Synthesis of diversely substituted adamantanes as a new class of antimicrobial agent

Article abstract of DOI:10.1007/s11164-014-1775-6

Abstract 4,8,9,10-tetraaryl-1,3-diazatricyclo[3.3.1.1]decan-6-ones are synthesized and reduced into its 4,8,9,10-tetraaryl-1,3-diazatricyclo[3.3.1.1]decan-6-ols (6a-m) with NaBH₄ in methanol (2v), benzene (1v) mixture as the solvent system. These compounds are characterized using spectral data such as IR, ¹H-NMR, and ¹³C-NMR data. These synthesized compounds are screened for their antimicrobial activity and were found to be effective anti-bacterials.

Full text of DOI:10.1007/s11164-014-1775-6

Res Chem Intermed
DOI 10.1007/s11164-014-1775-6
Synthesis of diversely substituted adamantanes as a new
class of antimicrobial agent
•
G. L. Balaji S. Sarveswari V. Vijayakumar
•
Received: 4 July 2014 / Accepted: 23 July 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract 4,8,9,10-tetraaryl-1,3-diazatricyclo[3.3.1.1]decan-6-ones are synthe-
sized and reduced into its 4,8,9,10-tetraaryl-1,3-diazatricyclo[3.3.1.1]decan-6-ols
(6a–m) with NaBH4 in methanol (2v), benzene (1v) mixture as the solvent system.
1
These compounds are characterized using spectral data such as IR, H-NMR, and
13C-NMR data. These synthesized compounds are screened for their antimicrobial
activity and were found to be effective anti-bacterials.
Keywords Adamantane ꢀ Adamantanol ꢀ Antimicrobial activity
Introduction
Adamantane (tricyclo[3.3.1.13,7]decane) is an important class of polycyclic
compounds with a number of interesting biological properties such as anticho-
linergic, antimicrobial, and antiviral. Adamantane was first synthesized by Prelog
in 1941 [1]. A more convenient method was found by Schleyer et al. [2]. The
unique structure of adamantine is reflected in its highly unusual physical and
chemical properties. The carbon skeleton of adamantane comprises a small cage
structure, and because of this, adamantane and diamondoids in general are
Electronic supplementary material The online version of this article (doi:10.1007/s11164-014-1775-6)
contains supplementary material, which is available to authorized users.
G. L. Balaji ꢀ S. Sarveswari ꢀ V. Vijayakumar (&)
Centre for Organic and Medicinal Chemistry, VIT University, Vellore 632 014, Tamil Nadu, India
e-mail: kvpsvijayakumar@gmail.com
123

G. L. Balaji et al.
commonly known as cage hydrocarbons. Adamantane crystallizes in a face-
centered cubic lattice and this is extremely unusual for an organic compound.
The molecule therefore should be completely free from both angle and torsional
strain. Diamantane, triamantane, and their alkyl-substituted compounds just as
adamantane are also present in certain petroleum fluids. Their concentrations in
these fluids are generally lower than that of adamantane and its alkyl-substituted
compounds. In rare cases, tetra, penta, and hexamantanes are also found in
petroleum fluids. Adamantane itself enjoys few applications since it is merely an
unfunctionalized hydrocarbon. It is used in some dry-etching masks [3]. It is also
used in some polymer formulations. In solid-state NMR, adamantane is a
common standard for chemical shift referencing. Adamantane cannot be
photoionized under atmosphere because its absorption bands lie in the vacuum-
ultraviolet region of the spectrum [4]. Urotropin or 1,3,5,7-tetraazaadamantane is
the best known of this class and has been used as an antigout agent in
pharmacology and with various additives for the prevention and treatment of
influenzas. The chemistry of adamantanes and its derivatives, particularly
nitroadamantanes, is of interest for their use as high-density energetic materials
[5]. Recent interest in adamantanes has extended into the area of host–guest
compounds [6], combinatorial chemistry, optically active organic molecules [7],
and dendritic macromolecules [8]. Tetraaryl-substituted cage hydrocarbons with
tetrahedral symmetry are the potential precursors of energetic materials,
dendrimers, star-shaped molecules, and molecules of interest in combinatorial
chemistry [9]. The intensive progress in the adamantane chemistry was
accompanied by the development of effective methods for functionalization of
adamantane nucleus. Many reliable and convenient procedures for preparation of
adamantane compounds have been proposed. The described methods for
synthesis of trisubstituted adamantanes are well elaborated only for compounds
with functional groups attached to the bridgehead positions of adamantane
moiety [10, 11] and for 2,2,5-trisubstituted derivatives [12, 13]. 1,3-Diazaada-
mantane derivatives are of great importance as conformationally rigid analogues
of pharmacologically active molecules [14, 15].
Results and discussion
Though the synthesis of 4,8,9,10-tetraaryl-1,3-diazatricyclo[3.3.1.1]decan-6-ones
and its corresponding alcohols have been reported [16–30] for a limited number of
derivatives, their biological significance is not yet explored and hence in the present
work 4,8,9,10-tetraaryl-1,3-diazatricyclo[3.3.1.1]decan-6-ones were synthesized
using the reports available in the literature [16–30], which in turn reduced into
4,8,9,10-tetraaryl-1,3-diazatricyclo[3.3.1.1]decan-6-ols using NaBH4; characterized
using IR, 1H NMR, 13C NMR, and mass spectral data and then subjected to
antimicrobial evaluation against various microbial strains and the results were
discussed.
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Synthesis of diversely substituted adamantanes
R
R
O
R
O
R
OH
R1
R
R
R
R1
R1
R1CHOH
O
2
EtOH
N
NaBH4
HCHO
N
∇
HN
1
R
R
R
R
R
O
NH4
N
R
N
NH
+
O
3
4(a-m)
5 (a-m)
6 (a-m)
Compound R1
R
Compound R1
R
-H
-Phenyl
-H
-H
-H
-H
-H
-H
-2-methoxyphenyl
-4-methoxyphenyl
-4-ethoxyphenyl
2,5-dimethoxyphenyl
3,4-dimethoxyphenyl
3,4,5-trimethoxyphenyl
5a, 6a,
5b, 6b
5c, 6c
5d, 6d
5e, 6e
5f, 6f
5h, 6h
5i, 6i
5j, 6j
5k, 6k
5l, 6l
5m, 6m
-CH3 -Phenyl
-H
-H
-H
-H
-H
-4-Fluorophenyl
-2-Chlorophenyl
-4-Chlorophenyl
-4-Bromophenyl
-4-Methylphenyl
5g, 6g
Scheme 1 Synthesis of 4,8,9,10-tetraaryl-1,3-diazaadamantan-6-ones (5a–m) and its corresponding
alcohols 6(a–m)
The 2,4,6,8-tetraaryl-3,7-diazabicyclo[3.3.1]nonan-9-ones 4a–m in C6H6 was
added with enough aq. formalin and the mixture was shaken vigorously for 15 min.
