Hansch analysis of veratric acid derivatives as antimicrobial agents

Article abstract of DOI:10.1016/j.ejmech.2008.05.008

The synthesis, characterization and antimicrobial evaluation of a new series of veratric acid derivatives are presented. Preliminary in vitro antimicrobial activity of the title compounds was assessed against a panel of microorganisms including Gram-positive and Gram-negative bacteria and fungi. Some of the veratric acid derivatives exhibited significant in vitro antimicrobial activity. QSAR investigation applied to find a correlation between different physicochemical parameters of the veratric acid derivatives and their antimicrobial activity indicated the importance of topological parameters in describing the antimicrobial activity.

Full text of DOI:10.1016/j.ejmech.2008.05.008

Available online at www.sciencedirect.com
European Journal of Medicinal Chemistry 44 (2009) 689e700
http://www.elsevier.com/locate/ejmech
Original article
Hansch analysis of veratric acid derivatives as antimicrobial agents
*
Balasubramanian Narasimhan , Sucheta Ohlan, Ruchita Ohlan, Vikramjeet Judge, Rakesh Narang
Department of Pharmaceutical Sciences, Guru Jambheshwar University of Science and Technology, Hisar 125001, Haryana, India
Received 17 December 2007; received in revised form 5 May 2008; accepted 14 May 2008
Available online 22 May 2008
Abstract
The synthesis, characterization and antimicrobial evaluation of a new series of veratric acid derivatives are presented. Preliminary in vitro
antimicrobial activity of the title compounds was assessed against a panel of microorganisms including Gram-positive and Gram-negative bac-
teria and fungi. Some of the veratric acid derivatives exhibited significant in vitro antimicrobial activity. QSAR investigation applied to find
a correlation between different physicochemical parameters of the veratric acid derivatives and their antimicrobial activity indicated the impor-
tance of topological parameters in describing the antimicrobial activity.
Ó 2008 Elsevier Masson SAS. All rights reserved.
Keywords: Veratric acid; Antibacterial activity; Antifungal activity; QSAR
1. Introduction
The derived relationship between molecular descriptors and ac-
tivity is used to estimate the property of other molecules and/or
to find the parameters affecting the biological activity [10].
We have previously reported the synthesis, antimicrobial
evaluation and QSAR studies of some simple organic acid de-
rivatives as possible antimicrobial agents [11e16] as a part of
our composite programme on rational drug design [11e23]. In
view of the above in the present work we have decided to syn-
thesize and evaluate the antimicrobial activity of veratric acid
derivatives. Further, we have decided to carry out the QSAR
studies to perceive the importance of molecular properties,
which are critical in accentuating the antimicrobial activity
of veratric acid derivatives.
Microbial infections are associated with rates of attributable
morbidity and mortality [1]. The resistance of common patho-
gens to standard antibiotic therapies is rapidly becoming a ma-
jor public health problem throughout the world. The incidence
of multi-drug resistant Gram-positive and Gram-negative bac-
teria is increasing and infections caused by them are becoming
problematic now-a-days [2]. There is an urgent need for the
discovery of new compounds endowed with antimicrobial ac-
tivity, possibly acting through mechanisms distinct from those
of well known classes of antimicrobial agents to which the
clinically relevant pathogens are now resistant [3].
Veratric acid isolated from the stem bark of Tabebuia
impetiginosa [4] have been reported to have antibacterial [5],
antifungal [6], antioxidant [7], anti-inflammatory [8] and anti-
spasmodic activities [9].
Quantitative structure activity relationship (QSAR), one of
the most important areas in chemistry, gives information that
is useful for drug design and medicinal chemistry. QSAR
models are mathematical equations relating chemical structure
to awidevariety of physical, chemical and biological properties.
2. Chemistry
Synthetic route to compounds 2e17 and 18e41 is shown in
Schemes 1 and 2, respectively. Esters of veratric acid (2e14
and 16) were synthesized by its reaction with corresponding
alcohol in the presence of sulphuric acid. Phenyl veratrate
(15) and 8-quinolinyl veratrate (17) were synthesized by the
reaction of phenol and 8-hydroxyquinoline with acid chloride
of veratric acid, which is prepared by the reaction of veratric
acid with thionyl chloride (Scheme 1). Amides and anilides
(18e41) were prepared by the reaction of veratryl chloride
* Corresponding author. Tel.: þ91 1662 263162; fax: þ91 1662 267240.
E-mail address: naru2000us@yahoo.com (B. Narasimhan).
0223-5234/$ - see front matter Ó 2008 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2008.05.008

690
B. Narasimhan et al. / European Journal of Medicinal Chemistry 44 (2009) 689e700
COOH
with corresponding amines/anilines (Scheme 2). The purity of
COOR
compounds was checked by single-spot thin layer chromatog-
raphy on silica gel G. The physicochemical properties of syn-
thesized compounds are presented in Table 1 and the
spectroanalytical data are presented in Table 2.
ROH
H+
OMe
OMe
OMe
OMe
2-14, 16
The formation of esters was confirmed in general by the ap-
pearance of IR bands (cmꢀ1) in the range of 3075e3085 (CH
str., aromatic), 2940e2970 (CH str., aliphatic), 2825e2840
(CH str., OCH3), 1695e1715 (C]O str., ester) and 1510e
1520 (C]C skeletal str., aromatic). Further, the IR spectra
of compound 6 (allyl ester) showed IR peaks at 1648 (C]C
str., RCH]CH2) and 3004 cmꢀ1 (CH str., RCH]CH2) in ad-
dition to the aforementioned general peaks for esters of vera-
tric acid which confirmed its formation. The IR spectra of
secondary amides of veratric acid (19e41 except 20, 24, 26
1
SOCl
2
COOR
COCl
OMe
ROH
OMe
OMe
OMe
1 5, 1 7
Table 1
Physicochemical characteristics of veratric acid derivatives
2= R = CH3; 3= R = C2H5; 4= R = C3H7; 5= R = (CH3)2CH;
6= R = CH2=CHCH2; 7= R = C4H9;
8= R = (CH3)2CHCH2; 9= R = CH3CH(CH3)CH2; 10= R = (CH3)3C;
11= R = C5H11; 12= R = (CH3)2CHCH2CH2; 13= R = CH3(CH2)4CH2;
14= R = CH3(CH2)5CH2; 15= R = C6H5;
Compound
Molecular
formula
M.wt.
M.P. (ꢁC)
Rf value
Yield (%)
1
C9H10O4
C10H12O4
182
196
210
224
224
222
238
238
238
238
252
252
266
280
258
272
309
181
195
209
209
223
225
269
271
251
249
196
257
292
292
292
271
271
271
287
287
302
302
336
273
176e178
48e50
34e36
0.15
0.41
0.43
0.67
0.28
0.65
0.63
0.52
0.61
0.28
0.79
0.75
0.67
0.58
0.64
0.86
0.71
0.43
0.52
0.11a
0.25
0.16
0.32
0.25
0.27
0.07
0.13
0.31
0.31
0.40
0.34
0.26
0.18
0.16
0.13
0.20a
0.38b
0.28b
0.30
0.25a
0.40
40.41
33.52
30.20
32.40
64.38
58.32
42.17
36.21
66.80
45.86
52.12
21.31
65.99
59.45
54.87
73.32
45.89
80.80
79.02
70.13
65.09
81.32
67.88
72.35
78.67
54.50
46.31
40.44
47.89
50.67
70.56
88.67
79.09
76.77
69.87
72.47
76.03
65.68
56.89
62.45
69.01
2
16= R = C6H5CH2
3
C11H14O4
C12H16O4
4
55e57
150e152
35e37
5
C12H16O4
C12H14O4
N
17= R =
6
7
C13H18O4
C13H18O4
152e154
110e112
100e102
170e172
38e40
Scheme 1. Synthetic route for esters of veratric acid.
8
9
C13H18O4
C13H18O4
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
C14H20O4
C14H20O4
160e162
144e148
25e27
C15H22O4
C16H24O4
COCl
OMe
COOH
SOCl2
C15H14O4
C16H16O4
120e122
42e44
70e72
R2
R6
R3
R5
OMe
OMe
MeO
C18H15O4N
C9H11O3N
C10H13O3N
C11H15O3N
C11H15O3N
C12H17O3N
C11H15O4N
C13H19O5N
C16H17O3N
C13H17O4N
C14H19O3N
C9H12O3N2
C15H15O3N
C15H14O3NCl
C15H14O3NCl
C15H14O3NCl
C16H17O3N
C16H17O3N
C16H17O3N
C16H17O4N
C16H17O4N
C15H14O5N2
C15H14O5N2
C15H14O3NBr
C15H15O4N
OMe
1
151e153
158e160
159e161
160e162
140e142
40e42
R4
NHR1
0 - 10°C
R-NH2
R6
R5
R3
COR
O
44e46
111e113
38e40
35e37
R4
C-N
R1
OMe
MeO
R2
OMe
150e152
160e162
116e118
105e107
200e202
150e152
80e82
18-28
29-41
18 = R = NH2
29 = R1, R2, R3, R4, R5, R6 = H
19 = R = CH3NH
20 = R = (CH3)2N
21 = R = C2H5NH
22 = R = C3H7NH
23 = R = HOC2H4NH
24 = R = (OHC2H4)2N
25 = R = C6H5CH2NH
26 = R = C4H8NO
30 = R1, R3, R4, R5, R6 = H, R2 = Cl
31 = R1, R2, R4, R5, R6 = H, R3 = Cl
32 = R1, R2, R3, R5, R6 = H, R4 = Cl
33 = R1, R3, R4, R5, R6 = H, R2 = CH3
34 = R1, R2, R4, R5, R6 = H, R3 = CH3
35 = R1, R2, R3, R5, R6 = H, R4 = CH3
36 = R1, R3, R4, R5, R6 = H, R2 = OCH3
37 = R1, R2, R3, R5, R6 = H, R4 = OCH3
38 = R1, R2, R4, R5, R6 = H, R3 = NO2
39 = R1, R2, R3, R5, R6 = H, R4 = NO2
40 = R1, R2, R3, R5, R6 = H, R4 = Br
41 = R1, R2, R4, R5, R6 = H, R3 = OH
150e152
70e72
170e172
163e165
120e122
194e196
194e196
27 = R = C5H10
N
28 = R = NH2NH
TLC mobile phase e toluene:chloroform (7:3).
a
Benzene.
Ethyl acetate:benzene (1:3).
b
Scheme 2. Synthetic route for amides/anilides of veratric acid.

