Promoting hydrolysis 2015 - Promoting hydrolysis of flavonoid glycosides by microwave irradiation

Promoting hydrolysis of flavonoid glycosides by microwave irradiation
Van-Son Nguyen,a,b Shuang-Lian Cai a, Tang Feng a and Qiu-An Wanga, ?
a College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, P. R. China: b Faculty of Chemical Engineering, Industry University of Ho chi minh City, Vietnam
Corresponding author: Professor Qiu-An Wang
College of Chemistry and Chemical Engineering
Hunan University
Changsha 410082
P. R. China
Phone: +86-731-888222275
Fax: +86-731-88713642
E-mail: wangqa-AT-hnu.edu.cn
ABSTRACT
The efficient hydrolysis of flavonoid glycosides hesperidin (1a), naringin (1b) and rutin (1c) to corresponding flavonoid aglycone hesperetin (2a), naringnin (2b) and quercetin (2c) respectively by employing microwave irradiation (MWI) method was studied. The test was designed to investigate the influential factors of the hydrolysis process under a microwave-assistance such as power of microwave, reaction temperature and irradiation time. The results show that microwave assistance can greatly accelerate the hydrolysis rate of flavonoid glycosides, shorten the reaction time, and increase the yield of flavonoid aglycone. The optimized parameters are: power 500-600 W, irradiation time 30-45 min, reaction temperature 80-90 oC. Therefore, the microwave assistance method has many advantages, such as, it is highly effective, it consumes less time, it is environmentally friendly and higher product purities.
Keywords: flavonoid glycoside; flavonoid aglycone; hydrolysis; microwave irradiation
1. Introduction
Over the past two decades, there has been growing interest in applying microwave irradiation (MWI) to organic synthesis. Microwave synthesis method has been a good choice for studying chemical reactions due to its simple operation, spectacular accelerations, higher yields under milder reaction conditions and higher product purities [1-3].
Flavonoids are phenolic secondary metabolites widely distributed throughout the plant kingdom. They have been identified as antitumor agents, antiinflammatory agents, antioxidants and free radical scavengers [4-6]. Essentially, two forms of flavonoids are present in natural products: aglycone and glycosylated flavonoids. Compared to the glycosylated forms, the aglycones show a higher biological activity and bioavailability [7, 8 ].
Hesperidin (1a), naringin (1b) and rutin (1c) are three very abundant and inexpensive natural sources of flavonoid, consisting of an aglycone and an attached disaccharide. The acid hydrolysis of hesperidin, naringin or rutin by conventional heating manner have been reported [9-11], but the cleavage of glycosidic bond used conventional water bath heating usually takes a long time and affords low yields. Thus, we turned to microwave assistance for removing of rutinosyl or neohesperidosyl. The influential factors of the hydrolysis process under microwave irradiation such as power of microwave, irradiation time and reaction temperature have been investigated. The results show that microwave assistance can greatly accelerate the hydrolysis rate of flavonoid glycosides, shorten the reaction time and increase the yield of flavonoid aglycone.
Scheme 1.
Scheme 1. Synthesis routes of flavonoid aglycones from flavonoid glycosides by microwave irradiation hydrolysis.
2. Results and discussion
Our present method provides an efficient synthesis of flavonoid aglycone hesperetin (2a), naringnin (2b) and quercetin (2c) from hesperidin (1a), naringin (1b) or rutin (1c), respectively, as depicted in Scheme 1.
From the process of hydrolysis of flavonoid glycosides hesperidin (1a), naringin (1b) and rutin (1c), it was found that the reaction did not happen at temperature below 60 oC, although we prolonged reaction time up to 45 minutes under microwave irradiation (power from 400 to 700 W). When the temperature was increased up to 70 oC under same MWI condition, the glycosidic bond cleavage of compound 1a, 1b and 1c happened. However, the process took place at a low efficiency (shown in Table 1). Many sub-products were formed that lead to some difficulty in product separation.
The process of hydrolysis occurred smoothly when the temperature was up to 80 oC or 90 oC, especially at the microwave irradiation power of 500 W or 600 W, and reaction time from 30 to 45 min. After finishing the reaction, the product was put into water immediately, followed by water washing. The average yields of flavonoid aglycone, which was obtained by averaging the data from three independent experiments, are shown in Table 1.
Table 1.
Table 1. The yields of flavonoid aglycone hesperetin (2a), naringnin (2b) or quercetin (2c) from corresponding flavonoid glycosides by MWI hydrolysis.
