New diorganotin(IV) complexes of tridentate Schiff bases derived from 1,3-indanedione derivative: Synthesis, spectral studies and in vitro antimicrobial activities

Article abstract of DOI:10.1080/10426507.2016.1248762

A series of 16 pentacoordinated diorganotin(IV) complexes has been reported here which were synthesized by reacting the appropriate dialkyl/diaryltin(IV)dichloride with four newly synthesized Schiff bases. The dianionic tridentate(ONO) Schiff base hydrazones have been conveniently synthesized in good yields by reacting 2,2-(3-methylbutanoyl)-1H-indene-1,3(2H)-dione with different acid hydrazides. The structures of the synthesized Schiff bases and their complexes have been established on the basis of IR, mass spectra, ¹H, ¹³C, ¹¹⁹Sn NMR spectroscopy and different physical techniques. The compounds have also been screened for antimicrobial activity against four bacterial strains, i.e., Gram positive Bacillus ceres (MTCC 10072), Styphyllococus aureus (MTCC 2901) and Gram negative Escherichia.coli (MTCC 732), Pseudomonas aeruginosa (MTCC 424), and three fungal strains, i.e., Aspergillus flavus (ITCC 7680), Aspergillus niger (MTCC 7678), Candida albicans (MTCC 227) by serial dilution method and it was found that most of the synthesized compounds were relatively active with the standard drugs especially in Gram positive bacteria and fungal strains.

Full text of DOI:10.1080/10426507.2016.1248762

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Bioactive Diorganotin(IV) complexes
New Diorganotin(IV) complexes of tridentate Schiff bases derived from 1,3-indanedione
derivative: Synthesis, Spectral studies and in vitro antimicrobial activities
Priyanka Khatkar, Sonika Asija*
Department of Chemistry, Guru Jambheshwar University of Science & Technology, Hisar-
125001, Haryana, India.
E-mail- sc_ic2001@yahoo.co.in
Abstract
A series of sixteen pentacoordinated diorganotin(IV) complexes has been reported here which
were synthesized by reacting the appropriate dialkyl/diaryltin(IV)dichloride with four newly
synthesized Schiff bases. The dianionic tridentate(ONO) Schiff base hydrazones have been
conveniently synthesized in good yields by reacting 2,2-(3-methylbutanoyl)-1H-indene-1,3(2H)-
dione with different acid hydrazides. The structures of the synthesized Schiff bases and their
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complexes Have been established on the basis of IR, Mass Spectra, H, 13C, 119Sn NMR
Spectroscopy and different physical techniques. The compounds have also been screened for
antimicrobial activity against four bacterial strains i.e. Gram positive Bacillus ceres (MTCC
10072), Styphyllococus aureus (MTCC 2901) and Gram negative Escherichia.coli (MTCC 732),
Pseudomonas aeruginosa (MTCC 424), and three fungal strains i.e. Aspergillus flavus (ITCC
7680), Aspergillus niger (MTCC 7678), C a n d i d a a l b i c a n s (MTCC 227) by
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serial dilution method and it was found that most of the synthesized compounds were relatively
active with the standard drugs especially in Gram positive bacteria and fungal strains.
Keywords
2-(3-methylbutanoyl)-1H-indene-1,3(2H)-dione; hydrazones; 119Sn NMR; antimicrobial activity
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INTRODUCTION
Despite of continuous research in the area of drug resistance towards pathogenic
microbes, problem is getting severe day by day. So to combat the above said problem there is a
need of the hours to design new antimicrobial drugs with reduced toxicity, improved efficacy
and better mechanism of action. Consequently, the most demanding thing for researcher is to
identify and design more novel and potent structural leads.1,2 In recent years, Schiff base metal
complexes are attractive target compounds for new drug development owing to their prominent
pharmacological applications.3,4 Schiff bases shows broad spectrum biological activity owing to
its ability to degrade DNA of the microorganisms.5 Further, these Schiff base metal complexes
expanded enormously due to high thermal stability, flexibility, medicinal efficiency6 and have
shown amazing superior biological activity. Some tumors, particularly leukemia and
neuroblastoma, are susceptible to metal ion chelation therapy because metal complexes become
more bacteriostatic and carcinostatic upon chelation as described by several in vitro studies and
clinical trials.7,8 Even the lethal cancer like disease was cured by these chelating metal
complexes.9
Particularly, some distinct characteristics of organotin complexes like variation in
coordination number, geometries, thermodynamic and kinetic characteristics and the intrinsic
properties of the metal ion itself, developed the interest of chemistry researchers to formulate
utilization of the assorted approaches in different fields like industrial, agricultural and
biomedical fields as wood preservatives, surface disinfectants,10 insecticides,11,12 antifouling
agents, and environmental applications.13 Further, Schiff bases and their derived organotin
complexes displayed, promising chemotherapeutic applications such as antimicrobial,14 anti
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inflammatory,15 antitumor,16,17 antiviral,18 antitubercular,19 antifertility.20 Prompted by these
facts, present study was designed to modify the bioactivities and optimization of lipophilic
character of organotin complexes by coordinating them with the Schiff bases hydrazones.
Therefore, we synthesized new organotin complexes in the surge of more potent and biospecific
antimicrobial and pharmacoactive drugs with better curing effects, which are less toxic to the
environment and host. During this course, a series of organotin complexes with tridentate Schiff
bases derived from the condensation of 2-(3-methylbutanoyl)-1H-indene-1,3(2H)-dione with
acid hydrazides were synthesized and characterized with the aid of elemental analysis, various
spectroscopic technique (1H, 13C, 119Sn, Mass). The compounds were also screened for
antibacterial and antifungal activities.
RESULTS AND DISCUSSION
The Organotin(IV) complexes have been synthesized by reacting 2-(3-methylbutanoyl)-1H-
indene-1,3(2H)-dione derived hydrazones with dialkyl/diaryltin(IV)dichloride in 1:1 molar ratio.
The purity of synthesized compounds was checked by thin layer chromatography (TLC). All the
metal complexes were colored solids, and were stable on exposure to air. The synthetic
procedure for the preparation of organotin compounds linked hydrazones (3) is presented in
1
13
Scheme 1. The Spectroscopic techniques (FT-IR, HNMR, C NMR, 119Sn NMR, Mass and
XRD) were used to determine the geometry of complexes which were found to be trigonal
bipyramidal. The ligands were found to be tridentate (ONO) and chelated to the central tin atom
with the replacement of hydrogen atom through enolization and due to chelation the biocidal
activity of the complexes was enhanced. The structures of all the newly synthesized compounds
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i.e. Schiff bases and tin metal linked complexes were predicted by adequate spectral (IR, H
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13
119
1
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NMR, C NMR,
Sn NMR and mass) data. The H NMR, C NMR, 119Sn NMR spectra of
compounds exhibited signals owing to different protons, carbons, and tin respectively in the
expected regions (vide experimental).
