Friendly synthesis, metallation, and phosphorylation of schiff base as a potential Pharmacological interest

Article abstract of DOI:10.1080/15533174.2010.522662

In view of the broad physiological activity of organometallic and organophosphorus compounds, the present paper deals with the synthesis of 2-(4-methoxybenzylidene amino) benzene-thiol, its metallation with mercury (II), nickel (II), palladium (II), and p

Full text of DOI:10.1080/15533174.2010.522662

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Friendly Synthesis, Metallation, and Phosphorylation
of Schiff Base as a Potential Pharmacological Interest
Emtithal A. El-Sawi a , Mona A. Hosny a , Wafaa A. Mokbel a & Tahany M. Sayed a
a Department of Chemistry, Faculty of Women for Arts, Science, and Education , Ain
Shams University , Heliopolis, Cairo, Egypt
Published online: 03 Dec 2010.
To cite this article: Emtithal A. El-Sawi , Mona A. Hosny , Wafaa A. Mokbel & Tahany M. Sayed (2010) Friendly Synthesis,
Metallation, and Phosphorylation of Schiff Base as a Potential Pharmacological Interest, Synthesis and Reactivity in
Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:10, 934-939
To link to this article: http://dx.doi.org/10.1080/15533174.2010.522662
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:934–939, 2010
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2010.522662
Friendly Synthesis, Metallation, and Phosphorylation of
Schiff Base as a Potential Pharmacological Interest
Emtithal A. El-Sawi, Mona A. Hosny, Wafaa A. Mokbel, and Tahany M. Sayed
Department of Chemistry, Faculty of Women for Arts, Science, and Education, Ain Shams University,
Heliopolis, Cairo, Egypt
bases derivatives of 4-methylpyridin-2-amine acquire antimi-
crobial activities.[11] The synthesis of some metallated Schiff
bases with Ni (II), Co (II), and Cu (II) were found to be killing
agents for Biomphalaria alexandrina snails without affecting the
surrounding environment.[12] More et al.[13] marked the biolog-
ical activity of Schiff bases synthesized from aminothiazoles.
Azomethines exhibit a wide range of pharmacological activities
like antimicrobial,[14] antiparasitic,[15] anti-inflammatory,[16]
anticancer,[17] etc. Biological activities of some palladium(II)
and platinum(II) compounds derivatives of 1-H-indol-2,3-dione
benzothiazoline and 5- nitro-1-H-indol-2,3-dione benzothiazo-
line were found greater than the parent benzothiazolines towards
a variety of fungal and bacterial strains.[18] The 4-Thiazolidinone
derivatives of phenophosphazines have been evaluated as an-
tibacterial and antifungal.[19] In this work, Schiff base and its
metallated and phosphorylated products were synthesized and
their biological activities were also studied, as well as the anti-
cancer activity of the palladated product.
In view of the broad physiological activity of organometallic
and organophosphorus compounds, the present paper deals with
the synthesis of 2-(4-methoxybenzylidene amino) benzene-thiol, its
metallation with mercury (II), nickel (II), palladium (II), and phos-
phorylation. The antimicrobial activities of all products were inves-
tigated. The palladated product displays a significant anticancer
activity against human breast carcinoma cell. All the new prod-
ucts were investigated and their structures were elucidated using
elemental analyses, thermal analysis, and spectroscopic data.
