Synthesis of Purine and 2-Aminopurine Conjugates with N-(4-Aminobenzoyl)-(S)-glutamic Acid

Article abstract of DOI:10.1134/S1070428019060034

Purine and 2-aminopurine conjugates with N-(4-aminobenzoyl)-(S)-glutamic acid connected to C⁶ of the purine system either directly or through an aminoethyl linker have been synthesized by nucleophilic substitution of chlorine in 6-chloropurine

Full text of DOI:10.1134/S1070428019060034

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2019, Vol. 55, No. 6, pp. 755–761. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Zhurnal Organicheskoi Khimii, 2019, Vol. 55, No. 6, pp. 848–855.
Dedicated to Full Member of the Russian Academy of Sciences
O.N. Chupakhin on his 85th anniversary
Synthesis of Purine and 2-Aminopurine Conjugates
with N-(4-Aminobenzoyl)-(S)-glutamic Acid
V. P. Krasnova,* A. Yu. Vigorova, E. N. Chulakova, I. A. Nizovaa, G. L. Levita,
M. A. Kravchenkob, and V. N. Charushina, c
a Postovskii Institute of Organic Synthesis, Ural Branch, Russian Academy of Sciences, Yekaterinburg, Russia
*e-mail: ca@ios.uran.ru
b Ural Research Institute of Phthisiopulmonology, National Medical Research Center,
Ministry of Healthcare of the Russian Federation, Yekaterinburg, Russia
c Institute of Chemical Engineering, Yeltsin Ural Federal University, Yekaterinburg, Russia
Received April 15, 2019; revised April 24, 2019; accepted April 25, 2019
Abstract—Purine and 2-aminopurine conjugates with N-(4-aminobenzoyl)-(S)-glutamic acid connected to C6
of the purine system either directly or through an aminoethyl linker have been synthesized by nucleophilic
substitution of chlorine in 6-chloropurine and 2-amino-6-chloropurine. 2-Aminopurine conjugate with 4-amino-
benzoic acid linked through a glycine residue has also been obtained. Testing of the synthesized compounds for
tuberculostatic activity in vitro has revealed a moderate activity of methyl 4-[2-(2-aminopurin-6-ylamino)-
acetyl]amino}benzoate.
Keywords: purines, conjugates, 4-aminobenzoic acid, glutamic acid, tuberculostatic activity.
DOI: 10.1134/S1070428019060034
Purine derivatives exhibit diverse biological
activity and are components of a number of medicines
[1–3]. We have recently found that some N-(purin-6-
yl)glycyl and N-(2-aminopurin-6-yl)glycyl amino acids
show pronounced antitubercular activity in vitro [4],
which may be related to their inhibitory effect on
mycobacterial glutamine synthetase [5, 6] or dihydro-
folate reductase [7].
benzoyl)-(S)-glutamic acid linked to C6 of the purine
fragment either directly or through an aminoethyl
linker, as well as 2-aminopurine conjugate with
4-aminobenzoic acid linked to C6 through a glycine
residue, and study their tuberculostatic activity in vitro.
Purine conjugates with N-(4-aminobenzoyl)-(S)-
glutamic acid were synthesized following an approach
based on successive appending of required fragments
to the initial purine molecule. The starting compounds
were commercially available 6-chloropurine (1a) and
2-amino-6-chloropurine (1b).
Interest in compounds containing both heterocyclic
fragment and N-(4-aminobenzoyl)glutamic acid resi-
due is determined by the fact that the latter is a struc-
tural unit of folic acid. Modification of the heterocyclic
fragment of folic acid opens the way to new biologi-
cally active compounds [8]. Some conjugates of
N-(4-aminobenzoyl)glutamic acid with heterocycles
showed antitubercular activity [9] and inhibited
aggrecanase (an enzyme promoting chondrocyte
apoptosis in joint pathologies) [10] and dihydrofolate
reductase [11].
The chlorine atom in 6-chloropurines 1a and 1b
was smoothly replaced by the 4-aminobenzoic acid
residue on heating in boiling water in the presence of
0.9 equiv of H2SO4 (Scheme 1) to produce 4-(purin-6-
ylamino)- and 4-(2-aminopurin-6-ylamino)benzoic
acids 2a and 2b, respectively; acid 2b was isolated as
a salt with H2SO4. Similar conditions (heating in
boiling water in the presence of H2SO4) were used
previously to obtain purine and 2-aminopurine con-
jugates containing a heterocyclic amine residue in
The goal of the present work was to synthesize con-
jugates of purine and 2-aminopurine with N-(4-amino-
755

KRASNOV et al.
756
Scheme 1.
Cl
NHC6H4COOH-4
N
COOH
H2SO4, H2O, ∆, 6 h
N
·nH2SO4
N
N
+
H2N
N
H
N
R
N
R
N
H
1a, 1b
2a (90%), 2b (92%)
O
O
O
COOMe
O
COOH
MeO
OMe
NH2·HCl
N
N
H
H
NaOH, H2O
8–10°C, 48 h
TBTU, DIPEA, DMSO
20–25°C, 24 h
HN
COOMe
HN
COOH
N
N
N
N
N
H
N
R
N
R
N
H
3a (68%), 3b (50%)
4a (51%), 4b (82%)
R = H (a), NH2 (b); 2, n = 0 (a), 0.6 (b).
afforded target conjugates 4a and 4b in which the
N-(4-aminobenzoyl)-(S)-glutamic acid fragment is
linked directly to C6 of the purine moiety (Scheme 1).
