2-Heteroarylimino-5-benzylidene-4-thiazolidinones analogues of 2-thiazolylimino-5-benzylidene-4-thiazolidinones with antimicrobial activity: Synthesis and structure-activity relationship

Article abstract of DOI:10.1016/j.bmc.2008.02.001

2-Heteroarylimino-5-benzylidene-4-thiazolidinones, unsubstituted or carrying hydroxy, methoxy, nitro and chloro groups on the benzene ring, were synthesised and assayed in vitro for their antimicrobial activity against Gram positive and Gram negative bacteria, yeasts and mould. The antimicrobial activity of the 2-benzo[d]thiazolyl- and of the 2-benzo[d]isothiazolyl-imino-5-benzylidene-4-thiazolidinones is, on the whole, lower in comparison with the high activity detected for the derivatives of the 2-thiazolylimino-5-benzylidene-4-thiazolidinone class. Nevertheless most of the benzo[d]thiazole analogues display good inhibition of the growth of Gram positive bacilli and staphylococci, including methicillin-resistant Staphylococcus strains. Among the 2-benzo[d]isothiazole analogues a few derivatives show a strong and selective activity against bacilli. Moreover, it is worth noting that the replacement of the thiazole nucleus for the benzo[d]thiazole bicyclic system in the parent 2-(benzo[d]thiazol-2-ylimino)thiazolidin-4-one leads to significant antifungal properties against both yeasts and moulds, properties not shown by the analogous 2-thiazolyl- and 2-benzo[d]isothiazolyl-imino)thiazolidin-4-ones. The structure-activity relationship of 33 analogues possessing the 2-heteroarylimino-4-thiazolidinone structure is analysed through QSAR models.

Full text of DOI:10.1016/j.bmc.2008.02.001

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry 16 (2008) 3714–3724
2-Heteroarylimino-5-benzylidene-4-thiazolidinones analogues
of 2-thiazolylimino-5-benzylidene-4-thiazolidinones
with antimicrobial activity:
Synthesis and structure–activity relationship
Paola Vicini,a,* Athina Geronikaki,b Matteo Incerti,a Franca Zani,a
John Deardenc and Mark Hewittc
a
`
Dipartimento Farmaceutico, Universita degli Studi di Parma, Viale G.P. Usberti 27/A, Parma 43100, Italy
bDepartment of Pharmaceutical Chemistry, School of Pharmacy, Aristotelian University of Thessaloniki,
Thessaloniki 54124, Greece
cLiverpool John Moores University, School of Pharmacy and Chemistry, Byrom Street, Liverpool L3 3AF, UK
Received 25 September 2007; accepted 1 February 2008
Available online 6 February 2008
Abstract—2-Heteroarylimino-5-benzylidene-4-thiazolidinones, unsubstituted or carrying hydroxy, methoxy, nitro and chloro
groups on the benzene ring, were synthesised and assayed in vitro for their antimicrobial activity against Gram positive and Gram
negative bacteria, yeasts and mould. The antimicrobial activity of the 2-benzo[d]thiazolyl- and of the 2-benzo[d]isothiazolyl-imino-5-
benzylidene-4-thiazolidinones is, on the whole, lower in comparison with the high activity detected for the derivatives of the 2-thia-
zolylimino-5-benzylidene-4-thiazolidinone class. Nevertheless most of the benzo[d]thiazole analogues display good inhibition of the
growth of Gram positive bacilli and staphylococci, including methicillin-resistant Staphylococcus strains. Among the 2-benzo[d]iso-
thiazole analogues a few derivatives show a strong and selective activity against bacilli. Moreover, it is worth noting that the replace-
ment of the thiazole nucleus for the benzo[d]thiazole bicyclic system in the parent 2-(benzo[d]thiazol-2-ylimino)thiazolidin-4-one
leads to significant antifungal properties against both yeasts and moulds, properties not shown by the analogous 2-thiazolyl- and
2-benzo[d]isothiazolyl-imino)thiazolidin-4-ones. The structure-activity relationship of 33 analogues possessing the 2-heteroarylimi-
no-4-thiazolidinone structure is analysed through QSAR models.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
displaying a broad spectrum of biological activity,
including antibacterial and antifungal properties,3–8
and on the basis of the assumption that a benzylidene
moiety at the 5-position of the 4-thiazolidinone is neces-
sary for the antimicrobial activity, we replaced the 2-thi-
azole ring with analogous groups.
A recent survey of novel small-molecule therapeutics
revealed that the majority of them result from an ana-
logue-based approach and that their market value repre-
sents two-thirds of all drug sales.1 Because of this, and
given our recent finding of a new class of antibacterial
agents, the 2-thiazolylimino-5-benzylidene-4-thiazolidi-
nones 1a–1j (Fig. 1),2 we decided to extend our research
to classes of analogues. Starting from the knowledge of
the potential of 4-thiazolidinone ring system, which is a
core structure in various synthetic pharmaceuticals
Our analogue-based design encompasses the synthesis of
a series of benzo[d]thiazole (benzologues, 2a–2j) and of
benzo[d]isothiazole (positional isomers of the latter,
3a–3j)9 derivatives (Fig. 1), to be tested for their antimi-
crobial properties. Furthermore, we have attempted to
rationalise the structure–activity relationship of all the
2-heteroarylimino-5-benzylidene-4-thiazolidinones through
a QSAR analysis. To increase the chance of selecting
structures with the greatest potential for development,
prediction of toxicity has been carried out with the
DEREK computer program.
Keywords: 4-Thiazolidinone derivatives; Antibacterial activity/anti-
fungal activity; QSAR; DEREK.
*
Corresponding author. Tel.: +39 521 905051; fax: +39 521 905006;
e-mail: paola.vicini@unipr.it
0968-0896/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2008.02.001

P. Vicini et al. / Bioorg. Med. Chem. 16 (2008) 3714–3724
3715
through a different procedure from that described by
Indian authors who started from benzothiazolylthiourea.14
The same authors reported in their paper also some of
the 2-(benzothiazolylimino)thiazolidin-5-benzylidene-4-
ones included in this study, but the physico-chemical data
and information on the antibacterial properties of these
compounds are not correct, or not understandable, or
not comparable to the ones obtained by us, while the
experimental protocols are lacking in details. We shall
point out in the experimental section the previously cited
compounds. The spectral data and the elemental analysis
of the new compounds of series 2 and 3 reported in this
study correlate with the proposed structures.
The mechanism suggested for the formation of all the
compounds under study is presented in Figure 3 for
compounds 2 and 2a–2j. The mechanism of the cyclo-
condensation step, the amino-imino tautomeric equilib-
rium of the heteroarylthiazolidinones and of their
benzylidene derivatives 2a–2j and 3a–3j and the E/Z po-
tential isomerism of the latter, was investigated through
1
the analysis of H NMR and IR spectral data and were
confirmed on the basis of the literature data.2,15
In the 1H NMR spectra of all the compounds of series 2
and 3, a NH proton appears at 12.18–13.06 ppm,
accounting for a lactam proton but not for an imine pro-
ton which is expected around 9.70 ppm. This was consid-
ered to be a strong confirmation for the ring closure
shown in Figure 3 (step a). Moreover, these low field
NH signals for compounds 2, 2a–2j, 3 and 3a–3j, as well
as for 1 and1a–1j, account for one ofthe imino tautomeric
form shown in Figure 3 (step a). The Z configuration of
the exocyclic C@C bond, in the 5-benzylidene derivatives
2a–2j and 3a–3j, was attributed on the basis of 1H NMR
spectral analysis, since the methine proton resonated, as
expected, at higher chemical shift values due to the desh-
ielding effect of the adjacent C@O, than it would do in E
isomers, because of the lower deshielding effect of 1-S
(Fig. 3, step b).
Figure 1. Design of the target compounds 2, 2a–2j and 3, 3a–3j. R = H
(a); 4-OH (b); 4-OCH3 (c); 3-OCH3,4-OH (d); 2-NO2 (e); 3-NO2 (f); 4-
NO2 (g); 2-Cl (h); 3-Cl (i); 4-Cl (j).