The C6H6 layer was separated and distilled out to afford the crude 4,8,9,10-tetraaryl-
1,3-diazatricyclo[3.3.1.1]decan-6-ones (5a–m) (also called as 4,8,9,10-tetraaryl-1,3-
diazaadamantan-6-one). The obtained crude product was recrystallized using an
ethanol–benzene (4:1) mixture and the purity of the compound was checked by
1
TLC. The compounds 5a–m were characterized by IR, H-NMR, and 13C-NMR.
Among these, the synthesis and their unambiguous chemical shift assignments of
and 5a–m (except 5c, 5e, 5f, 5h, 5l) were already reported, and their spectral values
were found to be in accord with the literature [16–21]; and hence the character-
izations of remaining compounds 5c, 5e, 5f, 5h, 5l were included in the
experimental section. However, the microbial screening of all these compounds
was not reported in the literature and hence all of these compounds were
synthesized. Then the reagent NaBH4 (dissolved in the minimum amount of water)
was added to the 4,8,9,10-tetraphenyl-1,3-diazatricyclo[3.3.1.1]decan-6-ones (dis-
solved in methanol-benzene mixture). The mixture was refluxed for 7 h and then
6 N NaOH was added to the reaction mixture and allowed to boil for 10–20 min,
then it was poured into crushed ice to afford the 4,8,9,10-tetraphenyl-1,3-
diazatricyclo[3.3.1.1]decan-6-ols (6a–m) (Scheme 1). The obtained product was
extracted with chloroform and the purity was checked by TLC. The NaBH4
reduction with iso-propanol solvent was reported, which afford only 65 % yield,
whereas the methanol-benzene solvent mixture afford more than 90 % yield. The
detailed procedures are given in the experimental section. The physical and
1
analytical data are reproduced. The products 6a–m were characterized by IR, H-
NMR, and 13C-NMR. Though some of these derivatives were already reported [16–
21]; their complete chemical shift assignments were not available and hence the
characterizations of 6a–m were included in the experimental section.
The 4,8,9,10-tetraaryl-1,3-diazatricyclo[3.3.1.1]decan-6-ols can be synthesized by
two different approaches. In the first approach, 2,4,6,8-tetraaryl-3,7-diazabicyclo
123

G. L. Balaji et al.
123

Synthesis of diversely substituted adamantanes
[3.3.1]nonan-9-ones reduced into 2,4,6,8-tetraaryl-3,7-diaza bicyclo[3.3.1]nonan-9-ols
using NaBH4, which in turn converted into 4,8,9,10-tetraaryl-1,3-diazatricyclo[3.3.1.1]
decan-6-ols using aq. formalin. In the other approach, the 2,4,6,8-tetraaryl-3,
7-diazabicyclo[3.3.1]nonan-9-ones can be converted into 4,8,9,10-tetraaryl-1,3-diazatri-
cyclo[3.3.1.1]decan-6-ones, which in turn reduced to 4,8,9,10-tetraaryl-1,3-diazatricy-
clo[3.3.1.1]decan-6-ols using NaBH4. The latter one has been already adopted and
towards the earlier method here, we have attempted (the conversion of 2,4,6,
8-tetraphenyl-3,7-diazabicyclo[3.3.1]nonan-9-one (4a) reduced into 2,4,6,8-tetraaryl-
3,7-diazabicyclo[3.3.1]nonan-9-ol (5aa) using NaBH4 then into 4,8,9,10-tetraphenyl-1,
3-diazatricyclo[3.3.1.1]decan-6-ol.) and found to afford almost the same yield.
The compounds 5a–m and 6a–m were screened for their antibacterial activity
against the three microorganisms Bacillus,S. aureus, and E. coli, and all the
compounds were found to exhibit moderate activity. The minimum inhibitory
concentration (MIC) values of 5a–m and 6a–m are given in Table 1. The
compounds 5j, 6c, 6e, 6f, and 6k exhibited better activity against Bacillus. The
compounds 5b, 5k, 5m, 6c, and 6f were found to exhibit better activity against S.
aureus and 5l and 6m exhibited better activity against E. coli. In general, the
compounds with fluoro, chloro, bromo, or alkoxy substituted aryls are found to
exhibit better activity than the unsubstituted aryls.
Conclusions
A series of 4,8,9,10-tetraaryl-1,3-diazatricyclo[3.3.1.1]decan-6-ones were synthe-
sized and reduced into 4,8,9,10-tetraaryl-1,3-diazatricyclo[3.3.1.1]decan-6-ols by
sodium borohydride. The use of methanol (2v) benzene (1v) mixture as the solvent
in the reduction afforded good yield. Unambiguous proton and carbon chemical
shift values were assigned for these compounds and then subjected to antimicrobial
evaluation and found to be an effective anti-bacterial.
Experimental
Solvents and reagents were commercially sourced and used without further
purification. Melting points were taken on an Elchem Microprocessor-based DT
apparatus in open capillary tubes and are uncorrected. IR spectra were obtained on
an Avatar-330 FTIR spectrophotometer (Thermo Nicolet) using KBr pellets, and
only noteworthy absorption levels (reciprocal centimeters) are listed. The NMR
spectra were recorded on Bruker 200-, 300-, and 500-MHz spectrometer using TMS
as internal standard (chemical shifts d in ppm). Mass spectra were recorded on
HRMS and LCMS by Agilent 1200 series LC and Micromass zQ spectrometer.
Thin-layered chromatography (TLC) was performed on preparative plates of silica
gel (s.d.fine). Visualization was made with an iodine chamber. Column chroma-
tography was performed by using silica gel (60-120 mesh).
Representative spectral characterization of 4,8,9,10-tetrakis(4-bromophenyl)-1,3-
diazaadamantan-6-one (5f).
