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Regioselective ortho-hydroxylations of flavonoids by yeast Sandra Sordon, Anna Madej, Jaros#aw Pop#o#ski, Agnieszka Bartma#ska, Tomasz Tronina, Ewa Brzezowska, Piotr Juszczyk, and Ewa Huszcza J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.6b02210 • Publication Date (Web): 21 Jun 2016 Downloaded from http://pubs.acs.org on June 23, 2016
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Journal of Agricultural and Food Chemistry
Regioselective ortho-hydroxylations of flavonoids by yeast
Sandra Sordon1*, Anna Madej1, Jarosław Popłoński1, Agnieszka Bartmańska1, Tomasz Tronina1, Ewa Brzezowska1, Piotr Juszczyk2, Ewa Huszcza1
1
) Department of Chemistry, Wrocław University of Environmental and Life Sciences,
Norwida 25, 50-375 Wroclaw, Poland 2
) Department of Biotechnology and Food Microbiology, Wrocław University of
Environmental and Life Sciences, Chełmońskiego 37/41, 51-630 Wrocław, Poland
*) Corresponding author: Sandra Sordon Tel.: 0048713205197, Fax: 00483207744, E-mail addresses:
[email protected] 1 Environment ACS Paragon Plus
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ABSTRACT
2
Natural flavonoids, such as naringenin, hesperetin, chrysin, apigenin, luteolin,
3
quercetin, epicatechin and biochanin A were subjected to microbiological transformations by
4
Rhodotorula glutinis. Yeast was able to regioselective C-8 hydroxylation of hesperetin, luteolin
5
and chrysin. Naringenin was transformed to 8- and 6-hydroxyderivatives. Quercetin,
6
epicatechin and biochanin A did not undergo biotransformation. A metabolic pathway for the
7
degradation of chrysin has been elucidated. The metabolism of chrysin proceeds via an initial
8
C-8 hydroxylation to norwogonin, followed by A-ring cleavage to 4-hydroxy-6-phenyl-2H-
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pyran-2-one.
10 11
Keywords: flavonoids, biotransformation, yeast, Rhodotorula glutinis, hydroxylation,
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regioselectivity
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Journal of Agricultural and Food Chemistry
INTRODUCTION
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Flavonoids are a diverse group of ubiquitous plant secondary metabolites. Health
15
benefits associated with them resulted in a significant increase of interest in this class of
16
compounds. Some flavonoids, such as naringenin, naringin, hesperidin or chrysin, are
17
inexpensively available in a large quantities (see supplementary data). They may serve as a
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viable source of lead compounds for the development of food additives, preservatives,
19
antioxidants and also drug components.1
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Biotransformation is one of the possible methods for the preparation of various
21
derivatives of flavonoids.2, 3 The use of microorganisms as a biocatalyst is a relevant strategy to
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obtain high added value natural compounds from both cheap and readily available substrates.3, 4
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These processes offer more advantages compared to conventional catalysts such as mild
24
reaction conditions, high catalytic activities with high regio- and stereoselectivity.4, 5 Moreover,
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according to the European Union Law, the products obtained by biotransformation of natural
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compounds may be considered as natural ones (EU Directive 88/388/EEC).
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It has been reported that that a protective effect of diet flavonoids against several
28
diseases, among them atherosclerosis6, is connected to their antioxidant properties. It is general
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considered that a higher number of hydroxyl groups in a flavonoid results in a higher
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antioxidant activity.7, 8 Briefly, the presence of two hydroxyl groups in an ortho position of ring
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B, especially the 3´,4´-dihydroxyphenolic structure, is the most important structure for
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scavenging actions. Also of importance is the presence of hydroxyl groups at positions 5, 6 and
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7 in the ring A. The ability of flavonoids to chelate metals results from the presence metal
34
complexing domains between the 5-hydroxyl and 4-carbonyl group, the 3-hydroxyl and 4-
35
carbonyl group and between the 3´,4´-hydroxyl groups. Consequently, development of
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microbial hydroxylation of flavonoids is significant in the synthesis of active antioxidants for
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biological activity in human.
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Our previous microbial transformation research indicated the capability of the yeast
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Rhodotorula marina to efficient hydroxylation of naringenin at C-6 or C-8 position to
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carthamidin and isocarthamidin, respectively.9,
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greater antioxidant activity than either naringenin and its glycoside naringin.11 These
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encouraging results prompted us to search for new useful red yeast biocatalysts, and then to
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undertake studies on preparation of valuable derivatives of natural flavonoids by
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biotransformation in the selected yeast cultures.
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These metabolites showed significantly
45 46
MATERIALS AND METHODS
47 48
Compounds
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Naringenin (1), hesperidin, chrysin (3), biochanin A, (-)-epicatechin, quercetin, ascorbic acid
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and DMSO-d6 were purchased from Sigma-Aldrich, Sephadex LH-20 from Pharmacia,
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acetonitrile HPLC grade, silica gel 60 and TLC plates from Merck, peptone from Biocorp
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(Poland). Other chemicals and solvents were purchased from POCH (Poland).
53 54
Hesperetin (2) was obtained by acidic hydrolysis of hesperidin.