In the solid state, the feature of a c-lactam heterocycle
for the majority of compounds of series 2 and 3 is sup-
ported by the IR spectral data showing a NH group as a
multiple band near 3100 cmꢀ1 and a strong band of the
C@O group in the 1725–1687 cmꢀ1 region. Compound
3c is one exception because it shows a single NH absorp-
tion band at lower frequencies (3234 cmꢀ1), typical of a
secondary amine.
2. Results and discussion
2.1. Chemistry
The compounds described in this paper (Fig. 1) were
synthesised by the multi-step reaction protocol reported
earlier by us.2
The synthetic procedures (Fig. 2) were carried out by
reacting the appropriate amine with chloroacetylchloride
in N,N-DMF at room temperature. After completion of
the reaction, which is usually two hours, cyclisation of
2-chloro-N-(etheroaryl)acetamide10–12 in the presence of
ammonium thiocyanate, in refluxing ethanol, afforded
in excellent yield and purity the 2-(heteroarylimino)thiaz-
olidin-4-ones 1, 2 and 3.13,14 The final compounds 1a–1j,
2a–2j and 3a–3j were obtained by refluxing the previous
intermediates with commercially available aldehydes
and anhydrous sodium acetate in glacial acetic acid. Dur-
ing the course of this study we obtained 2-(ben-
2.2. Antimicrobial activity
The 2-(heteroarylimino)thiazolidin-4-ones 2 and 3 and
their 5-benzylidene derivatives 2a–2j and 3a–3j were as-
sayed in vitro for their antimicrobial activity against
Gram positive and Gram negative bacteria, yeasts and
moulds and the minimal inhibitory concentrations that
inhibited the growth of the tested microorganisms
(MIC) were detected. The results of antimicrobial test-
ing against a panel of selected Gram positive bacteria
and Gram negative Haemophilus influenzae are reported
in Table 1, in comparison with those of the reference
drug ampicillin and of the analogues 1 and 1a–1j.2
zothiazolylimino)thiazolidin-4-one
2 in good yield

3716
P. Vicini et al. / Bioorg. Med. Chem. 16 (2008) 3714–3724
Figure 2. Scheme of synthesis. Reagents and conditions: (a) ClCOCH2Cl, N,N-DMF, rt; (b) NH4SCN, EtOH, reflux; (c) RC6H4CHO, MeCOOH,
MeCOONa, reflux.
Figure 3. (a) Mechanistic pathway for compound 2 and its tautomers; (b) the E/Z isomerism of compounds 2a–2j.

P. Vicini et al. / Bioorg. Med. Chem. 16 (2008) 3714–3724
3717
Table 1. Antibacterial activity of compounds 1, 1a–1j, 2, 2a–2j, 3, 3a–3j expressed as MIC (lg/mL)
Compound
Bacteriaa
BS
BM
BT
SL
SA
SAR
SE SER
SH
SAG
SF
SFU
SP
HI
b
12
50
0.7
3
—
—
3
—
3
>100
3
—
25
12
3
—
6
—
50
25
12
12
25
12
6
—
6
—
3
—
25
—
25
25
>100
25
25
50
>100
3
—
1.5
0.7
1.5
0.3
1.5
0.7
0.7
0.3
1a2
1b2
1c2
1d2
1e2
1f2
1g2
1h2
1i2
1.5
6
>100
25
12
6
12
6
25
12
12
6
25
6
25
12
12
12
25
6
12
3
25
1.5
3
1.5
12
3
>100
50
50
12
6
12
12
25
3
6
12
12
12
6
6
25
25
6
3
3
12
6
3
1.5
0.7
0.3
0.15
0.03
3
6
1.5
1.5
0.7
0.7
0.7
50
>100
>100
12
1.5
0.7
0.3
0.3
1.5
0.7
1.5
0.3
3
1.5
3
>100
12
50
3
1.5
1.5
1.5
3
3
3
0.15
0.3
1.5
0.15
1.5
0.7
1.5
1.5
3
1.5
0.3
3
12
3
1j2
3
3
3
0.15
2
12
>100
3
25
—
6
25
—
3
50
—
3
25
>100
6
25
—
3
100
—
6
100
—
12
—
12
—
6
50
—
>100
—
12
>100
—
100
>100
—
50
>100
—
0.7
>100
6
2a
2b
2c
2d
2e
2f
2g
2h
2i
12
—
6
—
>100
>100
>100
12
—
12
—
12
3
—
6
—
12
—
6
>100
6
—
6
—
6
—
>100
—
—
>100
—
—
>100
—
>100
>100
>100
>100
12
>100
—
>100
—
—
6
>100
6
25
—
6
—
6
>100
>100
>100
>100
100
>100
>100
>100
>100
>100
>100
>100
>100
>100
100
>100
>100
>100
>100
>100
>100
>100
25
12
12
3
6
6
6
12
25
12
12
12
12
12
12
6
12
12
12
12
25
12
25
>100
12
6
>100
>100
>100
12
12
>100
>100
2j
6
>100
12
3
50
100
—
>100
—
—
—
—
3
>100
—
—
>100
>100
>100
>100
>100
3
>100
—
—
>100
—
—
>100
—
—
>100
—
—
>100
—
—
>100
—
—
>100
—
—
>100
—
—
3
3a
3b
3c
>100
>100
>100
>100
>100
>100
0.7
>100
>100
>100
>100
1.5
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
3d
3e
—
>100
0.7
0.7
—
>100
>100
>100
—
50
>100
>100
50
>100
>100
>100
—
>100
>100
>100
—
>100
>100
>100
—
100
>100
>100
—
>100
>100
>100
—
>100
>100
>100
—
3f
1.5
1.5
—
—
6
>100
>100
>100
>100
>100
0.07
>100
>100
—
3
3g
3h
3i
>100
>100
>100
>100
0.07
>100
>100
3
—
—
—
—
>100
0.0015
—
>100
25
—
>100
25
—
>100
0.03
—
50
—
>100
0.7
—
>100
100
—
>100
0.007
3j
AMPc
0.7
0.07
>100
3
0.007
50
0.03
a Gram positive bacteria: BS, Bacillus subtilis ATCC 6633; BM, Bacillus megaterium BGSC 7A2; BT, Bacillus thuringiensis var. kurstaki BGSC 4D1;
SL, Sarcina lutea ATCC 9341; SA, Staphylococcus aureus ATCC 25923; SAR, penicillin-resistant Staphylococcus aureus (clinical isolate); SE,
Staphylococcus epidermidis ATCC 12228; SER, penicillin-resistant Staphylococcus epidermidis (clinical isolate); SH, Staphylococcus haemolyticus
(clinical isolate); SAG, Streptococcus agalactiae (clinical isolate); SF, Streptococcus faecalis (clinical isolate); SFU, Streptococcus faecium (clinical
isolate); SP, Streptococcus pyogenes (clinical isolate). Gram negative bacteria: HI, Haemophilus influenzae (clinical isolate).
b Not tested. Compounds resulted inactive against BS, SA and HI were not tested against the other bacterial strains.
c Ampicillin.
Many compounds display good inhibition of the growth
of Gram positive bacilli and staphylococci, including
methicillin-resistant Staphylococcus aureus and Staphylo-
coccus epidermidis strains. Concerning benzothiazole
derivatives 2 and 2a–2j, most compounds exhibit MIC
values in the 3–25 lg/mL range. It is noteworthy that, in
general, they inhibit in a similar manner both penicillin-
susceptible and penicillin-resistant S. aureus and S. epide-
rmidis bacteria; moreover, it should be noted that com-
pound 2g is found to be fourfold more potent against
S. aureus resistant strain (MIC 6 lg/mL) than against the
susceptible one (MIC 25 lg/mL). Compound 2b shows
the best antibacterial properties, including its activity
against all tested streptococci. Against the latter microor-
ganisms, compounds 2h and 2j are the only others active,
but their effectiveness is restricted to Streptococcus pyog-
enes (MIC 25 lg/mL) and Streptococcus faecalis (MIC
100 lg/mL), respectively. A few benzo[d]isothiazole
derivatives of series 3 are active and they exhibit mostly
a selective effect against bacilli. In fact a very significant
inhibitory potency is shown at a concentration of
0.7 lg/mL by compound 3g against Bacillus subtilis and
by compounds 3f, 3g and 3j against Bacillus megaterium,
whereas compounds 3f and 3g inhibit Bacillus thuringien-
sis at 1.5 lg/mL. A decreased antibacterial activity can be
detected for these compounds with respect to benzothia-
zole derivatives 2 against staphylococci and streptococci.
