Full text of DOI:10.1007/s10600-018-2503-z

DOI 10.1007/s10600-018-2503-z
Chemistry of Natural Compounds, Vol. 54, No. 5, September, 2018
SYNTHESIS AND BIOLOGICAL ACTIVITY OF PRENYLATED PHENOLS
1*
1
1
I. Yu. Chukicheva, I. V. Fedorova, N. A. Nizovtsev,
1
2
1
A. A. Koroleva, O. G. Shevchenko, and A. V. Kuchin
Prenylphenols and 2,2-dimethylbenzopyrans were synthesized via alkylation of resorcinol and pyrocatechol
with prenol in the presence of aluminum isopropylate and phenolate catalysts. Several process features
were determined. The antiradical, membrane-protective, and antioxidant activity of the synthesized
compounds were assessed using various models. 2,2-Dimethyl-7-isobornylchroman-6-ol was found to have
higher activity than 2,6-di-tert-butyl-4-methylphenol (ionol or BHT).
Keywords: resorcinol, pyrocatechol, prenol, organoaluminum catalysts, alkylation, membrane-protective, antiradical,
antioxidant activity.
The high biological activity of natural prenylphenols and benzopyrans [1–4] stimulates the development of synthetic
methods for their analogs. Alkylation is one of the main methods for preparing prenylphenols and can follow several pathways
depending on the alkylating agents and catalysts. Aromatic compounds undergo C- or O-alkylation with different selectivities
[5–8].
Herein, the effects of various conditions on alkylation of resorcinol and pyrocatechol by a simple allyl alcohol, i.e.,
prenol (3-methyl-2-buten-1-ol), in the presence of catalytic and equimolar amounts of organoaluminum catalysts (i-PrO) Al
3
and (PhO) Al at 120 and 160°C are studied.
3
1
O
1
O
1
O
O
O
OH
3
10a
10a
8a
4a
4a
4a
5
+
OH
cat.
9a
OH
5
O5
OH
7
OH
O
HO
8a
6a
8
2
1
7
Ra
6
7
6
5
7
4
3
cat. = (i-PrO) Al; (PhO) Al
3
3
1
O
OH
OH
OH
1'
OH
3
1
1
1
11
Rc
Ra
Ra
9
4a
3
3
3'
3
OH
9a,b
OH
OH
5
4
HO
OH
R
8
10
11
1''
1''
3''
1''
3''
3''
R =
a
c
b
Scheme 1
1) Institute of Chemistry, Komi Scientific Center, Ural Branch, Russian Academy of Sciences, 48 Pervomaiskaya St.,
Syktyvkar, 167000, Russian Federation, fax: +78212 218477, e-mail: chukichevaiy@mail.ru; 2) Institute of Biology, Komi
Scientific Center, Ural Branch, Russian Academy of Sciences, 28 Kommunisticheskaya St., Syktyvkar, 167982, Russian
Federation, fax: +78212 240163. Translated from Khimiya Prirodnykh Soedinenii, No. 5, September–October, 2018,
pp. 743–749. Original article submitted March 30, 2018.
©
0009-3130/18/5405-0875 2018 Springer Science+Business Media, LLC
875

TABLE 1. Conditions and Contents of Products from Alkylation of Resorcinol by Prenol, %
Resorcinol–prenol
ratio
Reaction
conditions
*
3
4
5
6
7
8
9à
9b
10
11
( -PrO) Al – catalytic method
i
3
1:1
1:2
11
19
58
–
36
3
31
3
4
–
–
8
22
–
26
8
8
–
15
13
–
–
3
–
–
–
–
–
–
–
–
–
–
3
–
120°Ñ, 3 h
160°Ñ, 3 h
12
24
25
10
°
120 Ñ, 3 h
24
24
160°Ñ, 3 h
(PhO)3Al – catalytic method
1:1
23
4
40
4
4
23
–
28
–
–
–
–
14
8
16
15
120°Ñ, 2 h
160°Ñ, 1 h
20
2
( -PrO) Al – reagent method
i
3
1:1
1:2
–
8
9
42
36
38
32
27
20
20
8
–
–
9
2
–
–
13
7
–
–
14
3
–
–
1
–
2
5
–
–
–
–
–
–
120°Ñ, 3 h
14
15
°
160 Ñ, 3 h
13
21
120°Ñ, 3 h
12
27
°
160 Ñ, 3 h
______
*Difficultly separated mixture of alkylation products.
Alkylation of resorcinol (1) by prenol (2) in the presence of (i-PrO) Al and (PhO) Al occurred with complete conversion
3
3
of prenol under all studied conditions. Primarily chromanes 3–7 and prenylphenols 8 and 9a were formed in the presence of
catalytic amounts of (i-PrO) Al at 120°C (Scheme 1, Table 1). The contents of ethers 3–6 increased to 97% if the reaction
3
temperature was increased to 160°C. The main product was 5 (58%). Mixtures of O- and C-alkylation products were obtained
and the reaction occurred non-selectively in the presence of a two-fold excess of 2 regardless of the temperature.
Chromanes, the main one of which was 5 (40%), were primarily formed already at 120°C if catalytic amounts of
(PhO) Al were used to alkylate resorcinol with prenol. Increasing the reaction temperature to 160°C decreased the amount of
3
chromanes and enhanced formation of di- and monoprenylated 1,3-dihydroxybenzenes 8 and 9 (23 and 28%, respectively).