Purine and 2-aminopurine conjugates with
N-(4-aminobenzoyl)-(S)-glutamic acid linked to C6
through an aminoethyl linker were obtained by heating
position 6 [12]. The condensation of acids 2a and 2b
with dimethyl (S)-glutamate in the presence of
O-(benzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium
tetrafluoroborate (TBTU) in the presence of ethyl-
(diisopropyl)amine (DIPEA) in DMSO gave diesters
3a and 3b, and alkaline hydrolysis of the latter
Scheme 2.
H
N
HN
N
Et3N, EtOH (1a) or BuOH (1b)
∆, 8 h
COOBu-t
N
1a, 1b
+
N
COOBu-t
H2N
N
N
H
H
R
5a (83%), 5b (84%)
O
O
MeO
OMe
H
H
N
NH2·HCl
N
COOMe
HN
N
HN
N
TFA, CH2Cl2
20–25°C, 4 h
TBTU, DIPEA, DMSO
20–25°C, 24 h
H
N
N
N
N
COOH
N
O
COOMe
N
N
R
R
H
H
6a (93%), 6b (89%)
7a (42%), 7b (57%)
H
N
COOH
HN
LiOH, H2O/THF
20–25°C, 24 h
H
N
N
N
O
COOH
N
R
N
H
8a (53%), 8b (86%)
R = H (a), NH2 (b).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 6 2019

SYNTHESIS OF PURINE AND 2-AMINOPURINE CONJUGATES
757
Scheme 3.
H
O
N
Cl
COOMe
Et3N, EtOH
∆, 30 h
N
OMe
N
O
HN
+
· TFA
H2N
37%
O
N
H
N
H2N
N
N
N
H
N
H
H2N
N
1b
9
10
6-chloropurines 1a and 1b with tert-butyl N-(2-amino-
ethyl)-4-aminobenzoate in ethanol or butan-1-ol in the
presence of triethylamine, followed by hydrolysis of
the ester group in 5a and 5b by the action of trifluoro-
acetic acid, condensation of acids 6a and 6b with
dimethyl (S)-glutamate, and alkaline hydrolysis of the
ester groups in dimethyl esters 7a and 7b. We thus
isolated conjugates 8a and 8b (Scheme 2).
Thus, we have synthesized conjugates of purine and
2-aminopurine with N-(4-aminobenzoyl)-(S)-glutamic
acid linked to C6 of the purine moiety both directly and
through an aminoethyl linker, as well as a 2-amino-
purine conjugate with methyl 4-aminobenzoate linked
through a glycine residue. The latter conjugate showed
a moderate tuberculostatic activity in vitro.
EXPERIMENTAL
We also tried to synthesize a conjugate of 2-amino-
purine with N-(4-aminobenzoyl)-(S)-glutamic acid
linked to C6 of the purine moiety through a glycine
residue. As shown previously, compounds containing
a [(2-aminopurin-6-yl)amino]glycine fragment exhibit
pronounced antitubercular activity in vitro [4]. The
reaction of 2-amino-6-chloropurine (1b) with methyl
4-[(2-amino-1-oxoethyl)amino]benzoate (trifluoro-
acetic acid salt) (9) gave methyl 4-{[2-(2-aminopurin-
6-ylamino)acetyl]amino}benzoate (10) in a moderate
yield (Scheme 3). However, attempted hydrolysis of
the ester group in 10 resulted in cleavage of the amide
bond between the glycine and 4-aminobenzoic acid
fragments with the formation of N-(2-aminopurin-6-
yl)glycine. It should be noted that the hydrolysis of
ethyl 4-{[2-(6-bromo-1H-indazol-4-ylamino)acetyl]-
amino}benzoate under similar conditions was reported
[13] to produce the target carboxylic acid in a mod-
erate yield (42%).
6-Chloropurine (1a) and 2-amino-6-chloropurine
(1b) were commercial products. tert-Butyl 4-(2-amino-
ethyl)aminobenzoate was synthesized from 4-fluoro-
benzoic acid according to the procedures described in
[15, 16]. N-(2-Aminopurin-6-yl)glycine necessary for
the identification of alkaline hydrolysis products of 10
was prepared as reported in [17].
1
The H NMR spectra were recorded at 25°C on
Bruker DRX-400 (400 MHz) and Bruker Avance 500
(500 MHz) spectrometers relative to tetramethylsilane
as internal standard. The 13C and 19F NMR spectra
were measured at 25°C on a Bruker Avance 500
instrument (126 and 470 MHz, respectively). The
melting points were determined with a Stuart SMP3
melting point apparatus (Barloworld Scientific, UK).