Concerning H. influenzae, only compounds 2, 2b, 2g, 3,
3e and 3f exert a certain effectiveness, with MIC values
ranging from 0.7 to 12 lg/mL.
In most cases the inhibitory potency exhibited by the
tested substances is lower than that of ampicillin. Note-
worthy exceptions arise with B. thuringiensis and both
penicillin-resistant S. aureus and S. epidermidis strains,

3718
P. Vicini et al. / Bioorg. Med. Chem. 16 (2008) 3714–3724
which appear to be more sensitive to the compounds of
the series 2 and 3 and to benzothiazole derivatives 2,
respectively, than to ampicillin.
azole (series 2) and benzisothiazole (series 3) bicyclic
derivatives exhibit a lower antibacterial activity when
compared with the thiazole analogues (series 1). This
shows the modulating effect of the fused benzene ring
for the antibacterial activity of the thiazolidinones under
study.
None of the tested compounds exhibits any activity
against Gram negative Escherichia coli SPA 27, yeasts
(Candida tropicalis ATCC 1369 and Saccharomyces cere-
visiae ATCC 9763), and moulds (Aspergillus niger ATCC
6275) up to a concentration of 100 lg/mL, with the excep-
tion only of compound 2 that, notably, shows moderate
antifungal properties against both yeasts (MIC 50 lg/
mL) and moulds (MIC 25 lg/mL). However the inhibi-
tion detected is lower than that exhibited by miconazole
standard control (data not shown).
2.3. Prediction of toxicity and QSAR studies
Most of the compounds were predicted by DEREK to
have no toxicity (Table 2). For 10 compounds (1, 1e–1g,
2e–2g, 3e–3g), carcinogenicity was predicted to be plausi-
ble. For most of the compounds the predicted carcinoge-
nicity was related to the presence of an aromatic nitro
group. Skin sensitisation was predicted to be plausible
for compounds 1d, 2d and 3d, because of the presence of
a catechol precursor. These predicted plausible toxicities
should not preclude the further investigation of these
compounds. However, if any of them is selected for devel-
opment, the appropriate toxicity tests should be carried
out.
All the active compounds exhibit microbiostatic proper-
ties having MBC and MFC values higher than the cor-
responding MICs (data not shown).
As regards the relationships between the structure of the
heterocyclic scaffold and the detected antibacterial prop-
erties, benzothiazoles are endowed with a wide spectrum
of activity against bacilli and staphylococci, including
penicillin-resistant ones, that decreases when the benzo-
thiazole nucleus is replaced by its isomer benzisothiazole.
Nevertheless, against bacilli, some benzisothiazole deriv-
atives show a better activity compared to the correspond-
ing benzothiazoles.
Good QSARs were obtained for activities against some
bacteria, but not for others. In part this was due to only
a small number of compounds yielding quantitative
MIC values against certain bacteria. This limits the num-
ber of descriptors that can be incorporated into a QSAR,
according to Topliss and Costello,16 which requires the
Table 2. DEREK predictions of compounds 1, 1a–1j, 2, 2a–2j, 3, 3a–3j
In contrast to the remarkable activity of 2-thiazolylimino-
5-benzylidene-4-thiazolidinone 1a against all the tested
microorganisms, it was observed that in both benzo-
and benzisothiazole thiazolidinones the introduction of
the benzylidene moiety, at the position 5 of the thiazolid-
inone ring, leads to compounds 2a and 3a with inhibitory
activity lower than that of the parent substances 2 and 3.
The effectiveness detected for the benzylidene derivatives
of classes 2 and 3 seems to be governed in part by the pres-
ence of the substituents on the benzene ring. Clearly, the
introduction of the bulky electron-withdrawing nitro
and chloro groups enhances the antibacterial properties
with respect to 2a and 3a. Surprisingly the most potent
and wide-spectrum antibacterial agent is 2b, having in
the benzene para position a hydroxy group endowed with
an electron-donating and hydrophilic character. On the
other hand, the introduction of a methoxy substituent
does not influence the activity of compounds 2c and 3c
with respect to the unsubstituted 2a and 3a, whereas the
antibacterial potencies decrease from 2b to 2d.
Compound Carcinogenicity Skin sensitisation
1
Plausible
None
None
None
None
1a
1b
1c
1d
1e
1f
1g
1h
1i
None
None
Plausible (catechol or precursor)
None
None
Plausible
Plausible
Plausible
None
None
None
None
None
None
None
None
None
1j
2
None
None
None
None
2a
2b
2c
2d
2e
2f
2g
2h
2i
None
None
None
None
None
Plausible (catechol or precursor)
Plausible
Plausible
Plausible
None
None
None
None
None
None
None
None
None
It seems also interesting to point out that, among the iso-
meric chloro substituted compounds 2h–2j, as well as
among the nitro substituted 3e–3g, the position of the
substituent exerts, in general, a certain effect, even if not
unilateral, on the activity against all the microorganisms.
Conversely, among the nitro substituted 2e–2g, the meta
(2f) and para (2g) compound possess the highest activity,
whereas, for the chloro substituted compounds 3h-3j it is
evident that the para derivative 3j has greater efficacy
towards bacilli compared with ortho 3h and meta 3i.
2j
3
None
None
None
None
3a
3b
3c
3d
3e
3f
3g
3h
3i
None
None
None
None
None
Plausible (catechol or precursor)
Plausible
Plausible
Plausible
None
None
None
None
None
None
None
None
None
Thus, excepting the parent compound 2, which is more
active than its thiazole analogue 1, the assayed benzothi-
3j

P. Vicini et al. / Bioorg. Med. Chem. 16 (2008) 3714–3724
3719
ratio of compounds to descriptors to be at least 5:1, in or-
der to minimise the risk of chance correlations.
The negative sign of SHDW4 indicates that smaller
molecules should be more active, whilst OctXYZ indi-
cates the importance of polarity in governing activity.
The R ESI term is difficult to interpret, as E-state val-
ues incorporate both steric and electronic compo-
nents; since the range of values of R ESI is very
small (26–64), it could be that this term is of little
significance.
In order to be of value, a QSAR must have good statis-
tics, in terms of both its correlation coefficient R and its
cross-validated R value, Q. Acceptable values are
R2 P 0.7 and Q2 P 0.5.17 The QSARs reported below
are those that satisfy those criteria. It is disappointing
that an acceptable QSAR could not be obtained for
Bacillus thuringiensis var. kurstaki (BT), since our com-
pounds were found to be potent against this bacillus.
Staphylococcus aureus (SA)
logð1=CÞ ¼ ꢀ0:00156IM2S þ 0:333LPZ
þ 0:00246OctXYY þ 2:57
The best QSAR found for the antimicrobial activity,
where n, number of compounds used to develop the
QSAR; R, multiple correlation coefficient; Q, cross val-
idated multiple correlation coefficient (leave-one-out
procedure); s, standard error of estimate and F, Fisher
statistic are
n ¼ 18 R2 ¼ 0:700 Q2 ¼ 0:566 s ¼ 0:262 F ¼ 10:9
ð4Þ
where IM2S = moment of inertia 2 (size); LPZ = lipole Z
vector and OctXYY = VAMP octupole in XYY
hyperplane.
Bacillus subtilis (BS)
logð1=CÞ ¼ ꢀ29:1Qꢀmax ꢀ 20:7Qmþax
The negative coefficient of IM2S indicates that smaller
molecules are more active. The LPZ term suggests that
lipophilicity improves activity, and, as with HI above,
lower values of OctXYY will enhance activity.
