Derivatization of secondary amino acids with 7-nitro-4-benzofurazanyl ethers

Abstract

Five 7-nltro-4-benzofurazanyl ethers have been synthesized and their water solubilities and reactivities have been determined. 4-Methoxy-7-nltrobenzofurazan (NBD-OCH3) has a solubility similar to that of 4-chloro-7-nltrobenzofurazan (NBD-CI) but reacts ~3.5 times faster with hydroxyproline. Hydroxyproline reacts quantitatively with NBD-OCH3 In acetonltrlle-water, while considerable losses are seen when NBD-CI Is used In this medium. 4-(2-Hydroxyethoxy)-7nitrobenzofurazan Is 16 times more soluble in water than NBD-CI and therefore permits complete derivatization of hydroxyproline in aqueous solutions without any organic solvent. It Is shown that high sensitivity analytical methods (pmol/mL range) can be designed by combining derivatization In a pure aqueous medium with injection of large volumes of sample onto a reversed-phase liquid chromatographic column.The reactivity of nitro-substituted aromatic ethers is documented as well as their use in organic synthesis (1-3). We here report on the use of one type of aromatic ethers as derivatizing agents for amines, namely, ethers of 7-nitrobenzofurazan. It was previously demonstrated (4) that 4-chloro-7-nitrobenzofurazan (NBD-CI), when reacting in a methanol/buffer medium, forms 4-methoxy-7-nitrobenzofurazan (NBD-OCHg) which itself reacts with amines. In this work it is shown that, apart from NBD-OCH3, other NBD ethers can be used as reagents for the determination of amines.4-(2-Hydroxyethoxy)-7-nitrobenzofurazan (NBD-OCH2CH2-OH) and NBD-OCH3 have been selected for a closer examination and comparison with NBD-CI. For this purpose the different reactions involved, shown in the general reaction scheme in Figure 1, have been studied. EXPERIMENTAL SECTIONSynthesis of 4-Methoxy-7-nitrobenzofurazan (NBD-OCHg). NBD-OCHg was synthesized from NBD-CI and CHgONa in CHgOH as described previously (4).Synthesis of 4-Ethoxy-7-nitrobenzofurazan (NBD-OC-H2CH3). NBD-OCH2CH3 was prepared by dropwise addition of 0.22 g (5.5 mmol) of NaOH in 20 mL of C2H5OH to 1.0 g (5.0 mmol) of NBD-CI in 80 mL of C2H5OH. After being stirred overnight the dark colored solution was acidified with HC1, diluted with water, and extracted with CH2C12. The extract was dried

Structural factors influencing the reaction rates of 4-aryloxy-7-nitrobenzofurazans with amino acids

“…The reaction of 2a with some amino acids was reported to yield fluorescent products 3 [48]. We decided to investigate the reaction of 2a-2f with six representative amino acids in order to study the influence of the aryl group Ar in 2.…”

Synthesis Of Labeled Glycosyl Phosphatidyl Inositol (GPI) Anchors

“…[22] Therefore the activated 5-azit combines compactness with high sensitivity. [21] In order ido-2-nitrobenzoate derivative 20 (Scheme 5) was prepared to increase the distance to the GPI anchor structure a β-following literature procedures. [22] Reaction of 20 with 5a alanine spacer was inserted.…”

Structure-Property Relationships in Benzofurazan Derivatives: A Combined Experimental and DFT/TD-DFT Investigation

“…In addition, the activated chlorine atom in 4-chloro-7-nitrobenzofurazan (NBD chloride, namely NBD-Cl) can undergo electrophilic aromatic substitution by phenoxide, primary or secondary cyclic amines [10][11][12][13] and some of 4,7 di-substituted benzofurazan compounds to generate weakly or non-fluorescents products. [14][15][16][17][18] A previous kinetic study of amino-substituted NBD showed that methoxy and aryloxy substituent's are better leaving groups than chloro and that a red-colored Meisenheimer complex immediate was formed during the reactions [19].…”