Synthesis of natural product-like polyprenylated phenols and quinones: Evaluation of their neuroprotective activities

Article abstract of DOI:10.1016/j.bmc.2019.115156

Twenty-seven natural product-like polyprenylated phenols and quinones were synthesized and their neuroprotective activity was tested using human monoamine oxidase B (MAO-B) and SH-SY5Y cells. Eight compounds inhibited MAO-B (IC₅₀ values < 25 μM

Full text of DOI:10.1016/j.bmc.2019.115156

Bioorganic&MedicinalChemistryxxx(xxxx)xxxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis of natural product-like polyprenylated phenols and quinones:
Evaluation of their neuroprotective activities
Hitoshi Kamauchi⁎, Takumi Oda, Kanayo Horiuchi, Koichi Takao, Yoshiaki Sugita
Laboratory of Bioorganic Chemistry, Department of Pharmaceutical Sciences, Faculty of Pharmacy and Pharmaceutical Sciences, Josai University, 1-1 Keyaki-dai, Sakado,
Saitama 350-0295, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords:
Twenty-seven natural product-like polyprenylated phenols and quinones were synthesized and their neuro-
protective activity was tested using human monoamine oxidase B (MAO-B) and SH-SY5Y cells. Eight compounds
inhibited MAO-B (IC50 values < 25 μM) and the inhibition mode and molecular docking of two (8c and 16c)
were investigated. Compounds inhibiting MAO-B activity were additionally tested for their ability to protect SH-
SY5Y cells from peroxide injury. Three derivatives (3c, 8c and 16c) exhibited both MAO-B inhibitory and
neuroprotective activity. A structure activity-relationship study showed that a phenolic hydroxyl group and a
longer side chain are important for both activities.
Fungal metabolites
Neogrifolin
Derivatization
MAO-B
SH-SY5Y cells
1. Introduction
polyprenylated phenols were isolated and evaluated their bioactivity
the structure activity relationship focused on the number of prenyl
The prenyl group is a natural functional group biosynthesized by
mevalonate or non-mevalonate pathways. Natural compounds with
prenyl subunits exhibit various bioactivities and are essential for the
melanogenesis activity of diketopiperazine derivatives reported by us
previously.1 The natural polyprenylated phenols grifolin and neo-
grifolin are secondary metabolites found in ascomycetes of Grifola spp.
and Albatrellus spp.2 Grifolic acid, ovinol and ovinal were isolated from
Albatrellus spp., have an aldehyde, carboxylic acid or hydroxyl group
(Fig. 1),3 and exhibit antimicrobial, antioxidative, and protective effects
against brain injury.4
group or their substituted group were not investigated.
In this study, the structure activity-relationship of the neuropro-
tective effects of polyprenylated phenol and quinone derivatives were
investigated. We describe the synthesis of neogrifolin and ubiquinone
derivatives containing a number of prenyl groups and tested their
neuroprotective activities using MAO-B and SH-SY5Y cells.
2. Results and discussion
2.1. Synthesis of neogrifolin derivatives
Ubiquinones are polyprenylated quinones such as vitamin E and are
biosynthesized from polyhydroxy phenols. Several terpenoid-quinones
exhibit biochemical activities in the human body; for example, ubi-
quinone 10 (Coenzyme Q10, Fig. 1) shows neuroprotective activity by
inhibiting amyloid β protein aggregation.5
The synthesis of neogrifolin derivatives involved a combination of
(1) alkylation (2) formylation (3) oxidation and (4) demethylation. The
alkylation of orcinol (1), the precursor of neogrifolin, with BF3·Et2O and
alkyl alcohol7 gave neogrifolin and the derivatives 2a-2c.8
Monoamine oxidase B (MAO-B) plays a critical role in neurological
disease, especially Parkinson’s disease. The MAO-B inhibitors selegiline
and resagiline are approved treatments for Parkinson’s disease world-
wide and recently have been used to treat Alzheimer’s disease (AD).
MAO-B expression is increased in the hippocampus and cerebral cortex
of AD patients. Oxidative deamination by MAO produces hydrogen
peroxide (H2O2) and injures neurons6 and thus polyprenylated aromatic
compounds hold promise as novel lead compounds for treating cranial
nerve diseases such as Parkinson’s and AD. Though various natural
Formylation was conducted using POCl3/DMF to yield aldehydes
3a-3c.9 To discover the structure activity-relationship, di-prenylated,
di-geranylated and di-farnesilated derivatives 3d-3f were synthesized
by a combination of alkylation and formylation of 1. Kraus-Pinnic
oxidation was performed on 3a-3c to provide the grifolic acid-type
derivatives 4a-4c10 in low yields (Scheme 1). Activity due to the hy-
droxyl group was investigated by methylating compounds 2a-c with
CH3I to give the methoxy derivatives 5a-5c2,11 (Scheme 1).
We synthesized trihydroxy derivatives using inexpensive
⁎ Corresponding author.
E-mail address: kamauchi@josai.ac.jp (H. Kamauchi).
https://doi.org/10.1016/j.bmc.2019.115156
Received 19 July 2019; Received in revised form 4 October 2019; Accepted 5 October 2019
0968-0896/©2019ElsevierLtd.Allrightsreserved.
Pleasecitethisarticleas:HitoshiKamauchi,etal.,Bioorganic&MedicinalChemistry,https://doi.org/10.1016/j.bmc.2019.115156

H. Kamauchi, et al.
Bioorganic&MedicinalChemistryxxx(xxxx)xxxx
Fig. 1. Structures of grifolin derivatives and coenzyme Q10.
Scheme 1. Synthesis of neogrifolin derivatives: (a) alkyl alcohol, BF3·Et2O; (b) POCl3, DMF; (c) NaClO2, Na2PO4; (d) CH3I, K2CO3.
polymethoxy toluene (6) as the starting material. Alkylation was per-
formed as described above to provide the polymethoxy neogrifolin
derivatives 7a-7c.12 However, demethylation of trimethoxy derivative
7a did not give expected the trihydroxy derivative 8a but rather tet-
rahydropyran 9. Similarly, although alkylation of tetramethoxy toluene
10 yielded the proposed tetramethoxy neogrifolin derivatives 11a-
11c,13 demethylation of 11a did not give tetrahydroxy derivative 12a
but rather 13 (Scheme 2).
with two alkyl side chains (3d-3f), only the di-prenylated derivative
showed activity. These results provided insights into the structure ac-
tivity-relationships of these compounds. Hydroxy groups at C-3 and C-5
are essential for inhibitory activity due to the comparison of IC50 values
of polyhydroxy derivatives (2c, 8b and 8c, IC50 = 1.3–10.5 μM) and
their polymethoxy derivatives (5b, 7b and 7c, IC50 = N.D.). In addi-
tion, in derivatives with mono-alkyl chains, the number of prenyl units
affected inhibitory activity, with longer (two or three) prenyl sidechains
(2c, 3c, 4c, 8c, 16b and 16c, IC50 1.3–26.5 μM) exhibiting stronger
activity than with a prenyl sidechain (2a, 3a, 4a, 8a, and 16a,
IC50 = N.D.). This relationship did not hold for derivatives with two
alkylated side chains (3d-3f), perhaps due to the poor solubility of 3e
and 3f in DMSO. Comparison of 2b (IC50 = N.D.) with 8b
(IC50 = 10.5 μM) and 2c (IC50 = 9.2 μM) with 8c (IC50 = 1.3 μM)
showed that an additional hydroxy group at C-4 enhances activity.
Derivatives with stronger activity (3c, 8c, 16b and 16c) typically had
an additional formyl, hydroxy or carbonyl group which might act as
hydrogen bond acceptors or donors with MAO-B. Therefore, these re-
sults discovered the importance of the number of prenyl group and
hydrogen bond acceptors to show MAO-B inhibitory activity.
Therefore, demethylation of 6 to 14 and 10 to 15 was attempted.
Alkylation of 14 gave the expected trihydroxy derivatives 8a-8c but the
alkylation of 15 did not yield tetramethoxy derivatives but rather the
unexpected compounds 16a-16c. The 13C NMR spectra of 16a-16c
showed two downshifted carbons (around 180 ppm) and HMBC corre-
lations between H-2 to C-5 and H-7 to C-2 were observed for 16a. These
spectroscopic data showed the presence of 2,3-dihydroxy-1,4-quinones.
Though synthesis of the ubiquinone derivatives from phenol derivatives
typically requires two steps (alkylation and oxidation)14 this result
showed could synthesis them only one step.
This is the first report of the synthesis of the neogrifolin derivative
natural compounds ovinal (3c) and ovinol (12c) in two or three steps.
The structures of the known compounds were confirmed by comparison
of their spectroscopic data with published data. The structures of the
new compounds (3d-3f, 4b-4c, 7b, 8a-8b, 13, 16a-16c) and known
compounds which their spectral data was not defined (3a, 5a and 9)
were established by analysis of their NMR and MS spectroscopic data.
