A convenient method for the synthesis of (prop-2-ynyloxy)benzene derivatives via reaction with propargyl bromide, their optimization, scope and biological evaluation

Article abstract of DOI:10.1371/journal.pone.0115457

A highly convenient method has been developed for the synthesis of (prop-2-ynyloxy) benzene and its derivatives. Differently substituted phenol and aniline derivatives were allowed to react with propargyl bromide in the presence of K₂CO₃

Full text of DOI:10.1371/journal.pone.0115457

RESEARCH ARTICLE
A Convenient Method for the Synthesis of
(Prop-2-Ynyloxy)Benzene Derivatives via
Reaction with Propargyl Bromide, Their
Optimization, Scope and Biological
Evaluation
Tannaza Batool1, Nasir Rasool1*, Yasmeen Gull1, Mnaza Noreen1,
Faiz-ul-Hassan Nasim2, Asma Yaqoob2, Muhammad Zubair1, Usman Ali Rana3,
Salah Ud-Din Khan3, M. Zia-Ul-Haq4, Hawa Z. E. Jaafar5*
1. Department of Chemistry, Government College University Faisalabad, Faisalabad, Pakistan, 2. Department
of Chemistry, Islamia University of Bahawalpur, Bahawalpur, Pakistan, 3. Deanship of scientific research,
College of Engineering, King Saud University, Riyadh, Saudi Arabia, 4. The Patent Office, Karachi, Pakistan,
5. Department of Crop Science, Faculty of Agriculture, 43400 UPM Serdang, Selangor, Malaysia
OPEN ACCESS
Citation: Batool T, Rasool N, Gull Y, Noreen M,
Nasim F-u-H, et al. (2014) A Convenient Method
for the Synthesis of (Prop-2-Ynyloxy)Benzene
Derivatives via Reaction with Propargyl Bromide,
Their Optimization, Scope and Biological
Evaluation. PLoS ONE 9(12): e115457. doi:10.
1371/journal.pone.0115457
*nasirrasool@gcuf.edu.pk (NR); hawazej@gmail.com (HJ)
Abstract
Editor: A. Ganesan, University of East Anglia,
United Kingdom
A highly convenient method has been developed for the synthesis of (prop-2-
ynyloxy) benzene and its derivatives. Differently substituted phenol and aniline
derivatives were allowed to react with propargyl bromide in the presence of K2CO3
base and acetone as solvent. The compounds were synthesized in good yields
(53–85%). Low cost, high yields and easy availability of compounds helped in the
synthesis. Electron withdrawing groups favor the formation of stable phenoxide ion
thus in turn favors the formation of product while electron donating groups do not
favor the reaction. Phenol derivatives gave good yields as compared to that of
aniline. As aprotic polar solvents favor SN2 type reactions so acetone provided best
solvation for the reactions. K2CO3 was proved to be good for the synthesis.
Antibacterial, Antiurease and NO scavenging activity of synthesized compounds
were also examined. 4-bromo-2-chloro-1-(prop-2-ynyloxy)benzene 2a was found
most active compound against urease enzyme with a percentage inhibition of
82.00¡0.09 at 100 mg/mL with IC50 value of 60.2. 2-bromo-4-methyl-1-(prop-2-
ynyloxy)benzene 2d was found potent antibacterial against Bacillus subtillus
showing excellent inhibitory action with percentage inhibition of 55.67¡0.26 at
100 mg/ml wih IC50 value of 79.9. Based on results, it can be concluded that some
Received: June 19, 2014
Accepted: November 24, 2014
Published: December 29, 2014
Copyright: ß 2014 Batool et al. This is an open-
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and repro-
duction in any medium, provided the original author
and source are credited.
Data Availability: The authors confirm that all data
underlying the findings are fully available without
restriction. All data are within the paper.
Funding: The present data is the part of M.Phil
thesis research work of Tannaza Batool. The
authors gratefully acknowledge the financial sup-
port by HEC (HEC Project No. 20-1465/R& D/09/
5458). S. U. Khan would like to extend his sincere
appreciation to the Deanship of Scientific Research
at King Saud University for its funding through the
Research Group Project no RGP-VPP-255. The
funders had no role in study design, data collection
and analysis, decision to publish, or preparation of
the manuscript.
Competing Interests: The authors have declared
that no competing interests exist.
PLOS ONE | DOI:10.1371/journal.pone.0115457 December 29, 2014
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
of the synthesized compounds may have potential antiurease and antibacterial
effects against several harmful substances.
Introduction
(Prop-2-ynyloxy)benzene is an important compound having vast synthetic
applications. Most important of all of its applications is its use as triazole
intermediate [1]. Synthetic methods of organic chemistry reveal alkyne groups to
be most reactive ones which increase the importance of the compound [2]. Low
cost, high yield of the compound has attracted the attention of scientists to
synthesize the compound as monomer for many polymeric compounds as it is
thermally reactive end capping agent. [3] The reaction became much more
important due to presence of terminal alkyne which helps in easy polymerization
reactions under mild reaction condition, low temperature which is more favorable
for linear and graft polymeric compounds. [4] (Prop-2-ynyloxy)benzene structure
is mainly found in compounds of medicinal importance specially of antimicrobial
importance. [5] (Prop-2-ynyloxy)benzene type compounds are also used in
synthesis of large number of polymeric compounds mainly included lignin [6],
azide functionalized dendrons [7], and b lactam fused enediynes [8], mono and
bis-1,2,3-triazole acyclonucleoside [9], symmetrical and asymmetrical, cyclic and
acylic enediynes [10] and sulfonated polytriazole proton exchange membrane for
methanol feul cells via click chemistry. [4] Synthetic importance of the compound
is revealed from its structure having easy approach for upcoming substances
joining them to form complex molecules more accurately with great ease [11].