.
Figure. 1. Graph of speed optimization of time, temperature, microwave power in the reaction of hydrolysis the glycosidic bond in of hesperidin (at 80 °C and 90 °C, in 30~45 min), afforded the product hesperetin in 90 % yield. Each column represents the average of three independent experiments.
In Figure 1, each column represents the average yields of three same process of hydrolysis of flavonoid glycosides, hesperidin did not happen hydrolysis at the temperature of 60 oC, or happened at a low efficiency at 70 oC, even though the time was adjusted up to 45 min, the obtained yield of hesperetin did not exceed 20%. The hydrolysis of hesperidin gives 90% yield of hesperetin in 30 min by increasing the temperature up to 80 or 90 oC. While the conventional method which takes 6-7 hours affords a very low yield of product (ca. 65%) mixed with many impurities.
Figure 2. Graph of speed optimization of time, temperature, capacity of the microwave power in the reaction of hydrolysis the glycosidic bond in of naringin (at 80 °C and 90 °C, in 30-45 min), afforded the product naringnin in 89% yield. Each column represents the average yield of three independent experiments.
For naringin, the hydrolysis of glycosidic bond was similar to the process of hydrolysis of hesperidin. Only an about 68% yield of naringnin was gained in traditional methods. But in our experiment results as depicted in Figure 2, it was found that the process gave a higher yield of naringnin when methanol was used because of the better solubility of hesperidin in methanol. In 45 min of time and 90 °C of temperature, the reaction efficiency was, lower than that of the process at 80 °C due to the elevated evaporation of solvent resulting in the higher acid and carbonation.
Figure. 3. Graph of speed optimization of time, temperature, capacity of the microwave-irradiated in the reaction of hydrolysis the glycosidic bond in of rutine (at 80 °C and 90 °C, in 30-45 min), afforded the product quercetin in 95% yield. Each column represents the average yield of three independent experiments.
Similar to the two above processes, the results are described in Figure 3. The hydrolysis of rutine was done at 60 and 70 °C to give the corresponding aglycone quercetin and obtained a good result at 80 or 90 °C (95% yield). If using the conventional method which takes 5-6 hours gave a very low yield of product (ca. 70%) mixed with many impurities.
3. Experimental
3.1 General experimental procedures
The 1H NMR (400 MHz) and 13C NMR(100 MHz) spectra were recorded on a Bruker AM-400 instrument, using tetramethylsilane as an internal standard, chemical shifts (δ) in ppm, coupling constants (J) in Hz, Mass spectra were determined with VG Autospec-3000 spectrometer by the EI method.. Melting points were determined by an XRC-1 apparatus and are uncorrected. Microwave irradiation were performed with XH-MC-1 microwave reactor (Beijing Xinghu Science and Technology Development Co., China). Commercially available AR or chemical pure reagents, and anhydrous solvent removed water and redistilled were employed.
3.2. Microwave-assistance hydrolysis of hesperidin, naringin and rutin.
The solution of hesperidin (1a), naringin (1b) or rutin (1c) (500 mg) in methanol or ethanol (15 mL) and 1.5 mL concentrated sulfuric acid was stirred under microwave irradiation at 400, 500, 600 and 700 W for 15, 30 and 45 min with the corresponding temperature from 60, 70, 80 and 90 °C respectively (the instrument adjust the heating power to keep this temperature constant and stable). The mixture was cooled to room temperature, and then poured into ice water. The resulting precipitate was filtered, then washed with water, drying, crystallized from methanol to give compounds 2a or 2b, 2c, the products yield as depicted in Table 1.
Compound 2a: Light-yellow solid; mp 230-232 °C (lit.[12]: 228-230 oC); 1H NMR (400 MHz, DMSO-d6): δ 12.14 (s, 1H, 5-OH), 10.84 (s, 1H, 7-OH), 9.13(s, 1H, 4’-OH), 7.01 ? 6.82 (m, 3H, 2’-H and 5’-H and 6’-H), 5.90 (d, J = 3.3 Hz, 2H, 6-H+ 8-H), 5.43 (dd, J= 9.2, 2.8 Hz, 1H, 2-H), 3.78 (s, 3H, 4’-OCH3), 3,20 (dd, 1H, J= 15.1, 2.4 Hz, 3-H trans), 2.871 (dd, 1H, J = 15.1, 2.8 Hz, 3-H cis); 13C NMR (100 MHz, DMSO-d6): δ 196.6 (C4), 167.1 (C7), 163.9 (C5), 163.2 (C8a), 148.3 (C4’), 146.9 (C3’), 131.6 (C1’), 118.2 (C6’), 114.5 (C5’), 112.4 (C2’), 102.3 (C4a), 96.3 (C8), 95.5 (C6), 78.7 (C2), 56.1 (4’-OCH3), 42.5 (C3); ESI-MS: m/z 303 [M+H]+.