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A solution of 1.25 g of hesperetin (2) (≥80%), 500 mg of ascorbic (added to prevent oxidation
56
of the products of hydrolysis), 50 mL of 2M hydrochloric acid and 50 mL of methanol was
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heated under reflux for 10 h. After cooling, Na2CO3 was added to reach the pH about 4 and the
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reaction mixture was extracted three times with 50 mL of ethyl acetate. The combined fractions
59
were washed with distilled water, dried over anhydrous magnesium sulfate and concentrated.
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After purification by column chromatography on silica gel 60 using mixture chloroform :
61
methanol (10 : 1, v/v) as eluent, 307.0 mg of hesperetin (2) was obtained with purity greater
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than 95% (according to HPLC).1H NMR (600 MHz, DMSO-d6) δ (ppm): 2.70 (dd, 1H, J =
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17.1, 3.1 Hz, H-3ax), 3.18 (dd, 1H, J = 17.1, 12.3 Hz, H-3eq), 3.77 (s, 3H, C4´-O-CH3), 5.42
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(dd, 1H, J = 12.3, 3.1 Hz, H-2), 5.88 (d, 1H, J = 2.1 Hz, H-6), 5.89 (d,1H, J = 2.1 Hz, H-8),
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6.87 (dd, 1H, J = 8.3, 2.1 Hz, H-6´), 6.92 (d, 1H, J = 2.0 Hz, H-2´), 6.93 (d, 1H, J = 8.3 Hz, H-
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5´), 8.29 (s, 1H, 3´-OH), 9.12 (s, 1H, 7-OH), 12.12 (s, 1H, 5-OH).
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DMSO-d6) δ (ppm): 42.1 (C-3), 55.8 (C4´-O-CH3), 78.3 (C-2), 95.1 (C-8), 95.9 (C-6), 101.9
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(C-10), 112.1 (C-5´), 114.1 (C-2´), 117.8 (C-6´), 131.2 (C-1´), 146.5 (C-3´), 148.0 (C-4´),
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162.9 (C-9), 163.6 (C-5), 166.7 (C-7), 196.3 (C-4).
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C NMR (150 MHz,
70 71
Apigenin (4) was obtined from naringenin (1) by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone
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(DDQ) - oxidation of C2-C3 bond according to the method described by Kim et al.12 1H NMR
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(600 MHz, DMSO-d6) δ (ppm): 6.19 (m, 1H, H-8), 6.48 (m, 1H, H-6), 6.77 (s, 1H, H-3), 6.92
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(m, 2H, H-3´,5´), 7.92 (m, 2H, H-2´, 6´), 10.35 (s, 1H, 4´-OH), 10.82 (s, 1H, 7-OH), 12.96 (s,
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1H, 5-OH).
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103.7 (C-10), 116.0 (C-3´,5´), 121.2 (C-1´), 128.5 (C-2´,6´), 157.3 (C-5), 161.2 (C-4´), 161.5
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(C-9), 163.7 (C-2), 164.1 (C-7), 181.8 (C-4).
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C NMR (150 MHz, DMSO-d6) δ (ppm): 94.0 (C-6), 98.8 (C-8), 102.9 (C-3),
78 79
Luteolin (5) was isolated from artichoke (Cynara scolymus L.) leaf dry extract. Flavonoid
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glycosides included in the dry extract of artichoke were hydrolyzed. For this purpose a mixture
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of 9 g of the extract, 200 mg of ascorbic (added to prevent oxidation of the products of
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hydrolysis), 240 mL of 2M hydrochloric acid and 240 mL of methanol was heated under reflux
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for 6 h. After cooling, Na2CO3 was added to reach the pH about 4 and the reaction mixture was
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extracted three times with 250 mL of ethyl acetate. The combined fractions were washed with
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distilled water, dried over anhydrous magnesium sulfate and concentrated to give 2.75 g of
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extract. After purification by column chromatography on Sephadex LH-20 using methanol as
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eluent, 86.2 mg of luteolin (5) was obtained with purity greater than 98% (according to HPLC).
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1
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Hz, H-6), 6.68 (s, 1H, H-3), 6.88 (d, 1H, J = 8.2 Hz, H-5´), 7.39 (s, 1H, H-2´), 7.41 (d, 1H, J =
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9.6 Hz, 6´-H), 9.49 (s, 1H, 4´-OH), 9.99 (s, 1H, 3´-OH), 10.84 (s, 1H, 7-OH), 12.98 (s, 1H, 5-
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OH). 13C NMR (150 MHz, DMSO-d6) δ (ppm): 93.9 (C-8), 98.9 (C-6), 102.9 (C-3), 103.8 (C-
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10), 113.4 (C-2´), 116.1 (C-5´), 119.1 (C-6´), 121.5 (C-1´), 145.8 (C-3´), 149.8 (C-4´), 157.4
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(C-9), 161.5 (C-5), 164.0 (C-2), 164.2 (C-7), 181.7 (C-4).
