Synthesis of new tetrazolyl derivatives of L- and D-phenylalanine

Article abstract of DOI:10.1134/S1070428016110221

New tetrazolyl derivatives of L- and D-phenylalanine were synthesized by azidation of n-propyl esters of (2S)- and (2R)-2-{[(9H-fluoren-9-ylmethoxy)carbonyl]amino}-3-(4-aminophenyl)propionic acids and by a series of subsequent chemical transformations. The structure and individuality of the compounds obtained were confirmed by using a complex of spectral and chromatographic methods.

Full text of DOI:10.1134/S1070428016110221

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2016, Vol. 52, No. 11, pp. 1681–1685. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © V.V. Tolstyakov, E.S. Tolstobrova, O.S. Zarubina, E.A. Popova, A.V. Protas, S.S. Chuprun, R.Е. Trifonov, 2016, published in
Zhurnal Organicheskoi Khimii, 2016, Vol. 52, No. 11, pp. 1686–1690.
Synthesis of New Tetrazolyl Derivatives
of L- and D-Phenylalanine
V. V. Tolstyakova, E. S. Tolstobrovaa, O. S. Zarubinaa, E. A. Popovab,
A. V. Protasb, S. S. Chuprunb, and R. Е. Trifonova,b*
a St. Petersburg State Technological Institute (Technical University), St. Petersburg, Russia
b St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, 199034 Russia
*e-mail: rost_trifonov@mail.ru; r.trifonov@spbu.ru
Received July 19, 2016
Abstract—New tetrazolyl derivatives of L- and D-phenylalanine were synthesized by azidation of n-propyl
esters of (2S)- and (2R)-2-{[(9H-fluoren-9-ylmethoxy)carbonyl]amino}-3-(4-aminophenyl)propionic acids and
by a series of subsequent chemical transformations. The structure and individuality of the compounds obtained
were confirmed by using a complex of spectral and chromatographic methods.
DOI: 10.1134/S1070428016110221
Tetrazolyl pharmacophore fragment which very
seldom occurs in the nature nevertheless is widely used
in developing highly efficient drugs [1–3]. Introduc-
tion of a tetrazolyl fragment to a molecule of the biolo-
gically active substrate quite often results not only in
increasing its efficiency but also in more prolonged
action with decreased acute toxicity [2]. It is known
that the 1H-tetrazolyl fragment is a bioisosteric analog
of carboxylic, cis-amide and some other functional groups
[3–6]. The approach to modification of amino acids by
introduction into their structure the tetrazolyl fragments
allowed to design of a number of highly efficient
pharmaceuticals of various action: antihypertensive drug
valsartan, semi-synthetic antibiotic of a broad spectrum
of activity cefazolin, a number of new agonists and
antagonists of glutamate receptors, drugs for diag-
nostics, etc. [3]. Optically active tetrazole-bearing
analogs and derivatives of amino acids can be used
further in synthesis of peptidomimetics as we have earlier
demonstrated with an octreotide analog [7]. Synthesis
of amino acids analogs and derivatives is possible in a
variety of ways: an aminolysis of halocarboxylic acids,
Streker synthesis, as well as hydantoin synthesis and
synthesis with malonic ester [8]. However, in the
course of these reactions racemates formation occurs.
It is possible to obtain enantiomerically pure com-
pounds when using natural amino acids as initial
substrates, and also applying common procedures for
the synthesis of optically pure compounds.
Earlier some tetrazolyl derivatives of L-phenyl-
alanine were described. So, the synthesis of a 4-(tetra-
zol-5-yl)phenylalanine derivative was described which
was planned to be used further in solid-phase synthesis
of peptidomimetics [9].
In the present work the derivatives L-and D-
phenylalanine containing tetrazolyl-1 fragment in the
position 4 of a benzene ring were synthesized for the
first time. The structure and individuality of the
obtained compounds were confirmed by a combination
1
of physical and chemical methods of analysis: H and
13C NMR, IR spectroscopy, mass spectrometry, and
TLC.
The synthesis of target compounds was carried out
according to the scheme. In the first stage we carried
out the nitration of initial L-and D-phenylalanines 1a
and 1b with a mixture of sulfuric and nitric acids at 8–
10°C within 3 hours according to the procedure [10,
11]. The reaction proceeded with high yield of nitro
compounds 2a and 2b, their properties corresponded to
the known data [10, 11]. In the next stage the α-amino
function of amino acid was protected. We have used 9-
fluorenylmethoxycarbonyl (Fmoc) protective group
which is rather stable in acid conditions, and the
obtained Fmoc-derivatives 3a and 3b as well as
products of their further transformations can be
directly used in solid-phase synthesis of peptides [7].