2.2.2. Kinetics
The kinetics of MAO-B inhibition was performed using 8c and 16c
and reported protocols. Lineweaver-Burk plots of the inhibitory activ-
ities of 8c and 16c towards MAO-B indicated they are mixed (non-
competitive) inhibitors (Fig. 2). On the other hands, some inhibitor
with inhibition mode defined as “tight-binding inhibition” was well-
known. Their Lineweaver-Burk plots showed mixed or noncompetitive
behavior, but ligands are bound to the enzyme active site. In this case,
the standard steady-state kinetic model used to describe the mechanism
of inhibition is no longer valid.15 Plotting the IC50 values for each
compound at different substrate concentrations found that 8c and 16c
show a linear correlation between IC50 value and substrate concentra-
tion, in full agreement with tight-binding competitive inhibition
(Fig. 3).15
2.2. Biological evaluation of the synthesized compounds
2.2.1. MAO-B inhibitory activity
The synthesized compounds were evaluated for their MAO-B in-
hibitory activity using kynuramine, a substrate of MAO-B, and mea-
suring the amount of quinolinol produced. Of the synthesized deriva-
tives, nine exhibited inhibitory activity and four (3c, 8c, 16b and 16c)
had IC50 values greater than 5 μM (Table 1). In contrast, all derivatives
with a methoxy group showed no inhibitory activity. Of the derivatives
2

H. Kamauchi, et al.
Bioorganic&MedicinalChemistryxxx(xxxx)xxxx
binding mode of 16c was predicted to involve a hydrogen bond be-
tween 4-OH and Cys 173 and π-alkyl interactions (Fig. S1). The binding
affinity of 16c to MAO-B was also high (−12.54 kJ/mol).
These binding simulations afforded two important findings. First, a
longer sidechain supplies accepters for π-alkyl interactions, with the
arborized methyl group interacting with various amino acids. Second
the catechol substructure (trihydroxy and quinone derivatives) might
act as a hydrogen bond acceptor and stabilize the conformation. These
results explained the strong inhibitory activity of 8c and 16c.
2.2.4. Neuroprotective effect towards SH-SY5Y cells
Synthesized compounds with long alkyl chains (geranyl or farnesyl)
showed MAO-B inhibitory activity and thus the ability of these com-
pounds to protect SH-SY5Y cells from H2O2 toxicity was estimated.18
Compounds showing MAO-B inhibitory activity were selected as test
compounds and the results are shown in Fig. 5. Treatment with H2O2
alone decreased cell viability to 46.7%. 3c, 8c and 16c at 10 μM re-
sulted in over 20% recovery from H2O2 without cytotoxicity and
showed concentration dependency (Fig. 6). On the other hand, 2c
showed cytotoxicity at 5 and 10 μM (< 70% of cell viability). These
results show that the formyl and polyhydroxy groups on the phenol and
the number of prenyl groups are important.
3. Conclusion
Polyprenyl aromatic compounds were synthesized with the struc-
tural features of neogrifolin. Three derivatives (3c, 8c and 16c) ex-
hibited both MAO-B inhibitory and SH-SY5Y neuroprotective activity
and are thus potent and multi-target inhibitors exhibiting neuropro-
tective activity. Furthermore, similar SAR results (structures with long
prenyl sidechain, catechol and formyl groups on the aromatic ring are
important scaffolds exhibiting neuroprotective activity) were obtained
using the two tests. Therefore, our results showed that the discovery of
novel pharmacophores for lead compounds targeting cranial nerve
diseases.
Scheme 2. Synthesis of polymethoxy, polyhydroxy and 1,4-quinone deriva-
tives: (a) alkyl alcohol, BF3·Et2O; (b) BBr3/CH2Cl2.
4. Experimenal section
2.2.3. Docking study
4.1. General experimental procedures
A molecular docking study was performed to investigate the mode
of binding of synthesized compounds 8c and 16c. Affinity was eval-
uated by calculating the stability of the ligands when docked with the
binding pocket of the published MAO-B crystal structure (PDB 4A79)16
using Auto Dock 4.2.17 The molecular interactions of 8c in the binding
pocket include hydrogen bonding with Leu 171 and π- alkyl interac-
tions with Leu 164, Ile 316, Ile 199, Phe 103, Tyr 326, Trp 119, Pro 104
and Leu 171 (Fig. 4). The binding affinity (−12.74 kJ/mol) was greater
than that of 3c and 1 (−11.59 and −5.11 kJ/mol). Similar to 8c, the
1H and 13C NMR spectra were measured with a Varian 400-MR
spectrometer (Agilent, Tokyo, Japan), using tetramethylsilane as the
internal standard. Low- and high-resolution FABMS spectra were
measured with a JEOL JMS-700 spectrometer (JEOL). Column chro-
matography was performed using Wakogel C-200 (FUJIFILM Wako
Pure Chemical Corporation, Osaka, Japan) and ODS-A (YMC, Kyoto,
Japan). All reagents and solvents were purchased from commercial
sources. Farnesol (TCI T0608) contains slightly cis isomer.
Table 1
MAO-B inhibitory activities of the synthesized compounds.
Inhibition rate (%)a
IC50 (μM)
Inhibition rate (%)a
IC50 (μM)
26.5
Inhibition rate (%)a
IC50 (μM)
2a
2b
2c
3a
3b
3c
3d
3e
3f
4.2
2.4
0.7
4a
4b
4c
5a
5b
5c
7a
7b
7c
16.3
31.2
49.2
5.4
6.1
1.7
8.6
11a
11b
11c
8a
7.2
2.5
1.2
30.7
96.4
36.3
77.4
91.2
84.7
48.1
48.8
38.0
15.2
32.7
88.7
97.8
38.3
92.2
93.1
0.1
1.4
2.5
0.3
0.3
0.8
1.2
9.2
2.4
2.4
5.6
0.1
1.3
0.1
0.4
2.5
19.7
2.3
N. D.c
10.8
18.6
5.9
8b
10.5
1.3
7.6
3.3
8c
5.5
16a
16b
16c
N. D.b
3.1
1.4
1.3
N. D.b
34.9
4.1
a
b
c
Results are shown as mean
SD (n = 3) at 25 μM.
Not determined due to poor solubility over 25 μM.
Not determined due to the inhibition rate was under 0%. Pargyline was used as positive control (IC50 = 0.22 μM).
3

H. Kamauchi, et al.
Bioorganic&MedicinalChemistryxxx(xxxx)xxxx
Fig. 2. Lineweaver–Burk plots for MAO-B inhibition by 8c and 16c.
4.2. Synthesis
4.2.4. General procedure D: methylation
A stirring mixture of alkylated derivatives, anhydrous K2CO3, and
methyl iodide in acetone was refluxed for 6 h. The crude mixture was
chromatographed on silica gel with n-Hex/EtOAc.
4.2.1. General procedure A: Alkylation
BF3·Et2O was slowly added dropwise, to a stirred solution of poly-
hydroxy or polymethoxy phenols and alkyl alchol in dioxane at 0 °C.
After the addition was completed, the stirring was continued for 3 h at
room temperature. The mixture was poured water and extracted with
EtOAc. The organic layer was dried over Na2SO4 and filtered. The
solvent was evaporated under reduced pressure. The crude was chro-
matographed on silica gel.
4.2.5. General procedure E: demethylation
Boron tribromide (17% in CH2Cl2, 4 eq.) was added to the solution
of 3,4,5-trimethoxytoluene or 2,3,4,5-tetramethoxytoluene (1 eq.) in
CH2Cl2 at 0 °C. The ice bath was removed, and the mixture was stirred
for 3 h. The reaction mixture was evaporated under reduced pressure
and the residue was used for the next reaction without further pur-
ification.
4.2.2. General procedure B: formylation
Phosphorus oxychloride (POCl3) was added dropwise into DMF
below 0 °C. Alkylated orcinol in of DMF was added slowly and then ice
bath was removed. The stirring was continued for overnight at room
temperature. Water was added end extracted by EtOAc. The organic
layer was over dried by Na2SO4 and filtered. The solvent was evapo-
rated under reduced pressure. The crude was chromatographed on si-
lica gel with n-Hex/EtOAc.
4.2.6. 5-Methyl-4-(3-methylbut-2-en-1-yl)benzene-1,3-diol (2a)
Alkylation of orcinol (300.0 mg, 2.4 mmol) with 3-methyl-2-buten-
1-ol (373 μL, 2.4 mmol) and BF3·Et2O (150 μL) followed to general
procedure A. Purification of the crude mixture by silica-gel column
chromatography (n-Hex/EtOAc, 5:1) yielded 2a as colorless oil
(95.0 mg, 21%). 1H NMR (400 MHz, CDCl3) δ 6.26 (d, J = 2.6 Hz, H-6),
6.21 (d, J = 2.6 Hz, H-4), 5.13 (m, H-2′), 3.28 (brd, J = 7.0 Hz, H-1′),
2.23 (s, H-7), 1.80 (s, H-5′) 1.73 (s, H-4′); 13C NMR (100 MHz, CDCl3) δ
155.4 (C-3), 154.3 (C-5), 138.6 (C-1), 134.0 (C-3′), 122.3 (C-2′), 118.1
(C-2), 109.8 (C-6), 101.1 (C-4), 25.9 (C-4′), 25.3 (C-1′), 20.2 (C-7), 18.0
(C-5′); HREIMS m/z: 192.1150 [M]+ (calcd. for C12H16O2, 192.1150).
The structure was confirmed by comparison of spectroscopic data with
the published data.7
4.2.3. General procedure C: oxidation
NaH2PO4 dissolved in H2O was added to DMSO-THF 1:1 solution of
aldehyde and then NaClO2 in H2O was added and stirred 12 h at room
temperature. The mixture was extracted with EtOAc and the organic
layer was dried over Na2SO4 and filtered. The solvent was evaporated
under reduced pressure. The crude was chromatographed on octade-
cylsilyl (ODS) silica gel with MeOH/H2O.
Fig. 3. Effects of substrate (S) concentration on the IC50 values of 8c and 16c.
