Synthesis, spectroscopic studies, and crystal structures of phenylorganotin derivatives with [bis(2,6-dimethylphenyl)amino]benzoic acid: Novel antituberculosis agents

Article abstract of DOI:10.1002/hlca.200490175

The novel triphenyl adduct of 2-[(2,6-dimethylphenyl)amino]benzoic acid (HDMPA; 1), i.e., [SnPh₃(DMPA)] (2), the dimeric tetraorganostannoxane [Ph₂(DMPA)SnOSn(DMPA)Ph₂] ₂ (3), and the monomeric adduct [SnPh

Full text of DOI:10.1002/hlca.200490175

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Helvetica Chimica Acta ± Vol. 87 (2004)
Synthesis, Spectroscopic Studies, and Crystal Structures of Phenylorganotin
Derivatives with [Bis(2,6-dimethylphenyl)amino]benzoic Acid:
Novel Antituberculosis Agents
a
a
b
a
by Vaso Dokorou ), Dimitra Kovala-Demertzi* ), Jerry P. Jasinski ), Angeliki Galani ),
a
and Mavroudis A. Demertzis )
a) Inorganic and Analytical Chemistry, Department of Chemistry, University of Ioannina,
4
)
5110 Ioannina, Greece (phone: ‡30-651-98425; fax: ‡30-651-98792; e-mail: dkovala@cc.uoi.gr)
b
Department of Chemistry, Keene State College, 229 Main Street, Keene, NH 03435-2110, USA
The novel triphenyl adduct of 2-[(2,6-dimethylphenyl)amino]benzoic acid (HDMPA; 1), i.e.,
SnPh (DMPA)] (2), the dimeric tetraorganostannoxane [Ph (DMPA)SnOSn(DMPA)Ph (3), and the
monomeric adduct [SnPh (DMPA) ] (4), where DMPA is monodeprotonated HDMPA, have been prepared
[
3
2
2 2
]
2
2
1
13
and structurally characterized by means of IR, H-NMR, and C-NMR spectroscopy. The structures of 1 and 2
have been determined by X-ray crystallography. Single-crystal X-ray-diffraction analysis of 1 revealed that
there are two molecules in the asymmetric unit, HD1 and HD2, differing in conformation, both forming
centrosymmetric dimers linked by H-bonds between the carboxylic O-atoms. X-Ray analysis of 2 revealed a
pentacoordinate structure containing Ph
interactions and intramolecular H-bonds stabilize the structures of 1 and 2, which self-assembled via CÀH/p
and p/p-stacking interactions. The Ph Sn adduct 2 was found to be a promising antimycobacterial lead
3
Sn coordinated to the carboxylato group. Significant CÀH/p
3
compound, displaying activity against Mycobacterium tuberculosis H37Rv. The cytotoxiciy in the Vero cell line
is also reported.
Introduction. ± 2-[(2,6-Dimethylphenyl)amino]benzoic acid (HDMPA; 1) resem-
bles mefenamic acid (ˆ2-[(2,3-dimethylphenyl)amino]benzoic acid), tolfenamic acid
(
(
ˆ2-[(3-chloro-2-methylphenyl)amino]benzoic acid), and flufenamic acid (ˆ2-{[3-
trifluoromethyl)phenyl]amino}benzoic acid), as well as other commercial fenamates
in clinical use. HDMPA was found to inhibit triiodothyronine (T ) uptake by H4
3
hepatocytes, and its octanol/H O partition coefficient was found to be 5.337 [1]. The
2
anti-inflammatory activity of HDMPA and its derivatives was measured by the anti-
UV-erythema test, and the minimum effective dose (MED) was found to be 50 mg/kg
[
[
2]. The crystal structures of the complexes [Bu (DMPA)SnOSn(DMPA)Bu ] and
2
2
2
Bu Sn(DMPA) ] have been reported [3].
2
2
Organotin(IV) carboxylates are an important class of compounds. They are often
used as catalysts and stabilizers, biocides, antifouling agents, and wood preservatives
4]. Information on the structures of organotin carboxylates continues to accumulate,
[
and, at the same time, new applications of such compounds are discovered that are
relevant for industrial, ecological, and medicinal applications. In recent years,
investigations have been carried out to test the antitumour activities of organotin(IV)
carboxylates. Several di- and triorganotin species have shown potential as antineo-
plastic agents [4 ± 7]. In general, triorganotin compounds display a higher biological
¹
2004 Verlag Helvetica Chimica Acta AG, Z¸rich

Helvetica Chimica Acta ± Vol. 87 (2004)
1941
activity than their di- and mono-organotin analogues. This has been attributed to their
ability to bind to proteins.
