4-Substituted thieno[2,3-d]pyrimidines as potent antibacterial agents: Rational design, microwave-assisted synthesis, biological evaluation and molecular docking studies

Article abstract of DOI:10.1111/cbdd.13028

In an attempt to discover a new class of antibacterial agents with improved efficacy and to overcome the drug-resistant problems, some novel 4-substituted thieno[2,3-d]pyrimidines have been synthesized via microwave-assisted methodology and evaluated for their in vitro antibacterial activity against various pathogenic bacterial strains. Compounds 12b and 13c showed the promising inhibitory potencies against Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa and Escherichia coli with MICs ranging from 2 to 10?μg/ml. Compound 13c was also found to be highly potent against methicillin-resistant S. aureus (MRSA) with MIC value of 4?μg/ml. Docking simulation studies have been performed to unravel the mode of action and association study indicate the binding of potent compounds with DHPS enzyme. In silico ADME studies suggest the drug-like characteristics of the potent compounds.

Full text of DOI:10.1111/cbdd.13028

DR. JITENDER BARIWAL (Orcid ID : 0000-0002-4521-5537)
Article type : Research Article
4-Substituted Thieno[2,3-d]pyrimidines as Potent Antibacterial Agents:
Rational Design, Microwave-Assisted Synthesis, Biological Evaluation and
Molecular Docking Studies
Rupinder K. Gilla,b, Harpreet Singh,c Tilak Rajd , Anuradha Sharmae , Gagandeep Singhf,
Jitender Bariwala,g*
aDepartment of Pharmaceutical Chemistry, ISF College of Pharmacy, Moga-142001, Punjab, India
bI. K. Gujral Punjab Technical University, Kapurthala, Jalandhar-144 601, Punjab, India
cDepartment of Chemistry, Guru Nanak Dev University, Amritsar, India, 143005
dToxicology Division, Forensic Science Laboratory, Phase-IV, Mohali, Punjab, India
eUniversity Institute of Pharmaceutical Sciences, Panjab University, Chandigarh 160014, India
fBioorganic and Photochemistry Laboratory, Department of Pharmaceutical Sciences, Guru Nanak Dev
University, Amritsar 143005, Punjab, India.
gSatiate Research & Anatech Pvt. Ltd., HSIIDC, Barwala, Panchkula-134118, Haryana, India.
*Corresponding author: Tel.: +91 1636 324200; fax: +91 1636 239515
E-mail: jitender.bariwal@gmail.com
ABSTRACT
In an attempt to discover a new class of antibacterial agents with improved efficacy
and to overcome the drug resistant problems, some novel 4-substituted thieno[2,3-
d
]pyrimidines have been synthesized via microwave assisted methodology and
evaluated for their in vitro antibacterial activity against various pathogenic bacterial
strains. Compounds 12 and 13 showed the promising inhibitory potencies against S.
aureus B. subtilis P. aeruginosa and E. coli with MICs ranging from 2 to 10 µg/ml.
Compound 13 was also found to be highly potent against methicillin resistant S.
b
c
,
,
c
aureus (MRSA) with MIC value of 4 µg/ml. Docking simulation studies have been
performed to unravel the mode of action and association study indicate the binding of
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doi: 10.1111/cbdd.13028
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potent compounds with DHPS enzyme. In silico ADME studies suggest the drug like
characteristics of the potent compounds.
KEYWORDS: Thieno[2,3-d]pyrimidines, Antibacterial activity, Molecular Docking
studies, ADME.
A large number of pyrimidine derived drugs such as trimethoprim, piromidic acid,
tetroxoprim and metioprim (1) are clinically used for antibacterial therapy. The fused
pyrimidines such as thieno[2,3-d]pyrimidines have been attracted considerable attention due
to their structural resemblance with biogenic pyrimidines and possess vast therapeutic
properties such as anti-inflammatory (2), antiviral (3), analgesic (4), herbicidal (5), anti-
proliferative (6), and antimicrobial (3, 7-8) activities.