The optical rotations were measured on a Perkin-Elmer
M341 polarimeter (USA). The elemental analyses
were obtained on a Perkin Elmer 2400 Series II
automated CHNS-O analyzer. The high-resolution
mass spectra were recorded on a Bruker maXis Impact
HD mass spectrometer under atmospheric pressure
chemical ionization or electrospray ionization
(nebulizer gas nitrogen, flow rate 4 L/min; nebulizer
pressure 0.4 bar; capillary voltage 4.5 kV). Thin-layer
chromatography was performed on Sorbfil plates
(Imid Ltd., Russia); spots were visualized under UV
light (λ 254 nm).
The in vitro tuberculostatic activity of the synthe-
sized compounds against Mycobacterium tuberculosis
H37Rv was studied at the Ural Research Institute of
Phthisiopulmonology (National Medical Research
Center, Ministry of Healthcare of the Russian Federa-
tion, Yekaterinburg) by the vertical diffusion method
on a Novaya solid nutrient medium according to the
procedure described in [14]. The minimum inhibitory
concentration (MIC) of compounds 2a, 2b, 3a, 4a, 4b,
7a, 7b, 8a, 8b, and 11 was higher than 12.5 μg/mL;
i.e., these compounds turned out to be inactive. The
MIC value for compound 10 was 1.5 μg/mL, which
indicated a moderate tuberculostatic activity.
4-(Purin-6-ylamino)benzoic acid (2a). Concen-
trated sulfuric acid, 0.102 mL (1.8 mmol), was added
to a suspension of 0.309 g (2.0 mmol) of 6-chloro-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 6 2019

KRASNOV et al.
758
purine (1a) and 0.329 g (2.4 mmol) of 4-aminobenzoic
acid in 26 mL of water, and the mixture was refluxed
for 6 h. The precipitate was filtered off and washed
with water. Yield 0.457 g (90%), light yellow crystals,
as described above for 3a. Yield 50%, white crystals,
mp 128–132°C (decomp.). H NMR spectrum
1
(400 MHz, DMSO-d6), δ, ppm: 2.03 m and 2.12 m (1H
each, CH2CH), 2.47 m (2H, CH2CO), 3.59 s (3H,
OMe), 3.65 s (3H, OMe), 4.46 d.d.d (1H, CHNH, J =
9.4, 7.4, 5.4 Hz), 6.67 br.s (2H, NH2), 7.86 d (2H,
Harom, J = 8.6 Hz), 8.04 br.s (1H, 8-H), 8.10 d (2H,
Harom, J = 8.6 Hz), 8.65 d (1H, CONH, J = 7.4 Hz),
10.03 br.s (1H, 6-NH), 12.4 br.s (1H, 9-H). Mass
spectrum (ESI): m/z 428.1672 [M + H]+. Found, %:
C 53.28; H 4.82; N 22.59. C19H21N7O5. Calculated, %:
C 53.39; H 4.95; N 22.94. M + H 428.1677.
1
mp >360°C. H NMR spectrum (500 MHz,
DMSO-d6), δ, ppm: 7.90 d (2H, Harom, J = 8.6 Hz),
8.15 d (2H, Harom, J = 8.6 Hz), 8.34 s (1H, 8-H), 8.46 s
(1H, 2-H), 10.17 s (1H, 6-NH), 12.58 br.s (1H,
COOH), 13.28 br.s (1H, 9-H). Mass spectrum (ESI):
m/z 254.0682 [M − H]−. Found, %: C 56.16; H 3.82;
N 27.16. C12H9N5O2. Calculated, %: C 56.47; H 3.55;
1
N 27.44. M – H 254.0683. The H NMR and mass
spectra of 4-(purin-6-ylamino)benzoic acid hydro-
chloride were given in [18].
(2S)-2-{[4-(Purin-6-ylamino)benzoyl]amino}-
pentanedioic acid (4a). A solution of 0.937 g
(2.27 mmol) of dimethyl ester 3a in 13.6 mL
(13.6 mmol) of 1 M aqueous sodium hydroxide was
kept for 4 days at 10°C. The mixture was filtered, the
filtrate was acidified to pH 5 with 1 M aqueous HCl,
and the jelly-like precipitate was separated by centri-
fugation and washed twice with water. Yield 0.443 g
(51%), white crystals, mp 260–270°C (decomp.),
4-(2-Aminopurin-6-ylamino)benzoic acid (2b,
sulfuric acid salt) was synthesized as described above
for compound 2a from 2-amino-6-chloropurine (1b).
Yield 92%, white crystals, mp 350–360°C (decomp.).
1H NMR spectrum (400 MHz, DMSO-d6), δ, ppm:
6.91 br.s (2H, NH2), 7.91 d (2H, Harom, J = 8.8 Hz),
8.10 s (1H, 8-H), 8.11 d (2H, Harom, J = 8.8 Hz),
10.14 s (1H, 6-NH), 12.35 br.s (2H, 9-H, COOH).
Found, %: C 43.78; H 3.59; N 25.12. C12H10N6O2·
0.6H2SO4. Calculated, %: C 43.80; H 3.43; N 25.54.