123

G. L. Balaji et al.
Proton chemical shift assignment: The careful examination of proton NMR
spectrum reveals that the singlet at d 3.85 ppm integrating for two protons is due to
the C-5, 7 protons, respectively. The singlets at d 4.71 ppm and integrating for two
protons represents the protons at C-4,10 and the singlet at d 4.67 ppm and
integrating for two protons represents the C-8, 9, respectively. The singlet at d
4.34 ppm and integrating for two protons is due to the C-2 protons, respectively.
The doublet at d 6.55 ppm and d 7.01 and integrating for four protons each with an
coupling constant of 8.4 Hz is due to the aryl protons at H-4b, 10b, 4b0, 10b0 and
H-4c, 10c, 4c0, 10c0. The doublet at d 7.45 ppm and d 7.56 and integrating for four
protons each with an coupling constant of 8.4 Hz is due to the aryl protons at H-8c,
9c, 8c0, 9c0 and H-8b, 9b, 8b0, 9b0.
Carbon chemical shift assignment: The 13C NMR spectrum reveals that the signal
at d 49.90 ppm corresponds to the carbons at C-5, 7 and the signal at d 68.48 ppm
corresponds to carbons at C-8, 9 respectively and the signal at d 63.40 ppm
corresponds to the carbons at C-4 and C-10 respectively. The signal at d 67.94 ppm
corresponds to the carbon at C-2 and the signal at d 211.90 ppm corresponds to
carbon at C-6 respectively and the rest of the signals appears at 132.28 (ipso),
130.37 (ipso0), 137.94 (para), 160.38, 136.23 (para0), 129.50 (ortho), 128.39
(ortho0), 121.80 (meta), 120.67 (meta0). The above discussion clearly reveals the
formation of desired 4,8,9,10-tetrakis(4-bromophenyl)-1,3-diazaadamantan-6-one.
In the similar way the carbon chemical shifts of other compounds has been assigned
and are included in the experimental section.
4,8,9,10-tetrakis(4-fluorophenyl)-1,3-diazatricyclo[3.3.1.1]decan-6-one
(5c):
Yield: 78 %, M.p., 256 °C; IR values: 1,701 cm-1 (C=O stretching), 3,062 cm-1
1
(Ar C–H stretching), 2,883 cm-1 (aliphatic C–H stretching); H-NMR chemical
shift (d) in ppm: 4.03[s, 2H, C5 and C7–H], 4.93[s, 2H, C4 and C10–H], 4.85[s, 2H,
C8 and C9–H], 4.51[s, 2H, C2–H], 7.70, 7.12[ddd, J = 5.9 Hz, ortho and ortho0-H],
7.27, 6.70[t, J = 8.7 Hz, meta and meta0-H]; 13C-NMR chemical shift (d) in ppm:
49.88 [C5 and C7], 68.50 [C8 and C9], 63.55 [C4 and C10], 67.90 [C2], 212.72 [C6],
135.15, 135.11[–ipso, 2 carbons], 133.09, 133.13[–ipso0, 2 carbons], 163.65,
162.77[para, 2 carbons], 160.38, 159.51[para0, 2 carbons], 129.54, 129.64[ortho, 4
carbons], 128.40, 128.50[ortho0, 4 carbons], 113.97, 114.25[meta, 4 carbons],
115.85, 116.14 [meta0, 4 carbons].
4,8,9,10-tetrakis(4-chlorophenyl)-1,3-diazatricyclo[3.3.1.1]decan-6-one
(5e):
Yield: 79 %, M.p., 248 °C; IR values: 1,703 cm-1(C=O stretching), 3,036 cm-1
1
(Ar C–H stretching), 2,959 cm-1 (aliphatic C–H stretching). H-NMR chemical
shift (d) in ppm: 4.08[s, 2H, C5 and C7–H], 5.02[s, 2H, C4 and C10–H], 4.85[s, 2H,
C8 and C9–H], 4.67[s, 2H, C2–H], 7.34, 7.12[t, J = 7.6 Hz, meta and meta0-H],
7.34, 6.8[q, J = 6.6 Hz, para and para0-H]. 13C-NMR chemical shift (d) in ppm:
51.31 [C5 and C7], 68.67 [C8 and C9], 60.48 [C4 and C10], 67.57[C2], 213.03 [C6],
130.44[–ipso, 2 carbons], 129.06, 129.76[–ipso0, 2 carbons], [para, 2 carbons],
159.52, 159.91[para0, 2 carbons], 124.60, 126.95 [ortho, 4 carbons], 123.09, 124.33
[ortho0, 4 carbons], 116.74, 116.97 [meta, 4 carbons], 114.88, 115.09 [meta0, 4
carbons].
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Synthesis of diversely substituted adamantanes
4,8,9,10-tetrakis(2-methoxyphenyl)-1,3-diazatricyclo[3.3.1.1]decan-6-one
(5h):
Yield: 70 %, M.p., 185 °C; IR values: 1,703.88 cm-1(C=O stretching),
3,030 cm-1 (Ar C–H stretching), 2,956 cm-1 (aliphatic C–H stretching). 1H-
NMR chemical shift (d) in ppm: 3.90[s, 2H, C5 and C7–H], 4.81[s, 2H, C4 and C10–
H], d 4.67[s, 2H, C8 and C9–H], 4.45[s, 2H, C2–H], 7.24, 6.57[s, ortho and ortho0-
H], 7.12, 6.86[d, para and para0-H]. 13C-NMR chemical shift (d) in ppm: 50.47 [C5
and C7], 69.23[C8 and C9], 64.28[C4 and C10], 68.72[C2], 213.28 [C6], 139.67[–
ipso, 2 carbons], 141.21[–ipso0, 2 carbons], [para, 2 carbons], 160.34[para0, 2
carbons], 118.93, 120.08[ortho, 4 carbons], 128.17,130.08 [ortho0, 4 carbons],
112.14, 112.72[meta, 4 carbons], 113.71, 113.86[meta0, 4 carbons].
4,8,9,10-tetrakis(3,4-dimethoxyphenyl)-1,3-diazatricyclo[3.3.1.1]decan-6-one (5l):
Yield: 70 %, M.p., 204 °C; IR values: 1,697 cm-1(C=O stretching), 2,999 cm-1
1
(Ar C–H stretching), 2,933 cm-1 (aliphatic C–H stretching); H-NMR chemical
shift (d) in ppm: 3.70[s, 2H, C5 and C7–H], 4.75[s, 2H, C4 and C10–H], 4.60[s, 2H,
C8 and C9–H], 4.35[s, 2H, C2–H], 6.3-7.5[m, aryl protons].
