A facile microwave assisted green chemical synthesis of novel piperidino 2-thioxoimidazolidin-4-ones and their in vitro microbiological evaluation

Article abstract of DOI:10.3109/14756361003691878

A series of novel hybrid heterocyclic compounds, 3-(3-alkyl-2,6- diarylpiperin-4-ylidene)-2-thioxoimidazolidin-4-ones were synthesised and a comparative study was also carried out under microwave irradiation. The synthesised compounds were characterised by their melting points, elemental analysis, MS, FT-IR, one-dimensional NMR (1H, D₂O exchanged 1H and ¹³C), two dimensional HOMOCOSY and NOESY spectroscopic data. All the synthesised title compounds were screened for their in vitro antibacterial and antifungal activity against clinically isolated strains namely B. subtilis, M. luteus, S. typhii, S. paratyphii B, S. felxneri, P. vulgaris, A. niger, Mucor, Rhizopus and M. gypsuem and the results were discussed.

Full text of DOI:10.3109/14756361003691878

Journal of Enzyme Inhibition and Medicinal Chemistry, 2011; 26(1): 67–77
Copyright © 2011 Informa UK Ltd
ISSN 1475-6366 print/ISSN 1475-6374 online
DOI: 10.3109/14756361003691878
RESEARCH ARTICLE
A facile microwave assisted green chemical synthesis of novel
piperidino 2-thioxoimidazolidin-4-ones and their
in vitro microbiological evaluation
V. Kanagarajan, J. anusu, and M. Gopalakrishnan
Synthetic Organic Chemistry Laboratory, Department of Chemistry, Annamalai University, Annamalai Nagar, Tamil
Nadu, India
Abstract
A series of novel hybrid heterocyclic compounds, 3-(3-alkyl-2,6-diarylpiperin-4-ylidene)-2-thioxoimidazolidin-4-
ones were synthesised and a comparative study was also carried out under microwave irradiation. The synthesised
compounds were characterised by their melting points, elemental analysis, MS, FT-IR, one-dimensional NMR (1H,
D2O exchanged 1H and 13C), two dimensional HOMOCOSY and NOESY spectroscopic data. All the synthesised title
compounds were screened for their in vitro antibacterial and antifungal activity against clinically isolated strains
namely B. subtilis, M. luteus, S. typhii, S. paratyphii B, S. felxneri, P. vulgaris, A. niger, Mucor, Rhizopus and M. gypsuem and
the results were discussed.
Keywords: 3-(3-alkyl-2,6-diarylpiperin-4-ylidene)-2-thioxoimidazolidin-4-ones, NaHSO4.SiO2, microwave irradiation,
antibacterial activity, antifungal activity
Introduction
reactions can be accelerated due to selective absorp-
Sulphur analogs of hydantoins with one or both carbo-
nyl groups replaced by thiocarbonyl groups are called
as thiohydantoins. ere has been much interest in the
synthesis and properties of 2-thiohydantoin derivatives
used as synthetic intermediates with a wide range of
applications [1,2] as hypolipidaemic, anticarcinogenic,
antimutagenic, antithyroidal, antiviral (e.g. against her-
pes simplex virus, HSV, human immunodeficiency virus
(HIV), tuberculosis, antimicrobial (antifungal and anti-
bacterial), anti-ulcer and anti-inflammatory agents, as
well as pesticides. Additionally, 2-thiohydantoins have
been used as reference standards for the development
of C-terminal protein sequencing, as reagents for the
development of dyes and in textile printing, metal cation
complexation and polymerisation catalysis. For these
reasons, an alternative synthetic methodology is of para-
mount importance for the synthesis of 2-thiohydantoins.
Microwave irradiation is well known to promote the
synthesis of a variety of compounds, where chemical
tion of microwaves by polar molecules. Microwave-
induced rate acceleration technology [3–5] has become
a powerful tool in organic synthesis in view of the mild,
clean, and convenient methodology and the enhanced
selectivity of the reaction process in comparison to con-
ventional solution reactions, and the associated ease of
manipulation. e coupling of microwave irradiation
together with solid supports under solvent free condi-
tions have received considerable attention recently as it
is one of the novel approaches to eco-friendly chemistry.
Heterogeneous reactions [6–11] facilitated by supported
reagents on various mineral oxides have received special
attention in recent years.
Silica gel supported sodium hydrogen sulphate
(NaHSO4.SiO2), is a non-toxic and inexpensive catalyst,
which has been used for a variety of organic transforma-
tions [7, 9–11]. Baliah et al. have reviewed the importance
of piperidin-4-ones as intermediates in the synthesis of
several physiologically active compounds [12,13]. In
Address for Correspondence: M. Gopalakrishnan, Synthetic Organic Chemistry Laboratory, Department of Chemistry, Annamalai
University, Annamalai Nagar, Tamil Nadu, India. Tel: + 91 4144 228 233; Email: profmgk@yahoo.co.in
(Received 25 September 2009; revised 18 January 2010; accepted 10 February 2010)
67

68
V. Kanagarajan et al.
corollary of the interesting biological and pharmaceuti-
cal properties and synthetic utility, there is substantial
interest in piperidones; this substructure containing
compounds are widely present in numerous alkaloids
and synthetically derived molecules of biological impor-
tance [14].
In view of our continued interest in the development
of simpler and more convenient synthetic routes for
achieving biologically challenging hybrid heterocyclic
systems [3–11], we have reported a simple method to
synthesise some piperidones based on 2-thiohydan-
toins namely 3-(3-alkyl-2,6-diarylpiperin-4-ylidene)-
2-thioxoimidazolidin-4-ones with good yields by the
reaction of 3-alkyl-2,6-diarylpiperidin-4-one thiosemi-
carbazones with chloroethyl acetate catalysed by
NaHSO4.SiO2 under microwave irradiation in dry media
and their in vitro antibacterial and antifungal activities
against clinically isolated bacterial and fungal strains
were evaluated.
hydrochloride was dispersed in acetone and concen-
trated aqueous ammonia added dropwise until a clear
solution was obtained. e clear solution was poured
into cold water and the solid precipitation was collected
and recrystallised from ethanol.
General procedure for the synthesis of 3-alkyl-2,
6-diarylpiperidin-4-one thiosemicarbazones 16–30
A mixture of the respective 3-substituted-2,6-diarylpi-
peridin-4-ones 1–15 (0.01 mol) and thiosemicarbazide
(0.01 mol) in ethanol (60 mL) was refluxed for 2 h on a
steambath.Itwascooledandthentheseparatedsolidwas
filtered and washed with water. e solid was subjected
to column chromatography using benzene:chloroform
(1:1) as eluent to afford compounds 16–30.
General procedure for the synthesis of 3-(3-alkyl-2,
6-diarylpiperin-4-ylidene)-2-thioxoimidazolidin-4-
ones 31–45
To a well stirred solution of 3-alkyl-2,6-diphenylpiperi-
din-4-one thiosemicarbazones 31–45 (0.01 mmol) and
anhydrous sodium acetate (0.01 mol) in 30 mL of ethanol,
chloroethyl acetate (0.01 mmol) in 15 mL of ethanol was
added drop wise through a funnel for about 10min and
the reaction mixture was refluxed for 4 h. After comple-
tion of the reaction, the reaction mixture was poured
into ice cold water and the solid mass was collected and
recrystallised twice from ethanol.
Experimental
General remarks
TLC was used to assess the reactions and the purity
of the products. All the reported melting points were
taken in open capillaries and were uncorrected. A
Biotage Initiator microwave synthesiser, Sweden a sci-
entific microwave oven was used for the irradiation.
IR spectra were recorded in KBr (pellet forms) on a
ermo Nicolet-Avatar–330 (ermo Fisher Scientific
Inc., Waltham, MA) FT-IR spectrophotometer (Bruker
Biospin International, Ag, Aegeristrasse, Switzerland)
and note worthy absorption values (cm−1) were listed.
One dimensional 1H and 13C NMR spectra were recorded
at 400 MHz and 100 MHz respectively on Bruker AMX
400 NMR spectrometer (Bruker Biospin International,
Ag, Aegeristrasse, Switzerland) using DMSO-d as sol-
vent. Two dimensional HOMOCOSY and NOESY spec-
tra were recorded at 500 MHz on Bruker DRX 500 NMR
spectrometer using DMSO-d as solvent. e electron
spray impact (ESI) positive (+ve) mass (MS) spectra
were recorded on a Bruker Daltonics LC-MS spectrom-
eter. Satisfactory microanalysis was obtained on Carlo
Erba 1106 CHN analyser (ermo Fisher Scientific Inc.,
Waltham, MA).