As a continuation of our studies on organotin species [8][9], we were interested in
the chemistry of organotin/HDMPA compounds and on the coordination chemistry of
nonsteroidal anti-inflammatory drugs of the phenylanthranilic acid type, such as
diclofenac (ˆ{2-[(2,6-dichlorophenyl)amino]phenyl}acetic acid), mefenamic acid, and
tolfenamic acid [10 ± 12]. We, thus, prepared and characterized the novel complexes
[
SnPh (DMPA)] (2), the dimeric tetraorganostannoxane [Ph (DMPA)SnOSn(DM-
3
2
1
PA)Ph ] (3), and the diphenyl adduct [SnPh (DMPA) ] (4) ).
2
2
2
2
Results and Discussion. ± Synthetic Aspects. Compound 1 was synthesized
according to UllmannÀGoldberg condensation from 2,6-dimethylaniline and potas-
sium 2-bromobenzoate in the presence of 4-ethylmorpholine and Cu(OAc) . Adducts
2
2
, 3 and 4 were obtained, under azeotropic removal of H O, by the reaction of 1 with
2
Ph SnOH or Ph SnO in a molar ratio of 1:1 for both 2 and 3, or in a ratio of 2 :1 for 3,
3
2
respectively (Scheme).
Scheme. Synthesis of Compounds 1 ± 4
Crystallographic Studies. We were able to obtain single-crystals of 1 and 2 and to
solve their structures by X-ray crystallography. Selected interatomic parameters are
collected in Table 1. Single-crystal X-ray-diffraction analysis of HDMPA (1) revealed
that there are two molecules in the asymmetric unit, HD1 and HD2, differing in
conformation. Both form centrosymmetric dimers linked by H-bonds between the
carboxylic O-atoms, as frequently observed for carboxylic acids (Fig. 1). The geometry
1)
DMPA represents deprotonated HDMPA (1).

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Helvetica Chimica Acta ± Vol. 87 (2004)
of the H-bonds is basically identical in both HDMPA modifications, O(1A) ¥¥¥ O(2A)
being 2.67 ä in HD1, and O(1B) ¥¥¥ O(2B) being 2.66 ä in HD2. The NH group is
located in a sterically hindered position and, in contrast to diclofenac [13], does not
participate in an intermolecular H-bond. Both conformers of HDMPA are stabilized by
an intramolecular N(1) ¥¥¥ O(2) H-bond of 2.70- and 2.72-ä length for HD1 and HD2,
respectively.
Table 1. Selected Bond Lengths (ä) and Angles (8) for 1 and 2
1
2
O(1A)ÀC(7A)
O(2A)ÀC(7A)
O(1B)ÀC(7B)
O(2B)ÀC(7B)
N(1A)ÀC(2A)
N(1A)ÀC(8A)
N(1B)ÀC(2B)
N(1B)ÀC(8B)
1.340(14)
1.241(15)
1.290(15)
1.222(15)
1.363(14)
1.465(14)
1.380(14)
1.432(15)
Sn(1) ÀO(1)
2.061(6)
2.626(7)
2.110(10)
2.115(9)
2.121(9)
1.310(10)
1.242(10)
1.385(11)
1.408(11)
110.5(3)
109.3(3)
120.6(4)
96.7(3)
Sn(1) ÀO(2)
Sn(1) ÀC(22)
Sn(1) ÀC(16)
Sn(1) ÀC(28)
O(1) ÀC(1)
O(2) ÀC(1)
N(1) ÀC(7)
N(1)ÀC(8)
C(2A)ÀN(1A)ÀC(8A)
C(2B)ÀN(1B)ÀC(8B)
N(1A)ÀC(2A)ÀC(1A)
N(1A)ÀC(2A)ÀC(3A)
O(1A)ÀC(7A)ÀC(1A)
O(2A)ÀC(7A)ÀC(1A)
O(1A)ÀC(7A)ÀO(2A)
N(1A)ÀC(8A)ÀC(13A)
N(1A)ÀC(8A)ÀC(9A)
122.1(9)
119.9(9)
O(1) ÀSn(1)ÀC(22)
O(1) ÀSn(1)ÀC(16)
C(22) ÀSn(1)ÀC(16)
O(1) ÀSn(1)ÀC(28)
C(22) ÀSn(1)ÀC(28)
O(2) ÀSn(1)ÀC(16)
O(2) ÀSn(1)ÀC(28)
O(2) ÀSn(1)ÀC(22)
O(2) ÀSn(1)ÀO(1)
C(16)ÀSn(1)ÀC(28)
C(1)ÀO(1)ÀSn(1)
C(7)ÀN(1)ÀC(8)
C(27)ÀC(22)ÀSn(1)
C(23)ÀC(22)ÀSn(1)
C(33)ÀC(28)ÀSn(1)
C(29)ÀC(28)ÀSn(1)
122.3(10)
120.3(10)
115.4(10)
124.2(11)
120.3(11)
120.6(10)
115.7(10)
108.4(3)
84.4(3)
150.7(3)
85.2(3)
54.0(2)
108.7(3)
106.4(5)
124.8(7)
122.8(8)
120.8(7)
123.5(7)
119.2(7)
A significant difference between HD1 and HD2 is the geometry of the amino group.
