Seven More Microcystins from Homer Lake Cells: Application of the General Method for Structure Assignment of Peptides Containing .alpha.,.beta.-Dehydroamino Acid Unit(s)

Abstract

Larger scale isolation of microcystins, cyclic heptapeptide hepatotoxins, from a water bloom of Microcystis spp. collected from Homer Lake (Illinois) gave the previously reported 1-5, additional quantities of [L-MeSer7]microcystin-LR ( 6), and microcystin-(H4)YR [8, (H4)Y = l',2',3',4'-tetrahydrotyrosine], which were previously isolated in insufficient amounts to complete the structure assignment, and seven more microcystins, 9-15. A general method for assigning the structures of cyclic peptides containing ,ß-unsaturated amino acid unit(s) developed with nodularin, a cyclic pentapeptide hepatotoxin, was applied to confirm the previously assigned structures of 1-5 and to assign the structures of [D-Asp*

Diversity and distribution of Microcystis (Cyanobacteria) oligopeptide chemotypes from natural communities studied by single-colony mass spectrometry

“…The numbers following the name then refer to the molecular mass [M]. References: (1) Lawton et al (1999); (2) Murakami et al (1995); (3) Matsuda et al (1996); (4) Neumann et al (1997); (5) (6) ; (7) Murakami et al (1997); (8) Shin et al (1998); (9) Erhard et al (1999); (10) Itou et al (1999); (11) Martin et al (1993); (12) Erhard 1999; (13) Harada et al (1991); (14) Okino et al (1993); (15) Botes et al (1985); (16) Kiviranta et al (1992); (17) Kusumi et al (1987); (18) Namikoshi et al (1995); (19) Ishida et al (1997); (20) Tsukamoto et al (1993); (21) Harada et al (1993). Individual peptides or peptide classes were detected with pronounced differences in frequency (Table 3).…”

A Dhb-microcystin from the filamentous cyanobacterium Planktothrix rubescens

“…From 2D NMR spectral analysis, such as COSY and HOHAHA, this amino acid unit was deduced to be homoisoleucine (Hil). Its stereochemistry was determined to be (2S, 4S) by synthesis of four stereoisomers and chiral GC analysis according to Namikoshi et al (1995). The amino acid sequence of 1 was determined from analysis of the HMBC spectrum.…”

“…The mixtures of all four isomers were synthesized from (AE)-1-bromo-2-methylbutane in the same way as (4S)-homoisoleucine (Namikoshi et al, 1995). The retention times of four isomers were found to be 10.72 min (2R, 4S), 10.86 min (2R, 4R), 11.49 min (2S, 4S), and 11.69 min (2S, 4R) by a chiral GC analysis in the same way as the amino acid analysis.…”

Appendix 3: Tables of Microcystins and Nodularins

“…In some cases, especially with MC-RR and related congeners, the dominant ion observed in mass spectrometry is the doubly protonated ion [M + 2H] 2+ . Acyclo-LR: [28,42,54] 105 [2,3,9] …”