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Alkaloidal constitutents of the marine sponge Cliona celata

University of British Columbia

Methanol extracts of the marine burrowing sponge Cliona celata Grant have yielded a complex mixture of 'imperfect' alkaloids. Fractionation of this mixture by a rapid acid partitioning procedure has facilitated the isolation of the major metabolite clionamide (53). The structure of this modified amino acid was determined by its conversion to tetracetylclionamide (46). The assigned structure of 46, previously isolated from acetylated extracts of C celata, was confirmed by the synthesis of its ultimate hydrogenation product 49. Clarification of the absolute stereochemistry of clionamide has been accomplished by hydrolysis and subsequent hydrogenolysis of 46 to give (S)-N-acetyltryptophanamide (52) which was characterized by comparison with an authentic sample. [diagrams not included] The remaining 18-22 alkaloids elaborated by Cliona celata bear close resemblance to a large family of peptide alkaloids found in higher plants. Derivatization of the crude sponge extract by acetylation and subjection of the resulting residue to repetitive silica and reversed-phase chromatography have effected the isolation of four novel linear peptide alkaloids. Structures of the 6-bromotryptophan-containing alkaloids, hexacetylcelenamide A (58), B (52) and pentacetylcelenamide C (59), and the bisdehydrotripeptide nonacetylcelenamide D (60), were established by interpretation of spectral data and chemical degradation by ozonolysis and acid-catalyzed hydrolysis. Demonstration of the presence of the unique amino acid αβ-didehydro-3,4,5-trihydroxyphenylalanine as a constituent of each of these compounds was aided by correlation with synthetic analogues. A small scale isolation employing acetic anhydride-dg has indicated that celenamides A (70), B (71), C (72) and D (74) are the naturally occurring sponge metabolites. [diagrams not included] A chemical comparison of specimens of Clionacelata from Massachusetts, Southern California and British Columbia is reported.

Text

2010-03-31

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http://hdl.handle.net/2429/23192

Chemistry

University of British Columbia

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