General procedure for the microwave assisted
synthesis of 3-(3-alkyl-2,6-diarylpiperin-4-ylidene)-2-
thioxoimidazolidin-4-ones catalysed by NaHSO4.SiO2
31–45
A mixture containing 3-alkyl-2,6-diphenylpiperidin-4-
ones 1–15 (0.01 mmol), thiosemicarbazide (0.01 mmol),
and chloroethyl acetate (0.01 mmol) and NaHSO4.SiO2
(25 mg) was added in an alumina bath, mixed thoroughly
with the aid of a glass rod (10 s) and then irradiated in
a microwave oven for 2–4 min. at 320 W (monitored
by TLC). After completion of the reaction, the reac-
tion mixture was extracted with dichloromethane
(3 × 5 mL). e catalyst and other solid wastes were
removed by filtration. e combined organic layer was
washed with water three times and then dried over
anhydrous MgSO4. e organic layer was concentrated
in vacuo to furnish the crude products and recrystallised
twice from ethanol.
General procedure for the synthesis of 3-alkyl-2,
6-diarylpiperidin-4-ones 1–15
Spectroscopic data
3-(2,6-diphenylpiperidin-4-ylideneamino)-2-
thioxoimidazolidin-4-one 31
A mixture of ammonium acetate (0.1 mol), the respec-
tive substituted benzaldehyde (0.2 mol) and appropriate
ketone (0.1 mol) (s.d. Fine chemicals, Mumbai, India)
were dissolved in 95% alcohol (80 mL) and the solution
was heated on a hot plate with gentle swirling until the
colour of the mixture changed to orange. e mixture
was cooled and poured into diethyl ether (100 mL) and
concentrated hydrochloric acid (14 mL) was added. e
precipitated hydrochloride was collected by filtration
and recrystallised from the ethanol-ether mixture. e
Irradiation reaction time = 3 min; IR (KBr) (cm−1): 3400,
3306, 3060, 3029, 2980, 2896, 2797, 1728, 1635, 1598,
1215, 701, 758, 1041; 1H NMR (δ ppm): 1.97–2.05 (m, 1H,
H3a), 2.37–2.41 (dd, 1H, H3e, J3e,3a = 13.64 Hz, J3e,2a = 2.96
Hz); 2.43–2.52 (m, 1H, H5a), 2.83 (s, 1H, NH of piperi-
dine), 3.62–3.66 (dd, H5e, J5e,5a = 2.96 Hz, J5e,6a = 13.52 Hz),
3.8 (s, 2H, CH2 of imidazolidine), 3.88–3.92 (dd, 1H, H2a,
Journal of Enzyme Inhibition and Medicinal Chemistry

In vitro microbiological evaluation of piperidino 2-thioxoimidazolidin-4-ones
69
J
J
2a,3e = 3.08 Hz, J2a,3a = 11.76 Hz), 4.15–4.19 (dd, 1H, H6a,
6a,5e = 3.2 Hz, J6a,5a = 11.88 Hz), 7.23–7.5 (m, 10H, Ar-H’s),
3-(2,6-dip-tolylpiperidin-4-ylideneamino)-2-
thioxoimidazolidin-4-one 35
11.78 (s, NH of imidazolidine); In the D2O exchanged 1H
NMR spectrum, two peaks at 2.83 ppm and 11.78 ppm
which resonances due to NH of piperidine and imidazo-
lidine respectively disappeared; 13C NMR (δ ppm): 29.6
C-3, 37.3 C-5, 43.6 CH2 of imidazolidine, 60.2 C-2, 61.1
C-6, 126.5–128.1 Ar-C’s, 144, 144.1 ipso-C, 163.1 C=N,
167.6 C=O, 173.8 C=S.
Irradiation reaction time = 3 min; IR (KBr) (cm−1): 3403,
3308, 3063, 3018, 2960, 2921, 2850, 1727, 1631, 1600, 1249,
1
1023, 828, 742, 524; H NMR (δ ppm): 1.97–2.05 (m, 1H,
H3a), 2.18 (s, 6H, CH3 at the phenyl rings), 2.34–2.38 (dd,
1H, H3e, J3e,3a = 13.5 Hz, J3e,2a = 2.97 Hz); 2.45–2.52 (m, 1H,
H5a), 2.84 (s, 1H, NH of piperidine), 3.49–3.52 (dd, 1H, H5e,
J5e,5a = 3.14 Hz, J5e,6a = 13.42 Hz), 3.76 (s, 2H, CH2 of imida-
zolidine), 3.88–3.9 (dd, 1H, H2a, J2a,3e = 3.14 Hz, J2a,3a = 11.66
Hz), 4.14–4.18 (dd, 1H, H6a, J6a,5e = 3.07 Hz, J6a,5a = 11.66 Hz),
7.17–7.39 (m, 8H, Ar-H’s), 11.76 (s, 1H, NH of imidazoli-
dine); 13C NMR (δ ppm): 22.2 -CH3 at the phenyl rings,
30.3 C-3, 37.2 C-5, 43.3 CH2 of imidazolidine, 60.1 C-2, 61
C-6, 127.1–143.9 Ar-C’s, 144.1, 147.2, ipso-C, 162.8 C=N,
167.5 C=O, 173.5 C=S.
3-(2,6-bis(4-fluorophenyl)piperidin-4-ylideneamino)-2-
thioxoimidazolidin-4-one 32
Irradiation reaction time = 4 min; IR (KBr) (cm−1): 3430,
3317, 3076, 3030, 2956, 2924, 2854, 1717, 1641, 1604, 1092,
1
835, 733, 519; H NMR (δ ppm): 1.98–2.05 (m, 1H, H3a),
2.39–2.44 (dd, 1H, H3e, J3e,3a = 13.52 Hz, J3e,2a = 2.96 Hz);
2.44–2.49 (m, 1H, H5a), 2.86 (s, 1H, NH of piperidine),
3.51–3.55 (dd, 1H, H5e, J5e,5a = 2.96 Hz, J5e,6a = 13.4 Hz),
3.77 (s, 2H, CH2 of imidazolidine), 3.85–3.89 (dd, 1H,
H2a, J2a,3e = 2.96 Hz, J2a,3a = 11.76 Hz), 4.16–4.2 (dd, 1H, H6a,
3-(3-methyl-2,6-diphenylpiperidin-4-ylideneamino)-2-
thioxoimidazolidin-4-one 36
Irradiation reaction time=2min; IR (KBr) (cm−1): 3420,
3311, 3063, 3031, 2978, 2933, 1713, 1634, 1600, 1232,
J
6a,5e = 3.32 Hz, J6a,5a = 11.96 Hz), 7.18–7.37 (m, 8H, Ar-H’s),
11.81 (s, 1H, NH of imidazolidine); 13C NMR (δ ppm):
30.1 C-3, 38.2 C-5, 43.4 CH2 of imidazolidine, 61.8 C-2,
62.9 C-6, 114.3–142.6 Ar-Cs, 142.9, 159.6 ipso-C, 162 C=N,
166.7 C=O, 173.7 C=S.
1
755, 702; H NMR (δ ppm): 0.77–0.79 (d, 3H, CH3 at C-3,
JCH3,3a =6.45 Hz), 2.05–2.11 (m, 1H, H5a), 2.55–2.59 (m, 1H,
H3a), the signal for 1H, NH of piperidine merged with water
peak,2.69–2.79(m,1H,H5e),3.45–3.48(d,1H,H2a,J2a,3a =9.98
Hz), 3.54–3.58 (dd, 1H, H6a, J6a,5e =2.5 Hz, J6a,5a =12.95 Hz),
3.76 (s, 2H, CH2 of imidazolidine), 7.24–7.47 (m, 10H,
Ar-H’s), 11.71 (s, NH of imidazolidine); 13C NMR (δ ppm):
11.9 -CH3 at C-3, 32.5 C-5, 37.3 C-3, 44.4 CH2 of imidazo-
lidine, 60.4 C-6, 68.7 C-2, 126.5–128.1 Ar-C’s, 144.9, 144,
ipso-C, 163.1 C=N, 167.5 C=O, 173.8 C=S.