In HD1, the two N(1)ÀC bonds are markedly different compared with the more-similar
distances in HD2 (Dd ˆ 0.1 vs. 0.05 ä for HD1 and HD2, resp.). The C(2)ÀN(1)ÀC(8)
angle is 122.18 and 119.98 in HD1 and HD2, respectively. In meclofenamic acid ((ˆ2-
[
(2,6-dichloro-3-methylphenyl)amino]benzoic acid), with two perpendicular phenyl
groups [14a], the CÀNÀC angle is 1238, and in niflumic acid (ˆ2-{[3-(trifluoro-
methyl)phenyl]amino}pyridine-3-carboxylic acid), where the two phenyl rings are
almost coplanar [14b], it is 1318. In the structure of tolfenamic acid, the angle is 124.38
for the white form, and 129.08 for the yellow form [15a].
HD1 and HD2 also differ significantly in the geometry of the COOH group, the
largest differences occurring in the CÀO bond lengths. More-effective p-electron
delocalization is observed in the COOH group of HD2 [O(1B)ÀC(7B) 1.290(15) and
O(2B)ÀC(7B) 1.222(15) ä] relative to HD1 [O(1A)ÀC(7A) 1.34 and O(2A)ÀC(7A)
1.24 ä]. The interplanar angle between the two aromatic rings is 88.2 vs. 86.78 for HD1
and HD2, respectively.

Helvetica Chimica Acta ± Vol. 87 (2004)
1943
Fig. 1. X-Ray crystal structure of the dimers HD1 and HD2 of compound 1
Flufenamic acid [15b], tolfenamic acid [14a], and diclofenac [13] have also been
isolated in two different crystal forms, respectively. The angles between the two phenyl
rings are 53 and 438 in the two conformers of flufenamic acid [15b]. In tolfenamic acid,
the interplanar angle is 738 for the white form and 468 for the yellow form [15a]. In
niflumic acid [14b], the two rings are almost coplanar, with an angle of 98, whereas in
meclofenamic acid, the two planes are virtually perpendicular, the corresponding angle
being 818 [14a]. It seems obvious that the conformation of the molecules is determined
by steric interactions between the substituents on the phenyl groups. Adjacent to the
amino group in meclofenamic acid and HDMPA, there are two equivalent Cl-atoms
and two Me groups, respectively, and the molecules are in a conformation where the
two phenyl rings are almost perpendicular to minimize steric interactions.
The crystallographically determined molecular structure of 2 is shown in Fig. 2. It
comprises discrete molecular units in which the COO group functions as an
anisobidentate chelating ligand [Sn ¥¥¥ O(1) 2.06 ä, Sn ¥¥¥ O(2) 2.62 ä], thus rendering
the Sn-atom five-coordinated. The Sn ¥¥¥ O(2) distance, 2.626(7) ä, is fairly long for an
intramolecularly five-coordinated Sn-atom, and indicates significant bonding inter-
actions. However, Sn ¥¥¥ O distances of 2.61 ± 3.02 ä have been reported for such
intramolecular bonds [16]. The intramolecular H-bond formed from the amino group
[
O(2) ¥¥¥ N(1) 2.68 ä] contributes to an elongated SnÀO(2) bond. A similar H-bonded
situation was found in the mefenamic acid adduct [Ph Sn[(mef)] [7].
3

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Helvetica Chimica Acta ± Vol. 87 (2004)
Fig. 2. X-Ray crystal structure of 2
Analysis of the shape-determining angles of 2 using the approach of Reedijk and co-
workers [17] yields a t (a À b)/60 value of 0.66 for Sn (t ˆ 0 and 1 for sp and tbp
geometries, resp.). The geometry at the Sn-atom is represented by a disorted cis-
trigonal bipyramid in which the carboxylato ligand spans equatorial and axial sites. The
two CÀO bond distances of the CˆO group are unequal [1.31 vs. 1.24 ä], the longer
CÀO distance being associated with the shorter SnÀO bond, and vice versa.