B. Narasimhan et al. / European Journal of Medicinal Chemistry 44 (2009) 689e700
691
Table 2
Spectroanalytical data of synthesized veratric acid derivatives
Compound
IR, n (cmꢀ1
)
1H NMR (d, ppm)
Elemental analysis, Calc (found)
10H12O4: C, 61.22 (60.87); H, 6.16 (6.24);
O, 32.62 (36.41)
2
3086 (CH str., aromatic), 2841 (CH str.,
OCH3), 1721 (C]O str., ester), 1518 (C]C
str., aromatic)
6.87e7.69 (m, 3H, Ar H), 3.93 (s, 6H, 2
(OCH3)), 3.89 (s, 3H, COOCH3)
C
3
4
3085 (CH str., aromatic), 2838 (CH str.,
OCH3), 1696 (C]O str., ester), 1517 (C]C
str., aromatic), 2968 (CeH str., aliphatic)
3085 (CH str., aromatic), 2838 (CH str.,
OCH3), 1709 (C]O str., ester), 1515 (C]C
str., aromatic), 2965 (CeH str., aliphatic)
3.95 (s, 6H, OCH3), 1.37e1.40 (t, 3H, CH3),
4.33e4.38 (q, 2H, CH2 of CH2CH3), 6.87e
7.76 (m, 3H, ArH)
C11H14O4: C, 62.85 (61.96); H, 6.71 (6.76);
O, 30.44 (30.02)
0.89e0.93 (t, 3H, CH3 of CH2CH3), 1.76e
1.81 (m, 2H, CH2 of CH2CH3), 3.94 (s, 6H,
OCH3), 4.24e4.28 (t, 2H, CH2 of OCH2),
6.87e7.70 (m, 3H, ArH)
C12H16O4: C, 64.27 (64.28); H, 7.19 (7.00);
O, 28.54 (29.04)
5
6
3009.7 (CH str., aromatic), 2938 (CH str.,
aliphatic), 2836 (CH str., OCH3), 1678
(C]O str., ester), 1516 (C]C str., aromatic)
1.35e1.37 (d, 6H, CH3 of CH(CH3)2),
3.90e3.96 (s, 6H, OCH3), 5.22e5.25 (m,
1H, CH of CH(CH3)2), 6.86e6.93 (m, 3H,
ArH)
C12H16O4: C, 64.27 (64.31); H, 7.19 (7.23);
O, 28.54 (28.89)
3085 (CH str., aromatic), 2839 (CH str.,
OCH3), 1715 (C]O str., ester), 1515 (C]C
str., aromatic), 2938 (CeH str., aliphatic),
3004 (CH str., of ReCH]CH2), 1648
(C]C str. of ReCH]CH2)
3.94 (s, 6H, OCH3), 4.79e4.81 (d, 2H, CH2
adjacent to COO), 5.29e5.30, 5.37e5.38
(dd, 2H, CH2 of CH]CH2, Jcis ¼ 4 Hz),
5.99e6.07 (m, 1H, CH of CH]CH2), 6.87e
7.72 (m, 33H, ArH)
C12H14O4: C, 64.85 (64.81); H, 6.35 (6.29);
O, 28.80 (29.20)
7
3084 (CH str., aromatic), 2873 (CH str.,
OCH3), 1713 (C]O str., ester), 1515 (C]C
str., aromatic), 2959 (CeH str., aliphatic)
0.93e0.95 (t, 3H, CH3 of butyl), 1.41e1.52
(m, 2H, CH2 of C3 of butyl), 1.70e1.78 (m,
2H, CH2 of C2 of butyl), 3.94 (s, 6H, OCH3),
4.29e4.32 (t, 2H, CH2 of C1 of butyl),
6.87e7.76 (m, 3H, ArH)
C13H18O4: C, 65.53 (65.47); H, 7.61 (7.65);
O, 26.86 (26.92)
8
3085 (CH str., aromatic), 2838 (CH str.,
OCH3), 1705 (C]O str., ester), 1513 (C]C
str., aromatic), 2967 (CeH str., aliphatic)
0.95e0.99 (t, 3H, CH3 of CHCH2CH3),
1.32e1.34 (t, 3H, CH3 of CHCH3), 1.64e
1.76 (m, 2H, CH2 of CHCH2CH3), 3.93e
3.95 (s, 6H, OCH3), 5.05e5.10 (m, 1H, CH
of CHCH3), 6.87e7.28 (m, 3H, ArH)
0.98e1.03 (d, 6H, CH3), 2.04e2.11 (m, 1H,
CH of CH(CH3)2), 3.94 (s, 6H, OCH3),
4.07e4.09 (d, 2H, CH2 adjacent to COO),
6.87e7.70 (m, 3H, ArH)
C13H18O4: C, 65.53 (65.51); H, 7.61 (7.63);
O, 26.86 (26.88)
9.
3085 (CH str., aromatic), 2839 (CH str.,
OCH3), 1710 (C]O str., ester), 1514 (C]C
str., aromatic), 2961 (CeH str., aliphatic)
C13H18O4: C, 65.53 (65.42); H, 7.61 (7.82);
O, 26.86 (26.94)
10
11
3003 (CH str., aromatic), 2836 (CH str.,
OCH3), 1677 (C]O str., ester), 1517 (C]C
str., aromatic), 2964 (CeH str., aliphatic)
3085 (CH str., aromatic), 2871 (CH str.,
OCH3), 1713 (C]O str., ester), 1515 (C]C
str., aromatic), 2957 (CeH str., aliphatic)
3.95 (s, 6H, OCH3), 6.91e7.80 (m, 3H,
ArH), 1.3 (s, 9H, CH3 of tert-butyl)
C13H18O4: C, 65.53 (64.98); H, 7.61 (7.34);
O, 26.86 (26.48)
0.93e0.95 (t, 3H, CH3 of amyl), 1.44e1.50
(m, 2H, CH2 of C3 of amyl), 1.63e1.80 (m,
2H, CH2 of C4 of amyl), 2.16e2.18 (m, 2H,
CH2 of C2 of amyl), 3.93 (s, 6H, OCH3),
4.31e4.35 (t, 2H, CH2 of C1 of amyl),
6.87e7.69 (m, 3H, ArH)
C14H20O4: C, 66.65 (66.27); H, 7.99 (7.72);
O, 25.37 (25.21)
12
13
14
2836 (CH str., OCH3), 1691 (C]O str.,
ester), 1513 (C]C str., aromatic), 2954 (Ce
H str., aliphatic)
0.91e0.93 (d, 6H, CH3), 1.47e1.53 (m, 2H,
CH2 of C2 of isoamyl), 1.63e1.75 (m, 1H,
CH of C3 of isoamyl), 3.92 (s, 6H, OCH3),
4.31e4.35 (t, 2H, CH2 of C1 of isoamyl),
6.87e7.68 (m, 3H, ArH)
C14H20O4: C, 66.65 (66.43); H, 7.99 (7.81);
O, 25.37 (25.32)
3084 (CH str., aromatic), 2857 (CH str.,
OCH3), 1713 (C]O str., ester), 1515 (C]C
str., aromatic), 2931 (CeH str., aliphatic)
0.86e0.90 (t, 3H, CH3 of hexyl), 1.26e1.32
(m, 4H, CH2 of C3 and C4 of hexyl), 1.72e
1.77 (m, 2H, CH2 of C2 of hexyl), 3.92 (s,
6H, OCH3), 4.27e4.31 (t, 2H, CH2 of C1 of
hexyl), 6.87e7.69 (m, 3H, ArH)
C15H22O4: C, 67.64 (67.62); H, 8.33 (8.27);
O, 24.03 (24.42)
3084 (CH str., aromatic), 2855 (CH str.,
OCH3), 1713 (C]O str., ester), 1515 (C]C
str., aromatic), 2933 (CeH str., aliphatic)
0.90 (t, 3H, CH3), 1.26e1.29 (m, 2H, CH2
adjacent to terminal CH3), 1.55e1.60 (m,
6H, CH2 of C3eC5 of heptyl), 1.65e1.78
(m, 2H, CH2 of C2 of heptyl), 3.91 (s, 6H,
OCH3), 4.27e4.30 (t, 2H, CH2 of C1 of
heptyl), 6.85e7.68 (m, 3H, ArH)
C16H24O4: C, 68.54 (68.29); H, 8.63 (8.57);
O, 22.83 (22.63)
15
16
3010 (CH str., aromatic), 2977 (CH str.,
aliphatic), 2842 (CH str., OCH3), 1727
(C]O str., ester), 1512 (C]C str., aromatic)
3082 (CH str., aromatic), 2846 (CH str.,
OCH3), 1703 (C]O str., ester), 1510 (C]C
str., aromatic), 2910 (CeH str., aliphatic)
6.94e7.40 (m, 8H, Ar H), 3.96 (s, 6H,
OCH3)
C15H14O4: C, 69.76 (69.72); H, 5.46 (5.43);
O, 24.78 (24.85)
3.86 (s, 6H, OCH3), 4.50 (s, 2H, CH2),
6.63e7.23 (m, 3H, ArH of veratric acid),
7.30e7.37 (m, 5H, ArH of benzyl alcohol)
C16H16O4: C, 70.57 (71.12); H, 5.92 (5.85);
O, 23.50 (23.98)
(continued on next page)

