Communication pubs.acs.org/IC
Selective Formation of Chromogen I from N‑Acetyl‑D‑glucosamine upon Lanthanide Coordination Xiu-Ying Zheng,†,‡ Jun-Bo Peng,†,‡ M. M. Varuni S. Livera,§ Yun Luo,† Ya-Yun Wang,† Xiang-Jian Kong,*,† La-Sheng Long,*,† Zhiping Zheng,*,§ and Lan-Sun Zheng† †
Collaborative Innovation Center of Chemistry for Energy Materials, State Key Laboratory of Physical Chemistry of Solid Surface, and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China § Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States S Supporting Information *
ABSTRACT: We report two nonanuclear lanthanide complexes, [Ln9(μ4-O)(μ3-OH)8(LH)4(OAc)4(H2O)12]· 5ClO4·24H2O (Ln = Gd, 1; Dy, 2), where LH2− is the doubly deprotonated chiral ligand Chromogen I (2acetamido-2,3-dideoxy-D-erythro-hex-2-enofuranose), one of the many products from the dehydration of N-acetylD-glucosamine (GlcNAc). Mass spectroscopic studies established the solution stability of these clusters. Through hydrogen bonding, the cluster complex self-organizes into a nanostructured 54-metal cagelike assembly featuring six of its units occupying the vertices of an octahedron. Free Chromogen I can be obtained in pure form and high yield by a straightforward workup of the cluster complex. This is the first report of dehydrating GlcNAc without the need of a catalyst or forcing conditions.
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elective and efficient conversion of renewable biomass into platform chemicals that are applicable as raw materials or synthetic intermediates for higher-value chemicals and materials has been actively pursued in green chemistry.1 One of the most abundant biomasses, second only to cellulose and the most abundant N-containing biomass, is chitin.2 Hydrolysis under strong acidic conditions or enzymatic degradation causes its depolymerization into its building block of N-acetyl-D-glucosamine (GlcNAc), a monosaccharide with applications as dietary supplements and in cosmetics and medicines.3 GlcNAc can further be transformed into a number of N-containing chemicals, among which those (Figure 1) from its dehydration have received much attention because of their biological activities for many realized or envisioned applications.4 The key challenges to fully realizing the application potentials of these value-adding chemicals include the low-yielding multistep synthesis and laborious chromatographic separation of individual components. Earlier studies in this vein involved alkaline degradation or treatment with borate of GlcNAc,5 producing in low yields mixtures that contain various dehydration derivatives of varying relative amounts.6 More recent studies resorted to noncatalytic routes with the use of high-temperature water and under high pressure.7 In spite of the progress made, the aforementioned challenges, namely, the lowyield synthesis and difficulty in separation, remain. We may have found a possible solution, at least for the preparation and purification of Chromogen I (2-acetamido-2,3© XXXX American Chemical Society
Figure 1. Proposed selective transformation of GlcNAc into Chromogen I in the presence of Ln3+ ions.
dideoxy-D-erythro-hex-2-enofuranose), one of the products of GlcNAc dehydration, in the unexpected selective formation of polynulcear lanthanide oxo/hydroxo complexes featuring deprotonated Chromogen I in an optically pure form as the supporting organic ligand. Specifically, we obtained two isostructural nonanuclear complexes of the common formula [Ln9 (μ4 -O)(μ3-OH)8 (LH) 4(OAc)4 (H 2O) 12 ]·5ClO 4·24H2 O (Ln = Gd, 1; Dy, 2; LH3 = Chromogen I, C8H13NO5) by heating a mixture of Ln(ClO4)3 (Ln = Gd, Dy), NaOAc·3H2O (OAc− = CH3CO2−), and GlcNAc in 1:1 (v/v) ethanol/water at ca. 80 °C for 2 h, during which the colorless solution gradually turned yellow. The product was obtained as pale-yellow block-shaped crystals in about 40% yield upon cooling and standing at room temperature of the reaction solution (see the Supporting Information). Optically pure Chromogen I can be obtained in high yield using a straightforward workup procedure (see below). Received: October 24, 2016
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DOI: 10.1021/acs.inorgchem.6b02589 Inorg. Chem. XXXX, XXX, XXX−XXX
Communication
Inorganic Chemistry The structures of both 1 and 2 were determined by singlecrystal X-ray diffraction, and that of 1 is shown in Figure 2 and
Figure 3. Ball-and-stick view of the cagelike assembly with six units of the nonanuclear complex. Color code: Gd, purple or cyan; O, red; C, gray; N, blue, H, white.