Keywords anticancer activity, antimicrobial, mercuration, metalla-
tion, palladation, phosphorylation, Schiff base
INTRODUCTION
Schiff bases occupy a special place in the realm of natural
and synthetic organic chemistry because many products that
contain this subunit exhibit useful and diverse biological activ-
ity. Many Schiff bases also have wide applications in several
fields such as fluorescence properties in acidic media and for
spectrofluorimetric monitoring of small pH change,[1] and bi-
ological inorganic and analytical chemistry.[2−6] Some Schiff
bases acquire excellent characteristics and structural similar-
ities with natural biological substances. Simple preparation,
procedures, and synthetic flexibility enable design of suitable
structural properties.[7,8] Some new Schiff bases were synthe-
sized via the reaction of 1,3-propenediamine with isatin, and
the reaction was found to proceed according to the mode of
addition to afford two products as well as two isomers, followed
by their metallation.[9] A series of Schiff base of Dapsone and
their derivatives exhibited potent antibacterial activity.[10] Schiff
EXPERIMENTAL
Melting points were taken on a Gallen Kamp melting point
apparatus and were uncorrected. Thin layer chromatography
was performed with fluorescent silica gel plates HF254 (Merck),
and plates were viewed under UV254 and 265 light. Elemental
analyses were performed by The Microanalytical Center, Cairo
University. Analyses of mercury were carried out by thiocyanate
method[20] using ferric alum as indicator or by mercurometry
using diphenyl carbazone-bromothymol blue as indicator.[21] In-
frared spectra (FT-IR) were recorded on Bruker Vector Germany
and on Mattson FT-IR 1000, using KBr disks. Mass spectra
1
are measured on GCQ Finnigan MAT. H-NMR spectra were
recorded on Gemini-200 MHZ NMR spectrometer in DMSO-
d6 spectra were internally referenced to TMS. The antibacte-
rial activity were determined in microanalytical center Cairo
University, and anticancer activity was done in National Can-
cer Institute, Cancer biology department, Pharmacology, Cairo
University.
Received 22 February 2010; accepted 2 August 2010.
Address correspondence to Emtithal A. El-Sawi, Department of
Chemistry, Faculty of Women for Arts, Science, and Education,
Ain Shams University, Heliopolis, Cairo, Egypt. E-mail: elsawi e@
yahoo.com
934

SYNTHESIS, METALLATION, AND PHOSPHORYLATION
935
str.), 1475 (C-H aliph. bend.), 622 (C-S), 510 (Hg-C)[23]. MS
m/z(%):241(100)+HgNCO,243(9.2)+HgCOCH3,228(4.6)+Hg-
Preparation of Schiff Base 2-(4-methoxybenzylidene
amino) Benzenethiol
A mixture of 2-aminothiophenol (0.125g, 1mmol) and CH=N,226(57.6)+HgCN,
(198,199,
200,
Anal.
201
for
(0.136g, 1mmol) of 4-methoxybenzaldehyde in 40 ml ethyl Hg+),439(1.5)
C11H12NO3SHg+.
calcd.
For
alcohol was refluxed for 4 hrs. The precipitated product was C11H11NSO4Hg2: C 20.17, H 1.68, N 2.14, S 4.89, Hg
filtered, dried, and crystallized from ethyl alcohol to give com- 61.32. Found: C 20.00, H 1.66, N 2.12, S 4.84, Hg 60.80.
pound (1). White crystals, 98% yield, m.p: 120–121◦C. I.R
Anisyl acetate: Its b.p = 139◦C/10mmHg, IR (νcm−1
,
ν (cm−1,KBr): 3059(C-H, arom.), 2992–2833(C-H, aliph.str.), KBr):3046(C-H,
arom.),
2954-2878(C-H,
aliph.str.),
2559 (S-H), 1598(C=N), 1475(C-H aliph.bend.), 1225 (C-O-C 1742 (C=O, ester), 1370(C-H,aliph.bend.),1219(C-O-C
Asymm. str.), 1024 (C-O-C sym. str).[22] 1H-NMR (DMSO- Asym.str.),1018 (C-O-C Sym.str.) Anal. calcd. for: C9H10O3:
d6)δ: 8.1 (1 H, -HC=N), 8-7.1 (8H, Ar. protons), 3.8 (3H, C 65.06, H 6.02. Found: C 65.00, H 5.90.
OCH3), 3.3 (1H, SH). Anal. calcd.for C14H13NOS: C 69.13,
Metallated product (3): Green crystals, 76% yield, m.p: 340-
H 5.349, N 5.76, S 13.16, Found: C 69.00, H 5.32, N 5.74, S 341◦C. I.R (νcm−1, KBr)3641-3400(O-H), 3316-3212(NH),
13.13.