ꢀ 3:43SHDW5 þ 1:24
n ¼ 21 R2 ¼ 0:822 Q2 ¼ 0:744 s ¼ 0:309 F ¼ 26:2
ð1Þ
Staphylococcus aureus penicillin-resistant (SAR)
where Qꢀmax and Qmþax = maximum negative and positive
charges on a molecule, and SHDW5 = normalised sha-
dow area in XZ plane.
logð1=CÞ ¼ ꢀ0:0527MW ꢀ 1:14IM2L þ 0:228MR
þ 3:31
n ¼ 18 R2 ¼ 0:752 Q2 ¼ 0:629 s ¼ 0:318 F ¼ 14:1
ð5Þ
where MW = molecular weight; IM2L = moment of
The sign of the SHDW5 termꢀindicatesþthat smaller mol-
ecules are more active. The Qmax and Qmax terms indicate
that a high maximum negative charge increases activity,
whereasahighmaximum positivechargedecreasesactivity.
inertia 2 (length) and MR = molar refractivity.
Bacillus megaterium (BM)
MW and IM2L both indicate that smaller molecules
have greater activity. MR can also be considered to rep-
resent molecular size, but also reflects polarisability. The
positive coefficient of this term suggests that a higher
proportion of non-polar surface area could enhance
activity.
logð1=CÞ ¼ ꢀ1:31RNCSAM1 þ 25:7SumðCaÞ=a
þ 0:239DPMY ꢀ 2:22
n ¼ 21 R2 ¼ 0:781 Q2 ¼ 0:672 s ¼ 0:383 F ¼ 20:3
ð2Þ
where RNCSAM1 = relative negatively charged surface
area calculated by AM1; Sum(Ca)/a = (sum of hydrogen
bond acceptor abilities)/molar polarisability and
DPMY = dipole moment Y vector.
Staphylococcus epidermidis (SE)
logð1=CÞ ¼ ꢀ1:83RNCSAM1 þ 1:08EHOMO
þ 64:25vch ꢀ 0:48
The negative coefficient of RNCSAM1 indicates that neg-
atively charged surface area lowers activity. On the
other hand, hydrogen bond acceptor ability, represented
by Sum(Ca)/a, improves activity. Increased dipole mo-
ment also improves activity.
n ¼ 19 R2 ¼ 0:759 Q2 ¼ 0:670 s ¼ 0:265 F ¼ 15:7
ð6Þ
where EHOMO = energy of highest occupied molecular
orbital and 5vch = 5th order chain molecular
connectivity.
Sarcina lutea (SL)
logð1=CÞ ¼ ꢀ15:8SHDW4 þ 0:0460RESI
þ 0:0102OctXYZ þ 6:71
The negative coefficient of RNCSAM1 indicates that neg-
atively charged surface area lowers activity, whilst EHO-
MO, with negative values, indicates that high values also
lower activity. This is consistent with the effect of
RNCSAM1, since EHOMO is a measure of electron-donat-
ing ability. The vch term can be considered in effect an
indicator variable for the presence of five-membered
rings, which clearly enhance activity.
n ¼ 18 R2 ¼ 0:746 Q2 ¼ 0:575 s ¼ 0:308 F ¼ 13:7
ð3Þ
5
where SHDW4 = shadow area 1 in XY plane, R ESI =
sum of electrotopological state indices, and OctXYZ
VAMP octupole in XYZ hyperplane.
=

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P. Vicini et al. / Bioorg. Med. Chem. 16 (2008) 3714–3724
Staphylococcus epidermidis penicillin-resistant (SER)
Haemophilus influenzae (HI)
logð1=CÞ ¼ 0:00170OctXYY þ 41:6FPSA3
ꢀ 0:0410PolXZ ꢀ 1:99
logð1=CÞ ¼ ꢀ0:876EDIF1 ꢀ 60:8HALO4
þ 8:34NHal þ 12:4
n ¼ 17 R2 ¼ 0:835 Q2 ¼ 0:629 s ¼ 0:238 F ¼ 21:9
ð10Þ
n ¼ 18 R2 ¼ 0:853 Q2 ¼ 0:775 s ¼ 0:205 F ¼ 27:1
ð7Þ
where EDIF1 = difference between maximum and mini-
mum atomic E-state values; HALO4 = (halogen partial
atomic surface area)/(total molecular surface area);
and NHal = number of halogen atoms.
where FPSA3 = fractional positively charged partial
surface area; and PolXZ = VAMP polarisation in XZ
plane.
All of these descriptors relate to polarity; OctXYY values
are negative, whilst PolXZ values are positive, so lower
values of both will enhance activity. On the other hand,
the sign on FPSA3 indicates that increased positively
charged surface area will also enhance activity. The
two are not mutually exclusive.
E-State values have both steric and electronic compo-
nents. The negative sign of EDIF1 suggests that smal-
ler molecules should contribute less to reduced
activity. HALO4 and NHal both relate to halogen
atoms, but are of opposite sign. Clearly the more hal-
ogen atoms the higher the activity. The negative sign
of HALO4 suggests that smaller halogen atoms, and/
or halogen atoms adjacent to one another, are better
for activity.
The descriptors selected by the software’s genetic algo-
rithm (GA) are, with only one exception (the lipophilic-
ity descriptor LPZ in Eq. 4), those representing
electronic and steric effects, and it can be concluded that
antimicrobial activity in the compounds studied is con-
trolled largely by these effects. Because of the good sta-
tistics of Eqs. 1–10, it should be possible to use each of
the QSARs to predict more active compounds against
each species.
Staphylococcus haemolyticus (SH)
logð1=CÞ ¼ ꢀ0:0906SRMN þ 0:0212OctXXZ þ 0:744
n ¼ 13 R2 ¼ 0:753 Q2 ¼ 0:604 s ¼ 0:259 F ¼ 15:3
ð8Þ
It can be seen that Eqs. 1–10 involve a wide variety of
descriptors. The GA algorithm that we used yielded
the best ten QSARs for activity against each species,
which allowed us to see whether there were any good
QSARs that were common to two or more microbial
species. This was found not to be so. We therefore inves-
tigated whether the descriptors selected for the best
QSAR for one species could be used to develop a good
QSAR for other species. This was found not to be the
case, from which we conclude that the mechanisms of
action are different for each species, although it should
be pointed out that several of the QSARs indicate that
smaller molecules should be more active, and that polar-
ity is important for activity.
where SRMN = minimum free radical superdelocalis-
ability; and OctXXZ = VAMP octupole in XXZ
hyperplane.
SRMN is a measure of the concentration of orbitals,
occupied and unoccupied, at each atom, and can be con-
sidered as the electron richness of each atom. Its values
are negative, and so the QSPR indicates that electron-
rich atoms will enhance activity. The presence of
OctXXZ, with positive values, suggests that increased
polarity will aid activity.
Streptococcus agalactiae (SAG)
logð1=CÞ ¼ ꢀ18:9SHDW4 ꢀ 48:4RNCGAM1
ꢀ 0:00794IM1S þ 19:3
3. Conclusion
We report the antimicrobial activity of novel
2-benzo[d]thiazolylimino-5-benzylidene-4-thiazolidinones
and their 2-benzo[d]isothiazolyl isomers and the compar-
ison of their properties with those of the previous potent
n ¼ 12 R2 ¼ 0:944 Q2 ¼ 0:864 s ¼ 0:155 F ¼ 44:9
ð9Þ
where RNCGAM1 = relative negative charge calculated
by AM1; and IM1S = whole molecule moment of inertia
1 (size).
analogous
thiazolylimino-5-benzylidene-4-thiazolidi-
nones. Most of the benzothiazoles show significant anti-
bacterial efficacy against bacilli and staphylococci,
including penicillin-resistant strains, whereas some of
the tested benzisothiazoles are selective against bacilli.
Overall, the activity depends on the substituents at the
5-benzylidene moiety. On the other hand, both the benzo-
thiazoles and benzisothiazoles exhibit decreased antibac-
terial properties when compared to the corresponding
thiazoles, suggesting that these bicyclic systems play a
negative role on the antimicrobial effectiveness of this
class of compounds. The QSAR study indicates that the
SHDW4 and IM1S are both related to molecular
size, and both have negative coefficients, indicating
that smaller molecules have greater activity. Charge
also plays a part, as indicated by the RNCGAM1
term; since the RNCGAM1 values themselves are po-
sitive, the negative sign of the coefficient means that
smaller relative negative charge results in increased
activity.