Figure 2. Ball-and-stick view of (a) the cationic [Gd9(μ4-O)(μ3OH)8(LH)4(OAc)4(H2O)12]5+ unit, (b) the [Gd9(μ4-O)(μ3-OH)8]17+ core, (c) the arrangement of the nine Gd3+ ions, and (d) the Gd(LH) coordination mode. Color code: Gd, purple or cyan; O, red; C, gray; N, blue, H, white.
disordered ClO4− ions; the remaining ClO4− ions and guest water molecules are located crystallographically outside this nanocage and were removed using the SQUEEZE protocol.9 The size of the nanocage is 10.43 × 10.43 × 10.43 Å. The identity/stability of the two compounds in solution was studied by high-resolution electrospray ionization mass spectrometry (HR-ESI-MS). For compound 2, three groups of peaks in the m/z range between 900 and 2100 amu are clearly shown (Figure 4). The first group consists of seven strong peaks concentrating in the m/z range of 932−976 amu. They are attributable to various 3+ charge fragments with continuously decreasing numbers of OAc− ions based on the unit of [Dy9(μ4O)(μ3-OH)8(LH)4(OAc)4]Cl2}3+, differing only in the number of chloride ions and solvent molecules. The second group contains nine major peaks in the m/z range of 1475−1594 amu. These peaks can be assigned to 2+ charge species derived from the {[Dy9(μ4-O)(μ3-OH)8(LH)4(OAc)4](OH)2Cl1}2+ unit. As in the previous group of peaks, the different m/z values reflect the presence of different numbers of guest molecules.10 The last group of peaks, appearing in the m/z range of 2060−2155 amu, are attributable to the 3+ charge species derived from the unit of {[Dy9(μ4-O)(μ3-OH)8(LH)4(OAc)4(H2O)12(OH)7]2}3+, suggesting the formation of dimeric species from the nonanuclear complex unit. As shown in Figures 4 and S10, all peaks are in excellent agreement with the calculated isotope patterns, suggesting that the nonanuclear cluster maintains its structural integrity in solution. Similar observations were made in the mass spectroscopic studies of compound 1 (Figure S9). We note that, although a large number of lanthanide cluster complexes exist in the literature,8,11,12 their solution stability has yet to be established. Thus, the present two compounds represent rare examples of highly stable lanthanide oxide/hydroxide clusters that may be used as secondary building units for the construction of even more sophisticated and higher-order architectures. The selective formation/crystallization of the cluster complexes with a deprotonated Chromogen I ligand, putatively transformed in situ from the starting GlcNAc, is significant. As noted above, although dehydration of GlcNAc into various derivatives including Chromogen I has been reported, catalysts
discussed below as a representative. The complex cation features a nonanuclear core of [Gd9(μ4-O)(μ3OH)8(LH)4(OAc)4(H2O)12]5+ (Figure 2a) that can be viewed as being built around a central square pyramid of [Gd5(μ4-O)(μ3OH)4]9+ (Figure 2b), with any two adjacent basal Gd3+ ions being connected with the vertex-occupying Gd3+ ion via a μ3-OH group. The basal Gd3+ ions are also bridged by a μ4-O2− group situated in the center of the basal plane. Each of the basal Gd···Gd pairs is further linked to one peripheral Gd3+ ion via a different μ3-OH group and two alkoxide O atoms from two different deprotonated Chromogen I (LH2−) ligands, affording a cuboidal Gd−O arrangement, that is, a cubane unit less one Gd vertex (Figure 2b,c). Each Chromogen I ligand coordinates three Gd3+ ions in a μ3:η1:η2:η2:η1 fashion (Figure 2d). We note that this is the first report of the structure of the Chromogen I ligand. Because Chromogen I is an intrinsically chiral ligand, both complexes crystallized in the chiral space group