Synthesis of structurally diverse biflavonoids

Article abstract of DOI:10.1016/j.tet.2018.05.003

Synthetic biflavonoids are associated with interesting biological activities, yet they remain poorly explored within drug discovery. Recent years have witnessed a growing interest in synthetic approaches that can provide access to structurally novel biflavonoids so that the biological usefulness of this compound class can be more fully investigated. Herein, we report upon the exploration of strategies based around Suzuki-Miyaura cross-coupling and alcohol methylenation for the synthesis of two classes of biflavonoids: (i) rare ‘hybrid’ derivatives containing flavonoid monomers belonging to different subclasses, and (ii) homodimeric compounds in which the two flavonoid monomers are linked by a methylenedioxy group. Application of these strategies enabled the preparation of a structurally diverse collection of novel biflavonoids from readily-available starting materials, thereby facilitating the probing of uncharted regions of biologically interesting chemical space.

Full text of DOI:10.1016/j.tet.2018.05.003

Accepted Manuscript
Synthesis of structurally diverse biflavonoids
Tze Jing Sum, Tze Han Sum, Warren R.J.D. Galloway, David G. Twigg, Joe J.
Ciardiello, David R. Spring
PII:
S0040-4020(18)30511-8
10.1016/j.tet.2018.05.003
TET 29510
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 1 March 2018
Revised Date: 27 April 2018
Accepted Date: 1 May 2018
Please cite this article as: Sum TJ, Sum TH, Galloway WRJD, Twigg DG, Ciardiello JJ, Spring DR,
Synthesis of structurally diverse biflavonoids, Tetrahedron (2018), doi: 10.1016/j.tet.2018.05.003.
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ACCEPTED MANUSCRIPT
Synthesis of structurally diverse biflavonoids
Tze Jing Sum, Tze Han Sum, Warren R. J. D. Galloway, David G. Twigg, Joe J. Ciardiello
and David R. Spring
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, UK
Graphical Abstract
O
O
O
O
O
Br
O
N
N
O
O
O
O
O
O
O
O
O
O
HO
N
Br
O
1

ACCEPTED MANUSCRIPT
Synthesis of structurally diverse biflavonoids
Tze Jing Sum, Tze Han Sum, Warren R. J. D. Galloway, David G. Twigg, Joe J. Ciardiello
and David R. Spring
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, UK
Corresponding author. Tel.: +44-1223-336-498; fax: +44-1223-336-362; e-mail:
spring@ch.cam.ac.uk
Keywords:
Biflavonoid
Suzuki-Miyaura cross-coupling
Methylenation
Hybrids
Structural diversity
Abstract
Synthetic biflavonoids are associated with interesting biological activities, yet they remain
poorly explored within drug discovery. Recent years have witnessed a growing interest in
synthetic approaches that can provide access to structurally novel biflavonoids so that the
biological usefulness of this compound class can be more fully investigated. Herein, we
report upon the exploration of strategies based around Suzuki-Miyaura cross-coupling and
alcohol methylenation for the synthesis of two classes of biflavonoids: (i) rare ‘hybrid’
derivatives containing flavonoid monomers belonging to different subclasses, and (ii)
homodimeric compounds in which the two flavonoid monomers are linked by a
methylenedioxy group. Application of these strategies enabled the preparation of a
structurally diverse collection of novel biflavonoids from readily-available starting materials,
thereby facilitating the probing of uncharted regions of biologically interesting chemical
space.
2

ACCEPTED MANUSCRIPT
1. Introduction
Biflavonoids are a class of compounds characterized by the presence of two flavonoid
monomers conjoined through an alkyl or an alkoxy-based linker.1,2 Natural biflavonoids,
ubiquitous in plants, fruits and vegetables, have been found to display a diverse range of
useful biological activities.1,2,3 Flavonoids themselves, which fall into a number of different
subclasses (for example, aurones, chalcones, flavonols and isoflavones) also exhibit a variety
of biological activities;4-6 in a number of cases the biological activity of a biflavonoid has
been found to be greater than that of the constituent flavonoid monomer(s).2,7,8 Synthetic
biflavonoids are also associated with interesting biological activities;1,2,7,8,9,10,11 however, they
remain poorly explored within drug discovery.1,2 In principle, there is considerable structural
diversity possible within the biflavonoid compound class, since the type of flavonoid units
present and the nature and the position of the linker moiety can all be varied, and large
swathes of potentially biologically relevant biflavonoid chemical space still remain untapped
or underexplored by current syntheses.1,2 This has stimulated a growing interest in the
exploration of synthetic approaches that can provide convenient access to collections of novel
and structurally diverse biflavonoids.1,2,7
The biological properties of biflavonoids can be affected by the structures of the flavonoid
sub-units and the linker system.2 We have previously reported a strategy for generation of a
library of biflavonoids which contain a carbon-carbon linkage between identical flavonoid
subunits.2 Herein, we report studies on the synthesis of two alternative types of biflavonoid.
Firstly, ‘hybrid’ biflavonoids containing flavonoid monomers belonging to different
subclasses, which we aimed to access using a Suzuki-Miyaura cross-coupling approach. The
generation of species that integrate two pharmacophoric entities is common in drug
discovery,12,13,14 and synthetic flavonoid dimer systems (both homo- and hetero-dimers) have
been reported to exhibit useful biological properties12. However, examples of synthetic
biflavonoid hybrids of the sort described herein are extremely rare. The second type of
biflavonoids targeted in this study are characterized by the presence of a methylenedioxy
linker group, which we envisaged could be generated via methylenation of the hydroxyl
functional groups of the different flavonoid monomers. Although more commonly occurring
than the hybrid-type, there are relatively few reported examples of libraries of such
methylene-bridged compounds and the diversity of flavonoid monomers present within these
3

ACCEPTED MANUSCRIPT
is generally limited. Overall, application of synthetic strategies based around Suzuki-
Miyaura cross-coupling and alcohol methylenation enabled access to a collection of 34
structurally diverse biflavonoids from readily available starting materials.
2. Results and discussion
2.1. Synthesis of biflavonoid hybrids via a Suzuki-Miyaura cross-coupling strategy
The Suzuki-Miyaura cross-coupling reaction is of proven utility for the synthesis of a variety
of symmetrical and unsymmetrical biflavonoids.1,4,15 However, examples of biflavonoid
hybrids (those that contain flavonoid monomers from different subclasses) generated using
this reaction appear to be extremely scarce. We envisaged that the Suzuki-Miyaura process
could be exploited to provide an underexplored yet convenient, modular and inherently
flexible route to this rare class of compound through the use of appropriate pairs of boronate-
and bromo-functionalized flavonoid monomers (Scheme 1).
flavonoid
monomer 1
flavonoid
monomer 2
biflavonoid hybrid
Suzuki-Miyaura
cross-coupling
O
flavonoid
monomer 1
flavonoid
monomer 2
Br
+
B
O
bromo flavonoid
boronate flavonoid
O
O
Isoflavone
Aurone
R
R
flavonoid
monomer 1
O
Chalcone
=
flavonoid
monomer 2
O
O
O
R
R
OH
Flavonol
O
Scheme 1. Strategy for the construction of biflavonoid hybrids containing flavonoid
monomers from different subclasses.
As a proof-of-principle, we targeted the generation of isoflavone-aurone biflavonoid 7,
isoflavone-chalcone biflavonoid 8, heteroaromatic isoflavone-chalcone biflavonoid 9 and
isoflavone-flavonol biflavonoid 10 (Fig. 1).
4

ACCEPTED MANUSCRIPT
HO
HO
O
O
HO
HO
O
O
O
O
O
O
O
7
8
O
O
O
O
O
O
O
O
O
OH
N
O
O
O
9
10
O
Figure 1. Target biflavonoid hybrids.
2.1.1. Synthesis of isoflavone-aurone biflavonoid 7
The construction of the isoflavone-aurone biflavonoid 7 commenced with the syntheses of
the isoflavone boronate 16 and bromoaurone 23 (Scheme 2). Acylation of commercially
available resorcinol 11 with 4-bromophenylacetic acid 12 in the presence of boron trifluoride
diethyl etherate afforded deoxybenzoin 13 in 77% yield.16 Treatment of 13 with
methanesulfonyl chloride16 in DMF afforded bromoisoflavone 14. Subsequent Miyaura
borylation17 with bis(pinacolato)diboron 15 gave the isoflavone boronate 16. Bromoaurone
23 was prepared in five steps from commercially available phloroglucinol 17. Reaction of 17
with chloroacetonitrile in the presence of ZnCl2 gave the imine intermediate 18.18
Subsequent hydrolysis under acidic conditions afforded ketone 19 and treatment with
methanolic sodium methoxide gave hydroxybenzofuranone 20.18 Methylation of the free
hydroxyl groups afforded benzofuranone 21 which was then condensed with 4-
bromobenzaldehyde 22 to yield the desired bromoaurone 23.18 Subsequent cross-coupling of
isoflavone boronate 16 and bromoaurone 23 under Suzuki conditions17,19 afforded the desired
isoflavone-aurone biflavonoid 7 in a low yield as a 1:1 inseparable mixture of (E)- and (Z)-
isomers. The generation of the (E)-isomer of 7 could potentially be attributed to
isomerization of the alkene in 23 (due to syn-β-hydride elimination by the Pd catalyst)
followed by cross-coupling with 16.
5

ACCEPTED MANUSCRIPT
HO
OH
BF3.OEt2
HO
OH
HO
O
CH3SO2Cl
BF3.OEt2
11
+
∆
O
O
DMF / 80 o
C
Br
Br
CO2H
13; 77%
14; 85%
Br
O O
B B
O O
12
PdCl2(dppf) / KOAc
DMF / 80 oC
HO
O
15
O
O
B
O
16; 58%
NC Cl
ZnCl2 / HCl
HO
OH
HO
OH
HO
OH
1 M HCl
∆
Et2O / 0 o
C
Cl
Cl
OH
OH NH
OH O
19; 25%
HCl
17
18; 43%
NaOCH3
MeOH / ∆
Br
O
Br
22
O
HO
O
O
O
CH3I / K2CO3
KOH / H2O
MeOH / rt
O
O
DMF / 80 o
C
O
O
OH
20; 71%
O
O
21; 79%
23; 94%
Br
O
O
HO
O
O
O
O
O
23
+
PdCl2(dppf) / Na2CO3
DMF / rt
O
HO
O
O
O
O
O
7; 4%
B
O
16
Scheme 2. Synthesis of isoflavone-aurone biflavonoid 7.
2.1.2. Synthesis of isoflavone-chalcone biflavonoid 8
With the successful synthesis of 7, we moved on to investigate the construction of different
hybrid biflavonoids using isoflavone boronate 16 and other bromoflavonoids.
Bromochalcone 27 was readily prepared from commercially available phloroglucinol 17 in
three steps (Scheme 3). Methylation of 17 with dimethyl sulfate in the presence of potassium
carbonate gave trimethoxybenzene 24.20 Subsequent Vilsmeier-Haack formylation21 afforded
the corresponding trimethoxybenzaldehyde 25 in an excellent yield.20 Base-catalyzed
Claisen-Schmidt condensation22 of 25 with 4-bromoacetophenone 26 generated 27 and
subsequent cross-coupling with 16 using the previously employed Suzuki protocol afforded
the target isoflavone-chalcone biflavonoid 8.
6

