High-performance liquid chromatographic separation of microcystins derivatized with a highly fluorescent dienophile

• Published in: Natural toxins Vol. 5; no. 5; pp. 201 - 207
• Main Authors: Harada, K, Oshikata, M, Shimada, T, Nagata, A, Ishikawa, N, Suzuki, M, Kondo, F, Shimizu, M, Yamada, S
• Format: Journal Article
• Language: English
• Published: United States 1997
• Subjects: animal health; Bacterial Toxins - analysis; Bacterial Toxins - chemistry; Chromatography, High Pressure Liquid; Cyanobacteria - metabolism; Fluorescent Dyes - chemistry; human health and safety; Luminescent Measurements; medicine; Microcystins; Peptides, Cyclic - analysis; Peptides, Cyclic - chemistry; Peptides, Cyclic - isolation & purification; Quinoxalines - chemistry; Spectrometry, Fluorescence; Triazoles - chemistry; veterinary medicine
• ISSN: 1056-9014; 1522-7189
• DOI: 10.1002/19970505NT5

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.