P. Vicini et al. / Bioorg. Med. Chem. 16 (2008) 3714–3724
3721
mechanisms of action are different for each species,
although several of the QSARs suggest that smaller mol-
ecules should be more active, and that polarity is impor-
tant for activity.
4.1.2. General procedure for synthesis of 2-heteroarylimi-
no-5-benzylidene-4-thiazolidinones 2a–2j, 3a–3j. A well-
stirred solution of 2-(heteroarylimino)thiazolidin-4-one
(4 mmol) in 35 mL of acetic acid was buffered with so-
dium acetate (8 mmol) and added with the appropriate
arylaldehyde (6 mmol). The solution was refluxed over
different periods till the completion of the reaction,
monitoring by TLC. The reaction mixture was then
cooled at room temperature and the solid precipitated
was filtered, abundantly washed with water and then
recrystallised.
4. Experimental
4.1. Chemistry
Melting points (mp °C) were determined with a Buchi
512 apparatus or with a Boetius apparatus and are
uncorrected. Elemental analysis was performed on a
ThermoQuest (Italia) FlashEA 1112 Elemental Ana-
lyser, for C, H, N and S. The values found for C, H,
N and S were within 0.4% of the theoretical ones. IR
spectra, such as KBr pellets, were recorded on a JASCO
FT-IR 300E spectrophotometer (Jasco Ltd, Tokyo,
Japan); wave numbers in the IR spectra are given in
4.1.2.1. 2-(Benzo[d]thiazol-2-ylimino)-5-benzylidene-
thiazolidin-4-one 2a.14 Reaction time: 5 h. Yield: 52%;
mp 281–284 °C (dioxane). TLC: eluent = toluene/diox-
ane/acetic acid 90/10/5. IR (KBr): m = 3120 (N–H), 1699
(C@O), 1574 (N@C) cmꢀ1 1H NMR (DMSO-d6 d,
.
ppm): 12.91 (s, 1H, NH); 7.99 (d, 1H, J = 7.8 H-4); 7.92
(d, 1H, J = 7.8 H-7); 7.79 (s, 1H, CH); 7.70 (d, 2H,
J = 7.2 H-20, H-60); 7.61–7.48 (m, 4H, H-5, H-6, H-30,
H-50); 7.38 (t, 1H, J = 7.5 H-40). Anal. calcd. for
C17H11N3OS2 (337.42): C, 60.51; H, 3.29; N, 12.45; S,
19.01. Found C, 60.43; H, 3.44; N, 12.15; S, 19.11%.
cmꢀ1
.
1H NMR spectra of the newly synthesised
compounds, in DMSO-d6 solutions, were recorded on
a Bruker AC 300 instrument at 298 K. Chemical shifts
are reported as d (ppm) relative to TMS as internal stan-
dard; coupling constants J are expressed in Hz. The pro-
gress of the reactions was monitored by thin layer
chromatography with F254 silica-gel precoated sheets
(Merck, Darmstadt, Germany). UV light was used for
detection.
4.1.2.2. 5-(4-Hydroxybenzylidene)-2-(benzo[d]thiazol-
2-ylimino)thiazolidin-4-one 2b.14 Reaction time: 6 h.
Yield: 45%; mp 293–294 °C (dioxane). TLC: elu-
ent = toluene/dioxane/acetic acid 90/10/5. IR (KBr):
m = 3400 (O–H), 3129 (N–H), 1696 (C@O), 1564
1
Solvents, unless otherwise specified, were of analytical
reagent grade or of the highest quality commercially
available. Synthetic starting material, reagents and sol-
vents were purchased from Aldrich Chemical Co. and
from Fluka.
(N@C) cmꢀ1. H NMR (DMSO-d6 d, ppm): 12.79 (s,
1H, NH); 10.38 (s, 1H, OH); 8.00–7.93 (m, 2H, H-4,
H-7); 7.70 (s, 1H, CH); 7.58 (d, 2H, J = 8.1 H-20, H-
60); 7.49 (t, 1H, J = 7.6 H-5); 7.36 (t, 1H, J = 7.6 H-6);
6.98 (d, 2H, J = 8.3 H-30, H-50). Anal. calcd for
C17H11N3O2S2 (353.42): C, 57.77; H, 3.14; N, 11.89; S,
18.15. Found C, 57.40; H, 3.32; N, 12.01; S, 18.10%.
4.1.1. General procedure for synthesis of 2-(heteroaryli-
mino)thiazolidin-4-ones 2 and 3. A solution of 2-chloro-
N-(etheroaryl)acetamide (5 mmol) and ammonium thio-
cyanate (10 mmol) in 20 mL of 96% ethanol was refluxed
for 1–3 h and allowed to stand overnight. The precipitate
was filtered, washed with water and then recrystallised.
4.1.2.3. 5-(4-Methoxybenzylidene)-2-(benzo[d]thiazol-
2-ylimino)thiazolidin-4-one 2c.14 Reaction time: 4 h.
Yield: 60%; mp 223–225 °C (dioxane). TLC: eluent = tol-
uene/dioxane/acetic acid 90/10/5. IR (KBr): m = 3143 (N–
H), 1699 (C@O), 1585 (N@C) cmꢀ1. 1H NMR (DMSO-d6
d, ppm): 12.81 (s, 1H, NH); 7.98 (d, 1H, J = 7.8 H-4); 7.91
(d, 1H, J = 7.8 H-7); 7.74 (s, 1H, CH); 7.65 (d, 2H, J = 8.7
H-20, H-60); 7.49 (t, 1H, J = 7.5 H-5); 7.36 (t, 1H, J = 7.5
H-6); 7.13 (d, 2H, J = 8.7 H-30, H-50); 3.84 (s, 3H, CH3O).
Anal. calcd for C18H13N3O2S2 (367.04): C, 58.84; H, 3.57;
N, 11.44; S, 17.45. Found C, 58.77; H, 3.69; N, 11.11; S,
17.55%.
4.1.1.1. 2-(Benzo[d]thiazol-2-ylimino)thiazolidin-4-one
2.14 Reaction time: 1 h. Yield: 65%; mp 189–190 °C
(dioxane). TLC: eluent = benzene/ethanol 8/2. IR
(KBr): m = 3158 (N–H), 1725 (C@O), 1568 (N@C) cmꢀ1
.
1H NMR (DMSO-d6 d, ppm): 12.27 (s, 1H, NH); 7.97 (d,
1H, J=8.4 H-7); 7.80 (d, 1H, J = 8.1 H-4); 7.45 (t, 1H,
J = 8.4 H-5); 7.33 (t, 1H, J = 8.2 H-6); 4.05 (s, 2H,
CH2). Anal. calcd for C10H7N3OS2 (249.31): C, 48.18;
H, 2.83; N, 16.85; S, 25.72. Found C, 48.38; H, 2.91; N,
16.64; S, 25.87%.
4.1.2.4. 5-(4-Hydroxy-3-methoxybenzylidene)-2-
(benzo[d]thiazol-2-ylimino)thiazolidin-4-one 2d. Reaction
time: 4 h. Yield: 83%; mp 178–180 °C (dioxane). TLC:
eluent = toluene/dioxane/acetic acid 90/10/5. IR (KBr):
m = 3440 (O–H), 3193 (N–H), 1698 (C@O), 1581
4.1.1.2. 2-(Benzo[d]isothiazol-3-ylimino)thiazolidin-4-
one 3. Reaction time: 3 h. Yield: 76%; mp 205–206 °C
(dioxane). TLC: eluent = CH2Cl2/EtOH 95/5. IR (KBr):
1
(N@C) cmꢀ1. H NMR (DMSO-d6 d, ppm): 12.79 (s,
m = 3110 (N–H), 1702 (C@O), 1575 (N@C) cmꢀ1
.
1H
1H, NH); 10.01 (s, 1H, OH); 8.01 (d, 1H, J = 8.1 H-7);
7.89 (d, 1H, J = 7.8 H-4); 7.71 (s, 1H, CH); 7.49 (t, 1H,
J = 7.9 H-5); 7.39–7.30 (m, 2H, H-20, H-60); 7.21 (d, 1H,
J = 8.1, H-60); 7.00 (d, 1H J = 8.4 H-50); 3.88 (s, 3H,
CH3O). Anal. calcd for C18H13N3O3S2 (383.45): C,
56.38; H, 3.42; N, 10.96; S, 16.73. Found C, 56.52; H,
3.82; N, 10.59; S, 16.96%.
