Preparation of n-phenylbenzo[h]quinolinium derivatives labeled with tritium

Article abstract of DOI:10.1007/s10593-012-1121-0

The possibility of a direct phenylation of benzoquinoline nitrogen atom with nucleogenic phenyl cations has been demonstrated. A simple method has been developed for obtaining previously unknown tritium labeled N-phenyl derivatives of benzo[h]quinolinium, which are promising radioactive markers for studying the biological action mechanisms of medicinal substances containing the benzoquinolinium structure.

Full text of DOI:10.1007/s10593-012-1121-0

Chemistry of Heterocyclic Compounds, Vol. 48, No. 8, November, 2012 (Russian Original Vol. 48, No. 8, August, 2012)
PREPARATION OF N-PHENYLBENZO[h]QUINOLINIUM
DERIVATIVES LABELED WITH TRITIUM
N. E. Shchepina1*, V. V. Avrorin2, G. A. Badun3, and I. I. Boiko4
The possibility of a direct phenylation of benzoquinoline nitrogen atom with nucleogenic phenyl cations
has been demonstrated. A simple method has been developed for obtaining previously unknown tritium
labeled N-phenyl derivatives of benzo[h]quinolinium, which are promising radioactive markers for
studying the biological action mechanisms of medicinal substances containing the benzoquinolinium
structure.
Keywords: nucleogenic phenyl cations, N-phenylbenzo[h]quinolinium salts, tritiated biological markers,
nuclear-chemical synthesis.
It is known that pyridinium salts possess pronounced biological activity [1-4], and the introduction of
phenyl rings (particularly with the formation of N-phenyl-substituted, and also annelated benzopyridinium and
benzoquinolinium derivatives) significantly increases the biological activity and broadens the spectrum of their
biological activity [5-11].
As in the case with other tricyclic nitrogen heterocycles, the direct phenylation of the nitrogen atom in
benzoquinoline by classical methods of organic chemistry is not feasible [12-13], and N-phenylbenzoquinol-
inium derivatives are largely unknown.
The nuclear-chemical method developed by us has been applied with success for the direct phenylation
by nucleogenic phenyl cations of heterocyclic nitrogen atoms in various derivatives of pyridine, quinoline,
acridine, and phenanthridine [14-17]. Extension of the nuclear-chemical method to preparation of unknown,
tritium labeled salts of N-phenylbenzo[h]quinoline, which are promising radioactive indicators for the study of
biological action mechanisms of medications. An outline of nucleogenic phenyl cation formation in the
investigated ion-molecular reactions with benzo[h]quinoline may be represented in the following way.
–
C6H4T+
+
3He
C6H4T2
_______
*To whom correspondence should be addressed, e-mail: neshchepina@mail.ru.
1Natural Science Institute, Perm State National Research University, 4 Genkelya St., Perm 614990, Russia.
2Saint Petersburg State University, 7/9 Universitetskaya nab., Saint Petersburg, 199034, Russia; e-mail:
VVAvrorin@yandex.ru.
3Moscow M. V. Lomonosov State University, 1, Build. 3 Leninskie gory, Moscow 119991, Russia; e-mail:
ga_ba@mail.ru.
4"Technolog Co. Ltd", 2/157 Mendeleeva St., Pereslavl-Zalessky 152025, Russia; e-mail: technolog@slavich.ru.
_________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1282-1286, August, 2012.
Original article submitted November 16, 2011.
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0009-3122/12/4808-1196©2012 Springer Science+Business Media New York

