Efficient synthesis, spectral analysis and antimicrobial studies of nitrogen and sulfur containing spiro heterocycles from 2,4-diaryl-3- azabicyclo[3.3.1]nonan-9-ones

Article abstract of DOI:10.1016/j.bmcl.2010.09.021

Acetyl and propionyl group substituted thiadiazole derivatives (4a-4h, 5a-5h, 6a, 6b, 7a and 7b) have been synthesized by the cyclization of 2,4-diaryl-3-azabicyclo[3.3.1]nonan-9-one thiosemicarbazones (2a-2h, 3a and 3b) with acetic anhydride/propionic anhydride and were characterized by Elemental analysis, IR, ¹H NMR and ¹³C NMR spectral analysis. Single crystal X-ray diffraction has also been recorded for compounds 4c and 5a. From the NMR and Single crystal X-ray diffraction analysis, compounds 4b-4d, 4f-4h, 5b, 5c, 5f-5h, 6a, 7a and 7b were found to adopt twin-chair conformations whereas compounds 4a, 4e, 5a, 5d, 5e and 6b adopt chair and boat conformation of cyclohexane and piperidine rings, respectively. Besides, the synthesized compounds were screened for antibacterial and antifungal activities using serial dilution method. The microbiological analysis showed that the electron withdrawing function substituted phenyl group at C-2 and C-4 of azabicyclononane based thiadiazoles 4c/4h and 5c/5h exposed significant antimicrobial activity against Salmonella typhi, Escherichia coli, Klebsiella pneumoniae, Aspergillus flavus, Aspergillus niger and Candida albicans at MIC of 6.25 μg/ml.

Full text of DOI:10.1016/j.bmcl.2010.09.021

Bioorganic & Medicinal Chemistry Letters 20 (2010) 6637–6643
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Efficient synthesis, spectral analysis and antimicrobial studies
of nitrogen and sulfur containing spiro heterocycles from
2,4-diaryl-3-azabicyclo[3.3.1]nonan-9-ones
⇑
M. Rani, R. Ramachandran, S. Kabilan
Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 June 2010
Revised 13 August 2010
Accepted 4 September 2010
Available online 15 September 2010
Acetyl and propionyl group substituted thiadiazole derivatives (4a–4h, 5a–5h, 6a, 6b, 7a and 7b) have
been synthesized by the cyclization of 2,4-diaryl-3-azabicyclo[3.3.1]nonan-9-one thiosemicarbazones
(2a–2h, 3a and 3b) with acetic anhydride/propionic anhydride and were characterized by Elemental
analysis, IR, 1H NMR and 13C NMR spectral analysis. Single crystal X-ray diffraction has also been recorded
for compounds 4c and 5a. From the NMR and Single crystal X-ray diffraction analysis, compounds 4b–4d,
4f–4h, 5b, 5c, 5f–5h, 6a, 7a and 7b were found to adopt twin-chair conformations whereas compounds
4a, 4e, 5a, 5d, 5e and 6b adopt chair and boat conformation of cyclohexane and piperidine rings, respec-
tively. Besides, the synthesized compounds were screened for antibacterial and antifungal activities using
serial dilution method. The microbiological analysis showed that the electron withdrawing function
substituted phenyl group at C-2 and C-4 of azabicyclononane based thiadiazoles 4c/4h and 5c/5h
exposed significant antimicrobial activity against Salmonella typhi, Escherichia coli, Klebsiella pneumoniae,
Keywords:
2,4-Diaryl-3-azabicyclo[3.3.1]nonan-9-ones
Thiadiazoles
Spiro
Cyclization
Conformational study
Antimicrobial activity
Aspergillus flavus, Aspergillus niger and Candida albicans at MIC of 6.25 lg/ml.
Ó 2010 Elsevier Ltd. All rights reserved.