1. Representative spectral characterization of 4,8,9,10-tetrakis(4-bromophe-
nyl)-1,3-diazaadamantan-6-ol (6f).
Proton chemical shift assignment: For 4,8,9,10-tetraphenyl-1,3-diazatricy-
clo[3.3.1.1]decan-6-ols, the compound 6f is taken as a representative example and
1
its chemical shift assignments have been discussed. The examination of H NMR
spectra of 6f clearly illustrates that two sets of aryl protons are available. This indicates
that all the aryl substituents are not present in the same environment. The singlet at
2.77 ppm is due to H-5, 7 couples with the doublet at 4.13 (3 Hz) ppm as well as with
the triplet at 4.35 ppm (4.5 Hz). The signals at 4.10 and 4.35 ppm are due to benzylic
protons at C4, C10 and C8, and C9, respectively. Based on our earlier studies, the
relatively upfield benzylic signal at 4.10 [t, J = 4.5 Hz] ppm has been assigned to
axially oriented H-8, 9 and the downfield doublet at 4.35 (with J = 3 Hz) is due to the
H-4, 10. A singlet at 2.16 ppm integrating for one proton may be due to the –OH and
the proton at H-6 appeared at 1.85 ppm. The singlet at 4.13 ppm is due to the H-2 s.
The doublet at 7.52 ppm integrating for four protons is due to the ortho protons of aryls
at C4 and C10. The doublet at 7.42 ppm integrating for four protons is due to the meta
protons of aryl at C4 and C10. Similarly the other set of aryl protons at C8 and C9
appeared as 6.93 and 7.31 ppm. The doublet at 6.93 ppm integrating for four protons is
due to the ortho protons of aryls at C8 and C9. The doublet at 7.31 ppm integrating for
four protons is due to the meta protons of aryl at C8 and C9.
Carbon chemical shift assignment: The 13C NMR spectrum reveals that the signal
at d 43.82 ppm corresponds to the carbons at C-5 and C-7, respectively, and the
signal at d 61.13 ppm corresponds to carbons at C-8 and C-9, respectively, and the
signal at d 58.25 ppm corresponds to the carbons at C-4 and C-10, respectively. The
signal at d 69.36 ppm corresponds to the carbon at C-2 and the signal at d
72.31 ppm corresponds carbons at C-6, respectively, and the rest of the signals
appears at 120.77 (C-4d, 10d), 121.47 (C-8d, 9d), 128.07 (C-4b, 10b, 4b0, 10b0),
128.34 (C-8c, 9c, 8c0, 9c0), 131.01 (C-4c, 10c, 4c0, 10c0), 131.97 (C-8b, 9b, 8b0, 9b0),
139.19 (C-4a, 10a), 140.09 (C-8a, 9a).
123

G. L. Balaji et al.
Summarized as follows: White crystalline solid; Yield: 73 %. M.p. 256-258 °C;
IR (KBr, cm-1): 3389 (–OH stretching), 3054 (aromatic-CH-stretching), 2801
(aliphatic-CH-stretching), 1712 (disappearance of –C=O); 1H-NMR (500 MHz,
CDCl3) dH: 2.19 (bs, 1H, –OH), 2.77 (s, 2H, H-5, 7), 4.07 (t, J = 3.8 Hz, 1H, H-6),
4.10 (s, 2H, H-8, 9), 4.13 (s, 2H, H-4, 10), 4.38 (s, 2H, H-2), 6.91 (d, J = 8.5 Hz,
4H, H-4b, 10b, 4b0, 10b0), 7.27 (d, J = 8.5 Hz, 4H, H-4c, 10c, 4c0, 10c0), 7.39 (d,
J = 8.5 Hz, 4H, H-8c, 9c, 8c0, 9c0), 7.46 (d, J = 8.5 Hz, 4H, H-8b, 9b, 8b0, 9b0);
13C-NMR (125 MHz, CDCl3) dC: 43.82 (C-5, 7), 58.25 (C-4, 10), 61.13 (C-8, 9),
69.36 (C-2), 72.31 (C-6), 120.77 (C-4d, 10d), 121.47 (C-8d, 9d), 128.07 (C-4b, 10b,
4b0, 10b0), 128.34 (C-8c, 9c, 8c0, 9c0), 131.01 (C-4c, 10c, 4c0, 10c0), 131.97 (C-8b,
9b, 8b0, 9b0), 139.19 (C-4a, 10a), 140.09 (C-8a, 9a). HRMS: m/z 773.1000 (M ? 4).
In a similar way all other members of the series were assigned and given.
2. 4,8,9,10-tetraphenyl-1,3-diazaadamantan-6-ol (6a): White crystalline solid;
Yield: 72 %. M.p. 236-238 °C; IR (KBr, cm-1): 3302 (–OH stretching), 3026
(aromatic-CH-stretching), 2974 (aliphatic-CH-stretching); 1H-NMR (500 MHz,
CDCl3) dH: 1.88 (bs, 1H, –OH), 2.86 (s, 2H, H-5, 7), 4.10 (t, J = 3.4 Hz, 1H,
H-6), 4.19 (s, 2H, H-8, 9), 4.21 (s, 2H, H-4, 10), 4.54 (s, 2H, H-2), 7.03 (t,
J = 7.6 Hz, 4H, H-4c, 10c), 7.08-7.09 (m, 6H, H-4b, 10b and 4d, 10d), 7.20 (t,
J = 7.6 Hz, 2H, H-8d, 9d), 7.31 (t, J = 7.6 Hz, 4H, H-8c, 9c), 7.55 (d, J = 7.6 Hz,
4H, H-8b, 9b); 13C-NMR (125 MHz, CDCl3) dC: 44.47 (C-5, 7), 59.06 (C-4, 10),
70.05 (C-8, 9), 62.06 (C-2), 72.65 (C-6), 126.33 (C-4d, 10d), 126.51 (C-8b, 9b),
127.00 (C-4c, 10c), 127.66 (C-8d, 9d), 128.68 (C-4b, 10b), 129.00 (C-8c, 9c),
140.85 (C-4a, 10a), 141.72 (C-8a, 9a).