4

H. Kamauchi, et al.
Bioorganic&MedicinalChemistryxxx(xxxx)xxxx
Fig. 6. Protective effect of farnesyl derivatives against H2O2 toxicity towards
,
###
SH-SY5Y cells (n = 3,
*
**, ***: P < 0.05, 0.01, 0.001 vs·H2O2,
:
P < 0.001 vs. cont.)·H2O2 was tested at 500 μM. Luteolin was used as positive
control.
Purification of the crude mixture by silica-gel column chromatography
(n-Hex/EtOAc, 5:1) yielded 2b as colorless oil (98.9 mg, 16%). 1H NMR
(400 MHz, CDCl3) δ 6.26 (d, J = 2.6 Hz, H-6), 6.21 (d, J = 2.6 Hz, H-4),
5.14 (m, H-2′), 5.04 (m, H-6′), 3.28 (brd, J = 6.7 Hz, H-1′), 2.23 (s, H-
7), 2.00–2.11 (overlapped, H-4′ and H-5′), 1.79 (s, H-9′), 1.65 (s, H-8′),
1.57 (s, H-10′); 13C NMR (100 MHz, CDCl3) δ 155.5 (C-3), 154.2 (C-5),
138.5 (C-1), 137.7 (C-3′), 131.9 (C-7′), 123.8 (C-6′), 122.0 (C-2′), 117.9
(C-2), 109.6 (C-6), 101.0 (C-4), 39.7 (C-4′), 26.4 (C-5′), 25.7(C-8′), 25.1
(C-1′), 20.1 (C-7), 17.7 (C-10′), 16.1 (C-9′); HREIMS m/z: 260.1778
[M]+ (calcd. for C17H24O2, 260.1776). The structure was confirmed by
comparison of spectroscopic data with the published data.7
4.2.8. Neogrifolin (2c)
Alkylation of orcinol (2.0 g, 16.1 mmol) with farnesol (4.0 mL,
16.1 mmol) and BF3·Et2O (660 μL) followed to general procedure A.
Purification of the crude mixture by silica-gel column chromatography
(n-Hex/EtOAc, 5:1) yielded 2c as colorless oil (1.3 g, 24%). 1H NMR
(400 MHz, CDCl3) δ 6.26 (d, J = 3.0 Hz, H-6), 6.21 (d, J = 3.0 Hz, H-4),
5.13 (m, H-2′), 5.06 (overlapped, H-6′ and H-10′), 3.28 (brd,
J = 6.8 Hz, H-1′), 2.23 (s, H-7), 1.95–2.10 (overlapped, H-4′ H-5′, H-8′
and H-9′), 1.80 (s, H-13′), 1.67 (s, H-12′), 1.59 (s, H-15′), 1.57 (s, H-
14′); 13C NMR (100 MHz, CDCl3) δ 155.3 (C-3), 154.2 (C-5), 138.5 (C-
1), 137.4 (C-3′), 135.6 (C-7′), 131.3 (C-11′), 124.4 (C-10′), 123.7 (C-6′),
122.1 (C-2′), 118.0 (C-2), 109.7 (C-6), 101.0 (C-4), 39.9 (C-4′), 39.7 (C-
8′), 26.7 (C-9′), 26.4 (C-5′), 25.7 (C-12′), 25.1 (C-1′), 20.1 (C-7), 17.7
(C-15′), 16.2 (C-13′), 16.0 (C-14′); HREIMS m/z: 328.2398 [M]+ (calcd.
for C22H32O2, 328.2402). The structure was confirmed by comparison
of spectroscopic data with the published data.2
Fig. 4. Molecular docking of 8c and MAO-B. (a) Predicted binding conforma-
tions. (b) The key residues and their interactions with 8c.
4.2.9. 4,6-Dihydroxy-2-methyl-3-(3-methylbut-2-en-1-yl)benzaldehyde
(3a)
Formylation of 2a (540.0 mg 2.8 mmol) with POCl3 (456 μL,
4.9 mmol) followed to general procedure B. Purification of the crude
mixture by silica-gel column chromatography (n-Hex/EtOAc, 5:1)
yielded 3a as colorless oil (122.8 mg, 20%). 1H NMR (400 MHz, CDCl3)
δ 12.5 (s, 5-OH), 10.2 (s, H-8), 6.23 (brs, H-4), 5.81 (brs, 3-OH), 5.06
(m, H-2′), 3.34 (brd, J = 6.7 Hz, H-1′), 2.49 (s, H-7), 1.80 (s, H-5′) 1.73
(s, H-4′); 13C NMR (100 MHz, CDCl3) δ 193.7 (C-8), 164.4 (C-5), 162.2
(C-3), 142.0 (C-1), 134.0 (C-3′), 121.5 (C-2′), 119.2 (C-2), 113.9 (C-6),
101.4 (C-4), 25.7 (C-4′), 24.7 (C-1′), 17.9 (C-5′), 13.8 (C-7); HREIMS m/
z: 220.1095 [M]+ (calcd. for C13H16O3, 220.1099).
Fig. 5. Protective effect of the tested compounds against H2O2 toxicity towards
SH-SY5Y cells (n = 3, *, ***: P < 0.05, 0.001 vs·H2O2, ###: P < 0.001 vs.
cont.). Synthesized compounds were tested at 10 μM·H2O2 was tested at
500 μM. Luteolin was used as positive control.
4.2.10. (E)-3-(3,7-dimethylocta-2,6-dien-1-yl)-4,6-Dihydroxy-2-
methylbenzaldehyde (3b)
4.2.7. (E)-4-(3,7-dimethylocta-2,6-dien-1-yl)-5-Methylbenzene-1,3-diol
(2b)
Formylation of 2b (160.0 mg 0.50 mmol) with POCl3 (103 μL,
1.1 mmol) followed to general procedure B. Purification of the crude
mixture by silica-gel column chromatography (n-Hex/EtOAc, 5:1)
Alkylation of orcinol (300 mg, 2.4 mmol) with geraniol (373 μL,
2.4 mmol) and BF3·Et2O (150 μL) followed to general procedure A.
5

H. Kamauchi, et al.
Bioorganic&MedicinalChemistryxxx(xxxx)xxxx
yielded 3b as colorless oil (84.6 mg, 59%). 1H NMR (400 MHz, CDCl3) δ
12.50 (s, 5-OH), 10.16 (s, H-8), 6.34 (brs, 4-OH), 6.24 (brs, H-4),
5.03–5.07 (overlapped, H-2′ and H-6′), 3.33 (brd, J = 6.4 Hz, H-1′),
2.48 (s, H-7), 2.01–2.09 (overlapped, H-4′ and H-5′), 1.79 (s, H-9′), 1.66
(s, H-8′), 1.58 (s, H-10′); 13C NMR (100 MHz, CDCl3) δ 193.7 (C-8),
164.4 (C-3), 162.5 (C-5), 142.1 (C-1), 137.5 (C-3′), 131.8 (C-7′), 123.9
(C-6′), 121.5 (C-2′), 119.5 (C-2), 113.8 (C-6), 101.3 (C-4), 39.6 (C-4′),
26.4 (C-5′), 25.7(C-8′), 24.6 (C-1′), 17.7 (C-10′), 16.3 (C-9′), 13.8 (C-7);
HREIMS m/z: 288.1723 [M]+ (calcd. for C18H24O3, 288.1725). The
structure was confirmed by comparison of spectroscopic data with the
published data.8
10″), 16.2 (2C, C-9′ and C-9″), 13.5 (C-7); HREIMS m/z: 424.2969 [M]+
(calcd. for C28H40O3, 424.2977).
4.2.14. 2,4-Dihydroxy-6-methyl-3,5-bis((2E,6E)-3,7,11-trimethyldodeca-
2,6,10-trien-1-yl)benzaldehyde (3f)
2,4-dihydroxy-6-methylbenzaldehyde (1.0 g 6.6 mmol) was sub-
jected to alkylation with farnesol (3.0 mL, 12 mmol) and BF3·Et2O
(600 μL) followed to general procedure A. Purification of the crude
mixture by silica-gel column chromatography (n-Hex/EtOAc, 20:1) and
ODS silica gel with MeOH/H2O yielded 3f as colorless oil (10.1 mg,
0.3%). 1H NMR (400 MHz, CDCl3) δ 12.9 (s, 5-OH), 10.2 (s, H-8), 6.34
(s, 3-OH), 5.24 (m, H-2″), 5.03–5.09 (overlapped, H-2′, H-6′, H-6″, H-
10′ and H-10″), 3.43 (brd, J = 7.1 Hz, H-1″), 3.32 (brd, J = 6.6 Hz, H-
1′), 2.45 (s, H-7), 1.92–2.13 (overlapped, H-4′, H-4″, H-5′, H-5″, H-8′,
H-8″, H-9′ and H-9″) 1.82, 1.77 (each, s, H-13′ and H-13″), 1.68
(overlapped, H-12′ and H-12″), 1.58 (overlapped, H-14′, H-14″, H-15′
and H-15″); 13C NMR (100 MHz, CDCl3) δ 193.6 (C-8), 161.7 (C-5),
161.3 (C-3), 139.7 (C-1), 139.4, 136.4 (C-3′ and C-3″), 135.8, 135.6 (C-
7′ and C-7″), 131.3, (2C, C-11′ and C-11″), 124.7, 124.3 (C-10′ and C-
10″), 123.9, 123.5 (C-6′ and C-6″), 122.1, 121.1 (C-2′ and C-2″), 119.7
(C-2), 113.3 (C-6), 111.1 (C-4), 39.7 (4C, C-4′, C-4″, C-8′ and C-8″),
26.7 (2C, C-9′ and C-9″), 26.3 (2C, C-5′ and C-5″), 25.7 (2C, C-12′and C-
12″), 24.6, 21.5 (C-1′ and C-1″), 17.7 (2C, C-15′ and C-15″), 16.3 (2C),
16.2, 16.0 (C-13′, C-13″, C-14′ and C-14″), 13.5 (C-7); HREIMS m/z:
560.4222 [M]+ (calcd. for C38H56O3, 560.4229).