In the past years considerable evidences have been accumu-
lated to demonstrate the efficacy of substituted 1,3,4-thiadiazoles
in antibacterial, antifungal and HIV activities.1–3 This analogue acts
as ‘hydrogen binding domain’ and ‘two-electron donor system’ and
naturally occur in four isomeric forms viz. 1,2,3-thiadiazole; 1,2,5-
thiadiazole; 1,2,4-thiadiazole and 1,3,4-thiadiazole. A glance at lit-
erature studies show that more work has been carried out on the
1,3,4-thiadiazole than the other isomers. This five membered
1,3,4-thiadiazoles show diverse biological activities, probably by
the virtue of @N–C–S moiety4 and their toxicity. The toxicity of
thiadiazole entity is related to substitutions like halogen, sulphur,
oxygen and nitrile groups, for example, herbicides and insecticides.
It also acts as a constrained pharmacophore. Many drugs contain-
ing thiadiazole nucleus are available in the market as acetazola-
mide,5 methazolamide,6 sulfamethazole,7 etc. The resistance
towards available drugs is rapidly becoming a major worldwide
problem. The necessity to design new compounds to overcome this
resistance has become one of the most important areas of research
today.
anticonvulsant,16 antioxidant/Radio protective activity,17 antimy-
cobacterial,18,19 antimicotic,20 antimalarial,21 antileukemic,22 antile-
ishmanial23,24 activities, pesticides11 and cardiotonic25 and their
action is being noticeable.
Recently, we have reported several mono and bicyclic deriva-
tives as antimicrobial agents.26–28 Some of them show good growth
inhibition at low concentration. Extending the research in this area,
we decided to obtain the derivatives which contain the bicyclic
based piperidine and 1,3,4-thiadiazole ring. The aim of this work
is to investigate the antibacterial and antifungal activities of the
target compounds by the modification of phenyl group substitu-
ents and the side chain (acetyl/propionyl group) in thiadiazole ring.
The synthesized compounds (4a–4h, 5a–5h, 6a, 6b, 7a and 7b) are
characterized by analytical and spectral techniques. Conforma-
tional assignments of all the compounds were unambiguously
achieved with the help of NMR and single crystal X-ray diffraction
analysis.
The reaction pathways of different thiadiazole modifications are
sketched in Scheme 1. The 2,4-diaryl-3-azbicyclo[3.3.1]nonan-9-
ones were prepared according to the precedent literature29 by
the one pot multi-component condensation of ammonium acetate,
benzaldehyde and cyclohexanone (1:2:1 ratio). This upon conden-
sation with thiosemicarbazide under acidic medium afforded 2,4-
diaryl-3-azbicyclo[3.3.1]nonan-9-one thiosemicarbazones along
with aryl thiosemicarbazones.27 In the present work, the key inter-
mediate thiosemicarbazones react with acid anhydride (acetic
1,3,4-Thiadiazoles represent one of the most biologically active
classes of compounds, possessing a wide spectrum of activities
such as antimicrobial,8 antiviral,9 anti-inflammatory,10 herbicidal,11
antidepressive,12 antitumoral,11 antitubercular,13,14 anticancer,15
⇑
Corresponding author. Tel.: +91 9443924629.
E-mail address: chemkabilan@rediffmail.com (S. Kabilan).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.09.021

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M. Rani et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6637–6643
Scheme 1. Schematic diagram showing the synthesis of 1,3,4-thiadiazoles (4a–7b). Reagents and conditions: (a) EtOH, slight warm then rt, 24 h; (b) NH2–NH–CS–NH2ꢁHCl,
CHCl3/EtOH (1:1), 4–5 h reflux; (c) PhNH–NH–CS–NH2ꢁHCl, CHCl3/EtOH (1:1), 6–7 h reflux; (d) acetic anhydride, 12–15 h reflux, 90 °C; (e) propionic anhydride, 5–8 h reflux,
90 °C; (f) acetic anhydride, 18–20 h reflux, 90 °C; (g) propionic anhdride, 7–10 h reflux, 90 °C.
anhydride/or propionic anhydride) under reflux condition (90 °C)
afforded the corresponding cyclised thiadiazole derivatives. Then
the synthesized compounds were purified by column chromatog-
raphy using benzene–ethyl acetate (2:1) as eluent on neutral
alumina.