1
In H NMR spectrum of compounds 3a and 3b there
1681

TOLSTYAKOV et al.
1682
O
OH
O
OH
O
OH
O
OH
*
*
*
*
HNO3, H2SO4
8_10°C
Fmoc-OSu
CH3CN
Zn, HCl
NHFmoc
NH2
NHFmoc
NH2
NO2
O
NH2
NO2
4a, 4b
3a, 3b
1a, 1b
2a, 2b
O
OPr-n
O
OH
OPr-n
O
OH
*
*
NH
*
*
NHFmoc
NH2
NHFmoc
NHFmoc
n-PrOH, SOCl2
NaN3, CH(OEt)3
CH3COOH
HCl
0_10°C
DMF
NH2
N
N
N
N
N
N
5a, 5b
N
N
N
N
N
N
8a, 8b
6a, 6b
7a, 7b
O
O
N
Fmoc-OSu
=
O
O
O
S-isomer (a), R-isomer (b).
are characteristic signals of the methylene and the
methine groups of the amino acid and of the fluorenyl-
methyl fragment. In C NMR spectrum two characte-
Synthesis of tetrazoles 6a and 6b was carried out by
interaction of amine with sodium azide and triethyl
orthoformate in acetic acid (see the scheme) [12–14].
Amines of aliphatic, aromatic, and heterocyclic series
[12] can enter this reaction. Propyl esters 5a and 5b,
were used as substrates in the heterocyclization since
they afforded the best yields in the reaction and no
tarring occurred. Esters 5a and 5b were prepared from
the corresponding carboxylic acid 4a and 4b by
treating with n-propanol in the presence of thionyl
13
ristic signals of carbon atoms of carboxy and amide
groups appear at 173.27 and 156.39 ppm, the group of
nine signals in the region of 120.56–146.75 ppm
corresponds to 18 aromatic atoms of carbon, and in the
upfield region there are four signals of carbon atoms of
aliphatic groups at 36.62, 47.03, 55.25, and 66.03 ppm.
In the IR spectra of compounds 3a and 3b strong
absorption bands of nitro group at 1350 and 1535 cm–1
are observed and also urethane and carboxy groups at
1693 and 1724 cm–1 are revealed.
1
chloride. In the H NMR spectrum of compounds 6a
and 6b there is a characteristic signal from the CH
group of 1H-tetrazolyl fragment at 10.03 ppm and
doublets of the aromatic protons of the para-substi-
tuted benzene ring are shifted to 7.54 and 7.63 ppm.
The 13C NMR spectrum has a characteristic signal of
the endocyclic carbon atom of the 5-unsubstituted 1H-
tetrazole at 142.61 ppm. Successive treating of com-
pounds 6a and 6b with hydrochloric acid to hydrolyze
the ester and by 4-methylpiperidine in DMF for
removing Fmoc-protecting group afforded in good
yield (2S)- and (2R)-3-[4-(1H-tetrazol-1-yl)phenyl]-2-
aminopropionic acids 8a and 8b. Thus, for the first
time in this study we have synthesized derivatives of L
- and D-phenylalanine containing tetrazolyl fragment
For the reduction of the nitro group we used the
system Zn – HCl – 2-propanol. It was shown by NMR
data that in the course of the reaction about 30% of
isopropyl ether of N-[(9H-fluoren-9-ylmethoxy)carbo-
nyl]-4-amino-L(D)-phenylalanine formed as a by-
product. To convert it to carboxylic acid form it was
isolated from the reaction mixture and boiled in 20%
1
hydrochloric acid for 6 hours. In the H NMR spec-
trum of compounds 4a and 4b the doublet signals of aro-
matic benzene ring shifted upfield (6.48 and 6.91 ppm).