4.2.11. Ovinal (3c)
Formylation of 2c (417.7 mg, 1.3 mmol) with POCl3 (236 μL,
2.5 mmol) followed to general procedure B. Purification of the crude
mixture by silica-gel column chromatography (n-Hex/EtOAc, 5:1)
yielded 3c as colorless oil (357.6 mg, 77%). 1H NMR (400 MHz, CDCl3)
δ 12.50 (s, 5-OH), 10.17 (s, H-8), 6.24 (s, H-4), 6.18 (brs, 3-OH),
5.04–5.09 (overlapped, H-2′, H-6′ and H-10′), 3.34 (brd, J = 6.6 Hz, H-
1′), 2.48 (s, H-7), 1.95–2.10 (overlapped, H-4′ H-5′, H-8′ and H-9′), 1.80
(s, H-13′), 1.67 (s, H-12′), 1.59 (s, H-15′), 1.59 (s, H-14′); 13C NMR
(100 MHz, CDCl3) δ 193.8 (C-8), 164.5 (C-3), 162.6 (C-5), 142.2 (C-1),
137.7 (C-3′), 135.7 (C-7′), 131.5 (C-11′), 124.4 (C-10′), 123.8 (C-6′),
122.6 (C-2′), 119.6 (C-2), 114.0 (C-6), 101.5 (C-4), 39.8 (C-4′), 39.8 (C-
8′), 26.8 (C-9′), 26.5 (C-5′), 25.9 (C-12′), 24.7 (C-1′), 17.8 (C-15′), 16.4
(C-13′), 16.2 (C-14′), 14.0 (C-7); HREIMS m/z: 356.2354 [M]+ (calcd.
for C23H32O3, 356.2351). The structure was confirmed by comparison
of spectroscopic data with the published data.3
4.2.15. 4,6-Dihydroxy-2-methyl-3-(3-methylbut-2-en-1-yl)benzoic
acid
(4a)
Oxidation of 3a (20.0 mg, 0.091 mmol) with NaH2PO4 (55.0 mg)
and NaClO2 (55.0 mg) followed to general procedure C. After pur-
ification 4a was yielded as white solid (14.1 mg 66%). 1H NMR
(400 MHz, CD3OD) δ 6.20 (brs, H-4), 5.00 (m, H-2′), 3.30 (overlapped
with CD3OD, H-1′), 2.43 (s, H-7), 1.75 (s, H-5′) 1.67 (s, H-4′); 13C NMR
(100 MHz, CD3OD) δ 173.7 (C-8), 161.9 (C-5), 160.1 (C-3), 140.7 (C-1),
130.1 (C-3′), 123.1 (C-2′), 120.2 (C-2), 105.5 (C-6), 99.7 (C-4), 24.5 (C-
4′), 24.3 (C-1′), 17.2 (C-5′), 16.5 (C-7); HREIMS m/z: 236.1042 [M]+
(calcd. for C13H16O4, 236.1049). The structure was confirmed by
comparison of spectroscopic data with the published data.9
4.2.12. 2,4-Dihydroxy-6-methyl-3,5-bis(3-methylbut-2-en-1-yl)
benzaldehyde (3d)
Formylation of orcinol (1.0 g, 7.0 mmol) with POCl3 (1.58 mL,
14.1 mmol) followed to general procedure B. Crystallization from
aqueous layer and purification from organic layer yielded 2,4-dihy-
droxy-6-methylbenzaldehyde (706.8 mg, 66%). This aldehyde
(230.0 mg, 1.5 mmol) was subjected to alkylation with 2-methyl-
3buten-2-ol (780 μL, 7.4 mmol) and BF3·Et2O (100 μL) followed to
general procedure A. Purification of the crude mixture by silica-gel
column chromatography (n-Hex/EtOAc, 20:1) yielded 3d as colorless
oil (54.8 mg, 13%). 1H NMR (400 MHz, CDCl3) δ 12.9 (s, 5-OH), 10.2 (s,
H-8), 6.33 (s, 3-OH), 5.23 (m, H-2″), 5.04 (m, H-2′), 3.42 (brd,
J = 7.1 Hz, H-1″), 3.32 (brd, J = 6.6 Hz, H-1′), 2.45 (s, H-7), 1.83, 1.78
(each s, H-5′ and H-5″) 1.76, 1.71 (each s, H-4′ and H-4″); 13C NMR
(100 MHz, CDCl3) δ 193.7 (C-8), 161.7 (C-5), 161.2 (C-3), 139.3 (C-1),
136.0 (C-3″), 133.0 (C-3′), 122.0 (C-2″), 121.2 (C-2′), 119.5 (C-2),
113.3 (C-6), 111.2 (C-4), 25.9, 25.7 (C-4′and C-4″), 24.8, 21.5 (C-1′ and
C-1″), 18.0, 17.9 (C-5′ and C-5″), 13.5 (C-7); HREIMS m/z: 288.1728
[M]+ (calcd. for C18H24O3, 288.1725).
4.2.16. (E)-3-(3,7-dimethylocta-2,6-dien-1-yl)-4,6-Dihydroxy-2-
methylbenzoic acid (4b)
Oxidation of 3b (79.0 mg, 0.27 mmol) with NaH2PO4 (106.0 mg)
and NaClO2 (65.0 mg) followed to general procedure C. After pur-
ification 4b was yielded as white solid (13.4 mg 16%). 1H NMR
(400 MHz, CD3OD) δ 6.20 (s, H-4), 5.04, 5.01 (each m, H-2′and H-6′),
3.30 (overlapped, H-1′), 2.43 (s, H-7), 2.06, 1.97 (overlapped, H-4′ and
H-5′) 1.74 (s, H-9′), 1.62 (s, H-8′), 1.56 (s, H-10′); 13C NMR (100 MHz,
CD3OD) δ 173.8 (C-8), 161.8 (C-5), 160.0 (C-3), 140.8 (C-1), 133.7 (C-
3′), 130.6 (C-7′), 124.0, (C-6′), 123.4 (C-2′), 120.2 (C-2), 105.7 (C-6),
99.6 (C-4), 39.7 (C-4′), 26.2 (C-5′), 24.4 (C-8′), 24.1 (C-1′), 17.2 (C-10′),
16.3 (C-9′), 14.8 (C-7); HREIMS m/z: 304.1673 [M]+ (calcd. for
4.2.13. 3,5-Bis((E)-3,7-dimethylocta-2,6-dien-1-yl)-2,4-dihydroxy-6-
methylbenzaldehyde (3e)
3b (380.0 mg, 1.2 mmol) was subjected to alkylation with geraniol
(236 μL, 1.3 mmol) and BF3·Et2O (100 μL) followed to general proce-
dure A. Purification of the crude mixture by silica-gel column chro-
matography (n-Hex/EtOAc, 20:1) and ODS silica gel with MeOH/H2O
yielded 3e as colorless oil (3.6 mg, 0.7%). 1H NMR (400 MHz, CDCl3) δ
12.8 (s, 5-OH), 10.2 (s, H-8), 6.37 (s, 3-OH), 5.24 (m, H-2″), 5.02–5.06
(overlapped, H-2′, H-6′ and H-6″), 3.42 (brd, J = 7.1 Hz, H-1″), 3.32
(brd, J = 6.6 Hz, H-1′), 2.45 (s, H-7), 1.98–2.15 (overlapped, H-4′, H-
4″, H-5′ and H-5″) 1.82, 1.77 (each, s, H-9′ and H-9″), 1.68, 1.66 (each
s, H-8′ and H-8″), 1.59, 1.58 (each s, H-10′ and H-10″); 13C NMR
(100 MHz, CDCl3) δ 193.6 (C-8), 161.7 (C-3), 161.4 (C-5), 139.8 (C-1),
139.4, 136.4 (C-3′ and C-3″), 132.1, 131.6 (C-7′ and C-7″), 124.0, 123.7
(C-6′ and C-6″), 122.1, 121.1 (C-2′ and C-2″), 119.7 (C-2), 113.3 (C-6),
111.4 (C-4), 39.7 (2C, C-4′ and C-4″), 26.5, 26.3 (C-5′ and C-5″), 25.7
(2C, C-8′and C-8″), 24.6, 21.5 (C-1′ and C-1″), 17.7 (2C, C-10′ and C-
C18H24O4, 304.1673).