Haung and coworkers observed that (Prop-2-ynyloxy)benzene type compounds
showed antimicrobial, antitumor, anti HIV, DNA scavenging inhibitors, anti
proliferating, anti obesity and central nervous system activities. [4] The main
intention of the present work is the synthesis of (Prop-2-ynyloxy)benzene
derivatives by reported methodologies [12–20] and our focused to adopt
optimization reaction condition such as effect of solvents, moler concentration of
bases, stirring and refluxing time. In addition evaluating their antibacterial,
antiurease and NO scavenging activities.
Results and Discussion
Chemistry
Krim and co-workers reported that (Prop-2-ynyloxy)benzene is an intermediate
in the synthesis of triazole via Huigen dipolar cycloaddition method using click
chemistry. Terminal alkynes provide an efficient method for the synthesis of
triazole, [21] which can be prepared by reaction of 3-Bromopropyne and aniline
derivatives in DMF [9, 22]. We reported the reaction of phenol and propargyl
PLOS ONE | DOI:10.1371/journal.pone.0115457 December 29, 2014
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
bromide for the synthesis of (Prop-2-ynyloxy)benzene derivatives under different
reaction conditions. [23–28] There is very little work on the synthesis of reported
compounds under these optimized reaction conditions and so far no information
was published for antibacterial, antiurease and NO scavenging activity of the
synthesized compounds.
We optimized the reaction conditions like temperature, solvents, bases and its
concentration for the synthesis of compounds (2a–2f) (Fig. 1, Table 1). It was
observed that successive addition of various bases and solvent types helped to
obtain moderate to very good yields (74–85%) of synthesized compounds. For the
synthesis of compound (2d) 2-bromo-4-methyl-1-(prop-2-ynyloxy) benzene, 2-
bromo-4-methyl phenol (0.535 mmol) was reacted with propargyl bromide (1.2
eq.) in THF using LiH (2 eq.) as base at room temperature producing no product.
It was noted that 2d was synthesized with almost 74% yield, when the reaction was
carried out in acetone and K2CO3 (2 eq.) under reflux conditions for 5 hrs.
Compound, 1-nitro-4-(prop-2-ynyloxy) benzene (2f) was prepared by using dry
acetone and K2CO3 (3.5 eq.) under reflux conditions for 5 hour producing 76%
yield. However when compound was first stirred in the presence of K2CO3 (3.5
eq.) and acetone at room temperature for 2 hour then adding propargyl bromide
(1.3 eq.) to the reaction mixture and stirring for 16 hour resulted in 53% yield. It
was surprisingly noted that acidity of phenoxide ion was also affected by nature of
substitutions. Electron withdrawing groups might increase the acidity to led
enhanced yield of products while electron donating groups allowed to decrease the
yield of synthesized compounds (Fig. 1, Table 1).
Compound 4a and 4b were prepared by reaction of 4,49-(propane-2,2-
diyl)diphenol (0.87 mmol) and 4,49-sulfonyldiphenol (0.8 mmol) with propargyl
bromide (2.4 eq.) in acetone using K2CO3 (4 eq.) as base under reflux conditions
(80 C) respectively. (Fig. 2, Table 2). It was noteworthy that 4b gave very good
˚
yield (73%) due to more acidic protons of 4,49-sulfonylbis((prop-2-ynyloxy)
benzene) while 4a gave moderate yield (70%) of 4,49-(propane-2,2-diyl)bis
((prop-2-ynyloxy)benzene) due to less acidic protons because of two methyl
moieties present in the molecule.
It was observed that naphthalene-1-ol (0.694 mmol) were allowed to react with
propargyl bromide (1.2 eq.) in the presence of K2CO3 base (3.5 eq.) and 3 ml dry
acetone as solvent to synthesize 1-(prop-2-ynyloxy)naphthalene 6a, (71%).
Naphthalene-2-ol (0.694 mmol) was first stirred in the presence of K2CO3 (3.5
eq.) and acetone at room temperature for 2 hour then adding propargyl bromide
(1.3 eq.) to the reaction mixture and stirring for 16 hour resulted in 73% yield of
2-(prop-2-ynyloxy)naphthalene 6b. The reaction completion was monitored by
TLC. No product was formed while refluxing the reaction mixture with 1 eq. of
K2CO3 base. It was surprisingly noted that increasing the eq. of K2CO3 base led to
reaction completion (Fig. 3, Table 3).
Moreover substituted aniline 7 (2.68 mmol) and 7a (0.699 mmol) were reacted
with propargyl bromide (1.3 eq.) to synthesize variously substiuted (prop-2-
ynyl)anilines, 8a–8d (Fig. 4, Table 4). It was noteworthy that reaction time was
prolonged as compared to phenolic compounds to provide more harsh conditions
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
Fig. 1. Synthesis of compounds 2a–f.
doi:10.1371/journal.pone.0115457.g001
in order to obtain desired products. In the presence of 1 eq. K2CO3 base 7a was
allowed to react with propargyl bromide (1.3 eq.), it was surprisingly noted that
reaction was failed however using 2–3 eq. base proved helpful for the completion
of reaction with very good yield of 8d (69%).
We explained a similar application of present method to obtain 10, N-(prop-2-
ynyl)-4-(prop-2-ynyloxy)aniline (Fig. 5, Table 5). It was observed that reaction
was carried out at room temperature by 16 hour stirring of 4-aminophenol
(0.917 mmol) and K2CO3 (2 eq.) as base with addition of propargyl bromide (2.4
eq.) in DMF as solvent during time interval of 20 min, after this reaction mixture
was refluxed for 48 h under nitrogen atmosphere to obtain desired product 10, no
Table 1. Optimization of reaction conditions for compounds 2a–2f.
Entry
Reactant
C6H4OBrCl
C6H4OBrCl
C6H4OBr2
C9H7OBr
Product
Solvents
Acetone
Acetone
Acetone
THF
Base
Temp.