ACCEPTED MANUSCRIPT
(MeO)2SO2
OH
K2CO3
O
O
O
O
HO
POCl3
DMF
O
acetone
O
O
OH
17
25; 91%
24; 47%
Br
KOH / H2O
EtOH / rt
O
O
Br
O
26
O
O
27; 80%
O
O
Br
HO
O
O
O
O
27
+
PdCl2(dppf) / Na2CO3
DMF / rt
O
O
HO
O
O
O
O
8; 18%
O
B
O
16
Scheme 3. Synthesis of isoflavone-chalcone biflavonoid 8.
2.1.3. Synthesis of heteroaromatic isoflavone-chalcone biflavonoid 9
Isoflavone-chalcone biflavonoid 9 was targeted in order to explore the potential to generate
biflavonoids with heteroaromatic moieties such as indoles which are known to be associated
with interesting biological properties.23 Preparation of the required indole bromochalcone 31
24
commenced with Vilsmeier-Haack formylation of indole 28 to give aldehyde 29 (Scheme
25
4). Methylation of 29 afforded indole-aldehyde 30
and Claisen-Schmidt aldol
condensation with bromoacetophenone 26 furnished indole bromochalcone 31. Application
of the previously employed Suzuki conditions enabled the successful cross-coupling of 31
with 16 to afford the desired heteroaromatic biflavonoid 9 (Scheme 4).
7

ACCEPTED MANUSCRIPT
O
O
NaH / CH3I
THF
POCl3
DMF
N
H
N
H
N
28
30; 97%
29; 86%
Br
Br
O
N
H
O
EtOH / ∆
26
N
31; 92%
Br
O
HO
O
O
N
31
+
PdCl2(dppf) / Na2CO3
DMF / rt
N
HO
O
O
O
O
B
9; 19%
O
16
Scheme 4. Synthesis of heteroaromatic isoflavone-chalcone biflavonoid 9.
2.1.4. Synthesis of isoflavone-flavonol biflavonoid 10
Finally, attention was directed towards the synthesis of the isoflavone-flavonol biflavonoid
10 (Scheme 5). Aldol condensation of trimethoxybenzaldehyde 32 and bromoacetophenone
33 gave bromochalcone 34 which was converted to the required bromoflavonol coupling
partner 35 by an Algar-Flynn-Oyamada (AFO) oxidation22.
Cross-coupling of
bromoflavonol 35 and isoflavone boronate 16 under the previously employed conditions gave
the final isoflavone-flavonol biflavonoid 10 in a low isolated yield.
8

ACCEPTED MANUSCRIPT
OMe
MeO
OMe
O
O
O
O
O
O
O
NaOH
H2O2
KOH
EtOH
32
+
O
O
OH
EtOH
OH
O
Br
OH
Br
O
Br
35; 85%
34; 68%
33
O
O
O
O
O
HO
O
O
Br
OH
O
OH
35
PdCl2(dppf) / Na2CO3
DMF / rt
+
O
HO
O
O
O
O
O
O
10; 2%
B
O
16
Scheme 5. Synthesis of isoflavone-flavonol biflavonoid 10.
2.1.5. Summary
The Suzuki-Miyaura cross-coupling strategy outlined in Scheme 1 was successfully applied
to the synthesis of four target hybrid biflavonoids 7-10. The yields of all the Suzuki-Miyaura
coupling reactions were disappointingly low. This can be attributed to several factors.
Firstly, there was incomplete consumption of both the bromo-flavonoid and boronoate-
flavonoid starting materials (as indicated by TLC and/or LCMS analysis of the reaction
mixtures) and recovery of these materials could not be achieved. In addition, LCMS analysis
of the crude reaction mixtures prior to purification indicated the presence of several
unidentifiable (possibly including polymeric) side products. Any attempts to improve the
efficiency of these reactions were unsuccessful. For example, in the case of the coupling of
16 and 23, a variety of different combinations of solvents (DMF, THF and DMSO), reaction
temperatures (room temperature, gentle heating and heating at reflux), bases (sodium
carbonate and sodium hydroxide) and palladium catalysts (PdCl2(dppf)·CH2Cl2, Pd(PPh3)4
and PdCl2(PPh3)2) were investigated but there was no improvement in the isolated yield of the
desired product. Analytically pure samples of all the target biflavonoids could be isolated by
column chromatography on silica gel. However, in all cases this process was practically
extremely challenging and laborious; significant streaking was observed on silica and there
may have been decomposition of both the target biflavonoids and residual starting materials
during chromatographic elution. Although the yields of the Suzuki-Miyaura coupling
reactions were disappointingly low, it is worth noting that milligram quantities of all target
9

ACCEPTED MANUSCRIPT
biflavonoids were successfully obtained; this should be sufficient material for screening in a
wide variety of biological assays. This work establishes the general feasibility of our
approach for the synthesis of this structurally rare and biologically interesting compound
class; it is anticipated that a larger range of functionalized flavonoid monomer building
blocks could be employed in order to access a highly structurally diverse library of such
compounds in a step-efficient fashion.
2.2. Synthesis of a library of biflavonoids that contain a methylenedioxy linker
Attention was next turned towards the generation of a library of unnatural homodimeric
biflavonoids that contain a methylenedioxy linker between the flavonoid monomers (Scheme
6). It was envisaged that such derivatives could be conveniently accessed via treatment of
hydroxyl-substituted flavonoid monomers with diiodomethane.26 It was anticipated that a
variety of functionalized flavonoid building blocks belonging to different flavonoid structural
classes could be employed in order to access a structurally diverse library of methylenedioxy-
linked biflavonoids. This study examined building blocks from six different flavonoid
subclasses: aurone, chalcone, dihydrochalcone,flavone, flavonol and isoflavone.
flavonoid
monomer
flavonoid
monomer
methylenedioxy-bridged
biflavonoids
O
O
nucleophilic substitution
flavonoid
monomer
2 x
OH +
I
I
OH
R
OH
R
=
flavonoid
monomer
OH
Dihydochalcone
O
O
Chalcone
O
O
OH
R
O
R
O
Isoflavone
OH
OH
OH
R
O
O
R
Flavonol
Flavone
O
Aurone
O
Scheme 6. Outline of the strategy towards diverse methylenedioxy-bridged biflavonoids.
2.2.1. Synthesis of a methylenedioxy-bridged bidihydrochalcone 40.
10

ACCEPTED MANUSCRIPT
The preparation of the methylenedioxy-bridged biflavonoid library commenced with the
synthesis of bidihydrochalcone 40 (Scheme 7). Acetophenone 37 was prepared in good yield
from 36 by the Eaton’s reagent-induced Fries rearrangement of 2-methoxyphenylacetate 36.28
Base-catalyzed Claisen-Schmidt condensation22 of 25 and 37 generated chalcone 38 and
subsequent hydrogenation furnished dihydrochalcone 39.27 Methylenation26 of 39 gave the
desired bidihydrochalcone 40 in a moderate yield.
OH
O
O
P2O5
O
O
CH3SO3H
O
O
36
37; 60%
O
O
O
O
O
OH
O
O
O
OH
O
PtO2 / H2
EtOAc
KOH
25
+
EtOH
O
O
O
O
OH
O
38; 37%
39; 80%
O
37
CH2I2 / K2CO3
Acetone / ∆
O
O
O
O
O
O
O
O
O
O
O
O
40; 40%
Scheme 7. Synthesis of methylenedioxy-bridged bidihydrochalcone 40.
2.2.2. Synthesis of methylenedioxy-bridged bichalcones 59-69 and 72.
Methylenedioxy-bridged bichalcones 59-69 and 72 were generated by the route shown in
Scheme 8. Claisen-Schmidt condensation22 of various aromatic and heteroaromatic aldehyde
building blocks with acetophenones 37 or 70 yielded chalcone precursors 38, 49-58 and 71.
Subsequent methylenation26 in the presence of diiodomethane and potassium carbonate
afforded the final bichalcone dimers 59-69 and 72.
2.2.3. Synthesis of methylenedioxy-bridged biflavones 96-104 and 114.
Claisen-Schmidt condensation29 of acetophenones 73-75 and 33 with various aromatic and
heteroaromatic aldehyde building blocks yielded chalcones 78-86 (Scheme 9). Subsequent
AFO oxidation22 generated the respective flavonols 87-95 (Scheme 9). Dimerization under
the common methylenation conditions26 afforded the desired biflavones 96-104.
Concurrently, biflavone 114 was synthesized by the route shown in Scheme 10, building
11

ACCEPTED MANUSCRIPT
upon our previous work on flavone synthesis27. Pyrogallol 105 was acylated in the presence
of glacial acetic acid and boron trifluoride diethyl etherate under reflux conditions to afford
gallacetophenone 106.30 Selective methylation of 106 with iodomethane and anhydrous
potassium carbonate in dry acetone afforded acetophenone 107.31 Benzaldehyde 109 was
acquired in 54% yield through benzylation of the phenol functionality of isovanillin 108
under basic conditions32. Condensation of 107 and 109 in ethanolic KOH solution at room
temperature afforded the chalcone 110 and subsequent intramolecular AFO oxidative
cyclization22 proceeded smoothly to produce the intermediate 3-hydroxyflavonoid 111.
Selective methylation of the 3-hydroxyl group of the flavone ring provided the corresponding
tetramethoxyflavone 112 in quantitative yield and subsequent debenzylation by
hydrogenolysis furnished the 5-deoxyflavone 113.27 Methylenation26 of 113 afforded the
desired biflavone 114 in a moderate yield.
O
O
O
O
O
O
O
41
O
25
42
Br
Br
O
Fe
44
R1
=
22
45
43
HO
O
+
O
R1
N
O
37
N
N
N
46
30
47
48
KOH
EtOH
49; R1 = 41; 63%
38; R1 = 25; 37%
50; R1 = 42, 71%
51; R1 = 22, 52%
52; R1 = 43, 59%
53; R1 = 44, 86%
54; R1 = 45, 89%
55; R1 = 46, 55%
56; R1 = 30, 36%
57; R1 = 47, 61%
58; R1 = 48, 68%
HO
O
R1
O
CH2I2 / K2CO3
Acetone / ∆
59; R1 = 41; 50%
60; R1 = 25; 39%
61; R1 = 42, 48%
62; R1 = 22, 17%
63; R1 = 43, 52%
64; R1 = 44, 53%
65; R1 = 45, 50%
66; R1 = 46, 51%
67; R1 = 30, 60%
68; R1 = 47, 49%
69; R1 = 48, 46%
O
O
O
R1
R1
O
O
O
O
HO
KOH / EtOH
O
+
R1
HO
R1
O
O
O
71; 75%
70
O
O
O
CH2I2 Acetone
R1 = 25
R1
R1
K2CO3
∆
O
O
O
72; 39%
12