[α]D25 = +19.7° (c = 0.3, 1 M NaOH). H NMR spec-
1
trum (400 MHz, DMSO-d6), δ, ppm: 1.97 m and
2.11 m (1H each, CH2CH), 2.37 t (2H, CH2CO, J =
7.4 Hz), 4.40 m (1H, CHCO), 7.87 d (2H, Harom, J =
8.5 Hz), 8.12 d (2H, Harom, J = 8.5 Hz), 8.34 s (1H,
8-H), 8.41 d (1H, CONH, J = 7.9 Hz), 8.46 s (1H,
2-H), 10.11 br.s (1H, 6-NH), 12.53 br.s (2H, COOH),
13.26 br.s (1H, 9-H). 13C NMR spectrum (126 MHz,
DMSO-d6), δC, ppm: 26.36 (CH2CH), 30.56 (CH2CO),
52.14 (CHCO), 119.13 (Cm), 123.93 (C5), 127.29 (Ci),
127.92 (Co), 130.06, 141.04, 142.95 (Cp), 150.71,
151.61, 165.94 (CONH), 173.93 (CO2H), 174.03
(CO2H). Found, %: C 53.29; H 4.18; N 21.83.
C17H16N6O5. Calculated, %: C 53.13; H 4.20; N 21.86.
Dimethyl (2S)-2-{[4-(purin-6-ylamino)benzoyl]-
amino}pentanedioate (3a). Triethylamine, 3.7 mL
(26.5 mmol), was added to a suspension of 0.564 g
(2.2 mmol) of acid 2a in 10 mL of anhydrous DMSO.
The mixture was stirred for 30 min, 0.935 g
(4.4 mmol) of dimethyl (S)-glutamate hydrochloride
and 1.42 g (4.42 mmol) of TBTU were added, and the
mixture was stirred for 24 h. The mixture was then
poured into 200 mL of water and kept in a refrigerator,
and the precipitate was filtered off and washed with
water. Yield 0.622 g (68%), white crystals, mp 160–
162°C, [α]D22 = +3.0° (c = 0.6, AcOH). H NMR spec-
1
(2S)-2-{[4-(2-Aminopurin-6-ylamino)benzoyl]-
amino}pentanedioic acid (4b). A solution of 0.23 g
(0.54 mmol) of dimethyl ester 3b in 3.22 mL
(3.22 mmol) of 1 M aqueous sodium hydroxide was
kept for 4 days at 10°C. The mixture was filtered, the
filtrate was acidified to pH with concentrated aqueous
HCl, and the precipitate was filtered off, washed with
water, dried under reduced pressure, and treated with
2.1 mL of boiling methanol. After cooling to room
temperature, the undissolved material was filtered off.
Yield 0.176 g (82%), white crystals, mp 263–265°C
(decomp.), [α]D25 = +21.6° (c = 0.5, 1 M NaOH).
1H NMR spectrum (500 MHz, DMSO-d6), δ, ppm:
1.97 m and 2.10 m (1H each, CH2CH), 2.37 t (2H,
CH2CO, J = 7.4 Hz), 4.40 d.d.d (1H, CHCO, J = 9.3,
trum (400 MHz, DMSO-d6), δ, ppm: 2.02 d.d.d.d (1H,
CH2CH, J = 13.8, 9.2, 7.1, 7.1 Hz), 2.13 d.d.d.d (1H,
CH2CH, J = 13.8, 7.7, 7.7, 5.4 Hz), 2.47 m (2H,
CH2CO), 3.59 s (3H, OMe), 3.65 s (3H, OMe),
4.46 d.d.d (1H, CHCO, J = 9.3, 7.3, 5.5 Hz), 7.86 d
(2H, Harom, J = 8.8 Hz), 8.12 d (2H, Harom, J = 8.8 Hz),
8.33 s (1H, 8-H), 8.45 s (1H, 2-H), 8.60 d (1H, CONH,
J = 7.4 Hz), 10.09 s (1H, 6-NH), 13.26 br.s (1H, 9-H).
Mass spectrum (APCI): m/z 413.1565 [M + H]+.
Found, %: C 55.28; H 4.80; N 20.48. C19H20N6O5.
Calculated, %: C 55.33; H 4.89; N 20.38. M + H
413.1568.
Dimethyl (2S)-2-{[4-(2-aminopurin-6-ylamino)-
benzoyl]amino}pentanedioate (3b) was synthesized
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 6 2019

SYNTHESIS OF PURINE AND 2-AMINOPURINE CONJUGATES
759
7.6, 5.0 Hz), 6.12 br.s (2H, NH2), 7.83 d (2H, Harom
,
the residue was treated with diethyl ether, the mixture
was stirred, and the precipitate was filtered off and
dried under reduced pressure. The product was dis-
persed in 50 mL of water, 0.8 mL (5 mmol) of N,N-di-
ethylaniline was added with stirring, and the precip-
itate was filtered off. Yield 1.17 g (93%), white crys-
J = 8.6 Hz), 7.86 br.s (1H, 8-H), 8.15 d (2H, Harom, J =
8.6 Hz), 8.44 d (1H, CONH, J = 7.6 Hz), 9.60 s (1H,
6-NH), 12.37 br.s (3H, 9-H, COOH). 13C NMR spec-
trum (126 MHz, DMSO-d6), δC, ppm: 25.98 (CH2CH),
30.42 (CH2CO), 51.86 (CHCO), 113.58 (C5), 118.72
(Cm), 126.42 (Ci), 127.90 (Co), 136.65 (C8), 143.51
(Cp), 151.59, 153.03, 159.73, 166.19 (CONH), 173.58
(CO2H), 173.89 (CO2H). Mass spectrum (ESI):
m/z 400.1360 [M + H]+. Found, %: C 50.78; H 4.38;
N 24.32. C17H17N7O5. Calculated, %: C 51.13; H 4.29;
N 24.55. M + H 400.1364.