Bisphenol 11 was typically formed with (PhO) Al catalyst.
3
Alkylation of resorcinol by prenol (1:1 ratio of starting reagents) at 120 and 160°C in the presence of equimolar
amounts of (i-PrO) Al gave mainly only chromanes 3–6 in overall yields up to 87–98%. o-Alkylated 1,3-dihydroxybenzene
3
10 was isolated as a side product (up to 5%). The selectivity decreased and prenylphenols 8 and 9 were formed if a two-fold
excess of 2 was used (120 and 160°C).
The structures of the synthesized compounds were confirmed using NMR and IR spectroscopy.
Pyrocatechol (12) was alkylated by prenol (2) in the presence of catalytic and equimolar amounts of (i-PrO) Al and
3
(PhO) A at 120 and 160°C (Scheme 2). Prenol was completely converted under all studied reaction conditions.
3
OH
OH
OH
1
O10
OH
OH
1
O
1
O
1
O
11
8
8
11a
8a
8a
Ra
6
Ra
OH
Ra
cat.
+
6a
6
OH
3
3
3
4a
4a
4a
3
2
12
4
5
5
5
4
cat. = (i-PrO) Al; (PhO) Al
15
16
13
14
3
3
OH
R
HO
OH
1'
OH
OH
1
O
9
OH
7
1
3
HO
Ra
11
3'
3
HO
OH
5
17
18
19
1''
1''
3''
3''
1''
3''
R =
a
c
b
Scheme 2
876

TABLE 2. Conditions and Preparative Yields of Products from Alkylation of Pyrocatechol by Prenol, %
Pyrocatechol–prenol
Reaction conditions
*
13
14
15
16
17
18
19
ratio
( -PrO) Al – catalytic method
i
3
–
–
33
86
–
–
–
–
9
2
15
12
33
–
–
–
–
–
10
–
–
120°Ñ, 5 h
160°Ñ, 5 h
1:1
1:2
13
7
87**
47**
°
120 Ñ, 3 h
–
38
8
160°Ñ, 3 h
(PhO)3Al – catalytic method
6
22
2
10
15
10
50
23
–
–
19
17
8
18
120°Ñ, 2 h
160°Ñ, 1 h
1:1
( -PrO) Al – reagent method
i
3
–
23
40
49
26
–
9
–
–
68
–
–
–
–
–
–
60
37
–
–
14
–
120°Ñ, 1.5 h
1:1
1:2
°
160 Ñ, 3 h
120°Ñ, 3 h
74
°
160 Ñ, 3 h
______
*Difficultly separated mixture of alkylation products; **difficultly separated mixture of di- and monoalkylated products with
different prenyl substituents a, b, and c.
Chromane 14 and mono- and diprenyl-1,2-dihydroxybenzenes 17 and 16 were formed in the presence of catalytic
amounts of (i-PrO) Al at 120°C (Table 2). Bisphenol 18 (33%) was obtained only under these conditions. Chromane 14 was
3
formed selectively in 86% yield if the reaction temperature was increased to 160°C. Mono- and dialkylated phenols 17 and 16
were isolated as side products. The reaction of pyrocatechol with a two-fold excess of 2 at 120 and 160°C occurred
non-selectively and gave a complicated product mixture, most of which were C-alkylation products. A mixture of bisphenols
19 (up to 38%) formed at 160°C.
Pyrocatechol was selectively prenylated at 120°C in the presence of catalytic amounts of (PhO) Al or equimolar
3
amounts of (i-PrO) Al to produce 3-prenyl-1,2-dihydroxybenzene 17.
3
Increasing the reaction temperature and using a two-fold excess of 2 in the presence of equimolar amounts of
(i-PrO) Al reduced significantly the selectivity and formed difficultly separated mixtures of chromanes 13–15, prenylphenols
3
16 and 17, and bisphenols 18 and 19.
Antioxidant, membrane-protective, and antiradical properties of the synthesized compounds were assessed in various
models and compared to those of 2,6-di-tert-butyl-4-methylphenol (ionol or BHT), Trolox, and previously prepared phenols
20–22 [9]. The structure–activity relationship for the terpene substituent was studied further by synthesizing 23 via alkylation
of 2-isobornyl-1,4-dihydroxybenzene with prenol in the presence of equimolar amounts of (i-PrO) Al at 160°C.
3
O 1
3
OH
O
8'
9'
10'
3'
7'
7
5
1'
HO
OH
5'
OH
OH
21
22
20
23
Antiradical activity (ARA) of 3, 5–8, 14, and 20–23 was assessed from their ability to react with the stable chromogenic
radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) [10]. An analysis of the results showed that all studied compounds
at a concentration of 100 μM except phenols 5 and 22 had high antiradical activity. Compounds 20, 21, and 23 had the greatest
ARA in the DPPH test and were more potent than the known antioxidant BHT (ionol) if the concentration was reduced to 10 μM.
Antioxidant activity (AOA) of the prenylphenols was assessed in vitro from the ability to inhibit lipid peroxidation
(LPO) of laboratory mouse brain. The activity of the compounds in this model were shown also to depend considerably on the
substituent structure. All synthesized compounds at a concentration of 100 μM exhibited very high AOA. Only compounds
7, 8, 20, and 23, which contained prenyl or terpene fragments, inhibited LPO below the spontaneous level if the concentration
was lowered to 10 μM. The activity of these compounds in this test were comparable with that of BHT and considerably
greater than that of Trolox (Table 3).