P23, which was subsequently supported by their circular dichroism spectra (Figure S12). In addition, there are 4 acetate and 12 terminal aqua ligands to complete the coordination sphere of the Gd3+ ions. Two coordination geometries are observed for the 9 octacoordinate Gd3+ ions, one being a bicapped trigonal prism or octahedron and the other being a square antiprism (Figure S3). The Gd−O bond lengths range between 2.195 and 2.770 Å, while the separation between the immediately adjacent Gd atoms falls in the range of 3.643−3.893 Å; both parameters are comparable to the corresponding values reported for Gd−O/ OH cluster complexes.8 Compound 2 is isostructural to 1, with the main differences being in the metric values of the bond lengths and angles. The distance ranges for the Dy−O bonds and Dy···Dy separations are 2.185−2.680 and 3.611−3.849 Å, respectively. Interestingly, six units of the nonanuclear cluster complex organize themselves via extensive hydrogen-bonding interactions into a cagelike assembly (Figure 3), inside which reside eight B
DOI: 10.1021/acs.inorgchem.6b02589 Inorg. Chem. XXXX, XXX, XXX−XXX
Communication
Inorganic Chemistry
Figure S6, the χMT value of 68.61 cm3 K mol−1 for 1 and 125.12 cm3 K mol−1 for 2 at 300 K are close to the calculated value of 70.83 cm3 K mol−1 for nine uncoupled Gd3+ and 127.50 cm3 K mol−1 for nine uncoupled Dy3+, respectively. For 1, upon lowering of the temperature, the χMT value decreased slightly to 62.00 cm3 K mol−1 at 24 K and then rapidly to 31.16 cm3 K mol−1 at 2 K. The χMT curve of 2 displayed a similar trend, arriving at 67.65 cm3 K mol−1 at 2 K. In summary, we unexpectedly obtained two isostructural nonanuclear chiral lanthanide oxo/hydroxo cluster complexes with deprotonated Chromogen I derived in situ from starting GlcNAc. Through extensive hydrogen-bonding interactions, six units of the nonanuclear cluster complex self-organize into a nanostructured cagelike 54-lanthanide assembly. We showed for the first time the production of various products from the dehydration of GlcNAc under ambient conditions that do not involve the use of a catalyst or any forcing conditions. It is probably the favorable coordination between the lanthanide ion and the otherwise low-yielding Chromogen I ligand that drives the dehydration of GlcNAc toward the increased production of Chromogen I. The solution stability of the cluster has been established, but free Chromogen I can be obtained in pure form and high yields by following a straightforward procedure for the workup of the cluster complex. Thus, the results reported here, although obtained unexpectedly, point to a new and effective means of producing and purifying the otherwise hard-to-obtain Chromogen I. More importantly, our findings suggest that the selective and efficient transformation of a readily available biomass into useful chemicals, as neatly illustrated herein, may be generally achievable and driven by the unique coordination chemistry of certain metal ions.
Figure 4. HR-ESI-MS spectra obtained using an ethanolic solution of 2, yielding peaks in three distinct m/z ranges: experimental peaks (black) versus calculated isotope patterns (colored).
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ASSOCIATED CONTENT
S Supporting Information *