Sulfonamides, which are widely prescribed antimicrobial agents, inhibits bacterial growth by
dihydropteroate synthase (DHPS) inhibition (9), therefore, DHPS has been considered as a
selective and promising target for developing antimicrobial agents. The widespread microbial
resistance and severe side effects of sulphonamides, limit their use (9-10) clinically, which
triggers an urgent need to develop new approaches that can overcome the problems of
microbial resistance. In this context, Yun et al. reported that sulfathiazole-6-hydroxymethyl-
7,8-dihydropterin-pyrophosphate (STZ-DHPP) adduct, which accommodates both p-
aminobenzoic acid (pABA) and pterin binding pockets of DHPS (Figure 1), bound to
Bacillus anthracis dihydropteroate synthase (BaDHPS) (11). Thus, bacterial resistance of
sulphonamides may be prevented by synthesizing such analogues that will target both sites of
DHPS enzyme. Inspired by this development, Nasr et al. reported some thiophene, pyrazole
and pyridine comprised sulfisoxazole moiety as DHPS inhibitors by targeting both pABA and
pterin binding pockets of the DHPS (12). Further, they also reported some 2,3-
dihydrothiazoles and 4-thiazolidinones containing sulfisoxazoles for the same purpose
(Figure 1) (13).
Inspired from the aforementioned facts to target DHPS enzyme by binding both pABA and
pterin binding pockets, and taking cognizance of antimicrobial potential of pyrimidine
analogs; it was decided to resynthesize 4-substituted thieno[2,3-d]pyrimidine analogues (9-
13) (14) along with some novel compounds (13e,f) and evaluated for antibacterial activity
(Figure 1). Further, molecular docking study has been performed to explore their binding
mode of action. Recently, we have reported the synthesis and biological activity of the similar
compounds for antiproliferative activity (14).
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Yun, 2012
Occupies the pABA
pocket of DHPS
Occupies the pterin
pocket of DHPS
H
O
N
S
S
N
O
N
NH
STZ-DHPP adduct obtained by interaction of
sulfathiazole STZ and DHPP
H
N
N
O
N
NH2
X=
H
Modification
Nasr, 2014
Nasr, 2015
R1
O
HN
Ar
H
O
CN
R3
N
N
S
O
S
NH
O
O
R1
N
H2N
N
H2N
N
X
R2
O
H
N
R1
N
R4
N
O
X= NC
S
R2
NC
O
O
O
O
S
N
S
N
X
R3
H
Current Work
Cl
O
N
N
N
H
N
S
; R1 = R2 = CH3
H
R1 R2 =
R2
R1
Figure 1. Design of antibacterial DHPS inhibitors.
Experimental
Chemistry
General Procedure for N-(4-substituted phenyl)-4-(thieno[2,3-d]pyrimidin-4-
ylamino)benzamide (13a-d)
To a microwave reaction vessel equipped with magnetic stirrer, a solution of appropriate 4-
(thieno[2,3-d]pyrimidin-4-yl-amino)benzoic acid (12a,b) (14) and DCC (1.2 equiv) in DMF
was added and stirred vigorously for 15 min at 0 oC. Then substituted aniline (1.2 equiv, 5a,e)
was added in microwave vessel and irradiated in microwave reactor at a ceiling temperature
o
of 110 C and maximum power of 80 W for 15-18 min. After completion of reaction, the
reaction mixture was poured on ice water and extracted with ethyl acetate. The organic layer
separated was concentrated under reduced pressure to obtain the desired product (13a,b).