877

TABLE 3. Assessment of Antiradical and Antioxidant Activity of Alkylated Phenols at Concentrations of 10 and 100 μM
ARA (inhibition, %)
AOA (TBA–AP content, nmol/mL)
Compound
10 μM
100 μM
10 μM
100 μM
3
5
6
7
8
14
20
21
22
3.3 0.6
2.0 0.2
6.7 0.1
30.7 1.1
13.2 0.7
33.4 0.8
83.3 1.4
77.5 1.0
86.6 0.3
94.3 0.4
91.9 0.2
4.7 0.2
71.0 0.8
68.2 0.5
55.1 0.2
4.7 0.3
3.65 0.4
3.77 0.2
3.12 0.2
3.20 0.3
3.10 0.1
3.03 0.2
3.34 0.3
3.63 0.4
10.99 0.4
3.00 0.2
4.7 0.5
21.2 0.2
21.1 0.3
19.4 0.6
45.4 1.4
29.9 2.6
0.2 0.1
48.4 0.6
13.5 1.2
51.9 0.78
3.7 0.1
49.3 0.5
19.0 0.3
46.1 0.7
66.4 1.6
3.3 0.4
23
ÂÍÒ
Trolox
81.5 4.3
72.0 4.0
94.9 0.2
5.0 0.8
66.9 0.63
3.6 0.2
______
2+
TBA–AP is the concentration of secondary LPO products in brain homogenate (ascorbate/Fe initiator). The TBA–AP
concentration in control samples without the tested compounds was 65.7 0.3 nmol/mL; in intact samples where LPO was not
induced, 28.8 0.4 nmol/mL.
TABLE 4. Effects of Phenols (1 μM) on H O -Induced Hemolysis of Erythrocytes
2
2
Fluorescence intensity,
rel. units
Compound
MPA, %
TBA–AP, nmol/mL
metHb/oxyHb, rel. units
Control
42.3 0.4
22.3 0.7
25.6 0.2
29.1 1.0
6.6 0.3
13.9 0.7
16.9 1.4
18.9 0.6
23.5 0.8
32.8 0.7
5.7 0.2
1.24 0.06
1.15 0.02
1.20 0.06
1.27 0.05
0.77 0.03
0.89 0.01
0.98 0.03
1.03 0.04
1.27 0.02
0.97 0.07
0.66 0.05
0.71 0.06
0.65 0.06
0.69 0.03
1.06 0.12
0.56 0.04
0.53 0.06
0.62 0.09
0.53 0.03
0.71 0.02
0.79 0.05
0.52 0.04
5.37 0.16
5.27 0.11
5.17 0.08
5.61 0.18
4.82 0.10
5.10 0.20
4.85 0.18
5.53 0.12
5.31 0.24
5.74 0.26
4.80 0.04
3
5
6
7
8
14
20
22
21
23
______
MPA is the degree of erythrocyte hemolysis by H O after incubation for 5 h; TBA–AP is the concentration of secondary LPO
2
2
products in blood erythrocytes (H O initiator); metHb/oxyHb is the ratio of oxygenated (methemoglobin) and native
2
2
(oxyhemoglobin) forms of hemoglobin in erythrocytes affected by H O .
2
2
Cytotoxicity, AOA, and membrane-protective activity (MPA) of phenols 3, 5–8, 14, and 20–23 were assessed using
laboratory mouse blood erythrocytes [11, 12]. The insignificant experimental cytotoxicity (at least 94% of cells survived at
a concentration of 10 μM) enabled further research on the antioxidant and membrane-protective activity of the synthesized
compounds using blood erythrocytes as a model. Compounds 7 and 23 had the greatest activity with respect to the parameter
set. They not only protected erythrocytes from death by H O but also prevented statistically significantly the accumulation
2
2
of secondary LPO products in the cells, the oxidation of oxyhemoglobin, and the oxidative degradation of heme. This was
inferred from the reduced fluorescence intensity of erythrocytes in the hemolysates (Table 4).
Regression analysis gave a good correlation for the MPA of the phenols in the cell model and their AOA in brain lipid
tests (R = 0.82, n = 11).
Compounds 7 and 23 were additionally tested at a concentration of 0.1 μM to find finer differences in their biological
activities. The lead compound for all parameters at the low concentration was 23, which included an isobornyl moiety
(Table 5). Furthermore, phenol 23 at this concentration was superior to the well-known antioxidant BHT with respect to
ability to protect cells from oxidative stress induced by H O . According to previous results, Trolox in this model exhibited
2
2
relatively low activity even at a concentration of 10 μM [13].
878

TABLE 5. Effects of Phenols (0.1 μM) on H O -Induced Erythrocyte Hemolysis
2
2
Fluorescence intensity,
rel. units
Compound Hemolysis (incubation for 5 h), %
TBA–AP, nmol/mL
metHb/oxyHb, rel. units
Control
7
23
44.2 0.7
37.6 0.8
20.3 1.9
36.0 1.4
1.36 0.04
1.62 0.08
1.30 0.06
1.41 0.05
1.59 0.080
1.31 0.07
0.88 0.07
1.13 0.14
7.38 0.08
7.23 0.14
6.53 0.09
7.30 0.09
ÂÍÒ
Thus, the activity of the studied phenols varied over a wide range and depended considerably on the molecular
structure. The lead compound according to the studied parameter set was 2,2-dimethyl-7-isobornylchroman-6-ol (23), which
was more active than ionol.