80 C
Time*
5 h
Yield*
79%
78%
85%
0%
1
2
3
4
C9H6OClBr 2a
C9H6OClBr 2b
C9H6OBr2 2c
C10H9OBr 2d
K2CO3
K2CO3
K2CO3
LiH
˚
80 C
˚
5 h
80 C
˚
5 h
r.t
24 h
5 h
Acetone
Acetone
Acetone
Acetone
K2CO3
K2CO3
K2CO3
K2CO3
80 C
˚
74%
79%
53%
76%
5
6
C6H4OBrF
C9H5O3N
C9H6OBrF 2e
C9H7O3N 2f
80 C
˚
5 h
80 C
˚
30 h
5 h
80 C
˚
*Time checked by TLC.
*Isolated Yield.
doi:10.1371/journal.pone.0115457.t001
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
Fig. 2. Synthesis of compounds 4a–b.
doi:10.1371/journal.pone.0115457.g002
product was formed. It was noteworthy that when the reaction was done with
K2CO3 (4 eq.) as base in dry acetone as solvent, compound 10 was obtained with
76% yield.
Reaction of 11 4-amino-5-hydroxynaphthalene-2,7-disulfonic acid
(0.313 mmol) and 11a 4-amino-3-hydroxynaphthalene-1-sulfonic acid
(0.418 mmol) with propargyl bromide (2.7 eq.) in basic conditions did not
confirm the formation of any product. It was noted that the reaction failed even
after addition of excess quantities of base and refluxing the reaction for prolonged
time (Fig. 6). It might be possible that failure of reactions were due to presence of
sulfonic acid functionality present in the molecule.
Pharmacology
Antiurease activity
Electron donating groups enhance the activity of compounds by donating the
electrons to phenyl group which enhances the binding of enzyme active site and
the molecule easily [29]. Bromine containing compounds more easily inhibit the
urease activity rather than compounds containing fluorine and chlorine due to
lesser electronegativity values of bromine. Methyl substituent and sulfur moiety
also increases the activity of compounds [30]. The compounds were tested to
inhibit the activity of urease enzyme at 50 mg/ml and 100 mg/ml concentrations
Table 2. Optimization of reaction conditions for compounds 4a–b.
Entry
Reactant
Product
Base
Solvent
Acetone
Acetone
Time
5 h
Temp.
80 C
Yield
70%
73%
1
2
C15H16O2
C12H10O4S2
C21H20O 4a
C14H14S2O2 4b
K2CO3
K2CO3
˚
5 h
80 C
˚
doi:10.1371/journal.pone.0115457.t002
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
Fig. 3. Synthesis of compounds 6a–b.
doi:10.1371/journal.pone.0115457.g003
and their results are given in table 3. Thiourea was used as positive control with
percentage inhibition activity of 65¡0.01 with IC50 value of 23.3 at 40 mg/ml.
The results revealed that electronic effects of aryl substitutions are playing a
significant role in activity manipulation. 2a, 2b and 2e contain bromine
substitution which enhances their activity due to lesser withdrawing effect. Chloro
and flouro groups decrease the activity of compounds due to more withdrawing
effect. 4a also exhibited remarkable results due to presence of methyl moieties. 2f
surprisingly gave contrasting results. As nitro group has withdrawing electronic
effect, which decreases the inhibitory effect of synthesized compound. But results
showed comparatively good results for the respective compound.
It was observed that all synthesized compounds 2a-10 showed moderate to very
good urease inhibition activity. 4-bromo-2-chloro-1-(prop-2-ynyloxy)benzene 2a
showed comparatively good results with a percentage inhibition of 42.5¡0.7 at 50
and 82.00¡0.09 at 100 mg/mL with IC50 value of 60.2. The 2b–6a showed good
inhibition activities with percentage inhibition of 81.07¡0.1, 86.45¡0.07,
85.89¡0.07, 79.59¡0.11, 65.8¡0.18, 89.42¡0.05, 74.9¡0.13, 65.3¡0.18 at
100 mg/ml with IC50 values ranging between 64.92, 70.1, 67.14, 62.15, 63.7, 62.3,
70.9 and 68 mg/ml respectively (Table 6). 6b did not show any satisfactory results.
Aniline derivatives showed comparatively lesser activities due to lack of binding
site at tertiary amine site. Ni acts as cofactor for urease enzyme, which helps in
chelation of ions by compounds containing amino groups, thus activating the
enzyme activity but in tertiary amines, chelation do not occur easily. Compound
8a-10 (Table 6) showed low inhibition activities with inhibition values of
Table 3. Optimization of reaction conditions for compounds 6a–b.
Entry
Reactant
C10H8O
C10H8O
Product
Base
Reaction
Complete
Complete
Solvent
Acetone
Acetone
Time
15 h
30 h
Yield
71%
73%
1
2
C13H10O 6a
C13H10O 6b
K2CO3
K2CO3
doi:10.1371/journal.pone.0115457.t003
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
Fig. 4. Synthesis of compounds 8a–d.
doi:10.1371/journal.pone.0115457.g004
55.65¡0.239, 50.83¡0.265, 56.5¡0.234, 51.5¡0.26 at 100 mg/ml with IC50
values of 90.7, 98.2, 89.6 and 91.7 mg/ml respectively. Compound 8c did not show
any satisfactory results.
Nitric oxide (NO) scavenging activity
Nitric oxide is a free radical causing oxidative damage to biomolecules, finally
leading to many disorders like cancer [31], aging and diabetes [32]. The
synthesized compounds (2a-10) exhibited good nitric oxide scavenging activity.
Vitamin C (Ascorbic acid) was used as a control with percentage inhibition values
38.5¡0.16 at 50 and 84.1¡0.12 at 100 mg/mL with IC50 value 50.43.
Electron withdrawing groups decreases the activity while electron donating
groups enhances the nitric oxide scavenging activity. Bromine containing
compounds exhibited more activity as 2c has maximum inhibitory activity due to
the presence of two bromine groups attached to aromatic ring. 4a also exhibited
Table 4. Optimization of reaction conditions for compounds 8a–d.
Entry
Reactant
C7H8NBr
C7H8NBr
C7H8NBr
C10H9N
Product
Base
Temp.