In the IR spectra of the compounds 4a and 4b there
were no characteristic absorption of nitro groups.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 52 No. 11 2016

SYNTHESIS OF NEW TETRAZOLYL DERIVATIVES OF L- AND D-PHENYLALANINE
1683
in the 4 position of the benzene ring, which may be
used for the synthesis of peptidomimetics, and other
practically important compounds.
to a suspension of 37.7 g (0.179 mol) of acid 2a and
2b in 200 mL of 2% NaOH aqueous solution until
complete dissolution. A solution of 61.8 g (0.183 mol)
of suspension of Fmoc-OSu in 100 mL of acetonitrile
was added to this solution. The reaction mixture was
stirred for 3 hours at room temperature and acidified
with 5% HCl to pH 4-5. The precipitated white crystals
were filtered off, washed with ethyl acetate, and dried.
The reaction product was recrystallized from ethanol-
dioxane mixture, 50 : 50. Yield 67% (3a), 71% (3b).
mp 230°C (mp 233–234°C [10]). IR spectrum ν, cm–1:
3429, 3202, 1724, 1693, 1601, 1520, 1447, 1354,
1223, 1057, 856, 760, 741. 1Н NMR spectrum (DMSO-
d6), δ, ppm: 2.90–3.09 m (1H, CH2), 3.25 d.d (1H,
CH2, J 13.7, J 4.3 Hz), 4.13–4.34 m (4H, 2CH2,
2CH), 7.23–7.45 m (4Harom), 7.54 d (2Harom, 3J 8.6 Hz),
7.60–7.64 m (2Harom), 7.79 d (1H, NH, 3J 8.6 Hz), 7.88
d (2Harom, 3J 7.5 Hz ), 8.14 d (2Harom, 3J 8.6 Hz ), 12.93
s (1H, COOH). 13С NMR spectrum (DMSO-d6), δ,
ppm: 36.62 (CH2), 47.03 (CH), 55.25 (CH), 66.03
(CH2), 120.56, 123.69, 125.62, 127.45, 128.07, 130.94,
141.16, 144.20, 146.73 (Сarom), 156.39 (CONH),
173.27 (COOH). Mass spectrum (ESI), m/z: 455.1214
[M + Na]+. C24H20N2O6. Calculated M 432.1321.
EXPERIMENTAL
1Н, 13C NMR spectra were registered on spec-
trometers Varian DPX-300 (at operating frequencies
300.0 and 75.5 MHz respectively) and Bruker Avance-
III-400 (operating frequencies 400 and 100 MHz
respectively) at 25°C using the residual signal of the
solvent as an internal reference.
Mass spectra were measured on high-resolution
instruments Bruker MicroTOF and Bruker Daltonik
GmbH “MaXis”.
2
3
IR spectra were taken on a spectrophotometer
Shimadzu FTIR 8400 from pellets with KBr. Melting
points were measured on a device PTP with heating
rate of 1 deg/min in the melting range. The specific
rotation angles of the polarization plane of
monochromatic light [α]tD were measured with an
instrument Automatic Polarimeter AA-55. Monitoring
of the reaction progress was carried out by TLC on
Silufol UR-254, Merck Kieselgel 60F254 plates using
eluent systems, individually selected for each
experiment.
(2S)- and (2R)-2-{[(9H-fluoren-9-ylmethoxy)car-
bonyl]amino}-3-(4-aminophenyl)propionic acids (4a
and 4b). Small portions of hydrochloric acid and zinc
metal powder were added in succession to a
suspension of 51.3 g (0.119 mol) 3a and 3b acids in a
mixture of 800 mL of 2-propanol and 600 mL of
water. The reaction mass was heated, the initial
compound dissolved. Monitoring consumption of the
starting compounds was performed by TLC. After
completion of the reaction, 2-propanol was distilled off
the mixture (pH 1) at a reduced pressure. The
precipitate was boiled in 20% hydrochloric acid for
6 h. After cooling the resulting suspension was
neutralized with aqueous sodium acetate to pH 4–5.
The precipitate was filtered off and dried. Yield 89%
(4a), 87% (4b), mp 214–215°C (mp 218–219°C [10]).
IR spectrum ν, cm–1: 3310, 2889, 2361, 1686, 1597,
1516, 1450, 1404, 1254, 1038, 737. 1Н NMR spectrum
(DMSO-d6), δ, ppm: 2.70–2.78 m (1H, CH2), 2.92 d.d
(1H, CH2, 2J 13.7, 3J 4.1 Hz), 4.02–4.26 m (4H, 2CH2,
(2S)- and (2R)-2-Amino-3-(4-nitrophenyl)pro-
pionic acids 2a and 2b were obtained as described in
[10]. A mixture of 44 mL of conc. HNO3 and 34.6 mL
of conc. H2SO4 was added dropwise to a solution of 50 g
(0.303 mol) of L(D)-phenylalanine in 150 mL of 85%
H2SO4, pre-cooled to 10°C. The reaction mixture was
stirred for 3 hours at 8–10°C, then the reaction mixture
was adjusted to pH 6 by addition of NaOH aqueous
solution. The precipitate was filtered off and dried. The
reaction product was recrystallized from water. Yield
91% (2а), 89% (2b). mp 240°C (mp 239–241°C [10]).