EXPERIMENTAL
13
PMR and C NMR spectra were recorded in CDCl at room temperature on a Bruker Avance II 300 spectrometer at
3
1
13
300 MHz for H and 75 MHz for C. Resonances of C(H)DCl (δ 7.26 ppm, δ 77.00 ppm) were used as internal standards.
3
H
C
13
Resonances were assigned using C NMR spectra recorded in JMOD mode and in certain instances including two-dimensional
NMR spectroscopy methods (COSY, HETCORR, and HSQC). TLC used Sorbfil plates. Reaction products were detected by
treating plates with KMnO solution (15 g KMnO , 300 mL H O, 0.5 mL conc. H SO ) or vanillin solution (1 g vanillin,
4
4
2
2
4
100 mL 95% EtOH, 5 mL conc. H SO ) followed by heating to 100–120°C. Reaction products were separated by column
2
4
chromatography over silica gel (Alfa Aesar, 70/230 μ) with elution by petroleum ether–Et O with increasing fraction of the
2
latter. Melting points were measured on a Sanyo Gallenkamp MDP350 apparatus and are uncorrected. Resorcinol and
pyrocatechol (chemically pure), 3-methyl-2-buten-1-ol (AlfaAesar, 97%), 2,6-di-tert-butyl-4-methylphenol (Alfa Aesar, 99%),
and Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid, Sigma-Aldrich, 97%) were used in the reactions.
The catalysts were (i-PrO) Al (Alfa Aesar) and (PhO) Al (synthesized in situ).
3
3
Spectral studies used equipment at the Khimiya CUC, IC, KSC, UB, RAS. Activities of the compounds were studied
using equipment at the Molecular Biology CUC, IB, KSC, UB, RAS. Animals from the scientific collection of experimental
animals of the IB, KSC, UB, RAS were used in the work (http://www.ckp-rf.ru/usu/471933/).
General Method forAlkylation of Resorcinol (Pyrocatechol) by Prenol in the Presence of (i-PrO) Al or (PhO) Al.
3
3
Resorcinol (pyrocatechol) (0.5 g, 4.5 mmol), prenol (0.39 g, 4.5 mmol), and (i-PrO) Al or (PhO) Al (0.05 g, 0.2 mmol for the
3
3
catalytic method or 0.92 g, 4.5 mmol for equimolar amounts of catalyst) were heated in a 100-mL two-necked flask equipped
with a thermometer and reflux condenser. The reaction mixtures were held at 120 and 160°C. The course of reactions was
monitored using TLC (petroleum ether–Et O, 3:1; vanillin detector). When the reaction was finished, the mixture was cooled,
2
diluted with Et O, treated with HCl solution (50%) to decompose the catalyst, and washed with saturated NaHCO solution
2
3
and H O until neutral. The organic layer was dried over anhydrous Na SO . The solvent was evaporated. The products were
2
2
4
separated by column chromatography using petroleum ether–Et O with increasing fraction of the latter. The structures of 3
2
and 4 agreed with the literature [8].
1
2,2,8,8-Tetramethyl-2,3,4,6,7,8-hexahydropyrano[3,2-g]chromane (3), light-brown oil. Í NMR spectrum
(300 MHz, CDCl , δ, ppm, J/Hz): 1.34 (12Í, s, 4CH ), 1.79 (4H, t, J = 6.8, Í-3, 7), 2.71 (4H, t, J = 6.8, Í-4, 6), 6.25 (1H, s,
3
3
13
H-10), 6.76 (1H, s, H-5). C NMR spectrum (75 MHz, CDCl , δ, ppm): 73.81 (C, Ñ-2, 8), 33.18 (2CH , C-3, 7), 21.81 (2CH ,
3
2
2
C-4, 6), 129.36 (CH, Ñ-5), 112.63 (2Ñ, C-4à, 6à), 104.75 (CH, C-10), 26.88 (4CH ), 154.59 (2Ñ, Ñ-9à, Ñ-10à) [14, 15].
3
1
2,2,8,8-Tetramethyl-2,3,4,8,9,10-hexahydropyrano[2,3-f]chromane (4), light-yellow oil. Í NMR spectrum
(300 MHz, CDCl , δ, ppm, J/Hz): 1.36 (12Í, s, 4CH ), 1.85 (4H, m, Í-3, 7), 2.65–2.70 (4H, m, Í-4, 8), 6.44 (1H, d, J = 8.7,
Í-10), 6.98 (2H, d, J = 8.7, Í-9). C NMR spectrum (75 MHz, CDCl , δ, ppm): 74.01 (Ñ, C-2, 6), 32.30 (2CH , C-3, 7), 17.24
3
3
13
3
2
(2CH , C-4, 8), 112.643 (2Ñ, C-4à, 8à), 124.08 (ÑÍ, Ñ-9), 109.35 (ÑÍ, Ñ-10), 154.23 (2Ñ, Ñ-5à, Ñ-10à), 22.89 (2CH ), 26.64
2
3
(2CH ).
3
1
2,2-Dimethylchroman-7-ol (5), brown oil. Í NMR spectrum (300 MHz, CDCl , δ, ppm, J/Hz): 1.37 (6Í, s, 2CH ),
3
3
1.82 (2Í, t, J = 6.8, Í-3), 2.73 (2H, t, J = 6.8, Í-4), 5.55 (1Í, s, OH), 6.35–6.42 (2H, m, Í-6, 8), 6.94 (1Í, d, J = 8.4, Í-5).