or forcing conditions were required. Analogous transformation under ambient conditions at below the boiling temperature of water and with atmospheric pressure as shown in this work has never been demonstrated. Furthermore, in the literature work, individual products were obtained only in low yields after painstaking chromatographic separation. In comparison, straightforward digestion of the crystals of 1 or 2 with HCl (aqueous 1.0 M) in methanol followed by trituration with a saturated aqueous solution of NaHCO3 led to the precipitation of lanthanide carbonate while leaving in the supernatant-free Chromogen I ligand (Figure S13). The pure product was obtained in 40% yield upon solvent distillation in vacuo. To verify the seemingly essential role played by the lanthanide ion in dehydrating GlcNAc and “sequestering” Chromogen I, one of many possible decomposition products, by selectively forming its lanthanide complex, comparative studies were carried out. The control reaction was carried using a reaction mixture without any lanthanides but otherwise under identical conditions. Analyses by high-performance liquid chromatography and 1H NMR indicated the low-yield presence of ManNAc, Chromogen I, 3,6-anhydromannofuranose, and 3,6anhydroglucofuranose in the product mixture (Figures S14 and S15). These species were also found in the mother liquor in the crystallization of compound 1 (Figure S14). The selective uptake of Chromogen I into the cluster complex thus manifests a favorable match in coordination between the ligand and a lanthanide ion, which in turn, skews the equilibrium toward the increased production of Chromogen I. The temperature dependence of the magnetic susceptibility of 1 and 2 was measured in 2−300 K with 1000 Oe. As shown in
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02589. Synthesis and characterization details (PDF) CIF file (CIF) CIF file (CIF)
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected] (X.-J.K.). *E-mail:
[email protected] (L.-S.L.). *E-mail:
[email protected] (Z.Z.). ORCID
Xiang-Jian Kong: 0000-0003-0676-6923 Author Contributions ‡
X.-Y.Z. and J.-B.P. contributed equally to this work.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the 973 Project (Grant 2014CB845601) from the Ministry of Science and Technology of China, the National Natural Science Foundation of China (Grants 21422106, 21371144, 21431005, and 21390391), the Fok Ying Tung Education Foundation (Grant 151013), and the U.S. National Science Foundation (Grant CHE-1152609). C
DOI: 10.1021/acs.inorgchem.6b02589 Inorg. Chem. XXXX, XXX, XXX−XXX
Communication
Inorganic Chemistry
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Ber. 1956, 89, 1473−1486. (c) Kuhn, R.; Kruger, G. Das Chromogen III der Morgan-Elson-Reaktion. Chem. Ber. 1957, 90, 264−277. (d) Derevitskaya, V. A.; Likhosherstov, L. M.; Schennikov, V. A.; Kochetkov, N. K. 2-Acetamido-3,6-anhydro-2-deoxy-D-hexoses: products of the alkaline degradation of 2-acetamido-2-deoxy-D-hexoses. Carbohydr. Res. 1971, 20, 285−291. (8) Peng, J. B.; Kong, X. J.; Zhang, Q. C.; Orendac, M.; Prokleska, J.; Ren, Y. P.; Long, L. S.; Zheng, Z.; Zheng, L. S. Beauty, symmetry, and magnetocaloric effect-four-shell keplerates with 104 lanthanide atoms. J. Am. Chem. Soc. 2014, 136, 17938−179418. (9) Farrugia, L. J. WinGX suite for small-molecule single-crystal crystallography. J. Appl. Crystallogr. 1999, 32, 837−838. (10) (a) Li, X. Y.; Su, H. F.; Zhou, R. Q.; Feng, S.; Tan, Y. Z.; Wang, X. P.; Jia, J.; Kurmoo, M.; Sun, D.; Zheng, L. S. General assembly of twisted trigonal-prismatic nonanuclear silver(I) clusters. Chem. - Eur. J. 2016, 22, 3019−3028. (b) Deng, Y. K.; Su, H. F.; Xu, J. H.; Wang, W. G.; Kurmoo, M.; Lin, S. C.; Tan, Y. Z.; Jia, J.; Sun, D.; Zheng, L. S. Hierarchical assembly of a {Mn(II)15Mn(III)4} brucite disc: step-by-step formation and ferrimagnetism. J. Am. Chem. Soc. 2016, 138, 1328−1334. (11) (a) Yang, X.; Schipper, D.; Jones, R. A.; Lytwak, L. A.; Holliday, B. J.; Huang, S. Anion-dependent self-assembly