An efficient one-pot access to N-(pyridin-2-ylmethyl) substituent biphenyl-4-sulfonamides through water-promoted, palladium-catalyzed, microwave-assisted reactions

Article abstract of DOI:10.1039/c5ra13302e

An efficient one-pot, Pd(PPh₃)₄ catalyzed, water-promoted method for the synthesis of N-(pyridin-2-ylmethyl) biphenyl-4-sulfonamides was developed under microwave irradiation. This methodology is acid free, has good substrate scope, excellent functional group compatibility, and excellent product yields, and is superior to the existing procedures for the synthesis of biphenyl-4-sulfonamides bearing a pyridin-2-ylmethyl group.

Full text of DOI:10.1039/c5ra13302e

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An efficient one-pot access to N-(pyridin-2-ylmethyl) substituent
biphenyl-4-sulfonamides through water-promoted, palladium-
catalyzed, microwave-assisted reactions†
Received 00th January 20xx,
Accepted 00th January 20xx
Zhi-You Huang,a Jing-Fang Yang,a Qian Chen,a Run-Jie Cao,a Wei Huang,a Ge-Fei Hao,*,a and Guang-
Fu Yang*,a,b
DOI: 10.1039/x0xx00000x
www.rsc.org/
(Scheme 1, method a). But, the yield is near 60%. This could be the
result of forming complex between N-(pyridin-2-ylmethyl) group
and palladium.12 Recent research also shown that the Boc
An efficient one-pot, Pd(PPh3)4 catalyzed, water-promoted
method for the synthesis of N-(pyridin-2-ylmethyl)biphenyl-4-
sulfonamides was developed under microwave irradiation. With
acid free, good substrate scope, excellent functional group
compatibility, and excellent product yields, this methodology is
superior to the existing procedures for the synthesis of biphenyl-4-
sulfonamides bearing pyridin-2-ylmethyl group.
The biphenyl-4-sulfonamides has been recognized as the significant
biological and pharmacological activities such as anticancer,1 anti-
tumor,2 antibacterial,3 anti-allergic,4 antiviral,5 and anti-
inflammatory.6 Two derivatives in this family, Valdecoxib and
Celecoxib, have been introduced to the market as anti-
inflammatory drug.7
The biphenyl-4-sulfonamide derivatives, N-(pyridin-2-ylmethyl)
biphenyl-4-sulfonamides also exhibit crucial biological activity.8 In
particular, agricultural chemists have focused on the core structure
to produce abscisic acid (ABA) agonist. For example, pyrabactin(Py)9
has been successfully designed to simulate the function of ABA
which plays a key role in overcoming the abiotic stresses such as
drought, cold and soil salinity, as well as in plant development.10
Being attracted by the biological properties of biphenyl-4-
Scheme 1 Selected methods to synthesize biphenyl-4-sulfonamides
protection of sulfonamino group could promote the coupling
reaction greatly (method b), while the strong acid was required for
deprotection.13 Otherwise the sulfonylation required very stable
sulfonamides,
a variety of strategies to synthesize the core
structure have been developed.1-7, 11 And, the palladium-catalyzed
reactions are confirmed to be the most efficient approaches.11
Recently, Covel et. al.8 reported a Suziki coupling reaction to
reactants.14 Moreover,
a boiling water-catalyzed neutral and
selective N-Boc deprotection from aromatic heterocycles, aromatic
amines, aliphatic amines, and amide has been developed.15 So, we
proposed the Suzuki coupling of N-Boc biphenyl-4-sulfonamides
followed by deprotection in one pot could produce the N-(pyridin-
2-ylmethyl)biphenyl-4-sulfonamides conveniently. To the best of
construct
the
N-(pyridin-2-ylmethyl)biphenyl-4-sulfonamides
a.Key Laboratory of Pesticide & Chemical Biology, Ministry of Education, Central
China Normal University, Wuhan 430079, P.R.China. E-mail:
gfyang@mail.ccnu.edu.cn
our knowledge, there has never been
a report on one-pot
palladium-catalyzed, water-promoted reaction to afford this
scaffold under microwave irradiation before.
b.Collaborative Innovation Center of Chemical Science and Engineering, Tianjing
300072, P.R.China
Our recent success in application of microwave irradiation16
prompted us to try the deprotection of 1a under the microwave
irradiation. As shown in Table 1, enhancing the reaction
temperature could accelerate the deprotection and increase the
† Electronic supplementary informaꢀon (ESI) available: Experimental
procedures,characterization data, and 1H, 13C and HRMS
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reaction yields (Table 1, entry 1-5). Subsequently, our study focused
on the screening of solvents (Table 1, entry 5-8). We found the
water-solubility of the solvent was important for the reaction. The
Table 2 Optimization of the Reaction Conditionsa
better the water solubility the higher the product yield. As a result,
dioxane- water was proved to be the suitable solvent.