692
B. Narasimhan et al. / European Journal of Medicinal Chemistry 44 (2009) 689e700
Table 2 (continued)
Compound
IR, n (cmꢀ1
)
1H NMR (d, ppm)
Elemental analysis, Calc (found)
18H15NO4: C, 69.89 (69.87); H, 4.89
(4.87); O, 20.69 (20.74); N, 4.53 (4.61)
17
3006 (CH str., aromatic), 2839 (CH str.,
OCH3), 1728 (C]O str., ester), 1516 (C]C
str., aromatic), 1433 (CeN str., aromatic)
3440 (NH str., 1ꢁ amide), 3084 (CH str.,
aromatic), 2836 (CH str., OCH3), 1690
(C]O str., 1ꢁ amide), 1516 (C]C str.,
aromatic)
3445 (NH str., 2ꢁ amide), 3084 (CH str.,
aromatic), 2830 (CH str., OCH3), 1675
(C]O str., amide), 1514 (C]C str.,
aromatic)
3447 (NH str., 2ꢁ amide), 3089 (CH str.,
aromatic), 2836 (CH str., OCH3), 1677
(C]O str., amide), 1516 (C]C str.,
aromatic)
3442 (NH str., 2ꢁ amide), 3085 (CH str.,
aromatic), 2834 (CH str., OCH3), 1673
(C]O str., amide), 1518 (C]C str.,
aromatic)
6.92e7.32 (m, 9H, Ar H), 3.95e3.98 (s, 6H,
OCH3)
C
18
19
20
21
22
3.92 (s, 6H, OCH3), 6.70e7.55 (m, 3H,
ArH), 7.85 (s, 2H, NH2)
C9H11NO3: C, 59.66 (59.62); H, 6.12 (6.23);
O, 26.49 (26.57); N, 7.73 (7.79)
2.87 (s, 3H, CH3), 3.89 (s, 6H, OCH3),
6.70e7.52 (m, 3H, ArH), 7.92 (s, 2H, NH2)
C10H13NO3: C, 61.53 (61.62); H, 6.71
(6.78); O, 24.59 (24.67); N, 7.18 (7.25)
2.10 (s, 6H, CH3), 3.92e3.96 (s, 6H, OCH3),
6.91e7.79 (m, 3H, ArH)
C11H15NO3: C, 63.14 (63.57); H, 7.23
(7.42); O, 22.94 (23.21); N, 6.69 (6.41)
1.46e149 (t, 3H, CH3), 3.42e3.45 (m, 2H,
CH2 of CH2CH3), 3.94 (s, 6H, OCH3),
6.78e7.70 (m, 3H, ArH), 8.15 (s, 1H, NH)
C11H15NO3: C, 63.14 (62.87); H, 7.23
(7.86); O, 22.94 (23.41); N, 6.69 (6.62)
3302 (NH str., amide), 3100 (CH str.,
aromatic), 2935 (CH str, aliphatic), 2837
(CH str., OCH3), 1678 (C]O str., amide),
1514 (C]C str., aromatic)
6.85e7.79 (m, 3H, Ar H), 3.92e3.96 (s, 6H,
OCH3), 3.40e3.45 (m, 2H, CH2 adjacent of
CH2CH3), 1.62e1.67 (m, 2H, CH3 of
CH2CH3), 0.97e1.01 (t, 3H, CH3 of
CH2CH3)
C12H17NO3: C, 64.55 (65.21); H, 7.67
(7.92); O, 21.50 (22.01); N, 6.27 (6.30)
23
24
25
26
3396 (NH str., 2ꢁ amide), 3080 (CH str.,
aromatic), 2840 (CH str., OCH3), 1621
(C]O str., amide), 1505 (C]C str.,
aromatic)
3367 (NH str., 3ꢁ amide), 2835 (CH str.,
OCH3), 1602 (C]O str., amide), 1516
(C]C str., aromatic)
3.56e3.60 (t, 2H, CH2 of NHCH2), 3.79e
3.82 (t, 2H, CH2 of CH2OH), 8.4 (s, 1H,
NH), 3.85 (s, 6H, OCH3), 6.75e7.41 (m, 3H,
ArH)
C
11H15NO4: C, 58.66 (58.25); H, 6.71
(6.43); O, 28.41 (28.21); N, 6.22 (6.15)
1.25 (s, 2H, OH), 3.15e3.30 (t, 4H, CH2 of
NCH2), 3.65e3.75 (m, 4H, CH2 of CH2OH),
3.92 (s, 6H, OCH3), 6.80e7.61 (m, 3H,
ArH)
C13H19NO5: C, 57.98 (57.87); H, 7.11
(7.24); O, 29.71 (29.48); N, 5.20 (5.20)
3294 (NH str., 2ꢁ amide), 3011 (CH str.,
aromatic), 2835 (CH str., OCH3), 1632
(C]O str., amide), 1511 (C]C str.,
aromatic)
3435 (NH str., 3ꢁ amide), 2964 (CH str.,
aliphatic), 2856 (CH str., OCH3), 1621
(C]O str., amide), 1515 (C]C str.,
aromatic) 3082 (CH str., aromatic), 2776
(CeOeC str., morpholine)
3.88e3.89 (s, 6H, OCH3), 4.59e4.61 (d, 2H,
CH2 of benzyl), 6.60e7.33 (m, 8H, ArH),
7.45 (s, 1H, NH)
C16H17NO3: C, 70.74 (70.81); H, 6.26
(6.15); O, 17.68 (17.80); N, 5.15 (5.25)
3.64e3.70 (t, 4H, CH2 of C2 and C6 of
morpholine), 3.20 (t, 4H, CH2, C3 and C5 of
morpholine), 3.90 (s, 6H, OCH3), 6.86e7.01
(m, 3H, ArH)
C13H17NO4: C, 62.14 (62.19); H, 6.82
(6.91); O, 25.47 (25.49); N, 5.57 (5.61)
27
28
29
30
3429 (NH str., 3ꢁ amide), 3001 (CH str.,
aromatic), 2856 (CH str., OCH3), 1683
(C]O str., amide), 1519 (C]C str.,
aromatic), 1462 (CH2 str., piperidine)
3210 (NH str., 2ꢁ amide), 3050 (CH str.,
aromatic), 2837 (CH str., OCH3), 1677
(C]O str., amide), 1514 (C]C str.,
aromatic)
3315 (NH str., 2ꢁ amide), 2937 (CH str.,
aromatic), 2838 (CH str., OCH3), 1647
(C]O str., amide), 1510 (C]C str.,
aromatic)
3280 (NH str., 2ꢁ amide), 3019 (CH str.,
aromatic), 2943 (CH str., aliphatic), 2839
(CH str., OCH3), 1650 (C]O str., amide),
1512 (C]C str., aromatic), 755 (Cl str., Are
Cl)
1.60e1.70 (m, 6H, CH2 of C3eC5 of
piperidine), 3.10 (t, 4H, CH2 of C1 and C6 of
piperidine), 3.92 (s, 6H, OCH3), 6.85e7.30
(m, 3H, ArH)
C14H19NO3: C, 67.74 (67.75); H, 7.62
(7.42); O, 19.29 (19.41); N, 5.61 (5.69)
7.7 (s, 1H, NH), 7.5e7.7 (m, 3H, Ar H),
3.85e3.93 (s, 6H, OCH3)
C9H12N2O3: C, 55.05 (55.91); H, 6.16
(6.12); O, 24.46 (24.42); N, 14.28 (14.31)
3.94 (s, 6H, OCH3), 6.89e7.62 (m, 8H,
ArH), 7.64 (s, 1H, NH)
C15H15NO3: C, 70.02 (70.17); H, 5.88
(5.92); O, 18.66 (18.71); N, 5.44 (5.37)
3.94e3.97 (s, 6H, OCH3), 6.94e8.53 (m,
7H, ArH), 8.55 (s, 1H, NH)
C15H14NO3Cl: C, 61.76 (61.67); H, 4.84
(4.86); O, 16.45 (16.41); N, 4.80 (4.76); Cl,
12.15 (12.21)
31
3309 (NH str., 2ꢁ amide), 3083 (CH str.,
aromatic), 2840 (CH str., OCH3), 1650
(C]O str., amide), 1505 (C]C str.,
aromatic), 751 (Cl str., AreCl)
3.92e3.94 (s, 6H, OCH3), 6.87e7.48 (m,
7H, ArH), 7.50 (s, 1H, NH)
C15H14NO3Cl: C, 61.76 (62.01); H, 4.84
(4.84); O, 16.45 (16.50); N, 4.80 (4.84); Cl,
12.15 (12.20)