According to Scheme 1, compounds 4b–4d/4f–4h, 5b–5c/5f–5h,
6a, 7a and 7b were failed to undergo either acetylation or prop-
ionylation reaction at nitrogen site of piperidine ring due to steric
hindrance caused by the presence of fluorine, chlorine and methyl
moiety on the phenyl group at C-2 and C-4, whereas in compounds
4a, 4e, 5a, 5d, 5e and 6b, the formation of N-acetylation or N-prop-
ionylation reveals that the phenyl group did not cause any steric
hindrance around the nitrogen site (piperidine ring). The target
compounds were confirmed by elemental analysis and IR spectral
analysis. The analytical data of the synthesized compounds were
given in Table 1. Further, the structural assignments of the title
compounds were made by using 1H and 13C NMR spectral analysis.
Besides, single crystal X-ray diffraction has also been recorded for
the representative compounds (4c and 5a). A well numbered target
compound structure was given in Figure 1 for structural and bio-
logical analysis.
IR spectra of 1,3,4-thiadiazoles (4a–4h, 5a–5h, 6a, 6b, 7a and
7b) showed weak absorption band in the region of 3090–
3000 cmꢀ1 which is due to aliphatic and aromatic C–H stretching.
A sharp and intense absorption band around 3200 and 3300 cmꢀ1
is assigned to NH stretching vibration of side chain acetyl amino
and piperidine analogue of compounds 4b–4d/4f–4h, 5b–5c/5f–
5h, 6a, 7a and 7b whereas in compounds 4a, 4e, 5a, 5d, 5e and
6b, the absence of stretching frequency around 3300 cmꢀ1 sug-
gests that the N-acetylation/propionylation occurred at nitrogen

M. Rani et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6637–6643
6639
Table 1
Analytical data for compounds 4a–7b
Entry
Molecular formulae
Yield (%)
Mp (°C)
Elemental analysis (%)
Calculated
H
Found
H
C
N
C
N
4a
4b
4c
4d
4e
4f
4g
4h
5a
5b
5c
5d
5e
5f
5g
5h
6a
6b
7a
7b
C
C
27H30N4O3S
25H26Cl2N4O2S
90
80
90
75
65
60
80
75
90
83
85
65
79
85
81
79
84
88
81
75
166
160
154
152
155
164
168
158
192
160
154
168
183
171
181
174
210
216
214
185
66.10
58.03
61.97
63.76
63.25
68.04
58.03
61.97
67.64
59.45
63.26
64.84
64.84
69.02
59.45
63.26
62.73
62.36
63.76
63.76
6.16
5.06
5.41
6.34
6.22
6.77
5.06
5.41
6.81
5.54
5.90
6.80
6.80
7.19
5.54
5.90
5.09
5.07
5.51
5.51
11.42
10.83
11.56
11.02
10.17
11.75
10.83
11.56
10.52
10.27
10.93
9.45
66.11
58.03
61.95
63.76
63.24
68.03
58.01
61.95
67.65
59.45
63.24
64.84
64.86
69.03
59.47
63.25
62.71
62.36
63.74
63.77
6.17
5.07
5.40
6.35
6.22
6.75
5.07
5.43
6.80
5.56
5.91
6.81
6.80
7.17
5.51
5.91
5.08
5.05
5.50
5.49
11.42
10.81
11.55
11.00
10.15
11.73
10.83
11.58
10.53
10.28
10.91
9.47
C25H26F2N4O2S
C
C
C
C
C
C
C
C
C
C
C
27H32N4O4S
29H34N4O5S
27H32N4O2S
25H26Cl2N4O2S
25H26F2N4O2S
30H36N4O3S
27H30Cl2N4O2S
27H30F2N4O2S
32H40N4O5S
32H40N4O5S
29H36N4O2S
9.45
9.44
11.10
10.27
10.93
9.44
8.81
9.01
11.10
10.25
10.94
9.44
8.80
9.02
C27H30Cl2N4O2S
C
C
C
C
C
27H30F2N4O2S
31H30Cl2N4O2S
33H32Cl2N4O3S
33H34Cl2N4O2S
33H34Cl2N4O2S
9.01
9.01
site. Generally, the mC
@
O bands of amide carbonyl30 group observed
ORTEP diagram is depicted in Figure 5 (with its important bond
length and bond angles). The crystallographic data and structure
refinement parameters of 5a are given in Supplementary data
(Table 2). According to XRD, the piperidine ring exists in half-boat
conformation whereas the cyclohexane ring exists in chair
conformation.