IR spectrum ν, cm–1: 3294, 2889, 1701, 1620, 1535,
1443, 1350, 880, 864, 745, 698, 525. 1Н NMR
spectrum (DMSO-d6), δ, ppm: 2.90–4.00 m (5H, CH,
3
CH2, NH2), 7.55 d (2Harom, J 8.5 Hz), 8.15 d (2Harom
,
3J 8.5 Hz). 13С NMR spectrum (DMSO-d6), δ, ppm:
40.79 (СН2), 57.28 (СН), 128.15, 129.79, 145.41,
168.48 (Сarom), 172.84 (СООН). Mass spectrum (ESI),
m/z: 211.0713 [M + H]+. C9H10N2O4. Calculated M
210.0641.
3
3
2CH), 6.48 d (2Harom, J 8.0 Hz), 6.91 d (2Harom, J
8.0 Hz ), 7.28–7.68 m (7H, 6CHarom, NH), 7.82 d
(2Harom, 3J 7.5 Hz ). 13С NMR spectrum (DMSO-d6), δ,
ppm: 36.55 (CH2), 47.10 (CH), 56.83 (CH), 65.97
(CH2), 114.20, 120.53, 125.72, 127.54, 128.07, 130.06,
141.13, 144.29, 147.28 (Сarom), 156.13 (CONH),
(2S)- and (2R)-2-{[(9H-fluoren-9-ylmethoxy)car-
bonyl]amino}-3-(4-nitrophenyl)propionic acids 3a
and 3b. A solution of 80 mL of acetonitrile was added
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 52 No. 11 2016

TOLSTYAKOV et al.
1684
173.95 (COOH). Mass spectrum (ESI), m/z: 425.1472
[M + Na]+. C24H22N2O4. Calculated M 402.1580.
121.43, 125.60, 127.47, 128.08, 131.20, 141.16 (Сarom),
142.61 (Сheter), 144.17 (Сarom), 156.41 (CONH), 172.11
(COOPr-n). Mass spectrum (ESI), m/z: 498.2136 [M +
H]+, 520.1958 [M + Na]+. C28H27N5O4. Calculated M
497.2063.
n-Propyl (2S)- and (2R)-2-{[(9H-fluoren-9-ylme-
thoxy)carbonyl]amino}-3-(4-aminophenyl)propio-
nates 5a and 5b. A solution of 38 g (0.319 mol) of
thionyl chloride was added dropwise to a solution of
20 g (0.05 mol) of acid 4a and 4b in 200 mL of 1-
propanol with stirring at 0–10°C. The reaction mixture
was stirred for 3 h at room temperature. The precipitate
was filtered off, washed with aqueous sodium acetate
and water, and dried. Yield 79% (5a), 70% (5b), mp
163°С. IR spectrum ν, cm–1: 3325, 2882, 1693, 1620,
(2S)- and (2R)-3-[4-(1H-Tetrazol-1-yl)phenyl]-2-
{[(9H-fluoren-9-ylmethoxy)carbonyl]amino}pro-
pionic acids 7a and 7b. 1.8 g (0.004 mol) of com-
pounds 6a and 6b were boiled in 20% HCl for 8 hours.