B. Narasimhan et al. / European Journal of Medicinal Chemistry 44 (2009) 689e700
693
Table 2 (continued)
Compound
IR, n (cmꢀ1
)
1H NMR (d, ppm)
Elemental analysis, Calc (found)
C15H14NO3Cl: C, 61.76 (61.72); H, 4.84
32
3298 (NH str., 2ꢁ amide), 3011 (CH str.,
aromatic), 2844 (CH str., OCH3), 1643
(C]O str., amide), 1508 (C]C str.,
aromatic), 768 (Cl str., AreCl)
3.93e3.94 (s, 6H, OCH3), 6.88e7.60 (m,
7H, ArH), 7.85 (s, 1H, NH)
(4.83); O, 16.45 (16.31); N, 4.80 (4.76); Cl,
12.15 (12.20)
33
3447 (NH str., 2ꢁ amide), 3002 (CH str.,
aromatic), 2836 (CH str., OCH3), 1677
(C]O str., amide), 1517 (C]C str.,
aromatic), 2964 (CH3 str.,
2.10 (s, 3H, CH3), 3.95e3.96 (s, 6H, OCH3),
6.91e7.60 (m, 7H, ArH), 7.77e7.80 (s, 1H,
NH)
C16H17NO3: C, 70.83 (70.78); H, 6.32
(6.27); O, 17.69 (17.57); N, 5.16 (5.22)
AreCH3)
34
35
36
37
38
39
40
41
3323 (NH str., 2ꢁ amide), 3080 (CH str.,
aromatic), 2833 (CH str., OCH3), 1644
(C]O str., amide), 1515 (C]C str.,
aromatic), 2910 (CH3 str., AreCH3)
3317 (NH str., 2ꢁ amide), 3085 (CH str.,
aromatic), 2844 (CH str., OCH3), 1646
(C]O str., amide), 1506 (C]C str.,
aromatic), 2943 (CH3 str., AreCH3)
3332 (NH str., 2ꢁ amide), 3089 (CH str.,
aromatic), 2837 (CH str., OCH3), 1651
(C]O str., amide), 1514 (C]C str.,
aromatic)
2.35 (s, 3H, CH3), 3.91e3.92 (s, 6H, OCH3),
6.85e7.49 (m, 7H, ArH), 7.89 (s, 1H, NH)
C16H17NO3: C, 70.83 (70.89); H, 6.32
(6.41); O, 17.69 (17.75); N, 5.16 (5.19)
2.33 (s, 3H, CH3), 3.93 (s, 6H, OCH3),
6.87e7.52 (m, 7H, ArH), 7.78 (s, 1H, NH)
C16H17NO3: C, 70.83 (70.82); H, 6.32
(6.31); O, 17.69 (17.59); N, 5.16 (5.18)
8.7 (s, 1H, NH), 6.94e8.23 (m, 7H, Ar H),
3.88e3.93 (s, 9H, OCH3)
C16H17NO4: C, 66.89 (66.82); H, 5.96
(5.88); O, 22.27 (22.30); N, 4.88 (4.82)
3295 (NH str., 2ꢁ amide), 3080 (CH str.,
aromatic), 2839 (CH str., OCH3), 1641
(C]O str., amide), 1513 (C]C str.,
aromatic)
3.81e3.93 (s, 9H, OCH3), 6.87e7.54 (m,
7H, ArH), 7.76 (s, 1H, NH)
C16H17NO4: C, 66.89 (66.76); H, 5.96
(5.91); O, 22.27 (22.31); N, 4.88 (5.12)
3327 (NH str., 2ꢁ amide), 3084 (CH str.,
aromatic), 2845 (CH str., OCH3), 1652
(C]O str., amide), 1511 (C]C str.,
aromatic), 1528 (NO2 str., AreNO2)
3325 (NH str., 2ꢁ amide), 3087 (CH str.,
aromatic), 2845 (CH str., OCH3), 1650
(C]O str., amide), 1514 (C]C str.,
aromatic), 1523 (NO2 str., AreNO2)
3295 (NH str., 2ꢁ amide), 3009 (CH str.,
aromatic), 2931 (CH str., aliphatic), 2846
(CH str., OCH3), 1643 (C]O str., amide),
1507 (C]C str., aromatic)
3.96e3.97 (s, 6H, OCH3), 6.92e8.11 (m,
7H, ArH), 8.47e8.48 (s, 1H, NH)
C15H14N2O5: C, 59.60 (59.48); H, 4.67
(4.72); O, 26.46 (26.51); N, 9.27 (9.32)
3.93 (s, 6H, OCH3), 6.91e8.15 (m, 7H,
ArH), 8.45e8.46 (s, 1H, NH)
C15H14N2O5: C, 59.60 (58.87); H, 4.67
(4.62); O, 26.46 (26.41); N, 9.27 (9.17)
7.85 (s, 1H, NH), 6.88e7.53 (m, 7H, Ar H,
AreBr), 3.94 (s, 6H, OCH3)
C15H14NO3Br: C, 53.59 (53.56); H, 4.20
(4.21); O, 14.28 (14.15); N, 4.17 (4.17), Br,
23.77 (23.80)
3333 (NH str., 2ꢁ amide), 3147 (CH str.,
aromatic), 2838 (CH str., OCH3), 1645
(C]O str., amide), 1510 (C]C str.,
aromatic), 1418 (OH str., AreOH)
3.89e3.97 (s, 6H, OCH3), 4.90 (s, 1H, OH),
6.91e7.58 (m, 7H, ArH), 7.77 (s, 1H, NH)
C15H15NO4: C, 65.92 (66.20); H, 5.53
(5.47); O, 23.42 (23.39); N, 5.13 (5.18)
and 27) showed the characteristic secondary amide peak at
1605e1630 cmꢀ1. Similarly, primary (18) and tertiary amides
(20, 24, 26 and 27) showed corresponding peaks at 1690 and
1630e1670 cmꢀ1, respectively.
aureus MTCC 1430, Bacillus subtilis MTCC 2423, Gram-
negative Escherichia coli MTCC 739, and antifungal activity
against Candida albicans MTCC 227 and Aspergillus niger
MTCC 2425 by standard serial dilution method [24] using ci-
profloxacin and fluconazole as reference compounds in case of
antibacterial and antifungal activities, respectively. Double
strength nutrient broth e I.P. and Sabouraud dextrose broth
e I.P. [25] have been employed as media for growth of bacte-
rial and fungal cells, respectively. The antimicrobial screening
has been performed in duplicate.
1
In general, the H NMR spectra of all synthesized veratric
acid derivatives showed signals at d (ppm) of 6.70e7.70 (Ar
H), 3.86e3.95 (OCH3) which indicated that the basic skeleton
of veratric acid is unaffected by the applied reaction conditions.
Further, the appearance of double doublet signal corresponding
to CH]CH2 of compound 6 at d (ppm) 5.29e5.30, 5.37e5.38
with a J value of 4 indicated that the double bond is of cis char-
acter in nature. Further, formation of secondary amides is con-
firmed by the appearance of proton NMR spectra signals
corresponding to NH at a d of 7.8e8.2 ppm.
4. Results
4.1. Antimicrobial activity
3. Microbiology
The results of antimicrobial study are presented in Tables 3
and 4 which indicated that 8-quinolinyl veratrate, p-bromo ve-
ratranilide, and m-nitro veratranilide (17, 40, and 38) were the
most active compounds. Compound 17 showed significant
The veratric acid derivatives were evaluated for their in vi-
tro antibacterial activity against Gram-positive Staphylococcus