13
C NMR spectrum (75 MHz, CDCl , δ, ppm): 74.55 (Ñ, C-2), 33.00 (CH , C-3), 21.77 (CH , C-4), 113.24 (Ñ, Ñ-4à), 130.14
3
2
2
(ÑÍ, Ñ-5), 107.59 (ÑÍ, C-6), 154.66 (Ñ, Ñ-7), 154.96 (Ñ, Ñ-8à), 103.86 (ÑÍ, C-8), 26.83 (2CH ).
3
879

1
2,2-Dimethylchroman-5-ol (6), light-brown powder, mp 114–115°C. Í NMR spectrum (300 MHz, CDCl , δ, ppm,
3
J/Hz): 1.39 (6Í, s, 2 CH ), 1.86 (2Í, t, J = 6.6, Í-3), 2.71 (2H, t, J = 6.6, Í-4), 5.21 (1Í, s, OH), 6.37 (1H, d, J = 8.1, Í-6), 6.48
3
13
(1Í, d, J = 8.1, Í-8), 6.99 (1Í, t, J = 8.1, Í-7). C NMR spectrum (75 MHz, CDCl , δ, ppm): 74.05 (Ñ, C-2), 32.23 (CH ,
3
2
C-3), 16.93 (CH , C-4), 108.61 (Ñ, Ñ-4à), 153.97 (Ñ, Ñ-5), 109.85 (ÑÍ, Ñ-6), 127.18 (ÑÍ, Ñ-7), 106.13 (ÑÍ, C-8), 154.59
2
(Ñ, Ñ-8à), 26.67 (2 CH ).
3
1
2,2-Dimethyl-6-(3-methylbut-2-enyl)chroman-5-ol (7), light-yellow oil. Í NMR spectrum (300 MHz, CDCl ,
3
δ, ppm, J/Hz): 1.36 (12Í, s, 4CH ), 1.75–1.84 (2Í, m, Í-3), 2.67–2.71 (2H, m, Í-4), 3.32 (2Í, d, J = 6.9, Í-1′′), 5.32 (1Í, s, OH),
3
13
5.35–5.38 (1Í, m, Í-2′′), 6.39 (1H, d, J = 8.1, Í-8), 6.87 (1Í, d, J = 8.1, Í-7). C NMR spectrum (75 MHz, CDCl , δ, ppm):
3
29.97 (CH , C-1′′), 73.61 (Ñ, C-2), 122.52 (ÑÍ, Ñ-2′′), 32.32 (CH , Ñ-3), 134.85 (Ñ, Ñ-3′′), 17.14 (CH , C-4), 108.88 (Ñ,
2
2
2
Ñ-4à), 152.62 (Ñ, Ñ-5), 116.62 (Ñ, Ñ-6), 127.76 (ÑÍ, Ñ-7), 109.08 (ÑÍ, C-8), 153.50 (Ñ, Ñ-8à), 17.70, 25.82, 26.92 (4CH ).
3
1
2,4-Bis(3-methylbut-2-en-1-yl)benzene-1,3-diol (8), light-yellow oil. Í NMR spectrum (300 MHz, CDCl , δ,
3
ppm, J/Hz): 1.82 (12Í, s, 4CH ), 3.32 (2H, d, J = 6.6, Í-1′′), 3.46 (2H, d, J = 6.6, Í-1′′′), 5.07 (1Í, s, OH), 5.28–5.36 (2H, m,
3
13
Í-2′′, 2′′′), 5.47 (1Í, s, OH), 6.38 (1Í, d, J = 8.4, Í-4), 6.86 (1Í, d, J = 8.4, Í-5). C NMR spectrum (75 MHz, CDCl , δ,
3
ppm): 22.64 (CH , C-1′′), 29.74 (CH , C-1′′′), 153.32 (C, Ñ-1), 121.87 (ÑÍ, C-2′′), 122.39 (ÑÍ, Ñ-2′′′), 119.09 (Ñ, C-2), 134.58
2
2
(Ñ, C-3′′), 1345.87 (Ñ, Ñ-3′′′), 153.53 (Ñ, C-3), 107.61 (ÑÍ, C-4), 127.53 (ÑÍ, C-5), 113.94 (Ñ, C-6), 17.84 (2CÍ ), 25.79
3
(2ÑÍ ).
3
1
4-(3-Methylbut-2-en-1-yl)benzene-1,3-diol (9a), light-brown oil. Í NMR spectrum (300 MHz, CDCl , δ, ppm, J/Hz):
3
1.36 (6Í, s, 2CH ), 3.46 (2H, d, J = 7.2, Í-1′′), 5.33 (1H, br.t, Í-2′′), 5.57 (2Í, s, 2-OH), 6.38 (1Í, s, H-6), 6.42–6.45 (1Í, m,
3
13
H-5), 6.95–6.98 (1Í, m, H-4). C NMR spectrum (75 MHz, CDCl , δ, ppm): 29.72 (CH , C-1′′), 154.90 (C, Ñ-1), 103.73
3
2
(ÑÍ, C-2), 121.63 (ÑÍ, C-2′′), 136.02 (Ñ, C-3′′), 154.98 (Ñ, C-3), 108.23 (ÑÍ, C-4), 127.25 (Ñ, C-5), 141.75 (Ñ, C-6), 17.66
(CÍ ), 25.78 (CÍ ).
