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<p>Natural naphthoquinone (NQ) dyes are gaining attention as safer and more sustainable alternative to synthetic colorants, and their glycosylation can enhance solubility and stability. In the present study, a novel, extracellular, highly stable, glycosylated derivative of NQ pigments (2-O-β-L-arabinofuranosyl-5,8-dihydroxy-1,4-naphthoquinone, C₁₅H₁₆O₈) was produced by the mangrove epiphytic fungus, <i>Aspergillus unguis</i>. Pigment production kinetics and solubility testing indicated the secondary metabolic behavior and high polarity of the pigment. HPLC separated the pigment into two isomeric fractions with retention times of 4.840 and 6.020&#xa0;min. Structural characterization was supported by several analyses, with a λ<sub>max</sub> at 300&#xa0;nm and R<sub>f</sub> values of 0.76–0.8. Furthermore, FTIR spectroscopy has revealed the key peaks of naphthazarin core at 1642, 1255–1262, 3331–3335, 1650, 918, 700, and 553&#xa0;cm⁻1. In addition, glycosylation characteristic peaks were found at 3396, 1200–1260, 1144, 1101, and 1028&#xa0;cm⁻1. Quinone carbonyls and α hydroxyls’ hydrogen bonding in the naphthazarin core was indicated by the peaks at 2920–2933&#xa0;cm<sup>-1</sup>. The molecular weight of the neutral compound was found to be 324&#xa0;Da via LCMS. NMR spectroscopy has displayed characteristic signals confirming the proposed structure. Proton NMR showed signals at δ 6.586 and 6.214 ppm (aromatic protons: H-6 and H-3 of the naphthazarin core); 4.892&#xa0;ppm (anomeric proton H-1΄ of the sugar moiety); 4.85–4.22&#xa0;ppm (anomeric protons of the pentose sugar). Moreover, <sup>13</sup>C NMR displayed signals at δ 97.38 ppm (anomeric carbon C-1΄), 77–70 ppm (oxygenated sugar carbons of pentose), 61.61 ppm (hydroxymethyl carbon C-5΄ that confirms the furanose structure).</p>

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Extraction and characterization of a novel glycosylated naphthazarin pigment from mangrove Aspergillus unguis AUMC15225

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  • 发表日期：

    2026年4月1日

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  • Basma M. Alkersh,
  • Hanan A. Ghozlan,
  • Soraya A. Sabry,
  • Sahar W. M. Hassan,
  • Amany El-Sikaily

摘要

Natural naphthoquinone (NQ) dyes are gaining attention as safer and more sustainable alternative to synthetic colorants, and their glycosylation can enhance solubility and stability. In the present study, a novel, extracellular, highly stable, glycosylated derivative of NQ pigments (2-O-β-L-arabinofuranosyl-5,8-dihydroxy-1,4-naphthoquinone, C₁₅H₁₆O₈) was produced by the mangrove epiphytic fungus, Aspergillus unguis. Pigment production kinetics and solubility testing indicated the secondary metabolic behavior and high polarity of the pigment. HPLC separated the pigment into two isomeric fractions with retention times of 4.840 and 6.020 min. Structural characterization was supported by several analyses, with a λmax at 300 nm and Rf values of 0.76–0.8. Furthermore, FTIR spectroscopy has revealed the key peaks of naphthazarin core at 1642, 1255–1262, 3331–3335, 1650, 918, 700, and 553 cm⁻1. In addition, glycosylation characteristic peaks were found at 3396, 1200–1260, 1144, 1101, and 1028 cm⁻1. Quinone carbonyls and α hydroxyls’ hydrogen bonding in the naphthazarin core was indicated by the peaks at 2920–2933 cm-1. The molecular weight of the neutral compound was found to be 324 Da via LCMS. NMR spectroscopy has displayed characteristic signals confirming the proposed structure. Proton NMR showed signals at δ 6.586 and 6.214 ppm (aromatic protons: H-6 and H-3 of the naphthazarin core); 4.892 ppm (anomeric proton H-1΄ of the sugar moiety); 4.85–4.22 ppm (anomeric protons of the pentose sugar). Moreover, 13C NMR displayed signals at δ 97.38 ppm (anomeric carbon C-1΄), 77–70 ppm (oxygenated sugar carbons of pentose), 61.61 ppm (hydroxymethyl carbon C-5΄ that confirms the furanose structure).