Table 1 The water-promoted the SO2N-Boc deprotectiona
However, we found the deprotection of 1a under the
conventional heating condition was very difficult. Hence, we chose
1a and 2a as a model to optimize the one-pot reaction conditions.
As shown in Table 2, 64 % of coupling and deprotection product
(3aa) was obtained with a temperature of 120 °C (Table 2, entry 1)
under microwave irradiation. Process monitoring indicated that 1a
could be removed directly and fast before the Suzuki coupling to
produce 1aa at high temperature (120 °C). Therefore, in order to
improve the yield of 3aa, we should carry out the coupling reaction
at low temperature and the subsequent Boc-deprotection reaction
at high temperature. Under this assumption, we optimized the
temperature for the Suzuki coupling to be 85°C (Table 2, entry 2-4)
and the temperature for the Boc-deprotection reaction to be 130 °C,
respectively. Finally, the yield increased to 94% by prolonging the
reaction time to 10 min (Table 2, entry 5). We next explored the
effect of the bases on this reaction, among the bases we
investigated (Na2CO3, K2CO3, K3PO4 and Cs2CO3), Na2CO3 was
identified as the best one (Table 2, entry 5-8).
Entry
Solvent( 4:1)
T(°C)
t(min)
Yield(%)b
1
2
3
4
5
6
7
8
9c
Dioxane : H2O
Dioxane : H2O
Dioxane : H2O
Dioxane : H2O
Dioxane : H2O
DME : H2O
85
6
<5
<5
76
92
96
93
90
<5
<5
100
110
120
130
130
130
130
Reflux
6
6
8
8
8
DMF : H2O
8
Toluene : H2O
Dioxane : H2O
15
600
a Reactions conditons : 1a 0.5 mmol, solvent 5 mL. b Isolated yield.
cConventional heating method.
Entry
R
Solvent (4 : 1)
Base
Pd(PPh3)4
Yieldb (3aa)
Yieldb (3a) Yieldb (1aa)
T1 (℃), t1 (min)
120, 10
80, 5
T2 (℃), t2 (min)
--, --
1
Boc
Boc
Boc
Boc
Boc
Boc
Boc
Boc
Boc
Boc
Boc
Boc
Dioxane : H2O
Dioxane : H2O
Dioxane : H2O
Dioxane : H2O
Dioxane : H2O
Dioxane : H2O
Dioxane : H2O
Dioxane : H2O
Dioxane : H2O
Dioxane : H2O
Toluene : H2O
DME : H O
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
K2CO3
2 mol %
2 mol %
2 mol %
2 mol %
2 mol %
2 mol %
2 mol %
2 mol %
2 mol %
--
64
35
53
48
94
91
89
86
0
0
0
0
0
0
0
0
0
0
0
86
0
29
58
42
36
0
2
130, 8
130, 8
130, 8
130, 8
130, 8
130, 8
130, 8
130, 8
130, 8
130, 8
130, 8
3
85, 5
4
90, 5
5
85, 10
85, 10
85, 10
85, 10
85, 10
85, 10
85, 10
85, 10
85, 10
85, 10
85, 90
6
0
7
K3PO3
<5
<5
96
95
<5
<5
8
Cs2CO3
--
9
10
11
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
0
2 mol %
2 mol %
2 mol %
2 mol %
2 mol %
<5
92
21|2J. Name., 2015, 00, 1-32
13
14
15c
This journal is © The Royal Society of Chemistry 2015
Boc
DMF : H2O
130, 8
87
63
<5
0
<5
29
<5
H
Dioxane : H2O
Dioxane : H2O
130, 8
0
Boc
reflux, 600
81
a Reactions conditons: 1 (0.5 mmol), 2a (0.5 mmol), Pd(PPh3)4 (2 mol%), base (1.0 mmol), solvent (5 mL), protected by N2. b Isolated yield.