Free nucleogenic phenyl cations are generated as a result of tritium β-decay in the labeled benzene,
which further interact with nucleophilic centers of heterocyclic molecules.
As a result of the large number of possible electrophilic substitution products at the two benzene rings
and one heterocyclic ring, only the product of addition at the nitrogen atom, namely N-phenylbenzo[h]quinol-
inium tetrafluoroborate, was selected for analysis.
X–
+
N
+
N
X–
AdE
C6H4T
C6H4T
C6H4T+
+
N
SE
TH4C6
C6H4T
;
;
N
N
N
TH4C6
X = BF4
The nuclear-chemical synthesis was carried out by the standard procedure in sealed glass ampoules
containing the source of nucleogenic phenyl cations (doubly tritiated benzene C6H4T2), benzo[h]quinoline in a
large molar excess (1:1000), and also a stabilizing salt KBF4. After accumulation of the ion-molecule reaction
products, the N-phenylbenzo[h]quinolinium salt was isolated by TLC (the N-phenylbenzo[f]quinolinium
tetrafluoroborate salt synthesized by us was used as reference). A radiochromatogram of the labeled products in
the system C6H4T2–benzo[h]quinoline–KBF4 is represented in Fig. 1 (for comparison a radiochromatogram for
the case of phenanthridine is shown by the dotted line (2)).
Fig. 1. Radiochromatograms of labeled products in the systems 1 – C6H4T2–benzo[h]quinoline–KBF4,
and 2 – C6H4T2–phenanthridine–KBF4.
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TABLE 1. Radiochemical Yields of Onium Salts for Condensed
Pyridinium Derivatives
Substrate
Yield of onium salt (AdE), %
Quinoline
21±3
14±2
17±1
15±1
Acridine
Phenanthridine
Benzo[h]quinoline
The radiochemical yield of an unknown salt, N-phenylbenzo[h]quinolinium tetrafluoroborate, is shown
in Table 1 (for comparison yields are given in Table 1 when using quinoline and tricyclic derivatives as
substrates [18]).
The small yield of N-phenylbenzoquinolinium salt was not unexpected, since, as in the case of
benzannelated acridine and phenanthridine, the predominance of the electrophilic substitution reaction (large
peak with Rf ~0.6 in Fig. 1) over the addition reaction at the nitrogen atom (peak with Rf ~0.05) was noted. On
comparing the radiochromatograms of the ion-molecule reactions of benzo[h]quinoline and phenanthridine
(lines 1 and 2 in Fig. 1), the analogy is evident.
The extented biological investigations of the nonradioactive benzoquinolinium salts carried out by us
previously [19] showed a significant promise of these structures as antibacterial preparations with a broad
spectrum of action.
The undoubted success of the developed nuclear-chemical synthesis is the possibility of carrying out the
direct phenylation of the nitrogen atom in benzoquinoline and the development of a method for simple
preparation of unknown, tritium labeled N-phenyl derivatives of benzo[h]quinolinium, which are promising
radioactive markers in the study of the biological action mechanisms of medicinal substances containing a
benzoquinolinium structure.
EXPERIMENTAL
To obtain benzene doubly labeled with tritium, gaseous tritium with an isotopic purity of 99% (NPO
Izotop) was used. Analysis of the ditritiobenzene was carried out by gas chromatography [18]. The reference
marker was the unlabeled salt N-phenylbenzo[f]quinolinium tetrafluoroborate, synthesized by a modified
procedure [20] by cyclization of phenyl-β-naphthylamine and paraldehyde. The salt was isolated by
crystallization from 50% acetic acid as needle-shaped crystals of mp 196-197°C (mp 196-198°C [21]).
Radiochromatography of the obtained tritiated compounds was carried out on glass plates with C18
Reverse Phase silica gel (Fluorescent Indicator) in MeCN. Bands of the chromatographic adsorption layer
measuring 0.5 cm in length were removed into dioxane scintillator and their β-radioactivity measured with the
aid of a RackBeta (USA) scintillation counter.
Benzene Doubly Labeled with Tritium. Benzene doubly labeled with tritium was obtained from
1,4-dibromobenzene (3.4 mg, 0.014 mmol), and n-Bu3N (5.0 μl, 0.020 mmol) in hexane, and tritium gas (3.3 Ci,