ACCEPTED MANUSCRIPT
Scheme 8. Synthesis of methylenedioxy-bridged bichalcones.
O
R1
R2
OH
O
O
O
Br
O
O
O
O
R3
+
Br
O
77
32
76
R3
=
73; R1 = OCH3, R2 = H
74; R1 = H, R2 = OCH3
33; R1 = H, R2 = Br
O
N
N
75; R1,R2 = OCH2O
45
46
30
KOH
EtOH
78; R1 = OCH3, R2 = H, R3 = 32; 59%
79; R1 = OCH3, R2 = H, R3 = 76; 42%
80; R1,R2 = OCH2O,
81; R1 = H, R2 = Br,
82; R1 = R2 = OCH2O, R3 = 46; 67%
83; R1 = H, R2 = Br,
84; R1 = H, R2 = Br,
R3 = 77; 42%
R3 = 45; 47%
R1
R2
OH R3
O
R3 = 46; 92%
R3 = 30; 94%
85; R1 = R2 = OCH2O, R3 = 30; 63%
86; R1 = H, R2 = OCH3, R3 = 30; 92%
NaOH
H2O2
87; R1 = OCH3, R2 = H, R3 = 32; 67%
88; R1 = OCH3, R2 = H, R3 = 76; 68%
89; R1 = R2 = OCH2O, R3 = 77; 39%
R1
R2
O
R3
90; R1 = H, R2 = Br,
R3 = 45; 81%
OH
91; R1 = R2 = OCH2O, R3 = 46; 36%
O
92; R1 = H, R2 = Br,
93; R1 = H, R2 = Br,
R3 = 46; 61%
R3 = 30; 79%
94; R1 = R2 = OCH2O, R3 = 30; 54%
95; R1 = H, R2 = OCH3, R3 = 30; 69%
CH2I2 / K2CO3
Acetone / ∆
R1
R2
O
O
R3
96; R1 = OCH3, R2 = H, R3 = 32; 49%
97; R1 = OCH3, R2 = H, R3 = 76; 51%
98; R1 = R2 = OCH2O, R3 = 77; 48%
O
99; R1 = H, R2 = Br,
R3 = 45; 28%
O
100; R1 = R2 = OCH2O, R3 = 46; 10%
O
R3
101; R1 = H, R2 = Br,
102; R1 = H, R2 = Br,
R3 = 46; 35%
R3 = 30; 28%
O
103; R1 = R2 = OCH2O, R3 = 30; 13%
104; R1 = H, R2 = OCH3, R3 = 30; 13%
R2
R1
Scheme 9. Synthesis of methylenedioxy-bridged biflavones.
13

ACCEPTED MANUSCRIPT
OH
O
OH
K2CO3
CH3I
BF3.OEt2
HO
OH
O
O
OH
HO
OH
NaOAc
CH3CO2H
Acetone
O
105
106; 76%
107; 55%
O
K2CO3
BnBr
O
O
O
O
HO
Acetone
108
109; 54%
O
O
O
O
O
O
O
O
OH
KOH
OH
O
+
EtOH
O
O
107
109
110; 51%
NaOH / H2O2
EtOH
O
O
O
K2CO3
(MeO)2SO2
O
O
O
O
O
O
O
O
O
Acetone
O
OH
112; 99%
111; 53%
Pd/C / H2
MeOH
O
O
O
O
CH2I2
K2CO3
O
O
O
O
O
O
O
O
O
O
OH
O
Acetone
∆
O
O
O
O
O
113; 52%
114; 32%
Scheme 10. Synthesis of methylenedioxy-bridged biflavone 114.
2.2.4. Synthesis of methylenedioxy-bridged biisoflavones
The isoflavone dimerization precursors were synthesized by the route shown in Scheme 11.
Acylation of phenols 11, 115 and 116 with phenylacetic acids 12 and 117-119 in the presence
of boron trifluoride diethyl etherate gave deoxybenzoins 13, 120-122.16 Heating with
methanesulfonyl chloride and DMF effected cyclization to generate dimerization precursors
14 and 123-125.16 Reaction under the standard methylenation conditions26 afforded the
desired biisoflavones 126-129 in moderate-to-good yields.
14

ACCEPTED MANUSCRIPT
CO2H
R3
12 ; R3 = H, R4 = Br
117; R3 = H, R4 = OH
118; R3 = H, R4 = OCH3
119; R3 = OH, R4 = H
R4
R1
R2
OH
R1
R2
OH
O
BF3.OEt2
R3
∆
R4
11 ; R1 = OH, R2 = H
115; R1 = OCH3, R2 = H
116; R1 = OCH3, R2 = OCH3
13 ; R1 = OH, R2 = H, R3 = H, R4 = Br; 77%
120; R1 = OCH3, R2 = H, R3 = H, R4 = OH; 78%
121; R1 = OH, R2 = H, R3 = H, R4 = OCH3; 36%
122; R1 = OCH3, R2 = OCH3, R3 = OH, R4 = H; 36%
CH3SO2Cl
BF3.OEt2
DMF / 90 o
C
14 ; R1 = OH, R2 = H, R3 = H, R4 = Br; 85%
123; R1 = OCH3, R2 = H, R3 = H, R4 = OH; 57%
124; R1 = OH, R2 = H, R3 = H, R4 = OCH3; 77%
R1
R2
O
O
R3
125; R1 = OCH3, R2 = OCH3, R3 = OH, R4 = H; 97%
R4
CH2I2 / K2CO3
Acetone / ∆
O
O
O
O
O
O
O
O
O
O
126; 51% (from 14)
Br
O
Br
O
O
O
O
O
O
O
O
O
O
O
O
O
127; 56% (from 123)
O
O
O
O
128; 43% (from124)
O
O
O
O
129; 23% (from 125)
Scheme 11. Synthesis of methylenedioxy-bridged biisoflavones.
2.2.5. Synthesis of methylenedioxy-bridged biaurones
Finally, we turned our attention towards the synthesis of methylenedioxy-bridged biaurones.
The required hydroxyuaurone precursors 133-135 were readily prepared by the
condensation18 of benzofuranone 21 with various hydroxybenzaldehydes 130-132 (Scheme
12). Methylenation under the standard conditions40 furnished the targeted biaurones 136-138.
15

ACCEPTED MANUSCRIPT
O
O
R2
O
O
R3
R1
21
O
KOH / H2O
MeOH/rt
130; R1 = OH, R2 = H, R3 = H
131; R1 = H, R2 = OH, R3 = H
132; R1 = H, R2 = H, R3 = OH
R2 R3
R1
O
O
133; R1 = OH, R2 = H, R3 = H
134; R1 = H, R2 = OH, R3 = H
135; R1 = H, R2 = H, R3 = OH
O
O
CH2I2 / K2CO3
Acetone / ∆
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
136; 36% (from 133)
137; 41% (from 134)
O
O
O
O
O
O
O
O
O
O
138; 60% (from135)
Scheme 12. Synthesis of methylenedioxy-bridged biaurones.
2.2.6. Summary
A range of flavonoid building blocks were successfully employed in the methylenation
strategy (Scheme 6) to generate a library of 30 diverse methylenedioxy-bridged biflavonoids.
Six different biologically-relevant flavonoid subclasses were incorporated into the library
(aurone, chalcone, dihydrochalcone, flavone, flavonol and isoflavone), and many of the
compounds feature additional structural motifs associated with biological activity (for
example, heterocyclic ring systems and hydrogen-bonding motifs) as well as an aryl bromide
group, which could conceivably serve as a synthetic handle for further modification via
metal-catalyzed cross-coupling processes.
3. Conclusions
In conclusion, we have reported strategies based around Suzuki-Miyaura cross-coupling and
alcohol methylenation for synthesis of two types of biologically interesting biflavonoid
derivatives: (i) ‘hybrid’ compounds containing flavonoid monomers belonging to different
subclasses, and (ii) homodimeric compounds featuring a methylenedioxy linker group
16

ACCEPTED MANUSCRIPT
between the flavonoid monomers. A structurally diverse library of 34 biflavonoids (4 hybrid
compounds and 30 methylenedioxy-bridged dimers) was successfully generated using these
strategies. All final compounds were isolated in milligram quantities, providing ample
material for their biological evaluation. Notable results from these screening studies will be
reported in due course.
4. Experimental section
4.1 General information
All reagents and solvents were purchased from commercial sources and used without further
purification unless otherwise stated. All the experiments were carried out under a nitrogen
atmosphere unless otherwise stated. Melting points were measured using a Büchi B545
melting point apparatus and are uncorrected. Thin layer chromatography (TLC) was
performed on precoated Merck silica gel GF254 plates. IR spectra were recorded on a
PerkinElmer Spectrum One (FT-IR) spectrophotometer. Flash column chromatography was
13
performed on silica gel (230–400 mesh). 1H NMR and C NMR were recorded on a Bruker
Avance 500 MHz instrument in CDCl3 and DMSO-d6. HRMS was recorded on a Micromass
Q-TOF mass spectrometer or a Waters LCT Premier Time of Flight mass spectrometer.
LCMS setup: Waters ACQUITY H-Class UPLC with an ESCi Multi-Mode Ionisation Waters
SQ Detector 2 spectrometer using MassLynx 4.1 software; LC system: solvent A: 2mM
NH4OAc in water/acetonitrile (95:5); solvent B: acetonitrile; solvent C: 2% formic acid;
column: ACQUITY UPLC CSH C18 (2.1 mm × 50 mm, 1.7 ꢀm, 130 Å) at 40 oC; gradient:
5-95% B with constant 5% C over 1 min at flow rate of 0.6 mL.min-1; detector: PDA eλ
Detector 220 nm - 800 nm, interval 1.2 nm.
4.2 General procedures
4.2.1 General procedure A: Synthesis of non-identical biflavonoids via Suzuki-Miyaura
cross-coupling strategy (GP-A). To a stirred solution of boronate flavonoid (1.0 equiv) and
PdCl2(dppf)·CH2Cl2 (1.0 equiv) in dry DMF (10 mL) were added aqueous Na2CO3 solution
(1 M, 5.0 equiv) and the corresponding bromo flavonoid (1.0 equiv). The reaction mixture
was stirred at room temperature for 72 h under nitrogen or until LCMS analysis indicated
17