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mixture of dioxane and water (v/v = 4:1) was proved to be the best
results. On the contrary, the coupling reaction between 1aa and 2a
under the same condition produced much lower yield of 3aa (Table
2, entry 14). Compared with conventional heating (Table 2, entry
15), microwave irradiation can significantly accelerate the reaction
and notably improve the yield of product.
Table 3 Scope of arylboronic acid (2) and 1aa
With the optimized reaction conditions in hand, we screened the
substrate scope of the one-pot reaction of Suzuki coupling and
deprotection. Various aryl and heteroarylboronic acids were tested,
the results were summarized in Table 3. The reactions between 1a
and arylboronic acids always went smoothly. Both electron-
donating and electron-withdrawing groups, such as methoxy, t-
butyl, halogen(F, Cl), and trifluoromethyl groups, afforded the
corresponding products in excellent yields(Table 3, entry 2-8, 12,
13). The reaction yields of brominated or nitrated phenylboronic
acids were moderate due to the self-coupling or other unexpected
side reactions (Table 3, entry 9-11). More importantly, the reaction
was proved to be well tolerant of valuable but unstable groups,
such as hydroxyl, acetyl and formyl (Table 3, entry 14-16). In
addition, disubstituted and heteroarylboronic acid were also
investigated and afforded the desired products in good to excellent
yields (Table 3, entry 17-24). To further examine the efficiency of
this one-pot reaction and rapidly expand our unique compound
collection, we also carried out the reaction between 4-bromo-N-
Boc-N-(pyridin-2-ylmethyl)-naphthalene-1-sulfonamide (1b) and
phenylboronic acids (2), which produced the desired products in
good to excellent yield (Table 4, entry 1-9).
Entry
1
Boronic acid (2)
2a: R1=R2=R3=R4=H
t1(min)
10
10
10
15
15
15
15
15
15
15
25
20
15
20
15
15
15
25
25
15
15
3
Yield (%)b
94
3aa
3ab
3ac
3ad
3ae
3af
3ag
3ah
3ai
3aj
3ak
3al
2
2b: R1=R2=R4=H, R3=OCH3
2c: R1=R2=R4=H, R3=tBu
2d: R1=R2=R4=H, R3=F
2e: R1=R3=R4=H, R2=F
2f: R2=R3=R4=H, R1=F
2g: R1=R2=R4=H, R3=Cl
2h: R1=R3=R4=H, R2=Cl
2i: R1=R3=R4=H, R2=Br
2j: R1=R2=R4=H, R3=Br
2k: R1=R2=R4=H, R3=NO2
2l: R1=R2=R4=H, R3=CF3
2m: R1=R2=R4=H, R3=OCF3
2n: R1=R2=R4=H, R3=Ac
2o: R1=R3=R4=H, R2=CHO
2p: R1=R3=R4=H, R2=OH
2q: R2=R4=H, R1=F, R3=Cl
2r: R1=R4=H, R2=Cl, R3=Cl
2s: R1=R3=H, ,R2=Cl, R4=Cl
2t: R1=R4=H, R2=CH3, R3=F
94
3
95
4
94
5
93
6
90
7
93
8
92
9
53
10
11
12
13
14
15
16
17
18
19
20
21
51
58
Through a further high-throughput computational screening,
compounds 3aa and 3ai have been found to be active on the ABA
receptor PYL1. Very interestingly, both compounds are predicted
91
3am 93
3an
3ao
3ap
3aq
3ar
3as
3at
3au
90
93
87
91
92
92
91
92
Table 4 Scope of phenylboronic acid (2) and 1ba
2u: [1,1'-biphenyl]-4-
ylboronic acid
22
23
2v: furan-2-ylboronic acid
20
25
3av
93
85
2w:dibenzo[b,d]furan-4-
3aw
ylboronic acid
24
2x: pyridin-3-ylboronic acid 20
3ax
89
Entry Boronic acid (2)
t1 (min)
10
3
Yield(%)b
93
a Reactions conditons: 1a (0.5 mmol), 2 (0.5 mmol), Pd(PPh3)4 (2
mol %), Na2CO3 (1.0 mmol), dioxane:H2O = 4 mL : 1 mL , T2 = 130 °C,
t2 = 8 min, protected by N2. b Isolated yield.