1
tals, mp 233–235°C. H NMR spectrum (500 MHz,
DMSO-d6), δ, ppm: 3.34 m (2H, CH2CH2, overlapped
by the signal of water), 3.67 m (2H, CH2CH2), 6.58–
6.68 m (3H, Harom, NH), 7.68 m (2H, Harom), 7.75 s
(1H, NH), 8.11 s (1H, 8-H), 8.24 s (1H, 2-H), 12.01 s
(1H, COOH), 12.94 s (1H, 9-H). Mass spectrum (ESI):
m/z 299.1266 [M + H]+. C14H15N6O2. Calculated:
M + H 299.1251.
tert-Butyl 4-{[2-(purin-6-ylamino)ethyl]amino}-
benzoate (5a). A mixture of 0.785 g (5.08 mmol) of
chloropurine 1a, 1.20 g (5.08 mmol) of tert-butyl
4-[(2-aminoethyl)amino]benzoate, and 0.71 mL
(5.08 mmol) of triethylamine in 20 mL of ethanol was
refluxed for 8 h. The mixture was cooled and dilute
with 60 mL of water, and the precipitate was filtered
off. Yield 1.50 g (83%), white crystals, mp 231–233°C.
1H NMR spectrum (500 MHz, DMSO-d6), δ, ppm:
1.50 s (9H, t-Bu), 3.33 m (2H, CH2CH2, overlapped by
the signal of H2O), 3.66 m (2H, CH2CH2), 6.58–
6.68 m (3H, Harom, NH), 7.63 m (2H, Harom), 7.74 s
(1H, NH), 8.11 s (1H, 8-H), 8.23 s (1H, 2-H), 12.94 s
(1H, 9-H). Mass spectrum (ESI): m/z 377.1700
[M + Na]+. Found, %: C 60.86; H 6.33; N 23.75.
C18H22N6O2. Calculated, %: C 61.00; H 6.26; N 23.71.
M + Na 377.1696.
4-{[2-(2-Aminopurin-6-ylamino)ethyl]amino}-
benzoic acid (6b). A solution of 0.94 g (2.53 mmol) of
ester 5b in a mixture of 23 mL of trifluoroacetic acid
and 23 mL of methylene chloride was stirred for 4 h at
room temperature. The mixture was evaporated to
dryness, the residue was treated with diethyl ether, the
mixture was stirred, and the precipitate was filtered off
and dried under reduced pressure. The product was
dissolved in 50 mL of aqueous methanol (1:1),
0.48 mL (3 mmol) of N,N-diethylaniline was added,
and the precipitate was filtered off. Yield 0.70 g (89%),
1
white crystals, mp 283–285°C. H NMR spectrum
(500 MHz, DMSO-d6), δ, ppm: 3.34 m (2H, CH2CH2,
overlapped by the signal of water), 3.65 m (2H,
CH2CH2), 5.90–7.00 br.s (2H, NH2), 6.58–6.68 m (3H,
H
arom, NH), 7.69 m (2H, Harom), 7.75–8.30 m (2H, NH,
tert-Butyl 4-{[2-(2-aminopurin-6-ylamino)ethyl]-
amino}benzoate (5b). A mixture of 0.764 g
(4.5 mmol) of chloropurine 1b, 1.07 g (4.5 mmol) of
tert-butyl 4-(2-aminoethylamino)benzoate, and
0.63 mL (4.5 mmol) of triethylamine in 60 mL of
butan-1-ol was refluxed for 8 h. The mixture was
evaporated to dryness, and the residue was recrystal-
lized from 150 mL of ethanol–water (1 :2). Yield
1.40 g (84%), off-white crystals, mp 162–165°C.
1H NMR spectrum (500 MHz, DMSO-d6), δ, ppm:
1.49 s (9H, t-Bu), 3.22–3.30 m and 3.60 m (2H each,
CH2CH2), 5.73 br.s (2H, NH2), 6.58–6.68 m (3H,
8-H), 11.80–12.80 m (2H, 9-H, COOH). Mass spec-
trum (ESI): m/z 314.1354 [M + H]+. C14H16N7O2. Cal-
culated: M + H 314.1360.
