| dc.description |
Microcystins are cyclic heptapeptides from cyanobacteria which are responsible for poisonings
of livestock and humans. Cyanobacteria also produce a range of peptides and other
compounds that can result in complex chromatograms when samples are analysed by LC–
MS. Thiol derivatization of the a,b-unsaturated amide present in most microcystins was
recently shown to simplify analysis of LC–MS chromatograms of a Microcystis culture,
making it easier to identify peaks corresponding to microcystins in complex mixtures. This
method was applied to analysis of extracts taken from a natural cyanobacteria bloom in
Mwanza Gulf, Lake Victoria, Tanzania, in 2010, revealing the presence of numerous putative
microcystin analogues in the sample. Results were verified using LC–MS2, LC–MS/MS
with precursor-ion scanning, and LC–HRMS, leading to identification of 8 major and 17
minor microcystins in the sample, including analogues of microcystin-RY, -RL and -RA.
Microcystin-YR (2), -RR (3), and -RY (9) were isolated from bloom material from Lake
Victoria, and the structure of 9 was confirmed by NMR spectroscopic analysis and NMR
spectral comparison with 2 and 3. Confirmation of the structure of MC-RY (9) facilitated
detailed analysis of its MS2 spectrum, thereby supporting the structures of related analogues
tentatively established on the basis of MS analyses |
|