ACCEPTED MANUSCRIPT
complete consumption of starting material. The resulting suspension was then poured into
H2O (50 mL) and the aqueous solution was extracted with CHCl3 (3 × 50 mL). The combined
organic layer was washed with H2O (2 × 50 mL), brine (2 × 50 mL), dried over anhydrous
MgSO4, filtered and the solvent removed under reduced pressure. The crude residue was
purified by flash column chromatography over silica to afford the corresponding
biflavonoids.
4.2.1 General procedure B: Synthesis of identical biflavonoids via methylenation strategy
(GP-B). To a stirred solution of the corresponding flavonoid (1.0 equiv) in dry acetone or
DMF (20 mL) were added CH2I2 (3.0 equiv) and anhydrous K2CO3 (3.0 equiv). The reaction
mixture was heated at reflux under a nitrogen atmosphere for 24 h or until TLC analysis
indicated complete consumption of starting material. The resulting mixture was allowed to
cool to room temperature and the solvent removed in vacuo. The crude residue was
redissolved in CHCl3 (50 mL), washed with H2O (2 × 50 mL), brine (2 × 50 mL), dried over
anhydrous MgSO4, filtered and the solvent removed in vacuo. The crude residue was purified
by flash column chromatography over silica and/or recrystallized from MeOH, EtOAc or
CHCl3 to afford the corresponding biflavonoids.
4.3 Experimental details and characterization data
4.3.1 Synthesis of 3-(4’-((4,6-Dimethoxy-3-oxobenzofuran-2(3H)-ylidene)methyl)-[1,1’-
biphenyl]-4-yl)-7-hydroxy-4H-chromen-4-one (Isoflavone-aurone biflavonoid) (7). A mixture
of boronate isoflavone 16 (304 mg, 0.835 mmol), bromoaurone 23 (299 mg, 0.829 mmol),
PdCl2(dppf)·CH2Cl2 (136 mg, 0.166 mmol) and aq. Na2CO3 (1 M, 5.0 mL, 5.00 mmol) in dry
DMF (30 mL) was reacted according to GP-A. The crude residue was purified by flash
column chromatography (SiO2, 0.5-10% MeOH/CH2Cl2) to afford biflavonoid 7 (19.1 mg,
4%) as a bright yellow powdery solid in a 1:1 inseparable mixture of (E)- and (Z)-isomers.
m.p. >300 °C. TLC Rf = 0.33 (5% MeOH/CH2Cl2). IR νmax (neat)/cm-1: 3242m(br) (O-H str),
2922w (C-H str), 2850w (C-H str), 1668m (C=O str), 1627s (C=C str), 1584s (C=C str),
1505m (C=C str), 1457m, 1422w, 1363m, 1246m, 1217s, 1158s, 1122m, 1077s, 1047w,
1
1017w, 1005w. H NMR (500 MHz, DMSO-d6): δ 3.89 (1.5H, s, -OCH3), 3.91 (3H, s, -
OCH3 and -OCH3’, overlap), 3.94 (1.5H, s, -OCH3’), 6.31 (0.5H, d, J 1.6 Hz, ArHa), 6.37
(0.5H, d, J 1.6 Hz, ArHb), 6.54 (0.5H, d, J 1.2 Hz, ArHa’), 6.75 (0.5H, d, J 1.6 Hz, ArHb’),
18

ACCEPTED MANUSCRIPT
6.79 (0.5H, s, -C=CHc), 6.91 (1H, d, J 2.4 Hz, ArH), 6.97 (1H, dd, J 8.8, 2.0 Hz, ArH), 7.08
(0.5H, s, -C=CHc’), 7.70-7.73 (2H, m, ArH), 7.79-7.87 (4H, m, ArH), 8.01 (1H, d, J 8.8 Hz,
ArH), 8.04 (1H, d, J 8.4 Hz, ArH), 8.30 (1H, d, J 8.8 Hz, ArH), 8.48 (1H, s, -C=CH), 10.85
(1H, s, OH). 13C NMR (500 MHz, DMSO-d6): δ 56.1, 56.2, 56.5, 56.6, 89.1, 90.0, 93.8, 94.5,
102.2, 104.0, 105.9, 109.1, 115.4, 116.6, 119.1, 123.0, 126.3, 126.4, 126.5, 127.0, 127.4,
129.5, 131.1, 131.5, 131.6, 131.8, 131.9, 138.4, 138.5, 140.5, 140.7, 147.5, 148.5, 154.0,
157.5, 159.0, 159.2, 162.7, 167.4, 168.2, 168.9, 169.0, 174.4, 177.7, 179.0. LCMS (ES-) m/z
+
= 517.1 ([M-H]-, tr = 1.65 min). HRMS (ESI+) m/z = 519.1436 [M+H]+ found, C32H23O7
required 519.1438.
4.3.2 Synthesis of (E)-7-Hydroxy-3-(4’-(3-(2,4,6-trimethoxyphenyl)acryloyl)-[1,1’-biphenyl]-
4-yl)-4H-chromen-4-one (Isoflavone-chalcone biflavonoid) (8). A mixture of boronate
isoflavone 16 (306 mg, 0.839 mmol), bromochalcone 27 (317 mg, 0.841 mmol),
PdCl2(dppf)·CH2Cl2 (108 mg, 0.133 mmol) and aq. Na2CO3 (1 M, 5.0 mL, 5.00 mmol) in dry
DMF (20 mL) was reacted according to GP-A. The crude residue was purified by flash
column chromatography (SiO2, 0.5-1% MeOH/CH2Cl2) and further recrystallized from
MeOH to afford biflavonoid 8 (82.4 mg, 18%) as a pale yellow-brown powdery solid. m.p.
>300 °C. TLC Rf = 0.43 (5% MeOH/CH2Cl2). IR νmax (neat)/cm-1: 3227m(br) (O-H str),
2940w (C-H str), 2847w (C-H str), 1653m (C=O str), 1620s, 1603s (C=C str), 1581s (C=C
str), 1566s (C=C str), 1455m, 1417w, 1337s, 1300m, 1267m, 1222s, 1204s, 1157m, 1121s,
1
1098m, 1054m, 1029m, 1005w. H NMR (500 MHz, DMSO-d6): δ 3.87 (3H, s, -OCH3),
3.94 (6H, s, 2 × -OCH3), 6.35 (2H, s, ArH), 6.91 (1H, d, J 1.6 Hz, ArH), 6.97 (1H, dd, J 8.4,
1.6 Hz, ArH), 7.74 (2H, d, J 8.4 Hz, ArH), 7.84 (2H, d, J 8.4 Hz, ArH), 7.93 (2H, d, J 8.8 Hz,
ArH), 7.93 (1H, d, J 16.0 Hz, -CH=CHCO-), 8.01 (1H, d, J 8.8 Hz, ArH), 8.08 (2H, d, J 8.4
Hz, ArH), 8.14 (1H, d, J 16.0 Hz, -CH=CHCO-), 8.50 (1H, s, -C=CH), 10.85 (1H, s, OH).
13C NMR (500 MHz, DMSO-d6): δ 55.6, 56.1, 91.1, 102.2, 105.1, 115.3, 116.6, 120.3, 122.9,
126.6, 126.9, 127.4, 128.8, 129.5, 132.2, 135.2, 137.4, 138.3, 143.5, 154.1, 157.5, 161.5,
162.7, 163.4, 174.4, 189.4. LCMS (ES+) m/z = 535.2 ([M+H]+, tr = 1.65 min). HRMS
+
(ESI+) m/z = 535.1751 [M+H]+ found, C33H27O7 required 535.1757.
4.3.3 Synthesis of (E)-7-Hydroxy-3-(4’-(3-(1-methyl-1H-indol-3-yl)acryloyl)-[1,1’-biphenyl]-
4-yl)-4H-chromen-4-one (Isoflavone-indole chalcone biflavonoid) (9). A mixture of boronate
19