The structures of a number of triorganotin carboxylates have been determined by
X-ray diffraction [18 ± 20]. In the crystalline state, these compounds generally adopt
either a polymeric structure with a five-coordinated Sn-atom, or a discrete five-
coordinated form. A polymeric structure for triphenyl carboxylates is associated with
À
the R' group, R'COO being electron-withdrawing. A delicate energy balance plays
between these two forms, although the electronegativity of the phenyl group has been
cited as a factor influencing the formation of the discrete form, since it gives more
access to an axial position of a trigonal bipyramid [19][20]. The axial Sn-ligand bond
lengths in both forms are subject to variations that depend on substituents, electro-
negativity, ring strain, H-bonds, and steric interactions [21]. The phenyl rings in 2 are
planar. The dihedral angle between the planes of the phenyl rings of DMPA in 2 is
68.68, while, for HD1 and HD2, it is 88.2 and 86.78, respectively. The crystal structure of
2
shows CÀH/p interactions and intramolecular H-bonds. The polar amino H-atom
participates in an intramolecular H-bond (Table 2). Complex 2 self-assembles via
CÀH/p and weak p/p stacking interactions (Fig. 3).

Helvetica Chimica Acta ± Vol. 87 (2004)
1945
Fig. 3. Crystal-structure packing of 2 viewed along the a-axis of the unit cell
Table 2. CÀH/p Interactions and Intramolecular H-Bonds and Distances (¥¥¥ ) for Compounds 1 and 2.
Distances in ä, angles in degrees (8); X is a C-, O-, or N-atom, Z is either a centroid (Cg) or an O-atom. See
Figs. 1 and 2 for atom numbering.
X
H
Z
H ¥¥¥ Z
X ¥¥¥ Z
a(XÀH ¥¥¥ Z)
CÀH/p (1)
C(14A)
C(14B)
a
a
H(3)
H(12)
Cg(1)
Cg(2)
)
)
2.75
2.75
3.54
3.57
141.6
134.0
H-bonds (1)
b
O(1B)
O(1A)
N(1A)
N(1B)
)
H(31)
H(34)
H(14)
H(13)
O(2B)
O(2A
O(2A)
O(2B)
1.89
1.83
2.07
2.14
2.67
2.66
2.70
2.72
138
140
121
120
CÀH/p (2)
c
d
C(5)
H(3)
H(8)
H(16)
H(21)
H(24)
Cg(3) ) )
2.78
2.99
3.20
2.94
3.28
3.58
3.65
3.79
3.82
3.96
142.0
127.9
121.3
155.3
129.6
e
C(30)
C(19)
C(23)
C(15)
Cg(4)
Cg(5)
Cg(5)
Cg(3)
)
f
)
e
g
)
)
H-bond (2)
N(1)
H(29)
O(2)
1.98
2.69
128
a) Cg(1) and Cg(2) refer to the centroids C(9B) ¥¥¥ C(13B) and C(9A) ¥¥¥ C(13A), resp.; symmetry: x, 1 ‡ y,
b
c
À1 ‡ z. ) Symmetry: À x, À y, 1 À z. ) Cg(3) to Cg(5) refer to the centroids C(8) ¥¥¥ C(13), C(16) ¥¥¥ C(21),
d
e
f
and C(28) ¥¥¥ C(33), resp. ) Symmetry: 3 À x, À y, 3 À z. ) Symmetry: 1 À x, À1 À y, 2 À z. ) Symmetry: x,
g
y, À1 ‡ z. ) Symmetry: 2 À x, À y, 2 À z.
Spectroscopic Studies. In the IR spectrum of HDMPA (1), the strong band at
À1
À1
3
2
340 cm was assigned to the NÀH stretching motion, and the broad band at ca.
980 cm to the n(NH ¥¥¥ O) and n(OH ¥¥¥ O) mode due to intra- and intermolecular H-
bonding [7][22], as confirmed by X-ray crystallography. The absence of large
systematic shifts of the n(NH) and d(NH) bands in the spectra of the complexes

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Helvetica Chimica Acta ± Vol. 87 (2004)
compared with those of the ligand indicates that there is no interaction between the NH
group and the metal ions. The nasym(COO) and nsym(COO) bands appear at ca. 1650 ±
À1
1
570 and 1450 ± 1390 cm , respectively. The n (COO) and nsym(COO) bands appear
asym
À1
À1
at 1654 and 1396 cm for 2, and at 1615 and 1361 cm for [SnPh (DMPA) ] (4). The
2
2
À1
difference nasym(COO) À n (COO) between these frequencies is 254 and 258 cm ,
sym
respectively, for 2 and 4, which is close to that found for the anisobidentate carboxylato
À1
group [3]. The nasym(COO) and nsym(COO) bands appear at 1615 and 1576 cm , and at
À1
1
394 and 1453 cm , respectively, for 3. The n (COO) À n (COO) value between
asym
sym
À1
these frequencies for 3 is close to that found for monodentate (221 cm ) and bridging
À1
À1
bidentate carboxylato groups (123 cm ). A very strong band near 600 cm for 3 is
À1
characteristic of the SnÀOÀSn linkage. Two bands at 600 ± 620 cm for 3 are assigned
to symmetric and asymmetric (SnO) vibrations, indicating nonlinear OÀSnÀO
2
À1
moieties. The bands at 320 ± 280 cm are assigned to the SnÀO (COO) stretching
À1
modes. The absorption bands at 360 ± 340 cm are attributed to n(SnÀC) stretching
modes [3][7][22].