IR spectra
The coordination sites of the ligands were assigned on the basis of shifts in the frequency
and lowering in the intensities of the absorptions in the complexes as compared to the ligands.
The IR spectra of Schiff bases hydrazones displayed medium intensity absorption bands in the
region at 3410-3460cm-1 (N–H stretching) which completely disappeared in the tin complexes,
indicating the loss of a proton on the nitrogen due to tautomerization after complexation with the
tin atom and sharp frequency in the regions at 1630–1655 cm-1>C=N– stretching, which was
shifted to a lower frequency in the complexes by 10-25 cm-1 signifying that coordination had
also certainly taken place through the azomethine nitrogen to the tin atom.21,22 The coordination
through the carbonyl oxygen to the tin after deprotonation was confirmed by appearance of 2
new bands in the region 1340 cm−1, 1215 cm−1 due to ν(NCO) and ν(C–O).14 In the complexes
the coordination occurs through nitrogen attached to C-1 rather than C-10 which gives a five-
membered stable ring after coordination, with lesser strain. The formation of the complexes was
also ascertained by appearance of new bands due to ν(Sn–O), ν(Sn–N) and ν(Sn–C) at 530 ± 10,
445 ± 15 and 608-731 ± 10cm-1 respectively.14,23,25
NMR Spectral analysis
The binding sites (ONO) of the Schiff base ligands were further confirmed by comparing
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the H NMR with their complexes which was in accordance with the IR spectra. The main
characteristic peak in the ligands was a singlet due to azomethine proton observed in the region
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at δ 11.92-12.04,24 and a singlet due to proton attached to C-2 was observed in the range δ 9.07-
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9.43 in the ligands which get completely disappeared in the H NMR of the complexes which
confirmed the coordination mode of the carbonyl oxygen with central tin atom through
tautomerization. The signals due to the remaining aliphatic protons in the ligands show a regular
pattern 6H of 2CH3 group as a doublet, 1H of CH as a multiplet and 2H of CH2 as doublet in the
range δ 0.88-3.03 which remained unchanged in the complexes showing non participation of
these protons. However, tin complexes exhibited additional signals at δ 0.73-0.93, δ 0.91-1.51, δ
0.82-1.52 and δ 7.23-8.23 owing to the protons of the methyl, ethyl, butyl and phenyl groups
respectively as expected.
13
The C NMR spectral data of all the synthesized compounds were found to be in the
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expected regions. The structure was further confirmed by comparing the shifts in the C NMR
spectra of the complexes and the spectra of ligands. The signal appeared as a singlet due to
carbonyl carbon and azomethine carbon appeared at δ 172.4-191.5, δ 147.3- 157.2 respectively.
The signals due to carbonyl carbon, azomethine carbon and the carbon adjacent to the
coordinating atoms shifted to downfield on complexation because of an electron-density transfer
from the ligand to the tin metal atom supported the coordination modes through azomethine
nitrogen and carbonyl carbon which favors the tridentate (ONO) coordinating mode of the
ligands.25 Aliphatic carbon atoms of ligands appeared in the range of δ 16.1-49.3 and the
aromatic carbons appeared in the expected range and remained unaffected in the complexes,
signifying their non participation in bond formation with central atom. In the complexes, the new
signals due to methyl, ethyl, butyl attached to central tin atom appeared at δ 26.8-28.1, δ 13.1-
40.8, δ 13.1-42.6 and phenyl carbon appeared in their normal aromatic range.14, 23, 25The value of
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119Sn spectra reflects the coordination number of the nucleus in the corresponding metal
complexes. The spectra in each case show only a sharp singlet, indicating the formation of a
single species, which is indicative of pentacoordinated environment around the tin atom. 119Sn
NMR spectra were recorded in CDCl3 and DMSO-d6. The δ value varies with coordination
number and the R group attached to the central tin atom. A large upfield shift was observed in
the spectra of complexes with increase in coordination number. The occurrence of chemical shift
in 119Sn NMR spectra in the ranges δ -143.11 to -161.3, δ -172.4 to -179.7, δ -179.4 to -220.5, δ -
323.1 to -351.2 for methyl, ethyl, butyl and phenyl complexes respectively were in accordance
with the literature and pentacoordinated geometries were implicit for all the synthesized
complexes.23,25,26
Mass spectra
The ESI mass spectra of all the synthesized compounds were found to be in good
agreement with their molecular formula. The main base peaks was clearly visible which
corresponds to the whole ligand and the molecular ion peaks of the tin complexes were found
with very low abundance. In the spectra, mass fragments display the natural abundance of the
central tin atom and the major mass fragment ions were due to the [R2SnL]+, [L]+, [RSnL]+,
[SnL]+, [Sn]+ which were in accordance with the literature reports.27 The molecular ion and
base peaks with the individual tin isotopes of n-Bu2SnL1 at m/z 349.10, 581.10 and Ph2SnL2 m/z
351.00, 623.00 due to [L]+ and [M+1]+ respectively, were measured and compared with the
theoretically calculated one and were found in agreement with the theoretical values.28 Sample
NMR and ESI-mass spectra are presented in Figures S 1 – S 58 (Supplemental Materials)
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X-ray diffraction
XRD study of the synthesized compounds was done by the X-ray powder diffraction
method over the range 2θ = 20-80° which was in agreement with the crystalline nature of the
complexes29; the peaks are depicted in Figure S 61 (Supplemental Materials). An X-ray
diffraction study of the complexes showed a clear crystalline peak with maxima at 2θ = 28.640°
and d = 3.114.2
Molar conductance
The values of molar conductance of compounds were found in accordance to the literature
values. The non-electrolytic nature of complexes was confirmed by the low observed
conductance values of 10-3 M solution which was in the range of 9–16 ohm-1 cm2 mol-1.
