High-performance liquid chromatographic separation of microcystins derivatized with a highly fluorescent dienophile.
Microcystins are potent hepatotoxins produced by cyanobacteria, and are also tumor promoters as well as potent inhibitors of the catalytic subunits of protein phosphatases 1 and 2A. In order to establish a physicochemical method for individual detection and determination of trace amounts of microcystins, we developed a derivatization method for fluorescence (FL) and chemiluminescence (CL) detection, in which a highly fluorescent dienophile, DMEQ-TAD (4-[2-(6,7-dimethoxy-4-methyl-3-oxo-3,4-dihydroquinoxalinyl) ethyl]-1,2,4-triazoline-3,5-dione), was used as the labeling reagent. DMEQ-TAD reacted smoothly with the conjugated diene of the Adda moiety to give 2 stereoisomers of the adducts. As a result of the extensive experiments, the following reaction conditions were optimized for the labeling: sample amount, 10 micrograms; reaction solvent, DMF:acetonitrile (1:1); reaction time, 15 minutes; reaction temperature, 70 degrees C; amount of DMEQ-TAD used relative to that of microcystin, 80 equivalent. The resulting 6 adducts from microcystins-LR, -YR, and -RR can be separated from one another using the following reversed phase HPLC conditions in combination with a clean-up using ODS silica gel: column, Cosmosil 5C18-AR (150 x 4.6 I.D. mm); mobile phase, methanol:0.05M phosphate buffer (pH 3) (1:1); flow rate, 1.0 ml/min; detection, FL lambda ex 370 nm, lambda em 440 nm. The detection limits of the DMEQ-TAD derivatives were estimated to be 100 and 500 pg for LR, and 65 and 2,500 pg for RR using FL and CL detections, respectively; and the detection behavior was different from that of the Dns-Cys derivatives, which were more sensitive to CL than FL.
Harada
K
K
Faculty of Pharmacy, Meijo University, Nagoya, Japan. kiharada@meijo-u.ac.jp
Oshikata
M
M
Shimada
T
T
Nagata
A
A
Ishikawa
N
N
Suzuki
M
M
Kondo
F
F
Shimizu
M
M
Yamada
S
S
D001427:Bacterial Toxins / Q000032:analysis* / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D000458:Cyanobacteria / Q000378:metabolism; D005456:Fluorescent Dyes / Q000737:chemistry*; D008163:Luminescent Measurements; D008387:Marine Toxins; D052998:Microcystins; D010456:Peptides, Cyclic / Q000032:analysis* / Q000737:chemistry / Q000302:isolation & purification; D011810:Quinoxalines / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D014230:Triazoles / Q000737:chemistry*
D001427:Bacterial Toxins; D005456:Fluorescent Dyes; D008387:Marine Toxins; D052998:Microcystins; D010456:Peptides, Cyclic; D011810:Quinoxalines; D014230:Triazoles; C070204:4-(2-(6,7-dimethoxy-4-methyl-3-oxo-3,4-dihydroquinoxalinyl)ethyl)-1,2,4-triazoline-3,5-dione; C078588:microcystin; C063855:microcystin RR