3-(2,6-bis(4-chlorophenyl)piperidin-4-ylideneamino)-2-
thioxoimidazolidin-4-one 33
Irradiation reaction time = 4 min; IR (KBr) (cm−1): 3400,
3309, 3065, 3032, 2978, 2923, 2852, 1724, 1628, 1595, 1195,
1
1014, 826, 722, 676, 634; H NMR (δ ppm): 1.98–2.05 (m,
1H, H3a), 2.38–2.42 (dd, 1H, H3e, J3e,3a = 13.52 Hz, J3e,2a = 2.98
Hz); 2.43–2.48 (m, 1H, H5a), 2.79 (s, 1H, NH of piperi-
dine), 3.52–3.56 (dd, 1H, H5e, J5e,5a = 3.08 Hz, J5e,6a = 13.42
Hz), 3.78 (s, 2H, CH2 of imidazolidine), 3.87–3.91 (dd, 1H,
H2a, J2a,3e = 3.08 Hz, J2a,3a = 11.76 Hz), 4.15–4.19 (dd, 1H, H6a,
3-(2,6-bis(4-fluorophenyl)-3-methylpiperidin-4-
ylideneamino)-2-thioxoimidazolidin-4-one 37
Irradiation reaction time = 3 min; IR (KBr) (cm−1):
3412, 3304, 3071, 3030, 2985, 2931, 2869, 1717, 1635,
1597, 1221, 1030, 535, 836, 766; 1H NMR (δ ppm):
0.78–0.8 (d, 3H, CH3 at C-3, JCH3,3a = 6.58 Hz), 2.07–2.09
(m, 1H, H5a), 2.54–2.59 (m, 1H, H3a), the signal for 1H,
NH of piperidine merged with water peak, 2.67–2.79
(m, 1H, H5e), 3.46–3.48 (d, 1H, H2a, J2a,3a = 10.61 Hz),
J6a,5e = 3.14 Hz, J6a,5a = 11.70 Hz), 7.3–7.58 (m, 8H, Ar-H’s),
11.79 (s, 1H, NH of imidazolidine); 13C NMR (δ ppm): 30
C-3, 38.8 C-5, 43.5 CH2 of imidazolidine, 60.9 C-2, 61.2
C-6, 126.7–140.4 Ar-C’s, 144.7, 145.3 ipso-C, 163.1 C=N,
166.8 C=O, 173.5 C=S.
3.54–3.58 (dd, 1H, H6a,
J6a,5e = 2.46 Hz, J6a,5a = 12.46
3-(2,6-bis(4-methoxyphenyl)piperidin-4-ylideneamino)-2-
thioxoimidazolidin-4-one 34
Hz), 3.78 (s, 2H, CH2 of imidazolidine), 7.12–7.51 (m,
8H, Ar-H’s), 11.72 (s, NH of imidazolidine); 13C NMR
(δ ppm): 11.8 -CH3 at C-3, 32.5 C-5, 37.2 C-3, 44.5 CH2
of imidazolidine, 61 C-6, 67.7 C-2, 114.6–160.7 Ar-C’s,
162.4, 162.5, ipso-C, 163.4 C=N, 169.2 C=O, 173.9 C=S.
Irradiation reaction time = 3 min; IR (KBr) (cm−1): 3400,
3306, 3065, 3020, 2962, 2924, 2853, 1728, 1630, 1601,
1251, 1031, 830, 749, 527; 1H NMR (δ ppm): 1.97–2.04 (m,
1H, H3a), 2.35–2.39 (dd, 1H, H3e, J3e,3a = 13.52 Hz, J3e,2a = 2.96
Hz); 2.43–2.5 (m, 1H, H5a), 2.89 (s, 1H, NH of piperidine),
3.48–3.53 (dd, 1H, H5e, J5e,5a = 3.16 Hz, J5e,6a = 13.4 Hz),
3.59 (s, 6H, OCH3 at the phenyl rings), 3.72 (s, 2H, CH2
of imidazolidine), 3.87–3.91 (dd, 1H, H2a, J2a,3e = 3.16 Hz,
3-(2,6-bis(4-chlorophenyl)-3-methylpiperidin-4-
ylideneamino)-2-thioxoimidazolidin-4-one 38
Irradiation reaction time = 4 min; IR (KBr) (cm−1): 3429,
3282, 3070, 3032, 2985, 2931, 1718, 1625, 1592, 1210,
1
J
J
2a,3a = 11.68 Hz), 4.13–4.17 (dd, 1H, H6a, J6a,5e = 3.08 Hz,
6a,5a = 11.68 Hz), 7.19–7.42 (m, 8H, Ar-H’s), 11.78 (s, 1H,
1017, 897, 823; H NMR (δ ppm): 0.77–0.79 (d, 3H, CH3
at C-3, JCH3,3a = 6.57 Hz), 2.01–2.07 (m, 1H, H5a), 2.53–2.57
(m, 1H, H3a), the signal for 1H, NH of piperidine merged
with water peak, 2.68–2.8 (m, 1H, H5e), 3.46–3.48 (d, 1H,
H2a, J2a,3a = 10.82 Hz), 3.54–3.58 (dd, 1H, H6a, J6a,5e = 2.44
Hz, J6a,5a = 12.45 Hz), 3.9 (s, 2H, CH2 of imidazolidine),
NH of imidazolidine); 13C NMR (δ ppm): 30.1 C-3, 37
C-5, 43.1 CH2 of imidazolidine, 54.2 -OCH3 at the phenyl
rings, 60.2 C-2, 61.1 C-6, 127.3–144.0 Ar-C’s, 144.1, 159.9,
ipso-C, 162.3 C=N, 167.7 C=O, 173.8 C=S.
© 2011 Informa UK, Ltd.

70
V. Kanagarajan et al.
7.37–7.49 (m, 8H, Ar-H’s), 11.74 (s, NH of imidazolidine);
13C NMR (δ ppm): 11.8 -CH3 at C-3, 31.8 C-5, 36.8 C-3, 44.3
CH2 of imidazolidine, 61 C-6, 67.7 C-2, 128-131.7 Ar-C’s,
141.8, 142.8 ipso-C, 160.8 C=N, 166.9 C=O, 171.5 C=S.
Hz), 2.8 (s, 1H, H1); 3.19–3.27 (m, 1H, H5a), 3.78 (s, 1H, H2a),
3.92 (s, 2H, CH2 of imidazolidine), 4.15–4.19 (dd, 1H, H6a,
J
6a,5e =3.6 Hz, J6a,5a =14.44 Hz), 7.3–7.59 (m, 8H, Harom), 11.79
(s, 1H, NH of imidazolidine); 13C NMR (δ ppm): 20.3, 20.7
two CH3 at C-4, 43.5 CH2 of imidazolidine, 46.4 C-5, 48.8
C-3, 61 C-6, 69.9 C-2, 113.9–140.4 Arom-C’s, 160.4, 160.6
ipso Cs, 163.3 C=N, 166.9 C=O, 173.8 C=S.
3-(2,6-bis(4-methoxyphenyl)-3-methylpiperidin-4-
ylideneamino)-2-thioxoimidazolidin-4-one 39
Irradiation reaction time = 2 min; IR (KBr) (cm−1): 3426,
3286, 3080, 2981, 2927, 1722, 1627, 1594, 1200, 1025, 897,
3-(2,6-bis(4-chlorophenyl)-3,3-dimethylpiperidin-4-
ylideneamino)-2-thioxoimidazolidin-4-one 43
1
812, 744, 527; H NMR (δ ppm): 0.78–0.8 (d, 3H, CH3 at
C-3, JCH3,3a = 6.45 Hz), 2.04–2.08 (m, 1H, H5a), 2.55–2.59
(m, 1H, H3a), the signal for 1H, NH of piperidine merged
with water peak, 2.69–2.79 (m, 1H, H5e), 3.46–3.48 (d, 1H,
H2a, J2a,3a = 10.72 Hz), 3.54–3.58 (dd, 1H, H6a, J6a,5e = 2.56 Hz,
Irradiation reaction time = 4 min; IR (KBr) (cm−1): 3400,
3306, 3093, 3030, 2974, 2928, 2852, 1722, 1630, 1203,
1
1015, 827, 766, 523; H NMR (δ ppm): 0.98 (s, 3H, CH3
at C-4), 1.28 (s, 3H, CH3 at C-4), 2.54–2.58 (dd, 1H, H5e,
J
6a,5a = 12.87 Hz), 3.28 (s, 6H, OCH3 at the phenyl rings),
J5e,5a = 13.92 Hz, J5e,6a = 3.64 Hz), 2.81 (s, 1H, H1); 3.18–3.25
3.78 (s, 2H, CH2 of imidazolidine), 6.86–7.36 (m, 8H,
Ar-H’s), 11.82 (s, NH of imidazolidine); 13C NMR (δ ppm):
11.9 -CH3 at C-3, 32.5 C-5, 37.3 C-3, 44.6 CH2 of imidazo-
lidine, 54.9 -OCH3 at the phenyl rings, 60.5 C-6, 68.1 C-2,
127.6–158.4 Ar-C’s, 160.5, 163.1 ipso-C, 166.9 C=N, 169.7
C=O, 173.9 C=S.