N-(4-chlorophenyl)-4-(5,6,7,8-tetrahydrobenzothieno[2,3-d]pyrimidin-4-ylamino)benzamide
(13a)
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Yield 86%; mp 158-162 oC; IR KBr, cm-1: 3460 (γCONH), 3314 (γNH), 2928 (γCH), 1647
(γCO); 1H NMR (400 MHz, DMSO-d6): 10.32 (s, 1H, CONH), 8.48 (s, 1H, NH), 8.45 (s, 1H,
C2-H), 8.05 (d, 2H, J = 7.8 Hz, Ar-Hs), 7.98 (d, 2H, J = 7.8 Hz, Ar-Hs), 7.84 (d, 2H, J = 8.6
Hz, 2H, Ar-Hs), 7.74 (d, 2H, J = 8.6 Hz, Ar-Hs), 3.16 (dist. s, 2H, C5-H), 2.85 (dist. s, 2H,
C6 & C7-Hs), 1.88-1.84 (m, 4H, C8-Hs); 13C NMR (125 MHz, DMSO-d6): 165.89, 154.54,
151.85, 148.66, 145.57, 141.21, 135.67, 130.09, 127.90 (X2), 126.52 (X2), 124.56, 123.29
(X2), 120.25 (X2), 117.01, 116.40, 25.57, 24.90, 22.52, 22.36. HRMS (microTOF-QII, MS,
ESI): m/z [M+Na]+ Calculated for C23H19ClN4OS: 457.9412, Obsd 457.9415.
The compounds (9-13) were synthesized following the general procedure as described above
and the characterization data of other compounds has been provided in the SI.
Biological Evaluation
All the synthesized compounds were screened for their antibacterial activity against various
bacterial strains, namely S. aureus (MTCC-740), B. subtilis (MTCC-441), P. aeruginosa
(MTCC- 741), E. coli (MTCC-119) and MRSA (MTCC-1430). The MICs of synthesized
compounds were determined by broth microdilution method [15, SI] .
Molecular Docking Study
Docking studies have been performed with the various module of Schrodinger Suite 2013.
Fluorescence Spectroscopy
Steady-state fluorescence was performed using a PerkinElmer Luminescence
spectrometer LS-55 using pyrene as an external fluorescent probe (2 × 10−6 M) at an
excitation wavelength of 300 nm at 298.15 K. The temperature was controlled using
built-in temperature controller within 0.1 K by using circulating water bath. The
spectra were recorded between 311 and 320 nm using an excitation and emission slit
width of 2.5 nm, each.
Results and Discussion
Chemistry
The synthetic strategy adopted for the synthesis of substituted thieno[2,3-d]pyrimidines is
outlined in scheme 1. The substituted 4-anilino thieno[2,3-d]pyrimidines (9a-l, 12a-c) were
synthesized by employing our previously reported methods via microwave irradiation
(Scheme1) (14). Initially, 2-amino-3-carbethoxy thiophenes 2a-c have been prepared using
Gewald reaction followed by cyclization with formamide and chlorination of the resultant
intermediate 3a-c with phosphorus oxychloride yielded 4a-c. Then, the nucleophilic
displacement of chloride atom at 4th position of 4a-c with appropriate amines (5-8) afforded
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the desired 4-anilino thieno[2,3-d]pyrimidines 9a-l, 10a-c, 11a-f and 12a-c, respectively, in
excellent yields (Table 1).
Finally, the synthesis of substituted amide analogues 13a-f was achieved in excellent yield by
reacting substituted benzoate 12a-c with 4-chloroaniline 5a,e in presence of N,N-
dicyclohexylcarbodiimide (DCC) under microwave-irradiation conditions.