H NMR (600 MHz, DMSO-d6) δ (ppm): 6.18 (d, 1H, J = 1.80 Hz, H-8), 6.44 (d, 1H, J = 1.8
94 95
Analytic procedures
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TLC was carried out on silica gel 60 F254 (0.2 mm thick) plates. Compounds were detected by
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spraying the plates with 1% Ce(SO4)2 and 2% H3[P(Mo3O10)4] in 10% H2SO4. HPLC was
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performed on a Waters 2695 Alliance instrument with a photodiode array detector Waters 2996
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(detection at 290 and 370 nm wavelength) equipped with the analytical HPLC column Agilent
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ZORBAX Eclipse XDB 5 µm (46 × 250 mm), which was eluted at 0.8 mL min. A linear
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gradient was composed of (A) acetonitrile and (B) 0.1% acetic acid in water. After injection
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solvent A increased from 25% to 38% over 10 min and held at 38% for 18 min, then further
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decreased from 38% to 25% over 2 min, and finally held 25% for 6 min.
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NMR spectra (1H NMR,
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(HSQC, HMBC)) were recorded on a MHz DRX Bruker Avance™ 600 (600 MHz) instrument
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in DMSO-d6. OD 600 nm analysis were performed using a Spectrofotometer Cintra 303, GBC,
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Positive-ion HR-ESIMS spectra were measured on a Bruker micrOTOF-Q spectrometer.
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C NMR, DEPT 135°, 1H-1H NMR (COSY), and 1H-13C NMR
108 109
Microorganisms
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Microorganisms used in this work were purchased from Institute of Biology and Botany,
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Wrocław Medical University (indexed AM) and Department of Chemistry, Wrocław
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University of Environmental and Life Sciences (indexed KCh). The red yeast cultures used for
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preliminary study were as follows: Rhodotorula glutinis AM242, Rhodotorula glutinis
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KCh735, Rhodotorula rubra AM4 and Rhodotorula rubra AM82.
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Biotransformation procedure
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The yeast were cultivated on rotary shakers (130 rpm, 6.5 amplitude) at 28 °C in 100-
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mL Erlenmeyer flasks with 30 mL of the medium in the preliminary screening experiments and
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in 300-mL Erlenmeyer flasks containing 100 mL of the medium in the preparative scale
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fermentation. The growth medium for biotransformation processes (Sabouraud medium)
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contained 3% glucose and 1% peptone. The cultures on agar slants were used to obtain the
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inoculation culture, and then 2-day inoculation culture were transferred to the main cultures
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media (1 mL to the 30 mL and 3 mL to the 100 mL). After three days of growth the substrates
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were added.
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In the screening studies, 5 mg of naringenin (1) dissolved in 0.5 mL of acetone was
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added to the culture. Experiments were performed in triplicate. Biotransformations were
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performed for 48 hours, acidified using 1M HCl to pH about 5. Then each of the reaction
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mixture was extracted with ethyl acetate (2 x 10 mL).
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In the preparative biotransformations, a total of 80 mg of each substrate dissolved in 4 mL of
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methanol (for substrates 1, 2, 5) and DMSO (for substrates 3, 4) or was equally distributed
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among four flasks with 3-day fungal cultures of OD600 = 22.40 ± 0.99 (1 mL each) to give a
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final concentration of 200 mg / L. Reactions were carried out for 1 to 6 days, acidified using
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1M HCl to pH about 5, and then each of the reaction mixture was extracted with ethyl acetate
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(3 x 40 mL).
135 136
The progress of biotransformations was monitored by TLC and HPLC. Substrate controls consisted of substrate and a sterile growth medium incubated without microorganism.
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Preparative transformation of chrysin (3) leading to its degradation was carried out under similar conditions except that tetrahydrofuran was used to dissolve the substrate.
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Products isolation and analysis
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Extracts were dried with anhydrous magnesium sulphate, filtered and evaporated to
142
dryness. The resulting materials were redissolved in methanol and analyzed by TLC and
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HPLC. The combined organic phases were evaporated and column chromatographed over
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Sephadex LH-20 gel using chloroform/methanol (4:1 v/v) as eluent for 1, 3, 4 and 5, and
145
chloroform/methanol (10:1 v/v) for 2. Quantitative analysis of the ethyl acetate extract of the
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biotransformation mixture was performed by means of HPLC, using calibration curves for the
147
substrate and for all the isolated products.
148 149
The structures of the obtained compounds were confirmed by NMR spectra analysis. Spectroscopic data of the products 6-12 are with agreement with literature data.10, 11, 13-19
150 151
carthamidin (5, 6, 7, 4´- tetrahydroxyflavanone, 6)
152
1
153
J = 17.1, 12.5 Hz, H-3ax), 5.36 (dd, 1H, J = 12.5, 2.9 Hz, H-2), 5.94 (s, 1H, H-8), 6.79 (d, 2H, J
154
= 8.5 Hz, H-3´, 5´), 7.31 (d, 2H, J = 8.5 Hz, H-2´,6´), 8.11 (s, 1H, 7-OH), 9.57 (s, 1H, 4´-OH),
155
10.42 (s, 1H, 6-OH), 11.98 (s, 1H, 5-OH). 13C NMR (150 MHz, DMSO-d6) δ (ppm): 42.3 (C-
156
3), 78.5 (C-2), 94.7 (C-8), 101.7 (C-10), 115.2 (C-3´, 5´), 126.3 (C-6), 128.3 (C-2´, 6´), 129.2
157
(C-1´), 150.2 (C-9), 155.3 (C-5), 155.8 (C-7), 157.7 (C-4´), 196.7 (C-4).
