Ircinianin

A NiCl2/CrCl2-mediated domino process of the chiral aldehyde 6/4-81 iodotriene 6/4-82 was used for the synthesis of (-)-ircinianin (6/4-79) and (+)-wistarin (6/4-80), as described by Uenishi and colleagues (Scheme 6/4.19) [299]. After the coupling to give 6/4-83, an intramolecular Diels-Alder reaction occurred at room temperature, leading to the desired cyclic product 6/4-84 in 60% yield. 

Four unstable sulfate esters (373-376) of known furanosesterterpenes were obtained from Ircinia variabilis and from /. or os from the northern Adriatic Sea [328], The 22-O-sulfates of palinurin (377) and fasiculatin (378) were isolated from 7. variabilis and from /. fasiculata respectively. Both were toxic to brine shrimp [329]. Ircinianin sulfate (379) was isolated from /. (Psammocinia) wistarii from the Great Barrier Reef as a very unstable metabolite [330]. 

A unique tetracyclic furanosesterterpene, wistarin (195), has been discovered in Ircinia wistarii in addition to the previously known isomer ircinianin (196) 131). 196 decomposed readily, whereas 195 was relatively stable. As wistarin (195) was not detected among the decomposition products of 196 and 196 did not undergo cyclization to 195 on treatment with dilute acid, base or Lewis acids, it was proposed that 195 was a natural product and not an artifact. The biosynthesis of these sesterterpenes must involve a different folding of the acyclic 25-precursor. 

In addition to the classical structures, certain genera of dictyoceratid sponges produce atypical terpenes, most often sesterterpenes, the carbon skeletons of which do not conform to the usual schemes of terpene biosynthesis. This is the case for the next to last carbon skeleton shown in Figure 19.118, which occurs in only a few molecules. These include the wistarins, the first known examples of natural enantiomers whose antipodes were isolated from two different species of the genus Ircinia, and ircinianin, whose sulfated derivative was not discovered until 20 years... 

Coll, J.C., Kearns, P.S., Rideout, J.A., and Hooper, J. (1997) Ircinianin sulfate from the marine sponge Irdnia Psammocinia) ivistarii. J. Nat. Prod., 60,1178-1179. 

Hofheinz, W. and Schdnholzer, P. (1977) Ircinianin a sesterterpene from a sponge, genus Ircinia. Hdv. Chim. Acta, 60, 1367-1370. 

Takeda, K., Sato, M., and Yoshii, E. (1986) Synthesis of ( )-ircinianin, a marine sponge sesterterpene. Tetrahedron Lett., 27, 3903—3906. 

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