microcystin and 4-(2-(6-7-dimethoxy-4-methyl-3-oxo-3-4-dihydroquinoxalinyl)ethyl)-1-2-4-triazoline-3-5-dione

We designed and synthesized a new sensitive and highly reactive fluorogenic reagent (1a, DMEQ-TAD) targeting a conjugated diene. DMEQ-TAD reacted quantitatively with major vitamin D metabolites and synthetic analogs under a variety of conditions to yield the corresponding 6,19-cycloadducts as a mixture of the C(6) epimers. The stereochemistry of the adducts was determined by their CD spectra on the basis of the exciton chirality method. The fluorescent products can be quantified linearly down to 10 fmol by HPLC. The new fluorometric method was successfully used in the assays of 25-OHD3, 24,25-(OH)2D3 and 25,26-(OH)2D3 in the human plasma. The method was proved to be reliable and precise compared with the HPLC-UV assay method. Reactions of DMEQ-TAD with retinoic acid (21a) and its geometrical isomers (21b-d) having a conjugated pentaene system afforded 7,10-adducts (24a-d) as major products together with 5,8-adducts (26a-d) in about 9:1 ratio (70-95% yield) except for the 9Z-isomer (21e) which gave only a 5,8,11,14-bis-adduct (27). DMEQ-TAD reacted with microcystins LR, YR and RR, at the conjugated diene part to yield 4,7-cycloadducts as a pair of epimers in good yield.

Topics: Fluorescent Dyes; Fluorometry; Humans; Microcystins; Peptides, Cyclic; Quinoxalines; Triazoles; Vitamin A; Vitamin D

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.

Topics: Bacterial Toxins; Chromatography, High Pressure Liquid; Cyanobacteria; Fluorescent Dyes; Luminescent Measurements; Marine Toxins; Microcystins; Peptides, Cyclic; Quinoxalines; Spectrometry, Fluorescence; Triazoles