NMR (DMSO-d6 d, ppm): 12.18 (s, 1H, NH); 8.13 (d,
1H, J = 8.4, H-4); 8.02 (d, 1H, J = 7.8, H-7); 7.62 (t, 1H,
J = 7.5, H-5); 7.51 (t, 1H, J = 7.5, H-6); 4.03 (s, 2H,
CH2). Anal. calcd for C10H7N3OS2 (249.31): C, 48.18;
H, 2.83; N, 16.85; S, 25.72. Found C, 48.17; H, 2.87; N,
16.89; S, 25.32%.

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P. Vicini et al. / Bioorg. Med. Chem. 16 (2008) 3714–3724
4.1.2.5. 5-(2-Nitrobenzylidene)-2-(benzo[d]thiazol-2-
dioxane/acetic acid 90/10/5. IR(KBr): m = 3120 (N–H),
1
ylimino)thiazolidin-4-one 2e. Reaction time: 4 h. Yield:
72%; mp 254–255 °C (dioxane). TLC: eluent = toluene/
dioxane/acetic acid 90/10/5. IR (KBr): m = 3156 (N–H),
1699 (C@O), 1575 (N@C) cmꢀ1. H NMR (DMSO-d6
d, ppm): 12.98 (s, 1H, NH); 8.03 (d, 1H, J = 7.5 H-4);
7.92 (d, 1H, J = 7.8 H-7); 7.78 (s, 1H, CH); 7.74 (d,
2H, J = 8.7 H-20, H-60); 7.64 (d, 2H, J = 8.7 H-40, H-
50); 7.51 (t, 1H, J = 7.5 H-5); 7.38 (t, 1H,J = 7.5 H-6).
C17H10ClN3OS2 (371.87): C, 54.91; H, 2.71; N, 11.30;
S, 17.25. Found C, 54.54; H, 2.85; N, 11.59; S, 17.52%.
1
1720 (C@O), 1583 (N@C) cmꢀ1. H NMR (DMSO-d6
d, ppm): 13.03 (s, 1H, NH); 8.24 (d, 1H, J = 8.1 H-30);
8.01–7.74 (m, 6H, H-4, H-7, H-40, H-50, H-60, CH);
7.46 (t, 1H, J=7.5 H-5); 7.36 (t, 1H, J = 7.5 H-6). Anal.
calcd for C17H10N4O3S2 (382.42): C, 53.39; H, 2.64; N,
14.65; S, 16.77. Found C, 53.52; H, 3.03; N, 14.49; S,
16.37%.
4.1.2.11. 2-(Benzo[d]isothiazol-3-ylimino)-5-benzylid-
enethiazolidin-4-one 3a. Reaction time: 5 h. Yield: 89%;
mp 210–211 °C (dioxane). TLC: eluent = methylene chlo-
ride/ethanol 95/5. IR(KBr): m = 3072 (N–H), 1704
(C@O), 1592 (C@N) cmꢀ1.1H NMR (DMSO-d6 d,
ppm): 12.83 (s, 1H, NH); 8.20 (d, 1H, J = 8.1, H-4); 8.08
(d, 1H, J = 7.2, H-7); 7.75 (s, 1H, CH); 7.69–7.47 (m,
7H, H-5, H-6, H-20, H-30, H-40, H-50, H-60). Anal. calcd
for C17H11N3OS2 (337.42): C, 60.51; H, 3.29; N, 12.45;
S, 19.01. Found C, 60.47; H, 3.32; N, 12.05; S, 18.78%.
4.1.2.6. 5-(3-Nitrobenzylidene)-2-(benzo[d]thiazol-2-yli-
mino)thiazolidin-4-one 2f. Reaction time: 4 h. Yield: 81%;
mp 255–256 °C (dioxane). TLC: eluent = toluene/diox-
ane/acetic acid 90/10/5. IR (KBr): m = 3156 (N–H), 1690
(C@O), 1594 (N@C) cmꢀ1 1H NMR (DMSO-d6 d,
.
ppm): 13.04 (s, 1H, NH); 8.54 (s, 1H, H-20); 8.29 (d,
1H, J = 8.1 H-40); 8.10 (d, 1H, J = 8.1 H-60); 8.01 (d,
1H, J=7.8 H-7); 7.90–7.83 (m, 3H, H-4, H-5, CH); 7.51
(t, 1H, J = 7.6 H-5); 7.38 (t, 1H, J = 7.6 H-6). Anal. calcd
for C17H10N4O3S2 (382.42): C, 53.39; H, 2.64; N, 14.65;
S, 16.77. Found C, 53.29; H, 2.78; N, 14.69; S, 16.87 %.
4.1.2.12. 2-(Benzo[d]isothiazol-3-ylimino)-5-(4-hydrox-
ybenzylidene)thiazolidin-4-one 3b. Reaction time: 7 h.
Yield: 75%; mp 270–272 °C (dioxane). TLC: eluent = tol-
uene/dioxane/acetic acid 90/10/5. IR(KBr): m = 3336
1
4.1.2.7. 5-(4-Nitrobenzylidene)-2-(benzo[d]thiazol-2-yli-
mino)thiazolidin-4-one 2g.14 Reaction time: 4 h. Yield:
84%; mp 288–290 °C (dioxane). TLC: eluent = toluene/
dioxane/acetic acid 90/10/5. IR (KBr): m = 3140 (N–H),
(OH), 3207 (N–H), 1687 (C@O), 1589 (C@N) cmꢀ1. H
NMR (DMSO-d6 d, ppm): 12.63 (s, 1H, NH); 10.28 (s,
1H, OH); 8.19 (d, 1H, J = 8.1, H-4); 8.08 (d, 1H,
J = 7.8, H-7); 7.67–7.62 (m, 2H, H-5, CH); 7.57–7.52
(m, 3H, H-6, H-20, H-60); 6.98 (d, 2H, J = 8.4, H-30, H-
50). Anal. calcd for C17H11N3O2S2 (353.42): C, 57.77; H,
3.14; N, 11.89; S, 18.15. Found C, 58.07; H, 3.43; N,
11.58; S, 17.95 %.
1
1720 (C@O), 1592 (N@C) cmꢀ1. H NMR (DMSO-d6
d, ppm): 13.01 (s, 1H, NH); 8.38 (d, 2H, J = 8.7 H-30,
H-50); 8.01 (d, 1H, J = 7.8 H-7); 7.95–7.93 (m, 3H, H-4,
H-20, H-60); 7.87 (s, 1H, CH); 7.52 (t, 1H, J = 7.3 H-5);
7.39 (t, 1H, J = 7.7 H-6). Anal. calcd for C17H10N4O3S2
(382.42): C, 53.39; H, 2.64; N, 14.65; S, 16.77. Found
C, 53.13; H, 2.76; N, 14.31; S, 16.72 %.
4.1.2.13. 2-(Benzo[d]isothiazol-3-ylimino)-5-(4-methoxy-
benzylidene)thiazolidin-4-one 3c. Reaction time: 5 h. Yield:
78%; mp 221–222 °C (dioxane). TLC: eluent = methylene
chloride/ethanol 95/5. IR(KBr): m = 3234 (N–H), 1716
4.1.2.8. 5-(2-Chlorobenzylidene)-2-(benzo[d]thiazol-2-
ylimino)thiazolidin-4-one 2h.14 Reaction time: 6 h.
Yield: 89%; mp 203–205 °C (dioxane). TLC: elu-
ent = toluene/dioxane/acetic acid 90/10/5. IR(KBr):
(C@O), 1592 (C@N) cmꢀ1 1H NMR (DMSO-d6 d,
.
ppm): 12.71 (s, 1H, NH); 8.17 (d, 1H, J = 8.1, H-4); 8.08
(d, 1H, J = 8.4, H-7); 7.70–7.62 (m, 4H, H-5, H-20, H-60,
CH); 7.54 (t, 1H, J = 8.1, H-6); 7.14 (d, 2H, J = 8.7, H-30,
H-50); 3.82 (s, 3H, CH3O). Anal. calcd for C18H13N3O2S2
(367.45): C, 58.84; H, 3.57; N, 11.44; S, 17.45. Found C,
58.83; H, 3.87; N, 11.06; S, 17.27%.
m = 3152 (N–H), 1698 (C@O), 1587 (N@C) cmꢀ1 1H
.