ACCEPTED MANUSCRIPT
isoflavone 16 (305 mg, 0.837 mmol), indole bromochalcone 31 (283 mg, 0.833 mmol),
PdCl2(dppf)·CH2Cl2 (107 mg, 0.131 mmol) and aq. Na2CO3 (1 M, 5.0 mL, 5.00 mmol) in dry
DMF (30 mL) was reacted according to GP-A. The crude residue was purified by flash
column chromatography (SiO2, 0.5-1% MeOH/CH2Cl2) to afford biflavonoid 9 (79.9 mg,
19%) as a bright yellow powdery solid. m.p. 280-282 °C. TLC Rf = 0.30 (5%
MeOH/CH2Cl2). IR νmax (neat)/cm-1: 3244w(br) (O-H str), 2925w (C-H str), 1718w (C=O
str), 1620m, 1602s (C=C str), 1581s (C=C str), 1566s (C=C str), 1526m (C=C str), 1465m,
1
1375s, 1281s, 1264s, 1219s, 1180s, 1133w, 1097w, 1042m, 1013w. H NMR (500 MHz,
DMSO-d6): δ 3.87 (3H, s, -NCH3), 6.91 (1H, d, J = 2.0 Hz, ArH-8), 6.97 (1H, dd, J = 8.8, 2.0
Hz, ArH-6), 7.28-7.35 (2H, m, ArH-25 and ArH-26), 7.57 (1H, d, J = 7.6 Hz, ArH-24), 7.70
(1H, d, J = 15.2 Hz, -CH=CHCO-), 7.74 (2H, d, J = 8.4 Hz, ArH-11 and ArH-13), 7.85 (2H,
d, J = 8.4 Hz, ArH-10 and ArH-14), 7.91 (2H, d, J = 8.4 Hz, ArH-16 and ArH-20), 8.02 (1H,
d, J = 9.2 Hz, ArH-5), 8.05 (1H, d, J = 15.6 Hz, -CH=CHCO-), 8.13-8.14 (2H, m, ArH-22
and ArH-27), 8.23 (2H, d, J = 8.4 Hz, ArH-17 and ArH-19), 8.49 (1H, s, -C=CH), 10.87 (1H,
13
s, OH). C NMR (500 MHz, DMSO-d6): δ 33.1, 102.2, 110.9, 111.8, 115.3, 116.6, 120.5,
121.5, 122.8, 122.9, 125.6, 126.7, 126.8, 127.4, 128.9, 129.5, 132.1, 136.7, 137.4, 138.0,
138.3, 138.4, 143.4, 154.1, 157.5, 162.7, 174.4, 188.1. LCMS (ES-) m/z = 496.3 ([M-H]-, tr =
1.82 min). HRMS (ESI+) m/z = 498.1702 [M+H]+ found, C33H24NO4 required 498.1705.
+
4.3.4 Synthesis of 3-Hydroxy-6-(4-(7-hydroxy-4-oxo-4H-chromen-3-yl)phenyl)-2-(2,3,4-
trimethoxyphenyl)-4H-chromen-4-one (Isoflavone-flavonol biflavonoid) (10). A mixture of
boronate isoflavone 16 (269 mg, 0.738 mmol), bromoflavonol 35 (304 mg, 0.747 mmol),
PdCl2(dppf)·CH2Cl2 (110 mg, 0.134 mmol) and aq. Na2CO3 (1 M, 5.0 mL, 5.00 mmol) in dry
DMF (20 mL) was reacted according to GP-A. The crude residue was purified by flash
column chromatography (SiO2, 1-10% MeOH/CH2Cl2) and further purified by preparative
HPLC (60-100% B) to afford biflavonoid 10 (7.10 mg, 2%) as an off-white powdery solid.
m.p. >300 °C. TLC Rf = 0.44 (10% MeOH/CH2Cl2). HPLC tr = 7.89 min (60-100% B), peak
area 90%. IR νmax (neat)/cm-1: 3285w(br) (O-H str), 2924m (C-H str), 2851w (C-H str),
1680m (C=O str), 1622s, 1600s (C=C str), 1569m (C=C str), 1453s, 1301m, 1272m, 1294m,
1
1272m, 1198s, 1190s, 1142s, 1124s, 1098s, 1027m. H NMR (500 MHz, DMSO-d6): δ 3.81
(3H, s, -OCH3), 3.87 (3H, s, -OCH3), 3.88 (3H, s, -OCH3), 6.91 (1H, d, J 2.0 Hz, ArH), 6.97
(2H, dd, J 8.8, 2.0 Hz, ArH), 7.30 (1H, d, J 8.8 Hz, ArH), 7.75 (2H, d, J 8.4 Hz, ArH), 7.77
(1H, d, J 8.8 Hz, ArH), 7.86 (2H, d, J 8.4 Hz, ArH), 8.02 (1H, d, J 8.8 Hz, ArH), 8.15 (1H,
20

ACCEPTED MANUSCRIPT
dd, J 8.8, 1.6 Hz, ArH), 8.38 (1H, d, J 2.0 Hz, ArH), 8.50 (1H, s, -C=CH), 9.07 (1H, s, OH),
10.87 (1H, s, OH). 13C NMR (500 MHz, DMSO-d6): δ 56.1, 60.5, 61.2, 102.2, 107.8, 115.4,
116.6, 117.6, 119.2, 121.9, 122.2, 123.0, 125.9, 126.6, 127.4, 129.6, 131.7, 132.1, 136.0,
137.9, 139.1, 142.0, 147.0, 151.8, 154.0, 154.4, 155.2, 157.5, 162.7, 172.7, 174.4. LCMS
(ES+) m/z = 565.2 ([M+H]+, tr = 1.84 min). HRMS (ESI+) m/z = 565.1477 [M+H]+ found,
+
C33H25O9 required 565.1493.
4.3.5 Synthesis of 1,1’-((Methylenebis(oxy))bis(3-methoxy-4,1-phenylene))bis(3-(2,4,6-
trimethoxyphenyl)propan-1-one) (40). A mixture of dihydrochalcone 39 (150 mg, 0.434
mmol), CH2I2 (0.12 mL, 1.49 mmol) and anhydrous K2CO3 (207 mg, 1.50 mmol) in dry
acetone (20 mL) was reacted according to GP-B. The crude residue was purified by
recrystallization from EtOAc to afford bidihydrochalcone 40 (124 mg, 40%) as a white
powdery solid. m.p. 198-200 °C. TLC Rf = 0.23 (1% MeOH/CH2Cl2). IR νmax (neat)/cm-1:
2987w (C-H str), 2950w (C-H str), 2840w (C-H str), 1684s (C=O str), 1609m, 1589s (C=C
str), 1514m (C=C str), 1504m (C=C str), 1452m, 1418s, 1363w, 1277m, 1254s, 1150s,
1108s, 1033m, 1014s, 1001s. 1H NMR (500 MHz, DMSO-d6): δ 2.78 (4H, t, J 8.5 Hz, 2 × -
CH2CH2CO-), 2.96 (4H, t, J 8.5 Hz, 2 × -CH2CH2CO-), 3.73 (12H, s, 4 × -OCH3), 3.75 (6H,
s, 2 × -OCH3), 3.80 (6H, s, 2 × -OCH3), 5.96 (2H, s, -OCH2O-), 6.21 (4H, s, ArH), 7.29 (2H,
d, J 8.0 Hz, ArH), 7.47 (2H, d, J 2.0 Hz, ArH), 7.62 (2H, dd, J 8.5, 2.0 Hz, ArH). 13C NMR
(500 MHz, DMSO-d6): δ 18.2, 38.0, 55.2, 55.6, 55.6, 90.6, 90.7, 108.4, 111.1, 115.3, 122.0,
131.4, 149.2, 158.3, 159.4, 198.6. LCMS (ES+) m/z = 705.3 ([M+H]+, tr = 1.85 min). HRMS
(ESI+) m/z = 705.2886 [M+H]+ found, C39H45O12+ required 705.2906.
4.3.6 Synthesis of (2E,2’E)-1,1’-((Methylenebis(oxy))bis(3-methoxy-4,1-phenylene))bis(3-(4-
methoxyphenyl)prop-2-en-1-one) (59). A mixture of chalcone 49 (306 mg, 1.08 mmol), CH2I2
(0.26 mL, 3.18 mmol) and anhydrous K2CO3 (449 mg, 3.25 mmol) in dry acetone (20 mL)
was reacted according to GP-B. The crude residue was purified by recrystallization from
EtOAc to afford bichalcone 59 (314 mg, 50%) as a pale yellow powdery solid. m.p. 228-230
°C. TLC Rf = 0.21 (1% MeOH/CH2Cl2). IR νmax (neat)/cm-1: 2978w (C-H str), 2845w (C-H
str), 1659m (C=O str), 1601s (C=C str), 1582s (C=C str), 1572m (C=C str), 1508s (C=C str),
1
1465m, 1448m, 1416m, 1334w, 1293m, 1250s, 1165s, 1133s, 1055w, 1010s. H NMR (500
MHz, DMSO-d6): δ 3.82 (6H, s, 2 × -OCH3), 3.87 (6H, s, 2 × -OCH3), 6.04 (2H, s, -OCH2O-
21

ACCEPTED MANUSCRIPT
), 7.02 (4H, d, J 8.4 Hz, ArH), 7.36 (2H, d, J 8.4 Hz, ArH), 7.66 (2H, d, J 2.0 Hz, ArH), 7.70
(2H, d, J 15.6 Hz, 2 × -CH=CHCO-), 7.81 (2H, d, J 15.6 Hz, 2 × -CH=CHCO-), 7.86 (4H, d,
J 8.8 Hz, ArH), 7.89 (2H, dd, J 8.4, 1.6 Hz, ArH). 13C NMR (500 MHz, DMSO-d6): δ 55.4,
55.8, 90.6, 111.6, 114.4, 115.2, 119.4, 122.6, 127.4, 130.8, 132.8, 143.5, 149.4, 149.4, 161.3,
187.4. LCMS (ES+) m/z = 581.2 ([M+H]+, tr = 1.84 min). HRMS (ESI+) m/z = 619.1730
[M+K]+ found, C35H32O8K+ required 619.1729.
4.3.7 Synthesis of (2E,2’E)-1,1’-((Methylenebis(oxy))bis(3-methoxy-4,1-phenylene))bis(3-
(2,4,6-trimethoxyphenyl)prop-2-en-1-one) (60). A mixture of chalcone 38 (302 mg, 0.877
mmol), CH2I2 (0.25 mL, 3.11 mmol) and anhydrous K2CO3 (382 mg, 2.77 mmol) in dry
acetone (20 mL) was reacted according to GP-B. The crude residue was purified by
recrystallization from EtOAc to afford bichalcone 60 (239 mg, 39%) as a pale yellow-white
powdery solid. m.p. 230-232 °C. TLC Rf = 0.35 (2% MeOH/CH2Cl2). IR νmax (neat)/cm-1:
2940w (C-H str), 2839w (C-H str), 1657m (C=O str), 1598s (C=C str), 1576s (C=C str),
1510m (C=C str), 1468m, 1418m, 1337m, 1300m, 1259m, 1200m, 1124s, 1065m, 1031m,
1012s. 1H NMR (500 MHz, DMSO-d6): δ 3.86 (6H, s, 2 × -OCH3), 3.86 (6H, s, 2 × -OCH3),
3.92 (12H, s, 4 × -OCH3), 5.99 (2H, s, -OCH2O-), 6.32 (4H, s, ArH), 7.34 (2H, d, J 8.5 Hz,
ArH), 7.54 (2H, d, J 2.0 Hz, ArH), 7.66 (2H, dd, J 8.5, 2.0 Hz, ArH), 7.89 (2H, d, J 16.0 Hz,
2 × -CH=CHCO-), 8.07 (2H, d, J 15.5 Hz, 2 × -CH=CHCO-). 13C NMR (500 MHz, DMSO-
d6): δ 55.6, 56.1, 90.9, 91.0, 105.1, 111.2, 115.5, 120.2, 121.9, 133.4, 134.7, 149.0, 149.4,
161.4, 163.2, 188.5. LCMS (ES+) m/z = 701.1 ([M+H]+, tr = 1.75 min). HRMS (ESI+) m/z =
701.2564 [M+H]+ found, C39H41O12+ required 701.2593.
4.3.8 Synthesis of (2E,2’E)-1,1’-((Methylenebis(oxy))bis(3-methoxy-4,1-phenylene))bis(3-
(2,3,4,6-tetramethoxyphenyl)prop-2-en-1-one) (61). A mixture of chalcone 50 (253 mg, 0.674
mmol), CH2I2 (0.20 mL, 2.49 mmol) and anhydrous K2CO3 (280 mg, 2.02 mmol) in dry
acetone (20 mL) was reacted according to GP-B. The crude residue was purified by flash
column chromatography (SiO2, 1% MeOH/CH2Cl2) and recrystallized from MeOH to afford
bichalcone 61 (249 mg, 48%) as a yellow powdery solid. m.p. 182-184 °C. TLC Rf = 0.31
(2% MeOH/CH2Cl2). IR νmax (neat)/cm-1: 2943w (C-H str), 2837w (C-H str), 1654m (C=O
str), 1598m (C=C str), 1564s (C=C str), 1504m (C=C str), 1467m, 1401m, 1341m, 1309m,
1
1259s, 1170m, 1135m, 1111s, 1067m, 1011s. H NMR (500 MHz, CDCl3): δ 3.85 (6H, s, 2
22