3
3
1
4-(2-Methylbut-3-en-2-yl)benzene-1,3-diol (9b), light-brown oil. Í NMR spectrum (300 MHz, CDCl , δ, ppm,
3
J/Hz): 1.75 (6Í, s, 2CH ), 5.26 (1Í, s, OH), 5.27–5.30 (2H, m, Í-3′′), 5.36 (1Í, s, ÎÍ), 6.12–6.22 (1H, m, Í-2′′), 6.38–6.40
3
13
(2Í, m, Í-5, 6), 6.69 (1Í, s, Í-2). C NMR spectrum (75 MHz, CDCl , δ, ppm): 14.10 (2CÍ ), 37.76 (Ñ, C-1′′), 114.06
3
3
(ÑÍ , C-3′′), 120.87 (2ÑÍ, C-2, 6), 126.03 (2ÑÍ, C-5), 130.11 (Ñ, C-4), 139.28 (ÑÍ, C-2′′), 146.12 (2Ñ, C-1, 3).
2
1
2-(Pentan-2-yl)benzene-1,3-diol (10), brown oil. Í NMR spectrum (300 MHz, CDCl , δ, ppm, J/Hz): 1.29–1.37
3
(6Í, s, 2 CH ), 1.41–1.47 (2Í, m, Í-3′′), 1.79–1.86 (2Í, m, Í-2′′), 3.06–3.09 (1H, m, Í-1′′), 4.55 (1Í, s, OH), 4.71 (1Í, s,
3
13
OH), 6.31–6.44 (2H, m, Í-6, 4), 6.77–6.88 (1Í, m, Í-5). C NMR spectrum (75 MHz, CDCl , δ, ppm): 24.98 (ÑÍ, C-1′′),
3
155.48 (Ñ, Ñ-1), 32.75 (CH , C-2′′), 112.25 (Ñ, Ñ-2), 21.81 (CH , C-3′′), 155.74 (Ñ, C-3), 20.84 (CH ), 107.44 (2ÑÍ , C-4, 6),
2
2
3
2
126.70 (ÑÍ , C-5), 12.66 (CH ).
2
3
1
4-[3-(5-Hydroxy-2,2-dimethylchroman-8-yl)-3-metylbutan-2-yl]benzene-1,3-diol (11), brown oil. Í NMR
spectrum (300 MHz, CDCl , δ, ppm, J/Hz): 1.37 (6Í, s, 2CH ), 1.43 (6Í, s, 2CH ), 1.80–1.82 (2Í, m, Í-10), 1.91–2.02 (2H,
3
3
3
m, Í-3), 2.24–2.30 (2Í, m, Í-4), 2.65–2.69 (2H, m, Í-11), 4.81, 5.10, 5.18 (1Í each, s, OH), 6.24–6.41 (3H, m, Í-6′, 7, 6), 6.75
13
(1Í, d, J = 8.1, Í-3′), 7.16 (1Í, d, J = 8.4, Í-4′). C NMR spectrum (75 MHz, CDCl , δ, ppm): 154.52 (Ñ, Ñ-1′), 73.55
3
(Ñ, C-2), 123.74 (2ÑÍ, Ñ-2′), 32.06 (CH , C-3), 127.14 (Ñ, Ñ-3′), 17.17 (CH , C-4), 104.41 (ÑÍ, Ñ-4′), 111.04 (Ñ, Ñ-4à), 151.77
2
2
(Ñ, Ñ-5), 155.29 (ÑÍ, Ñ-5′), 123.74 (ÑÍ, Ñ-6′), 107.01 (Ñ, Ñ-6), 127.14 (ÑÍ, Ñ-7), 130.04 (ÑÍ , Ñ-8), 154.96 (Ñ, Ñ-8à), 37.43
2
(ÑÍ , C-9), 42.40 (Ñ, C-10), 25.92 (ÑÍ, Ñ-11), 26.72 (2CH ), 28.46 (2CH ).
2
3
3
1
2,2,9,9-Tetramethyl-2,3,4,7,8,9-hexahydropyrano[3,2-h]chromene (13), light-brown oil. Í NMR spectrum
(300 MHz, CDCl , δ, ppm, J/Hz): 1.39 (12Í, s, 4 CH ), 1.81 (4H, t, J = 6.6, Í-3, 8), 2.74 (4H, t, J = 6.6, Í-4, 7), 6.57 (2H, s,
3
3
13
Í-5, 6). C NMR spectrum (75 MHz, CDCl , δ, ppm): 73.92 (2C, Ñ-2, 9), 32.93 (2 CH , C-3, 8), 22.61 (2 CH , C-4, 7),
3
2
2
119.40 (CH, Ñ-5, 6), 119.15 (2Ñ, C-4à, 6à), 26.64 (4CH ), 143.46 (2Ñ, Ñ-11, 11a).
3
1
2,2-Dimethylchroman-8-ol (14), brown oil. Í NMR spectrum (300 MHz, CDCl , δ, ppm, J/Hz): 1.42 (6Í, s,
3
13
2CH ), 1.89 (2Í, t, J = 6.6, Í-3), 2.82 (2H, t, J = 6.6, Í-4), 5.69 (1Í, s, OH), 6.67–6.84 (3H, m, Í-5, 6, 7). C NMR spectrum
3
(75 MHz, CDCl , δ, ppm): 75.43 (Ñ, C-2), 33.02 (CH , C-3), 22.06 (CH , C-4), 121.11 (Ñ, Ñ-4à), 120.28 (ÑÍ, Ñ-5), 119.68 (ÑÍ,
3
2
2
C-6), 112.08 (ÑÍ, C-7), 145.22 (Ñ, Ñ-8), 141.02 (Ñ, Ñ-8à), 26.91 (2CH ).
