Red pigment produced by the oxidation of L-scorbamic acid

Abstract

A crystalline red pigment was obtained by the oxidation of L-scorbamic acid which was thought to be an intermediate amino-reductone in the Strecker degradation of an a-amino acid with dehydro-L-ascorbic acid. The pigment which was soluble in water, MeOH, and EtOH, and insoluble in most other organic solvents was an ammonium salt and quite stable in a dry sta'te, but it was easily decolorized in an acid solution to give L-scorbamic acid and dehydro-L-ascorbic acid as hydrolysis products. Its molecular formula was ClzHlsNzOlo, and spectroscopic data (ir, nmr, uv, etc.), together with the results of quantitative analysis of hydrolysis products, proved it to be 2,2'-nitrilodi-2( 2') -deoxy-L-ascorbic acid monoammonium salt. It is a new pigment with a murexide-type chromophore.An intense red coloration is observed when a mixed solution of dehydro-L-ascorbic acid (DHA) and an a-amino acid is heated. The phenomenon was first reported by Koppanyi et al. '(1945), who heated L-ascorbic acid (ASA) with a-amino acid in the presence of HzOz. Since then, though considerable works (Nakabayashi and Shibata, 1967;Pecherer, 1951;Ranganna and Setty, 1968;Wurtz and North, 1963) have been done on this red pigment, its exact structure and formation mechanism are still unknown.It was pointed out previously that L-scorbamic acid (SCA) might be a precursor of the red pigment (Kurata and Sakurai, 1966;Kurata et al., 1971). SCA was first prepared by Micheel and Mittag (1937) as amorphous powder which produced a red pigment on oxidation, and two possible structures, namely a chain structure and a pyrazine ring structure, were proposed for the pigment. y-Methyl-a-amino tetronic acid was also known to produce a red pigment, and a dihydropyrazine ring structure was proposed in this case (Lecocq, 1951). In this paper, isolation and characterization of the red pigment produced by the oxidation of SCA were described. EXPERIMENTAL AND RESULTS SECTIONPrior to elementary analyses, all compounds were dried in uucuo over phosphorus pentoxide, unless otherwise stated. Melting points were uncorrected. Uv and visible spectra were recorded with a Hitachi recording spectrophotometer, Model EPS-3T. Ir spectra were determined with a Japan Spectroscopic Model IR-S infrared spectrophotometer, and nmr spectra were measured with a Japan Electron Optics JNM-4H-100 or JNM-MH-60 spectrometer. Mass spectra were recorded on a Hitachi RMU-6L spectrometer with an ionizing voltage of ca. 70 eV.Reagents and Chromatography. Anhydrous DHA was prepared as described previously . ASA and all other reagents were guaranteed grade (Kanto Chemical Co., Inc.) and used without further purification.Both silica gel G (E. Merck) and cellulose (Serva) were used as adsorbents for thin-layer chromatography (tlc). Solvent systems containing mixtures of toluene-ethyl acetate (5:l-1:l) were used for silica gel layers, and two solvent systems, ethyl acetate-pyridine-water (10:4: 3) and n-BuOH-EtOH-water (4:1:4 or 4:1:5), were used for cellulose layers. In the case of cellulose layers, color...

Non-enzymatic browning in citrus juice: chemical markers, their detection and ways to improve product quality

“…furfural, 5-(hydroxymethyl) furfural (HMF), or other carbonyl compounds, participates in juice browning and polymerize with each other or react with amino acids to yield browning materials (Clegg 1964;Kacem et al 1987;Kennedy et al 1990;Lee and Nagy 1988a, b;Robertson and Samaniego 1986;Sawamura et al 1991). A mixture of dehydroascorbic acid (DHA) and an amino acid in non-aqueous solution produced a red or yellow pigment as an intermediate in the browning pathway (Hayashi et al 1983a, b;Kurata et al 1973). It is believed that a similar browning reaction occurs in citrus juice as well as in the DHA aqueous model systems (Sawamura et al 1991).…”

Formation Mechanism of the Free Radical Product and Its Precursor by the Reaction of Dehydro-L-ascorbic Acid with Amino Acid

“…DHA, scorbamic acid (SCA) and the red pigment (4) were prepared by the methods previously described. 8 ) Other reagents used were of guaranteed grade.…”

On the Yellow Product and Browning of the Reaction of Dehydroascorbic Acid with Amino Acids

“…Instead, spin coupling was seen between each of the two and the signal for the C-5 proton (4.70 ppm). When the signals of group (1) are compared with those of C-4, C-5 and C-6 of AsA,8) the former two were shifted downfield by 0.46 and 0.22 ppm, respectively. This seems to suggest an AsA-like structure which slightly differs from AsA for C-2 and C-3.…”

“…The results of PMR are also shown in Table II. On the basis of the results of decoupling experiments, the PMR signals were classified into three groups, i.e., (1) 3.75, 4.32 and 5.44 ppm, (2) 3.72, 4.09 and 4.63 ppm, and (3) 4.12, 4.14, 4.70 and 5.24 ppm. These groups respectively correspond to the protons in the three DHA (or DHA and AsA) residues containing the C-6, C-5 'and C-4 protons.…”

“…From such a reaction mixture a red pigment has been isolated and identified to be the oxidized form of bis(2-deoxy-2-L-ascorbyl)amine as an intermediate of this reaction. 1) In the series of work concerning the amino-carbonyl reactions, we have shown the formation of three different free radical species R-A, R-B and R-C in the reacting mixture. 2 ) One of these, R-A, has been isolated in pure form on a chromatographic plate and proved to be a fairly stable free radical.…”