of near-infrared luminescent 24- and 32-metal Cd−Ln complexes with drum-like architectures. J. Am. Chem. Soc. 2013, 135, 8468−8471. (b) Liu, D. P.; Lin, X. P.; Zhang, H.; Zheng, X. Y.; Zhuang, G. L.; Kong, X. J.; Long, L. S.; Zheng, L. S. Magnetic properties of a single-molecule lanthanide− transition metal compound containing 52 gadolinium and 56 nickel atoms. Angew. Chem., Int. Ed. 2016, 55, 4532−4536. (c) Langley, S. K.; Chilton, N. F.; Moubaraki, B.; Hooper, T.; Brechin, E. K.; Evangelisti, M.; Murray, K. S. Molecular coolers: the case for [CuII5GdIII4]. Chem. Sci. 2011, 2, 1166−1169. (d) Chang, L. X.; Xiong, G.; Wang, L.; Cheng, P.; Zhao, B. A 24-Gd nanocapsule with a large magnetocaloric effect. Chem. Commun. 2013, 49, 1055−1057. (e) Chen, Y. C.; Guo, F. S.; Zheng, Y. Z.; Liu, J. L.; Leng, J. D.; Tarasenko, R.; Orendac, M.; Prokleska, J.; Sechovsky, V.; Tong, M. L. Gadolinium(III)-hydroxy ladders trapped in succinate frameworks with optimized magnetocaloric effect. Chem. - Eur. J. 2013, 19, 13504−13510. (f) Zheng, X. Y.; Wang, S. Q.; Tang, W.; Zhuang, G. L.; Kong, X. J.; Ren, Y. P.; Long, L. S.; Zheng, L. S. Two nanosized 3d−4f clusters featuring four Ln6 octahedra encapsulating a Zn4 tetrahedron. Chem. Commun. 2015, 51, 10687− 10690. (g) Zheng, Y. Z.; Evangelisti, M.; Winpenny, R. E. P. Large magnetocaloric effect in a Wells−Dawson type {Ni6Gd6P6} cage. Angew. Chem., Int. Ed. 2011, 50, 3692−3695. (h) Zhang, M. B.; Zhang, J.; Zheng, S. T.; Yang, G. Y. A 3D coordination framework based on linkages of nanosized hydroxo lanthanide clusters and copper centers by isonicotinate ligands. Angew. Chem., Int. Ed. 2005, 44, 1385−1388. (12) (a) Kong, X.-J.; Wu, Y.; Long, L.-S.; Zheng, L.-S.; Zheng, Z. A chiral 60-metal sodalite cage featuring 24 vertex-sharing [Er4(μ3-OH)4] cubanes. J. Am. Chem. Soc. 2009, 131, 6918−6919. (b) Zheng, X.-Y.; Peng, J.-B.; Kong, X.-J.; Long, L.-S.; Zheng, L.-S. Mixed-anion templated cage-like lanthanide clusters: Gd27 and Dy27. Inorg. Chem. Front. 2016, 3, 320−325. (c) Adhikary, A.; Jena, H. S.; Khatua, S.; Konar, S. Synthesis and characterization of two discrete Ln10 nanoscopic ladder-type cages: magnetic studies reveal a significant cryogenic magnetocaloric effect and slow magnetic relaxation. Chem. - Asian J. 2014, 9, 1083−1090. (d) Thielemann, D. T.; Wagner, A. T.; Lan, Y.; Oña-Burgos, P.; Fernández, I.; Rösch, E. S.; Kölmel, D. K.; Powell, A. K.; Bräse, S.; Roesky, P. W. Peptoid-ligated pentadecanuclear yttrium and dysprosium hydroxy clusters. Chem. - Eur. J. 2015, 21, 2813−2820. (e) Thielemann, D. T.; Wagner, A. T.; Rosch, E.; Kolmel, D. K.; Heck, J. G.; Rudat, B.; Neumaier, M.; Feldmann, C.; Schepers, U.; Brase, S.; Roesky, P. W. Luminescent cell-penetrating pentadecanuclear lanthanide clusters. J. Am. Chem. Soc. 2013, 135, 7454−7457.
REFERENCES
(1) (a) Dangi, A. K.; Rishi, P.; Tewari, R. Enhancing the yield of active recombinant chitobiase by physic-chemical and in vitro refolding studies. Protein J. 2016, 35, 72−79. (b) Zhang, A.; Gao, C.; Wang, J.; Chen, K.; Ouyang, P. An efficient enzymatic production of N-acetyl-Dglucosamine from crude chitin powders. Green Chem. 2016, 18, 2147− 2154. (c) Nguyen-Thi, N.; Doucet, N. Combining Chitinase C and Nacetylhexosaminidase from Streptomyces coelicolor A3(2) provides an efficient way to synthesize N-acetylglucosamine from crystalline chitin. J. Biotechnol. 2016, 220, 25−32. (d) Kumar, M. N. V. R.; Muzzarelli, R. A. A.; Muzzarelli, C.; Sashiwa, H.; Domb, A. J. Chitosan chemistry and pharmaceutical perspectives. Chem. Rev. 2004, 104, 6017−6084. (e) Lee, J. H.; Kim, N. H.; Winstel, V.; Kurokawa, K.; Larsen, J.; An, J. H.; Khan, A.; Seong, M. Y.; Lee, M. J.; Andersen, P. S.; Peschel, A.; Lee, B. L. Surface glycopolymers are crucial for in vitro antiwall teichoic acid lgG-Mediated complement activation and opsonophagocytosis of staphylococcus aureus. Infect. Immun. 