1
13
The H- and C-NMR chemical shifts of both the ligand and the complexes were
recorded in CDCl solution. The downfield chemical shift for NH in the H-NMR
1
3
spectrum of the ligand indicates that this H-atom is involved in H-bonding. The crystal
structure of HDMPA (1) shows the presence of an intramolecular H-bond between the
NH group and the carbonyl O-atom of the COO group. In the complexes 2 ± 4, HÀC(3)
À
is deshielded due to s-charge donation from the COO donor to the Sn center, which
reduces the electron density at the ligand. The observed upfield shift for both HÀC(4)
and C(4) para to the coordinating COO group could be due to a backflow of charge
from the Sn-atom to the aromatic ring [7][9][23].
The involvement of the COO group in bonding to Sn was confirmed by the d(C(1))
and d(C(6)) chemical shifts, which were strongly affected upon coordination. The
remaining d(C) values of the aromatic ring were not significantly shifted on binding.
13
Interestingly, no C-NMR resonance attributable to the COO group (C(1)) was
observed for the complexes, a behavior that has been noted previously for related
systems [7 ± 9].
Biological Activity. Compounds 1 and 2 were tested against Mycobacterium
tuberculosis H37Rv in BACTEK-12B medium, using the BACTEC 460-radiometetric
system at the single concentration of 6.25 mg/ml. Compounds 3 and 4 were not soluble
in DMSO or H O, and were not screened. Rifampicin was included as a positive drug
2
control. HDMPA (1) did not exhibit any inhibitory effect and was not screened any
further. Complex 2 exhibited the highest inhibitory activity (100%) and can be
considered an active compound. Generally, compounds that exhibit less than 90%
2
inhibition in the primary screen (MIC > 6.25 mg/ml) ) were not evaluated further.
Compound 2, effecting > 90% inhibition in the primary screen at 6.25 mg/ml, was
tested again at lower concentration against Mycobacterium tuberculosis H37Rv to
determine the MIC value in a broth-microdilution assay with Alamar Blue. The MIC
values determined were 0.78 for 2, 0.39 for [SnPh (mef)], and > 6.25 mg/ml for
3
[
SnBu (mef) ], where −mef× is deprotonated mefenamic acid (Table 3) [7].
2 2
2)
MIC stands for minimum inhibitory concentration.

Helvetica Chimica Acta ± Vol. 87 (2004)
1947
Table 3. Biological Activities of Compounds 1 and 2 towards Mycobacterium tuberculosis H37Rv Compared to
Selected Reference Compounds. Alamar Blue assay; drug conc. 6.25 mg/ml; for details, see the Exper. Part. The
term −mef× stands for deprotonated mefenamic acid (ˆ 2-[(2,3-dimethylphenyl)amino]benzoic acid).
Compound
Inhibition (%)
MIC [mg/ml]
IC50 [mg/ml]
HDMPA (1)
0
100
98
92
95
[
[
[
Sn(Ph)
SnPh (mef)] [7]
SnBu
3
(DMPA)] ( 2)
0.78
1.89
3
0.39
2
(mef)
2
] [7]
> 6.25
0.25
a
Rifampicin
)
113.6
a) Positive drug control.
Compound 2 was tested for cytotoxicity (IC ) in Vero cells at concentrations equal
50
to and greater than the MIC value for Mycobacterium tuberculosis H37Rv. The IC50
value was found to be 1.89 mg/ml for 2. The selectivity index (SI ˆ IC /MIC) was
50
calculated as 2.42, showing that this compound not only displays a considerable activity,
but also an increased cytotoxicity. The significance of the MIC value depends on several
factors such as compound structure, novelty, toxicity, and potential mechanism of
action. Generally, an MIC value of ꢀ 1 mg/ml for a novel compound is considered an
excellent lead.
Conclusions. ± Three novel phenyl adducts of 2-[(2,6-dimethylphenyl)amino]ben-
zoic acid (HDMPA; 1), i.e., [SnPh (DMPA)] (2), [Ph (DMPA)SnOSn(DMPA)Ph ]
2 2
3
2
(
3), and [SnPh (DMPA) ] (4) have been prepared and structurally characterized by
2 2
1
13
means of IR, H-NMR, and C-NMR spectroscopy. Based on spectroscopic data,
dimeric tetraorgannostannoxane and monomeric structures are proposed for 3 and 4,
respectively. The structures of 1 and 2 were determined by X-ray crystallography,
showing significant CÀH/p interactions and intramolecular H-bonds. The triphenyl
adduct 2 and the parent compound 1 were tested for their antimycobacterial activities
against Mycobacterium tuberculosis H37Rv. Compopund 2, a Ph Sn derivative of
3
anthranilic acid, was found to be an excellent lead compound, which makes this novel
class of compounds potential new antituberculosis agents.