694
B. Narasimhan et al. / European Journal of Medicinal Chemistry 44 (2009) 689e700
Table 3
Antimicrobial activity of veratric acid derivatives (mg/ml)
Table 4
Antimicrobial activity of veratric acid derivatives (pMIC in mM/ml)
Compound
MIC (mg/ml)
Compound
pMICsa
pMICbs
pMICec
pMICca
pMICan
S. aureus
B. subtilis
E. coli
C. albicans
A. niger
1
1.01
1.04
0.98
0.98
1.01
1.00
1.10
1.08
1.10
1.08
1.10
1.10
1.20
1.25
1.15
1.10
1.45
0.90
0.95
1.08
0.95
1.08
1.04
1.21
1.15
1.08
1.15
0.93
1.05
1.28
1.17
1.19
1.20
1.20
1.15
1.23
1.20
1.22
1.25
1.25
1.20
0.11
3.33b
1.31
1.20
1.12
1.20
1.20
1.25
1.20
1.23
1.17
1.20
1.31
1.31
1.33
1.35
1.27
1.34
1.53
1.09
1.18
1.21
1.21
1.23
1.18
1.31
1.32
1.28
1.33
1.15
1.25
1.39
1.39
1.28
1.26
1.31
1.31
1.34
1.38
1.46
1.41
1.40
1.26
0.09
3.33b
1.06
1.04
1.02
1.25
1.20
1.10
1.10
1.17
1.10
1.08
1.10
1.20
1.22
1.30
1.21
1.18
1.56
0.95
1.05
1.15
1.01
1.08
1.08
1.21
1.15
1.17
1.10
0.93
1.04
1.23
1.23
1.39
1.16
1.20
1.20
1.23
1.18
1.36
1.16
1.25
1.16
0.12
3.33b
1.22
1.20
1.23
1.10
1.35
1.10
1.20
1.25
1.34
1.38
1.10
1.20
1.30
1.25
1.30
1.30
1.35
1.25
1.28
1.31
1.31
1.25
1.29
1.31
1.32
1.37
1.25
1.15
1.20
1.34
1.29
1.34
1.31
1.42
1.32
1.29
1.36
1.27
1.32
1.34
1.36
0.08
2.64c
1.11
1.15
1.23
1.20
1.25
1.20
1.15
1.28
1.17
1.30
1.10
1.30
1.28
1.37
1.34
1.29
1.34
1.20
1.18
1.31
1.26
1.28
1.29
1.36
1.36
1.33
1.28
1.12
1.29
1.34
1.32
1.30
1.40
1.35
1.35
1.32
1.40
1.36
1.35
1.44
1.36
0.08
2.64c
2
1
18.00
18.00
22.00
24.00
22.00
22.00
19.00
20.00
19.00
20.00
20.00
20.00
16.50
16.00
18.00
21.50
11.00
23.00
22.00
17.00
23.50
19.00
21.00
16.50
19.00
21.00
17.50
23.00
23.00
15.00
20.00
19.00
17.00
17.00
18.50
17.00
18.00
18.00
17.00
19.00
17.00
9.00
12.00
16.00
14.00
14.00
12.50
15.00
14.00
16.00
15.00
12.50
12.50
12.50
12.50
14.00
12.50
9.00
16.00
18.00
20.00
12.50
14.00
18.00
19.00
16.00
19.00
20.00
20.00
16.00
16.00
14.00
16.00
18.00
8.50
11.00
12.00
12.00
18.00
10.00
18.00
15.00
13.50
11.00
10.00
20.00
16.00
13.00
16.00
12.50
13.50
13.50
10.00
13.00
10.00
10.00
12.50
11.50
12.50
13.00
11.00
14.00
14.00
16.00
13.50
15.00
13.50
13.00
10.00
13.00
15.00
12.50
16.00
14.00
15.00
12.00
14.00
14.00
12.00
14.00
12.50
14.00
17.00
12.50
16.00
12.00
20.00
12.50
14.00
12.00
11.50
14.00
14.00
11.00
12.50
10.00
11.50
12.00
11.50
12.00
12.00
12.00
13.00
15.00
13.00
13.50
14.00
14.50
11.00
12.50
12.50
14.00
11.50
13.00
13.00
12.50
12.00
3
2
4
3
5
4
6
5
7
6
8
7
9
8
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
SDa
Standard
a
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
15.00
13.00
13.00
13.00
13.00
15.00
12.50
13.00
13.00
12.00
14.00
14.00
12.00
12.00
15.00
15.00
13.00
13.00
13.00
12.00
10.50
11.50
13.00
15.00
20.00
17.00
15.00
20.00
19.00
19.00
16.50
19.00
17.00
20.00
23.00
23.00
17.00
17.00
17.00
18.50
17.00
17.00
17.00
19.00
13.00
21.00
19.00
19.00
Standard deviation.
Ciprofloxacin.
Fluconazole.
b
c
antimicrobial activity against S. aureus, B. subtilis, E. coli,
C. albicans and A. niger with pMIC values 1.45, 1.53, 1.56,
1.35 and 1.34, respectively. Compounds 17, 30, 39 and 40
were found to be more active against S. aureus having pMICsa
value more than 1.24, than other synthesized veratric acid de-
rivatives. Compounds 17, 38, 39, 40, 30 and 31 were found to
be more active against B. subtilis having pMICbs more than
1.38, than other compounds. Compounds 17, 32 and 38 were
found to be more active against E. coli having pMICec more
than 1.35, in comparison to other synthesized veratric acid deriv-
atives. Compounds 34, 10, 26 and 37 were found to be more ac-
tive against C. albicans having pMICca more than 1.35.
Compounds 40, 33 and 37 were more active with pMICan > 1.39
when compared to the antifungal activity of other compounds
against A. niger.
4.2. Quantitative structure activity relationship studies
In order to understand the experimental antimicrobial data
on theoretical basis, we established a quantitative structure
activity relationship (QSAR) between the in vitro antimicro-
bial activity of 41 veratric acid derivatives and descriptors
coding for lipophilic, electronic, steric and topological prop-
erties of the molecules under consideration using the linear
free energy relationship model (LFER) described by Hansch
and Fujita [10]. Biological activity data determined as MIC
values were first transformed into pMIC values on molar ba-
sis, which were used as dependent variables in QSAR study