H NMR (600 MHz, DMSO-d6) δ (ppm): 2.65 (dd, 1H, J = 17.1, 2.9 Hz, H-3eq), 3.22 (dd, 1H,
158 159
isocarthamidin (5, 7, 8, 4´- tetrahydroxyflavanone, 7)
160
1
161
J = 17.1, 12.3 Hz, H-3ax), 5.42 (dd, 1H, J = 12.3, 3.0 Hz, H-2), 5.93 (s, 1H, H-6), 6.79 (d, 2H, J
H NMR (600 MHz, DMSO-d6) δ (ppm): 2.71 (dd, 1H, J = 17.1, 3.0 Hz, H-3eq), 3.22 (dd, 1H,
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= 8.5 Hz, H-3´, 5´), 7.35 (d, 2H, J = 8.5 Hz, H-2´, 6´), 8.11 (s, 1H, 7-OH), 9.57 (s, 1H, 4´-OH);
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10.42 (s, 1H, 8-OH), 11.75 (s, 1H, 5-OH). 13C NMR (150 MHz, DMSO-d6) δ (ppm): 42.3 (C-
164
3), 78.5 (C-2), 95.4 (C-6), 101.7 (C-10), 115.1 (C-3´,5´), 125.6 (C-8), 128.4 (C-2´, 6´), 129.2
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(C-1´), 149.4 (C-9), 156.5 (C-5), 155.8 (C-7), 157.7 (C-4´), 196.6 (C-4).
166 167
8-hydroxyhesperetin (3´,5,7,8-tetrahydroxy-4´-metoxyflavanone, 8)
168
1
169
J = 11.8 Hz, 17.1 Hz, H-3ax), 3.77 (s, OCH3), 5.41 (1H, dd, J = 11.8, 3.1 Hz, H-2), 5.92 (1H, s,
170
H-6), 6.91 (1H, d, J = 1.8 Hz, H-2´), 6.94 (1H, dd, J =12.9, 1.8 Hz, H-6´), 6.95 (1H, d, J = 12.1
171
Hz, H-5´). 13C NMR (150 MHz, DMSO-d6) δ (ppm): 42.4 (C-3), 55.8 (OCH3), 78.3 (C-2), 95.5
172
(C-6), 101.8 (C-10), 112.0 (C-2´), 114.3 (C-5´), 117.8 (C-6´), 125.7 (C-8), 131.5 (C-1´), 146.5
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(C-3´), 147.9 (C-4´), 149.3 (C-9), 155.8 (C-7), 156.5 (C-5), 196.5 (C-4).
H NMR (600 MHz, DMSO-d6) δ (ppm): 2.72 (1H, dd, J = 17.1, 3.1 Hz, H-3eq); 3.15 (1H, dd,
174 175
norwogonin (5,7,8-trihydroxyflavone, 9)
176
1
177
5´), 8.16 (2H, m, H-2´,6´), 12.26 (1H, s, 5-OH). 13C NMR (150 MHz, DMSO-d6) δ (ppm): 98.8
178
(C-6), 103.6 (C-10), 104.7 (C-3), 125.2 (C-8), 126.6 (C-2´, 6´), 129.1 (C-3´, 5´), 130.9 (C-1´),
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132.0 (C-4´), 145.6 (C-9), 153.1 (C-5), 153.8 (C-7), 163.0 (C-2), 182.3 (C-4).
H NMR (600 MHz, DMSO-d6) δ: 6.30 (1H, s, H-6), 6.94 (1H, s, H-3), 7.59 (3H, m, H-3´, 4´,
180 181
4-hydroxy-6-phenyl-2H-pyran-2-one (10)
182
1
183
3´, 4´, 5´), 7.81-7.87 (2H, m, H- 2´, 6´). 13C NMR (150 MHz, DMSO-d6) δ (ppm): 89.7 (C-3),
184
98.5 (C-5) 125.6 (C-2´, 6´), 129.3 (C-3´, 5´), 131.1 (C-1´), 131.2 (C-4´), 160.25 (C-4), 163.5
185
(C-6), 170.8 (C-2). HRESI-MS [M+H]+ (calculated/found) (m/z 189.0546/189.0545).
H NMR (600 MHz, DMSO-d6) δ: 5.40 (1H, m, H-3), 6.75 (1H, m, H-5), 7.49-7.54 (3H, m, H-
186
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8-hydroxyapigenin (4´,5,7,8-tetrahydroxyflavone, 11)
188
1
189
8.01 (2H, m, H-2´,6´), 8.75 (1H, s, 8-OH), 10.33 (1H, s, 4´-OH), 10.46 (1H, s, 7-OH), 12.38
190
(1H, s, 5-OH).
191
10), 115.9 (C-3´, 5´), 121.4 (C-1´), 125.0 (C-8), 128.6 (C-2´, 6´), 145.5 (C-9), 153.0 (C-5),
192
153.4 (C-7), 161.1 (C-4´), 163.5 (C-2), 182.1 (C-4).
