Pectin is used as a gelling agent in food industry and is reported to have many biological activities. We isolated pectin from fruits of Citrus depressa [1,2] and C. tankan  grown in Okinawa, Japan. We report here the chemical structure of unusually branched pectin isolated from leaves of Artemisia indica which is used as herbal medicine and traditional food in Okinawa, Japan.
Leaves of Artemisia indica were purchased from the Public Market in Naha City, Okinawa, Japan. Polysaccharide was extracted at 80°C in distilled water for 2h and purified as the same methods described in published papers [1-3]. The polysaccharide was fractionated on DEAE Sepharose chromatography resulted in neutral and acidic fractions. ¹H- and ¹³C-NMR spectra were recorded on a FT-NMR Spectrometer (α500, JEOL, Co. Ltd., Japan) at 70°C. Methylation was carried out as described by Ciucanu and Kereck.
D-Galacturonic acid (molar ratio, 50), L-arabinose (6), D-galactose (4), L-rhamnose (3), D-xylose (1) D-glucuronic acid (1), acetic acid, methyl ester, and methyl ether were identified by chemical, HPLC-PAD, ¹H- and ¹³C-NMR and methylation analyses. The results indicated that the polysaccharide was identified as a pectin. The molecular mass of the pectin was estimated to be 1.3×10⁴. Each carbon atom from C1 (anomeric) to C6 of 1,4-linked α-D-galacturonic acid on ¹³C-NMR spectrum was assigned as pairing (double) signals suggesting that long 1,4-linked α-D-galacturonic acid side-chains were involved in the pectin molecule. Furthermore, single, but a little broad signal was assigned from H1 (anomeric) to H6 of D-galacturonic acid residue on proton NMR spectrum supporting that 1,4-linked α-D-galacturonan side-chains were involved. Seventeen of partially methylated alditol acetates were identified from native, neutral, and acidic fractions by methylation analysis. L-Rhamnose residues were branching sugar on the main chain of the pectin where substituted at C-2 or C-4. Three different side-chains (D-galacturonan, L-arabinan, and D-galactan) were involved in the pectin molecule. The chemical structure of the acidic fraction of the pectin was proposed. This study is the first to report on the long side chains of 1,4-linked α-D-galacturonan are involved in the pectin isolated from Artemisia indica.
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