3. 5-methyl-4,8,9,10-tetraphenyl-1,3-diazaadamantan-6-ol (6b): White crystal-
line solid; Yield: 72 %; M.p. 236-238 °C; IR (KBr, cm-1): 3302 (–OH stretching),
3026 (aromatic-CH-stretching), 2974 (aliphatic-CH-stretching); 1H-NMR
(500 MHz, CDCl3) dH: 1.28 (bs, 1H, –OH), 1.42 (s, 3H, H-5), 4.21 (t,
J = 4.0 Hz, 1H, H-7), 4.23 (s, 2H, H-8, 9), 4.44 (d, J = 6.4 Hz, 1H, H-6), 4.85
(s, 2H, H-4,10), 5.62 (s, 2H, H-2), 6.82 (t, J = 7.4 Hz, H-4b, 10b and 4d, 10d), 7.10
(d, J = 7.6 Hz, 4H, H-8c, 9c), 7.35 (t, J = 7.4 Hz, H-4c, 10c, H-8d, 9d), 7.58 (d,
J = 7.6 Hz, 2H, H-8b), 7.79 (d, J = 7.6 Hz, 2H, H-9b); 13C-NMR (125 MHz,
CDCl3) dC: 17.28 (C-5), 49.70 (C-7), 63.42 (C-4, 10), 68.64 (C-8, 9), 69.97 (C-2),
70.90 (C-6), 126.10 (C-4d), 126.30 (C-10d), 126.80 (C-8b), 126.92 (C-9b), 127.38
(C-4c), 128.28 (C-10c), 128.63 (C-8d, 9d), 130.54 (C-4b, 10b), 137.70 (C-8c, 9c),
138.04 (C-4a, 10a), 139.43 (C-8a, 9a).
4. 4,8,9,10-tetrakis(4-fluorophenyl)-1,3-diazaadamantan-6-ol (6c): White crys-
talline solid; Yield: 69 %. M.p. 224-226 °C; IR (KBr, cm-1): 3410 (–OH
stretching), 3305 (–OH stretching), 2907 (aromatic-CH-stretching), 2807 (ali-
phatic-CH-stretching), 1712 (disappearance of –C=O); 1H-NMR (500 MHz,
CDCl3) dH: 1.82 (bs, 1H, –OH), 2.79 (s, 2H, H-5, 7), 4.10 (t, J = 3.8 Hz, 1H,
H-6), 4.15 (s, 2H, H-8, 9), 4.17 (s, 2H, H-4, 10), 4.42 (s, 2H, H-2), 6.82 (t,
J = 6.8 Hz, 4H, H-8c, 9c, 8c0, 9c0), 7.00-7.03 (m, 8H, H-4b, 10b, 4b0, 10b0, 4c, 10c,
4c0, 10c0), 7.51 (q, J = 5.5 Hz, 4H, H-8b, 9b, 8b0, 9b0); 13C-NMR (125 MHz,
CDCl3) dC: 44.15 (C-5, 7), 58.26 (C-4, 10), 60.94 (C-8, 9), 69.47 (C-2), 72.17 (C-6),
123

Synthesis of diversely substituted adamantanes
114.53 (C-4c, 4c0), 114.70 (C-10c, 10c0), 115.54 (C-8c, 8c0), 115.71 (C-9c, 9c0),
127.85 (C-4b, 4b0), 127.92 (C-10b, 10b0), 129.04 (C-8b, 8b0), 129.10 (C-9b, 9b0),
135.93, 135.95 (C-4a, 10a), 136.98, 137.00 (C-8a, 9a), 160.59 and 161.11 (C-4d,
10d), 162.54 and 163.06 (C-8d, 9d). HRMS: m/z 530.1000 (M?).
5. 4,8,9,10-tetrakis(2-chlorophenyl)-1,3-diazaadamantan-6-ol (6d): White crys-
talline solid; Yield: 72 %. M.p. 248-250 °C; IR (KBr, cm-1): 3322 (–OH
stretching), 3050 (aromatic-CH-stretching), 2927 (aliphatic-CH-stretching); 1H-
NMR (500 MHz, CDCl3) dH: 1.59 (bs, 1H, –OH), 3.34 (s, 2H, H-5, 7), 4.23 (s, 2H,
H-8, 9), 4.38 (t, J = 4.0 Hz, 1H, H-6), 4.48 (s, 2H, H-4, 10), 5.12 (s, 2H, H-2),
7.04–7.09 (m, 4H, H-4c, 10c, 4c0, 10c0), 7.11 (t, J = 7.5 Hz, 2H, H-8c, 9c), 7.15
(dd, J = 6.5, 2H, H-8c0, 9c0), 7.20 (dd, J = 6.5, 2H, H-8b, 9b), 7.27–7.30 (m, 2H,
H-4d, 10d), 7.46 (dd, J = 6.5, 2H, H-8d, 9d), 8.09 (d, J = 6.5 Hz, 2H, H-4b, 10b);
HRMS: m/z 596.1000 (M ? 2).
6. 4,8,9,10-tetrakis(4-chlorophenyl)-1,3-diazaadamantan-6-ol (6e): White crys-
talline solid; Yield: 70 %. M.p. 260-262 °C; IR (KBr, cm-1): 3403 (–OH
stretching), 3044 (aromatic-CH-stretching), 2891 (aliphatic-CH-stretching), 1712
1
(disappearance of –C=O); H-NMR (500 MHz, CDCl3) dH: 1.82 (bs, 1H, –OH),
2.78 (s, 2H, H-5, 7), 4.88 (t, J = 3.8 Hz, 1H, H-6), 4.11 (s, 2H, H-8, 9), 4.15 (s, 2H,
H-4, 10), 4.42 (s, 2H, H-2), 6.97 (d, J = 8.5 Hz, 4H, H-4b, 10b, 4b0, 10b0), 7.12 (d,
J = 8.5 Hz, 4H, H-4c, 10c, 4c0, 10c0), 7.31 (d, J = 8.5 Hz, 4H, H-8c, 9c, 8c0, 9c0),
7.46 (d, J = 8.5 Hz, 4H, H-8b, 9b, 8b0, 9b0); 13C-NMR (125 MHz, CDCl3) dC:
43.89 (C-5, 7), 58.24 (C-4, 10), 61.06 (C-8, 9), 69.34 (C-2), 72.29 (C-6), 127.72 (C-
4b, 10b, 4b0, 10b0), 128.04 (C-8b, 9b, 8b0, 9b0), 128.83 (C-4c, 10c, 4c0, 10c0), 128.99
(C-8c, 9c, 8c0, 9c0), 132.54 (C-4d, 10d), 133.39 (C-8d, 9d), 138.67 (C-4a, 10a),
139.60 (C-8a, 9a). HRMS: m/z 596.2634 (M ? 2).