in the region 1690–1630 cmꢀ1. Likewise, the compounds in the
present series also exhibit similar absorptions around 1690 cmꢀ1
and 1595 cmꢀ1 are characteristic for N–C@O and C@N bond
stretching vibrations. In addition, the appearance of N–C–S bend-
ing vibration around 1375 cmꢀ1 is the confirmatory evidence for
five membered ring closure.
Among the cyclohexane ring proton (H-6, H-7 and H-8) signals,
H-7a proton resonated in the deshielded region than its corre-
sponding equatorial and other methylene (C-6 and C-8) protons.
This is due to the deshielding effect exerted by the nitrogen lone
pair and it creates steric interaction. Due to this, C–H(7a) bond be-
comes polarized and as a consequence, carbon and the attached
proton acquire negative and positive charges, respectively. As a re-
sult, the H-7a proton signal is highly deshielded. Hence, a multiplet
at 2.46 ppm is unambiguously assigned to H-7a proton for com-
pounds 4b–4d, 4f–4h, 5b–5c, 5f–5h, 6a, 7a and 7b and another
multiplet at 1.28 ppm is assigned to H-7e proton. Conversely for
compounds 4a, 4e, 5a, 5d, 5e and 6b the H-7a proton signal reso-
nated in the shielded region (around 1.40 ppm). This is due to the
absence of steric interaction between NH and H-7a proton (i.e., due
to N-acylation, the free NH proton is absent). This clearly supports
the N-acylation of these compounds 4a, 4e, 5a, 5d, 5e and 6b.
It is worthwhile mentioning that the equatorial proton in meth-
ylene carbon of cyclohexane ring is highly deshielded than the ax-
ial proton due to the anisotropy of the C–C single bonds. As a
consequence, multiplets centered at 1.74 and 1.34 ppm, each two
proton integral attributed to H-6e/H-8e and H-6a/H-8a protons,
respectively. In addition, two singlets at 2.26 and 2.22 ppm with
three protons integral confirms the methyl moieties of 4a–4h, 6a
and 6b series thiadiazoles but in the case of 5a–5h, 7a and 7b,
the side chain methyl and methylene protons observed as a triplet
and a quartet around 1.50 and 2.50 ppm with three and two pro-
tons integration, respectively.
In order to assign the ring proton and carbon signals, compound
4c has been chosen as representative compound. 1H NMR spec-
trum of thiadiazole (4c) gives a singlet at 4.95 ppm with two pro-
tons integral which is assignable to benzylic (H-2a and H-4a)
protons. Similarly, bridgehead protons (H-1e and H-5e) are reso-
nated as a singlet at 2.73 ppm with two protons integral. Instead
of doublet, a singlet was observed for benzylic and bridge head
protons, therefore, the coupling constant values could not be ex-
tracted well, but its chemical shift values are similar to already re-
ported twin-chair bicyclic compounds. So, we concluded that these
compounds (4b–4d, 4f–4h, 5b–5c, 5f–5h, 6a, 7a and 7b) may also
exist in twin-chair conformation with equatorial orientation of aryl
substituents as shown in Figure 2. Single crystal XRD analysis was
carried out for representative compound 2,4-[bis(m-fluorophenyl)-
3-azabicyclo[3.3.1]nonan-9-yl]-5-spiro-4-acetyl-2-(acetylamino)-
D
2-1,3,4-thiadiazoline 4c and its ORTEP diagram is shown in
Figure 3 with important bond length and bond angles. The XRD
analysis also proved that both the piperidine and cyclohexane rings
are exist in chair–chair conformation (Fig. 3). [Refer Supplementary
data for detailed spectral assignments and the crystallographic
data and refinement parameters of 4c (Table 1)].