4.2.17. 4,6-Dihydroxy-2-methyl-3-((2E,6E)-3,7,11-trimethyldodeca-
2,6,10-trien-1-yl)benzoic acid (4c)
Oxidation of 3c (357.0 mg, 1.0 mmol) with NaH2PO4 (390.0 mg)
and NaClO2 (225.0 mg) followed to general procedure C. After pur-
ification 4c was yielded as white solid (32.2 mg 9%). 1H NMR
(400 MHz, CD3OD) δ 6.20 (s, H-4), 4.98–5.06 (overlapped, H-2′, H-6′
and H-10′), 3.30 (overlapped, H-1′), 2.43 (s, H-7), 1.88–2.14 (over-
lapped, H-4′, H-5′, H-8′ and H-9′) 1.75 (s, H-13′), 1.63 (s, H-12′), 1.57,
1.55 (each, s, H-14′ and H-15′); 13C NMR (100 MHz, CD3OD) δ 173.8
(C-8), 162.0 (C-5), 160.2 (C-3), 140.9 (C-1), 134.4 (C-3′), 133.6 (C-7′),
130.5 (C-11′), 124.1, (C-10′), 124.0 (C-6′), 123.4 (C-2′), 120.2 (C-2),
105.4 (C-6), 99.7 (C-4), 39.7, 39.4 (C-4′ and C-8′), 26.2 (C-9′), 25.9 (C-
5′), 24.5 (C-12′), 24.2 (C-1′), 17.3 (C-15′), 16.3, 14.9 (C-13′ and C-14′),
6

H. Kamauchi, et al.
Bioorganic&MedicinalChemistryxxx(xxxx)xxxx
4.2.22. (E)-2-(3,7-dimethylocta-2,6-dien-1-yl)-3,4,5-Trimethoxy-1-
14.7 (C-7); HREIMS m/z: 372.2296 [M]+ (calcd. for C23H32O4,
372.2301).
methylbenzene (7b)
Alkylation of 3,4,5-trimethoxytoluene (1.0 g, 5.5 mmol) with ger-
aniol (963 μL, 5.5 mmol) and BF3·Et2O (330 μL) followed to general
procedure A. Purification of the crude mixture by silica-gel column
chromatography (n-Hex/EtOAc, 10:1) yielded 7b as colorless oil
(539.6 mg, 31%). 1H NMR (400 MHz, CDCl3) δ 6.50 (s, H-6), 5.02–5.07
(overlapped, H-2′ and H-6′), 3.85 (s, 4-OMe), 3.83 (s, 3-OMe and 5-
OMe), 3.29 (brd, J = 7.0 Hz, H-1′), 2.23 (s, H-7), 1.98–2.07 (over-
4.2.18. 1,5-Dimethoxy-3-methyl-2-(3-methylbut-2-en-1-yl)benzene (5a)
Methylation of 2a (100.0 mg 0.52 mmol) with anhydrous K2CO3
(360.0 mg, 2.6 mmol) and methyl iodide (160 μL, 2.6 mmol) followed to
general procedure D. The di-methylated derivative 5a was yielded as
colorless oil (69.1 mg 60%). 1H NMR (400 MHz, CDCl3) δ 6.35 (over-
lapped, H-4 and H-6), 5.07 (m, H-2′), 3.83, 3.80 (each s, 3-OMe and 5-
OMe), 3.30 (brd, J = 6.9 Hz, H-1′), 2.28 (s, H-7), 1.78 (s, H-5′), 1.68 (s,
H-4′); 13C NMR (100 MHz, CDCl3) δ 158.2 (C-3 and C-5), 138.0 (C-1),
130.8 (C-3′), 123.0 (C-2′), 121.0 (C-2), 106.5 (C-6), 96.2 (C-4), 55.6,
55.2 (3-OMe and 5-OMe), 25.8 (C-4′), 24.8 (C-1′), 20.0 (C-7), 17.8 (C-
5′); HREIMS m/z: 220.1461 [M]+ (calcd. for C14H20O2, 220.1463).
lapped, H-4′ and H-5′), 1.76 (s, H-9′), 1.65 (s, H-8′), 1.57 (s, H-10′); 13
C
NMR (100 MHz, CDCl3) δ 151.8 (C-5), 151.0 (C-3), 140.3 (C-4), 134.8
(C-3′), 132.0 (C-1), 131.3 (C-7′), 126.3 (C-2), 124.3 (C-6′), 123.1 (C-2′),
109.4 (C-6), 61.0 (5-OMe), 60.8 (3-OMe), 55.9 (4-OMe), 39.7 (C-4′),
26.6 (C-5′), 25.7(C-8′), 25.5 (C-1′), 19.7 (C-7), 17.7 (C-10′), 16.1 (C-9′);
HREIMS m/z: 318.2195 [M]+ (calcd. for C20H30O3, 318.2195).
4.2.19. (E)-2-(3,7-dimethylocta-2,6-dien-1-yl)-1,5-Dimethoxy-3-
methylbenzene (5b)
4.2.23. 1,2,3-Trimethoxy-5-methyl-4-((2E,6E)-3,7,11-trimethyldodeca-
2,6,10-trien-1-yl)benzene (7c)
Methylation of 2b (57.2 mg, 0.22 mmol) with anhydrous K2CO3
(151.0 mg, 1.1 mmol) and methyl iodide (155 μL, 2.5 mmol) followed to
general procedure D. The di-methylated derivative 5b was yielded as
colorless oil (49.5 mg, 78%). 1H NMR (400 MHz, CDCl3) δ 6.33 (s, H-4
and H-6), 5.02–5.07 (overlapped, H-2′ and H-6′), 3.79, 3.78 (each s, 3-
OMe and 5-OMe), 3.28 (brd, J = 6.7 Hz, H-1′), 2.25 (s, H-7), 1.94–2.06
(overlapped, H-4′ and H-5′), 1.75 (s, H-9′), 1.65 (s, H-8′), 1.57 (s, H-
10′); 13C NMR (100 MHz, CDCl3) δ 158.2, 158.2 (C-3 and C-5), 138.2
(C-1), 164.4 (C-3), 134.4 (C-3′), 131.2 (C-7′), 124.4 (C-6′), 123.0 (C-2′),
121.1 (C-2), 106.5 (C-6), 96.2 (C-4), 55.6, 55.2 (3-OMe and 5-OMe),
39.8 (C-4′), 26.7 (C-5′), 25.7(C-8′), 24.6 (C-1′), 20.0 (C-7), 17.6 (C-10′),
16.1 (C-9′); HREIMS m/z: 288.2091 [M]+ (calcd. for C19H28O2,
288.2089). The structure was confirmed by comparison of spectro-
scopic data with the published data.10
Alkylation of 3,4,5-trimethoxytoluene (1.0 g, 5.5 mmol) with far-
nesol (1372 μL, 5.5 mmol) and BF3·Et2O (330 μL) followed to general
procedure A. Purification of the crude mixture by silica-gel column
chromatography (n-Hex/EtOAc, 10:1) yielded 7c as colorless oil
(759.4 mg, 36%). 1H NMR (400 MHz, CDCl3) δ 6.50 (s, H-6), 5.03–5.10
(overlapped, H-2′, H-6′ and H-10′), 3.85 3.83, 3.83 (each s, 3-OMe, 4-
OMe and 5-OMe), 3.29 (brd, J = 7.1 Hz, H-1′), 2.23 (s, H-7), 1.95–2.08
(overlapped, H-4′ H-5′, H-8′ and H-9′), 1.77 (s, H-13′), 1.67 (s, H-12′),
1.59 (s, H-15′), 1.57 (s, H-14′); 13C NMR (100 MHz, CDCl3) δ 151.8,
151.0 (C-3 and C-5), 140.3 (C-4), 135.1 (C-7′), 134.8 (C-3′), 132.0 (C-
1), 131.3 (C-11′), 126.3 (C-2), 125.0 (C-10′), 124.3 (C-6′), 123.1 (C-2′),
109.4 (C-6), 61.0, 60.8, 55.9 (3-OMe, 4-OMe and 5-OMe), 40.0 (C-4′),
39.7 (C-8′), 26.7 (C-9′), 26.6 (C-5′), 25.7 (C-12′), 25.5 (C-1′), 19.7 (C-7),
17.6 (C-15′), 16.2 (C-13′), 16.0 (C-14′); HREIMS m/z: 386.2818 [M]+
(calcd. for C25H38O3, 386.2821). The structure was confirmed by
comparison of spectroscopic data with the published data.11
4.2.20. 1,5-Dimethoxy-3-methyl-2-((2E,6E)-3,7,11-trimethyldodeca-
2,6,10-trien-1-yl)benzene (5c)
Methylation of 2c (100.0 mg 0.30 mmol) with anhydrous K2CO3
(207.0 mg, 1.5 mmol) and methyl iodide (93 μL, 1.5 mmol) followed to
general procedure D. The di-methylated derivative 5c was yielded as
colorless oil (30.4 mg, 28%). 1H NMR (400 MHz, CDCl3) δ 6.33, 6.32
(each s, H-4 and H-6), 5.04–5.10 (overlapped, H-2′, H-6′ and H-10′),
3.79 3.78 (each s, 3-OMe and 5-OMe), 3.28 (brd, J = 6.7 Hz, H-1′), 2.25
(s, H-7), 1.93–2.09 (overlapped, H-4′ H-5′, H-8′ and H-9′), 1.75 (s, H-
13′), 1.67 (s, H-12′), 1.59 (s, H-15′), 1.57 (s, H-14′); 13C NMR
(100 MHz, CDCl3) δ 158.2, 158.2 (C-3 and C-5), 138.2 (C-1), 134.8 (C-
3′), 134.4 (C-7′), 131.2 (C-11′), 124.4 (C-10′), 124.2 (C-6′), 123.0 (C-