3040(CH, arom.), 2997- 2935 (C-H, aliph. Str.), 1732 (C=O),
1410(C-H, aliph.bend.), 662 (C-S), 517 (Ni-C). MS spectrum
m/z (%): M+ 514(30), the base peak at 60 (100) 60Ni+ or
CH3COOH+.. Anal. calcd. for C11H11NSO4Ni2.8H2O: C 25.66,
H 5.24, N 2.72, S 6.22, Ni 22.82. Found: C 25.60, H 5.22, N
2.71,S 6.20, Ni 22.74.
Palladated product (4): Orange crystals, 85% yield, m.p.
above 330◦C. IR (νcm−1, KBr): 3040(C-H, arom.), 2912–
2841(C-H,aliph.str.), 1598(C=N), 1440(C-H, aliph. bend.),
1219 (C-O-C asymm. str.), 1018 (C-O-C symm. str.), 431 (Pd-
C). MS spectrum m/z(%): the molecular ion peak at m/z 491
(0.1) and the base peak at m/z 241 (100)C14H12NOS+. 1H-NMR
(DMSO-d6)δ (ppm): 8-7.1 (8H, arom), 3.8 (3H, OCH3).Anal.
calcd. for C14H11NSO Pd.HCl. 3 1/3 CH3OH: C 42.44, H 5.16,
N 2.86, S 6.53 Pd 21.75 Found: C 42.22, H 5.14,N 2.83,S 6.48,
Pd 21.50.
Metallation of (1) to give (2), (3) and (4) (General
Procedure)
A mixture of (0.243 g, 1mmol) of Schiff base (1) and
(1 mmol) of mercuric acetate or nickel acetate in 30 ml toluene
and 2 ml acetic acid or palladium chloride in methanol and few
drops of HCl was refluxed for 3 hours, left to cool where crys-
talline products (2), (3), or (4) were precipitated after cooling,
filtered, dried, and crystallized from acetic acid to give (2) or
(3) and from methanol to give compound (4). The filtrate for the
product (2) and (3) was evaporated under reduced pressure and
the residue (oily part) was detected as anisyl acetate.
Product (2): 75% yield, m.p: 240–241◦C. IR (νcm−1,KBr):
3210(NH), 3039(C-H, arom.), 2950- 2834(C-H, aliph.
HS
HS
H
H
H
3CO
C
N
H
3 CO
O
C
H2N
+
1
+
PdCl2
S
Ni(OAc)2
Hg(OAc)2
O
H
S
O
H
C
S
Pd
CH COHg
3
C
CH CONi
3
C
H3 CO
N
N
H
N
H
NiOCCH3
O
HgOCCH3
O
4
3
2
OCCH3
O
+
CO
H3
OCCH3
O
+
H
3CO
SCH. 1.

936
E. A. EL-SAWI ET AL.
H
ClPd S
H
S
-HCl
+
H3CO
PdCl2
H3CO
N
N
Cl
H
Pd
S
S
Pd
-HCl
H3CO
N
4
H
3CO
N
obtain the metallated products. The overall metallation reactions
are summarized as follows in Scheme 1.
Phosphorylation of (2), (3), and (4) to give (5), (6), and (7)
(General Procedure)
The mechanism of the reaction with mercuric acetate may
proceed as follows (Scheme 2):
A mixture of (1mmol) of (2) or (3) or (4) and (1mmol) of
triphenylphosphine in 30 ml tetrahydrofuran was refluxed for 3
hrs, the precipitate formed was filtered, dried, and crystallized
from petroleum ether 40–60.