80 C
Solvent
Acetone
Acetone
Acetone
Acetone
Time
20 h
20 h
20 h
15 h
Yield
68%
71%
70%
69%
1
2
3
4
C10H10NBr 8a
C10H10NBr 8b
C10H10NBr 8c
C13H11N 8d
K2CO3
K2CO3
K2CO3
K2CO3
˚
80 C
˚
80 C
˚
80 C
˚
doi:10.1371/journal.pone.0115457.t004
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
Fig. 5. Synthesis of compound 10.
doi:10.1371/journal.pone.0115457.g005
remarkable results due to the presence of methyl moieties having donating effects
thus enhancing the activity. 2a, 2b and 2e have relatively lower IC50 values due to
electron withdrawing effects of fluorine and chlorine groups. 4b having SO2
groups showed lesser inhibitory activity. Aniline derivatives also showed lower
inhibitory activity as compared to that of phenolic ones.
Compounds 2,4-dibromo-1-(prop-2-ynyloxy)benzene 2c and 4,49-(propane-
2,2-diyl)bis((prop-2-ynyloxy)benzene) 4a were found good percentage inhibitors
against NO free radicals with value 39.67¡0.09 at 50 mg/mL and 77.03¡0.11 at
100 mg/mL with IC50 value 63.8 and percentage inhibition 40¡0.09 at 50 mg/mL
and 74.53¡0.13 at 100 mg/mL with IC50 value 64.4 respectively. 2a, 2b and 2e
exhibited fairly good NO percentage inhibition (76.09¡0.12, 68.44¡0.16 and
77.5¡0.11 at 100 mg/mL) with IC50 values 67.72, 67.9 and 68.8 respectively
(Table 7). Compounds 2d, 4b-10 were comparatively less active to scavenge NO
free radicals (69.95¡0.15, 59¡0.15, 63.17¡0.19, 65.19¡0.18, 68.65¡0.16,
57.98¡0.21, 62.8¡0.19 and 65.5¡0.18 at 100 mg/mL) with IC50 values 89.6, 83,
76.16, 79.4, 87.5, 78 and 78.1 for each compound respectively. 1-nitro-4-(prop-2-
ynyloxy)benzene 2f and N-(prop-2-ynyl)naphthalen-1-amine 8d did not show
any significant results and aniline derivatives showed lesser activity than that of
phenol.
Table 5. Optimization of reaction conditions for compound 10.
Entry
1
Reactant
Product
Solvents
DMF
Base
Temp
80 C
Time
64 h
10 h
Yield
0%
C6H7ON
C15H13ON
K2CO3
K2CO3
˚
Acetone
80 C
˚
76%
doi:10.1371/journal.pone.0115457.t005
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
Fig. 6. Synthesis of compounds 12a–b.
doi:10.1371/journal.pone.0115457.g006
Antibacterial activity
Disc diffusion method was adopted to test the antibacterial activity of synthesized
compounds 2a-10 against four different bacterial strains. Ampiciline was used as
positive control to check antibacterial activity of synthesized compounds. The
bacterial strains employed were: Escherichia coli, Bacillus subtillus, Shigella flexneri,
Table 6. Urease inhibition studies of (prop-2-ynyloxy)benzene.
Compound
Percentage inhibition at 50 ug/mL
42.5¡0.7
Percentage inhibition at 100 ug/mL
82.00¡0.09
81.07¡0.10
86.45¡0.07
85.89¡0.07
79.59¡0.11
65.8¡0.18
IC50 (ug/mL)
60.2
64.92
70.1
67.14
62.15
63.7
62.3
70.9
68
2a
2b
2c
2d
2e
2f
31.5¡0.22
36¡0.5
30.33¡0.6
40¡0.5
44¡0.43
4a
4b
6a
6b
8a
8b
8c
8d
10
37¡0.34
89.42¡0.05
74.9¡0.13
32¡0.28
41.33¡0.41
32¡0.38
65.3¡0.18
41.9¡0.313
55.65¡0.239
50.83¡0.265
45.26¡0.295
51.5¡0.26
---
25¡0.45
90.7
98.2
---
27¡0.45
32¡0.38
43¡0.42
91.7
89.6
25¡0.45
56.5¡0.234
40 ug/ml
20 ug/ml
Thiourea
47.1¡0.31
65¡0.01
23.3
doi:10.1371/journal.pone.0115457.t006
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
Table 7. Nitric oxide scavenging activity.
Percentage scavenging activity at 50
Compound
ug/ml
Percentage scavenging activity at 100 ug/ml
IC50 ug/ml
67.72
67.9
63.8
74.1
68.8
---
2a
35.67¡0.09
39.67¡0.09
39.67¡0.09
31.33¡0.10
33.33¡0.1
32¡0.10
76.09¡0.12
68.44¡0.16
77.03¡0.11
69.95¡0.15
77.5¡0.11
47.01¡0.27
74.53¡0.13
59¡0.15
2b
2c
2d
2e
2f
4a
40¡0.09
64.4
89.6
83
4b
15.33¡0.12
24.33¡0.12
33.33¡0.1
23.33¡0.11
26.33¡0.11
33.66¡0.09
7.67¡0.13
30¡0.10
6a
63.17¡0.19
65.19¡0.18
68.65¡0.16
57.98¡0.21
62.8¡0.19
38.38¡0.32
65.5¡0.18
84.1¡0.12
6b
76.16
79.4
87.5
78
8a
8b
8c
8d
---
10
78.1
50.43
Vit.C control
38.5¡0.16
doi:10.1371/journal.pone.0115457.t007
Table 8. Antibacterial activity of (prop-2-ynyloxy)benzene derivatives.