0.054 mmol) by dehalogenation on a 5% Pd/BaSO4 catalyst for 1 h at room temperature (preliminary activation
of catalyst was carried out at 160-180oC for 45 min in a dynamic vacuum of 10-3 mm Hg). The chemical purity
of the synthesized doubly labeled benzene was not less than 99%. The volume specific activity of the obtained
solution in hexane was 1 Ci/ml.
N-Phenylbenzo[h]quinolinium Tetrafluoroborate. Crystals of the stabilizing salt KBF4 (~200 mg)
were placed in a 0.5 ml glass ampoule, then benzo[h]quinoline (9.9 mg, 0.055 mmol) dissolved in ether was
placed on the salt crystals. The ether was distilled off in vacuum, and after cooling the ampoule with liquid
nitrogen, a C6H4T2 hexane solution (1 μl) was added. The concentration of C6H4T2 was selected so that the ratio
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of labeled benzene to substrate was not less than ~1:1000. The ampoule was sealed, and stored for 1-2 months at
-15°C for accumulation of the nuclear-chemical synthesis products. The ampoule was opened, the contents were
transferred to a special vial, benzene (0.5 ml) was added, followed by an acetone solution of carrier, the
unlabeled N-phenylbenzo[f]quinolinium salt (1 mg/ml) (0.5 ml). Unreacted C6H4T2 was removed by distillation
in vacuum. Acetone (0.5 ml) was added to the dry residue and samples (about 5 μl) were taken for isolation of
labeled compounds by TLC.
The work was carried out with the support of the Russian Foundation for Basic Research (grant 10-03-
00685).
REFERENCES
1.
A. R. Katritzky and C. W. Rees (editors), Comprehensive Heterocyclic Chemistry, Vol. 1, Pergamon,
Oxford (1984), p. 143.
2.
3.
E. Lukevics, Khim. Geterotsikl. Soedin., 723 (1995). [Chem. Heterocycl. Compd., 31, 639 (1995).]
P. Kapkova, N. Stiefl, U. Surig, B. Engels, K. Baumann, and U. Holzgrabe, Arch. Pharm., 336, 523
(2003).
4.
E. S. Krichevskii, L. M. Alekseeva, V. A. Parshin, M. A. Kalinkina, V. V. Chernyshev, and
V. G. Granik, Khim.-Farm. Zh., No. 10, 9 (2007).
5.
6.
D. Levy and Y. Ashani, Biochem. Pharmacol., 35, 1079 (1986).
R. Sanchez-Martin, J. M. Campos, A. Conejo-Garcia, O. Cruz-López, M. Báñez-Coronel,
A. Rodríguez-González, M. A. Gallo, J. C. Lacal, and A. Espinosa, J. Med. Chem., 48, 3354 (2005).
P. Srivani and G. N. Sastry, J. Mol. Graphics Modell., 27, 676 (2009).
W. S. Chen, G. H. Cocolas, C. J. Cavallito, and K. J. Chai, J. Med. Chem., 20, 1617 (1977).
W. S. Chen, G. H. Cocolas, and C. J. Cavallito, J. Pharm. Sci., 68, 1025 (1979).
J. DePriest, G. Y. Zheng, C. Woods, D. P. Rillema, N. A. Mikirova, and M. E. Zandler, Inorg. Chim.
Acta, 264, 287 (1997).
7.
8.
9.
10.
11.
M. A. Loza-Mejía, S. Olvera-Vázquez, K. Maldonado-Hernández, T. Guadarrama-Salgado, I. González-
Sanchez, F. Rodríguez-Hernández, J. D. Solano, R. Rodríguez-Sotres, and A. Lira-Rocha, Bioorg. Med.
Chem., 17, 3266 (2009).
12.
13.
K. H. Pausacker, Aust. J. Chem., 11, 200 (1958).
F. Brody and P. R. Ruby in: A. Klingsberg (editor), Pyridine and Its Derivatives, Part 1, Interscience,
New York (1960), p. 474.
14.
N. E. Shchepina, V. V. Avrorin, G. A. Badun, G. A. Aleksandrova, S. E. Ukhanov, V. M. Fedoseev,
S. B. Lewis, and I. I. Boiko, Khim. Geterotsikl. Soedin, 1008 (2009). [Chem. Heterocycl. Compd., 45,
796 (2009)].
15.
16.
17.
18.
N. E. Shchepina, V. V. Avrorin, G. A. Badun, S. B. Lewis, V. M. Fedoseev, and S. E. Ukhanov, Vestn.
Mosk. Gos. Univ., Ser. 2, Khimiya, 50, 311 (2009).
N. E. Shchepina, V. V. Avrorin, G. A. Badun, V. M. Fedoseev, and S. B. Lewis, Khim. Geterotsikl.
Soedin., 692 (2010). [Chem. Heterocycl. Compd., 46, 547 (2010).]
N. E. Shchepina, V. V. Avrorin, G. A. Aleksandrova, and G. A. Badun, Perspektivnye Materialy, 10,
339 (2011).
N. E. Shchepina, V. V. Avrorin, G. A. Badun, S. B. Lewis, and S. E. Ukhanov, Khim. Geterotsikl.
Soedin., 320 (2012). [Chem. Heterocycl. Compd., 48, 301 (2012).]
19.
20.
21.
N. E. Shchepina, I. I. Boiko, and G. A. Aleksandrova, Khim.-Farm. Zh., 45, No. 3, 30 (2011).
G. T. Pilyugin and E. P. Opanasenko, Ukr. Khim. Zh., 18, 625 (1952).
G. T. Pilyugin and E. P. Opanasenko, Zh. Obshch. Khim., 27, 1015 (1957).
1199