O
Cl
O
R1
R1
R2
O
N
R1
R2
O
POCl3
NC
COOC2H5
NH
HCONH2
R2
MW, 100 oC, 80 W,
12-15 min
R1
H
MW, 150 oC, 100 W,
20-25 min
N
R2
NH2
N
Diethylamine, S8, MeOH,
MW, 100 oC, 80 W, 2-9 min
S
S
S
1a-c
2a-c
4a-c
3a-c
R1, R2 = (CH2)4
R1 = R2 = CH3
R1 = Ph, R2 = H
NH2
R4
R3
R3
HN
R4
5a-d
R1
R2
N
Iso-propanol, MW,
100 oC, 80 W,
15-28 min
N
S
9a-l
R3 = CH3, H
4 = Cl, CH3, NO2, H
HN
R
N
6
R1
R2
N
(C2H5)3N, methanol,
MW, 100 oC, 80 W,
10-12 min
N
Cl
S
N
N
R1
R2
10a-c
X
X
S
4a-c
N
H
7a,b
N
R1, R2 = (CH2)4
R1 = R2 = CH3
R1 = Ph, R2 = H
N
N
R1
R2
MeOH, 0 oC, 5 min,
MW, 80 oC, 80 W,
5-8 min
S
11a-f
R4
X = CH2, O
OH
O
O
NH2
N
H
H2N
COOH
R1
HN
HN
5a,e
R1
N
N
N
R4
8
Iso-propanol,
MW, 110 oC, 80 W,
30-35 min
DCC, DMF, 0 oC, 15 min,
then MW, 110 oC, 80 W,
15-18 min
R2
N
R2
S
S
12a-c
13a-f
R4 = Cl, OCH3
Scheme 1. Synthesis of 4-substituted thieno[2,3-d]pyrimidines (9-13).
Antibacterial Activity
All the synthesized compounds were evaluated for antibacterial activity against Gram +ve, S.
aureus (MTCC-740) and B. subtilis (MTCC-441); and Gram -ve, P. aeruginosa (MTCC-
741) and E. coli (MTCC-119) strains using ciprofloxacin and sulfathiazole as standards (15).
From the results of antibacterial study, it was depicted that the most sensitive strain was S.
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aureus followed by B. subtilis, while, both P. aeruginosa and E. coli were least sensitive
towards the evaluated molecules (Table 1).
On observing the antibacterial activity of 4-substituted anilino thieno[2,3-d]pyrimidines 9a-l,
it was found that compounds 9e, 9f, 9g, 9h and 9l showed moderate inhibitory potential
against S. aureus, B. subtilis, P. aeruginosa and E. coli. Among the various substituents
present at C-4 position of aniline group in 4-anilino-thieno[2,3-d]pyrimidines, methyl group
derivative 9f possesses significant activity, specifically against S. aureus and B. subtilis,
while, on shifting methyl substitution from 4th to 2nd position as in 9h, further improvement
of the activity was observed. On the other hand, replacement of the anilino scaffold with
azacyclic ring (morpholine or piperidine) in 11a-f, significantly improved the antibacterial
activity against all pathogenic strains, with the only exception of compound 11a. Further, it
was apparent that 4-carboxyanilino substituted derivatives 12a-c displayed pronounced effect
against S. aureus and B. subtilis, while, compound 12b and 12c also showed significant
activity against P. aeruginosa and E. coli. The increased activity of 12b compared to 12c and
12a suggests the importance of 5,6-dimethyl substitution on thieno[2,3-d]pyrimidine than
cyclopentane fused tricyclic derivative. Benzamide derivatives 13a-f exhibited significant
antibacterial activity. Particularly, the N-4-chlorophenyl benzamide derivatives 13a, 13c and
13e exhibited better activity than N-4-methoxyphenyl benzamide derivatives 13b, 13d and
13f. The N-4-chlorophenyl benzamide derivatives 13a, 13c and 13e showed remarkable
inhibitory potential against S. aureus (MIC 12, 2 and 8 µg/ml, respectively), B. subtilis (MIC
12, 6 and 10 µg/ml, respectively), P. aeruginosa (MIC 6, 6 and 10 µg/ml) and E. coli (MIC
16, 10 and 12 µg/ml, respectively), which is also superior to the standard sulfathiazole and
comparable to the ciprofloxacin against S. aureus.