Compound
Staphylococcus aureus
Bacillus subtillus
50 ug/ml
40 ug/ml
100 ug/ml
IC50 ug/ml
97.7
87.7
87.7
95.9
85.1
NA
100 ug/ml
34.9¡0. 5
39.3¡0.36
55.01¡0.25
5.67¡0.26
7.9¡0. 75
57.9¡0.25
33.9¡0.45
50.9¡0.34
52.5¡0. 7
57.8¡0.26
53.6¡0.22
43.8¡0.35
36.0¡0.39
45.8¡0. 9
0.7¡0. 95
9. 8¡0.23
IC50 ug/ml
2a
29.13¡0.12
31.47¡0.19
31.47¡0.2
27.67¡0.35
31.99¡0.07
18.66¡0.3
29.06¡0.6
26.86¡0.35
–1.85¡0.3
21.44¡0.4
16.91¡0.7
13.39¡0.5
15.95¡0.69
5.85¡0.8
51¡0.5
56¡0.07
56¡0.1
52¡0.607
58¡0.9
39¡0.4
50¡0.2
53¡0.7
10¡0.9
51¡0.3
33¡0.8
36¡0.8
35¡0.2
31¡0.2
52¡0.1
73¡0.51
42.4¡0.35
40.37¡0.35
39.4¡0. 75
41.5¡0.3
NA
2b
NA
2c
83.79
79.9
NA
2d
2e
9.2¡0. 95
6.2¡0. 65
3.6¡0. 25
1.7¡0. 15
5.5¡0. 92
39.06¡0.05
30.5¡0.36
39.4¡0. 8
38.8¡0. 15
17.5¡0. 15
6.13¡0.35
9.9¡0.51
2f
87.5
NA
4a
97.7
94.21
NA
4b
97.6
92.6
79.2
92.2
NA
6a
6b
98.3
NA
8a
8b
NA
8c
NA
NA
8d
NA
NA
10
24.4¡0.11
29.9¡0.59
96.3
76
98.5
81
Ampicilline
doi:10.1371/journal.pone.0115457.t008
PLOS ONE | DOI:10.1371/journal.pone.0115457 December 29, 2014
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
Staphylococcus aureus, Pseudomonas aeroginosa and Salmonella typhi. Antibacterial
activity of synthesized compounds 2a–2e, 4a, 4b and 10 showed moderate activity
against Staphylococcus aureus while 2f, 6a and 8a–8d were found to be inactive
(Table 8).
Hence compounds 2c, 2f, 4b–8a and 10 have batter activity against Bacillus
subtillus. It was noted that 2d was found potent antibacterial against Bacillus
subtillus showing good inhibitory action. 2a, 2b, 2e, 4a, and 8b–8d did not show
any satisfactory result aginst Bacillus subtillus and were found to be inactive
(Table 8). All of the synthesized compounds 2a-10 were proved inactive against
Escherichia coli, Shigella flexneri, Pseudomonas aeroginosa and Salmonella typhi
providing no significant results.
Materials and Methods
Ethics statement
No specific permits were required for these field studies. No specific permissions
were required for these locations/activities because they were not carried out on
privately owned or protected areas. The field studies did not involve endangered
or protected species.
General
Melting points were determined using a Buchi melting point B-540 apparatus. All
reagents used were purchased from Alfa Aesar, Sigma Aldrich and E. Merck
1
Company. 13C-NMR and H-NMR spectra were recorded on Bruker ARX
400 MHz FT-NMR spectrophotometer and Bruker ARX 600 MHz FT-NMR
spectrophotometer while relishing CDCl3 as internal reference for the recording of
spectra. The chemical shift was given in d in ppm and coupling constant in Hz. EI-
MS spectras were recorded on a JMS-HX-110 spectrometer, with a data system.
For column chromatography technique, silica gel (70–230 mesh) and silica gel
(230–400 mesh) were used. The reactions were monitored on TLC, using Merk
Silica gel 60PF254 cards. The compounds were visualized by UV lamp (254, 365).
General procedure for the synthesis of (Prop-2-ynyloxy)benzene
derivatives
The synthesis of (Prop-2-ynyloxy)benzene derivatives was carried out by using
four methods.
Method A
To 1 eq (0.1 g) phenol (Figs. 1–6) added (1.2–2.7 eq.) propargyl bromide and (2–
4 eq.) K CO in acetone (3 ml) The reaction mixture was refluxed at 80 C till
˚
2
3
.
reaction completion based on TLC monitoring. On completion the reaction
mixture was cooled up to room temperature and solvent was removed under
PLOS ONE | DOI:10.1371/journal.pone.0115457 December 29, 2014
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
reduced pressure. The residue was dissolved in distilled water and then extraction
was done by twice addition of methylene chloride. Organic layer was separated
and dried with the help of anhydrous magnesium sulphate. Solvent was removed
under reduced pressure to obtain the desired product. After evaporation and
filtration process the product was purified by flash chromatography. 60/40
mixture of hexane and ethyl acetate was used as eluent [5, 33–34].
Method B
1 eq (0.1 g) of phenol (Fig. 1) and (1.2 eq.) of LiH was stirred in 6 ml of THF at
room temperature for 30 min, added (2 eq.) propargyl bromide to the reaction
mixture and stirred overnight at room temperature. Reaction completion was
monitored by TLC conditions. Evaporated the solvent under reduced pressure to
obtain the final product. Product was purified by flash chromatography. 60/40
mixture of hexane and ethyl acetate was used as eluent [9, 35].
Method C
Phenol (Fig. 1 and 3) 1eq (0.1 g) and K2CO3 (3.5 eq.) was stirred at room
temperature for two hours in 0.6 ml acetone. Propargyl bromide (1.3 eq.) in
1.66 ml acetone was added in 20 min and refluxed the reaction mixture for 16
hours under nitrogen atmosphere. Reaction completion was monitored by TLC.
After the reaction completion solvent was removed under reduced pressure. The
residue was dissolved in distilled water and organic layer was extracted using
dichloromethane thrice. Additional water was removed by drying with anhydrous
MgSO4 [11, 36].
Method D
1 eq (0.1 g) of 4-aminophenol (Fig. 5) and (3.5 eq.) anhydrous potassium
carbonate in 0.6 ml dry DMF was stirred at room temperature for about 16 hours.
2.4 eq propargyl bromide in 0.48 ml dry DMF was added slowly in about 15 min.
the reaction mixture was heated at 80 C for 48 hours under nitrogen atmosphere.
