Caledonine

Didemnum rodriguesi from New Caledonia contained the unusual peptidyl alkaloid caledonin (76), that formed a complex with Zn2+ and Cu+ ions between thiol and primary amine groups [100], The minalemines D-F (77-79) are peptide guanidine derivatives isolated from a Caribbean collection of D. rodriguesi and contain a sulfamic acid group [101]. The stereochemistry of cyclodidemniserinol trisulfate (80) from a Palauan specimen of Didemnum guttatum was partially determined [102]. 

Caledonin, a modified peptide isolated from the marine tunicate Didemnum ro-driguesi. The amino group of the central Phe residue is linked with (S)-3-amino-5-mercaptopentanoic acid, whereas the carboxy function is connected with a six-membered cycloguanidine ring system bearing a n-octyl side chain. Caledonin is a natural peptide bolaphile capable of com-plexing Zn + and Cu+ ions, and may also be involved in ion transport through membranes [M. J. Vazquez et al.. Tetrahedron Lett. 1995, 36, 8853]. 

A reinvestigation of P. oleides, and P. lyciiflora, prompted by the earlier observation of the effects of 167 and 172 on the neuroendocrine system, led to the isolation of additional new pyrrolidinoindoline alkaloids, the dimeric demethyl-mc50-chimonanthine derivative, 173, from P. lyciiflora, and three new oligomers from P. oleoides, quadrigemine I (174), oleoidine (175), and caledonine (176). The structure elucidation of the dimeric 173 was based on spectral data and via chemical correlation with mc o-chimonanthine (152). The structures and tentative stereochemistries of quadrigemine I (174), oleoidine (175), and caledonine (176) were provisionally assigned by a combination of two-dimensional (2-D) NMR analysis, CD spectra comparisons, and chemical correlations 112). 

Caledonin, isolated from Didemnum rodriguesi collected in Noumea, New Galedonia, is a powerful chelator of zinc and copper (I). This modified peptide contains a phenylalanine, a new P-amino add bearing a thiol group, 3(S)-amino-5-mercaptopentanoic acid, and a cycloguanidine... 

V quez et al, 1995). Caledonin is considered to be a natural bolaamphiphile (bolaphile) whose function may be the transport of ions through membranes. 

Another species of Didemnidae from the Great Barrier Reef Diplosoma virens, contains prenylated peptides with a thiazole nucleus, which is particularly common in cydic peptides and depsipeptides. Virenamides A-E are only weakly cytotoxic in vitro (Carroll et al, 1996a Feng and Bowden, 1997) and, like caledonin, these peptides may act as natural antifouling agents (Davis and Bremner, 1999). 

Vasquez, M.J., Quinoa, E., Riguera, R., Ocampo, A., Iglesias, T, and Debitus, C. (1995) Caledonin, a natural peptide bolaphile with Zn and Cu complexing properties from the tunicate Didemnum rodriguesl Tetrahedron Lett., 36,8853-8856. 

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