These results clearly indicated that compounds bearing benzamide 13a-f or 4-carboxyanilino
12a-c functionality displayed excellent inhibitory potential and the 5,6-dimethyl substituted
thieno[2,3-d]pyrimidines 9e-h, 12b, 13c and 13d possess higher antibacterial activity
followed by 5-phenyl substituted derivatives 9i-l, 12c, 13e and 13f and then the cyclopentane
fused tricyclic derivatives 9a-d, 12a, 13a and 13b.
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Table 1. Yield %, reaction time, in vitro antibacterial activities and G-score of the
synthesized compounds (9-13).
MIC (µg/ml)a
In-silico
Code
R1
R2
R3
X
R4
R5
Yield Time
Analysis
G-
(%)
(min)
S.
B.
P.
E.
aureus subtilis aeruginosa coli
Scoreb
9a
9b
9c
9d
9e
9f
9g
9h
9i
(CH2)4
(CH2)4
(CH2)4
4-Cl
4-CH3
4-NO2
2-CH3
4-Cl
4-CH3
4-NO2
2-CH3
4-Cl
4-CH3
4-NO2
2-CH3
H
H
H
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
H
H
H
H
H
H
H
H
H
H
H
H
CH3
CH3
CH3
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
85
92
80
62
85
87
79
57
73
75
66
55
68
62
65
64
61
56
53
65
66
60
58
54
86
92
84
86
75
78
15
15
15
20
24
24
24
28
15
18
18
20
10
12
10
07
5
08
07
07
05
30
35
32
15
15
18
18
15
15
76
70
>100
78
16
14
20
4
26
24
28
18
88
84
76
72
22
6
80
78
>100
86
20
18
18
12
28
20
34
16
>100
>100
88
76
20
14
14
18
12
12
8
68
70
>100
80
30
>100
12
>100
54
>100
>100
80
74
78
>100
>100
>100
40
88
36
84
>100
10
66
76
8
92
68
>100
70
>100
68
>100
74
>100
>100
>100
>100
>100
64
8
40
16
48
>100
6
18
16
28
10
32
12
34
-4.25
-3.84
-3.20
-3.89
-3.64
-3.99
-3.03
-6.02
-4.14
-3.70
-3.13
-4.05
-4.34
-3.77
-3.81
-4.65
-6.06
-5.80
-4.93
-5.74
-5.41
-4.86
-4.7
(CH2)4
CH3 CH3
CH3 CH3
CH3 CH3
CH3 CH3
Ph
Ph
Ph
Ph
H
H
H
H
9j
9k
9l
10a
10b
10c
11a
11b
11c
11d
11e
11f
12a
12b
12c
13a
13b
13c
13d
13e
13f
(CH2)4
CH3 CH3
Ph
(CH2)4
H
CH2
O
CH2
O
CH2
O
-
-
-
-
-
-
-
-
-
(CH2)4
CH3 CH3
CH3 CH3
-
-
-
-
-
-
-
-
-
-
-
-
Cl
OCH3
Cl
OCH3
Cl
8
Ph
Ph
H
H
12
10
6
4
6
12
16
2
8
8
-
(CH2)4
CH3 CH3 4-COOH
4-COOH
H
H
H
-
-
-
-
-
-
Ph
H
4-COOH
10
12
14
6
14
10
20
1.6
32
18
6
36
6
24
10
28
0.6
32
-4.74
-4.47
-4.26
-6.11
-4.32
-4.64
-4.20
-4.61
-3.77
(CH2)4
(CH2)4
CH3 CH3
CH3 CH3
-
-
-
-
-
-
Ph
Ph
H
H
OCH3
16
2
64
Ciprofloxacin
Sulfathiazole
1.2
16
a MIC values determination was performed in triplicate.
b calculated theoretically using Glide 5.9.
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The active compounds were further evaluated against methicillin resistant strain of S. aureus
(MRSA) to determine whether they were also susceptible to resistant strain. It was
noteworthy that all the tested compounds were found to show significant effect against
MRSA (Table 2).