Antimicrobial activities
The newly synthesized hydrazones and their organotin complexes (1–20) were screened
for their in vitro antimicrobial activity against four bacterial strains i.e. Gram positive Bacillus
ceres (MTCC 10072), Styphyllococus aureus (MTCC 2901) and Gram negative Escherichia.coli
(MTCC 732), Pseudomonas aeruginosa (MTCC 424), and three fungal strains i.e. Aspergillus
flavus (ITCC 7680), Aspergillus niger (MTCC 7678), Candida albicans (MTCC 227) by Serial
dilution technique. Ciprofloxacin and Fluconazole were used as reference drugs for antibacterial
and antifungal evaluation, respectively The data for the antibacterial and antifungal activity are
presented in Table S 1 and Figures S 59 – S 60 (Supplemental Materials). The occurrence of
C=N groups in the Schiff bases and R group attached to tin atom plays a vital role for biological
activity which helps in modification reaction in biological systems. The activity alters with
deviation of R groups, attached with the Sn atom. In fact, the purpose of the ligand is only to
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sustain the transfer of the active organotin (IV) moiety to the site of action where it is released by
hydrolysis. The tin complexes were found to be more active as compared to their parent Schiff
base ligands against the same micro-organism. This phenomenon was explained by the chelation
theory,29,30 in accordance to this concept the possible π electron delocalization occurs within
the whole chelate ring system and the polarity of the metal atom decreases due to partial sharing
of its positive charge with the donor R groups, due to this the lipophilic character of metal
complexes increases, which leads the penetration of them through the lipid layer of the cell
membrane31 there by deactivating respiration process by cleaving the DNA of the micro-
organism. The inhibitory activity of the organotin complexes increases in the order Sn-Ph> Sn-
Bu> Sn-Et > Sn-Me. Among the tested complexes, most of the compounds were found to be
more potent against microbial strains due to the fact that the R group increases the lipophilicity
of the complexes so that these complexes can bind easily with biological molecules by π-π
interactions which boost up the bioactivity of these complexes. Further, all compounds were
found to be more active against Gram positive bacterial strains as compared to Gram negative
because outer membrane of Gram negative bacteria is more complex, containing
lipopolysaccharide. Moreover, comparison of antibacterial and antifungal evaluation results
revealed that the antifungal activities are more prolific than antibacterial activities. With the help
of antimicrobial results, subsequently structure activity relationships (SAR) may be inferred-
1. The presence of azomethine (C=N) moiety in the ligands also show moderate antimicrobial
activity which further enhanced by ligating with tin atom against all the tested bacterial and
fungal strains in most of the cases.
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2. The presence of tin moiety augmented the antimicrobial activity but antifungal efficacy was
found to be more prominent against Aspergillus flavus, Aspergillus niger, Candida albicans
as compared to the antibacterial activity.
3. In some cases, presence of pyrazine moiety in the ligand improved the antimicrobial activity.
4. In most of the cases, presence of phenyl, butyl moiety in the tin complexes increased the
antimicrobial potency against all the tested microbial strains as compared to the ethyl and
methyl groups.
From these results, we conclude that there are necessities of unique structures for a compound to
be effective against different microbial strains still, no general trend towards structure activity
relationship (SAR) has been recognized for the antimicrobial activity of the tested compounds.
Experimental
All the chemicals such as diphenyltin(IV) dichloride, di-n-butyltin(IV) dichloride,
diethyltin (IV) dichloride, dimethyltin (IV) dichloride were purchased from (Aldrich) were used
as received without further purification and 2-(3-methylbutanoyl)-1H-indene-1,3(2H)-dione were
prepared according to the methods reported in the literature32. Solvents such as methanol, hexane
(Qualigens) were dried using standard procedures before use. All the synthesis were carried out
under an inert atmosphere. Melting points (mp, °C) of all the synthesized compounds were
measured on an electrothermal apparatus and are uncorrected. The elemental analyses were
analyzed on Thermo Scientific FLASH-2000 CHN analyser. IR spectra in the range 4000–400
cm-1 were obtained on a Perkin Elmer 983 spectrophotometer by using KBr pellets. The NMR
spectra (1H, 13C, and 119Sn) were obtained on a Bruker Avance 400MHz spectrometer by using
Me4Si as internal standard and there chemical shifts were recorded in ppm. Tin was estimated
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gravimetrically as SnO2. The mass spectra were recorded on LCMS-MS 6410 Agilent
technologies spectrophotometer. XRD powder diffraction measurement were carried out by
using Rigaku table top X-ray diffractometer with scan rate of 2 min in the range 20-80°. Molar
Conductances of the compounds were measured in DMSO with a conductivity bridge type
Model-306 Systronics The Supplemental Materials contain sample 1H, 13C, 119Sn NMR and ESI-
MS spectra for the ligands and tin complexes (Figures S 1 – S 58)
Synthesis of Schiff Base Ligands
The 2-(3-methylbutanoyl)-1H-indene-1,3(2H)-dione needed for the synthesis was
prepared by the Claisen condensation of diethylphthlate and appropriate ketone under the
influence of sodium methoxide according to the procedure as described in literature.32,33 Schiff
bases were synthesized by dissolving 1:1 molar ratio methanolic solution of 2-(3-
methylbutanoyl)-1H-indene-1,3(2H)-dione with benzoic acid, pyrazine acid, nicotinic acid and
isonicotinic acid hydrazides. The solution was stirred and refluxed for 5-6 h .The solution was
kept overnight at room temperature. The white and red color solids so obtained were filtered and
recrystallized in methanol and chloroform solution (1:1, v/v).
(Benzoic acid [1-(1,3-dioxo-indan-2-yl)-3-methyl-butylidene]-hydrazide) H2L1(1).
White solid; m.p: 170-172°C. Yield: 90%; Anal. Calc. for C21H20N2O3 (348.40): C, 72.40; H,
5.79; N, 8.04; O, 13.78%. Found: C, 72.34; H, 5.71; N, 8.02; O, 13.72 %. ESI-MS m/z:
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349.32[M + H]+. IR (KBr pellets, cm−1): 3212 ν(N–H), 1588.46 ν(C=N), 1638.28 ν(C=O). H
NMR (CDCl3, 400 MHz, δH): 11.95 (s, 1H, NH), 9.38 (s, 1H, C2-H), 8.03(d, 1H, J = 8 Hz), 7.86
(d, 2H, J = 8Hz), 7.60-7.38 (m, 6H), 2.92 (d, 2H, CH2, J = 8Hz), 2.07-1.93 (m, 1H, CH), 0.88 (d,
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6H, CH3, J = 4Hz) ppm. 13C (CDCl3, 100 MHz, δC): 193.2, 170.1 (C=O), 144.0 (C=N), 143.3,
143.2, 143.2, 142.9, 139.6, 138.1, 121.0, 99.4, 33.6, 27.9, 22.1ppm.
(Pyrazine-2-carboxylic acid [1-(1,3-dioxo-indan-2-yl)-3-methyl-butylidene]-hydrazide)
H2L2(2).
