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stirred (500 rpm). After the reaction, the mixture was centrifuged
for 20 min (4000 rpm) to separate the catalyst. After filtration of
the collected supernatant solution by a filter (Millex-LG 0.20 mm),
a part of the solution was analyzed by HPLC analysis.
acids were confirmed by NMR and mass spectroscopy meas-
urements (see the Supporting Information, SI).
In summary, we have demonstrated the versatility of Au
nanoparticles supported on basic materials as a reusable heter-
ogeneous catalyst for aerobic oxidation of glucosamine deriva-
tives into the corresponding a-amino acids in water under
mild reaction conditions. Further application of the presented
catalytic system for the selective transformation of biomass-de-
rived compounds into value-added chemicals is currently
under investigation.[32]
Product analysis by HPLC: Yield of GlcNA was determined by using
a HPLC (WATERS 515 pump) equipped with Shodex Asahipak
NH22P-50 3E column and using
(WATERS 2414). The conditions were set as follows: eluent 40%
aqueous EtOH; column temperature 323 K; flow rate 0.5 mLminꢀ1
a refractive index detector
.
For HPLC analysis of GaINA, GlcNAcA, GalNAcA, and ManNAcA,
pure water was used as an eluent with 1 mLminꢀ1 flow rate.
Isolation of products: After the reaction, the heterogeneous mix-
ture was centrifuged for 20 min (4000 rpm) to separate the cata-
lyst. The collected supernatant was condensed under a vacuum at
room temperature. In the case of the oxidation of GlcN-HCl, the
condensed liquid was mixed with MeOH. After centrifuging the
mixture for 20 min (4000 rpm), the precipitate was recovered and
dried under a vacuum, yielding a white powder. The powder was
subjected to 1H-, 13C-, HMQC NMR, and ESI-MS spectroscopy.
Comparison with authentic samples confirmed that the isolated
compound was GlcNA (see SI in the Supporting Information). In
the case of the oxidation of GaIN-HCl into GalNA, the condensed
liquid was mixed with MeOH and acetone (acetone/condensed
liquid=1:6 in volume). After centrifuging the mixture for 20 min
(4000 rpm), a precipitate was recovered and dried under a vacuum,
Experimental Section
Materials: HAuCl4·4H2O, ammonium solution (25%, aqueous), gal-
actosamine hydrochloride (GalN-HCl), and N-acetyl-galactosamine
(GaINAc) were purchased from Wako Pure Chemicals. d-(+)-glucos-
amine hydrochloride (GlcN-HCl, 98% purity), N-acetyl-glucosamine
(GlcNAc), and N-acetyl-mannosamine (ManNAc) were purchased
from TCI. d-glucosaminic acid (GlcNA) was purchased from Tronto
Research Chemical Inc. Hydrotalcite (HT, Mg/Al=5, AD-550 PF) was
supplied by Tomita Pharmaceuticals Co., Ltd. MgO was obtained
from the Catalysis Society of Japan as JRC-MGO-4 (particle size;
1000 ꢁ). MeOH and acetone were purchased from Kanto
Chemicals.
1
yielding a white powders. The powders were subjected to H-, 13C-,
1H-1H COSY, HSQC NMR, and FT-ICR MS spectroscopy. For the prod-
ucts of GlcNAcA, GaINAcA, and ManNAcA, the condensed liquid
was simply evaporated, and the obtained precipitate was dried
under a vacuum, yieldin a white powders. All data are consistent
with the structures of GlcNAcA, GaINAcA, and ManNAcA (see SI in
the Supporting Information).
Preparation of supported Au nanoparticle catalysts: HT (2 g) was
added to an aqueous solution of HAuCl4·4H2O (0.2 mmol, 80 mL),
and the mixture was stirred at room temperature. After 10 min stir-
ring, an aqueous NH3 solution (25%, 0.8 mL) was added, and the
mixture was stirred for 6 h at room temperature (pH=10–11), fol-
lowed by refluxing for 30 min. The resultant solid (pale yellow) was
filtered and washed with water (1.0 L) and dried at room tempera-
ture. The obtained solid was calcined at 473 K for 4 h, affording
Au0/HT catalyst (pale purplish red). The Au0 nanoparticles on vari-
ous supports were also prepared by performing the same proce-
dure. The real loading amounts of Au for each sample were esti-
mated by means an inductively coupled plasma (ICP) analysis and
are listed in Table 1.
Acknowledgements
S.N. is thankful for the support from Intellectual Property High-
way Promotion of the Japan Science and Technology Agency
(JST), Japan. K.E. appreciates the Grant-in-Aid for Scientific Re-
search (C) (No.22560764) support by the Ministry of Education,
Culture, Sports, Science, and Technology (MEXT), Japan. The syn-
chrotron radiation experiments were performed at BL01B1 in the
SPring-8 under the approval of the Japan Synchrotron Radiation
Research Institute (JASRI) (proposal No. 2012B1610).
Characterization: Inductively coupled plasma atomic emission
spectroscopy (ICP-AES) was performed by using a Shimadzu ICPS-
7000 ver.2 to estimate the weight% of Au in the catalysts. Trans-
mission electron microscopy (TEM; Hitachi H-7100) was performed
at 100 kV accelerating voltage. X-ray absorption fine structure
(XAFS) measurements was performed at the BL01B1 station in
SPring-8 synchrotron radiation facility, Japan. Au L3-edge XAFS
spectra was recorded at room temperature by the transmission
method. NMR spectra were measured using AVANCE III (Bruker
Keywords: amino acids
·
heterogeneous catalysis
·
nanoparticle · oxidation · sugars
1
1
BopSin Inc.) at 400 MHz for H, 101 MHz for 13C, H–1H correlation
spectroscopy (COSY), hetero-nuclear multiple quantum coherence
(HMQC), and hetero-nuclery multiple-bond connectivity (HMBC
modes). Analysis of the product by oxidation of GlcN-HCl was per-
formed on ESI mass spectroscopy (LCQ DECA XP, Thermoelectron
Co. Ltd.). Fourier transform ion cyclotron resonance (FT-ICR) mass
spectroscopy was measured by using a Solarix-JA (Bruker Daltonics
Co. Ltd.) to determine the precise mass of GaINA, GlcNAcA, GalNA-
cA, and ManNAcA.
[1] J. Zhang, W. Xia, P. Liu, Q. Cheng, T. Tahirou, W. Gu, B. Li, Marine Drugs
61, 29–38; b) J. S. Mojarrad, M. Nemati, H. Valizadeh, M. Ansarin, S.
General Oxidation Procedure: Oxidation of GlcN-HCl was per-
formed in a Schlenk flask equipped with a reflux condenser. The re-
action was typically carried out using GlcN-HCl (442 mg, 4 mmol),
Au/HT (0.5 g), and distilled water (20 mL) at 313 K for 3 h under an
O2 flow (50 mLminꢀ1). The reaction mixture was magnetically
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2013, 6, 2259 – 2262 2261