Interestingly, compounds 4a, 4e, 5a, 5d, 5e and 6b showed two
benzylic proton signals in the deshielded region (around 6.0 ppm).
This deshielding of chemical shift is due to the introduction of elec-
tron withdrawing acetyl or propionyl group at nitrogen site in
piperidine ring. Due to the presence of N-acetyl/propionyl group,
coplanarity was created between N–C@O bond to avoid A1,3 allylic
strain. Therefore, these compounds 4a, 4e, 5a, 5d, 5e and 6b should
adopt boat–chair conformations of the piperidine and cyclohexane
rings, respectively (Fig. 4) and the aryl groups occupy equatorial
orientation. In order to confirm these assignments, single crystal
XRD analysis was carried out for representative compound N-pro-
pionyl-2,4-[diphenyl-3-azabicyclo[3.3.1]nonan-9-yl]-5-spiro-4-
In compounds 4b–4d, 4f–4h, 5b, 5c, 5f–5h, 6a, 7a and 7b, the
NH protons signal in piperidine and thiadiazole moiety resonated
as singlets at 1.62 and 8.20 ppm, respectively, whereas in com-
pounds 4a, 4e, 5a, 5d, 5e and 6b the expected NH proton signal
in piperidine analogue was not observed. Instead, the acetyl and
propionyl group protons signal appeared as a singlet, triplet and
quartet around 2.20, 1.80 and 2.0–2.50 ppm with three and two
protons integral, respectively. Therefore, the shielding of H-7a
propionyl-2-(propionylamino)-D
2-1,3,4-thiadiazoline 5a and its

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M. Rani et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6637–6643
Figure 1. A well numbered target molecules (4a–7b).
proton signal and the presence of methyl and methylene protons
signal strongly confirms the N-acylation. The aryl protons appeared
in the region of 6.97–7.32 ppm.
In 13C NMR spectrum of target compounds (4a–4h, 5a–5h, 6a,
6b, 7a and 7b), the disappearance of thiocarbonyl (C@S) signal
around 180 ppm confirmed the cyclization. In addition, a new sig-
nal observed around 90 ppm is assigned to C-9 ipso (spiro) carbon.
Similarly, the carbonyl, methyl and methylene moieties of the acet-
yl/propionyl groups signal further supports the formation of spiro
thiadiazole analogue. Moreover, two sets of signals appeared in the
downfield and upfield region at 172.6/167.8 and 25.7/23.6 ppm are
due to carbonyl and methyl moieties of secondary and tertiary
amide nitrogens, respectively, whereas the C@N signal is appeared
around 156 ppm.
The benzylic (C-2/C-4) and bridgehead (C-1/C-5) carbon signals
appeared at 60.2 and 41.9 ppm, respectively. Moreover, the signals
which are appeared in the aliphatic region at 25.32 and 19.33 ppm
are assigned to C-8/C-6 and C-7 carbon, respectively. A collection of
signals resonated in the region of 129.87–113.40 ppm and a signal
Figure 2. Chair–chair conformation with equatorial orientation of the phenyl/
substituted phenyl groups at C-2 and C-4.