Table 2. MIC (µg/ml) value of compounds against methicillin resistant S. aureus (MRSA).
Compd. 11c 11d 12a 12b 12c 13a 13c 13d 13e 13f Ciprofloxacin
(17)
10
12
10
6
14
10
4
8
12
20
4
MRSA
Molecular Docking Studies
Considering the potent activity of synthesized compounds against various bacterial strains,
molecular docking studies were performed to investigate whether the synthesized compounds
fit well in the active site of Bacillus anthracis dihydropteroate synthase (BaDHPS, PDB ID:
3TYE, Figure 2) (11). The reliability of proposed docking algorithm was validated by
redocking of the crystallographic ligand, STZ-DHPP adduct, in the BaDHPS crystal structure
and the top ranked pose showed heavy-atom root-mean-square deviation (RMSD) value of
0.84 Å (Figure S1).
Figure 2. (a) The crystal structure of Bacillus anthracis dihydropteroate synthase with its grid by receptor grid
generation. (b) The hypothetical binding pose of STZ-DHPP adduct (STZ: sulfathiazole, DHPP: 6-
hydroxymethyl-7,8-dihydropterin-pyrophosphate) showing the active amino acids around it after extraction.
The affinities of all the synthesized compounds were evaluated in terms of G-score (Glide
score), which is in the range from -6.11 to -3.03 (Table 1). The docking of BaDHPS with
compound 13c revealed that its dock score (-6.11) was quite comparable to ciprofloxacin
(-4.61) and sulfathiazole (-3.77). The hydrophilic and hydrophobic maps in Figure 3a
represent the important interactions of compound 13c and it was observed that it targets both
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pterin and pABA binding pockets of BaDHPS. Moreover, it was disclosed that compound
13c occupies the same position in pABA binding pocket as observed in STZ-DHPP-BaDHPS
complex i.e. carbonyl and NH of amide group forms hydrogen bond with Ser221 (3.39Ǻ) and
Gly188 (2.22Ǻ), respectively (Figure S2). Additionally, thienopyrimidine ring occupies the
pterin binding pocket by forming hydrogen bond between terminal nitrogen and Lys220 with
distance of 3.50Ǻ and thiophene forms co-ordination bond to positively charged nitrogen of
histidine with distance of 3.21Ǻ. 2D-picture clearly depicts the surrounding amino acids
within the cavity of the enzyme (Figure 3b). Therefore, docking results suggest that the 4-
substituted thieno[2,3-d]pyrimidines, particularly compound 13c may act as inhibitors of
bacterial dihydropteroate synthase.
Figure 3. (a) The postulated binding mode of the most potent compound 13c within the cavity showing the
hydrophilic and hydrophobic maps of the crystal structure of the receptor. (b) The binding interactions of the
same compound with surrounding amino acids within the cavity of the gorge.
Association constant using fluorescence spectroscopy
To further investigate the binding of potent compounds 12b and 13c with DHPS enzyme,
association constant or binding constant (Ka) of potent compounds 12b and 13c with DHPS
enzyme was determined using sensitive fluorescence spectroscopic technique (Figure S3-S5)
(18-22). The results of investigations revealed that both compounds 12b and 13c showed
appreciable Ka = 13.08 and 19.71 x 103 M-1 (Table S1), respectively, which, indicates that
13c-[DHPS] binding is stronger than 12b-[DHPS].