Dimethyl (2S)-2-[({4-[2-(purin-6-ylamino)ethyl]-
amino}benzoyl)amino]pentanedioate (7a). Acid 6a,
1.17 g (3.92 mmol), was dissolved in 15 mL of
DMSO, 1.52 g (11.75 mmol) of DIPEA, 1.26 g
(3.92 mmol) of TBTU, and 0.83 g (3.92 mmol) of
dimethyl (S)-glutamate hydrochloride were added. The
mixture was stirred for 24 h at room temperature,
poured into 250 mL of water, neutralized to pH 7 with
6 M aqueous HCl, and extracted with butan-1-ol
(3×50 mL). The combined extracts were dried over
MgSO4 and evaporated to dryness, and the product
was isolated from the residue by flash chromatography
using chloroform–methanol–aqueous ammonia as
eluent. Yield 0.75 g (42%), light yellow crystals,
Harom, NH), 7.26 s (1H, NH), 7.58–7.70 m (3H, Harom
,
8-H), 12.09 s (1H, 9-H). Mass spectrum (ESI):
m/z 370.1989 [M + H]+. C18H24N7O2. Calculated:
M + H 370.1986.
4-{[2-(Purin-6-ylamino)ethyl]amino}benzoic acid
(6a). A solution of 1.50 g (4.23 mmol) of ester 5a in
a mixture of 35 mL of trifluoroacetic acid and 35 mL
of methylene chloride was stirred for 4 h at room
temperature. The mixture was evaporated to dryness,
mp 96–98°C, [α]D25 = −2.65° (c = 1.0, DMF). H NMR
spectrum (500 MHz, DMSO-d6), δ, ppm: 1.92–2.03 m
and 2.05–2.13 m (1H each, CH2CH), 2.43 t (2H,
1
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 6 2019

KRASNOV et al.
760
CH2CO, J = 7.5 Hz), 3.34 m (2H, CH2CH2, overlapped
by the signal of water), 3.58 s (3H, OMe), 3.62 s (3H,
OMe), 3.66 m (2H, CH2CH2), 4.40 d.d.d (1H, CHCO,
J = 9.6, 7.4, 5.3 Hz), 6.43 t (1H, NHCH2, J = 5.7 Hz),
6.65 m (2H, Harom), 7.67 m (2Harom), 7.74 s (1H, NH),
8.10 s (1H, 8-H), 8.22 s (1H, 2-H), 8.27 d (1H, CHNH,
J = 7.4 Hz), 12.93 s (1H, 9-H). Mass spectrum (ESI):
m/z 462.2070 [M + Li]+. C21H25LiN7O5. Calculated:
M + Li 462.2072.
white crystals, mp 213–216°C (decomp.), [α]D25
=
1
+5.41° (c = 0.6, DMF). H NMR spectrum (500 MHz,
DMSO-d6), δ, ppm: 1.87–1.98 m and 1.98–2.08 m
(1H each, CH2CH), 2.32 m (2H, CH2CO), 3.37 m and
3.60 m (2H each, CH2CH2), 4.34 m (1H, CHCO),
5.74 s (2H, NH2), 6.41 m (1H, NHCH2), 6.63 m
(2H, Harom), 7.29 s (1H, NH), 7.67 m (3H, Harom
,
8-H), 8.06 d (1H, NHCH, J = 7.1 Hz), 11.20–
13.15 br.s (3H, COOH, 9-H). Mass spectrum (ESI):
m/z 449.1876 [M + Li]+. C19H22LiN8O5. Calculated:
M + Li 449.1868.
Dimethyl (2S)-2-[({4-[2-(2-aminopurin-6-yl-
amino)ethyl]amino}benzoyl)amino]pentanedioate
(7b) was synthesized as described above for 7a. Yield
57%, off-white crystals, mp 148–150°C. [α]D25 = −2.25°
Methyl 4-[(aminoacetyl)amino]benzoate tri-
fluoroacetic acid salt (9). A solution of 1 mL of
trifluoroacetic acid in 4 mL of methylene chloride was
added to 0.50 g (1.62 mmol) of methyl 4-{[(tert-
butoxycarbonylamino)acetyl]amino}benzoate prepared
as described in [19]. The resulting solution was kept
for 2 h at 20°C and evaporated to dryness, and the
residue was recrystallized from ethyl acetate. Yield
0.367 g (71%), white crystals, mp 194–195°C. 1H NMR
spectrum (500 MHz, DMSO-d6), δ, ppm: 3.83 s (3H,
OMe), 3.84 s (2H, CH2CO), 7.73 d (2H, Harom, J =
8.8 Hz), 7.97 d (2H, Harom, J = 8.8 Hz), 8.18 br.s (3H,
NH3+), 10.82 s (1H, NH). 19F NMR spectrum
(470 MHz, DMSO-d6): δF 89.03 ppm, s (CF3).
1
(c = 1.0, DMF). H NMR spectrum (500 MHz,
DMSO-d6), δ, ppm: 1.92–2.03 m and 2.05–2.13 m (1H
each, CH2CH), 2.43 t (2H, CH2CO, J = 7.5 Hz),
3.27 m (2H, CH2CH2), 3.34 s (3H, OMe), 3.50–3.70 m
(2H, CH2CH2, overlapped by the OMe signal), 3.58 s
(3H, OMe), 4.40 d.d.d (1H,CHCO, J = 9.6, 7.4,
5.4 Hz), 5.73 s (2H, NH2), 6.44 t (1H, NHCH2, J =
5.2 Hz), 6.63 m (2H, Harom), 7.27 s (1H, NH), 7.58–
7.74 m (3H, Harom, 8-H), 8.27 d (1H, CHNH, J =
7.4 Hz), 12.09 s (1H, 9-H). Mass spectrum (ESI):
m/z 477.2174 [M + Li]+. C21H26LiN8O5. Calculated:
M + Li 477.2181.