M. Rani et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6637–6643
6641
Staphylococcus aureus (ATCC-25930), Bacillus subtilis (ATCC-530),
Salmonella typhi (ATCC-25021), Escherichia coli (ATCC-26032) and
Klebsiella pneumoniae (ATCC-16425) and antifungal activity against
Candida albicans (ATCC-3430), Cryptococcus neoformans (ATCC-
3235), Rhizopus species (ATCC-2842), Aspergillus niger (ATCC-635)
and Aspergillus flavus (ATCC-525) and the MIC values were deter-
mined by serial dilution method.31 Here, Streptomycin and
Amphotericin B were used as standard drugs for bacterial and fun-
gal studies, respectively. Tables 2 and 3 show the various bacterial
and fungal growth inhibition level of compound 4a–4h, 5a–5h, 6a,
6b, 7a and 7b against different pathogenic strains.
All the compounds were shown their antibacterial activity rang-
ing from 6.25 to 200 lg/ml. Table 2 revealed that the compounds
4a–4h, 6a, 6b (cyclised compounds using acetic anhydride) were
found to exhibit superior antibacterial activity against the tested
bacterial strains than the compounds 5a–5h, 7a, 7b (cyclised com-
pounds using propionic anhydride). Among the different patho-
genic strains, the compounds with unsubstituted phenyl groups
at C-2 and C-4 of azabicyclononane based thiadiazoles (either acet-
ylated or propionylated) showed better activity (12.5
lg/ml)
against S. aureus and moderate activity (50–100
lg/ml) against rest
of the strains used.
Conversely, the introduction of fluoro function at the meta/para
position of 4a (compounds 4c, 5c and 4h, 5h) showed a noticeable
improvement in their activity even at very low concentration
(6.25 lg/ml) against all the strains. Particularly, 4c against S. typhi,
E. coli and K. pneumoniae, 5c against B. subtilis, E. coli and S. typhi,
and 4h/5h against B. subtilis, S. typhi exerted superior activity at
MIC of 6.25
function in 4h/5h (compounds 4g/5g) registered one fold dimin-
ished activity (12.5 g/ml) against B. subtilis and S. typhi. Whereas
lg/ml. But, replacement of fluoro function by chloro
l
the same compounds showed one fold increased activity against S.
aureus and K. pneumoniae when phenyl group was substituted at
amide nitrogen spiro (compounds 6a and 7b). In lieu of halogens,
methyl substituted compounds 4f and 5f were more potent
(12.5 lg/ml) against B. subtilis and K. pneumoniae, respectively.
But the substitution of methoxy function in 4a/5a (compound
Figure 3. ORTEP diagram of compound 4c with 50% probability. The important
bond length (Å): C(3)–N(2) = 1.482 (4) ; C(3)–S(1) = 1.860 (3); N(2)–N(3) = 1.433
(4); C(21)–N(3) = 1.273 (4); C(21)–N(4) = 1.382 (4); C(21)–S(1) = 1.746 (3); C(22)–
O(1) = 1.196 (5); C(22)–N(4) = 1.365 (5); C(24)–O(2) = 1.218 (4); C(24)–N(2) = 1.374
(4). The important bond angles (°): N(3)–C(21)–N(4) = 119.9 (3); N(3)–C(21)–
S(1) = 118.3 (2); O(1)–C(22)–N(4) = 121.6 (4); N(4)–C(22)–C(23) = 115.6 (4); O(2)–
C(24)–N(2) = 122.7 (3); N(2)–C(24)–C(25) = 116.8 (3); N(3)–N(2)–C(3) = 110.3 (2);
N(2)–C(3)–S(1) = 100.68 (19).
4d/5d) did not show any inhibition against E. coli and S. typhi even
at maximum concentration (200 lg/ml), respectively.
The above discussion and the data of Table 2 disclosed that the
activity is sensitive to position of the substituent in the aryl ring.