Experimental Part
General. All reagents were commercially available (Aldrich or Merck) and used as supplied. Solvents were
purified according to standard procedures. Melting points (m.p.) were determined in open capillaries and are
À1
uncorrected. IR and far-IR Spectra: Nicolet 55XC FT-IR spectrophotometer, KBr pellets (4000 ± 400 cm ), and
À1
1
13
nujol mulls dispersed between polyethylene disks (400 ± 40 cm ). H- and C-NMR Spectra: Bruker AMX- 400
1
13
3
and Bruker AC-250 spectrometers; at 250.13 MHz ( H) and 62.90 MHz ( C) in CDCl soln. at r.t.; chemical
shifts d in ppm rel. to residual solvent signal (7.24 ppm). Elemental analyses were carried out by the
microanalytical service of the University of Ioannina, Greece.
2-[(2,6-Dimethylphenyl)amino]benzoic Acid (HDMPA; 1). This compound was synthesized by Ull-
mannÀGoldberg condensation [1]. 2,6-Dimethylaniline (5.60 g, 46 mmol), potassium 2-bromobenzoate
(11.36 g, 47 mmol), 4-ethylmorpholine (5.46 g, 47 mmole), and anh. Cu(OAc)
2
(0.5 g) in distilled DMF
(
20 ml) were refluxed for 3 h under N atmosphere. The resulting soln. was treated with DMF (13 ml) and 12%
2
aq. HCl soln. (19 ml). The aq. layer was decanted, and MeOH was added. The solid was collected and
recrystallized three times from acetone to afford 1 (2.70 g, 24%). M.p. 209 ± 2108. IR (KBr): 3348 (v(OH)),
1
3
289, 2980 (v(NH)), 1610 (nasym(COO)), 1448 (nsym(COO)). H-NMR (CDCl
3
): 8.90 (s, NH); 8.04 (d, HÀC(6));

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Helvetica Chimica Acta ± Vol. 87 (2004)
7
.27 (t, HÀC(4)); 7.15 (m, HÀC(3',4',5')); 6.66 (t, HÀC(5)); 6.22 (d, HÀC(4)); 2.22 (s, 2 Me). 13C-NMR: 170.7
(COOH); 156.8 (C(2)); 135.6 (C(4)); 132.5 (C(6)); 116.2 (C(1)); 115.7 (C(5)); 112.7 (C(3)); 18.2 (2 Me). Anal.
À1
calc. for C15
H
15NO
2
; 241.11 g mol : C 74.76, H 6.27, N 5.81; found: C 73.9, H 6.6, N 5.8. X-Ray single-crystal
structure: see Fig. 1 and Tables 1, 2, and 4.
2-[(2,6-Dimethylphenyl)amino]benzoato)triphenyltin(IV) (2). Ph
0.241 g, 1.00 mmol) in benzene (40 ml) were refluxed overnight under azeotropic removal of H
(
3
SnOH (0.422 g, 1.15 mmol) and 1
O (Dean-
(
2
ÀStark trap). The resulting clear yellow soln. was concentrated in vacuo to a small volume, chilled, and
triturated with trifluoroacetic acid (TFA) to afford a white-yellow solid. Drops of acetone were added, and,
after slow evaporation, compound 2 was isolated by filtration, washed with acetone, and dried in vacuo over
silica gel. Yield: 0.416 g (70%). White-yellow powder. M.p. 178 ± 1808. IR (KBr): 3298 (n(NH)), 1615
1
(
(
n
asym(COO)), 1361 (nsym(COO)), 347 (br., n(SnÀC)), 323, 283 (n(SnÀO)), 177, 154 (d(SnÀO)). H-NMR
CDCl
3
): 9.12 (s, NH); 8.15 (d, HÀC(6)); 7.79 (s, o-H of Ph); 7.39 (s, m-H of Ph); 7.44 (s, p-H of Ph); 7.12 (t,
13
HÀC(4)); 7.12 (m, HÀC(3',4',5'); 6.62 (t, HÀC(5)); 6.19 (d, HÀC(3)); 2.16 (s, 2 Me). C-NMR: 149.9 (C(2));
1
1
38.9 (o-C of Ph); 130.0 (m-C of Ph); 134.5 (C(6)); 134.5 (C(4)); 128.8 (p-C of Ph); 126.4 (C(1)); 115.5 (C(5));
À1
12.4 (C(3)), 29.7; 18.3 (2 Me). Anal. calc. for C33
H
29NO
2
Sn (590.30 g mol ): C 67.14, H 4.95, N 2.37; found:
C 66.81, H 4.99, N 2.40. X-Ray single-crystal structure: see Figs. 2 and 3, and Tables 1, 2, and 4.
