Abstract
[D-Leu1]MC-LY (1) ([M + H]+ m/z 1044.5673, Δ 2.0 ppm), a new microcystin, was isolated from Microcystis aeruginosa strain CPCC-464. The compound was characterized by 1H and 13C NMR spectroscopy, liquid chromatography–high resolution tandem mass spectrometry (LC–HRMS/MS) and UV spectroscopy. A calibration reference material was produced after quantitation by 1H NMR spectroscopy and LC with chemiluminescence nitrogen detection. The potency of 1 in a protein phosphatase 2A inhibition assay was essentially the same as for MC-LR (2). Related microcystins, [D-Leu1]MC-LR (3) ([M + H]+ m/z 1037.6041, Δ 1.0 ppm), [D-Leu1]MC-M(O)R (6) ([M + H]+ m/z 1071.5565, Δ 2.0 ppm) and [D-Leu1]MC-MR (7) ([M + H]+ m/z 1055.5617, Δ 2.2 ppm), were also identified in culture extracts, along with traces of [D-Leu1]MC-M(O2)R (8) ([M + H]+ m/z 1087.5510, Δ 1.6 ppm), by a combination of chemical derivatization and LC–HRMS/MS experiments. The relative abundances of 1, 3, 6, 7 and 8 in a freshly extracted culture in the positive ionization mode LC–HRMS were ca. 84, 100, 3.0, 11 and 0.05, respectively. These and other results indicate that [D-Leu1]-containing MCs may be more common in cyanobacterial blooms than is generally appreciated but are easily overlooked with standard targeted LC–MS/MS screening methods.
Highlights
Microcystins (MCs), such as MC-LR (2), are cyclic heptapeptide hepatotoxins (Figure 1) produced primarily in cyanobacterial genera such as Microcystis, Dolichospermum (Anabaena), Nostoc and Toxins 2020, 12, 77; doi:10.3390/toxins12020077 www.mdpi.com/journal/toxins dienoic acid (Adda) at position 5 (Figure 1) [3]
A very samples analyzed, two Microcystis aeruginosa cultures from Saskatchewan and Alberta, CPCC-464 similar profile was observed with culture CPCC-299, with the only differences being in relative peak and CPCC-299, showed the presence of a new microcystin tentatively identified as [D-Leu1 ]MC-LY
[D-Leu1 ]MC-LY (1) was tentatively identified recently by LC–HRMS/MS in a cyanobacterial bloom sample from southwestern Ontario, Canada [9], indicating that it may be a significant component of natural cyanobacterial blooms in this and other parts of the world
Summary
Microcystins (MCs), such as MC-LR (2), are cyclic heptapeptide hepatotoxins (Figure 1) produced primarily in cyanobacterial genera such as Microcystis, Dolichospermum (Anabaena), Nostoc and Toxins 2020, 12, 77; doi:10.3390/toxins12020077 www.mdpi.com/journal/toxins dienoic acid (Adda) at position 5 (Figure 1) [3]. Leu1]MC-LY (1) was tentatively identified recently by LC–HRMS/MS in a cyanobacterial bloom the toxins’ mechanism of action and animal studies have demonstrated that MCs are potent tumor sample from southwestern Ontario, Canada [9], indicating that it may be a significant component of promoters [1]. The number of identified MCs continues to increase and more than 250 analogues natural cyanobacterial blooms in this and other parts of the world. Due to a lack of standards for these analogues, very few studies the structure, and to evaluate its toxicity relative to other MCs because limited data are available on have adequately assessed their distribution in natural waters. Numbered starting from the carboxyl carbon of each amino acid
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