B. Narasimhan et al. / European Journal of Medicinal Chemistry 44 (2009) 689e700
695
and are listed in Table 4. The different molecular descriptors
(independent variables) calculated for the present study are
5. Discussion
logarithm of octanolewater partition coefficient (log P), mo-
5.1. Antimicrobial evaluation
0
lar refractivity (MR), Kier’s molecular connectivity (0c, cv,
1
2
1c, cv, c2, cv) and shape (k1, ka1) topological indices, Ran-
dic topological index (R), Balaban topological index (J ),
Wiener topological index (W ), total energy (Te), energies of
highest occupied molecular orbital (HOMO) and lowest unoc-
cupied molecular orbital (LUMO), dipole moment (m), elec-
tronic energy (Ele.E), nuclear energy (Nu.E) and molecular
surface area (SA) [26e31]. The values of selected molecular
descriptors of veratric acid derivatives used in linear regres-
sion analysis are depicted in Table 5. Table 6 presents the cor-
relation matrix of the antimicrobial activity and Table 7
represents the correlation of different molecular descriptors
with antimicrobial activity of veratric acid derivatives.
From the observed antimicrobial results of veratric acid de-
rivatives, some structure activity relationship (SAR) can be de-
rived as follows:
1. The presence of electron withdrawing groups like Cl,
NO2, and Br improved the antibacterial activity of vera-
tric acid derivatives which is evidenced by the antibacte-
rial data of compounds 17, 30, 32, 38, and 40 in Table 4
against different representative bacteria. The role of elec-
tron withdrawing group in improving the antimicrobial
activities is supported by the studies of Sharma et al.
[32].
Table 5
Values of selected descriptors of veratric acid derivatives used in LR analysis
Compound
Log P
MR
0c
1c
1cv
2c
2cv
W
Te
1
1.24
1.27
1.61
2.08
2.03
2.01
2.48
2.49
2.50
2.11
2.88
2.81
3.27
3.67
2.95
3.05
3.04
0.37
0.62
0.87
0.96
1.43
0.18
ꢀ0.02
2.40
0.53
1.59
0.36
2.30
2.82
2.82
2.82
2.77
2.77
2.77
2.05
2.05
2.26
2.26
3.09
2.02
45.74
50.51
55.26
59.78
59.68
59.67
64.39
64.26
64.20
64.32
68.99
68.93
73.59
78.19
70.29
75.12
84.21
47.57
52.46
57.36
57.21
61.73
58.75
69.94
77.07
66.43
69.50
52.05
72.24
77.04
77.04
77.04
77.28
77.28
77.28
78.70
78.70
79.56
79.56
79.86
73.93
9.84
6.19
3.64
4.03
4.62
5.12
5.01
4.73
5.62
5.47
5.55
5.33
6.12
5.97
6.62
7.12
5.74
6.17
7.01
3.71
4.17
4.53
4.73
5.23
4.84
5.91
6.28
5.85
6.27
3.96
5.83
6.34
6.34
6.34
6.24
6.24
6.24
6.36
6.35
6.33
6.33
6.74
5.96
5.15
5.30
5.68
6.03
6.52
6.03
6.38
6.86
6.64
7.65
6.74
7.21
7.09
7.44
7.63
7.97
9.52
5.15
5.30
6.01
5.68
6.03
6.03
7.11
7.97
7.17
7.17
5.30
7.63
8.14
8.26
8.25
8.14
8.26
8.25
8.34
8.42
9.08
9.15
8.25
8.26
2.37
2.56
2.79
3.21
3.52
2.96
3.56
4.06
3.69
4.57
3.91
4.39
4.27
4.62
3.77
4.13
4.79
2.43
2.65
3.27
2.93
3.33
3.05
3.81
4.24
3.97
4.42
2.54
3.89
4.44
4.51
4.50
4.34
4.39
4.39
4.22
4.25
4.30
4.33
4.97
4.07
246.00
ꢀ2571.42
ꢀ2726.66
ꢀ2882.45
ꢀ3038.28
ꢀ3038.16
ꢀ3009.57
ꢀ3194.11
ꢀ3193.97
ꢀ3193.96
ꢀ3193.73
ꢀ3349.95
ꢀ3349.84
ꢀ3505.78
ꢀ3661.62
ꢀ3393.29
ꢀ3549.38
ꢀ3997.55
ꢀ2471.44
ꢀ2626.77
ꢀ2782.05
ꢀ2782.59
ꢀ2938.41
ꢀ3103.24
ꢀ3734.94
ꢀ3449.60
ꢀ3386.32
ꢀ3221.97
ꢀ2691.27
ꢀ3293.88
ꢀ3654.00
ꢀ3653.97
ꢀ3654.00
ꢀ3449.73
ꢀ3449.75
ꢀ3449.75
ꢀ3769.74
ꢀ3769.72
ꢀ4124.81
ꢀ4124.81
ꢀ3633.51
ꢀ3614.51
2
10.55
11.26
11.97
12.13
11.97
12.67
12.84
12.84
13.05
13.38
13.54
14.09
14.79
13.66
14.37
16.23
9.84
6.72
7.22
7.72
7.58
7.72
8.22
8.08
8.12
7.87
8.72
8.58
9.22
9.72
9.24
9.74
11.22
6.19
6.72
7.10
7.22
7.72
7.72
9.17
9.74
8.76
8.76
6.72
9.24
9.65
9.63
9.63
9.65
9.63
9.63
10.19
10.17
10.56
10.55
9.63
9.63
307.00
382.00
472.00
459.00
472.00
578.00
564.00
552.00
538.00
701.00
686.00
842.00
1002.00
756.00
910.00
1238.00
246.00
307.00
370.00
382.00
472.00
472.00
734.00
910.00
621.00
621.00
307.00
756.00
858.00
871.00
884.00
858.00
871.00
884.00
980.00
1032.00
1104.00
1182.00
884.00
871.00
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
10.55
11.42
11.26
11.97
11.97
14.25
14.37
12.96
12.96
10.55
13.66
14.54
14.54
14.54
14.54
14.54
14.54
15.24
15.24
16.11
16.11
14.54
14.54

696
B. Narasimhan et al. / European Journal of Medicinal Chemistry 44 (2009) 689e700
Table 6
Correlation matrix for the antibacterial activity of veratric acid derivatives against S. aureus
pMICsa
Log P
MR
0c
1c
1cv
2c
2cv
R
W
Te
pMICsa
Log P
MR
0c
1.000
0.590
0.882
0.891
0.890
0.865
0.867
0.834
0.890
0.892
ꢀ0.882
1.000
0.696
0.649
0.640
0.726
0.630
0.714
0.640
0.659
ꢀ0.574
1.000
0.981
0.984
0.967
0.957
0.928
0.984
0.971
ꢀ0.941
1.000
1c
0.988
0.937
0.969
0.898
0.988
0.985
ꢀ0.981
1.000
1cv
2c
2cv
0.938
0.963
0.876
1.000
0.882
0.945
0.938
1.000
0.902
0.963
0.957
1.000
0.876
0.858
R
1.000
0.989
1.000
0.989
W
Te
0.919
ꢀ0.905
1.000
ꢀ0.964
ꢀ0.967
ꢀ0.938
ꢀ0.853
ꢀ0.967
1.000
2. In contrary to the antibacterial activity, the presence of
electron donating substituents like OCH3, R groups
(compounds 10, 26, 33, 34 and 37 in Table 4) im-
proved the antifungal activity. This indicates that there
may be a difference in the structural requirements for
antifungal activity of synthesized veratric acid deriva-
tives against C. albicans and A. niger. The different
structural requirements for activity against different
microorganisms are similar to the results observed by
Sortino et al. [33].
3. In general the amides and anilides of veratric acid have
more antimicrobial activity than its esters. The exception-
ally high antibacterial activity shown by compound 17,
i.e. 8-hydroxyquinoline ester of veratric acid may be
due to the presence of fused heterocyclic ring in its struc-
ture. Further, the anilides with electron withdrawing
group were generally more active than simple amides
which may be attributed to the presence of aromatic
ring in case of anilides. The positive contribution of aro-
matic ring may be due to the involvement of aromatic
ring in enhancing the binding of molecules with the
target.
5.2. QSAR analysis
In the present work a set of veratric acid derivatives consist-
ing of 41 molecules were used for linear regression model
generation. The reference drugs were not included in model
generation as they belong to a different structural series. Pre-
liminary analysis was carried out in terms of correlation anal-
ysis. A correlation matrix constructed for antibacterial activity
of veratric acid derivatives against S. aureus is presented in
Table 6. The high interrelationship was observed between W
and R (r ¼ 0.989), 1c and 0c (r ¼ 0.988), R and 0c
(r ¼ 0.988) and low interrelationship was observed between
Te and log P (r ¼ ꢀ0.574).
The correlation of different parameters with antimicrobial
activity of veratric acid derivatives is presented in Table 7.
The above table indicated the predominance of topological pa-
rameter (W ) in describing the antimicrobial activity of veratric
acid derivatives against S. aureus [Eq. (1)].
The linear regression equations developed using the
highly correlated topological indices are reported in Eqs.
(1)e(5) together with statistical parameters of regression.
Apart from these equations, i.e. Eqs. (1)e(5), the other sta-
tistically significant equations derived for antimicrobial ac-
tivity of veratric acid derivatives are presented in Table 8.
Further, it is important to note that all these models were de-
veloped by using the entire set (n ¼ 41), since no outliers
were identified.
The above facts are summarized in Fig. 1.
Table 7
Correlation of different molecular descriptors with antimicrobial activity of
veratric acid derivatives
pMICsa
pMICbs
pMICec
pMICca
pMICan
OMe
Log P
MR
0c
0cv
1c
1cv
2c
2cv
0.590
0.882
0.891
0.878
0.890
0.865
0.867
0.834
0.890
ꢀ0.882
0.892
0.860
0.839
0.542
0.800
0.813
0.771
0.827
0.770
0.804
0.731
0.827
ꢀ0.826
0.845
0.769
0.730
0.583
0.733
0.751
0.750
0.749
0.732
0.734
0.707
0.749
ꢀ0.758
0.752
0.728
0.718
0.110
0.447
0.445
0.442
0.428
0.389
0.533
0.492
0.428
ꢀ0.410
0.418
0.366
0.333
0.335
0.766
0.746
0.742
0.740
0.705
0.768
0.741
0.740
ꢀ0.706
0.721
0.698
0.660
ELECTRON WITHDRAWING GROUPS
[ANTIBACTERIAL]
MeO
ELECTRON DONATING GROUPS
[ANTIFUNGAL]
N
H
R
Te
O
W
k1
Alkyl or substituted aryl
ka1
Fig. 1. SAR of antimicrobial activity of synthesized veratric acid derivatives.