White solid; m.p.: 129°C. Yield: 86%; Anal. Calc. for C19H18N4O3 (350.37), C, 65.13; H,
5.18;N, 15.99; O, 13.70%. Found: C, 65.07; H, 5.15; N, 15.95; O, 13.67 %. ESI-MS m/z:
351.21[M + H]+. IR (KBr pellets, cm−1): 3334.24 ν(N–H), 1568.02 ν(C=N), 1643.73 ν(C=O). 1H
NMR (CDCl3, 400 MHz, δH): 12.04 (s, 1H, NH), 9.43 (s, 1H, C2-H), 9.60 (s, 1H), 8.89 (d, 1H, J
= 8Hz), 8.06 (d, 1H, J = 8Hz), 7.62 (d, 2H), 7.73 (dd, 2H), 3.00 (d, 2H, CH2, J = 8Hz), 2.14-2.07
13
(m, 1H, CH), 1.05 (d, 6H, CH3, J = 8Hz) ppm. C NMR (CDCl3, 100 MHz, δC): 188.9, 170.4
(C=O), 162.0, 147.3(C=N), 142.9, 139.6, 138.1, 133.1, 132.9, 121.0, 120.7, 101.8, 33.6, 27.9,
22.1 ppm.
(Isonicotinic acid [1-(1,3-dioxo-indan-2-yl)-3-methyl-butylidene]-hydrazide) H2L3(3).
Red solid; m.p.: 241-243°C. Yield: 82%; Anal. Calc. for C20H19N3O3 (349.38): C, 68.75; H, 5.48;
N, 12.03; O, 13.74%. Found: C, 68.71; H, 5.45; N, 11.98; O, 13.71 %. ESI-MS m/z: 349.14 [M +
H]+. IR (KBr pellets, cm−1): 3324 ν(N–H), 1578.67 ν(C=N), 1659.18 ν(C=O). 1H NMR (DMSO-
d6, 400 MHz, δH): 11.99 (s, 1H, NH), 9.38 (s, 1H, C2-H), 8.83 (d, 2H, J = 8Hz), 7.85 (d, 2H, J =
8Hz), 7.70-7.66 (d, 4H, J = 8Hz), 3.03 (d, 2H, CH2, J = 8Hz), 2.08-2.00 (m, 1H, CH), 0.95 (d,
6H, CH3, J = 8Hz) ppm. 13C NMR (DMSO-d6, 100 MHz, δC): 181.0, 173.9 (C=O), 149.4 (C=N),
148.5, 142.4, 132.3, 130.7, 128.6, 122.5, 93.6, 35.7, 22.2, 20.2 ppm.
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(Nicotinic acid [1-(1,3-dioxo-indan-2-yl)-3-methyl-butylidene]-hydrazide) H2L4(4).
Orange solid; m.p.: 179-182°C. Yield: 93%; Anal. Calc. for C20H19N3O3 (349.38): C, 68.75; H,
5.48; N, 12.03; O, 13.74%. Found: C, 68.73; H, 5.44; N, 12.01; O, 13.72 %. ESI-MS m/z:
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349.14[M + H]+. IR (KBr pellets, cm−1): 3245 ν(N–H), 1582.54 ν(C=N), 1676.58 ν(C=O). H
NMR (DMSO-d6, 400 MHz, δH): 11.92 (s, NH), 9.07(s, 1H, C2-H), 9.43 (d, 1H, J = 8Hz ), 8.64
(d, 1H, J = 8Hz), 7.94-7.56 (m, 6H), 2.91 (d, 2H, CH2, J = 8Hz), 2.07-1.92 (m, 1H, CH), 0.83 (d,
6H, CH3, J = 8Hz) ppm. 13C NMR (DMSO-d6, 100 MHz, δC): 182.0, 172.6(C=O), 151.5, 149.6
(C=N), 148.2, 137.3, 136.3, 133.4, 131.7, 130.7, 129.7, 95.5, 34.6, 21.4, 20.4 ppm.
Synthesis of Organotin complexes
Organotin(IV) complexes of the Schiff base-ligands were synthesized from the the Schiff
base and suitable diorganotin(IV)dichloride as follows: Schiff base ligand (2.0 mmol) was
dissolved in specially dried methanol (15 mL), a few drops of concentrated sodium methoxide in
methanol were added, and the mixture was stirred and then refluxed for 3 h. under an inert
atmosphere of dry nitrogen. The solution was allowed to cool and a methanolic solution of
R2SnCl (1 mmol) was added to it with constant stirring. The solution was further refluxed at 40–
50◦C for another 12-15 h. The mixture was kept overnight at room temperature. The mixture was
filtered in order to remove sodium chloride salt formed and the excess solvent was slowly
removed by evaporation under a vacuum pump. The solid thus obtained was recrystallized from
methanol-chloroform (1:1, v/v) mixture. The depiction of the individual complexes was as
follows:
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(4E,6Z)-7-isobutyl-2,2,4-triphenyl-8H-indeno[2,1-h][1,3,5,6,2]dioxadiazastannonin-8-one
Ph2SnL1 (5).
Yellow solid; m.p.: 159-163°C. Yield: 71%; Anal. Calc. for C33H28N2O3Sn: C, 64.00; H, 4.56;
N, 4.52; O, 7.75; Sn, 19.17%. Found: C, 63.98; H, 4.53; N, 4.49; O, 7.73; Sn, 19.14%. ESI-MS
m/z: 620.11[M + H]+. IR (KBr, cm−1): 1698 ν(C=O), 1569 ν(C=N), 1543 ν(C–O), 525 ν(Sn–O),
446 ν(Sn←N). 1H NMR (CDCl3, 400 MHz, δH): 8.21-7.26 (m, 19H), 3.45 (d, 2H, CH2, J =
8Hz), 2.77-2.42 (m, 1H, CH), 1.06 (d, 6H, CH3, J = 8Hz) ppm. 13C NMR (CDCl3, 100 MHz, δC):
190.3, 183.4 (C-O), 171.9 (C=O), 157.2 (C=N), 136.5, 134.4, 132.4, 130.3, 129.9, 129.1, 128.2,
125.8, 128.13, 121.3, 114.8, 102.2, 41.4, 23.9, 21.5, ppm. 119Sn NMR (CDCl3, 149 MHz, δSn): -
323.76 ppm.
(4E,6Z)-2,2-dibutyl-7-isobutyl-4-phenyl-8H-indeno[2,1-h][1,3,5,6,2]dioxadiazastannonin-8-
one n-Bu2 SnL1 (6).