(m, 1H, H5a), 3.77 (s, 1H, H2a), 3.94 (s, 2H, CH2 of imidazo-
lidine), 4.16–4.21 (dd, 1H, H6a, J6a,5e = 3.64 Hz, J6a,5a = 14.48
Hz), 7.37–7.89 (m, 8H, Harom), 11.85 (s, 1H, NH of imidazo-
lidine); 13C NMR (δ ppm): 20.2, 20.8 two CH3 at C-4, 43.4
CH2 of imidazolidine, 46 C-5, 48.5 C-3, 61.4 C-6, 68.6 C-2,
113.4–139.2 Arom-C’s, 158.8, 159.2 ipso Cs, 163.2 C=N,
165.9 C=O, 173.5 C=S.
3-(3-methyl-2,6-dip-tolylpiperidin-4-ylideneamino)-2-
thioxoimidazolidin-4-one 40
3-(2,6-bis(4-methoxyphenyl)-3,3-dimethylpiperidin-4-
ylideneamino)-2-thioxoimidazolidin-4-one 44
Irradiation reaction time=2min; IR (KBr) (cm−1): 3441,
3312, 3229, 3060, 2971, 2931, 1727, 1634, 1607, 1247, 1031,
542, 833, 753; 1H NMR (δppm): 0.78–0.8 (d, 3H, CH3 at C-3,
Irradiation reaction time = 3 min; IR (KBr) (cm−1): 3448,
3317, 3098, 3027, 2976, 2924, 2861, 1702, 1626, 1211,
1
JCH3,3a =6.38 Hz), 2.01–2.07 (m, 1H, H5a), 2.19 (s, 6H, CH3 at
1028, 818, 747, 519; H NMR (δ ppm): 0.98 (s, 3H, CH3
the phenyl rings), 2.54–2.58 (m, 1H, H3a), the signal for 1H,
NH of piperidine merged with water peak, 2.69–2.79 (m,
1H, H5e), 3.44–3.47 (d, 1H, H2a, J2a,3a =10.85 Hz), 3.54–3.58
(dd, 1H, H6a, J6a,5e =2.55 Hz, J6a,5a =12.89 Hz), 3.89 (s, 2H,
CH2 of imidazolidine), 7.1–7.33 (m, 8H, Ar-H’s), 11.75 (s,
NH of imidazolidine); 13C NMR (δ ppm): 11.9 -CH3 at C-3,
20.6 -CH3 at the phenyl rings, 32.5 C-5, 37 C-3, 44.5 CH2
of imidazolidine, 60.2 C-6, 68.4 C-2, 126.3–136.2 Ar-C’s,
139.9, 140.9 ipso-C, 166.8 C=N, 169.6 C=O, 171.5 C=S.
at C-4), 1.16 (s, 3H, CH3 at C-4), 2.54–2.58 (dd, 1H, H5e,
J5e,5a = 13.94 Hz, J5e,6a = 3.66 Hz), 2.76 (s, 1H, H1); 3.19–3.25
(m, 1H, H5a), 3.56 (s, 6H, OCH3 at the phenyl rings),3.79
(s, 1H, H2a), 3.91 (s, 2H, CH2 of imidazolidine), 4.17–4.22
(dd, 1H, H6a, J6a,5e = 3.66 Hz, J6a,5a = 14.5 Hz), 7.19–7.76 (m,
8H, Harom), 11.79 (s, 1H, NH of imidazolidine); 13C NMR
(δ ppm): 20.3, 20.7 two CH3 at C-4, 43.5 CH2 of imidazoli-
dine, 46.5 C-5, 48.9 C-3, 54 -OCH3 at the phenyl rings, 61
C-6, 68.2 C-2, 126.4–141.1 Arom-C’s, 141.3, 142.2 ipso C’s,
163.1 C=N, 166.8 C=O, 173.8 C=S.
3-(3,3-dimethyl-2,6-diphenylpiperidin-4-ylideneamino)-2-
thioxoimidazolidin-4-one 41
3-(3,3-dimethyl-2,6-dip-tolylpiperidin-4-ylideneamino)-2-
thioxoimidazolidin-4-one 45
Irradiation reaction time=2min; IR (KBr) (cm−1): 3496,
3307, 3060, 3027, 2973, 2926, 2852, 1719, 1625, 1206, 1028,
Irradiation reaction time=2min; IR (KBr) (cm−1): 3450,
3318, 3093, 3022, 2974, 2925, 2864, 1705, 1628, 1209, 1023,
1
758, 703; H NMR (δ ppm): 0.97 (s, 3H, CH3 at C-4), 1.19
1
(s, 3H, CH3 at C-4), 2.52–2.56 (dd, 1H, H5e, J5e,5a =13.96 Hz,
817, 749, 516; H NMR (δ ppm): 0.99 (s, 3H, CH3 at C-4),
J
5e,6a =3.64 Hz), 2.75 (s, 1H, H1); 3.18–3.25 (m, 1H, H5a), 3.72
1.18 (s, 3H, CH3 at C-4), 2.24 (s, 6H, CH3 of phenyl rings),
2.55–2.59 (dd, 1H, H5e, J5e,5a =13.96 Hz, J5e,6a =3.68 Hz), 2.77
(s, 1H, H1); 3.19–3.26 (m, 1H, H5a), 3.8 (s, 1H, H2a), 3.92 (s,
2H, CH2 ofimidazolidine), 4.18–4.23(dd, 1H, H6a, J6a,5e =3.68
Hz, J6a,5a =14.52 Hz), 7.21–7.8 (m, 8H, Harom), 11.8 (s, 1H, NH
of imidazolidine); 13C NMR (δ ppm): 20.3, 20.7 two CH3 at
C-4, 22.7 (-CH3 of phenyl rings), 43.5 CH2 of imidazolidine,
46.5 C-5, 48.9 C-3, 61 C-6, 68.2 C-2, 126.4–141.1 Arom-C’s,
141.3, 142.2 ipso Cs, 163.1 C=N, 166.8 C=O, 173.8 C=S.
(s, 1H, H2a), 3.91 (s, 2H, CH2 of imidazolidine), 4.13–4.18
(dd, 1H, H6a, J6a,5e =3.64 Hz, J6a,5a =14.44 Hz), 7.21–7.53 (m,
10H, Harom), 11.8 (s, 1H, NH of imidazolidine); 13C NMR (δ
ppm): 20.4, 20.8 two CH3 at C-4, 43.5 CH2 of imidazolidine,
46.4 C-5, 48.8 C-3, 61 C-6, 69.8 C-2, 126.5–140.3 Arom-C’s,
143.5, 144.2 ipso Cs, 163.1 C=N, 167.3 C=O, 173.8 C=S.
3-(2,6-bis(4-fluorophenyl)-3,3-dimethylpiperidin-4-
ylideneamino)-2-thioxoimidazolidin-4-one 42
Irradiation reaction time=3min; IR (KBr) (cm−1): 3480,
3309, 3147, 3072, 2975, 2923, 1719, 1628, 1222, 836, 702, 656,
525; 1H NMR (δ ppm): 0.96 (s, 3H, CH3 at C-4), 1.18 (s, 3H,
CH3 at C-4), 2.53–2.58 (dd, 1H, H5e, J5e,5a =13.8 Hz, J5e,6a =3.6
Microbiology
Materials
All the clinically isolated bacterial strains namely Bacillus
subtilis,Micrococcusluteus,Salmonellatyphii,Salmonella
Journal of Enzyme Inhibition and Medicinal Chemistry

In vitro microbiological evaluation of piperidino 2-thioxoimidazolidin-4-ones
71
paratyphii-B, Shigella felxneri, Proteus vulgaris and fun-
gal strains namely Aspergillus niger, Mucor, Rhizopus and
Microsporum gypsuem, were obtained from the Faculty
of Medicine, Annamalai University, Annamalainagar-608
002, Tamil Nadu, India.
e NaHSO4.SiO2 catalyst was shown to be one of the
most efficient MW absorbers with a very high specific-
ity to MW heating. It was able to reach a temperature of
110°C after 3 minutes of irradiation in a domestic oven
(320 W). A mere 25 mg of NaHSO4.SiO2 catalyst to 0.01
moles of substrates was the most acceptable ratio in
terms of efficiency and safety; a power level of 320 watts
was the most suitable. Moreover, the catalyst assists in
the removal of water molecules and facilitates the con-
densation reaction to form the title compounds.
