Ritterella tokioka, alkaloids from

Fukuzawa, S., Matsunaga, S., and Fusetani, N., Ritterazine A, a highly cytotoxic dimeric steroidal alkaloid, from the tunicate Ritterella tokioka, J. Org. Chem., 59, 6164, 1994. 

Ritterella tokioka Kott, a tunicate of the family Polyclinidae, collected from the Izu Peninsula 100 km southwest of Tokyo, on extraction and partitioning between a number of solvent systems followed by repeated chromatography, afforded another series of bis-steroidal pyrazine alkaloids, ritterazines A-M (26-38). Structures of these alkaloids were found to be related to the cephalostatins isolated from the hemichordate Cephalo-discus gilchristii. 

Pettit et al., have proposed a biogenetic pathway for the dimeric pyrazine-containing steroidal alkaloids, the cephalostatins isolated from the marine worm Cephalodiscus gilchristi and the tunicate Ritterella tokioka. These alkaloids contain at least 13 fused rings, which constitutes the largest such system known in marine animals. 

The bis-steroidal alkaloids cephalostatins 1-15 (11-25) (24-30) and rit-terazines A-M (26-38) (31-33) isolated from the marine worm Cephalodis-cus gilchristi and the tunicate Ritterella tokioka, respectively, also exhibit powerful cell growth inhibitory activity against a number of cell lines. 

Ritterazines. Group of more than 25 disteroidal alkaloids with a central pyiazine structure from the "tunicate Ritterella tokioka with potent cytotoxic and antitumor activities. 

The ritterazines are highly ox ygenated dimeric steroidal alkaloids isolated by Fusetani and co-workers from 1994 to 1997 from the colonial tunicate Ritterella tokioka (family Policlinidae) [107, 108],... 

Alkaloid from the tunicate Ritterella tokioka. Shows potent cytotoxicity against P388 murine leukaemia cells. Glassy solid, [aj +112.0 (c, 0.1 in MeOH). 

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