Lissoclinum vareau

Lissoclinum perforatum (ascidian) Lissoclinum vareau (ascidian) ... 

Varacin (13), the methyl ether of Lissoclinotoxin A, has been reported from Lissoclinum vareau [24], and from a Far Eastern Polycitor sp. (where it was also isolated as its N-acetyl derivative after acetylation of the crude extract to facilitate separation) [22]. A number of syntheses of varacin have been reported [20,25,26,27]. Desmethylvaracin (14) was... 

Davidson, B.S., Molinski, T.F., Barrows, L.R., and Ireland, C.M. (1991) Varacin a novel benzo-pentathiepin from Lissoclinum vareau that is cytotoxic toward a human colon tumor. /. Am. Chem. Soc., 113, 4709-4710. 

Varacin (114), a cytotoxic compound closely related to lissoclinotoxin A (106), was isolated from a Fijian sample of L vareau and a benzopentathiepin structure was proposed on the basis of spectral data [131]. Two total syntheses of varacin (114) have been carried out [132,133] and later, further syntheses were described [134-135]. N,N-dimethyl-5-(methylthio)varacin (115) and the corresponding trithiane (116) were obtained from L. japonicum from Palau and 3,4-desmethylvaracin (117) was isolated from a Eudistoma sp. from Pohnpei [136], An inseparable mixture of 5-(methylthio)varacin (118) and the corresponding trithiane (119) was obtained from a Pohnpeian Lissoclinum sp. [136]. Three additional antimicrobial polysulfides of the varacin family (120-122) were isolated from Polycitor sp., collected by dredging in the Sea of Japan [137]. 

The eudistomins constitute a broad family of P-carboline alkaloids which are found mainly in the genus Eudistoma (mostly from E. olivaceum) but also in a few species of Lissoclinum (eudistomine U, isolated from L. vareau see above) and in Ritterella (see below), which all belong to the order Aplousobranchia. This series of alkaloids was discovered in 1978 during the same expedition of the American vessel Alpha Helix that led to the discovery of the didemnins. The 30 eudistomins currently known are almost all brominated and may be divided into four structural types, which are presented in Figure 28.19. 

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