˚
Reflux conditions were used for heating the reaction mixture. Reaction
completion was monitored by TLC and reaction time varied according to the
condition of product. After reaction completion the solvent was removed reduced
pressure. Residue was dissolved in water and then organic compound was
extracted by addition of dichloromethane thrice the volume of water. Excess water
was removed by adding MgSO4. The solvent was removed under reduced pressure
and the compound separated was recrystallised using methanol thrice [11, 36].
Synthesis of 4-bromo-2-chloro-1-(prop-2-ynyloxy)benzene (2a)
1
Brown solid, M.p. 29 C, 79% Yield, H-NMR (400 MHz, CDCl ): d57.50 (d,
˚
J52.4 Hz, 1H-Ar), 7.33–7.25 (m, 1H-Ar), 6.96 (d, J58.8 Hz, 1H-Ar), 4.74 (d,
3
J52.4 Hz, 2H-CH2), 2.53 (t, 1H-acetylene). 13C-NMR (100 MHz, CDCl3+
PLOS ONE | DOI:10.1371/journal.pone.0115457 December 29, 2014
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
CD3OD): d5156.5, 134, 129.6, 122.2, 75.2, 51.2; EIMS (m/z -ion mode): 245 [M-
H2]; [M-CH2CCH fragment]25206; [M-Br fragment]25165.
Synthesis of 2-bromo-4-chloro-1-(prop-2-ynyloxy)benzene (2b)
Brown liquid. 78% Yield, 1H-NMR (400 MHz, CDCl3): d57.54 (d, J52.4 Hz, 1H-
Ar), 7.23–7.15 (m, 1H-Ar), 6.98 (d, J58.8 Hz, 1H-Ar), 4.77 (d, J52.0 Hz, 2H-
CH2), 2.53 (t, 1H-acetylene). 13C-NMR (100 MHz, CDCl3+ CD3OD): d5161,
137.5, 131, 125.2, 115.5, 76.8, 72.1, 51.2; EIMS (m/z -ion mode): 245 [M-H2];
[M-CH2CCH fragment]25206; [M-OCH2CCH fragment]25191; [M-Br frag-
ment]25165.
Synthesis of 2,4-dibromo-1-(prop-2-ynyloxy)benzene (2c)
Brown solid. M.p. 157.95 C, 85% Yield, 1H-NMR (600 MHz, CDCl ): d57.68 (d,
˚
3
J52.4 Hz, 1H-Ar), 7.39–7.30 (m, 1H-Ar), 6.95 (d, J59.0 Hz, 1H-Ar), 4.76 (d,
J52.4 Hz, 2H-CH2), 2.55 (t, 1H-acetylene). 13C-NMR (100 MHz, CDCl3+
CD3OD): d5167.9, 140.7, 127.8, 116, 76.5, 74.1, 51.2; EIMS (m/z -ion mode): 289
[M-H2]; [M-CH2CCH and CO fragment]25221; [M-Br fragment]25207; [M-
OCH2CCH and Br fragment]25149.
Synthesis of 2-bromo-4-methyl-1-(prop-2-ynyloxy)benzene (2d)
Yellow oily liquid. 74% Yield, 1H-NMR (400 MHz, CDCl3): d57.27 (d, J52.4 Hz,
1H-Ar), 6.97–6.88 (m, 1H-Ar), 6.67 (d, J59 Hz 1H-Ar), 4.69 (d, J52.1 Hz, 2H-
CH2), 2.99 (t, 1H-acetylene), 1.55 (s, 3H-CH3). 13C-NMR (100 MHz, CDCl3+
CD3OD): d5157, 138.9, 129, 79.3, 75.7, 51.2, 19.8; EIMS (m/z -ion mode): 224
[M-H2]; [M-CH2CCH fragment]25186; [M-Br fragment]25145; [M-CH2CCH
and Br fragment]25107.
2-bromo-4-fluoro-1-(prop-2-ynyloxy)benzene (2e)
Brown liquid. 79% Yield, 1H-NMR (400 MHz, CDCl3): d57.02–6.97 (m, 3H-Ar),
4.72 (d, J52. 4 Hz, 2H-CH2), 2.51 (t, 1H-acetylene). 13C-NMR (100 MHz,
CDCl3+ CD3OD): d5154.8, 124.3, 120.1, 79.4, 55.6; EIMS (m/z -ion mode): 231
[M-H2]; [M-CH2CCH fragment]25193; [M-CO and CH2CCH frag-
ment]25165.
Synthesis of 1-nitro-4-(prop-2-ynyloxy)benzene (2f)
Yellow crystals. M.p. 129 C, 76% Yield, -1H-NMR (400 MHz, CDCl ): d58.216
˚
3
(d, J59 Hz, 1H-Ar), 7.05 (d, J59 Hz, 1H-Ar), 4.77 (d, J52.4 Hz, 2H-CH2), 2.56
(t, 1H-acetylene). 13C-NMR (100 MHz, CDCl3+ CD3OD): d5166.5, 142.2, 129,
77, 57.8; EIMS (m/z -ion mode): 177 (M-H2]; [M-NO2 fragment]25131; [M-
NO2 and OCH2CCH fragment]2577.
Synthesis of 4,49-(propane-2,2-diyl)bis((prop-2-ynyloxy)benzene) (4a)
1
Light brown greasy liquid. 73% Yield, H–NMR (600 MHz, CDCl3): d57.164–
7.147 (m, 4H-Ar), 7.103–7.083 (m, 4H-Ar), 4.66 (d, J52.4 Hz, 4H-CH2), 2.90 (s,
6H-CH3), 2.52 (t, 2H-acetylene). 13C-NMR (100 MHz, CDCl3+ CD3OD): d5156,
151, 130.9, 117, 77.5, 31.8; EIMS (m/z -ion mode): 304 [M-H2]; [M-CH3
PLOS ONE | DOI:10.1371/journal.pone.0115457 December 29, 2014
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
fragment]25289; [M-CH2CCH fragment]25266; [M-benzene, CH3 and
OCH2CCH fragment]25169.