B. Narasimhan et al. / European Journal of Medicinal Chemistry 44 (2009) 689e700
697
Table 8
Other statistically significant QSAR models for antimicrobial activity of veratric acid derivatives
S. no.
QSAR model (pMIC)
n
r
r2cv
F
S
B. subtilis
1
2
3
4
0.059 (ꢂ0.006)1c þ 0.765 (ꢂ0.056)
0.059 (ꢂ0.006)R þ 0.765 (ꢂ0.056)
ꢀ0.0002 (ꢂ0.000)Te þ 0.670 (ꢂ0.067)
0.044 (ꢂ 0.0005)0c þ 0.698(ꢂ0.067)
41
41
41
41
0.827
0.827
0.826
0.813
0.631
0.631
0.636
0.519
84.701
0.053
0.053
0.053
0.055
84.701
84.040
76.03
S. aureus
5
6
7
8
0.058 (ꢂ0.005)0c þ 0.346 (ꢂ0.064)
0.077 (ꢂ 0.006)1c þ 0.447 (ꢂ0.056)
0.077 (ꢂ 0.006)R þ 0.447 (ꢂ0.056)
ꢀ0.0002 (ꢂ 0.000)Te þ 0.329 (ꢂ0.068)
41
41
41
41
0.891
0.890
0.890
0.882
0.763
0.761
0.762
0.745
150.25
148.33
148.33
137.21
0.052
0.052
0.052
0.054
E. coli
9
10
0.00033 (ꢂ0.000)W þ 0.934 (ꢂ0.034)
0.51 (ꢂ0.007)0c þ 0.483 (ꢂ0.096)
0.061 (ꢂ0.009)0cv þ 0.51 (ꢂ0.093)
0.068 (ꢂ 0.010)1c þ 0.574 (ꢂ0.084)
41
41
41
41
0.752
0.751
0.750
0.749
0.494
0.502
0.508
0.496
50.61
50.57
50.18
49.80
0.078
0.078
0.078
0.078
11
12
C. albicans
13
14
15
16
0.052 (ꢂ0.015)2cv þ 1.079 (ꢂ0.057)
0.0033 (ꢂ0.001)MR þ 1.053 (ꢂ0.073)
0.020 (ꢂ0.006)0c þ 1.016 (ꢂ0.085)
0.023 (ꢂ0.008)0cv þ 1.027 (ꢂ0.082)
41
41
41
41
0.492
0.447
0.445
0.442
0.174
0.133
0.131
0.128
12.48
9.72
9.62
9.50
0.067
0.069
0.069
0.069
A. niger
17
18
0.0063 (ꢂ0.001)MR þ 0.856 (ꢂ0.058)
0.037 (ꢂ0.005)0c þ 0.797 (ꢂ0.070)
0.043 (ꢂ0.006)0cv þ 0.817 (ꢂ0.0068)
0.087 (ꢂ0.013)2cv þ 0.951 (ꢂ0.491)
41
41
41
41
0.766
0.746
0.742
0.741
0.551
0.517
0.513
0.512
55.31
48.96
47.88
47.59
0.055
0.057
0.057
0.057
19
20
The quality of the models is indicated by the following pa-
rameters: r e correlation coefficient; F e Fisher’s statistics; s
e standard error of estimation; and r2cv e cross-validated r2
obtained by ‘leave one out’ (LOO) method.
The coefficient of W in the mono-parametric model in Eq.
(1) is positive indicating thereby that the antibacterial activity
of veratric acid derivatives against S. aureus is directly propor-
tional to the magnitude of W. The antibacterial activity in-
creases with increase in magnitude of W. This is evidenced
by the values of W in Table 5. The values of W for compounds
17 and 39 are 1238.00 and 1182.00 (Table 5), respectively,
which are higher than the W values of other compounds and
thus make them to be the most effective one against S. aureus
with pMICsa values of 1.45 and 1.25, respectively (Table 4).
Similarly, compounds 1 and 18 having minimum W values
(246.0 and 246.0, Table 5) have minimum activity against S.
aureus with pMICsa values of 1.01 and 0.90, respectively
(Table 4). Similar trend was observed in case of B. subtilis,
E. coli, C. albicans and A. niger with W, Te, 2c and 2c,
respectively.
QSAR model for antibacterial activity against S. aureus
pMICsa ¼ 0:00038ðꢂ 0:000ÞW þ0:860ðꢂ 0:022Þ
ð1Þ
n ¼ 41 r ¼ 0:892 rc2v ¼ 0:766 s¼ 0:052 F ¼ 151:22
QSAR model for antibacterial activity against B. subtilis
pMICbs ¼ 0:000293ðꢂ 0:000ÞW þ1:077ðꢂ 0:022Þ
ð2Þ
n ¼ 41 r ¼ 0:845 rc2v ¼ 0:673 s ¼ 0:050 F ¼ 97:705
QSAR model for antibacterial activity against E. coli
The topological index, 2c, signifies the degree of branching,
connectivity of atoms and the unsaturation in the molecule
which accounts for variation in the activity [34]. The other
significant parameter Wiener index (W ) was introduced by
Wiener [30] to demonstrate the correlations between the phys-
icochemical properties of organic compounds and the topolog-
ical structure of their molecular graphs in terms of sum of
distances between any two carbon atoms in the molecule, in
terms of carbonecarbon bonds. The total energy (Te) calcu-
lated by semiempirical methods can be used as a measure of
non-specific interactions of a drug with its target site i.e. the
total energies of the protonated and neutral forms of the mol-
ecule, can be considered as a good measure of the strength of
pMICec ¼ ꢀ0:00021ðꢂ 0:000ÞTe þ 0:456ðꢂ 0:098Þ
ð3Þ
n ¼ 41 r ¼ 0:758 rc2v ¼ 0:508 s ¼ 0:077 F ¼ 52:62
QSAR model for antifungal activity against C. albicans
2
pMICca ¼ 0:034ðꢂ 0:009Þ c þ 1:037ðꢂ 0:062Þ
ð4Þ
n ¼ 41 r ¼ 0:533 rc2v ¼ 0:219 s ¼ 0:066 F ¼ 15:47
QSAR model for antifungal activity against A. niger
2
pMICan ¼ 0:054ðꢂ 0:007Þ c þ 0:898ðꢂ 0:052Þ
ð5Þ
n ¼ 41 r ¼ 0:768 rc2v ¼ 0:549 s ¼ 0:055 F ¼ 56:08