2015, 83, 4247−4255. (f) Zeng, L.; Burne, R. A. Nagr differentially regulates the expression of the glmS and nagAB genes required for amino sugar metabolism by streptococcus mutans. J. Bacteriol. 2015, 197, 3533−3544. (g) Sheldon, R. A. Green and sustainable manufacture of chemicals from biomass: state of the art. Green Chem. 2014, 16, 950−963. (h) Farmer, T. J.; Mascal, M. Platform Molecules. In Introduction to Chemicals from Biomass, 2nd ed.; Clark, J., Deswarte, F., Eds.; John Wiley & Sons, Ltd.: Chichester, U.K., 2015. (i) Yabushita, M. A Study on Catalytic Conversion of Non-Food Biomass into Chemicals. Fusion of Chemical Sciences and Engineering; Springer: Berlin, 2016. (2) Chen, J. K.; Shen, C. R.; Liu, C. L. N-acetylglucosamine: production and applications. Mar. Drugs 2010, 8, 2493−2516. (3) (a) Noren-Muller, A.; Reis-Correa, I., Jr.; Prinz, H.; Rosenbaum, C.; Saxena, K.; Schwalbe, H. J.; Vestweber, D.; Cagna, G.; Schunk, S.; Schwarz, O.; Schiewe, H.; Waldmann, H. Discovery of protein phosphatase inhibitor classes by biology-oriented synthesis. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 10606−10611. (b) Kikuchi, H.; Saito, Y.; Komiya, J.; Takaya, Y.; Honma, S.; Nakahata, N.; Ito, A.; Oshima, Y. Furanodictine A and B: amino sugar analogues produced by cellular slime mold dictyostelium discoideum showing neuronal differentiation activity. J. Org. Chem. 2001, 66, 6982−6987. (4) (a) Salvatore, S.; Heuschkel, R.; Tomlin, S.; Davies, S. E.; Edwards, S.; Walker-Smith, J. A.; French, I.; Murch, S. H. A pilot study of N-acetyl glucosamine, a nutritional substrate for glycosaminoglycan synthesis, in paediatric chronic inflammatory bowel disease. Aliment. Pharmacol. Ther. 2000, 14, 1567−1579. (b) Aam, B. B.; Heggset, E. B.; Norberg, A. L.; Sorlie, M.; Varum, K. M.; Eijsink, V. G. Production of chitooligosaccharides and their potential applications in medicine. Mar. Drugs 2010, 8, 1482−1517. (c) Suzuki, K.; Mikami, T.; Okawa, Y.; Tokoro, A.; Suzuki, S.; Suzuki, M. Antitumor effect of hexa-Nacetylchitohexaose and chitohexaose. Carbohydr. Res. 1986, 151, 403− 408. (5) (a) Ogata, M.; Hattori, T.; Takeuchi, R.; Usui, T. Novel and facile synthesis of furanodictines A and B based on transformation of 2acetamido-2-deoxy-d-glucose into 3,6-anhydro hexofuranoses. Carbohydr. Res. 2010, 345, 230−234. (b) Chiku, K.; Nishimoto, M.; Kitaoka, M. Thermal decomposition of β-D-galactopyranosyl-(1−3)-2-acetamido-2-deoxy-D-hexopyranoses under neutral conditions. Carbohydr. Res. 2010, 345, 1901−1908. (c) Drover, M. W.; Omari, K. W.; Murphy, J. N.; Kerton, F. M. Formation of a renewable amide, 3-acetamido-5acetylfuran, via direct conversion of N-acetyl-D-glucosamine. RSC Adv. 2012, 2, 4642−4644. (6) (a) Morgan, W. T. J.; Elson, L. A. A colorimetric method for the determination of N-acetylglucosamine and N-acetylchrondrosamine. Biochem. J. 1934, 28, 988−995. (b) Beau, J. M.; Rollin, P.; Sinay, P. Structure du chromogène i de la éaction de morgan-eljon. Carbohydr. Res. 1977, 53, 187−195. (7) (a) Osada, M.; Kikuta, K.; Yoshida, K.; Totani, K.; Ogata, M.; Usui, T. Non-catalytic synthesis of Chromogen I and III from N-acetyl-Dglucosamine in high-temperature water. Green Chem. 2013, 15, 2960− 2966. (b) Kuhn, R.; Kruger, G. 3-Acetamino-furan aus N-acetyl-Dglicosamin; ein Beitrag Zur Theorie der Morgan-Elson-Reaktion. Chem. D
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