Synthesis of 4,49-sulfonylbis((prop-2-ynyloxy)benzene) (4b)
1
White solid. M.p. 136 C, 69% Yield, H-NMR (400 MHz, CDCl ): d57.86–7.83
˚
3
(m, 4H-Ar), 7.24–7.00 (m, 4H-Ar), 4.71 (d, J52. 4 Hz, 4H-CH2), 2.52 (t, 2H-
acetylene). 13C-NMR (100 MHz, CDCl3+ CD3OD): d5170, 140.7, 128, 119.3,
80.4, 77.5; EIMS (m/z -ion mode): 325 [M-H2]; [M-CH2CCH fragment]25288;
[M-2CH2CCH fragment]25250; [M- CH2CCH and CO fragment]25223; [M-
CH2CCH and 2CO fragment]25195.
Synthesis of 1-(prop-2-ynyloxy)naphthalene (6a)
1
Light brown liquid. 71% Yield, H-NMR (400 MHz, CDCl3): d57.77–7.73 (m,
3H-Ar), 7.45–7.32 (m, 3H-Ar), 7.18–7.09 (m, 1H-Ar), 4.80 (d, J52.0 Hz, 2H-
CH2), 2.53 (t, 1H-acetylene). 13C-NMR (100 MHz, CDCl3+ CD3OD): d5158,
135, 130.6, 126, 77.8, 63; EIMS (m/z -ion mode): 182 [M-H2]; [M-CH2CCH
fragment]25143; [M-CH2CCH and CO fragment]25115; [M-benzene and
OCH2CCH fragment]2577.
Synthesis of 2-(prop-2-ynyloxy)naphthalene (6b)
1
Dark brown greasy liquid. 73% yield, H-NMR (400 MHz, CDCl3): d57.82–6.75
(m, 7H-Ar), 4.81 (d, J52.07 Hz, 2H-CH2), 3.01 (t, 1H-acetylene). 13C-NMR (100
MHz, CDCl3+ CD3OD): d5160, 128.3, 126, 122.7, 116.5, 77.5, 58; EIMS (m/z -ion
mode): 182 [M-H2]; [M-CH2CCH fragment]25143; [M-CH2CCH and CO
fragment]25115; [M-benzene and OCH2CCH fragment]2577.
Synthesis of 4-bromo-2-methyl-N,N-di(prop-2-ynyl)aniline (8a)
1
Dark brown liquid. 68% Yield, H-NMR (400 MHz, CDCl3): d57.20 (d,
J51.96 Hz, 1H-Ar), 7.14–7.05 (m, 1H-Ar), 6.58 (d, J59 Hz, 1H-Ar), 3.94 (d,
J52.4 Hz, 2H-CH2), 2.71 (t, 1H-acetylene), 2.18 (s, 3H-CH3), 1.18 (s, 1H-NH).
13C-NMR (100 MHz, CDCl3+ CD3OD): d5154.2, 140, 138.9, 120.4, 79, 75.3, 45,
18.5; EIMS (m/z -ion mode): 224 [M-H2]; [M-CH2CCH fragment]25184; [M-
Br fragment]25144; [M-CH2CCH and Br fragment]25106.
Synthesis of 2-bromo-4-methyl-N-(prop-2-ynyl)aniline (8b)
1
Dark brown liquid. 71% Yield, H-NMR (400 MHz, CDCl3): d57.26 (s, 1H-Ar),
6.98–6.91 (m, 1H-Ar), 6.64 (d, J58 Hz, 1H-Ar), 3.96–3.90 (m, 4H-CH2), 2.22
(t, 2H-acetylene), 1.55 (s, 3H-CH3). 13C-NMR (100 MHz, CDCl3+ CD3OD):
d5140.5, 137.8, 129.9, 117, 80, 76.5, 46, 20.9; EIMS (m/z -ion mode): 224
[M-H2]; [M-CH2CCH fragment]25184; [M-Br fragment]25144; [M-CH2CCH
and Br fragment]25106.
Synthesis of 4-bromo-3-methyl-N-(prop-2-ynyl)aniline (8c)
Dark brown solid. M.p. 40.85 C, 70% Yield, 1H-NMR (400 MHz, CDCl ): d57.17
(d, J56 Hz, 1H-Ar), 6.63–6.55 (m, 1H-Ar), 6.36 (d, J57 Hz, 1H-Ar), 4.06 (d,
˚
3
J52.4 Hz, 4H-CH2), 2.86 (t, 2H-acetylene), 2.18 (s, 3H-CH3). 13C-NMR (100
PLOS ONE | DOI:10.1371/journal.pone.0115457 December 29, 2014
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
MHz, CDCl3+ CD3OD): d5150.6, 135.9, 130, 117.2, 80, 75, 45, 23.8; EIMS (m/z -
ion mode): 224 [M-H2]; [M-CH2CCH fragment]25184; [M-Br frag-
ment]25144; [M-CH2CCH and Br fragment]25106.
Synthesis of N-(prop-2-ynyl)naphthalen-1-amine (8d)
1
Brown greasy liquid. 69% Yield, H-NMR (400 MHz, CDCl3): d57.78–6.7 (m,
7H-Ar), 4.11 (d, J52.40 Hz, 2H-CH2), 2.88 (t, 1H-acetylene), 2.26 (s, 1H-NH).
13C-NMR (100 MHz, CDCl3+ CD3OD): d5149, 135, 126, 107.6, 80.8, 75.5, 31;
EIMS (m/z -ion mode): 180 [M-H2]; M-CH2CCH fragment]25143; [M-HCN
fragment]25115; [M-benzene and HNCH2CCH]2577.