7. 4,8,9,10-tetrakis(4-methylphenyl)-1,3-diazaadamantan-6-ol (6g): White
crystalline solid; Yield: 79 %. M.p. 216-218 °C; IR (KBr, cm-1): 3377 (–OH
stretching), 3057 (aromatic-CH-stretching), 2920 (aliphatic-CH-stretching); 1H-
NMR (500 MHz, CDCl3) dH: 1.83 (bs, 1H, –OH), 2.89 (s, 6H, –CH3), 2.91 (s, 6H, –
CH3), 2.77 (s, 2H, H-5, 7), 4.03 (t, J = 3.2 Hz, 1H, H-6), 4.16 (s, 2H, H-8, 9), 4.23
(s, 2H, H-4, 10), 4.54 (s, 2H, H-2), 6.63-6.94 (m, 8H, H-4b, 10b, 4b0, 10b0, H-4c,
10c, 4c0, 10c0), 7.14 (d, J = 8 Hz, 4H, H-8c, 9c, 8c0, 9c0), 7.42 (d, J = 8 Hz, 4H,
H-8b, 9b, 8b0, 9b0); 13C-NMR (125 MHz, CDCl3) dC: 20.84 (–CH3 carbon at C-4d,
10d), 20.98 (–CH3 carbon at C-8d, 9d), 44.73 (C-4, 10), 58.69 (C-5, 7), 62.01 (C-8,
9), 69.42 (C-6), 72.69 (C-2), 126.53 (C-4b, 10b, 4b0, 10b0), 126.92 (C-8b, 9b, 8b0,
9b0), 127.62 (C-4c, 10c), 128.06 (C-4c0, 10c0), 128.33 (C-8c, 9c), 129.30 (C-8c0,
9c0), 129.68 (C-4d, 10d), 135.59 (C-8d, 9d), 136.87 (C-4a, 10a), 138.16 (C-8a, 9a).
HRMS: m/z 514.2985 (M?).
8. 4,8,9,10-tetrakis(2-methoxyphenyl)-1,3-diazaadamantan-6-ol (6h): White
crystalline solid; Yield: 56 %. M.p. 208-210 °C; IR (KBr, cm-1): 3420 (–OH
stretching), 3070 (aromatic-CH-stretching), 2835 (aliphatic-CH-stretching); 1H-
NMR (500 MHz, CDCl3) dH: 2.19 (bs, 1H, –OH), 3.20 (s, 2H, H-5, 7), 3.74 (s, 6H, –
OCH3 at 4b0, 10b0), 3.80 (s, 6H, –OCH3 at 8b0, 9b0), 4.28 (t, J = 3.2 Hz, 1H, H-6),
4.35 (s, 2H, H-8, 9), 4.36 (s, 2H, H-4, 10), 4.98 (s, 2H, H-2), 6.58 (d, J = 8 Hz, 2H,
123

G. L. Balaji et al.
H-4b, 10b), 6.62 (d, 2H, J = 8 Hz, 2H, H-4d, 10d), 6.73 (t, J = 7.4 Hz, 2H, H-8d,
9d), 6.86 (t, J = 7.5 Hz, 2H, H-8c, 9c), 6.98-7.02 (m, 4H, H-4c, 10c, 4c0, 10c0), 7.35
(d, J = 7.5 Hz, 2H, H-8c0, 9c0), 7.88 (d, J = 7.5 Hz, 2H, H-8b, 9b); HRMS: m/z
578.3353 (M?).
9. 4,8,9,10-tetrakis(4-methoxyphenyl)-1,3-diazaadamantan-6-ol (6i): White
crystalline solid; Yield: 58 %. M.p. 188-190 °C; IR (KBr, cm-1): 3420 (–OH
stretching), 3070 (aromatic-CH-stretching), 2835 (aliphatic-CH-stretching); 1H-
NMR (500 MHz, CDCl3) dH: 1.62 (bs, 1H, –OH), 2.85 (s, 2H, H-5, 7), 3.65 (s, 6H, –
OCH3 at 4d, 10d), 3.78 (s, 6H, –OCH3 at 8d, 9d), 4.08 (t, J = 3.8 Hz, 1H, H-6),
4.14 (s, 2H, H-8, 9), 4.25 (s, 2H, H-4, 10), 4.53 (s, 2H, H-2), 6.65-6.78 (m, 8H,
H-4b, 10b, 4b0, 10b0, 8c, 9c, 8c0, 9c0), 7.03-7.26 (m, 8H, H-4c, 10c, 4c0, 10c0, 8b, 9b,
8b0, 9b0); HRMS: m/z 578.1000 (M?).
10. 4,8,9,10-tetrakis(4-ethoxyphenyl)-1,3-diazaadamantan-6-ol (6j): White
crystalline solid; Yield: 68 %. M.p. 242-244 °C; IR (KBr, cm-1): 3306 (–OH
stretching), 3060 (aromatic-CH-stretching), 2880 (aliphatic-CH-stretching), 1712
1
(disappearance of –C=O); H-NMR (500 MHz, CDCl3) dH: 1.36 (m, 12H, –CH3,
H-4d00, 10d00, –CH3, H-8d00, 9d00), 4.02–4.04 (m, 8H, –CH2, H-4d0, 10d0, H-8d0, 9d0),
4.46 (s, 2H, H-2), 4.92–5.03 (m, 8H, H-5, 7, H-8, 9; H-4, 10 and H-6, –OH), 6.65 (d,
J = 8.5 Hz, 4H, H-4b, 10b, 4b0, 10b0), 6.83 (d, J = 8.5 Hz, 4H, H-4c, 10c, 4c0,
10c0), 6.97 (d, J = 8.5 Hz, 4H, H-8c, 9c, 8c0, 9c0), 7.42 (d, J = 8.5 Hz, 4H, H-8b,
9b, 8b0, 9b0). HRMS: m/z 634.1000 (M?).