H NMR (600 MHz, DMSO-d6) δ: 6.26 (1H, s, H-6), 6.74 (1H, s, H-3), 6.93 (2H, m, H-3´, 5´),
13
C NMR (150 MHz, DMSO-d6) δ (ppm): 98.6 (C-6), 102.3 (C-3), 103.3 (C-
193 194
hypoletin (3´,4´,5,7,8-pentahydroxyflavone, 12)
195
1
196
8.2 Hz, H-5´), 7.49 (2H, d, J = 12.6 Hz, H-2´, 6´); 13C NMR (150 MHz, DMSO-d6) δ (ppm):
197
98.6 (C-6), 102.4 (C-3), 103.4 (C-10), 113.7 (C- 2´), 116.0 (C-5´), 119.2 (C-6´), 121.8 (C-1´),
198
125.1 (C-8), 145.6 (C-3´), 145.7 (C-5), 149.7 (C-4´), 153.0 (C-7), 153.3 (C-9), 163.8 (C-2),
199
182.1 (C-4).
H NMR (600 MHz, DMSO-d6) δ (ppm): 6.26 (1H, s, H-6), 6.63 (1H, s, H-3), 6.89 (1H, d, J =
200 201
RESULTS AND DISCUSSION
202
Screening test carried out on four red yeasts cultured on Sabouraud medium with
203
naringenin (1) as a model substrate lead to selection of Rhodotorula glutinis KCh735 strain,
204
which was capable for transformation of 1. The oleaginous species of Rhodotorula glutinis can
205
be potentially used for biodiesel production and also other important products, such as
206
carotenoids.20, 21
207
Our studies carried out on a larger scale with the use of four natural flavonoids, having
208
flavanone (1, 2), flavone (3, 4, 5), flavonol (quercetin), flavane (epicatechin) and isoflavone
209
(biochanin A) skeletons, have demonstrated the ability of this organism to perform
210
hydroxylation reaction of the first two flavonoid groups (Fig. 1). Hydroxylation reaction is the
211
capacity rarely observed in yeast. Preparative-scale biotransformations afforded seven
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metabolites (6-12). The structures of the products were identified and confirmed by comparison
213
of the spectroscopic data with those reported in literature.10, 11, 13-19
214
Naringenin (1) after 24 h was converted to carthamidin (6) and isocarthamidin (7) in a
215
ratio of 1 : 19, respectively (according to HPLC). The starting material was not observed. The
216
35.8 mg of mixture of 5 and 6 was isolated with the yield of 42.3%. These metabolites were
217
investigated by Miyake et al. by using of free radical-scavening system of 1,1-diphenyl-2-
218
picrylhydrazyl (DPPH) and the methyl linoleate oxidative system.11 In both of these assays
219
they exhibited higher antioxidant activity than the naringenin (1). The activity of the
220
isocarthamidin (7) was stronger that of carthamidin (6) and nearly equal to the α-tocopherol.
221
The both products of naringenin (1) biotransformation were also recognized and patented as a
222
antidiabetic agents.22 Recent study on the screening of new tyrosinase inhibitors resulted in the
223
identification of isocarthamidin (5,7,8,4´-tetrahydroxyflavanone, 7), and other orto-
224
hydroxylated flavonoids (6,7,4´-trihydroxyisoflavone, 7,8,4´-trihydroxyisoflavone and 5,7,8,4´-
225
tetrahydroxyisoflavone) as a potent tyrosinase inhibitors.23-25 C-6 and C-7 hydroxyl groups in
226
the A-ring strongly affect both the inhibitory strength and the inhibitory mode of the flavonoids
227
on mushroom tyrosinase. Inhibiting the tyrosinase activity has been the subject of many studies
228
because this enzyme is responsible among others for the undesirable hyperpigmentation in skin
229
and browning in fruits.26 In light of these information the yeast Rhodotorula glutinis which lead
230
regioselective hydroxylation in these key positions flavonoids may be a very useful tool for
231
obtaining natural inhibitors of tyrosinase.
232
The content of 6 and 7 in plants is very low27, therefore from a pharmaceutical point of view
233
the preparation of these valuable compounds in an efficient biotransformation of much cheaper
234
substrate (see supplementary data) is very promising. Biohydroxylation of 1 at position 6 or 8
235
was earlier described for filamentous fungi Aspergillus saitoi11, Aspergillus niger28 and for
236
yeast Rhodotorula marina.9,10 In the process using the yeast R. marina substrate conversion and
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the ratio of products in the biotransformation mixture were comparable to results obtained for
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the fungus A. niger (the maximum concentration of isocarthamidin was 21.7 mg/L and
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carthamidin 21.5 mg/L, with the initial concentration naringenin equal to 60 mg/L), however 5-
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fold more of the substrate can be introduced to the yeast culture (300 mg /L).
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The results of biotransformations described in this article, concerning another species of
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red yeast - Rhodotorula glutinis, indicate high similarity in metabolizing of 1 for both
243
organisms. The application of R. glutinis gave acceptable ratio of more valuable isocarthamidin
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(7) to carthamidin (6) (1:19), but the most important advantage of the newly selected
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biocatalyst is its ability to regioselective ortho-hydroxylation of other natural flavonoids. The
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tested yeast was capable of converting flavonoids that belong to the flavanones and flavones
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groups, but did not metabolize substrates having flavonol, flavane and isoflavone skeletons.
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Biotransformations of hesperetin (2), chrysin (3), apigenin (4) and luteolin (5) are described
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below.
