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Tasiamide B Structure Elucidation

Tasiamide B

The Initial Challenge

In 2003, Philip Williams and co-workers1 isolated a new cytotoxic peptide, Tasiamide B, from the marine cyanobacterium Symploca sp, which contained the unusual amino acid-derived residue 4-amino-3-hydroxy-5-phenylpentanoic acid (AHPPA). The structure of the peptide was determined through a combination of 2D NMR experiments and HPLC analysis of degradation products. The initial experimental data was then submitted to the Structure Elucidator Challenge to determine if the software could propose the same structure.

The Evidence

The CASE (Computer Assisted Structure Elucidation) Investigation



The Molecular Connectivity Diagram produced by Structure Elucidator

Conclusions

The addition of two 1-AR fragments helped to reduce the number of ambiguous connectivities and ultimately reduce the structures generation time. The ambiguity arises from the coincidental chemical shifts of hydrogen atoms in the aromatic region.

The problem demonstrates the benefits of introducing User Fragments which are easily revealed in the experimental data during the preliminary evaluation.

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dF—the average deviation between the experimentally observed carbon chemical shifts and the carbon chemical shifts predicted using fast (increment based) prediction methods
dH—the average deviation between the experimentally observed proton chemical shifts and the predicted proton chemical shifts using accurate (HOSE code based) prediction methods
dΣ = dA + 20-dH—generalized match factor that takes into account deviations calculated by the accurate prediction methods both for 13C and 1H NMR spectra

1P.G. Williams, W.Y. Yoshida, R.E. Moore, V.J. Paul J. Nat. Prod., 66:1006–1009, 2003.

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