Synthesis of Precursor Glucosamine Building Blocks of Chitin
Department of Chemistry, National Institute of Technology, Warangal, India
- *Corresponding Author:
- Sonnaila SK
Chemistry, National Institute of Technology, Warangal,
Received date: 16-07-2016; Accepted date: 29-07-2016; Published date: 05-08-2016
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The acylation reaction is an important process for biological and chemical applications. Biologically, this reaction is used in a mechanism critical to numerous cellular processes, such as protein assembly and regulation. This article reviews the state of the art of microwave-assisted reactions and the influence of microwaves on mass and heat transfer. The heating behaviour of representative test reactions and single substances is compared for heating with microwaves and thermal energy.
Homogenous reactions, Acylation,
Beckmann rearrangements, NMR.
Differentially protected glucosamines are very important structural units of many bioactive products which
are synthesized in human body. β–(1-4) linked N-acetyl glucosamine moiety is a frequently occurring structural unit
in various naturally and biologically important oligosaccharides and their conjugates.
Chitin is a structural polysaccharide in crab shells, and chitobiose is usually found at the reducing end of Nglycan
residues of glycoproteins. Of these biologically active chitooligosaccharides, chitotetraose has the highest
affinity among chitooligosaccharides to bind to rat NKR-PL antigen, a carbohydrate-binding protein in rat natural
killer (NK) cells [1-16].
Chitosan is one of the most abundant renewable polysaccharides prepared from chitin by deacetylation.
Chitosan and chitosanase are attracting a wide attention in their potential application in medicine, industry and
agriculture. Also, chitooligosaccharides have received much more interest, because they are not only water-soluble but also possess distinctive biological activity [16-24], such as antitumor, antifungal and antibacterial activities,
immuno-enhancing effects [24-29], and promote host defense against infection of certain pathogens in mice.
The main objective of the project is to synthesize the precursor monomer building block from glucosamine
hydrochloride as starting material.
Results and Discussions
Synthesis of differentially protected glucosamines
Glucosamine derivatives are most important building blocks in carbohydrate chemistry for synthesizing
oligosaccharides [29-38]. Synthesis of our monosaccharide building block starts with insitu preparation of triflic azide
from triflic anhydride and sodium azide for the conversion of 2-amino group in the glucosamine to azide followed by
peracetylation and anomeric deacetyation furnishes the common precursor.
1H NMR and 13C NMR were recorded on Bruker Avance-400MHz NMR machine using solution in CDCl3. 1H
NMR referred respectively to TMS used as an internal standard and the central line for CDCl3. Chemical shifts were
reported in (δ) ppm and coupling constants (J) reported in Hz. Pyridine was purchased from Merck. Triflic
anhydride and other chemicals used were purchased from Aldrich. DCM was freshly distilled from CaH2 [39-53].
Methanol was distilled from MgSO4. Column Chromatography was performed over silica gel from SISCO, using
hexanes and ethyl acetate mixture as eluent. Solvents were removed under reduced pressure on rotovap. Organic
extracts were dried with anhydrous Na2SO4. The visualization of spots on TLC plates was effected by exposure to
5%MeOH in H2SO4.
Preparation of -2-azido-2-deoxy-D-glucose
1. Preparation of TfN3:
To a solution of NaN3 (15g, 230mmol) in water (30mL) CH2Cl2 (40mL) was added at 0°C. The mixture is
stirred vigorously and treated with Tf2O (7.8mL, 46.36mmol). The reaction mixture was stirred at 0°C for 2.5h. The
aqueous phase was extracted with CH2Cl2. Combined organic layers were washed with saturated Na2CO3, dried over
Na2SO4 and concentrated in vacuo then immediately used for the reaction [54-69].
2. Conversion of 2-amino group to azide:
To a solution of glucosamine hydrochloride (5g, 23.18mmol) in water (74mL), CuSO4 5H2O (55mg,
0.22mmol) and K2CO3 (4.8g, 36mmol) were added. Then methanol (50mL) was added to the reaction mixture
followed by addition of TfN3 solution (prepared from triflic anhydride and sodium azide) [70-84]. Methanol was added
until the solution become homogenous (~25mL). The light blue color solution was allowed to stir for 24h at room
temperature. After completion of the reaction, solvents were removed to obtain compound 2 which was used
directly for the next step.
Preparation of 1, 3, 4, 6-tetra-O-acetyl-2-azido-2-deoxy α/β-D-glucopyranose:
To the azido compound 2 in pyridine (25mL), Ac2O (25mL) and catalytic DMAP were added and the
reaction mixture was allowed to stir for 12h [85-89]. After completion of the reaction by TLC monitoring, it was worked
up with EtOAc and dried over Na2SO4 followed by removal of solvent on rotovap and purified by column
chromatography with Hexane and Ethyl acetate as eluents (3:1) to afford desired compound 3.
Yield = 35%
1H NMR (400 MHz, CDCl3): δ 5.55 (d, J = 8.6 Hz, 1H), 5.09-5.05 (m, 2H), 4.3 (dd, J=12.5, 4.4 Hz, 1H), 4.08 (dd, J=1.9, 12.5 Hz, 1H), 3.75 (m, 1H), 2.2 (s, 3H), 2.10 (s, 3H), 2.08 (s, 1H), 2.03 (s, 3H).
Preparation of 3, 4, 6-tetra-O-acetyl-2-azido-2-deoxy α/β-D-glucopyranose:
Peracetylated compound 3 (3g, 8.1mmol) was dissolved in dry DMF (30mL), to this ammonium acetate (1.25g, 16.2mmol) was added. The reaction mixture was stirred at room temperature overnight [90-96]. After completion of the reaction, solvent was removed and pure compound 4 (958mg, 8.04mmol) was obtained by column chromatography (Hexane/EtoAc 3:1) [97-100].
1H NMR (400 MHz, CDCl3): δ 5.48 (m, 1H), 5.4 (d, J=6.4 Hz, 1H), 5.27 (m, 1H),
4.29-4.41(m, 2H), 4.12 (m, 1H), 3.17(m, 1H), 2.2-2.02(m, 9H).
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