698
B. Narasimhan et al. / European Journal of Medicinal Chemistry 44 (2009) 689e700
1.5
1.4
1.3
1.2
1.1
hydrogen bonds (the higher the energy, the stronger the bond)
and can be used to determine the correct localization of the
most favorable hydrogen bond acceptor site [35].
In order to confirm our results we have predicted the activ-
ities of veratric acid derivatives using the model expressed by
Eqs. (1)e(5) and compared them with the observed values
(Figs. 2e6), which indicated that the values are close to
each other.
The cross-validation of the models was also done by leave
one out (LOO) technique [36]. The cross-validated correlation
coefficient (r2cv > 0.5) values obtained for the best QSAR
models indicated their reliability in predicting the antimicro-
bial activity of veratric acid derivatives. In case of C. albicans
the r2cv value is less than 0.5, which shows that the developed
model is an invalid one. But one should not forget the recom-
mendations of Golbraikh and Tropsha [37] who have recently
reported that the only way to estimate the true predictive
power of a model is to test their ability to predict accurately
the biological activities of compounds. As the observed and
predicted values are close to each other, the QSAR model
for C. albicans [Eq. (4)] is a valid one.
Even though the sample size and the ‘Rule of Thumb’ [19]
allowed us to go for the development of multi-parametric model
in multiple linear regression analysis, the high interrelationship
among the parameters restricted us for mono-parametric model.
The multi-colinearity occurs when two independent variables
are correlated with each other. One should note that the change
in signs of the coefficients, a change in the values of previous
coefficient, change of significant variable into insignificant
one or an increase in standard error of the estimate on addition
of an additional parameter to the model are indications of high
interrelationship among descriptors [13].
1.0
1.1
1.2
1.3
Observed pMICbs
1.4
1.5
1.6
Fig. 3. Plot of predicted pMICbs values against experimental pMICbs values for
the linear regression developed model by Eq. (2).
the low residual values (Figs. 2e6). This is in accordance
with the results suggested by Bajaj et al. [38], who stated that
the reliability of the QSAR model lies in its predictive ability
even though the activity data are in the narrow range. Further,
recent literature reveals that the QSAR has been applied to de-
scribe the relationship between the narrow range of biological
activity and the physicochemical properties of the molecules
[16,39e41]. When biological activity data lie in the narrow
range, the presence of minimum standard deviation of the bio-
logical activity justifies its use in QSAR studies [16,21]. The
minimum standard deviation (Table 4) observed in the antimi-
crobial activity data justifies its use in QSAR studies.
Generally for QSAR studies, the biological activities of
compounds should span 2e3 orders of magnitude. But in the
present study the range of antimicrobial activities of the synthe-
sized compounds is within 1 order of magnitude. But it is im-
portant to note that the predictability of the QSAR models
developed in the present study is high, which is evidenced by
6. Conclusion
Summarizing, a number of veratric acid derivatives have been
synthesized in efficient yields. The synthesized compounds
1.4
1.3
1.2
1.1
1.0
.9
1.4
1.3
1.2
1.1
1.0
.9
.8
.9
1.0
1.1
1.2
Observed pMICsa
1.3
1.4
1.5
.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
Observed pMICec
Fig. 2. Plot of predicted pMICsa values against experimental pMICsa values for
the linear regression developed model by Eq. (1).
Fig. 4. Plot of predicted pMICec values against experimental pMICec values for
the linear regression developed model by Eq. (3).

B. Narasimhan et al. / European Journal of Medicinal Chemistry 44 (2009) 689e700
699
1.38
1.36
1.34
1.32
1.30
1.28
1.26
1.24
1.22
1.20
TMS as an internal standard (chemical shift in d, ppm). The
purity of compounds was checked by thin layer chromatogra-
phy (TLC) on silica gel G plates. The spots were detected by
exposure to iodine vapours. The elemental analysis of com-
pounds was performed on Vario EL instrument.
7.1. General procedure for preparation of esters of
veratric acid derivatives (2e17)
A mixture of veratric acid (0.08 mol) and appropriate alco-
hol (0.74 mol) was heated under reflux in the presence of sul-
phuric acid (0.2 ml) till the completion of reaction. Once the
reaction has been completed, the reaction mixture was added
to 200 ml ice cold water and the resultant ester was extracted
with ether (50 ml). The ether layer on evaporation yielded the
crude ester, which was then recrystallized from alcohol.
1.0
1.1
1.2 1.3
Observed pMICca
1.4
1.5
Fig. 5. Plot of predicted pMICca values against experimental pMICca values for
the linear regression developed model by Eq. (4).
7.2. General procedure for synthesis of amides/anilides
(18e28/29e41)
The acid chloride of veratric acid was prepared by the re-
action of veratric acid with thionyl chloride. The solution of
corresponding amine (0.1 mol)/aniline (0.1 mol) in ether
(50 ml) was added drop-wise to a solution of acid chloride
(0.1 mol) in ether (50 ml) maintained at 0e10 ꢁC at room tem-
perature. The solution was stirred for 30 min and the precipi-
tated amide was separated by filtration. The crude amide was
recrystallized from alcohol. In case of anilides, the precipitates
of crude anilide were treated with water and the ether layer
was separated, washed successively with 5% hydrochloric
acid, 4% sodium carbonate and water to remove residual ani-
line. Evaporation of ether layer yielded anilides, which were
then recrystallized from alcohol.
exhibited good in vitro antibacterial and antifungal profiles. The
trend of antimicrobial studies showed that these title compounds
were highly effective against Gram-positive bacteria. Moreover,
quantitative structure activity relationship study revealed that
the antimicrobial activity of these synthesized derivatives
against microorganisms under test is mainly governed by the
topological parameters, namely, Wiener topological index (W )
and the second order molecular connectivity index (2c).
7. Experimental
Melting points in degree Celsius were determined with El-
ico melting point apparatus and are uncorrected. The FTIR
spectra were recorded in KBr pellets on Perkin Elmer IR spec-
7.3. Antimicrobial evaluation
1
trophotometer. H NMR was recorded on Bruker Avance II
400 NMR spectrophotometer using CDCl3 as a solvent and
7.3.1. Antibacterial assay
A 24-h fresh culture was obtained by inoculation of respec-
tive bacteria in double strength nutrient broth e I.P. followed
by incubation at 37 ꢂ 1 ꢁC. The stock solution of synthesized
veratric acid derivatives was serially diluted in tube containing
1 ml of sterile double strength nutrient broth e I.P. to get a con-
centration of 50e3.125 mg/ml and then inoculated with 100 ml
of suspension (with a count of 105 cfu/ml) of respective micro-
organisms (Gram-positive S. aureus MTCC 1430, B. subtilis
MTCC 2423, Gram-negative E. coli MTCC 739) in sterile sa-
line. The inoculated tubes were incubated at 37 ꢂ 1 ꢁC for
24 h and minimum inhibitory concentrations (MICs) were de-
termined. From the observed MIC values, the exact MIC
values were determined by making suitable dilution of the
stock solution.
1.5
1.4
1.3
1.2
1.1
7.3.2. Antifungal assay
1.0
1.1
1.2
Observed pMICan
1.3
1.4
1.5
The antifungal activity of synthesized veratric acid deriva-
tives against the fungal species C. albicans MTCC 227 and A.
niger MTCC 2425 was determined by serial dilution method
similar to antibacterial assay (Section 7.3.1) using Sabouraud
Fig. 6. Plot of predicted pMICan values against experimental pMICan values for
the linear regression developed model by Eq. (5).

700
B. Narasimhan et al. / European Journal of Medicinal Chemistry 44 (2009) 689e700
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37 ꢂ 1 ꢁC and 25 ꢂ 1 ꢁC for a period of 2 and 7 days in
case of C. albicans and A. niger, respectively.
7.4. QSAR studies
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regressed with its molecular descriptor values. Our data set
consisted of 41 veratric acid analogs, synthesized and biolog-
ically evaluated, for antimicrobial activity by tube dilution
method. Descriptor is any molecular property which is charac-
teristic of a molecule and can be utilized to determine new
QSAR. The number of descriptors selected for the present
study fell into four categories, viz. electronic, steric, lipophilic,
and topological [28e33] (Table 5). The structure of veratric
acid derivatives was optimized by energy minimization. The
lowest energy structure was used for each molecule to calcu-
late the physicochemical properties using TSAR 3.3 software
for Windows [42]. Further, the regression analysis was per-
formed using the SPSS software package [43].
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X
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ꢁ
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$
$
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P
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