2′), 121.1 (C-2), 106.5 (C-6), 96.2 (C-4), 55.6, 55.2 (3-OMe and 5-
OMe), 39.8 (C-4′), 39.7 (C-8′), 26.7 (C-9′), 26.6 (C-5′), 25.8 (C-12′),
24.6 (C-1′), 20.0 (C-7), 17.8 (C-15′), 16.1 (C-13′), 16.0 (C-14′); HREIMS
m/z: 356.2723 [M]+ (calcd. for C24H36O2, 356.2715). The structure
was confirmed by comparison of spectroscopic data with the published
data.2
4.2.24. 1,2,3,4-Tetramethoxy-5-methyl-6-(3-methylbut-2-en-1-yl)benzene
(11a)
Alkylation of 2,3,4,5-tetrahydroxyoluene (300.0 mg, 1.41 mmol)
with 3-methyl-2-buten-1-ol (141 μL, 1.41 mmol) followed to general
procedure A. Purification of the crude mixture by silica-gel column
chromatography (n-Hex/EtOAc, 50:1) yielded 11a as colorless oil
(97.5 mg, 25%). 1H NMR (400 MHz, CDCl3) δ 5.04 (m, H-2′), 3.91,
3.90, 3.79, 3.78 (each s, 3-OMe, 4-OMe, 5-OMe and 6-OMe), 3.31 (brd,
J = 6.7 Hz, H-1′), 2.15 (s, H-7), 1.77 (s, H-5′), 1.69 (s, H-4′); 13C NMR
(100 MHz, CDCl3) δ 147.8, 147.6 (C-3 and C-6), 144.9, 144.7 (C-4 and
C-5), 131.4 (C-3′), 129.2 (C-2), 125.3 (C-2′), 122.8 (C-1), 61.1, 61.1,
61.1, 60.7 (3-OMe, 4-OMe, 5-OMe and 6-OMe), 25.9 (C-4′), 25.8 (C-1′),
17.9 (C-5′), 11.7 (C-7′); HREIMS m/z: 280.1677 [M]+ (calcd. for
C
16H24O4, 280.1675). The structure was confirmed by comparison of
spectroscopic data with the published data.12
4.2.21. 1,2,3-Trimethoxy-5-methyl-4-(3-methylbut-2-en-1-yl)benzene
(7a)
4.2.25. (E)-1-(3,7-dimethylocta-2,6-dien-1-yl)-2,3,4,5-Tetramethoxy-6-
methylbenzene (11b)
Alkylation of 3,4,5-trimethoxytoluene (1.0 g, 5.5 mmol) with 3-
methyl-2-buten-1-ol (549 μL, 5.5 mmol) and BF3·Et2O (330 μL) followed
to general procedure A. Purification of the crude mixture by silica-gel
column chromatography (n-Hex/EtOAc, 10:1) yielded 7a as colorless
oil (482.9 mg, 35%). 1H NMR (400 MHz, CDCl3) δ 6.50 (s, H-6), 5.04
(m, H-2′), 3.85, 3.84, 3.82 (each s, 3-OMe, 4-OMe and 5-OMe), 3.28
(brd, J = 6.9 Hz, H-1′), 2.23 (s, H-7), 1.77 (s, H-5′), 1.68 (s, H-4′); 13C
NMR (100 MHz, CDCl3) δ 151.9, 151.2 (C-3 and C-5), 140.5 (C-4),
132.0 (C-1), 131.2 (C-3′), 126.4 (C-2), 123.3 (C-2′), 109.6 (C-6), 61.1,
60.9, 56.1 (3-OMe, 4-OMe and 5-OMe), 25.9 (C-4′), 25.8 (C-1′), 19.8 (C-
7), 17.8 (C-5′); HREIMS m/z: 250.1567 [M]+ (calcd. for C15H22O3,
250.1569). The structure was confirmed by comparison of spectro-
scopic data with the published data.11
Alkylation of 2,3,4,5-tetrahydroxyoluene (300.0 mg, 1.41 mmol)
with geraniol (246 μL, 1.41 mmol) followed to general procedure A.
Purification of the crude mixture by silica-gel column chromatography
(n-Hex/EtOAc, 50:1) yielded 11b as colorless oil (45.7 mg, 9%). 1H
NMR (400 MHz, CDCl3) δ 4.93–5.22 (overlapped, H-2′ and H-6′), 3.91,
3.90, 3.79, 3.79 (each s, 3-OMe, 4-OMe, 5-OMe and 6-OMe), 3.32 (brd,
J = 6.7 Hz, H-1′), 2.14 (s, H-7), 1.99–2.08 (overlapped, H-4′ and H-5′),
1.76 (s, H-9′), 1.64 (s, H-8′), 1.58 (s, H-10′); 13C NMR (100 MHz, CDCl3)
δ 147.8, 147.7 (C-3 and C-6), 144.9, 144.7 (C-4 and C-5), 135.0 (C-7′),
131.3 (C-3′), 129.3 (C-2), 125.4 (C-2′), 124.3 (C-6′), 122.9 (C-1), 61.1,
61.1, 61.1, 60.7 (3-OMe, 4-OMe, 5-OMe and 6-OMe), 39.7 (C-4′), 26.6
(C-5′), 25.7 (C-8′), 25.7 (C-1′), 17.7 (C-10′), 16.2 (C-9′), 11.7 (C-7);
HREIMS m/z: 348.2301 [M]+ (calcd. for C21H32O4, 348.2301). The
7

H. Kamauchi, et al.
Bioorganic&MedicinalChemistryxxx(xxxx)xxxx
structure was confirmed by comparison of spectroscopic data with the
published data.12
(C-6), 39.6 (C-4′), 26.4 (C-5′), 25.7 (C-8′), 25.7 (C-1′), 19.4 (C-7), 17.7
(C-10′), 16.1 (C-9′); HREIMS m/z: 276.1728 [M]+ (calcd. for C17H24O3,
276.1725).
4.2.26. 1,2,3,4-Tetramethoxy-5-methyl-6-((2E,6E)-3,7,11-
trimethyldodeca-2,6,10-trien-1-yl)benzene (11c)
4.2.31. 5-Methyl-4-((2E,6E)-3,7,11-trimethyldodeca-2,6,10-trien-1-yl)
benzene-1,2,3-triol (8c)
Alkylation of 2,3,4,5-tetrahydroxyoluene (200.0 mg, 0.94 mmol)
with farnesol (470 μL, 1.89 mmol) followed to general procedure A.
Purification of the crude mixture by silica-gel column chromatography
(n-Hex/EtOAc, 50:1) yielded 11c as colorless oil (15.5 mg, 4%). 1H
NMR (400 MHz, CDCl3) δ 4.61–5.79 (overlapped, H-2′, H-6′ and H-10′),
3.91 3.90, 3.78, 3.78 (each s, 3-OMe, 4-OMe, 5-OMe and 6-OMe), 3.29
(brd, J = 7.1 Hz, H-1′), 2.23 (s, H-7), 1.95–2.08 (overlapped, H-4′ H-5′,
H-8′ and H-9′), 1.77 (s, H-13′), 1.67 (s, H-12′), 1.59 (s, H-15′), 1.57 (s,
H-14′); 13C NMR (100 MHz, CDCl3) δ 147.8, 147.7 (C-3 and C-6), 144.9,
144.7 (C-4 and C-5), 135.1 (C-7′), 135.0 (C-3′), 131.5 (C-11′), 129.3 (C-
2), 126.3 (C-2′), 124.3 (C-6′), 124.1 (C-10′), 122.9 (C-1), 61.1, 61.1,
61.1, 60.7 (3-OMe, 4-OMe, 5-OMe and 6-OMe), 39.8 (C-4′), 39.7 (C-8′),
26.7 (C-9′), 26.6 (C-5′), 25.8 (C-12′), 25.7 (C-1′), 17.7 (C-15′), 16.2 (C-
13′), 16.0 (C-14′), 11.7 (C-7); HREIMS m/z: 416.2931 [M]+ (calcd. for
C26H40O4, 416.2927). The structure was confirmed by comparison of
spectroscopic data with the published data.12
Alkylation of 14 (100.0 mg, 0.71 mmol) with geraniol (177 μL,
0.71 mmol) followed to general procedure A. Purification of the crude
mixture by silica-gel column chromatography (CHCl3/MeOH, 50:1)
yielded 8c as colorless oil (34.8 mg, 14%). 1H NMR (400 MHz, CDCl3) δ
6.34 (s, H-6), 5.06–5.17 (overlapped, H-2′, H-6′ and H-10′), 3.30 (brd,
J = 6.8 Hz, H-1′), 2.18 (s, H-7), 2.01–2.07 (overlapped, H-4′ H-5′, H-8′
and H-9′), 1.79 (s, H-13′), 1.68 (s, H-12′), 1.59 (s, H-15′), 1.59 (s, H-
14′); 13C NMR (100 MHz, CDCl3) δ 142.7 (C-7), 141.7 (C-5), 137.7 (C-
3′), 135.6 (C-7′), 131.4 (C-11′), 129.9 (C-4), 127.7 (C-1), 124.3 (C-10′),
123.6 (C-6′), 122.1 (C-2′), 118.0 (C-2), 109.2 (C-6), 39.9 (C-8′), 39.7 (C-
4′), 26.7 (C-9′), 26.3 (C-5′), 25.7 (C-12′), 25.7 (C-1′), 19.4 (C-7), 17.7
(C-15′), 16.3 (C-13′), 16.1 (C-14′); HREIMS m/z: 344.2353 [M]+ (calcd.