3
1
2,2-Dimethyl-7-(3-methylbut-2-enyl)chroman-8-ol (15), brown oil. Í NMR spectrum (300 MHz, CDCl , δ, ppm,
3
J/Hz): 1.41 (12Í, s, 4CH ), 1.87–1.89 (2Í, m, Í-3), 2.78–2.83 (2H, m, Í-4), 3.34 (2Í, d, J = 6.9, Í-1′′), 5.34–5.38 (1Í, m,
3
13
Í-2′′), 5.61 (1Í, s, OH), 6.64–6.81 (1H, m, Í-5, 6). C NMR spectrum (75 MHz, CDCl , δ, ppm): 31.05 (CH , C-1′′), 75.43
3
2
(Ñ, C-2), 120.24 (ÑÍ, Ñ-2′′), 32.94 (CH , Ñ-3), 122.93 (ÑÍ, Ñ-3′′), 22.04 (CH , C-4), 121.08 (Ñ, C-4à), 112.70 (ÑÍ, Ñ-5),
2
2
119.65 (ÑÍ, C-6), 131.62 (Ñ, Ñ-7), 26.75, 145.20 (Ñ, Ñ-8), 141.62 (Ñ, Ñ-8à), 26.90 (4CH ).
3
880

1
3,6-Bis(3-methylbut-2-enyl)benzene-1,2-diol (16), light-brown oil. Í NMR spectrum (300 MHz, CDCl , δ, ppm,
3
J/Hz): 1.73 (6Í, s, 2CH ), 1.78 (6Í, s, 2CH ), 3.24 (4H, d, J = 6.9, Í-1′′, 1′′′), 5.17 (2Í, s, 2 OH), 5.23–5.28 (2H, m, Í-2′′,
3
3
13
2′′′), 6.71 (2Í, m, Í-4, 5). C NMR spectrum (75 MHz, CDCl , δ, ppm): 30.83 (2CH , C-1′′,-1′′′), 141.30 (2Ñ, C-1, 2),
3
2
123.11 (2ÑÍ, C-2′′, 2′′′), 132.36 (2C, Ñ-3′′, 3′′′), 116.18 (2ÑÍ, C-4, 5), 110.73 (2Ñ, C-6, 3), 17.83 (2CÍ ), 25.76 (2CÍ ).
3
3
1
3-(3-Methylbut-2-enyl)benzene-1,2-diol (17), light-brown oil. Í NMR spectrum (300 MHz, CDCl , δ, ppm,
3
J/Hz): 1.73 (3Í, s, CH ), 1.78 (3Í, s, CH ), 3.24 (2H, d, J = 7.2, Í-1′′), 5.09 (1Í, s, OH), 5.23–5.28 (1H, m, Í-2′′), 5.46 (1Í,
3
3
13
s, ÎÍ), 6.71–6.81 (3Í, m, Í-4, 5, 6). C NMR spectrum (75 MHz, CDCl , δ, ppm): 143.35 (C, Ñ-1), 143.44 (Ñ, C-2), 33.59
3
(CH , C-1′′), 123.35 (ÑÍ, C-2′′), 115.49 (ÑÍ, C-3), 135.14 (Ñ, C-3′′), 121.28 (ÑÍ, C-4), 120.72 (ÑÍ, C-5), 115.40 (Ñ,
2
C-6), 17.83 (CÍ ), 25.76 (CÍ ).
3
3
1
3-[4-(8-Hydroxy-2,2-dimethylchroman-7-yl)-2-methylbutan-2-yl]benzene-1,2-diol (18), brown oil. Í NMR
spectrum (300 MHz, CDCl , δ, ppm): 1.22 (6Í, s, 2CH ), 1.31 (6Í, s, 2CH ), 1.72 (2Í, m, Í-6), 1.91 (2H, br.t, Í-3), 2.54–2.60
3
3
3
(2Í, m, Í-9), 2.79 (2H, br.t, Í-4), 5.02, 5.05, 5.08 (1Í each, s, OH), 6.59–6.74 (2H, m, Í-5, 6), 6.77–6.92 (3Í, m, Í-5′, 4′, 3′).
13
C NMR spectrum (75 MHz, CDCl , δ, ppm): 143.60 (Ñ, Ñ-1′), 75.48 (Ñ, C-2), 143.68 (Ñ, Ñ-2′), 33.59 (CH , C-3), 29.61 (CH ,
3
2
2
C-4), 121.20 (ÑÍ, Ñ-4′), 124.91 (Ñ, Ñ-4à), 111.51 (ÑÍ, Ñ-5), 115.55 (2ÑÍ, Ñ-5′, 3′), 120.62 (ÑÍ, Ñ-6), 132.96 (Ñ, Ñ-6′), 142.04 (Ñ,
Ñ-7), 141.73 (Ñ, Ñ-8), 135.17 (Ñ, Ñ-8à), 29.95 (ÑÍ , Ñ-9), 45.28 (ÑÍ , C-10), 41.77 (Ñ, C-11), 28.34 (2CH ), 28.91 (2CH ).