Yellow solid; m.p.: 134-136°C; Yield: 73%; Anal. Calc. for C29H36N2O3Sn: C, 60.12; H, 6.26;
N, 4.84; O, 8.29; Sn, 20.49%. Found: C, 60.09; H, 6.22; N, 4.81; O, 8.26; Sn, 20.45%. ESI-MS
m/z: 581.60 [M + H]+. IR (KBr pellets, cm−1): 1571 ν (C=N), 1701 ν(C=O), 676 ν(Sn -C), 741.44
ν(Sn -O), 449 ν(Sn -N). 1HNMR (CDCl3, 400 MHz, δH): 8.06-8.03 (d, 2H),7.90-7.88 (d, 2H, J =
8Hz), 7.76-7.38 (m, 5H) 3.66 (d, 2H, J = 8Hz), 3.06-3.00 (m, 2H), 2.29-2.13 (d, 1H, J = 8Hz),
2.11-2.02 (m, 1H), 1.79-1.41 (m, 6H), 1.39-1.20 (m, 2H), 1.08-0.94 (m, 10H), 0.88-0.82 (m, 3H)
ppm. 13C NMR (CDCl3, 100 MHz, δC): 186.7, 177.3, 167.2, 149.5 (C=N), 140.3, 136.7, 131.7,
129.4, 127.4, 123.1, 120.2, 103.1, 45.4, 35.5, 27.6, 26.0, 25.0, 21.7, 13.5 ppm. 119Sn NMR
(CDCl3, 149 MHz, δSn): -184.7 ppm.
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(4E,6Z)-2,2-diethyl-7-isobutyl-4-phenyl-8H-indeno[2,1-h][1,3,5,6,2]dioxadiazastannonin-8-
one n-Et2 SnL1(7).
Yellow solid; m.p.: 146-149°C. Yield: 73%; Anal. Calc. for C25H28N2O3Sn: C, 57.39; H, 5.39;
N, 5.35; O, 9.17; Sn, 22.69%. Found: C, 57.37; H, 5.36; N, 5.31; O, 9.12; Sn, 22.64%. ESI-MS
m/z: 524.63 [M + H]+. IR (KBr pellets, cm−1): 1571 ν(C=N), 1697 ν(C=O), 672 ν(Sn -C), 736
1
ν(Sn -O), 441 ν(Sn -N). HNMR (CDCl3, 400 MHz, δH): 7.94-7.72 (m, 9H), 2.97(d, 2H), 1.99-
1.88 (m, 1H, CH), 1.47-1.38 (m, 4H, CH2), 1.19-0.87 (m, 12H, CH3) ppm. 13C NMR (CDCl3,
100 MHz, δC): 181.8, 179.1, 174.2 (C=O), 157.4 (C=N), 133.0, 132.7, 131.4, 130.4, 129.8,
129.1, 128.1, 102.0, 49.4, 38.2, 28.3, 21.7, 18.9, ppm. 119Sn NMR (CDCl3, 149 MHz, δSn): -
179.3 ppm.
(4E,6Z)-7-isobutyl-2,2-dimethyl-4-phenyl-8H-indeno[2,1-h][1,3,5,6,2]dioxadiazastannonin-
8-one Me2SnL1(8).
Yellow solid; m.p.: 140-143°C. Yield: 76%; Anal. Calc. for C23H24N2O3Sn: C, 55.79; H, 4.89;
N, 5.66; O, 9.69; Sn, 23.97%. Found: C, 55.73; H, 4.86; N, 5.62; O, 9.64; Sn, 23.92%. ESI-MS
m/z: 497.36 [M + H]+. IR (KBr pellets, cm−1): 1679 ν(C=O), 1563 ν(C=N), 1542 ν (C–O), 1311
1
ν(C–O), 529 ν(Sn–O), 443 ν(Sn←N). H NMR (CDCl3, 400 MHz, δH): 8.62 (d, 1H, J = 8Hz),
8.06-8.03 (m, 3H), 7.86-7.39 (m, 5H), 3.65 (d, 2H, CH2, J = 8Hz), 2.16-2.09 (m, 1H, CH), 0.92
(d, 6H, CH3, J = 8Hz), 0.73 (s, 6H, CH3) ppm. 13C NMR (CDCl3, 100 MHz, δC): 183.4, 178.8,
173.6, 156.1 (C=N), 138.3, 131.1, 130.7, 129.5, 129.7, 129.1, 128.1, 102.1, 39.2, 28.0, 23.3,
21.4, ppm. 119Sn NMR (CDCl3, 149 MHz, δSn): -143.1 ppm.
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(4E,6Z)-7-isobutyl-2,2-diphenyl-4-(pyrazin-2-yl)-8H-indeno[2,1-
h][1,3,5,6,2]dioxadiazastannonin-8-one Ph2SnL2(9).
Yellow solid; m.p.: 109-111°C. Yield: 68%; Anal. Calc. for C31H26N4O3Sn: C, 59.93; H, 4.22;
N, 9.02; O, 7.73; Sn, 19.11%. Found: C, 59.90; H, 4.19; N, 8.99; O, 7.69; Sn, 19.10 %. ESI-MS
m/z: 622.19 [M + H]+. IR (KBr pellets, cm−1): 1553.02 ν(C=N), 1631.73 ν(C=O), 679 ν(Sn-C),
716 ν(Sn -O), 453 ν(Sn←N). 1H NMR (CDCl3, 400 MHz, δH): 8.86 (s, 1H), 8.51-8.47 (dd, 2H),
7.64-7.42 (m, 14H), 2.93 (d, 2H, J = 8Hz), 2.10-2.02 (m, 1-H), 0.95 (d, 6H, J = 8Hz) ppm. 13C
NMR (CDCl3, 100 MHz, δC) 189.4, 178.0, 174.4 (C=O), 158.9(C=N), 135.6, 133.24, 132.8,
130.7, 129.5, 129.1, 127.9, 126.2, 125.0, 124.2, 124.2, 101.0, 40.2 (C-7), 24.7, 20.2, ppm. 119Sn
NMR (CDCl3, 149 MHz, δSn): -334.8 ppm
(4E,6Z)-2,2-dibutyl-7-isobutyl-4-(pyrazin-2-yl)-8H-indeno[2,1-
h][1,3,5,6,2]dioxadiazastannonin-8-one n-Bu2 SnL2(10).