,2 :3,4-Di-m -2-[(2,3-dimethylphenyl)amino]benzoato-O,O-1,3-bis-2-[(2,3-dimethylphenyl)amino]benzo-
ato-O-1,2,4 :2,3,4-di-m -oxo-tetrakis[diphenyltin(IV)] (3). Ph SnO (0.332 g, 1.15 mmol) and 1 (0.241 g,
.00 mmol) in benzene (40 ml) were refluxed for 24 h under azeotropic removal of H
1
2
3
2
1
2
O (DeanÀStark trap).
The resulting clear soln. was concentrated in vacuo to a small volume. Drops of MeOH were added, and, after
slow evaporation, 3 was isolated by filtration, washed with acetone, and dried in vacuo over silica gel. Yield:
0
.482 g (53%). White powder. M.p. 150 ± 1528. IR (KBr): 3346, 3299 (n(NH)), 1615 (nasym(COO)), 1394
(
(
n
sym(COO)), 1576 (nsym(COO)), 1453 (nsym(COO)), 663 (n(SnÀO)
2
), 366, 348, (n(SnÀC)), 313, 296, 277
1
n(SnÀO)), 148 (d(SnÀO)). H-NMR (CDCl
3
): 8.92 (br., NH); 8.18, 8.08 (d, HÀC(6)); 7.81 (s, o-H of Ph),
7
(
.36 ± 7.45 (m, m-H and p-H of Ph); 7.25 (m, HÀC(3',4',5')); 7.12 (t, 5 H); 6.66 (m, 4 H); 6.21 (m, 6 H); 3.48, 2.18
13
2s, 8 Me). C-NMR: 139.4 (C(2)); 138.9 (o-C of Ph); 135.4 (C(4); 133.5 (C(6)); 130.0 (m-C of Ph); 128.5 (p-C
À1
of Ph); 126.5 (C(1)); 115.6 (C(5)); 112.5 (C(3)); 18.3 (8 Me). Anal. calc. for C108
C 62.22, H 4.64, N 2.69; found: C 62.18, H 4.23; N 3.15.
H
96
N
4
O
10Sn
4
(2084.77 g mol
)
(
Bis-2-[(2,6-dimethylphenyl)amino]benzoato)diphenyltin(IV) (4). Ph
2
SnO (0.289 g, 1.00 mmol) and 1
(
0.519 g, 2.15 mmol) in benzene (40 ml) were refluxed for 24 h under azeotropic removal of H
2
O (DeanÀStark
trap). The resulting clear soln. was concentrated in vacuo to a small volume. The oily product was dissolved in
MeOH. After slow evaporation, 4 was isolated by filtration, washed with acetone, and dried in vacuo over silica
gel. Yield: 0.550 g (70%). White-yellow powder. M.p. 180 ± 1848. IR (KBr): 3341 (n(NH)), 1654 (nasym(COO)),
1
1
396 (nsym(COO)), 364, 352 (n(SnÀC)), 314, 298 (n(SnÀO)), 177 (d(SnÀO)). H-NMR (CDCl
3
): 8.88 (br.,
NH); 8.07 (d, HÀC(6)), 6.68 (t, HÀC(5)); 7.13 (t, HÀC(4)); 6.22 (d, HÀC(3)); 7.21 (m, HÀC(3',4',5')); 2.18 (s,
1
3
8
1
Me); 7.86 (s, o-H of Ph); 7.45 (m, m-H and p-H of Ph). C-NMR: 150.6 (C(2)); 126.7 (C(1)); 136.8 (C(6));
15.7 (C(5)); 135.6 (C(4)); 112.7 (C(3)); 136.9 (o-C of Ph), 130.0 (m-C of Ph), 128.5 (p-C of Ph), 27.9, 18.3 (4
À1
Me). Anal. calc. for C42
H
38
N
2
O
4
Sn (753.47 g mol ): C 66.95, H 5.08, N 3.72; found: C 66.58, H 5.28, N 3.63.
X-Ray Crystallography. The crystallographic data for 1 and 2 are given in Table 4, together with refinement
details. All measurements were performed on a Rigaku AFC6S diffractometer, with graphite-monochromated
MoK radiation. The data were collected in the w-2q mode to a maximum 2q value of 55.28. The structures of 1
a
and 2 were solved by direct methods and expanded by Fourier techniques [24]. The non-H-atoms were refined
anisotropically. H-atoms were included, but not refined. All calculations were performed with the teXsan [24]
crystallographic software package (Molecular Structure Corporation), except for refinement, which was
performed with SHELXL-97 [25]. Crytallographic data for the structural analysess have been deposited with
the Cambridge Crystallographic Data Centre, as deposition numbers CCDC-233330 (1) and CCDC-233331 (2).