11. 4,8,9,10-tetrakis(2,5-dimethoxyphenyl)-1,3-diazaadamantan-6-ol (6 k):
White crystalline solid; Yield: 72 %. M.p. 242-244 °C; IR (KBr, cm-1): 3298
(–OH stretching), 2998 (aromatic-CH-stretching), 2834 (aliphatic-CH-stretching),
1
1721 (–C=O); H-NMR (500 MHz, CDCl3) dH: 1.69 (bs, 1H, –OH), 3.12 (s, 2H,
H-5, 7), 3.68 (s, 6H, –OCH3, H-4b0, 10b0), 3.71 (s, 6H, –OCH3, H-8b0, 9b0), 3.72 (s,
6H, –OCH3, H-4c, 10c), 3.77 (s, 6H, –OCH3, H-8c, 9c), 4.22 (t, J = 4 Hz, 1H, H-6),
4.30 (s, 2H, H-8, 9), 4.38 (s, 2H, H-4, 10), 4.99 (s, 2H, H-2), 6.5-6.58 (m, 8H, H-8b,
9b, 4b, 10b, 8d, 9d, 4d, 10d), 6.97 (s, 2H, H-4c0, 10c0), 7.40 (s, 2H, H-8c0, 9c0); 13C-
NMR (125 MHz, CDCl3) dC: 38.74 (C-4, 10), 51.77 (C-8, 9), 54.12 (–OCH3 at
C-4c), 54.81(–OCH3 carbon at C-10c), 55.29 (–OCH3 carbon at C-8c), 55.46
(–OCH3 carbon at C-9c), 55.72 (–OCH3 carbon at C-4b0), 55.78(–OCH3 carbon at
C-10b0), 55.82 (–OCH3 carbon at C-8b0), 55.91(–OCH3 carbon at C-9b0), 56.22
(C-5, 7), 70.10 (C-6), 71.59 (C-2), 110.41 (C-4c0, 10c0, 4c0, 10c0), 111.47 (C-4d),
111.74 (C-10d), 112.17 (C-8d), 112.43 (C-9d), 113.55 (C-4b), 115.64 (C-10b),
115.82 (C-8b), 116.68 (C-9b), 130.15 (C-4a, 10a), 130.95 (C-8a, 9a), 150.52 (C-4b0,
10b0), 151.56 (C-8b0, 9b0), 152.12 (C-4c), 152.58 (C-10c), 152.89 (C-8c), 153.34
(C-9c). HRMS: m/z 698.3370 (M?).
12.
4,8,9,10-tetrakis(3,4-dimethoxyphenyl)-1,3-diazaadamantan-6-ol
(6l):
White crystalline solid; Yield: 65 %. M.p. 246-248 °C; IR (KBr, cm-1): 3312
(–OH stretching), 2960 (aromatic-CH-stretching), 2833 (aliphatic-CH-stretching),
1
1712 (disappearance of –C=O); H-NMR (500 MHz, CDCl3) dH: 1.64 (bs, 1H,
–OH), 2.72 (s, 2H, H-5, 7), 3.67 (s, 6H, –OCH3 at C-4c0, 10c0), 3.82 (s, 6H, –OCH3
at C-8d, 9d), 3.84 (s, 6H, –OCH3 at C-4d, 10d), 3.85 (s, 6H, –OCH3 at C-8c0, 9c0),
123

Synthesis of diversely substituted adamantanes
4.03 (t, J = 4 Hz, 1H, H-6), 4.09 (s, 2H, H-8, 9), 4.28 (s, 2H, H-4, 10), 4.50 (s, 2H,
H-2), 6.56 (s, 2H, H-4b0, 10b0), 6.66 (d, J = 8.0, 2H, H-4b, 10b), 6.75 (d, J = 8.0,
2H, H-8c, 9c), 6.81 (d, J = 8.0 Hz, 2H, H-4c, 10c), 7.03 (s, 2H, H-8b0, 9b0), 7.13 (d,
J = 8.0, 2H, H-8b, 9b). HRMS: m/z 698.0100 (M?).
13. 4,8,9,10-tetrakis(3,4,5-trimethoxyphenyl)-1,3-diazaadamantan-6-ol (6m):
White crystalline solid; Yield: 76 %. M.p. 244-246 °C; IR (KBr, cm-1): 3322
(–OH stretching), 2937 (aromatic-CH-stretching), 2834 (aliphatic-CH-stretching),
1
1712 (disappearance of –C=O); H-NMR (500 MHz, CDCl3) dH: 1.68 (bs, 1H,
–OH), 2.87 (s, 2H, H-5, 7), 3.69 (s, 12H, –OCH3 at 4c, 10c, 4c0, 10c0), 3.78 (s, 6H,
–OCH3 at 4d, 10d), 3.80 (s, 6H, –OCH3 at 8d, 9d), 3.81 (s, 12H, –OCH3 at 8c, 9c,
8c0, 9c0), 4.01 (t, J = 3.8 Hz, 1H, H-6), 4.09 (s, 2H, H-8, 9), 4.35 (s, 2H, H-4, 10),
4.47 (s, 2H, H-2), 6.39 (s, 4H, H-4b, 10b, 4b0, 10b0), 6.78 (s, 4H, H-8b, 9b, 8b0, 9b0);
HRMS: m/z 818.1000 (M?).
The spectral characterization of 2,4,6,8-tetraphenyl-3,7-diazabicyclo[3.3.1]
nonan-9-ol (5aa):
Proton chemical shift assignment: The careful examination of 1H NMR spectrum
of 5aa reveals that the singlet at d 1.30 and 2.22 ppm integrating for one proton
each is due to the NH-7 and NH-3 protons, respectively. The singlet at d 2.63 ppm
integrating for two protons represents the bridgehead protons at C-1, 5 and the
singlet at d 4.17 ppm integrating for one proton represents the proton at C-9
obtained from NaBH4. The two additional singlets at d 4.20 ppm and d 4.31 ppm
integrating two protons each represent the proton at C-6, 8. The remaining aryl
region protons are exactly matching with the target molecule. The above discussion
clearly reveals the formation of desired 2,4,6,8-tetraphenyl-3,7-diazabicy-
clo[3.3.1]nonan-9-ol (5aa).
Carbon chemical shift assignment: The 13C NMR spectrum of 5aa reveals that
the signal at d 48.93 ppm corresponds to the bridgehead carbons at C-1, 5 and the
signals at d 57.55 ppm and d 61.51 ppm corresponds to the benzylic carbons at C-6,
8 and C-2, 4, respectively. The signal at d 75.27 ppm corresponds to the carbon at
C-9. The signal at d 126.58 ppm and d 127.25 ppm corresponds to the p-carbons at
6d, 8d and 2d, 4d, respectively. The rest of the signals appears at d 126.72 (C-2b,
4b), 126.86 (C-6c, 8c), 128.14 (C-6b, 8b), 128.50 (C-2c, 4c). The signal at d
142.38 ppm and d 145.63 ppm corresponds to the boat and chair ipso carbons at
C-6a, 8a and C-2a, 4a, respectively. The above discussion revealed the formation of
desired 2,4,6,8-tetraphenyl-3,7-diazabicyclo[3.3.1]nonan-9-ol (5aa).