1
2
3
4
5
6
7
8
2b: R1=R2=R4=H, R3=OCH3
3bb
3bc
3bd
3be
3bh
3bj
2c: R1=R2=R4=H, R3=tBu
2d: R1=R2=R4=H, R3=F
2e: R1=R3=R4=H, R2=F
2h: R1=R3=R4=H, R2=Cl
2j: R1=R3=R4=H, R2=Br
2m: R1=R2=R4=H, R3=OCF3
2q: R2=R4=H, R1=F, R3=Cl
10
95
10
91
15
92
15
93
In addition, we noted that the coupling reaction will not take
place in the absence of catalyst or base, but the deprotection
reaction can go smoothly (Table 2, entry 9, 10). Subsequently, we
screened the reaction solvents, such as the water mixed with
dioxane, toluene, DMF, and DME (Table 2, entry 5, 11-13). The
15
52
15
3bm
3bq
91
15
90
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2r: R1=R4=H, R2=Cl, R3=Cl
15
3br
91
The research was supported in part by the National Natural
Science Foundation of China (No.21332004 and 21202055),
Specialized Research Fund for the Doctoral Program of Higher
Education (No. 20201263001), and the Fok Ying-Tong
Education Foundation (No. 142017).
9
a Reactions conditons: 1a (0.5 mmol), 2 (0.5 mmol), Pd(PPh3)4 (2
mol %), Na2CO3 (1.0 mmol), dioxane : H2O = 4 mL : 1 mL , T2 = 130 °C,
t2 = 8 min, protected by N2. b Isolated yield.
Notes and references
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Fig 1. Computational modeling and chemical mediated root growth
inhibition. (A). Computational modeling of pyrabactin(Py) in PYL1
(PDB code: 3NEG). (B). Computational modeling of 3ai in PYL1. (C).
Computational modeling of 3aa in PYL1. (D). Arabidopsis plant wild
type lines show sensitivity in root growth with 100 μM treated
chemicals. The root growth in Py, 3ai, and 3aa-containing medium
is more inhibited than ABA. (E). The chemical structures of
Pyrabactin, 3aa, and 3ai.
Lavanya and M. Pal-Bhadra, Bioorg. Med. Chem., 2012, 20
2054-2066.
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(a) S. Hinsberger, J. C. de Jong, M. Groh, J. Haupenthal and R.
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S. Mitsumori, T. Tsuri, T. Honma, Y. Hiramatsu, T. Okada, H.
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to bind PYL1 in a similar fashion to a known ABA agonist pyrabactin
(Fig. 1). The sulfonamide functional group of 3ai and 3aa can form
hydrogen bond with residue E100. The pyridine ring can form
another hydrogen bond with residue K65 and π-π stacking
interaction with residue Y126 (Fig. 1B and 1C). The binding
differences can be found in the other side of the pocket. There is a
hydrophobic interaction between bromine atom and residue P94.
However, the biphenyl group makes 3ai and 3aa bind with P94
more closely. The estimated binding free energies are respectively -
8.89 kcal/mol and -8.20 kcal/mol for 3ai and 3aa, which area little
lower than that of pyrabactin (-7.98 kcal/mol). The root growth
inhibition experiment showed that Arabidopsis thaliana plant is a
little more sensitive to the treatment of 3ai, 3aa, and pyrabactin
than ABA (Fig. 1D). As shown in Fig. S1 (supporting information), the
root growth inhibition rates of 3ai, 3aa, and pyrabactin were
82±12 %, 98±5 %, and 94±7 %, respectively, while that of ABA was
only 68±13 %.
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In summary, we have reported an efficient method to prepare N-
(pyridin-2-ylmethyl)biphenyl-4-sulfonamides via
a
palladium-
catalyzed, water-promoted and microwave-assisted one-pot
reaction. In addition, the excellent reactivity and broad substrate
scopes make the developed methodology operationally concise and
facilitate rapid library construction. Further efforts to examine the
bioactivity of these compounds are underway and will be reported
in due course.
7
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Acknowledgment
4
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For selected recent examples of pyrabactin’s biological
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