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The incubation of hesperetin (2) with Rhodotorula glutinis for 72 hours gave 8-
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hydroxyhesperetin (8) (14.3 mg, 17.0%). The antioxidant activity of this compound
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investigated by Miyake et al. is high, its ability to scavenge DPPH radicals is similar to α-
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tocopferol, at a concentration of 10 µM was 63%.11
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8-Hydroxyhesperetin (8) was previously obtained by biotransformation of hesperetin
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(2) in the cultures of filamentous fungi Aspergillus saitoi11 and Mucor ramannianus ATCC
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2628.14 Both of these transformations occurred with the low yield (3.5%, 0.03%) and - in the
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case of Aspergillus saitoi - in a long process lasting 20 days. Our new method for preparing 8-
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hydroksyhesperetin (8) by using the yeast Rhodotorula glutinis shortens the time of
259
transformation to three days and allows to obtain the product with the nearly five times higher
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yield.
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Preparative scale 6-day fermentation of chrysin (3) yielded one metabolite -
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norwogonin (9) (26.2 mg, 30.8%), which is the one of the active components in the root of
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Scutellaria baicalensis. According to literature, 9 is more effective than wogonin (5,7-
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dihydroxy-8-methoxy flavone) in induction of apoptosis in leukemia HL-60 cells.32 It is also
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one of the most potent antimicrobial natural compound against multidrug-resistant bacteria
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Acinetobacter baumannii.33 Thus, the above described experiment may serve after optimizing
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as a method for obtaining valuable norwogonin (9) from chrysin (3) - a cheap source, in a one-
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step simple biotransformation process.
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In the described biotransformation it was also observed the presence of trace amounts of
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the second product, which interestingly was the main product in the analogous process, in
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which chrysin (3) was added to the culture as a solution in tetrahydrofuran. Transformation of
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chrysin (3) added to the yeast culture in tetrahydrofuran for 48 hours led to 4-hydroxy-6-
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phenyl-2H-pyran-2-one (10) (30.5 mg, 50.2%). The product had the molecular formula
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C11H8O3 as indicated by HR-ESIMS of the [M+M]+ ion peak at m/z 189.0545 (calc. 189.0546).
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The
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signals what suggested degradation of substrate. Signals of B-ring had nearly the same
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chemical shifts as recorded for chrysin (3). Three signals at the lower field belongs to C-ring
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carbons: C-2 (170.8 ppm), C-6 (163.5 ppm) and C-4 (160.3 ppm). Further evidence came from
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the 1H-NMR spectrum which showed only four signals from seven protons. The absence of two
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singlets at 12.8 ppm (C5-OH), 10.92 ppm (C7-OH) and two doublets at 6.22 ppm (H-6) and
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6.52 ppm (H-8), presented in the spectrum of the substrate, confirmed degradation of the A-
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ring of chrysin (3). Correlations observed in the HMBC spectrum permitted the assignment of
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the H-3 and H-5 protons of lactone product (Fig. 2). The aromatic A-ring proton appeared as a
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multiplet at 6.75 ppm resonated with four carbons: at 89.7 ppm (C-3), 131.1 ppm (C-1´), 160.3
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ppm (C-4) and 170.8 ppm (C-2), what suggested that it is bonded to the carbon atom C-5. In
13
C NMR spectrum differed from that of starting compound (3) in the reduction of four
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turn the other A-ring proton appeared as a multiplet at 5.40 ppm resonated with three carbons:
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at 98.5 ppm (C-5), 163.5 ppm (C-6) and 170.8 ppm (C-2). No correlation of this proton with
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the C-1´ carbon atom indicates the considerable spatial distance between mentioned atoms and
289
unambiguously assigns it to the carbon C-3.
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The chemical synthesis of 4-hydroxy-6-phenyl-2H-pyran-2-one (10) has been
291
described.18 No information is found on the direct use of the product 9, but it is considered that
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compounds containing in their molecule the structure of 4-hydroxy-6-phenyl-2H-pyran-2-one
293
can be HIV protease inhibitors so that they can show antiviral activity.31 The simple one-pot
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process for preparing 4-hydroxy-6-phenyl-2H-pyran-2-one (10) by biotransformation can be an
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alternative to the mentioned three step chemical method.
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Degradation of chrysin (3) in the culture of Rhodotorula glutinis, involving the break-
297
up of the A-ring, prompted us to investigate its course. The presence of the lactone moiety in
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the product 10 allow to assume that an intermediate of this pathway have a hydroxyl group and
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the C-8 position of flavone skeleton. This assumption is also consistent with the demonstrated
300
ability of yeast selected by us to ortho-hydroxylation of the A ring of other flavones and
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flavanones. The OH groups makes the flavonoids capable of autooxidation under prolonged
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aerobic environments, which becomes more rapid in alkaline conditions. The course of the A-
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ring cleavage by Rhodotorula glutinis proceeds via an initial C-8 hydroxylation of chrysin (3)
304
to norwogonin (9), oxidative ring-fission followed by a hydrolase-type reaction to yield 4-
305
hydroxy-6-phenyl-2H-pyran-2-one (10).
