Molecules 2016, 21, 620
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.5. Effects of Glycosylation on Water Solubility
We also determined the water solubilities of the EGCG and EGCG glycosides. The solubility
of EGCG was 16.05 mM, whereas the solubilities of EGCG-G1 and EGCG-G2 were 240.93 mM and
04.73 mM, or 15 and 31 times higher than for EGCG. Table 2 shows the increase in the water solubility
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of the EGCG glycosides and that the number of glycol units improved the aqueous solubility of
the compounds.
Table 2. Solubilities of EGCG and EGCG glycosides.
Compound
Solubility in Water a (mM)
Relative Solubility
EGCG
EGCG-G1
EGCG-G2
16.05 ˘ 1.23
240.93 ˘ 1.91
504.73 ˘ 0.57
1
15
31
a. Mean ˘ standard deviation (n = 3).
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. Experimental Section
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.1. General Information
D-Glucose was purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).
EGCG was obtained from Chengdu Biopurify Phytochemicals, Ltd. (Chengdu, China). 3-(4,5-Dimethyl-
thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) was obtained from Sigma Aldrich (St. Louis,
MO, USA). Quantitative Assay Kit was purchased from Sangon Biotech Co., Ltd. (Shanghai, China).
H O Quantitative Assay Kit was purchased from Sangon Biotech Co., Ltd. The ZORBAX SB-C
18
2
2
HPLC column was purchased from Agilent Technologies Co., Ltd. (Guangzhou, SC, China). KQ-300DE
ultrasonic cleaner was purchased from Kun Shan Ultrasonic Instruments Co., Ltd. (Jiangsu, China).
MCF-7 and MDA-MB-231 were purchased from the American Type Culture Collection (Rockville,
MD, USA). All other chemicals used were of analytical grade. MS data were obtained in the ESI
mode on an Qstar Pulsar instrument (API, Manchester, UK). HRMS data were obtained in the ESI
mode on an LCMS-IT-TOF instrument (Shimadzu, Kyoto, Japan). NMR spectra were acquired on
a Bruker AV-400 or DRX-500 instrument (Bruker BioSpin GmbH, Rheinstetten, Germany), using
tetramethylsilane (TMS) as an internal standard. Column chromatography (CC) was performed on
flash silica gel (200–300 mesh; Qingdao Makall Group Co., Ltd.; Qingdao, China). All reactions were
monitored using thin-layer chromatography (TLC) on silica gel plates.
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.2. General Procedure for the Synthesis of EGCG-G1 and EGCG-G2
D-Glucose (18 g, 100 mmol) was suspended in acetic anhydride (100 mL), and sodium acetate
˝
11 g, 130 mmol) was added with heating and stirring at 100 C for 20 min. The mixture was
(
cooled, poured into 500 mL of ice water and stirred for 1 h. The product was washed with aqueous
saturated sodium bicarbonate solution and brine, dried, and evaporated to a syrup, from which
the pentacetate crystallized from 95% alcohol. Next, the crystals were treated with a 33% (w/w)
solution of hydrobromic acid in acetic acid (90 mL, 0.5 mmol). After 90 min, the solution was
diluted with dichloromethane (150 mL) and washed with ice-cold water (3
aqueous saturated sodium bicarbonate solution (150 mL). The organic phase was dried with anhydrous
magnesium sulfate, filtered and concentrated to afford crude 2,3,4,6-tetra-O-acetyl- -D-glucopyranosyl
ˆ
150 mL), followed by
α
bromide as a white solid (38 g, 94%) [35]. EGCG (1 g, 2.2 mmol) was dissolved in acetone (10 mL),
and potassium carbonate (0.6 g, 4.3 mmol) was added with slow stirring over 30 min. Then, glucosyl
˝
bromide (0.9 g, 2.2 mmol) was added with heating and stirring at 55 C for 12 h. The mixture was
cooled and filtered, the filtrate was concentrated and dried in vacuo overnight. A potassium hydroxide
solution (1.2 mmol dissolved in 3 mL of H O) was added to an ice-cooled solution of crude product
2
˝
in CH OH (3 mL). The mixture was stirred at 0–4 C for 3 days and then neutralized with Dowex
3