ACCEPTED MANUSCRIPT
× -OCH3), 3.93 (6H, s, 2 × -OCH3), 3.94 (6H, s, 2 × -OCH3), 3.95 (6H, s, 2 × -OCH3), 3.96
(6H, s, 2 × -OCH3), 5.93 (2H, s, -OCH2O-), 6.31 (2H, s, ArH), 7.37 (2H, d, J 8.0 Hz, ArH),
7.65 (2H, dd, J 8.4, 2.0 Hz, ArH), 7.67 (2H, d, J 1.6 Hz, ArH), 7.96 (2H, d, J 16.0 Hz, 2 × -
13
CH=CHCO-), 8.13 (2H, d, J 16.0 Hz, 2 × -CH=CHCO-). C NMR (500 MHz, CDCl3): δ
56.0, 56.0, 61.1, 61.2, 92.0, 92.3, 111.0, 111.8, 116.0, 122.4, 122.8, 134.4, 135.6, 136.5,
149.5, 149.9, 154.7, 155.6, 156.6, 190.3. LCMS (ES+) m/z = 761.3 ([M+H]+, tr = 1.88 min).
HRMS (ESI+) m/z = 761.2834 [M+H]+ found, C41H45O14+ required 761.2809.
4.3.9 Synthesis of (2E,2’E)-1,1’-((Methylenebis(oxy))bis(3-methoxy-4,1-phenylene))bis(3-(4-
bromophenyl)prop-2-en-1-one) (62). A mixture of chalcone 51 (305 mg, 0.915 mmol), CH2I2
(0.25 mL, 3.11 mmol) and anhydrous K2CO3 (382 mg, 2.76 mmol) in dry acetone (20 mL)
was reacted according to GP-B. The crude residue was purified by flash column
chromatography (SiO2, CH2Cl2) and recrystallized from MeOH to afford bichalcone 62 (104
mg, 17%) as an off-white powdery solid. m.p. 206-208 °C. TLC Rf = 0.47 (1%
MeOH/CH2Cl2). IR νmax (neat)/cm-1: 2939w (C-H str), 1660m (C=O str), 1607m (C=C str),
1584s (C=C str), 1510m (C=C str), 1487m, 1467w, 1419s, 1322w, 1258s, 1220m, 1169m,
1136s, 1073w, 1031m, 1007s. 1H NMR (500 MHz, CDCl3): δ 3.96 (6H, s, 2 × -OCH3), 5.95
(2H, s, -OCH2O-), 7.38 (2H, d, J 8.8 Hz, ArH), 7.51 (4H, d, J 8.8 Hz, ArH), 7.52 (2H, d, J
15.6 Hz, 2 × -CH=CHCO-), 7.57 (4H, d, J 8.8 Hz, ArH), 7.64-7.66 (4H, m, ArH), 7.75 (2H,
13
d, J 15.6 Hz, 2 × -CH=CHCO-). C NMR (500 MHz, CDCl3): δ 56.1, 92.0, 111.7, 115.9,
122.1, 122.5, 124.7, 129.8, 132.2, 133.4, 133.8, 143.0, 150.0, 150.2, 188.5. LCMS (ES+) m/z
79
= 676.9 ([M+H]+ for Br2, tr = 2.09 min). HRMS (ESI+) m/z = 698.9968 [M+Na]+ found,
C33H26O6 Br2Na+ required 698.9988.
79
4.3.10 Synthesis of (2E,2’E)-1,1’-((Methylenebis(oxy))bis(3-methoxy-4,1-phenylene))bis(3-
(3-bromophenyl)prop-2-en-1-one) (63). A mixture of chalcone 52 (306 mg, 0.919 mmol),
CH2I2 (0.22 mL, 2.74 mmol) and anhydrous K2CO3 (419 mg, 3.03 mmol) in dry acetone (20
mL) was reacted according to GP-B. The crude residue was purified by flash column
chromatography (SiO2, 1% MeOH/CH2Cl2) to afford bichalcone 63 (321 mg, 52%) as a pale
yellow-white powdery solid. m.p. 118-120 °C. TLC Rf = 0.39 (1% MeOH/CH2Cl2). IR νmax
(neat)/cm-1: 2941w (C-H str), 1708w, 1657m (C=O str), 1605m (C=C str), 1584s (C=C str),
1563m (C=C str), 1509s (C=C str), 1469m, 1419s, 1312m, 1254s, 1221w, 1169m, 1135s,
23

ACCEPTED MANUSCRIPT
1007s. 1H NMR (500 MHz, CDCl3): δ 3.95 (6H, s, 2 × -OCH3), 5.95 (2H, s, -OCH2O-), 7.29
(2H, t, J 8.0 Hz, ArH), 7.37 (2H, dd, J 8.0, 0.5 Hz, ArH), 7.50-7.55 (4H, m, ArH), 7.51 (2H,
d, J 15.5 Hz, 2 × -CH=CHCO-), 7.64-7.66 (2H, m, ArH), 7.72 (2H, d, J 16.0 Hz, 2 × -
CH=CHCO-), 7.79 (2H, t, J 1.5 Hz, ArH). 13C NMR (500 MHz, CDCl3): δ 56.1, 91.9, 111.6,
115.9, 122.6, 122.7, 123.0, 127.2, 130.4, 130.7, 133.1, 133.2, 137.0, 142.5, 150.0, 150.1,
79
188.2. LCMS (ES+) m/z = 677.1 ([M+H]+ for Br2, tr = 1.99 min). HRMS (ESI+) m/z =
79
+
677.0144 [M+H]+ found, C33H27O6 Br2 required 677.0169.
4.3.11 Synthesis of (2E,2’E)-1,1’-((Methylenebis(oxy))bis(3-methoxy-4,1-phenylene))bis(3-
(ferrocenyl)prop-2-en-1-one) (64). A mixture of chalcone 53 (308 mg, 0.850 mmol), CH2I2
(0.20 mL, 2.49 mmol) and anhydrous K2CO3 (357 mg, 2.58 mmol) in dry acetone (20 mL)
was reacted according to GP-B. The crude residue was purified by flash column
chromatography (SiO2, 0.5% MeOH/CH2Cl2) to afford bichalcone 64 (329 mg, 53%) as a
dark purple microcrystalline solid. m.p. 124-126 °C. TLC Rf = 0.32 (1% MeOH/CH2Cl2). IR
νmax (neat)/cm-1: 3011w (C-H str), 2842w (C-H str), 1697w (C=O str), 1654m (C=C str),
1596s (C=C str), 1575s (C=C str), 1510m (C=C str), 1463m, 1419m, 1342w, 1296m, 1259s,
1
1196m, 1132s, 1106m, 1029m, 1002s. H NMR (500 MHz, CDCl3): δ 3.97 (6H, s, 2 × -
OCH3), 4.19 (10H, s, 2 × -C5H5), 4.50 (4H, t, J 2.0 Hz, 2 × -C5H4), 4.61 (4H, t, J 2.0 Hz, 2 × -
C5H4), 5.94 (2H, s, -OCH2O-), 7.13 (2H, d, J 15.5 Hz, 2 × -CH=CHCO-), 7.37 (2H, d, J 8.5
Hz, ArH), 7.60 (2H, dd, J 8.5, 2.0 Hz, ArH), 7.64 (2H, d, J 2.0 Hz, ArH), 7.76 (2H, d, J 15.5
13
Hz, 2 × -CH=CHCO-). C NMR (500 MHz, CDCl3): δ 56.1, 69.0, 69.8, 71.3, 79.3, 92.1,
111.7, 116.0, 118.7, 122.2, 134.0, 146.4, 150.0, 150.1, 188.2. LCMS (ES+) m/z = 736.1
([M+H]+, tr = 2.06 min). HRMS (ESI+) m/z = 737.1259 [M+H]+ found, C41H37O6Fe2
+
required 737.1283.
4.3.12 Synthesis of (2E,2’E)-1,1’-((Methylenebis(oxy))bis(3-methoxy-4,1-phenylene))bis(3-
(furan-2-yl)prop-2-en-1-one) (65). A mixture of chalcone 54 (636 mg, 2.60 mmol), CH2I2
(0.30 mL, 3.74 mmol) and anhydrous K2CO3 (540 mg, 3.91 mmol) in dry acetone (20 mL)
was reacted according to GP-B. The crude residue was purified by recrystallization from
EtOAc to afford bichalcone 65 (645 mg, 50%) as a pale brown-white powdery solid. m.p.
258-260 °C. TLC Rf = 0.35 (1% MeOH/CH2Cl2). IR νmax (neat)/cm-1: 3115w (C-H str),
2949w (C-H str), 2910w (C-H str), 1740w, 1650m (C=O str), 1596s (C=C str), 1577s (C=C
24