The precipitate was filtered off, washed with water,
and dried. The reaction product was recrystallized
from a mixture of 2-propanol-water, 1 : 1. Yield 79%,
[α]D23.5 –15.05 (c 0.3, DMF) (7a); yield 76%, [α]D23.5
+15.05 (c 0.3, DMF) (7b), mp 163°С. IR spectrum ν,
cm–1: 3310, 3067, 2924, 2855, 2361, 1693, 1543, 1520,
1
1516, 1447, 1258, 1196, 760, 737. Н NMR spectrum
(DMSO-d6), δ, ppm: 0.89 t (3H, CH3, 3J 7.4 Hz ), 1.55–
1.63 m (2H, CH2), 2.72–2.82 m (1H, CH2), 2.88 d.d
2
3
3
1
(1H, CH2, J 8.5, J 5.2 Hz ), 4.00 t (2H, CH2, J 6.5
1447, 741, 1265, 760. Н NMR spectrum (DMSO-d6),
δ, ppm: 2.95–3.04 m (1H, CH2), 3.21 d.d (1H, CH2, 2J
Hz ), 4.12–4.23 m (4H, 2CH2, 2CH), 5.35 br.s (2H,
3
3
NH2) 5.35 br.s (2H, NH2), 6.53 d (2Harom, J 8.0 Hz ),
9.5, J 4.0 Hz ), 4.12–4.30 m (4H, 2CH2, 2CH), 7.25–
6.93 d (2Harom, 3J 8.0 Hz ), 7.25–7.70 m (7H, 6CHarom
,
3
7.45 m (4Harom), 7.54 d (2Harom, J 8.1 Hz ), 7.64 d
NH), 7.83 d (2Harom, J 7.5 Hz ). 13С NMR spectrum
(DMSO-d6), δ, ppm: 10.62 (CH3), 21.93 (CH2), 36.55
(CH2), 47.05 (CH), 56.26 (CH), 66.11 (CH2O), 66.43
(OCH2), 119.24, 120.57, 125.68, 127.52, 128.11, 13
0.42, 131.87, 138.55, 141.17, 144.20 (Сarom), 156.38
(CONH), 172.36 (COOPr-n). Mass spectrum (ESI),
m/z: 467.1941 [M + Na]+. C27H28N2O4. Calculated M
444.2049.
3
3
(2Harom, J 7.4 Hz ), 7.70–7.91 m (5H, 4CHarom, NH),
10.02 s (1Hheter). 13С NMR spectrum (DMSO -d6), δ,
ppm: 36.46 (CH2), 47.05 (CH), 55.80 (CH), 66.07
(CH2O), 120.54, 121.34, 125.66, 127.48, 128.07,
131.20, 132.64, 140.50, 141.15 (Сarom), 142.60 (Сheter),
144.20 (Сarom), 156.41 (CONH), 172.11 (COOH).
Mass spectrum (ESI), m/z: 478.1486 [M + Na]+.
C25H21N5O4. Calculated M 455.1594.
n-Propyl (2S)- and (2R)-3-[4-(1H-tetrazol-1-yl)-
phenyl]-2-{[(9H-fluoren-9-ylmethoxy)carbonyl]-
amino}-propionates 6a and 6b. A solution of 0.51 g
(0.008 mol) of NaN3 was added to a suspension of 3 g
(0.007 mol) of propyl esters 5a and 5b in 3 mL of
glacial acetic acid and 1.45 g (0.01 mol) of triethyl
orthoformate. The reaction mixture was stirred at 100-
105°C (bath temperature) for 5 hours, then poured into
water (100 mL). The precipitate was filtered off,
washed with water, and dried. The reaction product
was recrystallized from a mixture of 2-propanol-water,
1 : 1. Yield 1.92 g (57%) (6a), 1.8 g (54%) (6b), mp
121°С. IR spectrum ν, cm–1: 3325, 3128, 2966, 2889,
1732, 1693, 1520, 1447, 1261, 737. 1Н NMR spectrum
(DMSO-d6), δ, ppm: 0.86 t (3H, CH3, 3J 7.4 Hz), 1.50–
1.56 m (2H, CH2), 2.97–3.09 m (1H, CH2), 3.18 d.d (1H,
CH2, J 13.8, J 5.0 Hz), 4.03 t (2H, CH2, J 6.5 Hz),
4.12–4.30 m (4H, 2CH2, 2CH), 7.25–7.45 m
(4CHarom), 7.54 d (2Harom, 3J 8.4 Hz), 7.63 d (2Harom, 3J
5.9 Hz), 7.81–7.92 m (5H, 4CHarom, NH), 10.03 s
(1Hheter). 13С NMR spectrum (DMSO-d6), δ, ppm:
10.61 (CH3), 21.93 (CH2), 36.34 (CH2), 47.03 (CH),
56.74 (CH), 66.09 (CH2O), 66.58 (OCH2) 120.57,
(2S)- and (2R)-3-[4-(1H-tetrazol-1-yl)phenyl]-2-
amino-propionic acids 8a and 8b. A 20% solution of
4-methylpiperidine in 20 mL of DMF was added to 1 g
(0.002 mol) of acids 7a and 7b. The suspension was
stirred for 2 hours at room temperature. The reaction
mixture was poured into 50 mL of water, the
precipitate was filtered off. The filtrate was evaporated
in a vacuum. The residue was recrystallized from
ethanol. Yield 0.47 g (92%), [α]D23.5 +2.5 (c 0.2, 0.01
M HCl) (8a); yield 0.48 g (94%), [α]D23.5 –2.5 (c 0.2,
1
0.01 M HCl) (8b), temp. decomp. 250°С. Н NMR
spectrum (DCl–D2O), δ, ppm: 3.24 m (CH2), 4.34 m
3
(1Н, СН), 7.45 d (2H, 2CHAr, J 8.0 Hz ), 7.66 d (2H,
2CHAr, 3J 8.0 Hz ), 9.52 s (1H, tetrazol-1-yl). 13C NMR
spectrum (DCl–D2O), δ, ppm: 35.1 (CH2), 53.7 (CH),
122.0 (CHAr), 131.1 (CHAr), 133.0 (CHAr), 136.4 (CHAr),
142.26 (CH, tetrazol-1-yl), 170.9 (COOH). Mass
spectrum (ESI), m/z: 234.0997 [M + Н]+. C10H11N5O2.