In vitro antibacterial and antifungal activity
e MIC as μg/mL values was determined by a two-fold
serial dilution method [15]. e respective test com-
pounds 31–45 were dissolved in dimethyl sulphoxide
(DMSO) to obtain a 1 mg mL−1 stock solution. Seeded
broth (broth containing microbial spores) was prepared
in nutrient broth (NB) from 24 h old bacterial cultures
on nutrient agar (Hi-media, Mumbai) at 37 1°C while
fungal spores from 1 to 7 days old Sabouraud’s agar
(Hi-media, Mumbai) slant cultures were suspended in
Sabouraud’s dextrose broth (SDB). e colony form-
ing units (CFU) of the seeded broth were determined
by a plating technique and adjusted within the range of
104–105 CFU/mL. e final inoculum size was 105 CFU/
mL for the antibacterial assay and 1.1–1.5× 102 CFU/mL
for the antifungal assay. e testing was performed at pH
7.4 0.2 for bacteria (NB) and at pH 5.6 for fungi (SDB).
Exactly 0.4 mL of the test compound solution was added
to 1.6 mL of the seeded broth to form the first dilution.
One milliliter of this was diluted with a further 1mL of
seeded broth to give the second dilution and so on till six
such dilutions were obtained. A set of assay tubes con-
taining only the seeded broth was kept as a control. e
tubes were incubated in biochemical oxygen demand
(BOD) (Sigma Instruments, Chennai, India) incubators
at 37 1°C for bacteria and 28 1°C for fungi. MICs were
recorded by visual observations after 24 h (for bacteria)
and 72–96 h (for fungi) of incubation. Penicillin was used
as the standard for bacterial studies and amphotericin B
was used as the standard for fungal studies.
e conversion of 3-alkyl-2,6-diarylpiperidin-4-ones
1–15 into 3-(3-alkyl-2,6-diarylpiperin-4-ylidene)-2-
thioxoimidazolidin-4-ones 31–45 using this method
was followed via the 3-alkyl-2,6-diarylpiperidin-4-one
thiosemicarbazone derivatives 16–31. In the first step,
3-alkyl-2,6-diarylpiperidin-4-ones were converted to
their respective thiosemicarbazones and rapidly rear-
range to give 3-(3-alkyl-2,6-diarylpiperin-4-ylidene)-2
-thioxoimidazolidin-4-ones 31–45 in the second step.
e attempt to isolate the respective thiosemicarba-
zones from the reaction mixture was unsuccessful. e
formation of 3-(3-alkyl-2,6-diarylpiperin-4-ylidene)-2-
thioxoimidazolidin-4-ones 31–45 via the thiosemicar-
bazones were confirmed by the same kind of reactions
carried out using the NaHSO4.SiO2 catalyst and 3-alkyl-
2,6-diarylpiperidin-4-ones thiosemicarbazones 16–30
and under microwave irradiation for 2–4 min. e prod-
ucts formed from the above two methods were found
to be the same. e structures of all the synthesised
compounds 3-(3-alkyl-2,6-diarylpiperin-4-ylidene)-2
-thioxoimidazolidin-4-ones 31-45 were characterised
on the basis of their mps, elemental analysis, FT-IR,
MS, one-dimensional NMR (1H, 13C), two dimensional
HOMOCOSY and NOESY spectra which were in good
agreement with the proposed structures.
Spectral assignments for the newly synthesised
compound 31
Results and discussion
In order to investigate the spectral assignments, com-
pound 31 was chosen as a representative compound.
e IR spectrum of 3-(2,6-diphenylpiperidin-4-
ylideneamino)-2-thioxoimidazolidin-4-one 31 shows
characteristic frequencies at 1728, 1215 cm−1 were due
to the presence of carbonyl and thiocarbonyl groups.
e absorption frequencies shown in the region of
3300-3426 cm-1 suggested the presence of -NH groups.
In addition, the absorption frequency at 1635 cm−1 was
due to C=N stretching vibration. e mass spectrum of
compound 31 shows a molecular ion peak at an m/z of
365.25 (M+•+1) which was consistent with the proposed
molecular formula of 31. e elemental analysis (Ccal
65.87, Cobs 65.91; Hcal 5.53, Hobs 5.5; Ncal 15.37, Nobs
15.33) were consistent with the proposed molecular for-
mula (C20H20N40S) of 31.
In the current work, the classical synthetic strategy
adopted to obtain the a new series of hybrid hetero-
cycles comprising both piperidine and thiohydantoin
nuclei namely 3-(3-alkyl-2,6-diarylpiperin-4-ylidene)-
2-thioxoimidazolidin-4-ones 31–45 was synthesised
by the treatment of the respective thiosemicarbazones
16–30 with chloroethyl acetate and anhydrous sodium
acetate in refluxing ethanol for 4 h. e synthetic route
for the formation of compounds 31–45 is given in
Scheme 1. e physical and analytical data is in Table
1. In order to avoid the use of solvent, to minimise the
reaction time and to improve the yield of the product,
a ‘one-pot’ reaction procedure was developed by the
treatment of 3-alkyl-2,6-diarylpiperidin-4-ones 1–15,
thiosemicarbazide and chloroethyl acetate in the ratio
of 1:1:1 the same reaction was also performed under
microwave irradiation in a scientific microwave oven
using a catalytic amount of NaHSO4.SiO2 (25 mg) to
afford the title compounds in high yields in dry media.
1
e assignment of signals in the H NMR spectrum
of compound 31 were based on total widths and spin
multiplicities. ere were two double doublet centered
at 3.9 ppm and 4.17 ppm. Each signal corresponded to
© 2011 Informa UK, Ltd.

72
V. Kanagarajan et al.
S
O
H2N
N
S
R1
R2
H2N
NH
N
H
NH2
EtOH
reflux,2h
Reaction Pathway-1
N
H
R1
R2
R2
(1-15)
R1
Compounds
X
X
X
N
H
S
1,16,31
2,17,32
3,18,33
4,19,34
5,20,35
6,21,36
7,22,37
8,23,38
9,24,39
10,25,40
11,26,41
12,27,42
13,28,43
14,29,44
15,30,45
H
H
H
H
H
F
(16-30)
H2N
H
H
Cl
Reaction Pathway-2
N
H
NH2
CH3
X
X
H
H
OCH3
CH3
H
NaHSO4.SiO2
MW,320W
2-4min.
H
H
O
O
ClCH2CO2Et
O
O
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
Anhyd.CH3COONa
EtOH
CH3
H
F
Cl
OCH3
CH3
H
F
Cl
OCH3
H
reflux,4h
Cl
H
Cl
H
CH3
O
N
O
CH3
CH3
CH3
5
2
5
2
4
4
3
1
HN
1
HN
3
N
N
CH3 CH3 CH3
N
S
S
R1
R2
3
R1
R2
3
4
1
4
1
5
6
5
2
2
6
N
N
H
H
(31-45)
(31-45)
X
X
X
X
Scheme 1. A facile synthetic route for the synthesis of 3-(3-substituted-2,6-diarylpiperidin-4-ylideneamino)-2-thioxoimidazolidin-4-ones.
one proton. ese two signals were due to the benzylic
protons H2a and H6a (3.9/H2a, 4.17/H6a). Two coupling
constants were extracted from the double doublet at
3.88–3.92 and the values were found to be 11.76 Hz and
3.08 Hz. e lower value was due to the vicinal coupling
of J2a,3e and the higher value corresponds to the trans cou-
pling of J2a,3a. e two coupling constants were calculated
from the double doublet at 4.15–4.19 ppm and the values
were 11.88 Hz and 3.20 Hz. e lower value was due to
the vicinal coupling of J6a,5e and the higher value is due to
the trans coupling of J6a,5a. e double doublets observed
at 2.41–2.37 ppm and 3.62–3.66 ppm were due to the
equatorial methylenic protons H3e and H5e respectively.