ACCEPTED MANUSCRIPT
str), 1552s (C=C str), 1508m (C=C str), 1479m, 1467m, 1420s, 1311m, 1293m, 1259s,
1
1210s, 1163s, 1138s, 1023s. H NMR (500 MHz, DMSO-d6): δ 3.86 (6H, s, 2 × -OCH3),
6.02 (2H, s, -OCH2O-), 6.69-6.70 (2H, m, ArH), 7.10 (2H, d, J 3.2 Hz, ArH), 7.35 (2H, d, J
8.4 Hz, ArH), 7.56 (4H, s, 2 × -CH=CHCO- and 2 × -CH=CHCO-), 7.61 (2H, d, J 1.6 Hz,
ArH), 7.79 (2H, dd, J 8.4, 1.6 Hz, ArH), 7.92 (2H, d, J 1.2 Hz, ArH). 13C NMR (500 MHz,
DMSO-d6): δ 55.7, 90.6, 111.5, 113.1, 115.3, 116.9, 118.6, 122.5, 130.1, 132.4, 146.1, 149.5,
151.2, 187.0. LCMS (ES-) m/z = 500.3 ([M-H]-, tr = 2.04 min). HRMS (ESI+) m/z =
+
501.1532 [M+H]+ found, C29H25O8 required 501.1549.
4.3.13 Synthesis of (2E,2’E)-1,1’-((Methylenebis(oxy))bis(3-methoxy-4,1-phenylene))bis(3-
(1-methyl-1H-pyrrol-2-yl)prop-2-en-1-one) (66). A mixture of chalcone 55 (202 mg, 0.786
mmol), CH2I2 (0.20 mL, 2.49 mmol) and anhydrous K2CO3 (331 mg, 2.39 mmol) in dry
acetone (20 mL) was reacted according to GP-B. The crude residue was purified by flash
column chromatography (SiO2, 1% MeOH/CH2Cl2) to afford bichalcone 66 (210 mg, 51%)
as a bright yellow powdery solid. m.p. 228-230 °C. TLC Rf = 0.48 (2% MeOH/CH2Cl2). IR
νmax (neat)/cm-1: 2926w (C-H str), 2833w (C-H str), 1648m (C=O str), 1597m (C=C str),
1575s (C=C str), 1512m (C=C str), 1481m, 1459m, 1409m, 1380w, 1329m, 1260s, 1249s,
1
1188m, 1140s, 1092w, 1059m, 1001s. H NMR (500 MHz, CDCl3): δ 3.78 (6H, s, 2 × -
NCH3), 3.96 (6H, s, 2 × -OCH3), 5.93 (2H, s, -OCH2O-), 6.23-6.24 (2H, m, ArH), 6.82 (2H,
t, J 2.5 Hz, ArH), 6.85 (2H, dd, J 4.0, 1.0 Hz, ArH), 7.30 (2H, d, J 15.0 Hz, 2 × -CH=CHCO-
), 7.36 (2H, d, J 8.0 Hz, ArH), 7.63 (2H, dd, J 8.5, 2.0 Hz, ArH), 7.65 (2H, d, J 2.0 Hz, ArH),
7.81 (2H, d, J 15.0 Hz, 2 × -CH=CHCO-). 13C NMR (500 MHz, CDCl3): δ 34.4, 56.1, 92.1,
109.7, 111.6, 112.3, 116.0, 116.3, 122.0, 127.7, 130.3, 131.9, 134.1, 149.6, 150.0, 188.3.
LCMS (ES+) m/z = 527.3 ([M+H]+, tr = 1.74 min). HRMS (ESI+) m/z = 527.2163 [M+H]+
+
found, C31H31O6N2 required 527.2177.
4.3.14 Synthesis of (2E,2’E)-1,1’-((Methylenebis(oxy))bis(3-methoxy-4,1-phenylene))bis(3-
(1-methyl-1H-indol-3-yl)prop-2-en-1-one) (67). A mixture of chalcone 56 (207 mg, 0.674
mmol), CH2I2 (0.20 mL, 2.49 mmol) and anhydrous K2CO3 (330 mg, 2.17 mmol) in dry
acetone (20 mL) was reacted according to GP-B. The crude residue was purified by
recrystallization from CHCl3 to afford bichalcone 67 (253 mg, 60%) as a pale yellow-brown
powdery solid. m.p. >300 °C. TLC Rf = 0.26 (2% MeOH/CH2Cl2). IR νmax (neat)/cm-1:
25

ACCEPTED MANUSCRIPT
2922w (C-H str), 2841w (C-H str), 1651m (C=O str), 1597s (C=C str), 1568s (C=C str),
1531m (C=C str), 1514m (C=C str), 1474m, 1377s, 1335m, 1283s, 1262s, 1252s, 1200m,
1177m, 1117s, 1074m, 1016s. 1H NMR (500 MHz, CDCl3): δ 3.87 (6H, s, 2 × -NCH3), 3.98
(6H, s, 2 × -OCH3), 5.96 (2H, s, -OCH2O-), 7.31-7.36 (4H, m, ArH), 7.40 (4H, d, J 8.8 Hz,
ArH), 7.50 (2H, s, ArH), 7.56 (2H, d, J 15.6 Hz, 2 × -CH=CHCO-), 7.70-7.71 (4H, m, ArH),
8.03 (2H, d, J 6.8 Hz, ArH), 8.10 (2H, d, J 15.2 Hz, 2 × -CH=CHCO-). 13C NMR (500 MHz,
CDCl3): δ 33.3, 56.1, 92.3, 110.1, 111.7, 113.1, 116.1, 116.7, 120.8, 121.6, 122.1, 123.2,
126.2, 134.4, 134.5, 138.3, 148.2, 149.4, 150.0, 189.2. LCMS (ES+) m/z = 627.2 ([M+H]+, tr
+
= 1.86 min). HRMS (ESI+) m/z = 627.2472 [M+H]+ found, C39H35O6N2 required 627.2490.
4.3.15 Synthesis of (2E,2’E)-1,1’-((Methylenebis(oxy))bis(3-methoxy-4,1-phenylene))bis(3-
(pyridin-2-yl)prop-2-en-1-one) (68). A mixture of chalcone 57 (303 mmg, 1.19 mmol), CH2I2
(0.28 mL, 3.49 mmol) and anhydrous K2CO3 (509 mg, 3.68 mmol) in dry acetone (20 mL)
was reacted according to GP-B. The crude residue was purified by flash column
chromatography (SiO2, 0.5% MeOH/CH2Cl2) to afford bichalcone 68 (303 mg, 49%) as an
off-white powdery solid. m.p. 248-250 °C. TLC Rf = 0.39 (5% MeOH/CH2Cl2). IR νmax
(neat)/cm-1: 2943w (C-H str), 2843w (C-H str), 1658m (C=O str), 1582s (C=C str), 1565m
(C=C str), 1509s (C=C str), 1460m, 1415s, 1323s, 1303m, 1258s, 1206m, 1163m, 1137s,
1
1026m. H NMR (500 MHz, CDCl3): δ 3.95 (6H, s, 2 × -OCH3), 5.94 (2H, s, -OCH2O-),
7.29-7.30 (2H, m, ArH), 7.36 (2H, d, J 8.4 Hz, ArH), 7.47 (2H, d, J 7.6 Hz, ArH), 7.68 (2H,
d, J 1.6 Hz, ArH), 7.71-7.77 (4H, m, ArH), 7.77 (2H, d, J 15.2 Hz, 2 × -CH=CHCO-), 8.11
13
(2H, d, J 15.2 Hz, 2 × -CH=CHCO-), 8.68 (2H, d, J 4.0 Hz, ArH). C NMR (500 MHz,
CDCl3): δ 56.1, 91.9, 111.7, 115.9, 123.1, 124.4, 125.1, 125.4, 133.2, 136.9, 142.4, 150.1,
150.1, 153.2, 188.7. LCMS (ES+) m/z = 523.3 ([M+H]+, tr = 1.65 min). HRMS (ESI+) m/z =
+
523.1844 [M+H]+ found, C31H27O6N2 required 523.1864.
4.3.16 Synthesis of (2E,2’E)-1,1’-((Methylenebis(oxy))bis(3-methoxy-4,1-phenylene))bis(3-
(quinolin-2-yl)prop-2-en-1-one) (69). A mixture of chalcone 58 (310 mmg, 1.01 mmol),
CH2I2 (0.25 mL, 3.11 mmol) and anhydrous K2CO3 (447 mg, 3.23 mmol) in dry DMF (20
mL) was reacted according to GP-B. The crude residue was purified by recrystallization from
EtOAc to afford bichalcone 69 (291 mg, 46%) as a pale brown powdery solid. m.p. 238-240
°C. TLC Rf = 0.37 (3% MeOH/CH2Cl2). IR νmax (neat)/cm-1: 3056w (C-H str), 2952w (C-H
26

ACCEPTED MANUSCRIPT
str), 1655m (C=O str), 1592m (C=C str), 1577s (C=C str), 1510m (C=C str), 1461w, 1447w,
1
1416s, 1349m, 1293s, 1262s, 1219m, 1191m, 1166m, 1140s, 1037m. H NMR (500 MHz,
DMSO-d6): δ 3.90 (6H, s, 2 × -OCH3), 6.09 (2H, s, -OCH2O-), 7.43 (2H, d, J 8.8 Hz, ArH),
7.66 (2H, t, J 8.0 Hz, ArH), 7.70 (2H, d, J 2.0 Hz, ArH), 7.82 (2H, t, J 7.2 Hz, ArH), 7.84
(2H, d, J 15.6 Hz, 2 × -CH=CHCO-), 7.96 (2H, dd, J 8.4, 1.6 Hz, ArH), 8.02 (2H, d, J 8.0
Hz, ArH), 8.09 (2H, d, J 8.4 Hz, ArH), 8.24 (2H, d, J 8.4 Hz, ArH), 8.34 (2H, d, J 15.6 Hz, 2
× -CH=CHCO-), 8.49 (2H, d, J 8.8 Hz, ArH). 13C NMR (500 MHz, DMSO-d6): δ 55.8, 90.5,
111.7, 115.3, 120.8, 123.1, 126.9, 127.5, 127.8, 127.9, 129.2, 130.2, 132.1, 136.9, 143.1,
147.6, 149.6, 149.8, 153.7, 187.7. LCMS (ES+) m/z = 623.2 ([M+H]+, tr = 1.90 min). HRMS
+
(ESI+) m/z = 623.2161 [M+H]+ found, C39H31O6N2 required 623.2177.
4.3.17 Synthesis of (2E,2’E)-1,1’-((Methylenebis(oxy))bis(4-methoxy-3,1-phenylene))bis(3-
(2,4,6-trimethoxyphenyl)prop-2-en-1-one) (72). A mixture of chalcone 71 (301 mg, 0.873
mmol), CH2I2 (0.21 mL, 2.61 mmol) and anhydrous K2CO3 (404 mg, 3.15 mmol) in dry
acetone (20 mL) was reacted according to GP-B. The crude residue was purified by
recrystallization from EtOAc to afford bichalcone 72 (241 mg, 39%) as a pale yellow
powdery solid. m.p. 248-250 °C. TLC Rf = 0.21 (2% MeOH/CH2Cl2). IR νmax (neat)/cm-1:
2939w (C-H str), 2837w (C-H str), 1648m (C=O str), 1598m (C=C str), 1566s (C=C str),
1513m (C=C str), 1457m, 1415m, 1336m, 1319m, 1258m, 1222m, 1148m, 1113s, 1059m,
1005s. 1H NMR (500 MHz, DMSO-d6): δ 3.85 (6H, s, 2 × -OCH3), 3.86 (6H, s, 2 × -OCH3),
3.89 (12H, s, 4 × -OCH3), 5.91 (2H, s, -OCH2O-), 6.31 (4H, s, ArH), 7.17 (2H, d, J 8.4 Hz,
ArH), 7.77 (2H, dd, J 8.4, 1.6 Hz, ArH), 7.86 (2H, d, J 1.6 Hz, ArH), 7.89 (2H, d, J 16.0 Hz,
2 × -CH=CHCO-), 8.07 (2H, d, J 15.6 Hz, 2 × -CH=CHCO-). 13C NMR (500 MHz, DMSO-
d6): δ 55.5, 55.8, 56.0, 91.0, 92.3, 105.1, 111.9, 116.4, 120.1, 124.4, 131.3, 134.5, 145.4,
153.5, 161.3, 163.2, 188.0. LCMS (ES+) m/z = 701.3 ([M+H]+, tr = 1.67 min). HRMS
(ESI+) m/z = 701.2587 [M+H]+ found, C39H41O12+ required 701.2593.
4.3.18 Synthesis of 3,3’-(Methylenebis(oxy))bis(7-methoxy-2-(2,3,4-trimethoxyphenyl)-4H-
chromen-4-one) (96). A mixture of flavonol 87 (301 mg, 0.841 mmol), CH2I2 (0.20 mL, 2.51
mmol) and anhydrous K2CO3 (362 mg, 2.62 mmol) in dry acetone (20 mL) was reacted
according to GP-B. The crude residue was purified by flash column chromatography (SiO2,
1-5% MeOH/CH2Cl2) to afford biflavone 96 (299 mg, 49%) as a pale yellow-brown powdery
27