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Flavonoids were generally decomposed via C-ring fission.34,35 To the best our
307
knowledge degradation of flavonoids via A-ring cleavage was described only for bacteria from
308
the genus Pseudomonas. Pseudomonas sp. grown on (+)-catechin, oxidized dihydrogossypetin
309
(3´,4´,5,7,8-pentahydroxyflavanonol) by cleaving the A-ring to form 5-(3,4-dihydroxyphenyl)-
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4-hydroxy-3-oxovalero-8-lactone and oxaloacetic acid.36 If the lactone - type intermediates
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311
have a C-3 hydroxyl group at an unsaturated site, they can be substrates for a second
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dioxygenase
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Hydroxyflavanones, such as taxifolin, were not oxidized.
and
underwent
further
degradation
by
Pseudomonas
putida.37
3-
314
Chrysin (4) biotransformations described above indicate a substantial influence of the
315
solvent in which the substrate is administered, on the rate of its metabolism. Addition of
316
terahydrofuran to the well - grown yeast culture accelerates chrysin (4) degradation.
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8-Hydroxyapigenin (11) was the only product of the 6-day biotransformation of
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apigenin (4). The amount of 10.9 mg of this compound was isolated with the yield of 12.9%.
319
Apigenin (4) is widely used as nutritional supplement. The rich source of 4 are among others
320
parsley and celery. 8-Hydroxyapigenin (11) significantly inhibited lung virus proliferation
321
when administered intranasally or orally to mice without being toxic against mice.38
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Biotransformation of luteolin (3) was carried out for 36 hours and hypoletin (12) was
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the only product isolated (21.3 mg, 25.3%). Hypoletin (12) is present in plants in small
324
quantities, and exhibits anti-inflammatory29 and antidiabetic activities.30
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To sum up, Rhodotorula glutinis KCh735 was found to be the only one of tested red
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yeast strains, which showed the ability of naringenin biotransformation in the preliminary
327
studies. This selected strain is capable of regioselective ortho-hydroxylation of the A-ring of
328
flavonoids, that is unique in the phylum of yeasts. Described biotransformations of natural
329
flavones and flavanones using this biocatalyst are the method that allows to specifically convert
330
cheap natural bioactive molecules into rare and pharmacologically improved metabolites.
331
Further optimization of fermentation conditions may provide an efficient route for massive
332
production of this valuable substances.
333 334 335
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336
SUPPORTING INFORMATION
337
The Supporting Information is available free of charge on the ACS Publications website at
338
DOI:
339 340
Detailed spectroscopic and structural information of biotransformation substrates and products,
341
the approximate prices list of same used and obtained flavonoids (PDF).
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11. Miyake, Y.; Minato, K.; Fukumoto, S.; Yamamoto, K.; Oya-Ito, T.; Kawakishi, S.; Osawa, T. New potent antioxidative hydroxyflavanones produced with Aspergillus saitoi from flavanone glycoside in citrus fruit. Biosci. Biotechnol. Biochem. 2003, 67, 1443-1450. 12. Kim, J.; Park, K.-S.; Lee, C.; Chong, Y. Synthesis of a complete series of O-methyl analogues of naringenin and apigenin. Bull. Korean Chem. Soc. 2007, 28, 2527-2530. 13. Obara, H.; Onodera, J.; Kurihara, Y.; Yamamoto, F. Synthesis of 2´,3´,4,4´,6´pentahydroxychalcone, an aglycone of carthamin, and its isomerization into 4´,5,6,7and 4´,5,7,8-tetrahydroxyflavanone, carthamidin and isocarthamidin. Bull. Chem. Soc. Jpn. 1978, 51, 3627-3630. 14. Herath, W.; Khan, I. A. Microbial metabolism. Part 13. Metabolites of hesperetin. Bioorg. Med. Chem. Lett. 2011, 21, 5784-5786. 15. Bilia, A.R.; Ciampi, L.; Mendez, J.; Morelli, I. Phytochemical investigation of Licania genus. Flavonoids from Licania pyrifolia. Pharm. Acta Helv. 1996, 71, 199-204. 16. Gurung, S.K.; Pyo Kim, H.; Park, H. Inhibition of prostaglandin E2 production by synthetic wogonin analogs. Arch. Pharm. Res. 2009, 32, 1503-1508. 17. Tomimori, T.; Miyaichi, Y.; Imoto, Y.; Kizu, H.; Tanabe, Y. Studies on the constituents of Scutellaria species. II. On the flavonoid constituents of the root of Scutellaria baicalensis Georgi (2). Yakugaku Zasshi. 1983, 103, 607-611. 18. Schmidt, D.; Conrad, J.; Klaiber, I.; Beifuss, U. Synthesis of the bis-potassium salts of 5-hydroxy-3-oxopent-4-enoic acids and their use for the efficient preparation of 4hydroxy-2H-pyran-2-ones and other heterocycles. Chem. Commun. 2006, 4732–4734. 19. Teles, Y. C.; Horta, C. C.; de Fátima Agra, M.; Siheri, W.; Boyd, M.; Igoli, J. O.; Gray, A. I.; de Fátima Vanderlei de Souza, M. New sulphated flavonoids from Wissadula periplocifolia (L.) C. Presl (Malvaceae). Molecules 2015, 20, 20161-20172.