A double doublet was expected for the axial methylenic
proton H5a, but a multiplet was obtained at 2.43–2.52 ppm
corresponding to the H5a proton. A double doublet at
2.37–2.41 ppm had two coupling constants and the cou-
pling values were 2.96 Hz and 13.64 Hz. e lower value
corresponds to vicinal coupling of J3e,2a and the higher
value corresponds to geminal coupling of J3e,3a. e two
coupling constant values were extracted from the dou-
ble doublet at 3.62–3.66 ppm. e lower value 2.96 Hz
was due to vicinal coupling of J5e, 6a and the higher value
13.52 Hz is due to geminal coupling of J5e, 5a. A sharp
singlet observed at 3.80 ppm was due to the methylene
protons of the imidazolidine moiety. A double doublet
was expected for the axial methylenic proton H3a. but a
multiplet was obtained at 1.97–2.05 ppm corresponding
to the H3a proton. e NH proton of the piperidone
moiety was observed as a broad singlet at 2.83 ppm. e
broad signal at 11.78 ppm was due to the NH proton of
the imidazolidine moiety. A multiplet appeared in the
range of 7.23 −7.5 ppm due to the aromatic ring protons
at the C-2 and C-6 positions.
In the 13C NMR spectrum of 31, resonances in the
aliphatic range 29.62, 37.3, 60.23, 61.12, 43.64 ppm were
observed. e signals appeaing at 29.62 and 37.3 ppm
were due to the C-3 and C-5 carbons respectively.
Among the signals at 60.23 ppm and 61.12 ppm for the
benzylic carbons, the one at 60.23ppm was due to C-2
and the signal at 61.12 ppm was due to C-6 carbon. e
13C resonance at 43.64 ppm must be due to the methylene
carbon of the imidazolidine moiety (at C-5). e signal
at 163.19 ppm was conveniently assigned to the C=N car-
bon of the piperidone moiety. e 13C resonance of the
carbonyl carbon and the thiocarbonyl carbon at the C-4
and C-2 of the midazolidine moiety appeared at 167.63
and 173.87 ppm (C=S/173.87; C=O/167.63) respectively.
e ipso carbons appeared at 144.01 and 144.16 ppm. e
signals appearing in the region of 126.51–128.15 were due
to the aromatic carbons in the two phenyl rings at the C-2
and C-6 positions. All the above mentioned assignments
were further confirmed by HOMOCOSY and NOESY
spectra.
In the HOMOCOSY spectrum of 31, the signal at
3.9 ppm showed cross peaks with the signals at 2.01 ppm
Journal of Enzyme Inhibition and Medicinal Chemistry

In vitro microbiological evaluation of piperidino 2-thioxoimidazolidin-4-ones
73
Table 1. Physical and analytical data of compounds 31–45.
O
5
2
4
1
HN
3
N
N
4
S
R1
R2
3
2
5
6
1
N
H
(31-45)
X
X
Elemental analysis (%)
Yield Δ
(MW) (%) mp (°C) C Found (calculated) H Found (calculated) N Found (calculated)
m/z (M+1)+.
Molecular
formula
Compound R1 R2
X
H
F
31
32
H
H
H
H
74 (90)
78 (92)
108
103
65.85 (65.91)
59.91 (59.99)
5.45 (5.53)
4.44 (4.53)
15.3 (15.37)
13.9 (13.99)
365.2 C20H20N4OS
400.4
C20H18F2N4OS
33
H
H
Cl
67 (82)
167
55.39 (55.43)
4.15 (4.19)
12.81 (12.93)
432.3
C20H18Cl2N4OS
34
35
36
37
H
H
H
H
H
OCH3 72 (90)
158
142
171
182
62.2 (62.24)
67.3 (67.32)
66.6 (66.64)
60.81 (60.85)
5.66 (5.7)
6.1 (6.16)
5.82 (5.86)
4.82 (4.86)
13.17 (13.20)
14.23 (14.27)
14.76 (14.8)
13.48 (13.52)
424.0 C22H24N4O3S
392.3 C22H24N4OS
378.2 C21H22N4OS
H
CH3
H
70 (88)
75 (95)
78 (92)
CH3
CH3
F
414.1
C21H20F2N4OS
38
CH3
H
Cl
75 (85)
187
56.35 (56.38)
4.4 (4.51)
12.43 (12.52)
446.3
C21H20Cl2N4OS
39
40
41
42
CH3
CH3
H
H
OCH3 72 (90)
182
136
148
134
62.95 (62.99)
67.9 (67.95)
67.28 (67.32)
61.64 (61.67)
5.95 (5.98)
6.41 (6.45)
6.1 (6.16)
5.11 (5.17)
12.68 (12.78)
13.75 (13.78)
14.21 (14.27)
13.03 (13.08)
438.5 C23H26N4O3S
406.4 C23H26N4OS
392 C22H24N4OS
CH3
H
70 (94)
76 (96)
77 (95)
CH3 CH3
CH3 CH3
F
428.2
C22H22F2N4OS
43
44
45
CH3 CH3 Cl
75 (90)
176
132
124
57.21 (57.27)
63.6 (63.69)
68.44 (68.54)
4.78 (4.81)
6.1 (6.24)
6.65 (6.71)
12.11 (12.14)
12.31 (12.38)
13.2 (13.32)
460 C22H22Cl2N4OS
452.4 C24H28N4O3S
420.1 C24H28N4OS
CH3 CH3 OCH3 72 (85)
CH3 CH3 CH3 71 (88)
and 2.39 ppm. e signal at 4.17 ppm showed cross peaks
with the signals at 2.48 and 3.64 ppm. Consequently, the
signal at 3.9 ppm must be due to the benzylic proton H2a.
Since this can have coupling only with the H3e and H3a
protons, the two signals at 2.01 ppm and 2.39 ppm were
assigned to the H3a and H3e protons respectively. e sig-
nal at 4.17 ppm must be due to the benzylic proton H6a,
since this can have coupling with the H5a and H3e protons.
e two signals at 2.48 and 3.64 ppm were assigned to the
H5a and H5e protons respectively. e individual assign-
ments can be made by using its NOESY spectrum.
In the NOESY spectrum of 31, the signals of the ben-
zylic proton (H2a,H6a) have a strong nOe with the signals
of the methylene protons (H3e and H5a proton). Hence
the signal at 3.9 ppm has a strong nuclear Overhauser
effect (nOe) with the signal at 2.39 ppm. e signal at
4.17 ppm has a strong nOe with the signal 2.48 ppm.
From this it was concluded that the signal at 3.9 ppm
must be due to the benzylic proton H2a. e signal at
4.17 ppm must be due to the benzylic proton H6a. e
signals at 2.39 ppm and 2.48 ppm must be due to the
H3e and the H5a proton respectively. Moreover, an inter-
esting observation from the NOESY spectrum of com-
pound 31 was that the signal at 11.78 ppm had a strong
nOe with the signal at 2.01 ppm. Hence, the signal at
11.78 must be due to the NH proton of the imidazoli-
dine moiety and the signal at 2.01 ppm must be due to
the H3a proton. e signal at 3.80 ppm has strong nOe
with the signals at 2.01 ppm and 2.39 ppm. e signal
at 3.8 ppm must be due to the methylene proton of the
imidazolidine moiety. e signal at 2.39 ppm was due to
the H3e proton. From the NOESY spectrum, we concluded
that the imidazolidine moiety of 46 presents toward the
H3a and H3e protons of the piperidone moiety of 31. From
the view of nOes of -NH and CH2 protons of the imidazo-
lidine moiety, the -NH signal (11.78 ppm) and CH2 signal
(3.8 ppm) must be very close to the methylene protons of
the piperidone moiety at the C-3 position.
© 2011 Informa UK, Ltd.