13C NMR spectrum (126 MHz, DMSO-d6), δC, ppm:
(2S)-2-[({4-[2-(Purin-6-ylamino)ethyl]amino}-
benzoyl)amino]pentanedioic acid (8a). A solution of
0.33 g (0.72 mmol) of dimethyl ester 7a in 18 mL of
THF was cooled to –5°C, 18 mL of a 0.2 M solution of
lithium hydroxide (3.6 mmol) was added, and the
mixture was stirred for 24 h at room temperature. The
mixture was filtered, the filtrate was washed with
10 mL of chloroform, the aqueous phase was acidified
to pH 2 with 6 M aqueous HCl, and the precipitate was
filtered off and recrystallized from ethanol. Yield
0.165 g (53%), white crystals, mp 228–230°C
1
41.19 (CH2CO), 51.95 (OCH3), 117.26 q (CF3, JCF
=
300 Hz), 118.60 (Cm), 124.60 (Ci), 130.49 (Co), 142.49
(Cp), 158.05 q (CO2−, JCF = 30.6 Hz), 165.45 (CO),
2
165.68 (CO). Found, %: C 44.54; H 4.00; F 17.42;
N 8.51. C10H12N2O3 · CF3CO2H. Calculated, %:
C 44.73; H 4.07; F 17.69; N 8.69.
Methyl 4-{[(2-aminopurin-6-ylamino)acetyl]-
amino}benzoate hemihydrate (10). A suspension of
0.111 g (0.66 mmol) of chloropurine 1b, 0.315 g
(0.98 mmol) of compound 9, and 0.25 mL (1.79 mmol)
of triethylamine in 5 mL of ethanol was refluxed for
30 h. The mixture was cooled to room temperature,
and the precipitate was filtered off and recrystallized
from 40 mL of methanol. Yield 0.085 g (37%), white
crystals, mp 243–245°C (decomp.). 1H NMR spectrum
(500 MHz, DMSO-d6), δ, ppm: 3.82 s (3H, OMe),
4.27 m (2H, CH2CO), 5.79 br.s (2H, NH2), 7.31 br.s
(1H, NHCH2), 7.72 s (1H, 8-H), 7.75 d (2H, Harom, J =
8.6 Hz), 7.92 d (2H, Harom, J = 8.6 Hz), 10.41 s (1H,
CONH), 12.18 br.s (1H, 9-H). 13C NMR spectrum
(126 MHz, DMSO-d6), δC, ppm: 43.99 (CH2CO),
51.78 (OCH3), 112.86 (C5), 118.43 (Cm), 123.82 (Ci),
130.22 (Co), 135.85 (C8), 143.33 (Cp), 152.35, 154.43,
159.80, 165.75 (CONH), 169.18 (CO2CH3). Mass
(decomp.). [α]D25 = +4.67° (c = 1.0, DMF). H NMR
1
spectrum (500 MHz, DMSO-d6), δ, ppm: 1.84–2.00 m
and 2.01–2.11 m (1H each, CH2CH), 2.33 t (2H,
CH2CO, J = 7.5 Hz), 3.36 m (2H, CH2CH2, overlapped
by the signal of water), 3.67 m (2H, CH2CH2),
4.35 d.d.d (1H, CHCO, J = 9.7, 7.9, 5.1 Hz), 6.41 m
(1H, NHCH2), 6.66 m (2H, Harom), 7.68 m (2H, Harom),
7.74 s (1H, NH), 8.00–8.17 m (2H, 8-H, NHCH),
8.24 s (1H, 2-H), 12.32 br.s (2H, COOH), 12.93 s (1H,
9-H). Mass spectrum (ESI): m/z 434.1765 [M + Li]+.
C19H21LiN7O5. Calculated: M + Li 434.1759.
(2S)-2-[({4-[2-(2-Aminopurin-6-ylamino)ethyl]-
amino}benzoyl)amino]pentanedioic acid (8b) was
synthesized as described above for 8a. Yield 86%,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 6 2019

SYNTHESIS OF PURINE AND 2-AMINOPURINE CONJUGATES
761
spectrum (ESI): m/z 340.1167 [M − H]−. Found, %:
C 51.65; H 4.48; N 28.04. C15H15N7O3·0.5H2O. Cal-
culated, %: C 51.42; H 4.57; N 28.00.
7. Shelke, R.U., Degani, M.S., Raju, A., Ray, M.K., and
Rajan, M.G.R., Arch. Pharm. (Weinheim, Ger.), 2016,
vol. 349, p. 602. doi 10.1002/ardp.201600066
8. Visentin, M., Zhao, R., and Goldman, I.D., Hematol./
Oncol. Clin. North Am., 2012, vol. 26, p. 629. doi
10.1016/j.hoc.2012.02.002
ACKNOWLEDGMENTS
The authors thank Dr. M. I. Kodess and
M.A. Ezhikova for recording the NMR spectra,
Dr. I.N. Ganebnykh for recording the high-resolution
mass spectra, and the Group of Elemental Analysis
under the guidance of Dr. L.N. Bazhenova (Institute
of Organic Synthesis, Ural Branch, Russian Academy
of Sciences). This study was performed using the
equipment of the “Spectroscopy and Analysis of
Organic Compounds” joint center.