The para methoxy substituted compounds (4e/5e) exhibited three
fold increased activity (25
moniae than the meta methoxy substituted compounds (4d/5d),
that is, MIC at 100 g/ml. This suggests that besides electronic ef-
lg/ml) against S. aureus, S. typhi, K. pneu-
l
fects other factors also influence the activity.
A glance at the MIC50 value of Table 3 indicates that all thiadi-
azole compounds under this series exhibit their growth inhibition
in the range of 6.25–200
derivatives 4a–4h, 6a, 6b and 5a–5h, 7a, 7b, unsubstituted phenyl
bearing compound (4a) showed moderate activity (50–100 g/ml).
lg/ml. However, among the thiadiazole
l
The modification of the acetyl group by propionyl group in 4a
(compound 5a) does not show any change in activity against the
tested organism. But the introduction of chloro function at ortho/
para position of phenyl group in 4a and 5a (compound 4b, 5b
and 4g, 5g) showed two fold increased growth inhibition (6.25–
50
pus sp. 5b and 5g against A. niger and 4b against A. flavus were
shown to possess significant antibacterial activity at 12.5 g/ml.
Replacement of chlorine from ortho to para in 4b (compound 4g)
registered two fold enhanced activity (6.25 g/ml) against C. neo-
lg/ml). More precisely, 4b and 5g against C. albicans and Rhizo-
l
Figure 4. Boat–chair conformation with equatorial orientation of the phenyl/
substituted phenyl groups at C-2 and C-4.
l
formans and moderate activity against other strains but no signifi-
cant change was noticed against the used strains when the amide
group was modified (compound 6b). Besides, Compound 4b
at 164.21/161.77 ppm are assigned to aryl carbons and fluorine at-
tached ipso carbons (C-2000 and C-4000), respectively.
All the newly synthesized compounds (4a–4h, 5a–5h, 6a, 6b, 7a
and 7b) were screened for in vitro antibacterial activity against
against A. niger is almost inactive up to 200
of phenyl group in the amide nitrogen in 4b (compound 6a)
lg/ml, but introduction

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M. Rani et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6637–6643
Figure 5. ORTEP diagram of compound 5a with 50% probability. The important bond lengths (Å): C(1)–N(1) = 1.488 (3); C(1)–S(1) = 1.531 (3); N(1)–N(2) = 1.422 (3); C(28)–
N(2) = 1.279 (3); C(28)–N(3) = 1.384 (3); C(28)–S(1) = 1.738 (2); C(29)–O(3) = 1.206 (3); C(29)–C(30) = 1.496 (4); C(30)–C(31) = 1.444 (5); C(25)–N(1) = 1.347 (4); C(3)–
N(4) = 1.495 (3); N(4)–C(22) = 1.371 (3); N(4)–C(5) = 1.488 (3); C(22)–O(2) = 1.227 (3); C(22)–C(23) = 1.513 (4); C(23)–C(24) = 1.460 (4). The important bond angles (°): N(2)–
N(1)–C(1) = 112.17 (18); N(1)–C(1)–S(1) = 100.46 (14); C(28)–S(1)–C(1) = 87.68 (11); N(2)–C(28)–N(3) = 120.0 (2); N(2)–C(28)–S(1) = 118.52 (18); N(3)–C(29)–C(30) = 114.8
(2); C(31)–C(30)–C(29) = 114.7 (3); C(27)–C(26)–C(25) = 113.5 (3); N(1)–C(25)–C(26) = 117.8 (2); N(4)–C(3)–C(10) = 113.88 (18); C(22)–N(4)–C(5) = 118.09 (19); C(22)–
N(4)–C(3) = 112.79 (18).