Synthesis of N-(prop-2-ynyl)-4-(prop-2-ynyloxy)aniline (10)
Dark brown greasy liquid. 53% Yield, 1H-NMR (400 MHz, CDCl3): d5): d57.24–
7.03 (m, 4H-Ar), 3.98 (d, J52.40 Hz, 6H-CH2), 2.88 (t, 3H-acetylene). 13C-NMR
(100 MHz, CDCl3+ CD3OD): d5149, 145.5, 118.7, 118.6, 76, 71, 61, 45; EIMS (m/
z -ion mode): 1855[M-H2]; [M-CH2CCH fragment]25146; [M-2CH2CCH
fragment]25108; [M-2CH2CCH and CO fragment]2580.
Antiurease Activity
Antiurease activity of the synthesized compounds was determined by using the
modified phenol-hypochlorite method [37]. Varying concentrations were used to
prepare the urease inhibition curve of Thiourea (a known inhibitor of Urease) in
the reaction mixture. Phosphate buffer solution of pH 7 containing 1 unit of
enzyme was added about 200 ml in the test tube which was followed by the
addition of 230 ml of phosphate buffer and 20 ml of thiourea from a scrupulous
stock solution for the particular concentration of thiourea in the reaction mixture
respectively. Test sample solutions were added instead of thiourea solution in case
of test samples. The reaction mixture were mixed and incubated at 25 C for
˚
5 min. 400 ml of urea stock (20 mM) was added in each test tube. In order to
allow the action of urease on urea, all the test tubes were incubated at 40 C.
˚
Phenol hypochlorite reagent (1150 ml) was added after 10 min incubation at
40 C. Test tubes were again incubated at 56 C for 25 min. A blue coloured
˚
˚
complex was formed in the reaction mixture. The samples were allowed to cool
for 5 min and then their absorbance values were measured at 625 nm and the
%age inhibition was calculated. Experiment was repeated three times to get the
SD values.
NO Scavenging Activity
Solutions of known concentration were prepared by dissolving the synthesized
compounds in appropriate solvents. [38] A mixture of sample solution (20 ml),
10 mM sodium nitropruside solution (200 ml) and phosphate buffer of 7.4 pH
(1780 ml) was taken in a dry test tube and the mixture was incubated at 37 C for 2
˚
hours. 200 ml Griess reagent (0.3% Sulphanilic acid in glacial acetic acid, 0.1%
Naphthyl ethylene diamine HCL (NED): Mixed equal volume of both solutions
PLOS ONE | DOI:10.1371/journal.pone.0115457 December 29, 2014
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
just before use) was added after the incubation period is over. After 20 min
keeping the solution at room temperature, its absorbance at 528 nm was
measured. Each sample was analyzed in triplicate. Positive control of any known
antioxidant and control of all samples were run in parallel. Use of negative control
was to calibrate the instrument. Sample blanks were also prepared in case if the
samples were coloured. Correction in the absorbance values was made by
subtracting the sample blank reading from the sample reading.
Antibacterial Activity
Disc diffusion method was used for the determination of antibacterial activity.
[39] synthetic organic compounds were examined to evaluate their antibacterial
potential against four different strains of bacteria i.e. Staphlococcus aureus (Gram
+ ive), Pseudomonas- aeroginosa (Gram2ive) and Escherichia coli (Gram2ive),
Bacillus subtilis (Gram + ive), Salmonella typhi (Gram2ive) and Shigella flexneri
(2ive). The synthetic organic compounds were dissolved in an appropriate
solvent to get the solution of known concentration (5 mg/ml or 10 mg/ml). In order
to prepare discs of different potencies known volume of extract/synthetic organic
compound solution was applied on the discs, air dried and used. After preparation
of the sterilized nutrient agar and nutrient broth medium, the sterilized nutrient
agar medium was poured under aseptic conditions into sterile glass petri dishes/
plates. A known volume of bacterial growth culture can also be poured on the
surface of agar medium solidified in petri dishes. After inoculation petri plates
were kept at room temperature for 15–30 minutes so that the poured medium is
adsorbed. All the discs, including test sample, +ive and –ve controls were placed
onto the inoculated nutrient agar medium solidified in petri dishes with the help
of sterile forceps and incubated the petri plates at 37 C¡2 C for 16–24 hours.
˚
˚
Zone of inhibition was measured in mm using ordinary scale. Experiment was
repeated three times to get the SD values.
Conclusions
We have reported the synthesis of (prop-2-ynyloxy)benzene derivatives with
efficient yields under mild conditions. Some of the reactions were proceeded using
comparatively harsh conditions. Using more than one method helped in
comparison of reaction conditions and finding out the best one. Potassium
carbonate is a mild base, which provides best reaction conditions. Other bases
used were comparatively harsh which may also affect the aromatic ring rendring it
unfavorable for reaction products. Harsh bases like LiH, NaOH deactivate the
aromatic ring. Acetone favours SN2 type reaction providing aprotic polar
conditions so acetone and potassium carbonate were proven to be best for the
synthesis of desired products. The synthesized compounds were proved to be
good antiurease, antioxidant and antibacterial substances. Phenolic Compounds
containing electron donating groups were proved to be better urease inhibitors
PLOS ONE | DOI:10.1371/journal.pone.0115457 December 29, 2014
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Synthesis of (Prop-2-Ynyloxy)Benzene Derivatives by Propargyl Bromide
and good NO scavenging activity than those compounds containing electron
withdrawing groups. In contrast synthesized phenolic compounds containing
both electron donating and electron withdrawing functionality gave better results
against bacterial strains. It also noted Aniline derivatives showed lesser activity
than phenolic compounds. The results of this study revealed that these
compounds may have potential inhibitory activity and can be used as
antibacterial, antiurease and antioxidant molecules.
Acknowledgments
The present data is the part of M.Phil thesis research work of Tannaza Batool. The
authors gratefully acknowledge the financial support by HEC (HEC Project
No. 20-1465/R&D/09/5458).S. U. Khan would like to extend his sincere
appreciation to the Deanship of Scientific Research at King Saud University for its
funding through the Research Group Project no RGP-VPP-255.
Author Contributions
Conceived and designed the experiments: NR FN MZ. Performed the
experiments: TB YG MN AY. Analyzed the data: UAR SUK MZH. Contributed to
the writing of the manuscript: MZH HZEJ.
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