Biosynthetic signatures

We consider that all of the dolastatins will prove to be of cyanobacterial or other dietary origin. There are some important biosynthetic signatures, for exanqile, which suggest that dolastatin 15 (2) (Figure 1) is most probably derived from L majuscula. These signatures include the presence of the N,N-dimethylvaline residue, a valine-N-methylvaline-proline sequence also found in the microcolins (27, 28) (Figure 7) and the presence of a pyrrolidone ring presumably derived from condensation of phenylalanine and acetate. A... 

Dolastatin 18 (32) (Figure 7) also contains significant biosynthetic signatures that imply that it is of cyanobacterial origin. These include a 2,2-dimethyl-1,3-dicarbonyl moiety found in lyngbyastatin 1 (4a) and majusculamide C (6) and a dolaphenine residue found in symplostatin 1 (10) and barbamide (11). 

Farquhar J, Wing BA (2003) Multiple sulfur isotope analysis applications in geochemistry and cosmochemistry. Earth Planet Sci. Lett 213 1-13 Farquhar J, Johnston DT, Wing BA, Habicht KS, Canfield DE, Airieau S, Thiemens MH (2003) Multiple sulphur isotope interpretations for biosynthetic pathways implications for biological signatures in the sulphur isotope record. Geobiology 1 27-36... 

With the obtained data, the desired AS C values are calculated and doping rule violations either verified or falsified. The formerly valid generic threshold of 3%o represented a means to identify suspicious differences in carbon isotope signatures of biosynthetic precursors and corresponding metabolites however, the customized thresholds for defined pairs of precursors/metabolites substantially enhance the level of confidence as well as the discrimination power of IRMS. 

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