74
V. Kanagarajan et al.
H
at 2.74ppm must be due to the H5e proton. is showed
that the signal at 3.56ppm should be due to the benzylic
proton H6a. e signal at 3.76ppm had a strong nOe with
the signal at 2.08ppm. Hence the signal at 3.76ppm must
be due to the methylene proton of the imidazolidine moi-
ety. e NH proton signal at 11.71ppm of the imidazoli-
dine moiety had a strong nOe with the methine proton
signal at 2.74ppm. Hence, the NH and CH2 protons of the
imidazolidine moiety must be very close to the methylene
protons at C-5 position of piperidone moiety. erefore,
with reference to HOMOCOSY and NOESY correlations
in compound 36, the assignments made for its ring and
substituent protons were confirmed. Hence based on the
obtained chemical shifts and coupling constant values, a
normal chair conformation (Figure 2) was proposed for
compound 36.
O
N
H
N
3
4
6
H
2
4
5
5
H
1
N
2
S
3
1
H
N
H
H
H
Figure 1. Chair conformation for compound 31.
erefore, taking into account the HOMOCOSY and
NOESY correlations for compound 31, the tentative
assignments made for its ring and substituent protons
were confirmed. It has been shown that the 2,6-diarylpi-
peridin-4-one ring mostly and favourably adopts the
chair conformation with all its substituents at an equato-
rial disposition [12]. Moreover the equatorial disposition
of the phenyl group at the C-2 and C-6 makes the chair
conformation more rigid thereby preventing interconver-
tion of one chair form into another. Hence, based on the
obtained chemical shifts and coupling constant values,
the normal chair conformation (Figure 1) was proposed
for compound 31.
Two dimensional HOMOCOSY and NOESY NMR
spectral assignments for the newly synthesised 3-(3,3-
dimethyl-2,6-diphenylpiperidin-4-ylideneamino)-2-
thioxoimidazolidin-4-one 41
Two singlets of the two methyl proton at 0.97 and
1.19 ppm had a cross peak with the signal at 3.72 ppm.
Hence, the signal at 3.72 ppm must be due to the H2a pro-
ton. e double doublet at 4.15ppm had cross peaks with
the signal at 2.54ppm and vice versa. is mutual correla-
tion clearly showed that the signal at 4.15ppm was due to
the H6a proton and the signal at 2.54ppm must be due to
the H5e proton. e individual assignments can be made
by using its NOESY spectrum.
Two dimensional HOMOCOSY and NOESY NMR
spectral assignments for the newly synthesised 3-(3-
methyl-2,6-diphenylpiperidin-4-ylideneamino)-2-
thioxoimidazolidin-4-one 36
In the HOMOCOSY spectrum of 36, the double doublet
at 3.56 ppm had cross peaks with the signals at 2.08 ppm
and 2.74 ppm and vice versa. is mutual correlation
clearly showed that these two signals must be due to
the H5a and H5e proton. e signal at 3.56 ppm must be
due to the benzylic proton H6a. Besides, the doublet at
3.46 ppm had a cross peak with the signal at 2.59 ppm
and 0.78 ppm. erefore, the signal at 3.46 ppm must be
due to the benzylic proton H2a and the signal at 2.59 ppm
should be due to the H3a proton. Likewise, the methyl
proton doublet at 0.78 ppm had a strong cross peak with
the signal at 2.59 ppm. Hence, the signal at 2.59 ppm
must be due to the H3a proton. e individual assign-
ments can be made by using the NOESY spectrum.
From the NOESY spectrum of compound 36, it was
interesting to note that the signal at 0.78ppm of C-3 methyl
protons had strong nOe with the benzylic proton signal
at 3.46ppm and the methine proton signal at 2.59ppm.
It further confirmed the assignment of the doublet at
3.46ppm to the benzylic proton H2a and the signal centred
at 2.59ppm to the methine proton using the HOMOCOSY
spectrum of the same compound. e benzylic proton sig-
nal at 3.46ppm had a nOe with the methine proton signal
at 2.59ppm and the C-3 methyl proton signal at 0.78ppm.
Hence, the signals at 2.59ppm and 3.46ppm must be due
to the H3a and H2a protons respectively. e double dou-
blet at 3.56ppm had a cross peak with the methine proton
signals at 2.08ppm and 2.74ppm. is suggested that the
signal at 2.08ppm was due to the H5a proton and the signal
From the NOESY spectrum of compound 41, it was
interestingtonotethatthetwomethylprotonsat0.97 ppm
and 1.19 ppm had a nOe with protons at 3.72 ppm. is
shows that the signal at 3.72 ppm should be due to the H2a
proton. e double doublet at 4.15 ppm had a strong nOe
with the proton at 2.54 ppm. is revealed that the signal
at 2.54 ppm must be due to the H5e proton. In addition,
the signal at 3.91 ppm had a strong nOe with the proton
signal at 2.54 ppm and a weak nOe with the proton signal
at 3.21 ppm. Hence, the signal at 3.91 ppm must be due
to the methylene proton of the imidazolidine moiety.
e signal at 3.21 ppm must be due to the H5a proton. e
NH proton signal (11.8 ppm) of the imidazolidine moiety
had a strong nOe with the methine proton signals at 2.54
and 3.21 ppm. is showed clearly that the NH and CH2
protons of the imidazolidine moiety must be very close to
the methylene protons at the C-5 position of piperidone
moiety. erefore, with reference to HOMOCOSY and
NOESY correlations in compound 41, the assignments
made for its ring and substitutent protons were con-
firmed. Hence based on the obtained chemical shifts and
coupling constant values, a normal chair conformation
(Figure 3) was proposed for compound 41.
Antibacterial activity
New 3-(3-alkyl-2,6-diarylpiperin-4-ylidene)-2-thioxoimida-
zolidin-4-ones 31–45 were tested for their antibacterial activ-
ity in vitro against clinically isolated bacterial strains namely
Journal of Enzyme Inhibition and Medicinal Chemistry

In vitro microbiological evaluation of piperidino 2-thioxoimidazolidin-4-ones
75
B. subtilis, M. luteus, S. typhii, S. paratyphii B, S. felxneri and
P. vulgaris. Penicillin was used as the standard drug. e
minimum inhibitory concentration (MIC) in μg/mL values
was reproduced in Table 2. Compound 31 which doesn’t
have a substituent at the para position of the phenyl
ring at positions 2 and 6 of the piperidone ring exhibited
antibacterial activity against B. subtilis at a MIC value of 100
μg/mL. Introduction of a methyl substituent at position 3 of
the piperidone ring in compound 36 enhanced its activity
with a MIC value of 12.5 μg/mL. Further introduction of a
dimethyl substituent at position 3 of the piperidone ring in
compound 41 enhanced the antibacterial activity against
B. subtilis with a MIC value of 6.25 μg/mL. Compounds 32
and 33 which have electron withdrawing fluoro and chloro
functional group at the para position of the phenyl rings at
positions 2 and 6 of the piperidone ring respectively were
inactive against B. subtilis and exhibited a MIC of 200μg/mL.
Similar results were observed for compounds 37, 38, 42 and
43 against B. subtilis. But introduction of electron donating
methoxy and methyl functional group at the para position
of the phenyl rings at positions 2 and 4 of the piperidone ring
in compounds 34 and 35 showed moderate activity against
B. subtilis. In addition to an electron donating methoxy and
methyl functional group at the para position of the phenyl
rings at positions 2 and 4 of the piperidone ring, a methyl
substituent at position 3 of piperidone ring in compounds
39 and 40 were inactive against B. subtilis. Against B. subtilis,
analogous results were observed in the dimethyl substituted
compounds, 44 and 45. Compound 31, the methyl substi-
tutedcompound36andthedimethylsubstitutedcompound
41 none of which had a substituent at the para positionofthe
phenyl rings at positions 2 and 6 of the piperidone ring exhib-
ited antibacterial activity against M. luteus at a MIC value of
200 μg/mL. e introduction of an electron withdrawing
fluoro and chloro functional group at the para position of
the phenyl rings at positions 2 and 6 of the piperidone ring
respectively in compounds 32 and 33 were active against
M. luteus and exhibited a MIC of 12.5 μg/mL. Methyl sub-
stitution at position 3 of the piperidone ring for compounds
37 and 38 which also have electron withdrawing fluoro and
chloro functional group at the para position of the phenyl
rings at positions 2 and 6 of the piperidone ring respectively,
were potent against M. luteus and exhibited a MIC of 6.25 μg/
O
5
HN
4
3
1
2
N
H
S
N
H
6
H
4
5
H
2
1
3
CH3
N
H
H
Figure 2. Chair conformation for compound 36.