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20. Bhosale, P.; Gadre, R. V. Production of β-carotene by a Rhodotorula glutinis mutant in sea water medium. Biores. Technol. 2001, 76, 53-55. 21. Xue, F.; Miao, J.; Zhang, X.; Tan, T. A new strategy for lipid production by mix cultivation of Spirulina platensis and Rhodotorula glutinis. Appl. Biochem. Biotechnol. 2010, 160, 498-503. 22. Satoru, K.; Tsumoru, W.; Yoshiharu, I.; Atsuko E. Antidiabetic agent, JP 2008133192 A, 2007. 23. Chang, T. S.; Ding, H. Y.; Lin, H. C. Identifying 6,7,4´-trihydroxyisoflavone as a potent tyrosinase inhibitor. Biosci. Biotechnol. Biochem. 2005, 69, 1999-2001. 24. Chang, T. S. Two potent suicide substrates of mushroom tyrosinase: 7,8,4´trihydroxyisoflavone and 5,7,8,4´-tetrahydroxyisoflavone. J. Agric. Food Chem. 2007, 55, 2010-2015. 25. Chang, T. S.; Lin, M. Y.; Lin, H. J. Identifying 8-hydroxynaringenin as a suicide substrate of mushroom tyrosinase. J. Cosmet. Sci. 2010, 61, 205-210. 26. Rescigno, A.; Sollai, F.; Pisu, B.; Rinaldi, A.; Sanjust, E. Tyrosinase inhibition: General and applied aspects, J. Enzyme Inhib. Med. Chem. 2003, 17, 207-218. 27. Werawattanachai, N.; Kaewamatawong, R. Chemical constituents from Parinari anamense. Biochem. Syst. Ecol. 2010, 38, 836-838. 28. Xu, J.; Yang, L.; Wang, Z. T.; Zhao, S. J.; Hu, Z. B. An efficient way from naringenin to carthamidine and isocarthamidine by Aspergillus niger. World J. Microbiol. Biotechnol. 2012, 28, 1803-1806. 29. Ferrándiz, M. L.; Alcaraz, M. J. Anti-inflammatory activity and inhibition of arachidonic acid metabolism by flavonoids. Agents Actions. 1991, 32, 283-288.
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30. Kato, A.; Nasu, N.; Takebayashi, K.; Adachi, I.; Minami, Y.; Sanae, F.; Asano, N.; Watson, A. A.; Nash, R. J. Structure-activity relationships of flavonoids as potential inhibitors of glycogen phosphorylase. J. Agric Food Chem. 2008. 56, 4469-4473. 31. Prasad, V. J. V. N.; Tummino, P. J.; Ferguson, D.; Saunders, J.; Roest, S. V.; McQuade, T. J.; Heldsinger, A.; Reyner, E. L.; Stewart, B. H.; Guttendorf, R. J.; Para, K. S.; Lunney, E. A.; Gracheck, S. J.; Domagala, J. M. Nonpeptidic HIV protease inhibitors: 4-hydroxy-pyran-2-one inhibitors with functional tethers to P1 phenyl ring to reach S3 pocket of the enzyme. Biochem. Biophys. Res. Commun. 1996, 221, 815-820. 32. Chow, J. M.; Huang, G. C.; Shen, S. C.; Wu, C. Y.; Lin, C. W.; Chen, Y. C. Differential apoptotic effect of wogonin and nor-wogonin via stimulation of ROS production in human leukemia cells. J. Cell Biochem. 2008, 103, 1394-404. 33. Miyasaki, Y.; Rabenstein, J. D.; Rhea, J., Crouch, M. L.; Mocek, U. M.; Kittell, P. E.; Morgan, M. A.; Nichols, W. S.; Van Benschoten, M. M.; Hardy, W. D.; Liu, G. Y. Isolation and characterization of antimicrobial compounds in plant extracts against multidrug-resistant Acinetobacter baumannii. PLoS One, 2013, 8, e61594. 34. Rao, J. R.; Cooper, J. E. Rhizobia catabolize nod gene-inducing flavonoids via C-ring fission mechanisms. J. Bacteriol. 1994, 176, 5409-5413. 35. Winter, J.; Moore, L. H.; Dowell, V. R.; Bokkenheuser, V. D. C-ring cleavage of flavonoids by intestinal bacteria. Appl. Environ. Microbiol. 1989, 55, 1203-1208. 36. Jeffrey, A. M.; Jerina, D. M.; Self, R.; Evans, W. C. The bacterial degradation of flavonoids. Oxidative fission of the A-ring of dihydrogossypetin by a Pseudomonas sp. Biochem. J. 1972, 130, 383-390. 37. Schultz, E.; Engle, F. E.; Wood, J. M. New oxygenases in the degradation of flavones and flavanones by Pseudomonas putida. Biochem. 1974, 13, 1768-1776.
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38. Nagai, T.; Miyaichi, Y.; Tomimori, T.; Suzuki, Y.; Yamada, H. In vivo anti-influenza virus activity of plant flavonoids possessing inhibitory activity for influenza virus sialidase. Antiviral Res. 1992, 19, 207-217.
Funding Information The Project was supported by Wroclaw Centre of Biotechnology, The Leading National Research Centre Programme (KNOW) for years 2014-2018.
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FIGURE CAPTIONS Figure 1. Transformation of naringenin (1), hesperetin (2), chrysin (3), apigenin (4) and luteolin (5) by Rhodotorula glutinis. Figure 2. Key HMBC correlations for compound 10. Figure 3. Putative pathway of chrysin (3) degradation via A-ring cleavage conducted by Rhodotorula glutinis.
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Figure 1
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Figure 2
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Figure 3
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