NMR (DMSO-d6 d, ppm): 13.06 (s, 1H, NH); 8.02 (d,
1H J = 7.5 H-4); 7.91–7.88 (d, 1H, J = 7.2 H-7); 7.76
(d, 1H, J = 7.2 H-60); 7.68–7.46 (m, 5H, H-5, H-30, H-
40, H-50, CH); 7.37 (t, 1H, J = 7.3 H-6). Anal. calcd
for C17H10ClN3OS2 (371.87): C, 54.91; H, 2.71; N,
11.30; S, 17.25. Found C, 54.97; H, 3.04; N, 10.91; S,
17.55%.
4.1.2.14. 2-(Benzo[d]isothiazol-3-ylimino)-5-(4-hydro-
xy-3- methoxybenzylidene)thiazolidin-4-one 3d. Reaction
time: 20 h. Yield: 88%; mp 207–208 °C (dioxane). TLC:
eluent = methylene chloride/ethanol 95/5. IR(KBr):
m = 3395 (OH), 3174 (NH), 1706 (C@O), 1579 (C@N))
cmꢀ1. 1H NMR (DMSO-d6 d, ppm): 12.31 (s, 1H, NH);
9.94 (s, 1H, OH); 8.18 (d, 1H, J = 8.1, H-4); 8.08 (d, 1H,
J = 7.8, H-7); 7.67–7.62 (m, 2H, H-5, CH); 7.54 (t, 1H,
J = 7.8, H-6); 7.28 (d, 1H, J = 1.8, H-20); 7.16 (dd, 1H,
J = 8.4, 2.1, H-60); 7.01 (d, 1H, J = 8.4, H-50); 3.83 (s,
3H, CH3O). Anal. calcd for C18H13N3O3S2 (383.45): C,
56.38; H, 3.42; N, 10.96; S, 16.73. Found C, 56.65; H,
3.62; N, 10.72; S, 16.37%.
4.1.2.9. 5-(3-Chlorobenzylidene)-2-(benzo[d]thiazol-2-
ylimino)thiazolidin-4-one 2i. Reaction time: 6 h. Yield:
81%; mp 208–210 °C (dioxane). TLC: eluent = toluene/
dioxane/acetic acid 90/10/5. IR(KBr): m = 3145 (N–H),
1
1708 (C@O), 1576 (N@C) cmꢀ1. H NMR (DMSO-d6
d, ppm): 13.03 (s, 1H, NH); 8.02 (d, 1H J = 7.5 H-4);
7.91 (d, 1H, J = 7.8 H-7); 7.70 -7.47 (m, 6H, H-5, H-
20, H-40, H-50, H-60, CH); 7,37 (t, 1H, J = 7.5 H-6);
C17H10ClN3OS2 (371.87): C, 54.91; H, 2.71; N, 11.30;
S, 17.25. Found C, 54.51; H, 2.46; N, 11.03; S, 17.30%.
4.1.2.15. 2-(Benzo[d]isothiazol-3-ylimino)-5-(2-nitroben-
zylidene)thiazolidin-4-one 3e. Reaction time: 1 h. Yield:
78%; mp 208–210 °C (dioxane). TLC: eluent = methylene
chloride/ethanol 95/5. IR(KBr): m = 3190 (NH), 1705
4.1.2.10. 5-(4-Chlorobenzylidene)-2-(benzo[d]thiazol-2-
ylimino)thiazolidin-4-one 2h. Reaction time: 10 h. Yield:
45%; mp 248–250 °C (dioxane). TLC: eluent = toluene/

P. Vicini et al. / Bioorg. Med. Chem. 16 (2008) 3714–3724
3723
1
(C@O), 1593 (C@N), 1514, 1332 (NO2) cmꢀ1. H NMR
(DMSO-d6 d, ppm): 12.92 (s,1H, NH); 8.22 (d,
1H,J = 8.4, H-30); 8.15 (d, 1H, J = 8.1, H-60); 8.06 (d, 1H,
J = 7.8, H-4); 7.95–7.92 (m, 2H, CH, H-40); 7.82 (d, 1H,
J = 7.2, H-7); 7.73 (t, 1H, J = 7.6, H-50); 7.65 (t, 1H,
J = 7.2, H-5); 7.54 (t, 1H, J = 7.0, H-6). Anal. calcd for
C17H10N4O3S2 (382.42): C, 53.39; H, 2.64; N, 14.65; S,
16.77. Found C, 53.55; H, 2.83; N, 14.32; S, 16.61 %.
(C@O), 1621(C@N) cmꢀ1. 1H NMR (DMSO-d6 d, ppm):
12.85 (s, 1H, NH); 8.18 (d, 1H, J = 8.1, H-4); 8.07 (d, 1H,
J = 8.4, H-7); 7.73–7.63 (m, 6H, H-5, H-20, H-60, H-30,
H-50, CH); 7.55 (t, 1H, J = 7.8, 6). Anal. calcd for
C17H10ClN3OS2 (371.87): C, 54.91; H, 2.71; N, 11.30; S,
17.25. Found C, 54.88; H, 2.92; N, 10.94; S, 17.16 %.
4.2. Microbiology
4.1.2.16. 2-(Benzo[d]isothiazol-3-ylimino)-5-(3-nitro-
benzylidene)thiazolidin-4-one 3f. Reaction time: 1 h.
Yield: 98%; mp 221–222 °C (dioxane). TLC: eluent =
methylene chloride/ethanol 95/5. IR(KBr): m = 3135
(NH), 1700 (C@O), 1604 (C@N), 1527, 1353 (NO2)
The antimicrobial activity was assayed in vitro by the two-
fold broth dilution technique18 against Gram positive
bacteria (Bacillus megaterium BGSC 7A2, Bacillus subtilis
ATCC 6633, Bacillus thuringiensis var. kurstaki BGSC
4D1, Sarcina lutea ATCC 9341, Staphylococcus aureus
ATCC 25923, Staphylococcus epidermidis ATCC 12228
and clinical isolates of methicillin-resistant Staphylococ-
cus aureus, methicillin-resistant Staphylococcus epidermi-
1
cmꢀ1. H NMR (DMSO-d6 d, ppm): 12.96 (s,1H, NH);
8.52 (s, 1H, H-20); 8.29 (dd, 1H, J = 8.4, 2.4, H-40); 8.19
(d, 1H, J = 8.4, H-60); 8.09–8.07 (m, 2H, H-4, H-7);
7.87–7.84 (m, 2H, CH, H-50); 7.67 (t, 1H, J = 7.3, H-5);
7.55 (t, 1H, J = 7.2, H-6). Anal. calcd for C17H10N4O3S2
(382.42): C, 53.39; H, 2.64; N, 14.65; S, 16.77. Found C,
53.52; H, 2.75; N, 14.46; S, 16.71%.
dis,
Staphylococcus
haemolyticus,
Streptococcus
agalactiae, Streptococcus faecalis, Streptococcus faecium
and Streptococcus pyogenes), Gram negative bacteria
(Escherichia coli SPA 27 and a clinical isolate of Hae-
mophilus influenzae), yeasts (Candida tropicalis ATCC
1369 and Saccharomyces cerevisiae ATCC 9763) and
moulds (Aspergillus niger ATCC 6275). The minimal
inhibitory concentrations (MIC, lg/mL) were defined as
the lowest concentrations of compound that completely
inhibited the growth of each strain. All compounds, dis-
solved in dimethylsulfoxide, were added to culture media
(Haemophilus Test Medium for H. influenzae, Tryptose
Phosphate Broth for S. pyogenes, Mueller Hinton Broth
for other bacteria and Sabouraud Liquid Medium for
fungi) to obtain final concentrations ranging from
100 lg/mL to 0.0015 lg/mL. The amount ofdimethylsulf-
oxide never exceeded 1% v/v. Inocula consisted of 5.104
bacteria/mL and 1.103 fungi/mL. The MICs were read
after incubation at 37 °C for 24 h (bacteria) and at
30 °C for 48 h (fungi). Media and media with 1% v/v
dimethylsulfoxide were employed as growth controls.
