As the first step in establishing our proposed method, the
advanced Marfey's method, which is planned for the
simultaneous determination of the absolute configuration
of amino acids in a peptide, we applied Marfey's method
to commercially available amino acids, and the separation
behavior was examined in detail. Although good
resolution of the diastereomeric pair of an individual amino acid
was obtained for all amino acids tested and the
applicability of the method was confirmed, the (1-fluoro-2,4-dinitrophenyl)-5-l-alaninamide (FDAA) derivative of
the
l-amino acid was not always eluted prior to its
corresponding d-amino acid derivative. Because this
proposed
method relies on the elution order of a derivatized amino
acid with FDAA to determine its absolute configuration,
its separation mechanism was carefully investigated using
UV and NMR spectral techniques. The results suggested
that the resulting conformations of the l- and
d-amino acid
derivatives are stable and that the resolution between the
l- and d-amino acid derivatives is due to the
difference in
their hydrophobicity, which is derived from the cis- or
trans-type arrangement of two more hydrophobic substituents at both α-carbons of an amino acid and
l-alanine
amide, so that the FDAA derivative of the cis
(Z)-type
arrangement interacts more strongly with ODS silica gel
and has a longer retention time than that of the trans
(E)-type arrangement. Therefore, the l-amino acid
derivative
is usually eluted from the column before its corresponding
d-amino acid derivative in Marfey's method.
According
to this separation mechanism, the elution order of a
desired amino acid can be elucidated from the average
retention time of the l- and d-amino acid
derivatives, and
the dl-serine and -asparagine derivatives are critical
for
Marfey's method.
LC/MS/MS under ion trap conditions was used to analyze microcystins produced by cyanobacteria. Tandem mass spectrometry using MS 2 was quite effective since ions arising from cleavage at a peptide bond provide useful sequence information. The fragmentation was confirmed by a shifting technique using structurally-related microcystins and the resulting fragmentation pattern was different from those determined by triple stage MS/MS and four sector MS/MS. Analysis of a mixture of microcystins in a bloom sample was successfully performed and two new microcystins were identified by LC/MS/MS under ion trap conditions. Thus, LC/MS/MS under ion trap conditions is effective for the structural characterization of microcystins.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
The relationship between Microcystis composition and the production of microcystins and nontoxic peptides in bloom cells, which was regularly collected in Lake Suwa, Japan, in the summer season from 1991 to 1994, was investigated. In order to determine the structures of the nontoxic peptides, we collected large amounts of bloom materials from the same lake on July 23, 1991, and isolated three nontoxic peptides. They were named as aeruginopeptins 917S-A, -B, and -C, and their structures were mainly determined by a mass spectrometry/mass spectrometry (MS/MS) technique as 19-membered cyclic depsipeptides possessing the Ahp (3-amino-6-hydroxy-2-piperidone) moiety. An analysis of the microcystins and aeruginopeptins in the collected blood cells and their Microcystis composition suggested that the M. aeruginosa large cell size produces both microcystins and aeruginopeptins, and the production of both compounds is genetically closely related.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.