Calculated M 233.0913.
2
3
3
Spectral investigations were carried out using the
equipment of the Resource Centers of Saint-Petersburg
State University “The Centre for Magnetic Resonance”
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 52 No. 11 2016

SYNTHESIS OF NEW TETRAZOLYL DERIVATIVES OF L- AND D-PHENYLALANINE
1685
6. Allen, F.H., Groom, C.R., Liebeschuetz, J.W.,
Bardwell, D.A., Olsson, T.S.G., and Wood, P.A.,
J. Chem. Inf. Model., 2012, vol. 52, p. 857.
and “The Centre for Chemical Analysis and Materials”
The study was performed under the financial
support of the Saint-Petersburg State University (grant
no.12.38.428.2015).
7. Popova, E.A., Nikolskaia, S.K., Gluzdikov, I.A., and
Trifonov, R.E., Tetrahedron Lett., 2014, vol. 55, p. 5041.
8. Jakubke, H.-D. and Jeschkeit, H., Aminosäuren,
Peptide, Proteine, Weinheim, Verlag Chemie, 1982.
REFERENCES
9. McMurray, J.S., Khabashesku, О., Birtwistle, J.S., and
Wang, W., Tetrahedron Lett., 2000, vol. 41, p. 6555.
10. Devies, J.S., and Mohammed, A.K.A., J. Chem. Soc.,
Perkin Trans. 2, 1984, p. 1723.
1. Ostrovskii, V.A., Koldobskii, G.I., and Trifonov, R.E.,
Compr. Heterocycl. Chem. III, Katritzky, A.R.,
Ramsden, C.A., Scriven, E.F.V., Taylor, R.J.K., and
Zhdankin, V.V., Eds., Oxford: Elsevier, 2008, vol. 6,
p. 257.
11. Qiu, J., Xu, B., and Huang, Z., Bioorg. Med. Chem.,
2. Ostrovskii V.A., Trifonov R.E., Popova E.A., Russ.
Chem. Bull., 2012, vol. 61, p. 768.
3. Popova, E.A. and Trifonov, R.E., Russ. Chem. Rev.,
2015, vol. 84, p. 891.
2011, vol. 19, p. 5352.
12. Gaponik, P.N., Khimicheskie problemy sozdaniya
novykh materialov i tekhnologii (Chemical Problems of
the Creation of New Materials and Technologies), 1998.
4. Voitekhovich, S.V., Gaponik, P.N., Grigor’ev, Yu.V.,
and Ivashkevich, O.A., Khimicheskie problemy soz-
daniya novykh materialov i tekhnologii (Chemical
Problems of the Creation of New Materials and
Technologies), 2008.
13. Gaponik, P.N., Karavai, V.P., Davshko, I.E., Degtya-
rik, M.M., and Bogatikov, A.N., Chem. Heterocycl.
Compd., 1990, vol. 26, p. 1274.
14. Chuprun, S.S., Popova, E.A., Mukhametshina, A.V.,
and Trifonov, R.E., Russ. J. Org. Chem., 2015, vol. 51,
p. 1671.
5. Herr, R.J., Bioorg. Med. Chem., 2002, vol. 10, p. 3379.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 52 No. 11 2016