for C22H32O3, 344.2351). The structure was confirmed by comparison
of spectroscopic data with the published data.3
4.2.32. 2,3-Dihydroxy-5-methyl-6-(3-methylbut-2-en-1-yl)cyclohexa-2,5-
diene-1,4-dione (16a)
4.2.27. 2,2,5-Trimethylchromane-7,8-diol (9)
Demethylation of 7a (100.0 mg, 0.71 mmol) followed to general
Alkylation of 15 (100.0 mg, 0.64 mmol) with 3-methyl-2-buten-1-ol
(64 μL, 0.64 mmol) followed to general procedure A. Purification of the
crude mixture by silica-gel column chromatography (CHCl3/MeOH,
50:1) and ODS silica gel column chromatography (MeOH/H2O 8:2)
yielded 16a as red oil (38.1 mg, 27%). 1H NMR (400 MHz, CDCl3) δ
6.36 (overlapped, 4-OH and 5-OH), 4.92 (m, H-2′), 3.19 (brd,
J = 7.2 Hz, H-1′), 2.06 (s, H-7), 1.73 (s, H-5′), 1.68 (s, H-4′); 13C NMR
(100 MHz, CDCl3) δ 184.5 (C-6), 183.8 (C-3), 140.9, 138.0 (C-1 and C-
2), 134.5, 133.9 (C-4 and C-5), 133.9 (C-3′), 118.5 (C-2′), 25.7 (C-4′),
18.0 (C-5′), 11.7 (C-7); HREIMS m/z: 222.0890 [M]+ (calcd. for
procedure
E
yielded
9
as colorless oil (11.4 mg, 8%). 1H NMR
(400 MHz, CDCl3) δ 6.36 (s, H-6), 5.21 (overlapped, 4-OH and 5-OH),
2.56 (t, J = 6.8 Hz, H-1′), 2.12 (s, H-7), 1.82 (t, J = 6.8 Hz, H-2′), 1.34
(s, H-4′ and H-5′); 13C NMR (100 MHz, CDCl3) δ 141.3, 141.1 (C-3 and
C-5), 129.8 (C-4), 127.3 (C-1), 111.6 (C-2), 108.3 (C-6), 74.8 (C-3′),
32.9 (C-1′), 26.7 (C-4′ and C-5′), 19.8 (C-2′), 18.6 (C-7); HREIMS m/z:
208.1102 [M]+ (calcd. for C12H16O3, 208.1099).
4.2.28. 2,2,5-trimethylchromane-6,7,8-triol (13)
Demethylation of 11a (50.0 mg, 0.18 mmol) followed to general
procedure E yielded 13 as colorless oil (15.3 mg, 38%). 1H NMR
(400 MHz, CDCl3) δ 5.25 (overlapped, 4-OH 5-OH and 6-OH), 2.56 (t,
J = 6.8 Hz, H-1′), 2.07 (s, H-7), 1.82 (t, J = 6.8 Hz, H-2′), 1.31 (s, H-4′
and H-5′); 13C NMR (100 MHz, CDCl3) δ 136.0, 134.5, 130.2 (C-3, C-4
and C-5), 129.3 (C-1), 112.4 (C-2), 111.4 (C-6), 74.2 (C-3′), 33.3 (C-1′),
26.5 (C-4′ and C-5′), 19.9 (C-2′), 10.4 (C-7); HREIMS m/z: 224.1052
[M]+ (calcd. for C12H16O4, 224.1052).
C12H14O4, 222.0892).
4.2.33. (E)-2-(3,7-dimethylocta-2,6-dien-1-yl)-5,6-Dihydroxy-3-
methylcyclohexa-2,5-diene-1,4-dione (16b)
Alkylation of 15 (100.0 mg, 0.64 mmol) with geraniol (112 μL,
0.64 mmol) followed to general procedure A. Purification of the crude
mixture by silica-gel column chromatography (CHCl3/MeOH, 50:1) and
ODS silica gel column chromatography (MeOH/H2O 8:2) yielded 16b
as red oil (14.1 mg, 8%). 1H NMR (400 MHz, CDCl3) δ 6.23 (overlapped,
4-OH and 5-OH), 5.03 (m, H-2′), 4.92 (m, H-6′), 3.21 (brd, J = 7.0 Hz,
H-1′), 2.06 (s, H-7), 1.96–2.05 (overlapped, H-4′ and H-5′), 1.73 (s, H-
9′), 1.65 (s, H-8′), 1.57 (s, H-10′); 13C NMR (100 MHz, CDCl3) δ 184.4
(C-6), 183.7 (C-3), 141.0, 138.0 (C-1 and C-2), 138.0, 133.9 (C-4 and C-
5), 133.8, 131.6 (C-3′ and C-7′), 123.9 (C-6′), 118.5 (C-2′), 39.6 (C-4′),
26.4 (C-5′), 25.7 (C-8′), 25.1 (C-1′), 17.7 (C-10′), 16.3 (C-9′), 11.7 (C-7);
HREIMS m/z: 290.1525 [M]+ (calcd. for C17H22O4, 290.1518).
4.2.29. 5-Methyl-4-(3-methylbut-2-en-1-yl)benzene-1,2,3-triol (8a)
Alkylation of 14 (100.0 mg, 0.71 mmol) with 3-methyl-2-buten-1-ol
(71 μL, 0.71 mmol) followed to general procedure A. Purification of the
crude mixture by silica-gel column chromatography (CHCl3/MeOH,
50:1) yielded 8aas colorless oil (17.0 mg, 12%). 1H NMR (400 MHz,
CDCl3) δ 6.15 (s, H-6), 5.05 (m, H-2′), 4.87 (overlapped, 3-OH, 4-OH
and 5-OH), 3.23 (brd, J = 6.8 Hz, H-1′), 2.08 (s, H-7), 1.74 (s, H-5′),
1.65 (s, H-4′); 13C NMR (100 MHz, CDCl3) δ 145.3 (C-3), 144.4 (C-5),
131.9 (C-3′), 130.8 (C-4), 128.4 (C-1), 125.0 (C-2′), 119.6 (C-2), 109.5
(C-6), 26.1 (C-4′), 25.9 (C-1′), 19.4 (C-7), 17.9 (C-5′); HREIMS m/z:
208.1101 [M]+ (calcd. for C12H16O3, 208.1099).
4.2.34. 2,3-Dihydroxy-5-methyl-6-((2E,6E)-3,7,11-trimethyldodeca-
2,6,10-trien-1-yl)cyclohexa-2,5-diene-1,4-dione (16c)
Alkylation of 15 (200.0 mg, 1.28 mmol) with farnesol (319 μL,
1.28 mmol) followed to general procedure A. Purification of the crude
mixture by silica-gel column chromatography (CHCl3/MeOH, 50:1) and
ODS silica gel column chromatography (MeOH/H2O 8:2) yielded 16c as
red oil (43.0 mg, 9%). 1H NMR (400 MHz, CDCl3) δ 6.27 (overlapped, 4-
OH and 5-OH), 5.04 (overlapped, H-6′and H-10′), 4.93 (m, H-2′), 3.22
(brd, J = 6.9 Hz, H-1′), 2.05 (s, H-7), 1.84–2.07 (overlapped, H-4′ H-5′,
H-8′ and H-9′), 1.72 (s, H-13′), 1.68 (s, H-12′), 1.58 (s H-14′), 1.57 (s, H-
15′); 13C NMR (100 MHz, CDCl3) δ 184.4 (C-6), 183.7 (C-3), 140.9,
138.1 (C-1 and C-2), 138.0 (C-3′), 135.4 (C-7′), 135.3, 133.9 (C-4 and C-
5), 131.6 (C-11′), 124.5 (C-10′), 124.2 (C-6′), 118.4 (C-2′), 39.7 (C-4′
and C-8′), 26.7, 26.6 (C-5′ and C-9′), 25.7 (C-12′), 25.1 (C-1′), 17.7 (C-
15′), 16.3 (C-13′), 16.0 (C-14′), 11.7 (C-7); HREIMS m/z: 358.2142
[M]+ (calcd. for C22H30O4, 358.2144).
4.2.30. (E)-4-(3,7-dimethylocta-2,6-dien-1-yl)-5-Methylbenzene-1,2,3-
triol (8b)
Alkylation of 14 (100.0 mg, 0.71 mmol) with geraniol (124 μL,
0.71 mmol) followed to general procedure A. Purification of the crude
mixture by silica-gel column chromatography (CHCl3/MeOH, 50:1) and
ODS silica gel column chromatography (MeOH/H2O 8:2) yielded 8bas
colorless oil (55.5 mg, 28%). 1H NMR (400 MHz, CDCl3) δ 6.34 (s, H-6),
5.28 (overlapped, 3-OH, 4-OH and 5-OH), 5.17 (m, H-2′), 5.04 (m, H-
6′), 3.30 (brd, J = 6.9 Hz, H-1′), 2.18 (s, H-7), 2.00–2.14 (overlapped,
H-4′ and H-5′), 1.79 (s, H-9′), 1.67 (s, H-8′), 1.59 (s, H-10′); 13C NMR
(100 MHz, CDCl3) δ 142.6 (C-3), 141.5 (C-5), 137.8 (C-3′), 132.0 (C-7′),
130.0 (C-4), 127.8 (C-1), 123.8 (C-6′), 122.2 (C-2′), 118.1 (C-2), 109.3
8

H. Kamauchi, et al.
Bioorganic&MedicinalChemistryxxx(xxxx)xxxx
4.3. MAO-B inhibition assay
Declaration of Competing Interest
MAO-B inhibitory activity was assayed using the method of
Novaroli et al. with slight modifications.19 0.1 M potassium phosphate
buffer (pH 7.4), 8 μL of 0.75 mM kynuramine (Sigma-Aldrich, St. Louis,
MO), and 2 μL of a dimethyl sulfoxide (DMSO) inhibitor solution (final
DMSO concentration of 1% (v/v), were preincubated at 37 °C for
10 min. Diluted human recombinant MAO-B (M7441, Sigma-Aldrich)
was then added to obtain a final protein concentration of 0.015 mg/mL
in the assay mixture. The reaction mixture was further incubated at
37 °C and the reaction was stopped after 20 min by the addition of 75 μL
of 2 M NaOH. The product generated by MAO-B, 4-quinolinol, is
fluorescent and was measured at Ex 310 nm/Em 400 nm using a mi-
croplate reader (SPECTRA MAX M2, Molecular Devices, Tokyo, Japan).