1
The data obtained from IR, H-NMR, MS, and elemental
analysis was consistent with the proposed structure. The reaction
of nickel acetate with compound (1) gave rise to product (3) and
anisyl acetate. The IR spectra for products (2) and (3) showed
Phosphorylated product (5): Pale blue crystals, 30% yield,
m.p: decomposed at 288◦C. IR (ν cm−1, KBr): 3056(C-
H, arom.), 1433 (P–Ph), 524 (Hg-C). Anal. calcd. for
C61H48NSP3Hg: C 65.38, H 4.28, N 1.25, S 2.85, P 8.30, Hg
17.91. Found: C 65.50, H 4.29, N 1.25, S 2.86, P 8.32, Hg 17.94.
Phosophorylated product (6): Greenish- white crystals,
90% yield, m.p: 240-241◦C. IR (ν cm−1, KBr): 3340-
3210(NH),3040(CH, arom.), 2997- 2935 (C-H, aliph. Str.), 1732
(C=O), 1470(CH, aliph.bend.), 1433 (P-Ph), 662 (C-S), 530(Ni-
C),. MS spectrum m/z(%): the base peak at m/z 77 (100) C6H+5 ,
92 (16.7) C6H5NHꢀ+, 109 (16.7) C6H5Sꢀ+, m/z 60 (11.1), m/z
61 (13.9), m/z 62 (10) Ni isotopes, m/z 277 (88.2%) Ph3P =
NHꢀ+, m/z 278 (17.6) Ph3P = NH2ꢀ+, m/z 395 (13.9) Ph3PH-
NH-NiOAcꢀ+. Anal. calcd. for C29H26NSO4PNi2: C55.02, H
4.11, N 2.21, S 5.06, P 4.90, Ni 18.56. Found: C 55.76, H 4.16,
N 2.33, S 5.13, P 4.97, Ni 18.80.
new bands for νHg−C, νHg−N, νC−S, and νNi−C, νNi−N, and νC−S
.
The other product produced via bond cleavage was assigned to
be anisyl acetate according to its boiling point, IR, and elemental
analysis. The structures were confirmed also considering the
data obtained from1H-NMR and MS spectra.
Compound (4) may form via the following suggested mech-
anism:
1
All the data obtained confirm the structure of (4). The H-
NMR spectrum shows δ 8.0–7.12 ppm for aromatic protons(8H),
and δ 3.88 ppm for OCH3(3H).
Measurement of Potential Cytotoxicity of Compound (4)
by SRB Assay
Potential cytotoxicity of the compound was tested using the
method of Skehan.[24] Cells were plated in 96-multiwell plate
(104 cells/ well) for 24 hrs before treatment with the com-
pound to allow attachment of cells to the wall of the plate.
Different concentrations of the compound under test (0, 5, 12.5,
Phosphorylated product (7): Orange crystals, 94%
yield, m.p: 145–146◦C. I.R (ν cm−1, KBr): 3059(C-H,
arom.), 2995- 2831(C-H, aliph.str.), 1598(C=N), 1475(C-
H aliph.bend.), 1431 (P-Ph). 1225 (C-O-C Asymm. str.),
1024 (C-O-C sym. str). MS m/z(%) 51(100)C4H+3 ,
65(10.6)C5H+5 ,
77(60.2)C6H+5 ,
103(4.4)C6H5CN+,
107(33.6)C7H7O+, 108(81.4)C6H5S+, 133(4.4)C7H4NS+.,
183(63.7)C12H9NO+, 185(13.3)PPh+2 , 186(4.4)C12H12NO+,
262(50.4)P-Ph3+ Anal. calcd. for C32H26NSOP. HCl. CH3OH:
C 69.29, H 5.42, N 2.44, P 5.42 Found: C 69.50, H 5.43, N
2.44, P 5.43.
TABLE 1
In vitro cytotoxic activity of the newly synthesized compound
(4), in comparison to 5-Flurouracil and Doxorubicin
Conc.