Red solid; m.p.: 119-121°C. Yield: 73%; Anal. Calc. C27H34N4O3Sn: C, 55.79; H, 5.90; N, 9.64;
O, 8.26; Sn, 20.42%. Found: C, 55.76; H, 5.88; N, 9.61; O, 8.24; Sn, 20.39%. ESI-MS m/z:
581.60 [M + H]+. IR (KBr pellets, cm−1): 1573 ν(C=N), 1633 ν(C=O), 672 ν(Sn -C), 736.44 ν(Sn
-O), 451 ν(Sn ←N). 1HNMR (CDCl3, 400 MHz, δH): 9.44-9.36 (m, 2H), 8.89-8.60 (m, 2H), 8.45
(d, 1H, J = 8Hz), 7.74 (d, 2H, J = 4Hz), 7.61 (d, 2H, J = 4Hz), 3.54 (d, 2H, J = 8Hz), 3.07-2.98
(m, 2H), 2.99 (d, 2H, J = 8Hz), 2.39-2.33 (d, 1H, J = 8Hz), 2.09 (d, 6H, J = 8Hz), 1.59-1.24 (m,
6H), 1.07-1.03 (m, 12H), 0.86-0.82, ppm. 13C NMR (CDCl3, 100 MHz, δC): 191.7, 178.1, 173.2
(C=O), 155.18 (C=N), 135.3, 132.4, 131.1, 130.4, 129.0, 128.3, 99.4, 42.8, 41.5, 25.7, 24.3, 22.0,
20.4, 13.4, ppm. 119Sn NMR (CDCl3, 149 MHz, δSn): -210.5 ppm.
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(4E,6Z)-2,2-diethyl-7-isobutyl-4-(pyrazin-2-yl)-8H-indeno[2,1-
h][1,3,5,6,2]dioxadiazastannonin-8-one n-Et2 SnL2(11).
Yellow solid; m.p.: 112-115°C. Yield: 73%; Anal. Calc. C23H26N4O3Sn: C, 52.60; H, 4.99; N,
10.67; O, 9.14; Sn, 22.60%. Found: C, 52.58; H, 4.99; N, 10.67; O, 9.11; Sn, 22.55%. IR (cm−1):
1577 ν (C=N), 1678 ν(C=O), 667 ν(Sn -C), 737 ν(Sn -O), 458 ν(Sn←N). ESI-MS m/z: 526.10
[M + H]+. 1HNMR (CDCl3, 400 MHz, δH): 8.82 (s, 1H), 8.71 (d, 1H, J = 8Hz), 8.38 (d, 1H, J =
8Hz), 7.79 (d, 2H, J = 8Hz), 7.52 (d, 2H, J = 8Hz) 2.31-2.00 (m, 1H, CH), 1.49-1.39 (m, 6H,
13
CH2), 1.28-0.91 (m, 12H, CH3) ppm. C NMR (CDCl3, 100 MHz, δC): 181.2, 179.8, 170.3
(C=O), 153.5 (C=N), 135.0, 130.7, 129.1, 132.0, 131.1, 129.7, 128.1, 100.8, 41.5, 40.5, 24.0,
22.7, 21.4 ppm. 119Sn NMR (CDCl3, 149MHz, δSn): -178.5 ppm
(4E,6Z)-7-isobutyl-2,2-dimethyl-4-(pyrazin-2-yl)-8H-indeno[2,1-
h][1,3,5,6,2]dioxadiazastannonin-8-one Me2SnL2(12).
Yellow solid; m.p.: 101-103°C. Yield: 65%; Anal. Calc. for C21H22N4O3Sn: C, 50.74; H, 4.46;
N, 11.27; O, 9.65; Sn, 23.88%. Found: C, 50.72; H, 4.43; N, 11.26; O, 9.62; Sn, 23.84%. ESI-
MS m/z: 498.17 [M + H]+. IR (KBr pellets, cm−1): 1682 ν(C=O), 1573 ν(C=N), 1546 ν(C–O),
1
1309 ν(C–O), 531 ν(Sn–O), 449 ν(Sn←N). H NMR(CDCl3, 400 MHz, δH): 8.69 (d, 1H, J =
8Hz), 8.50 (d, 2H, J = 8Hz), 7.72 (d, 1H, J = 8Hz), 7.58-7.47 (m, 4H), 2.90 (d, 2H, CH2, J =
8Hz), 2.02-1.81 (m, 1H, CH), 1.32 (s, 6H, CH3, J = 8Hz), 0.87 (d, 6H, CH3) ppm. 13C NMR
(CDCl3, 100 MHz, δC): 180.2, 178.1, 170.3 (C-10, C=O), 155.1 (C=N), 137.7, 131.4, 130.7,
130.1, 129.7, 129.0, 101.4, 128.5, 40.8, 28.3, 22.4, 21.0, ppm. 119Sn NMR (CDCl3, 149 MHz,
δSn): -161.4 ppm.
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(4E,6Z)-7-isobutyl-2,2-diphenyl-4-(pyridin-4-yl)-8H-indeno[2,1-
h][1,3,5,6,2]dioxadiazastannonin-8-one Ph2SnL3(13).
Red solid; m.p.: 153-155°C. Yield: 63%; Anal. Calc. for C32H27N3O3Sn: C, 61.96; H, 4.39; N,
6.77; O, 7.74; Sn, 19.14%. Found: C, 61.94; H, 4.36; N, 6.75; O, 7.76; Sn, 19.13%. ESI-MS m/z:
621.13 [M + H]+. IR (KBr pellets, cm−1): 1681 ν(C=O), 1575 ν(C=N), 1542 ν(C–O), 1302 ν(C–
1
O), 537 ν(Sn–O), 451 ν(Sn←N). H NMR (DMSO-d6, 400 MHz, δH): 8.18 (d, 2H, J = 8Hz),
8.10 (d, 2H, J = 8Hz), 8.02 (d, 2H, J = 8Hz), 7.26-7.98 (m, 12H) 3.05 (d, 2H, CH2, J = 8Hz),
2.05-2.22 (m, 1H, CH), 1.07-0.85 (d, 6H, CH3 J = 8Hz) ppm. 13C (DMSO-d6, 100 MHz, δC):
193.9, 181.3 (C-O), 173.1 (C=O), 155.1(C=N), 149.9, 138.9, 136.8, 131.5, 129.5, 129.1, 128.7,
127.9, 127.4, 125.0, 101.8, 43.9, 23.9, 21.8, ppm. 119Sn NMR (DMSO-d6, 149 MHz, δSn): -351.3
ppm.
(4E,6Z)-2,2-dibutyl-7-isobutyl-4-(pyridin-4-yl)-8H-indeno[2,1-
h][1,3,5,6,2]dioxadiazastannonin-8-one n-Bu2 SnL3(14).