Compound 2b: Light-yellow solid; mp 224-226 °C (lit.[13]: 225-226 oC); 1H NMR (400 MHz, DMSO-d6): δ 12.17 (s, 1H. 5-OH), 10.81 (s, 1H, 4’-OH), 9.62 (s, 1H, 7-OH), 7.32 (d, J = 8.2 Hz, 2H, 2’-H and 6’-H), 6.81 (d, J = 8.2 Hz, 2H, 3’-H and 5’-H), 5.91 (s, 2H, 5-H and 8-H), 5.43 (d, J = 9.8 Hz, 1H, 2-H), 3.24 ((dd, J= 15.3, 2.2 Hz, 1H, 3-H trans), 2.69 (dd, J= 15.3, 2.5 Hz, 1H, 3-H cis); 13C NMR (100 MHz, DMSO-d6): δ 196.8 (C4), 167.1 (C7), 163.9 (C5), 163.4 (C8a), 158.2 (C4’), 129.3 (C1’), 128.9 (C2’ and C6’), 115.7 (C3’ and C5’), 102.2 (C4a), 96.3 (C8), 95.5 (C6), 78.9 (C2), 42.4 (C3); ESI-MS: m/z 273 [M+H]+.
Compound 2c: Yellow solid; mp 315-316 °C (lit.[14]: 112-116 oC); 1H NMR (400 MHz, DMSO-d6): δ 12.56 (s, 1H, 5-OH), 10.87 (s, 1H, 3-OH), 9.69 (s, 1H, 7-OH), 9.46 (s, 1H, 3’-OH), 9.40 (s, 1H, 4’-OH), 7.73 (s, 1 H, 6’-H), 7.60 (d, J = 8.5 Hz, 1H, 5’-H), 6.94 (d, J = 8.5 Hz, 1H, 2’-H), 6.47 (s, 1H, 6-H), 6.25 (s, 1H, 8-H); 13C NMR (100 MHz, DMSO-d6): δ 176.3 (C4), 164.3 (C7), 161.2 (C5), 156.6 (C8a), 148.1 (C4’), 147.3 (C5’), 145.5 (C2), 136.2 (C3), 122.4 (C1’), 120.5 (C2’), 116.1 (C3’), 115.5 (C6’), 103.5 (C4a), 98.6 (C8), 93.8 (C6); ESI-MS: m/z 303 [M+H]+.
Acknowledgments
We thank the National Twelfth Five-year plan for science &Technology Support (No. 2012BAD31BO2) and the Natural Science Foundation of Hunan Province (No. 14JJ2048) for financial support
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Captions
Scheme 1.
Table 1.
temp [°C] Power/W 500 600 700 400 500 600 700 400 500 600 700
Time 400
(min) Product yield (%) 2a 2a 2a 2b 2b 2b 2b 2c 2c 2c 2c
　 2a
　 15 0 0 0 0 0 0 0 0 0 0 0 0
60 30 0 0 0 0 0 0 0 0 0 0 0 0
　 45 0 0 0 0 0 0 0 0 0 0 0 0
　 15 3 5 7 6 7 9 9 7 5 6 5 7
70 30 13 16 17 15 12 15 13 15 13 17 15 19
　 45 17 18 19 19 18 18 15 17 19 21 25 21
　 15 55 61 63 63 56 63 67 60 63 65 59 67
80 30 82 83 89 83 72 80 89 87 87 90 93 78
　 45 81 82 87 76 75 78 81 81 89 91 87 81
　 15 60 63 65 67 64 68 69 63 71 66 77 68
90 30 88 87 90 87 73 79 88 87 87 91 95 86
　 45 76 80 85 71 72 65 72 77 86 93 89 84
Graphical Abstract
Promoting hydrolysis of flavonoid glycosides by microwave irradiation
Van-Son Nguyen, Shuang-Lian Cai, Feng Tang, Qiu-An Wang