µg/ml
MCF7-5-
MCF7-
Doxorubicin
MCF7-4
Flurouracil
0.000
5.000
12.50
25.00
50.00
IC50 µg/ml
1.000
1.000
1.000
RESULTS AND DISCUSSION
0.4158
0.2275
0.1825
0.2366
5.43
0.3369
0.1818
0.0883
0.0880
4.437
0.1942
0.1717
0.1855
0.2013
4.165
o-Aminothiophenol reacted with p-methoxybenzaldehyde
to afford Schiff base 2-(4-methoxybenzylidene amino) ben-
zenethiol (1).
Product (1) was allowed to react with some metal salts such
as mercuric acetate, nickel acetate, and palladium chloride to

SYNTHESIS, METALLATION, AND PHOSPHORYLATION
937
1,1
1
HS
H
O
MCF7-4
MCF7-FU
MCF7-Dox
Hg (OCCH3)2
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0
C
H3CO
+
N
-
S
H
C
H
CO
3
+
N
H
..
0
10
20
30
40
50
60
Conc.ug/ml
Hg (OCCH3)2
O
FIG. 1. Drug cytotoxicity of compound (4) , 5-flurouracil and Doxorubicin.
IC50 for compound (4)= 5.43µg/ml; IC50 for flurouracil = 4.43 µg/ml; and
IC50 for Doxorubicin= 4.17 µg/ml.
S
H
C
H CO
+
CH3COOH
3
N
H
Hg OC CH
O
3
Hg(OCCH3)2
O
H
S
C
H
CO
3
N
H
-
CH CO
3
HgOCCH
+
3
O
FIG. 2. TGA of phosphorylated product (5).
HgOCCH3
O
O
antitumor activity against the tested human breast carcinoma
cell line MCF7 (in vitro) with varying intensities in comparison
to the known anticancer drugs 5-Flurouracil and Doxorubicin.
Moreover, compound (4) showed cytotoxic activity (IC50 equal
5.43 µg/ml) while 5-Flurouracil (IC50 equal 4.43 µg/ml) and
Doxorubicin (IC50 equal 4.16 µg/ml). The reaction of triph-
enylphosphine with the metallated products (2-4) in THF under
reflux for 3 hrs, afforded phosphorylated compounds (5), (6),
(7).
O
O
H
S
OCCH3
C
H3CCOHg
CO
H
+
3
N
H
HgOCCH3
2
O
The structures were elucidated considering elemental anal-
yses, IR, MS, and thermal analysis of compound (7). The MS
spectrum of compound (6) showed the base peak at m/z 77 can
SCH. 2.
25, 50 µg /ml) were prepared for each individual dose. Mono- be attributed to C6H+5 and m/z 277(88.26%) due to Ph3P=N+,
layer cells were incubated with the compound for 48 hrs at m/z 395(13.6%) due to Ph3P=N-NiOAc+.. Trials for reaction
37◦C and in an atmosphere of 5% CO2. After 48 hrs, they of triphenylphosphine with compound (1) in order to obtain
were fixed, washed, and stained with sulfo-rhodamine-B stain. compound (7) directly failed; this indicated that only in the
Excess stain was washed with acetic acid and attached stain presence of Pd in compound (4) facilitates the replacement by
was recovered with tris base. Color intensity was measured in triphenylphosphine.
an ELIZA reader. The relation between surviving fraction and
Structure identification of compounds (5), (7) by thermal
drug conc. was plotted (Table 1 and Figure 1) to get the survival analyses:[25]
curve of each tumor cell line after the specified compound. The
The thermogravimetric analysis (TG) of the phosphory-
antitumor activity result indicated that compound (4) showed lated product (5) is shown in (Figure2). One step of weight

938
E. A. EL-SAWI ET AL.
loss (82.41%) (calculated 82.08%), the remaining may be Hg
(17.91%) or HgO (19.34%).
The thermogravimetric analysis (TG) of the phosphorylated
product (7) is shown in Figure 2a, differential thermogravimetric
(DTG) is shown in Figure 2b and differential thermal analysis
(DTA) is shown in Figure 2c. Three steps of weight loss; the
first methyl group by 3.7% (calculated 3.0%) then the second
step loss of triphenylphosphine sulphide Ph3P=S with weight
loss 59% (calculated 58.45%), the third one loss by 30.6% loss
of all the remaining organic compound. This indicated also by 3
endothermic peaks at 65.22, 227.42, and 287.77◦C, respectively.