Yellow solid; m.p.: 196-198°C. Yield: 73%. Anal. Calc. C28H35N3O3Sn: C, 57.95; H, 6.08; N,
7.24; O, 8.27; Sn, 20.46%. Found: C, 57.93; H, 6.06; N, 7.21; O, 8.25; Sn, 20.43%. IR (KBr
pellets, cm−1): 1675 ν(C=O), 1569 ν(C=N), 671 ν(Sn -C), 721 ν(Sn -O), 462 ν(Sn←N). ESI-MS
m/z: 581.60 [M + H]+. 1HNMR (CDCl3, 400 MHz, δH): 8.61 (d, 2H, J = 8Hz), 7.90-7.52 (m, 4H),
7.56-7.48 (d, 2H, J = 4Hz), 3.19 (d, 2H, J = 8Hz), 2.56-2.12 (m, 1H), 1.57-1.41 (m, 6H), 1.04-
0.77 (m, 18H), ppm. 13C NMR (CDCl3, 100 MHz, δC): 186.7, 179.5, 172.6 (C=O), 154.5 (C=N),
134.4, 131.7, 129.8, 101.4, 137.3, 129.3, 128.1, 41.5, 40.1, 25.7, 24.3, 22.4, 20.0, 13.8, ppm.
119Sn NMR (CDCl3, 149 MHz, δSn): -188.7 ppm.
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(4E,6Z)-2,2-diethyl-7-isobutyl-4-(pyridin-4-yl)-8H-indeno[2,1-
h][1,3,5,6,2]dioxadiazastannonin-8-one n-Et2 SnL3(15).
Red solid; m.p.: 180-182°C. Yield: 73%; Anal. Calc. C24H27N3O3Sn: C, 54.99; H, 5.19; N, 8.02;
O, 9.16; Sn, 22.65%. Found: C, 54.96; H, 5.17; N, 8.00; O, 9.12; Sn, 22.63%. IR (KBr pellets,
cm−1): 1689 ν(C=O), 1573 ν(C=N), 669 ν(Sn -C), 729 ν(Sn -O), 471 ν(Sn←N). ESI-MS m/z:
525.11 [M + H]+. 1HNMR (CDCl3, 400 MHz, δH): 8.72 (d, 2H, J = 8Hz ), 7.76 (d, 2H, J = 8Hz),
7.67-7.52 (m, 4H), 2.31-1.98 (m, 1H, CH), 1.51-1.42 (m, 6H, CH2), 1.31-0.97 (m, 12H, CH3)
ppm. 13C NMR (CDCl3, 100 MHz, δC): 179.8, 178.5, 171.3 (C=O), 151.2 (C=N), 133.7, 131.1,
129.7, 99.18, 135.07, 130.4, 128.13, 38.8, 32.5, 25.1, 22.7, 22.0, ppm. 119Sn NMR (CDCl3, 149
MHz, δSn): -172.5 ppm.
(4E,6Z)-7-isobutyl-2,2-dimethyl-4-(pyridin-4-yl)-8H-indeno[2,1-
h][1,3,5,6,2]dioxadiazastannonin-8-one Me2SnL3 (16).
Yellow solid; m.p.: 176-178°C. Yield: 63%; Anal. Calc. for C22H23N3O3Sn: C, 53.26; H, 4.67;
N, 8.47; O, 9.67; Sn, 23.93%. Found: C, 53.23; H, 4.64; N, 8.45; O, 9.64; Sn, 23.90%. ESI-MS
m/z: 497.14 [M + H]+. IR (KBr pellets, cm−1): 1678 ν(C=O), 1569 ν(C=N), 1542 ν(C–O), 1307
1
ν(C–O), 534 ν(Sn–O), 451 ν(Sn←N). H NMR (CDCl3, 400 MHz, δH): 8.61 (d, 2H, J = 8Hz),
8.02 (d, 2H, J = 8Hz), 7.47 (d, 2H, J = 8Hz), 7.37-7.33 (d, 2H, J = 8Hz), 2.88 (d, 2H, CH2, J =
13
8Hz), 1.91-1.81(m, 1H, CH), 1.32 (s, 6H, CH3, J = 8Hz), 0.98 (d, 6H, CH3) ppm. C NMR
(CDCl3, 100 MHz, δC): 182.83, 177.89, 173.42 (C=O), 154.7 (C=N), 137.9, 129.8, 129.4, 100.1,
130.7, 129.1, 128.7, 40.1, 28.6, 21.4, 21.0, ppm. 119Sn NMR (CDCl3, 149 MHz, δSn): -152.4
ppm.
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(4E,6Z)-7-isobutyl-2,2-diphenyl-4-(pyridin-3-yl)-8H-indeno[2,1-
h][1,3,5,6,2]dioxadiazastannonin-8-one Ph2SnL4(17).
Yellow solid; m.p.: 82-84°C. Yield: 76%; Anal. %. Calc. for C32H27N3O3Sn: C, 61.96; H, 4.39;
N, 6.77; O, 7.74; Sn, 19.14%. Found: C, 61.94; H, 4.37; N, 6.75; O, 7.72; Sn, 19.11%. ESI-MS
m/z: 621.72 [M + H]+. IR (KBr, cm−1): 1577 ν(C=N), 1671 ν(C=O), 1549 ν(C–O), 1312 ν(C–O),
1
547 ν(Sn–O), 447 ν(Sn←N). H NMR (DMSO-d6, 400 MHz, δH): 9.23 (1H, d, J = 8Hz), 8.40-
7.36 (m, 17H), 3.06 (d, 2H, CH2, J = 4Hz), 2.16-2.02 (m, 1H, CH), 0.96(d, 6H, CH3, J = 8Hz)
13
ppm. C NMR (DMSO-d6, 100 MHz, δC): 192.3, 180.5, 172.3 (C=O), 154.87 (C=N), 153.1,
152.8, 136.06, 133.2, 131.9, 130.7, 129.5, 129.9, 126.6, 124.2, 123.4, 123.0, 99.78, 41.0, 22.3,
21.8, ppm. 119Sn NMR (DMSO-d6, 149 MHz, δSn): -326.4 ppm
(4E,6Z)-2,2-dibutyl-7-isobutyl-4-(pyridin-3-yl)-8H-indeno[2,1-
h][1,3,5,6,2]dioxadiazastannonin-8-one n-Bu2 SnL4 (18).