Table 2
Table 3
Antibacterial activity of compounds 4a–7b against some bacterial strains (MIC in
lg/
Antifungal activity of compounds 4a–7b against some fungal strains (MIC in lg/ml)
ml)
Compounds
Minimum inhibitory concentration (MIC) in
lg/ml
Compounds
Minimum inhibitory concentration (MIC) in lg/ml
C. neoformans C. albicans Rhizopus sp. A. niger A. flavus
S. aureus
B. Subtilis
S. typhi
E. coli
K. pneumonia
4a
4b
4c
4d
4e
4f
4g
4h
5a
5b
5c
5d
5e
5f
5g
5h
6a
6b
7a
7b
50
50
25
50
25
50
6.25
12.5
6.25
50
25
200
50
25
25
25
50
50
200
—
100
12.5
25
25
25
25
25
6.25
50
12.5
25
25
25
25
12.5
6.25
6.25
100
50
50
25
—
25
100
—
100
12.5
6.25
200
12.5
12.5
50
6.25
12.5
50
4a
4b
4c
4d
4e
4f
4g
4h
5a
5b
5c
5d
5e
5f
5g
5h
12.5
12.5
50
100
25
25
25
50
12.5
50
100
100
25
50
200
25
100
12.5
25
50
50
12.5
—
6.25
50
12.5
6.25
50
25
50
100
25
6.25
100
25
12.5
50
12.5
50
25
50
—
25
25
100
25
100
50
25
12.5
12.5
50
100
25
200
50
12.5
100
25
50
100
50
12.5
6.25
25
12.5
100
200
25
12.5
6.25
—
50
100
25
6.25
25
25
6.25
200
25
12.5
6.25
200
50
100
12.5
12.5
50
50
6.25
50
50
25
50
25
6.25
50
12.5
12.5
—
50
25
25
100
200
50
6.25
100
200
50
—
100
12.5
12.5
12.5
—
50
50
50
100
12.5
6.25
12.5
25
50
100
12.5
50
12.5
6.25
100
12.5
25
25
12.5
50
25
50
6a
6b
7a
7b
25
12.5
6.25
12.5
50
25
25
50
50
50
50
25
12.5
200
25
Amphotericin 25
B
Streptomycin
—, no inhibition even at maximum concentration.
—, no inhibition even at maximum concentration.
showed significant activity (12.5
l
g/ml) against the same strain.
displacement of fluoro function from para to meta position in 4h
and 5h (compounds 4c and 5c) showed one fold decreased activity
against all the fungal strain except A. flavus and A. niger, which
But moderate activity (50–100
lg/ml) was observed against all
the strains for 6b, 7a and 7b.
In order to gain more structure activity relationship in thiadia-
zole derivatives, chlorine function is replaced by fluoro function in
4g and 5g (compounds 4h and 5h); 4h showed one fold decreased
exhibited the same activity (6.25/12.5 lg/ml).
Surprisingly, the substitution of methoxy/methyl in 4a and 5a
afforded 4d, 4e, 4f and 5d, 5e, 5f; all of them (either acetylated
spiro or propionylated spiro compounds) endowed moderate activ-
activity against C. neoformans (12.5
lg/ml), two and three fold in-
creased activity against C. albicans, A. niger and A. flavus, (6.25
lg/
ity (25 lg/ml) against C. albicans but poor activity (100–200 lg/ml)
ml), respectively, when compared to 4g. Compound 5h registered
the analogous MIC values against C. albicans and A. flavus when
the acetyl analogue is replaced by propionyl moiety in 4h. The
was registered against rest of the strains for the aforementioned
spiro compounds. Besides, 4f (p-methyl substituted acetylated
spiro compound) were found to be more potent against A. flavus

M. Rani et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6637–6643
6643
(12.5
lg/ml) whereas 5f (p-methyl substituted propionylated spiro
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Supplementary data (complete experimental details and spec-
tral data (IR, 1H NMR and 13C NMR) for all the reported compounds
and single crystal X-ray data for compounds 4c and 5a were given.
The crystallographic data of 4c and 5a have been deposited at Cam-
bridge Crystallography Data Center (CCDC Nos. 706266 and
778612, respectively)) associated with this article can be found,
in the online version, at doi:10.1016/j.bmcl.2010.09.021.