Ampicillin and miconazole were used as reference anti-
bacterial and antifungal drugs, respectively.
4.1.2.17. 2-(Benzo[d]isothiazol-3-ylimino)-5-(4-nitroben-
zylidene)thiazolidin-4-one 3g. Reaction time: 2 h. Yield:
72%; mp 287–289 °C (dioxane). TLC: eluent = methylene
chloride/ethanol 95/5. IR(KBr): m = 3114 (NH), 1708
1
(C@O), 1654 (C@N), 1511, 1344 (NO2) cmꢀ1. H NMR
(DMSO-d6 d, ppm): 12,94 (s,1H, NH); 8.37 (d, 2H,
J = 8.7, H-30, H-50); 8.18 (d, 1H, J = 8.1, H-4); 8.07 (d,
1H, J = 8.1, H-7); 7.89 (d, 2H, J = 8.7, H-20, H-60); 7.79
(s, 1H, CH); 7.65 (t, 1H, J = 7.8, H-5); 7.54 (t, 1H,
J = 7.8 H-6). Anal. calcd for C17H10N4O3S2 (382.42): C,
53.39; H, 2.64; N, 14.65; S, 16.77. Found C, 53.51; H,
2.69; N, 14.70; S, 16.46 %.
4.1.2.18. 2-(Benzo[d]isothiazol-3-ylimino)-5-(2-chloro-
benzylidene)thiazolidin-4-one 3h. Reaction time: 1 h.
Yield: 92%; mp 214–215 °C (dioxane). TLC: elu-
ent = methylene chloride/ethanol 95/5. IR(KBr): m =
1
3145 (NH), 1706 (C@O), 1590 (C@N) cmꢀ1. H NMR
(DMSO-d6 d, ppm): 12.93 (s, 1H, NH); 8.19 (d, 1H,
J = 8.4, H-4); 8.08 (d, 1H, J = 8.1, H-7); 7.87 (s, 1H,
CH); 7.72–7.47 (m, 6H, H-5, H-6, H-30, H-40, H-50, H-
60). Anal. calcd for C17H10ClN3OS2 (371.87): C, 54.91;
H, 2.71; N, 11.30; S, 17.25. Found C, 55.06; H, 2.74; N,
11.55; S, 17.29%.
To detect the type of antimicrobial activity, subcultures
were performed by transferring 100 lL of each mixture
remaining clear in 1 mL of fresh medium. The minimal
bactericidal concentrations (MBC, lg/mL) and the min-
imal fungicidal concentrations (MFC, lg/mL) were read
after incubation at 37 °C for 24 h and at 30 °C for 48 h,
respectively.
4.1.2.19. 2-(Benzo[d]isothiazol-3-ylimino)-5-(3-chloro-
benzylidene)thiazolidin-4-one 3i. Reaction time: 3 h.
Yield: 85%; mp 227–228 °C (ethanol). TLC: eluent =
methylene chloride/ethanol 95/5. IR(KBr): m = 3170
All experiments were performed in triplicate and re-
peated three times.
(NH), 1704 (C@O), 1610 (C@N) cmꢀ1
.
1H NMR
(DMSO-d6 d, ppm): 12.86 (s, 1H, NH); 8.17 (d, 1H, J =
8.1, H-4); 8.06 (d, 1H, J = 8.1, H-7); 7.74–7.72 (m, 2H,
H-20, CH); 7.69–7.61 (m, 3H, H-5, H-50, H-60); 7.59–
7.53 (m, 2H, H-6, H-40). Anal. calcd for C17H10ClN3OS2
(371.87): C, 54.91; H, 2.71; N, 11.30; S, 17.25. Found C,
55.29; H, 2.85; N, 11.00; S, 17.18 %.
4.3. Computational methods
The compounds were processed through the DEREK
software,19 which predicts the probability of toxicity
for a number of endpoints.
For the QSAR analysis, a large number of molecular
descriptors were calculated using TSAR,20 HYBOT21
and ADMEWORKS Predictor22 software. The ADME-
WORKS Predictor software includes the ADAPT soft-
ware developed by Jurs23 [ADAPT].
4.1.2.20. 2-(Benzo[d]isothiazol-3-ylimino)-5-(4-chloro-
benzylidene)thiazolidin-4-one 3j. Reaction time: 9 h. Yield:
91%; mp 208–209 °C (dioxane). TLC: eluent = methylene
chloride/ethanol 95/5. IR(KBr): m = 3120 (NH), 1718

3724
P. Vicini et al. / Bioorg. Med. Chem. 16 (2008) 3714–3724
7. Trivedi, V. P.; Undavia, N. K.; Trivedi, P. B. J. Indian
Chem. Soc. 2004, 81, 506.
The biological endpoint values were used in logarithmic
form, both because QSARs are considered to be free en-
ergy relationships, and because logarithmic values tend
to be less skewed. For the QSAR calculations the concen-
tration results (MIC) were converted from lg/mL to
mmol/L.
8. Andres, C. J.; Bronson, J. J.; D’Andrea, S. V.; Deshpande,
M. S.; Falk, P. J.; Grant-Young, K. A.; Harte, W. E.;
Robertson, J. G. Bioorg. Med. Chem. Lett. 2000, 10, 715.
9. Geronikaki, A.; Incerti, M.; Zani, F.; Vicini, P. Abstracts
of papers, III International Conference on the Chemistry
and Biological Activity of Nitrogen-Containing Hetero-
cycles, Moscow (Russia), June 20–23, 2006; Kartsev V. G.,
Ed.; ICSPF Press: Moscow, 2006; Vol. 1, pp 268–271.
10. Geronikaki, A.; Theophilidis, G. Eur. J. Med. Chem. 1992,
27, 709.
Using the MOBYDIGS software,24 we removed one of
each pair of descriptors with high collinearity, and used
the software’s genetic algorithm (GA) procedure to se-
lect the best 10 QSAR models for each endpoint, from
the remaining 256 descriptors.
11. Papadopoulou, C.; Geronikaki, A.; Hadjipavlou-Litina,
D. Farmaco 2005, 60, 969.
12. Vicini, P.; Amoretti, L.; Chiavarini, M.; Impicciatore, M.
Il Farmaco 1990, 45, 933.
13. Cesur, Z. Pharmazie 1987, 11, 716.
Acknowledgment
14. Dhal, P. N.; Achary, T. E.; Nayak, A. J. Indian Chem.
Soc. 1974, 51, 931.
The authors acknowledge the financial support of the
`
Ministero dell’Universita e della Ricerca, Italy, and are
grateful to the Centro Interdipartimentale Misure, Uni-
versity of Parma, for the use of NMR instruments.
`
15. Ottana, R.; Maccari, R.; Barreca, M. L.; Bruno, G.;
Rotondo, A.; Rossi, A.; Chiricosta, G.; Di Paola, R.;
Sautebin, L.; Cuzzocrea, S.; Vigorita, M. G. Bioorg. Med.
Chem. 2005, 13, 4243.
16. Topliss, J. G.; Costello, R. J. J. Med. Chem. 1972, 15,
1066.
References and notes
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D.; McDowell, R. M.; Gramatica, P. Environ. Health
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18. Jorgensen, J. H. et al. In Manual of Clinical Microbiology;
Tonover, F. C., Ed.; ASM Press: Washington, DC, 1995;
pp 1275–1434.
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19. DEREK. www.lhasalimited.org.
20. TSAR. www.accelrys.com.
4. Bondock, S.; Khalifa, W.; Fadda, A. A. Eur. J. Med.
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21. HYBOT. software.timtec.net/hybot-plus.htm.
22. ADMEWORKS Predictor. www.fqs.pl.
23. ADAPT. research.chem.psu.edu/pcjgroup/adapt.html.
24. MOBYDIGS. www.talete.mi.it/mobydigs.htm.
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