O
5
HN
S
4
3
N
1
2
H
N
H
6
H
4
5
H
2
1
3
CH3
N
H
H3C
Figure 3. Chair conformation for compound 41.
Table 2. In vitro antibacterial activity of compounds 31–45 against clinically isolated bacterial strains.
Minimum inhibitory concentration (MIC) in µg/mL
Compound
B. subtilis
100
200
200
25
M. luteus
200
12.5
12.5
50
S. typhii
‘-‘
S. paratyphii B
S. felxneri
50
P. vulgaris
100
50
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
Penicillin
200
25
12.5
25
200
100
12.5
12.5
50
25
50
100
100
‘-‘
100
50
25
25
100
200
6.25
6.25
25
25
12.5
100
100
200
200
6.25
200
‘-‘
200
12.5
12.5
200
100
‘-‘
200
25
12.5
12.5
50
100
100
12.5
25
25
12.5
12.5
50
50
50
200
25
‘-‘
100
200
200
6.25
12.5
25
6.25
6.25
25
6.25
6.25
100
100
25
12.5
12.5
6.25
6.25
12.5
25
100
100
25
50
50
25
12.5
25
‘-‘ No inhibition even at a higher concentration of 200 µg/mL
© 2011 Informa UK, Ltd.

76
V. Kanagarajan et al.
phenyl rings at positions 2 and 6 of the piperidone ring
exerted good activity at a MIC of 12.5 μg/mL against A.
niger. e dimethyl substituted compounds of 42 and 43
with electron withdrawing fluoro and chloro functional
groups at the para position of the phenyl rings at posi-
tions 2 and 6 of the piperidone ring exerted good activity
at a MIC of 6.25 and 12.5 μg/mL respectively against A.
niger. Against Mucor, the electron withdrawing fluoro
and chloro substituted compounds 32, 33, 37, 38, 42 and
43 exhibited good antifungal activity at a concentration
of 12.5-6.25 μg/mL. Compounds 34, 35, 39, 40, 44 and
45 which all have electron donating methoxy and methyl
functional group at the para position of the phenyl rings
at positions 2 and 6 of the piperidone ring exerted good
activity at a MIC of 6.25 and 12.5 μg/mL against Rhizopus.
Similarly compounds 34 and 35, which have electron
donating methoxy and methyl functional group at the
para position of the phenyl rings at positions 2 and 6 of
the piperidone ring exerted excellent antifungal activity
against M. gypsuem at a MIC of 6.25 and 12.5 μg/mL.
Table 3. In vitro antifungal activity of compounds 31–45 against
clinically isolated fungal strains.
Minimum inhibitory oncentration (MIC) in µg/mL
Compound
A. niger
200
25
Mucor
100
6.25
12.5
100
100
100
6.25
6.25
200
200
100
12.5
12.5
50
Rhizopus M. gypsuem
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
200
100
200
6.25
6.25
50
200
100
100
12.5
6.25
50
25
50
50
‘-‘
12.5
12.5
50
200
200
12.5
25
‘-‘
200
25
50
25
100
6.25
12.5
100
100
25
100
100
100
200
200
50
100
50
50
100
100
25
50
Amphotericin
B
25
‘-‘, No inhibition even at a higher concentration of 200 µg/mL
Conclusion
mL whereas dimethyl substitution at position 3 of the piperi-
done ring for compounds 42 and 43 were inactive against M.
luteus. Compound 34, 35, methyl substituted compound 39,
40 and dimethyl substituted compound 44, 45 whichallhave
an electron donating methoxy and methyl functional group
at the para position of the phenyl rings at positions 2 and 6 of
the piperidone ring exhibited moderate antibacterial activity
against M. luteus. Against S. typhii, compounds 31, 36 and
41 were inactive. e electron withdrawing substituted com-
pounds of 32, 33, 37, 38, 42 and 43 showed potent activity
against S. typhii at a MIC value of 12.5–6.25 μg/mL. e elec-
tron donating substituted compounds of 34, 35, 39, 40, 44
and 45 showed moderate activity against S. typhii at a MIC
value of 100–25μg/mL. e electron withdrawing substi-
tuted compounds of 37, 38, 42 and 43 were active against S.
paratyphii B. e electron donating substituted compounds
of 34, 35, 39, 40, 44 and 45 were active against S. felxneri.
Against P.vulgaris all the compounds exerted activity at a
MIC value of 100–6.25 μg/mL.
e 3-(3-Alkyl-2,6-diarylpiperin-4-ylidene)-2-thioxoim-
idazolidin-4-ones, a class of novel hybrid heterocyclic
compounds can be synthesised from various 3-alkyl-2-
,6-diphenylpiperidin-4-one thiosemicarbazones, anhy-
drous sodium acetate and chloroethyl acetate in refluxing
ethanol and a comparative study was also carried out
under microwave irradiation. e synthesised com-
pounds were characterised by mps, elemental analysis,
MS, FT-IR, one-dimensional NMR (1H, D2O exchanged
1H & 13C), two dimensional HOMOCOSY and NOESY
spectroscopic data. e in vitro microbiological screen-
ing studies carried out to evaluate the antibacterial and
antifungal potencies of the newly synthesised 3-(3-alkyl-
2,6-diarylpiperin-4-ylidene)-2-thioxoimidazolidin-4-
ones 31–45 are shown in Table 2 and Table 3. A close
inspection of the in vitro antibacterial and antifungal
activity profile in differently electron withdrawing (F and
Cl) and electron donating (OCH3 and CH3) functional
groups substituted phenyl rings of novel 3-(3-alkyl-2,6-
diarylpiperin-4-ylidene)-2-thioxoimidazolidin-4-ones
31–45 exerted strong antibacterial activity against all
the clinically isolated tested bacterial and fungal strains
namely: B. subtilis, M. luteus, S. typhii, S. paratyphii B,
S. felxneri, P. vulgaris, A. niger, Mucor, Rhizopus and M.
gypsuem. ese observations may promote further devel-
opment of our research into this group of pyrido 2-thiox-
oimidazolidin-4-ones and may lead to the development
of compounds with a better pharmacological profile than
the standard antibacterial and antifungal drugs.
Antifungal activity
e in vitro antifungal activity of the 3-(3-alkyl-2,6-
diarylpiperin-4-ylidene)-2-thioxoimidazolidin-4-ones
31-45 was studied against clinically isolated the fol-
lowing fungal strains: A. niger, Mucor, Rhizopus and
M. gypsuem. Fluconazole was used as a standard drug.
Minimum inhibitory concentration (MIC) in μg/mL
values are reproduced in Table 3. Compound 36 which
doesn’t have a substitutent at the para position of the
phenyl rings at positions 2 and 4 of the piperidone ring
but does have an electron donating methyl substituent at
position 3 of the piperidone ring did not exert any anti-
fungal activity against A. niger and M. gypsuem even at a
high concentration of 200 μg/mL. e methyl substituted
compoundsof37and38withelectronwithdrawingfluoro
and chloro functional groups at the para position of the
Acknowledgements
e authors would like to thank the NMR Research
Centre, Indian Institute of Science, Bangalore for record-
ing spectra.
Journal of Enzyme Inhibition and Medicinal Chemistry

In vitro microbiological evaluation of piperidino 2-thioxoimidazolidin-4-ones
77
acylation in solvent-free conditions: A facile and rapid synthesis
of aryl ketones under microwave irradiation. Catalysis Commun
2005;6:753–756.
Declaration of interest
V. Kanagarajan is grateful to the Council of Scientific and
Industrial Research (CSIR), New Delhi, Republic of India
for providing financial support in the form of CSIR-Senior
Research Fellowship (SRF) in Organic Chemistry. e
authors report no conflicts of interest. e authors alone
are responsible for the content and writing of the paper.
7. Gopalakrishnan M, Sureshkumar P, Kanagarajan V, anusu J,
Govindaraju R. Silica gel supported sodium hydrogen sulfate as an
efficient and reusable heterogeneous catalyst for the synthesis of
imines in solvent-free conditions under microwave irradiation. J
Chem Res 2005;5:299–303.
8. Gopalakrishnan M, Sureshkumar P, Kanagarajan V, anusu J.
Organic synthesis in solid media. Alumina supported sodium
hydrogen sulfate as an effective and reusable catalyst for ‘one-pot’
synthesis of amides from ketones in dry media under microwave
irradiation. Lett Org Chem 2005;2:444–446.
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© 2011 Informa UK, Ltd.