Copies of these data may be obtained, free of charge, from CCDC, 12 Union Road, Cambridge CB2 1EZ, UK,
via fax (‡44-1223-336-033), e-mail (deposit@ccdc.cam.ac.uk), or internet (www.ccdc.cam.ac.uk).
Antituberculosis Assay. In vitro evaluation of the activity of 1 and 2 against Mycobacterium tuberculosis
H37Rv was determined with the modified BACTEC-460 system. A screen was conducted at 6.25 mg/ml against
M. tuberculosis H37Rv in BACTEC-12B medium, using the BACTEC-460 radiometric system. Compounds
effecting < 90% inhibition in the primary screen (MIC > 6.25 mg/ml) were not evaluated further. Compounds
demonstrating at least 90% inhibition were re-investigated at lower concentration in a broth-microdilution
assay with Alamar Blue (MABA). The minimum inhibitory concentration (MIC) was defined as the lowest
concentration effecting a reduction in fluorescence of 90% relative to blanks. Rifampicin, used as a positive
drug control, was dissolved in DMSO and added to BACTEC-12 broth to achieve a range of concentrations for

Helvetica Chimica Acta ± Vol. 87 (2004)
1949
Table 4. X-Ray Crystal Data and Structure Refinement
1
2
Crystallized from
Crystal size [mm]
Formula
THF/acetone
Benzene/EtOH
0.30 Â 0.40 Â 0.40
0.30 Â 0.30 Â 0.50
C
15
H
15NO
2
33 2
C H29NO S
M
T [K]
l [ä]
Crystal system
Space group
Cell dimensions:
a [ä]
b [ä]
c [ä]
a [8]
b [ä]
g [ä]
V [ä ]
r
241.28
590.26
296(2)
296(2)
0.71069
Triclinic
0.71069
Triclinic
≈
≈
P1 (No. 2)
P1 (No. 2)
15.8375(16)
7.5311(7)
11.1845(12)
83.728(9)
104.806(9)
79.038(8)
1248.6(2)
4
9.733(8)
17.73(1)
8.844(6)
90.20(6)
107.38(6)
105.49(6)
1398(2)
2
3
Z
À3
D
c
[Mg m
]
1.283
1.402
Absorption coefficient
F(000)
0.085
512
0.943
600
q Range [8]
1.9 to 27.5
2.26 to 27.58
Ranges of h,k,l
Refl. collected, unique
R(int)
0 ꢀ h ꢀ 20, À 9 ꢀ k ꢀ 9, 14 ꢀ l ꢀ 14
0 ꢀ h ꢀ 12, À23 ꢀ k ꢀ 22, À1 ꢀ l ꢀ 10
5948, 5738
6833 / 6450
0.152
0.118
Refinement
Full-matrix least-squares on F2
5738, 0, 325
Full-matrix least-squares on F2
6450, 0, 334
Data, restraints, parameters
2
Goodness-of-fit on F
0.83
1.039
Final R
Largest diff. peak/hole [e ä
1
/wR
2
(I > 2s(I))
0.0553, 0.3875
À 0.28, 0.26
0.0597, 0.2179
1.012, À1.300
À3
]
the determination of the MIC value, the lowest concentration inhibiting 99% of the inocola. The MIC value of
Rifampicin is 0.25 mg/ml, with 95% inhibition of the H37Rv strain.
Cytotoxicity Assay. Compound 2 was tested for its cytotoxicity (in terms of IC50) in Vero cells at
concentrations ꢀ 6.25 mg/ml, or ten times the MIC value for M. tuberculosis H37Rv. After 72 h of exposure,
viability was assessed on the basis of cellular conversion of MTT into a formazan product, using the Promega
CellTier-96 Nonradiactive Cell-Proliferation Assay. The selectivity index, SI, is the ratio of the measured IC50
value in Vero cells to the MIC value described above. IC50 and SI Values for controls: rifampicin, IC50 ˆ 113.6 mg/
ml (SI > 800); DMSO ˆ 0.0099; DMSO at 1 :50 > 1%.
We thank the European Community and the Greek Ministry of Education and Religion for funding via the
epeak herakleitos research program. V. D. thanks the same authorities for a scholarship. We also thank the NMR
service of the University of Ioannina, Greece. We are grateful to Dr. Cecil D. Kwong (Tuberculosis
Antimicrobial Acquisition & Coordinating Facility (TAACF), National Institute of Allergy and Infectious
Diseases Southern Research Institute, GWL Hansen×s Disease Center, Colorado State University, Birmingham,
Alabama, USA) for the in vitro evaluation of antimycobacterial activity.

1
950
Helvetica Chimica Acta ± Vol. 87 (2004)
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Received March 11, 2004