesterterpenoids have been obtained from species of marine sponge. These are ircinin-1 (3) and ircinin-2 (4) from Ircinia oros and fasciculatin (5) from Ircinia fasciculata The C-21 compounds nitenin (6) and dihydronitenin... 

Ircinin-4 is part of a family of furanoterpenes, produced by the Mediterranean sponges Ircinia oros and /. fasciculata, that exhibit high activity in the brine shrimp assay and turn out to be selective inhibitors of phospholipase A2. The first total synthesis was recently described by Furstner et al. and was based on the Pd-catalyzed opening of vinyloxirane (Scheme 21) employing the Tsuji-Trost conditions. Treatment of the epoxide 108, obtained from the reaction of 3-furyl-acetaldehyde with a sulfur ylide, with catalytic amounts of... 

CiMiNO, G., S. DE Stefano, L. Minale, and E. Fattorusso Ircinin-1 and -2, Linear Sesterterpenes from the Marine Sponge Ircinia oros. Tetrahedron 28, 333 (1972). 

Two more linear C21 compounds, ircinin-3 and -4, have been isolated in small yield from Ircinia oros (49). They were shown to have structures (88) and (89) which are closely related to the isomeric sesterterpenes... 

Four related furanoid sesterterpenes have been isolated from sponges of the genus Ircinia. Ircinin-1 (94) and ircinin-2 (95) from Ircinia oros were found to be isomeric difurano-sesterterpenes containing an unusual conjugated tetronic acid moiety 60). Fasciculatin (96) from Ircinia fasci-culata 37) and variabilin (97) from /. variabilis 84) were shown to be closely related monofurano-sesterterpenes. 

Ircinin-1 (94) and -2 (95) proved to be resistant to all attempts at separation and work on their constitution was carried out on the mixture of the two isomers 60). The presence of two furan rings linked to each other by a methylene group was indicated by n.m.r. spectroscopy (five broad 1 H... 

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