The 4,8,9,10-tetraaryl-1,3-diazatricyclo[3.3.1.1]decan-6-ones (5a–m), 4,8,9,10-
tetraaryl-1,3-diazatricyclo[3.3.1.1]decan-6-ols (6a–m) were evaluated for their
in vitro antibacterial activity against standard pathological bacterial strains
Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, and Bacillus
subtilis ATCC 29212 by agar well diffusion method (Balaji et al., 2012).
Suspensions of each microorganism were prepared from their 24-h cultures to
obtain approximately 106 colony-forming units (cfu) per milliliter for plating.
DMSO was chosen as control and the compound under test was dissolved in DMSO
123

G. L. Balaji et al.
at a concentration of 50 lg/0.05 ml. It was aseptically transferred and applied into
the cups created on the dry surface of the inoculated plates and then incubated at
37 °C overnight (*18–20 h). This assay was performed in duplicate and the mean
diameters of the clear inhibition zones (mm) were recorded disregarding the single
colony or a faint haze caused by the inoculums.
Acknowledgments The authors are thankful to the administration of VIT University, Vellore, India, for
providing facilities to carry out our research work, and are also thankful to SAIF, IIT-Madras, SIF-
Chemistry, VIT University, and VIT-TBI for providing NMR, mass, and IR spectral facilities,
respectively. The author G.L. Balaji is thankful to VIT University for providing a research associate.
References
¨
1. V. Prelog, R. Seiwerth, Uber die Synthese des Adamantans. Berichte der deutschen chemischen
Gesellschaft (A and B Series) 74, 1644–1648 (1941)
2. P.V.R. Schleyer, M.M. Donaldson, R.D. Nicholas, C. Cupas, Org. Synth. 5, 16–17 (1973)
3. K. Watanabe, et al., Resist Composition and Pattern Forming Process. United States Patent
Application 20010006752. Bandwidth Market, Ltd. Retrieved 14 Oct 2005
4. K. Lenzke, L. Landt, M. Hoener, J Chem Phys 127, 084320 (2007). doi:10.1063/1.2773725
5. G.P. Sollot, E.E. Gilbert, J. Org. Chem. 45, 5405–5408 (1980)
6. O. Ermer, J. Am. Chem. Soc. 110, 3747–3754 (1988)
7. K. Naemura, Y. Hokura, M. Nakazaki, Tetrahedron 42, 1763–1768 (1986)
8. G.R. Newkome, C.N. Moorefield, G.R. Baker, Aldrichimica Acta 25, 31–38 (1992)
9. S. Borman, Chem. Eng. News 34, 23–25 (1994)
10. P.D. Harvey, I.S. Butler, D.F.R. Gilson, P.T.T. Wong, J. Phy, Chemistry 90, 4546–4549 (1986)
11. X. Jiang, C.P. Klages, Diam. Relat. Mater. 2, 1112–1113 (1993)
12. L. Claisen, Chem. Ber. 45, 3157–3166 (1912)
13. V.R. Paul Schleyer, My Thirty Years in Hydrocarbon Cages: From Adamantane to Dodecahedrane,
In Cage Hydrocarbons, ed. by G. A. Olah (Wiley, New York 1990), pp. l–45
14. R. Jeyaraman, T. Ravindran, M. Sujatha, Ind J Chem 31B, 362–362 (1992)
15. U. Schoen, W. Kehrbach, K. Wolf, D.E. German Offen, Chem Abstr 110, 212804e (1989)
16. L.M. Jackman, T.S. Dunne, B. Muller, H. Quast, Chem. Ber. 115, 2872–2891 (1982)
17. H. Quast, B. Muller, E.M. Peters, K. Peters, H.G. von Schnering, Chem. Ber. 115, 3631–3652 (1982)
18. S. Sivasubramanian, M. Sundaravadivelu, N. Arumugam, Org. Prep. Proced. Int. 22, 645–648 (1990)
19. V. Vijayakumar, M. Sundaravadivelu, S. Perumal, A. Lycka, Mag Reson Chem 39, 645–647 (2001)
20. V. Vijayakumar, M. Sundaravadivelu, S. Perumal, Mag Reson Chem 39, 101–104 (2001)
21. V. Vijayakumar, M. Sundaravadivelu, S. Perumal, M.J.E. Hewlines, Mag Reson Chem 38, 883–885
(2000)
22. V. Vijayakumar, M. Sundaravadivelu, Mag Reson Chem 43, 479–482 (2005)
23. G.L. Balaji, V. Vijayakumar, K. Rajesh, Arab J Chem (2012). doi:10.1016/j.arabjc.2011.12.011
24. G.L. Balaji, K. Rajesh, R. Janardhanan, V. Vijayakumar, Research on chemical intermediates. doi:10.
1007/s11164-014-1756-9
25. R.V. Krishnakumar, V. Vijayakumar, M. Sundaravadivelu, S. Natarajan, S. Perumal, S. Selvaraj,
Acta Cryst E57, o305–o306 (2001)
26. R.V. Krishnakumar, M. Subha Nandhini, V. Vijayakumar, S. Natarajan, M. Sundaravadivelu, S.
Perumal, A. Mostad, Acta Cryst E57, o860–o862 (2001)
27. M. Subha Nandhini, R.V. Krishnakumar, T. Narasimhamurthy, V. Vijayakumar, M. Sundaravadiv-
elu, S. Natarajan, Acta Cryst E58, o675–o677 (2002)
28. M. Subha Nandhini, R.V. Krishnakumar, T. Narasimhamurthy, V. Vijayakumar, M. Sundaravadiv-
elu, S. Natarajan, Acta Cryst E58, o1210–o1212 (2002)
29. S. Natarajan, K. Uthayasankari, K.E. Sathes Goud, C. Gangadurai, V. Vijayakumar, J. Suresh, Anal
Sci X-ray Struct Anal 2008(24), X249–X250 (2008)
30. S. Natarajan, V. Sudha Priya, V. Vijayakumar, J. Suresh, P.L. Nilantha Lakshman, Acta Cryst E65,
o1530–o1530 (2009)
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