9. Corona, P., Vitale, G., Loriga, M., Paglietti, G.,
La Colla, P., Collu, G., Sanna, G., and Loddo, R., Eur. J.
Med. Chem., 2006, vol. 41, p. 1102. doi 10.1016/
j.ejmech.2006.05.015
10. Sum, P.-E., How, D.W., Sabatini, J.J., Xiang, J.S.,
Ipek, M., and Feyfant, E., Int. Patent Appl.
no. WO 2007 008994; Chem. Abstr., 2007, vol. 146,
no. 163390.
11. Garro Martinez, J.C., Andrada, M.F., Vega-Hissi, E.G.,
Garibotto, F.M., Nogueras, M., Rodriguez, R., Cobo, J.,
Enriz, R.D., and Estrada, M.R., Med. Chem. Res., 2016,
vol. 26, p. 247. doi 10.1007/s00044-016-1742-4
FUNDING
This study was performed under financial support
by the Russian Science Foundation (project no. 19-
13-00231).
12. Gruzdev, D.A., Musiyak, V.V., Chulakov, E.N.,
Levit, G.L., and Krasnov, V.P., Chem. Heterocycl.
Compd., 2015, vol. 51, p. 738. doi 10.1007/s10593-015-
1767-5
CONFLICT OF INTERESTS
13. Qian, S., He, T., Wang, W., He, Y., Zhang, M., Yang, L.,
Li, G., and Wang, Z., Bioorg. Med. Chem., 2016,
vol. 24, p. 6194. doi 10.1016/j.bmc.2016.10.003
The authors declare the absence of conflict of
interests.
14. Krasnov, V.P., Vigorov, A.Yu., Gruzdev, D.A.,
Levit, G.L., Kravchenko, M.A., Skornyakov, S.N.,
Bekker, O.B., Maslov, D.A., Danilenko, V.N., and
Charushin, V.N., Pharm. Chem. J., 2017, vol. 51,
p. 769. doi 10.1007/s11094-017-1690-4
REFERENCES
1. Rosemeyer, H., Chem. Biodiversity, 2004, vol. 1, p. 361.
doi 10.1002/cbdv.200490033
15. Davison, H.R., Solano, D.M., Phuan, P.-W.,
Verkman, A.S., and Kurth, M.J., Bioorg. Med. Chem.
Lett., 2012, vol. 22, p. 1602. doi 10.1016/
j.bmcl.2011.12.128
2. Legraverend, M. and Grierson, D.S., Bioorg. Med.
Chem., 2006, vol. 14, p. 3987. doi 10.1016/
j.bmc.2005.12.060
3. Pozharskii, A.F., Soldatenkov, A.T., and Katritzky, A.R.,
Heterocycles in Life and Society: An Introduction to
Heterocyclic Chemistry, Biochemistry, and Applications,
Chichester: Wiley, 2011, 2nd ed.
4. Krasnov, V.P., Vigorov, A.Yu., Musiyak, V.V., Nizo-
va, I.A., Gruzdev, D.A., Matveeva, T.V., Levit, G.L.,
Kravchenko, M.A., Skornyakov, S.N., Bekker, O.B.,
Danilenko, V.N., and Charushin, V.N., Bioorg. Med.
Chem. Lett., 2016, vol. 26, p. 2645. doi 10.1016/
j.bmcl.2016.04.017
16. Kalindjian, S.B. and Smith, R.A.G., Biochem. J., 1987,
vol. 248, p. 409. doi 10.1042/bj2480409
17. Krasnov, V.P., Vigorov, A.Yu., Gruzdev, D.A.,
Levit, G.L., Demin, A.M., Nizova, I.A., Tuma-
shov, A.A., Sadretdinova, L.Sh., Gorbunov, E.B., and
Charushin, V.N., Russ. Chem. Bull., Int. Ed., 2015,
vol. 64, p. 2106. doi 10.1007/s11172-015-1125-x
18. Pogorelcnik, B., Brvar, M., Zegura, B., Filipic, M.,
Solmajer, T., and Perdih, A., ChemMedChem, 2015,
vol. 10, p. 345. doi 10.1002/cmdc.201402459
5. Berlicki, L., Mini-Rev. Med. Chem., 2008, vol. 8, p. 869.
doi 10.2174/138955708785132800
19. Bartkovitz, D.J., Chu, X.-J., Ding, Q., Karnachi, P.S.,
Liu, J.-J., So, S.-S., Zhang, J., and Zhang, Z., Int. Patent
Appl. no. WO 2012 022707; Chem. Abstr., 2012,
vol. 156, no. 311006.
6. Mowbray, S.L., Kathiravan, M.K., Pandey, A.A., and
Odell, L.R., Molecules, 2014, vol. 19, p. 13161. doi
10.3390/molecules190913161
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 6 2019