DMSO without test compound was used as the negative control and
None.
Appendix A. Supplementary material
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.bmc.2019.115156.
References
1. Kamauchi H, Kinoshita K, Sugita T, Koyama K. Conditional changes enhanced pro-
duction of bioactive metabolites of marine derived fungus Eurotium rubrum. Bioorg
Med Chem Lett. 2016;26:4911–4914. https://doi.org/10.1016/j.bmcl.2016.09.017.
2. a) Goto T, Kakisawa H, Hirata Y. The structure of grifolin, an antibiotic from a ba-
sidiomycete. Tetrahedron. 1963;19:2079–2083. https://doi.org/10.1016/0040-
4020(63)85023-1
pargyline (Sigma-Aldrich) was used as
a
positive control
b) Vrkoč J, Buděšinsky M, Dolejš L. Phenolic from the Basidiomycete Albatrellus
ovinus. Phytochemistry. 1977;16:1409–1411. https://doi.org/10.1016/S0031-
9422(00)88793-2.
(IC50 = 0.22 μM). The IC50 values were estimated using Prism software
(version 5.02; GraphPad, San Diego, CA).
3. Dekermendjian K, Shan R, Nielsen M, Stadler M, Sterner O, Witt MR. The affinity to
the brain dopamine D1receptor in vitro of triprenyl phenols isolated from the fruit
bodies of Albatrellus ovinus. Eur J Med Chem. 1997;32:351–356. https://doi.org/10.
1016/S0223-5234(97)89088-5.
4.4. Cell culture
4. Jing S, Ying P, Hu X, et al. Protective effect of grifolin against brain injury in an acute
cerebral ischemia rat model. Trop J Pharm Res. 2017;16:1299–1305. https://doi.org/
10.4314/tjpr.v16i6.13.
Human neuroblastoma SH-SY5Y cells were purchased from
European Collection of Authenticated Cell Cultures and cultured at
37 °C, 5% CO2 in Eagle's Minimal Essential Medium/Ham’s F-12
medium (E-MEM/F12: FUJIFILM Wako Pure Chemical Corporation)
supplemented with 0.3% fetal bovine serum (FBS: Funakoshi, Tokyo,
Japan), 0.01% penicillin (MP Bio Japan, Tokyo, Japan) and 0.01%
Minimal Essential Medium Non-Essential Amino Acids (MP Bio Japan).
5. Yang X, Yang Y, Li G, Wang J, Yang ES. Coenzyme Q10 attenuates β-amyloid pa-
thology in the aged transgenic mice with Alzheimer presenilin 1 mutation. J Mol
Neurosci. 2008;34:165–171. https://doi.org/10.1007/s12031-007-9033-7.
6. Borroni E, Bohrmann B, Grueninger F, et al. Sembragiline: A novel, selective
monoamine oxidase type B inhibitor for the treatment of Alzheimer’s disease. J
Pharmacol Exp Ther. 2017;362:413–423. https://doi.org/10.1124/jpet.117.241653.
7. Taborga L, Díaz K, Olea AF, et al. Effect of polymer micelles on antifungal activity of
geranylorcinol compounds against Botrytis cinerea. J Agric Food Chem.
2015;63:6890–6896. https://doi.org/10.1021/acs.jafc.5b01920.
4.5. Protective effect on SH-SY5Y against H2O2 toxicity assay
8. Manners G, Jurd L, Stevens K. Biogenetic-type syntheses of isoprenoid and diiso-
prenoid derivatives of orcinol. Tetrahedron. 1972;28:2949–2959. https://doi.org/10.
1016/0040-4020(72)80009-7.
Each compound was dissolved in DMSO. The final DMSO con-
centration in the culture medium was less than 0.5% and this con-
centration had no effect on SH-SY5Y cells. Cells were seeded on the 96-
well plate (5.0 × 104 cells/100 μL/well). After incubation for 24 h, the
usual medium was removed, then each test sample and H2O2 (the final
concentration was 500 μM) was added in the E-MEM/F12 medium
without FBS. After incubation for 24 h at 37 °C in 5% CO2, cell viability
was determined using the MTT assay. The medium was removed and
100 μL of MTT reagent solved in E-MEM/F12 medium (5 mg/mL) was
added to each well. The plate was incubated for 24 h at 37 °C in 5%
CO2, then the absorbance at 595 nm was measured. Results are shown
9. Mori K, Sato K. A general synthetic method for prenylated phenols of microbial
origin. Tetrahedron. 1982;38:1221–1225. https://doi.org/10.1016/0040-4020(82)
85107-7.
10. Zhou K, Ludwig L, Li SM. Friedel-crafts alkylation of acylphloroglucinols catalyzed
by a fungal indole prenyltransferase. J Nat Prod. 2015;78:929–933. https://doi.org/
10.1021/np5009784.
11. Taborga L, Espinoza L, Moller A, Carrasco H, Cuellar M, Villena J. Antiproliferative
effect and apoptotic activity of linear geranylphenol derivatives from phloroglucinol
and orcinol. Chem Biol Interact. 2016;247:22–29. https://doi.org/10.1016/j.cbi.
2016.01.016.
12. a) Tarselli MA, Liu A, Gagné MR. Gold(I)-catalyzed intermolecular hydroarylation of
allenes with nucleophilic arenes: scope and limitations. Tetrahedron.
2009;65:1785–1789. https://doi.org/10.1016/j.tet.2008.10.110
b) Nukata M, Hashimoto T, Yamamoto I, Iwasaki N, Tanaka M, Asakawa Y.
Neogrifolin derivatives possessing anti-oxidative activity from the mushroom
Albatrellus ovinus. Phytochemistry. 2002;59:731–737. https://doi.org/10.1016/
S0031-9422(02)00050-X.
as mean
SD (n = 3). Data were analyzed using one-way ANOVA,
followed by Dunnet’s test using Prism software. The cytotoxic activity
of 2c, 3c, 8c and 16c was tested with the same method without H2O2.
2c showed cytotoxicity at 5 and 10 μM (63 and 60% of cell viability).
3c, 8c and 16c didn’t show cytotoxicity at most 10 μM.
13. a) Terao S, Shiraishi M, Kato K, Ohkawa S, Ashida Y, Maki Y. Quinones. Part 2.
general synthetic routes to quinone derivatives with modified polyprenyl side chains
and the inhibitory effects. J Chem Soc Perkin Trans. 1982;1:2909–2920. https://doi.
org/10.1002/chin.198313356
b) Lipshutz BH, Bulow G, Lowe RF, Stevens KL. A novel route to coenzyme Q(n). J
Am Chem Soc. 1996;118:5512–5513. https://doi.org/10.1021/ja961285b.
14. Baeza E, Catalán K, Peña-Cortés H, Espinoza L, Villena J, Carrasco H. Synthesis of
geranylhydroquinone derivatives with potencial cytotoxic activity. Quim Nova.
2012;35:523–526. https://doi.org/10.1590/S0100-40422012000300015.
15. Reis J, Manzella N, Cagide F, et al. Tight-binding inhibition of human monoamine
oxidase B by chromone analogs: A kinetic, crystallographic, and biological analysis. J
Med Chem. 2018;61:4203–4212. https://doi.org/10.1021/acs.jmedchem.8b00357.
16. Binda C, Aldeco M, Geldenhuys WJ, Tortorici M, Mattevi A, Edmondson DE.
Molecular insights into human monoamine oxidase B inhibition by the glitazone
antidiabetes drugs. ACS Med Chem Lett. 2012;3:39–42. https://doi.org/10.1021/
ml200196p.
4.6. Docking study
The MAO-B crystal structure was retrieved from the Protein Data
Bank (PDB code: 4A79) and imported into the Auto-Dock program
(Version 4.2). The structures of compounds were drawn using
ChemBioDrawUltra 11.0 and subjected to energy minimization using
molecular mechanics (MM2). AutoGrid was used to calculate the grid
maps and the grid was centered on the ligand binding site of MAO-B
such that it would totally cover the ligand molecule. The centroid of the
grid map was set to X: 17, Y: 125, Z: 29, and the number of grid points
was X: 54, Y: 60, Z: 54. The maximum number of energy evaluations
was set to 250,000. Both ligand and receptor docking were performed
using the Lamarckian Genetic Algorithm (Runs 20) after using the de-
fault parameter settings generated by AutoDockTools for docking. The
binding mode was visualized by Discovery Studio Visualizer (version
19; Accelrys, Inc. San Diego, CA).
17. Cosconati S, Forli S, Perryman AL, Harris R, Goodsell DS, Olson AJ. Virtual screening
with AutoDock: theory and practice. Expert Opin Drug Discov. 2010;5:597–607.
https://doi.org/10.1517/17460441.2010.484460.
18. Zhou L, Yao GD, Song XY, et al. Neuroprotective effects of 1,2-diarylpropane type
phenylpropanoid enantiomers from red raspberry against H2O2 -induced oxidative
stress in human neuroblastoma SH-SY5Y cells. J Agric Food Chem. 2018;66:331–338.
https://doi.org/10.1021/acs.jafc.7b04430.
19. Novaroli L, Reist M, Favre E, Carotti A, Catto M, Carrupt PA. Human recombinant
monoamine oxidase B as reliable and efficient enzyme source for inhibitor screening.
Bioorganic Med Chem. 2005;13:6212–6217. https://doi.org/10.1016/j.bmc.2005.06.043.
9