2-Cyanobenz isoindole

A new cyanide dye for derivatizing thiols has been reported (65). This thiol label can be used with a visible diode laser and provide a detection limit of 8 X 10 M of the tested thiol. A highly sensitive laser-induced fluorescence detector for analysis of biogenic amines has been developed that employs a He—Cd laser (66). The amines are derivatized by naphthalenedicarboxaldehyde in the presence of cyanide ion to produce a cyanobenz[ isoindole which absorbs radiation at the output of He—Cd laser (441.6 nm). Optimization of the detection system yielded a detection limit of 2 x 10 M. 

Naphthalene-2,3-dicarboxaldehyde (NDA), which reacts with primary amines to give highly fluorescent cyanobenz[/]isoindole (CBI) derivatives, has also been used for determination of amphetamine-related compounds [70], dopamine, and norepinephrine [72] sub-fmol to fmol amounts of these were detected by HPLC with the PO-CL detection. 

NDA derivatization has also been automated for analysis of amino acids in brain tissue and microdialysates (Shah et al, 1999). NDA reacts with primary amines in the presence of cyanide to form a highly stable N-substituted l-cyanobenz[/] isoindole (GBI) derivative. Addition of a nucleophile, such as cyanide, hydrogen sulphite, isothiocyanate, or 2-mercaptoethanol, is essential for the formation of the derivative. 

In the first class, different fluorophores were bound to the amino terminus of ferrioxamine B including NBD, Af-methylanthranilic acid (MA) and l-cyanobenz[/]isoindole (CBI) to form 185, 186 and 187, respectively. The NBD-DFO was examined for the determination of Fe(III) under physiological conditions and monitoring the interaction with ferritin and transferrin. 

FIGURE 9 Electropherograms of the chiral resolution of (I) l-cyanobenz[/]isoindole (CBI)-selenomethionine and (II) CBI-selenoethionine enantiomers using a mixture of boric acid (10 mM) and phosphate buffer (30 mM, pH 7) as the mobile phase containing [i-cyclodextrin (30 mM) and taurodeoxycholic acid (50 mM) as CMPAs with sodium dodecyl sulfate (50 mM) as the mobile phase modifier (from Ref. 97). 

Recently, an analog of OPA, NDA, which yields more stable derivatives, was introduced. NDA reacts with primary amines in the presence of cyanide to produce highly fluorescent cyanobenz-[/]isoindole (CBI) derivatives. The reaction time is 20min, as opposed to 2 min with OPA. However, the resulting CBI derivatives are considerably more stable than their OPA/mercaptoethanol counterparts most derivatives exhibit little or no degradation after 16h in the dark. Detection limits as low as 100 fmol have been reported. 

The derivatization process (5) is accomplished in aqueous media at basic pH (pH 7-10) in a matter of approximately 15 min to yield a 2-cyanobenz[f]isoindole (CBI), which is stable for 10 to 12 hr in solution. As shown in Figure 1, the absorption characteristics of the CBI adducts are also readily accessible for assay by standard fluorescence or ultraviolet detection. In addition to the absorption between 200 and 300 nm, there are two maxima in the visible spectrum at approximately 420 and 440 nm accessible for fluorescence or ultraviolet detection. A probable mechanism (5,11) for the CBI formation is illustrated in Scheme 1. 

Figure 1. Absorption and fluorescence spectra of the cyanobenz-[f]isoindole chromophore CBI-Ala.

Figure 16. Chromatogram of cyanobenz[f]isoindole derivatives of catecholamines.

Much higher stabilities and partly higher fluorescence yields were obtained by Stobough et al. [86]. Naphthaline-2,3-dialdehyde (NDA), which reacts with primary amines in the presence of cyanide ions to Af-substituted l-cyanobenz[f isoindoles (CBI), was used as a reagent... 

NDA reacts with primary amines in the presence of cyanide to produce 1-cyanobenz[f]isoindole (CBI) derivatives (Figure 5) [131]. Cyclic voltammetry reveals that the oxidation of the CBI involves the loss of an electron from the heterocyclic nitrogen forming a radical cation that further reacts and is therefore not available for reduction. In addition, the electrochemistry of NDA derivatives is virtually pH independent, indicating no gain or loss of a proton. 

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