2
2
3
3
2,2-Dimethyl-7-(1,7,7-trimethylbicyclo[2.2.1]hept-exo-2-yl)chroman-6-ol (23). 2-Isobornyl-1,4-dihydroxybenzene
(0.20 g, 0.8 mmol), prenol 2 (0.35 g, 4.0 mmol), and (i-PrO) Al (0.02 g, 0.1 mmol) in a 100-mL two-necked flask equipped
3
with a thermometer and reflux condenser were heated to 160°C until 2 was fully converted. The course of the reaction was
monitored using TLC (petroleum ether–Et O, 3:1; vanillin detector). The reaction mixture was worked up and products were
2
1
separated analogously as above. The yield of 23 was 10% as a brown oil. Í NMR spectrum (300 MHz, CDCl , δ, ppm,
3
J/Hz): 0.84 (3Í, s, CH -10′), 0.86 (3Í, s, CH -9′), 0.93 (3Í, s, CH -8′), 1.31 (3Í, s, CH ), 1.37 (3Í, s, ÑÍ ), 1.56–1.87 (7Í,
3
3
3
3
3
m, 1Í-4′, 2Í-5′, 2Í-6′, 2Í-3), 2.16–2.23 (2H, m, Í-3′), 2.71 (2Í, t, J = 6.6, Í-4), 3.04 (1Í, t, J = 8.7, Í-2′), 4.30 (1Í, s, OH),
13
6.51 (1H, s, Í-5), 6.76 (1Í, s, H-8). C NMR spectrum (75 MHz, CDCl , δ, ppm): 12.40 (CH , C-10′), 20.52 (CH , C-9′), 21.43
3
3
3
(CH , C-8′), 22.11 (CH , C-3), 26.15 (CH ), 27.42 (CH ), 27.51 (CH , C-5′), 32.89 (CH , C-4), 34.15 (CH , C-3′), 39.92 (CH ,
3
2
3
3
2
2
2
2
C-6′), 45.57 (CH, Ñ-4′), 45.71 (CH, Ñ-2′), 47.96 (C, C-1′), 49.72 (C, C-7′), 73.63 (C, Ñ-2), 103.39 (CH , C-5), 112.15 (C, C-4a),
2
118.52 (C, Ñ-7), 129.21 (CH, Ñ-8), 147.53 (C, Ñ-8a), 147.77 (C, Ñ-6).
Antiradical, Antioxidant, and Membrane-protective Activity and Cytotoxicity of the Synthesized Compounds.
Antiradical activity was assessed from the ability to react with a stable chromogenic radical. Tested compounds were added to
a MeOH solution of DPPH at concentrations of 10 and 100 μM and stirred. Optical density of the solution at 517 nm was
measured after 30 min using a Thermo Spectronic Genesys 20 spectrophotometer (USA). Degree of inhibition was calculated
in percent relative to the optical density of a solution without the tested compounds [10].
Antioxidant activity of the prenylphenols was assessed in vitro from the ability to inhibit LPO in laboratory mouse
brain [16–19]. Tested samples were incubated for 1 h at 37°C with slow stirring. The contents of secondary LPO products
reacting with 2-thiobarbituric acid (TBA–AP) were determined using a Thermo Spectronic Genesys 20 spectrophotometer
5
–1
–1
(USA) at 532 nm. An extinction coefficient of 1.56 × 10 M cm was used for the calculations [17].
Cytotoxicity, AOA, and MPA of the compounds were assessed using laboratory mouse erythrocyte suspension
(0.5% v/v) in phosphate-buffered saline (PBS, pH 7.4). The tested compounds were dissolved beforehand in Me CO.
2
The cytotoxicity of the compounds was assessed in vitro from the degree of erythrocyte hemolysis 5 h after administration of
the test-compound solutions.
Membrane-protective and AOA were determined from the degree of inhibition of H O -induced hemolysis, slowed
2
2
accumulation of secondary LPO products, and oxidation of oxyhemoglobin in erythrocytes. Hemolysis was initiated by H O
2
2
solution (0.006%). The reaction mixture was incubated in a thermostatted shaker with slow stirring at 37°C for 5 h. An aliquot
of the incubation medium was taken every hour and centrifuged for 5 min at 1600 g. The degree of hemolysis was determined
from the hemoglobin content in the supernatant on a Thermo Spectronic Genesys 20 spectrophotometer (USA) at 524 nm [11].
The percent hemolysis was calculated from the ratio to total hemolysis of the sample.
Secondary LPO products reacting with 2-thiobarbituric acid (TBA–AP) were determined spectrophotometrically as
above. Accumulation of hemoglobin oxidation products was estimated from absorption spectra in the range 540–640 nm.
The contents of different hemoglobin species (oxyHb and metHb) were calculated taking into account the corresponding
extinction coefficients [20]. Fluorescence intensities of maxima at 472–490 nm (Flyuorat-02-Panorama spectrofluorimeter,
excitation at 321 nm, emission at 400–600 nm, spectral recording step 2 nm) were used to estimate the concentration of heme
degradation products formed by oxidation of membrane-bound hemoglobin by reactive oxygen species [21]. Each experiment
881

was performed in 4–6 replicates. Results were processed statistically and diagrams were constructed using Microsoft Office
Excel 2007 software.
ACKNOWLEDGMENT
The work was sponsored by state task Reg. No. AAAA-A18-118012490385-8.
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