Yellow solid, m.p.: 133-135°C. Yield: 64%; Anal. Calc. for C28H35N3O3Sn: C, 57.95; H, 6.08; N,
7.24; O, 8.27; Sn, 20.46%. Found: C, C, 57.92; H, 6.05; N, 7.22; O, 8.25; Sn, 20.43 %. ESI-MS
m/z: 581.60 [M + H]+. IR (KBr pellets, cm−1): 1677 ν(C=O), 1565 ν(C=N), 678 ν(Sn -C), 698
ν(Sn -O), 454 ν(Sn←N). 1H NMR (CDCl3, 400 MHz, δH): 8.87-7.36 (m, 8H), 3.63-3.05 (m, 2H),
13
2.22-2.05 (m, 1H), 1.63 (s, 6H), 1.25-0.85 (m, 18H) ppm. C NMR (CDCl3, 100 MHz, δC):
188.0, 178.5, 171.9 (C=O), 155.8 (C=N), 137.7, 132.4, 129.1, 101.4, 133.0, 129.5, 134.0, 128.5,
40.8, 38.2, 25.08, 24.0, 22.4, 20.0, 13.8, ppm. 119Sn NMR (CDCl3, 149 MHz, δSn): -179.5 ppm
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(4E,6Z)-2,2-diethyl-7-isobutyl-4-(pyridin-3-yl)-8H-indeno[2,1-
h][1,3,5,6,2]dioxadiazastannonin-8-one Et2 SnL4(19).
Yellow solid; m.p.: 136-138°C. Yield: 64%; Anal. Calc. C24H27N3O3Sn: C, 54.99; H, 5.19; N,
8.02; O, 9.16; Sn, 22.65%. Found: C, 54.96; H, 5.16; N, 7.99; O, 9.12; Sn, 22.63%. ESI-MS
m/z: 525.11 [M + H]+. IR (KBr pellets, cm−1): 1676 ν(C=O), 1565 ν(C=N), 677 ν(Sn -C), 696
1
ν(Sn -O), 474 ν(Sn -N). HNMR (CDCl3, 400 MHz, δH): 8.68 (s, 1H), 8.34 (d, 2H, J = 8Hz),
7.94-7.76 (m, 3H), 7.69-7.38 (m, 3H), 3.26 (d, 2H), 2.55-2.33 (m, 1H), 1.14 (d, 6H), 1.04 (s, 6H)
ppm. 13C NMR (CDCl3, 100 MHz, δC): 183.1, 178.37, 172.39 (C=O), 155.4 (C=N), 137.3, 133.0,
132.4, 131.7, 129.1, 129.7, 128.7, 99.1, 41.1, 40.1, 25.7, 24.7, 22.0, ppm. 119Sn NMR (CDCl3,
149 MHz, δSn): -173.06 ppm.
(4E,6Z)-7-isobutyl-2,2-dimethyl-4-(pyridin-3-yl)-8H-indeno[2,1-
h][1,3,5,6,2]dioxadiazastannonin-8-one Me2SnL4 (20).
Yellow solid; m.p.: 141-143°C. Yield: 63%; Anal. Calc. for C22H23N3O3Sn: C, 53.26; H, 4.67;
N, 8.47; O, 9.67; Sn, 23.93%. Found: C, 53.24; H, 4.63; N, 8.44; O, 9.65; Sn, 23.92 %. ESI-MS
m/z: 497.11 [M + H]+. IR (KBr pellets, cm−1): 1674 ν(C=O), 1563 ν(C=N), 1541ν(C–O), 536
ν(Sn–O), 465 ν(Sn←N). 1H NMR (CDCl3, 400 MHz, δH): 9.29-7.32 (m, 9H), 3.64 (d, 2H, CH2, J
13
= 8Hz), 2.23-2.29 (m, 1H), 0.87 (d, 6H, J = 8Hz), 0.81 (s, 6H) ppm. C NMR (CDCl3, 100
MHz, δC): 180.8, 177.1, 173.9 (C=O), 154.53 (C=N), 136.3, 129.1, 129.4, 99.8, 131.1, 129.8,
130.7, 128.1, 41.8, 26.3, 21.0, 20.43, ppm. 119Sn NMR (CDCl3, 149 MHz, δSn): -143.2 ppm.
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Pharmacology
All the newly synthesized ligands (1-4) and organotin complexes (5-20) were assesed for their in
vitro antimicrobial activity against four bacterial strains i.e. Gram positive Bacillus ceres (MTCC
10072), Styphyllococus aureus (MTCC 2901) and Gram negative Escherichia.coli (MTCC 732),
Pseudomonas aeruginosa (MTCC 424), and three fungal strains i.e. Aspergillus flavus (ITCC
7680), Aspergillus niger (MTCC 7678), Candida albicans (MTCC 227) by employing serial
dilution technique.23,27,34 The fresh cultures of bacteria and fungi were prepared by
inoculation of respective microorganisms in suitable media i.e Nutrient agar and PDB (Potato
dextrose broth), respectively. The stock solution was prepared by by dissolving weighed amounts
of synthesized compounds in DMSO (1.0 mg of the test compound in 10 mL DMSO) to get a
final concentration of 100 μg/mL and then it was further diluted to make concentration of 50, 25,
12.5, 6.25, 3.12, 1.56, 0.75 μg/mL. The bacteria and the fungi were inoculated to each solution
followed by incubation at 37 ± 1 °C for (all bacteria) and 25 ± 1 ºC for 7 days for (fungi). Then,
the MIC (minimum inhibitory concentration) was determined in µmol/mL. The experimental
values were compared with standard drugs i.e. Ciprofloxacin for antibacterial activity and
Fluconazole for antifungal activity which were also tested under analogous conditions for
comparison with the synthesized compounds. Microbial growth was checked visually and
spectrophotometrically after incubation, and the results were recorded in terms of Minimum
Inhibitory Concentration (MIC, μmol/mL). The data for the antimicrobial activity are presented
in Table S 1.
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Conclusion
We have synthesized a series of twenty new compounds by employing chemical alterations. All
the synthesized organotin compounds have been tested for their in vitro antimicrobial activity
towards Gram-positive and Gram-negative bacterial strains as well as the fungal strains. Most of
the investigated compounds showed moderate to good activity. Among the synthesized
derivatives, 9 against P. aeruginosa , A. flavus ; compound 5 against P. aeruginosa , A. flavus ,
C.albicans, 13, 17 against B. ceres, A . flavus , A. niger, C.albicans were found to be as good as
with the standard drug against antimicrobial strains, which could lead to further potent drug
discovery against antimicrobial infections.
Acknowledgment
The authors are grateful to Dr. Namita Singh, Department of Bio- and Nanotechnology, Guru
Jambheshwar University of Science and Technology, Hisar, for her assistance in carrying out
antimicrobial evaluation.
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Scheme 1: Synthetic Route for Schiff Base Ligands and their Organotin Complexes
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