ACCEPTED MANUSCRIPT
solid. m.p. 228-230 °C. TLC Rf = 0.32 (3% MeOH/CH2Cl2). IR νmax (neat)/cm-1: 2941w (C-
H str), 2844w (C-H str), 1735w, 1611s (C=O str), 1574m (C=C str), 1495m, 1463m, 1443s,
1412m, 1395w, 1364w, 1245s, 1202m, 1168m, 1097s, 1056w. 1H NMR (500 MHz, CDCl3):
δ 3.77 (6H, s, 2 × -OCH3), 3.81 (6H, s, 2 × -OCH3), 3.85 (6H, s, 2 × -OCH3), 3.90 (6H, s, 2 ×
-OCH3), 6.03 (2H, s, -OCH2O-), 6.39 (2H, d, J 8.4 Hz, ArH), 6.80 (2H, d, J 2.0 Hz, ArH),
6.95 (2H, dd, J 8.8, 2.0 Hz, ArH), 7.12 (2H, d, J 8.8 Hz, ArH), 8.06 (2H, d, J 8.8 Hz, ArH).
13C NMR (500 MHz, CDCl3): δ 55.8, 60.8, 61.3, 94.5, 99.9, 106.5, 114.1, 117.5, 118.2,
125.8, 127.1, 137.4, 142.0, 152.2, 155.1, 155.3, 157.1, 163.7, 173.6. LCMS (ES+) m/z =
+
729.1 ([M+H]+, tr = 1.66 min). HRMS (ESI+) m/z = 729.2160 [M+H]+ found, C39H37O14
required 729.2178.
4.3.19 Synthesis of 3,3’-(Methylenebis(oxy))bis(2-(4-bromo-2,5-dimethoxyphenyl)-7-
methoxy-4H-chromen-4-one) (97). A mixture of flavonol 88 (506 mg, 1.24 mmol), CH2I2
(0.30 mL, 3.68 mmol) and anhydrous K2CO3 (512 mg, 3.71 mmol) in dry acetone (20 mL)
was reacted according to GP-B. The crude residue was purified by flash column
chromatography (SiO2, 1-5% MeOH/CH2Cl2) to afford biflavone 97 (520 mg, 51%) as a pale
yellow-white powdery solid. m.p. 242-244 °C. TLC Rf = 0.56 (3% MeOH/CH2Cl2). IR νmax
(neat)/cm-1: 2941w (C-H str), 2843w (C-H str), 1734w, 1627s (C=O str), 1613s, 1577w (C=C
1
str), 1493s, 1441m, 1390w, 1376w, 1246s, 1216s, 1199s, 1163m, 1103m, 1050m, 1023s. H
NMR (500 MHz, CDCl3): δ 3.70 (6H, s, 2 × -OCH3), 3.72 (6H, s, 2 × -OCH3), 3.92 (6H, s, 2
× -OCH3), 6.04 (2H, s, -OCH2O-), 6.80 (2H, d, J 2.5 Hz, ArH), 6.97-6.99 (4H, m, ArH), 7.13
(2H, s, ArH), 8.04 (2H, d, J 9.0 Hz, ArH). 13C NMR (500 MHz, CDCl3): δ 55.8, 56.6, 56.7,
95.2, 100.0, 114.4, 114.6, 114.9, 117.0, 117.9, 119.0, 126.9, 137.6, 149.4, 151.5, 154.2,
157.2, 164.0, 173.5. LCMS (ES+) m/z = 827.0 ([M+H]+, tr = 2.14 min). HRMS (ESI+) m/z =
+
825.0151 [M+H]+ found, C37H31O12Br2 required 825.0177.
4.3.20 Synthesis of 7,7’-(Methylenebis(oxy))bis(6-(5-bromo-2,4-dimethoxyphenyl)-8H-
[1,3]dioxolo[4,5-g]chromen-8-one) (98). A mixture of flavonol 89 (204 mg, 0.484 mmol),
CH2I2 (0.11 mL, 1.42 mmol) and anhydrous K2CO3 (209 mg, 1.51 mmol) in dry acetone (20
mL) was reacted according to GP-B. The crude residue was purified by flash column
chromatography (SiO2, 1-5% MeOH/CH2Cl2) to afford biflavone 98 (200 mg, 48%) as a pale
yellow-brown powdery solid. m.p. 198-200 °C. TLC Rf = 0.34 (3% MeOH/CH2Cl2). IR νmax
28

ACCEPTED MANUSCRIPT
(neat)/cm-1: 2922w (C-H str), 2850w (C-H str), 1620s (C=O str), 1598s (C=C str), 1568w
(C=C str), 1500m (C=C str), 1461s, 1348m, 1303w, 1256s, 1205s, 1186w, 1177m, 1158m,
1148w, 1057w, 1025s. 1H NMR (500 MHz, CDCl3): δ 3.78 (6H, s, 2 × -OCH3), 3.86 (6H, s,
2 × -OCH3), 6.11 (6H, s, 3 × -OCH2O-), 6.30 (2H, s, ArH), 6.79 (2H, s, ArH), 7.43 (2H, s,
ArH), 7.53 (2H, s, ArH). 13C NMR (500 MHz, CDCl3): δ 56.1, 56.2, 93.7, 96.2, 97.8, 101.5,
102.1, 102.3, 113.4, 119.2, 134.4, 137.2, 145.7, 152.4, 152.7, 152.9, 158.0, 158.2, 173.0.
LCMS (ES+) m/z = 855.0 ([M+H]+, tr = 1.74 min). HRMS (ESI+) m/z = 852.9783 [M+H]+
+
found, C37H27O14Br2 required 852.9762.
4.3.21 Synthesis of 3,3’-(Methylenebis(oxy))bis(6-bromo-2-(furan-2-yl)-4H-chromen-4-one)
(99). A mixture of flavonol 90 (310 mg, 1.01 mmol), CH2I2 (0.24 mL, 2.93 mmol) and
anhydrous K2CO3 (451 mg, 3.26 mmol) in dry acetone (20 mL) was reacted according to GP-
B. The crude residue was purified by flash column chromatography (SiO2, 1-5%
MeOH/CH2Cl2) to afford biflavone 99 (177 mg, 28%) as a pale yellow-white powdery solid.
m.p. 258-260 °C. TLC Rf = 0.46 (0.5% MeOH/CH2Cl2). IR νmax (neat)/cm-1: 3099w (C-H
str), 2852w (C-H str), 1636s (C=O str), 1610s, 1572m (C=C str), 1553m (C=C str), 1483m,
1
1464s, 1438s, 1360m, 1270m, 1250s, 1194s, 1165s, 1118m, 1018m. H NMR (500 MHz,
CDCl3): δ 6.10-6.11 (2H, m, ArH), 6.65 (2H, s, -OCH2O-), 7.00 (2H, dd, J 3.5, 0.5 Hz, ArH),
7.34 (2H, d, J 9.0 Hz, ArH), 7.37 (2H, dd, J 1.5, 1.0 Hz, ArH), 7.73 (2H, dd, J 9.0, 2.5 Hz,
ArH), 8.33 (2H, d, J 2.5 Hz, ArH). 13C NMR (500 MHz, CDCl3): δ 92.7, 112.0, 117.6, 118.2,
119.7, 125.4, 128.1, 134.8, 136.3, 143.1, 145.0, 147.8, 153.1, 171.9. LCMS (ES+) m/z =
627.0 ([M+H]+, tr = 2.20 min). HRMS (ESI+) m/z = 646.8924 [M+Na]+ found,
C27H14O8Br2Na+ required 646.8948.
4.3.22
Synthesis
of
7,7’-(Methylenebis(oxy))bis(6-(1-methyl-1H-pyrrol-2-yl)-8H-
[1,3]dioxolo[4,5-g]chromen-8-one) (100). A mixture of flavonol 91 (301 mg, 1.05 mmol),
CH2I2 (0.25 mL, 3.16 mmol) and anhydrous K2CO3 (449 mg, 3.25 mmol) in dry acetone (20
mL) was reacted according to GP-B. The crude residue was purified by flash column
chromatography (SiO2, 1-5% MeOH/CH2Cl2) to afford biflavone 100 (58.8 mg, 10%) as a
pale yellow-brown powdery solid. m.p. 222-224 °C. TLC Rf = 0.28 (3% MeOH/CH2Cl2). IR
νmax (neat)/cm-1: 3107w (C-H str), 2921w (C-H str), 1627m (C=O str), 1610m, 1577m (C=C
str), 1559s (C=C str), 1505w (C=C str), 1462s, 1414s, 1360m, 1306m, 1262s, 1210s, 1163s,
29