Physicochemical and ADME properties
It was evident that most of the potential drug candidates usually fail to reach the clinic due to
their unfavourable ADME (Adsorption, Distribution, Metabolism, Excretion and Toxicity)
profile; thus, initial evaluation of ADME parameters is a best way to avoid this problem. For
this purpose, computational study of the synthesized compounds was performed by using
Qikprop v3.6 tool of Schrodinger software (Table S2 and 3) (23). Absorption (% ABS) was
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calculated by: % ABS = 109- (0.345 X TPSA) (24). It was observed that the potent
compounds showed good % absorption in a range of 79.34–84.31% (Table 3). Further,
Lipinski’s rule of 5 states that for a molecule to develop as active drug candidate, it should
possess no more than one violation of the criteria’s given in Table S1 and 3 (25). The result of
ADME study revealed that none of the compounds violated the Lipinski’s rule of five, which
indicates that 4-substituted thieno[2,3-d]pyrimidines may be utilized to develop drug-like
antibacterial candidates.
Table 3. In silico predicted physicochemical pharmacokinetic properties.
Entry
%
n-ON
n-OHNH
ROF TPSA
(Å2)
QP
logP
≤5
QP
logS
≤5
QP
logK
≤5
QP
logBB
≤5
MW
ABS acceptors donors
Rule
-
<10
<5
≤1
≤140
<500
79.45
84.31
4
5
2
2
0
0
85.65
71.55
2.70
4.72
-3.91
-6.71
-0.09
0.70
-0.98
-0.49
299.34
408.90
12b
13c
% ABS: percentage absorption, n-ON acceptors: number of H-bond acceptors; n-OHNH donors: number of H-
bond donors; ROF: Rule of Five: number of violations; TPSA: topological polar surface area; QP logP:
predicted octanol/water partition coefficient; QP logS: predicted aqueous solubility; QP logK: prediction of
binding to human serum albumin; QP logBB: prediction of Blood/Brain partition coefficient; MW: molecular
weight.
Conclusion
Variedly substituted 4-substituted thieno[2,3-d]pyrimidines were synthesized via microwave
assisted methodology and evaluated for in vitro antibacterial activity. Compounds 13c and
12b were found to exhibit the excellent inhibitory potential against various susceptible and
resistant strains; this might be attributed to the presence of N-4-chlorophenyl benzamide and
benzoate moiety, respectively, at 4th position of anilino thienopyrimidine. Molecular docking
studies showed that thienopyrimidines accommodate both pABA and pterin binding pocket
of DHPS, in the same manner as reported for STZ-DHPP adduct, suggesting that they may
act as DHPS inhibitors. Further, binding study using fluorescence spectroscopy revealed that
both the potent compounds 13c and 12b showed appreciable association with DHPS enzyme.
In silico ADME analysis of synthesized compounds indicated that the thienopyrimidine
derivatives have prospective to develop as drug candidate. These studies suggests that the
potent compounds such as 13c and 12b may serve as potent “lead” for the drug design and
drug development as dihydropteroate synthase inhibitor.
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Acknowledgements
Authors are thankful to Department of Sciences and Technology (DST) for providing
research grant to Dr. Jitender Bariwal (Letter No. SR/FT/CS-59/2011). Authors
acknowledged I. K. Gujral Punjab Technical University, Kapurthala, Punjab for providing
necessary infrastructure and motivational environment and Mr. Praveen Garg, Chairman, ISF
College of Pharmacy, Moga, Punjab for his continuous support and encouragement.
Conflict of interest
The authors declare they have no conflict of interests.
Figure Legends
Figure 1. Design of antibacterial DHPS inhibitors.
Figure 2. (a) The crystal structure of Bacillus anthracis dihydropteroate synthase with its
grid by receptor grid generation. (b) The hypothetical binding pose of STZ-DHPP adduct
(STZ: sulfathiazole, DHPP: 6-hydroxymethyl-7,8-dihydropterin-pyrophosphate) showing the
active amino acids around it after extraction.
Figure 3. (a) The postulated binding mode of the most potent compound 13c within the
cavity showing the hydrophilic and hydrophobic maps of the crystal structure of the receptor.
(b) The binding interactions of the same compound with surrounding amino acids within the
cavity of the gorge.
Scheme 1. Synthesis of 4-substituted thieno[2,3-d]pyrimidines (9-13).
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