Measurement of Antimicrobial Activity Using Diffusion
Disc Method
A filter paper sterilized disc saturated with measured quantity
of the sample was placed on plate containing solid bacterial
medium (nutrient agar broth) or fungal medium (Doxs medium)
that has been heavily seeded with the spore suspension of the
tested organism. After inoculation, the diameter of the clear
zone of inhibition surrounding the sample is taken as a measure
of the inhibitory power of the sample against the particular test
organism.[26−29] The antimicrobial activity of all compounds
were tested and the results showed that compound (1) has no
activity, while the rest compounds acquire antimicrobial activity
towards some types of bacteria as shown in Table 2. The order
of increasing activity is (5)>(2)>(3)>(6)>(7)>(4).
CONCLUSION
2-(4-methoxybenzylidene amino) benzenethiol (1) was syn-
thesized, metallated using mercuric acetate, nickel acetate to af-
ford dimetallated products (2),(3) accompanied by bond cleav-
age, with the liberation of anisyl acetate, and with palladium
chloride to form monopalladated product (4).The suggested
reaction mechanisms are given. The metallated products re-
acted with triphenylphosphine to give tri-phosphorylated prod-
uct (5) and phosphorylated 6-membered hetero ring products
(6), (7) with the loss of palladium metal (product 7). The
elucidation of the structures based on IR, MS, and elemen-
tal analyses. Compound 7 studied by thermogravimetric anal-
ysis. The antimicrobial activity of all compounds were tested
and the results showed that compound (1) has no activity,
while the rest compounds exhibit antibacterial activities towards
FIG. 3. (a) TGA of phosphorylated product (7); (b) DTGA of phosphorylated
product (7); (c) DTA of phosphorylated product (7).
Ph
Ph
O
H
P
Ph
Ph
Ph
S
S
S
CH CONi
3
Ph
P
P
C
Ph
Ph
P
Ph
N
P
N
H
Ph
Ph
N
Ph
Ph
Ph
Hg
NiOCOCH3
CH O
3
5
6
7
Ph

SYNTHESIS, METALLATION, AND PHOSPHORYLATION
939
TABLE 2
Antimicrobial activity of the products towards some types of bacteria
Inhibition zone diameter(mm/ mg sample
Escherichia
Pseudomonas
Staphylococcus
Streptococcus
Sample
coli (G−)
aeruginosa (G−)
aurous (G+)
faecalis (G+)
(1)
(2)
(3)
(4)
(5)
(6)
(7)
0.0
14
19
15
35
16
13
0.0
39
17
15
35
15
16
0.0
13
28
14
36
18
15
0.0
37
16
14
32
16
16
Escherichia coli, Pseudomonas aeruginosa, Staphylococcus au- 14. Chambhare, R.V., Khadse, B.G., Bobde, A.S., and Bahekar, R.H.Eur. J.
Med. Chem., 2003, 38, 89–100.
15. Rathelot, P., Azas, N., El-Kashef, H., and Delmas, F. Eur. J. Med.Chem.
rous, and Streptococcus faecalis. The order of increasing ac-
tivity is (5)>(2)>(3)>(6)>(7)>(4). However, product (4) was
found to have anticancer activity compared with the known 5-
Flurouracil and Doxorubicin.
2002, 37, 671–679.
16. Holla, B. S., Malini, K.V., Rao, B.S., Sarojini, B.K., and Kumari, N.S. Eur.
J. Med. Chem., 2003, 38, 313–318.
17. Holla, B. S., Veerendra, B., Shivananda, M.K., and Poojary, B. Eur. J. Med.
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19. Lokhandwala, S.R., and Desai, K.R. Phosphosphorus Sulfur, and Silicon
and the Related Elements, 2008, 183, 1264–1271.
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