Adenine and uracil derivatives with antitubercular activity

Article abstract of DOI:10.1023/A:1011973514672

We have carried out the synthesis and investigated the antitubercular activity of adenine and 5-fluorouracil derivatives. It was found that a comparatively large, lipophilic fragment is needed in the active molecule to inhibit the tuberculosis pathogen.

Full text of DOI:10.1023/A:1011973514672

Chemistry of Heterocyclic Compounds, Vol. 37, No. 6, 2001
ADENINE AND URACIL DERIVATIVES
WITH ANTITUBERCULAR ACTIVITY
E. Alksnis, D. Korneeva, and E. Lukevics
We have carried out the synthesis and investigated the antitubercular activity of adenine and
5-fluorouracil derivatives. It was found that a comparatively large, lipophilic fragment is needed in the
active molecule to inhibit the tuberculosis pathogen.
Keywords: pyrimidines, purines, alkylation, tuberculosis.
Tuberculosis is one of the most widespread and dangerous infectious diseases and the so called
opportunistic tubercular infection is the main reason for the death of those who are ill with acquired
immunodeficiency syndrome (AIDS). With the association that the tuberculosis stimulus rapidly acquires
resistance to chemotherapeutic agents, it is constantly necessary to search for novel active preparations [1, 2].
The primary screening of the adenine, uracil, and xanthine derivatives synthesized by us was carried out
in the USA under the Antimicrobial Acquisition and Coordinating Facility and showed compounds 1 and 2 to be
characterized by limited antitubercular activity.
Cl
Cl
O
N
Cl
Cl
O
F
Cl
HN
O
N
Cl
F
HN
Cl
F
Cl
O
Cl
N
O
N
H
3
O
Cl
Cl
Cl
2
4
Cl
N
N
N
Cl
N
N
N
N
N
N
Cl
+
Cl
N
N
N
N
N
N
Cl
H
5
Cl
Cl
6
1
__________________________________________________________________________________________
Latvian Institute of Organic Synthesis, Riga LV-1006; e-mail: pilsonis@osi.lv. Translated from
Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 807-810, June, 2001. Original article submitted
October 11, 1998; revision submitted August 22, 2000.
0009-3122/01/3706-0743$25.00©2001 Plenum Publishing Corporation
743

Cl
N
N
N
H
N
N
N
N
N
Cl
N
N
Cl
Cl
8
7
Cl
R1
R
N
11 R = NMe2, R1 = Cl
R
N
N
Cl
N
N
NH
R1 = Cl
R1 = H
O
12 R =
Cl
N
H
N
N
R1
9 R = NMe2
NH
NH
O
O
13 R =
10 R =
Cl
Cl
Cl
O
N
N
N
N
N
N
N
Cl
N
N
Cl
Cl
Cl
14
15
We have further synthesized analogs of the compounds referred to (4, 6, 8, 11-14).
3(9)-Substituted derivatives of 6-diethylaminopurine 1, 6 and 5-fluorouracil 2, 4 were obtained by the
alkylation of 6-diethylaminopurine (5) and 5-fluorouracil (3) using benzyl chlorides under phase-transfer
catalytic conditions. The trisubstituted adenine derivative 14 was obtained in the same way. The mixtures of
3- and 9- substituted adenine derivatives 1, 6 were separated chromatographically on silica gel and the isomers
were identified using UV and 1H NMR spectroscopic methods as described in the study [3].
The 3-substituted adenine derivatives 11-13 were prepared by aralkylation of the adenines 9, 10 using
benzyl chlorides in dimethylformamide and subsequent rearrangement in basic medium. The purine derivatives
8, 15 were synthesized from 6-chloro-9-(2,6-dichlorobenzyl)purine (7), similarly to the method reported in
[3, 4].
Investigation of the antitubercular activity of the synthesized compounds (Table 1) has shown that the
active substance molecule needs a comparatively large, lipophilic fragment differing in specific features for the
efficient inhibition of the tuberculosis pathogen.
The most active of the compounds obtained (8) was 80 times inferior to the standard used in the
1
experiment (rifampin). The structure of the novel compounds was proved using H NMR spectroscopy (see
Table 2).
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TABLE 1. Antitubercular Activity of the Purine and Pyrimidine Derivatives
Compound
8
12
2
6
13
1
4
11
14
15
Inhibition
73
53
44
31
20
19
13
4
0
0
Mycobacterium
tuberculosis H37Rv, %*
_______
* At a concentration of 12.5 g/ml.
µ
TABLE 2. 1H NMR Spectra of the Purine and Pyrimidine Derivatives
Compound
Chemical shift, δ, ppm (CDCl3)
1.20 (6H, t, СН3); 3.86 (4H, q, СН2); 5.49 (2H, s, СН2);
7.11-7.42 (4H, m, Рh, purine ring); 8.27 (1H, s, purine ring)
1
2*
5.03 (2H, s, СН2); 7.43 (3H, m, Рh); 7.62 (1H, d, pyrimidine ring);
11.72 (1H, br. s, NН)
4.76 (2H, s, СН2); 4.99 (2H, s, СН2); 6.93-7.54 (7H, m, Рh, pyrimidine ring)
4
6
1.50 (6H, m, 2СН3); 3.73 (2H, m, N(6)СН2); 4.40 (2H, m, N(6)СН2);
5.82 (2H, s, СН2); 7.16-7.53 (4H, m, Рh, purine ring); 8.00 (1H, s, purine ring)
1.65 (6H, s, СН2); 4.17 (4H, s, N(6)СН2); 5.54 (2H, s, СН2);
8
7.15-7.44 (4H, m, Рh, purine ring); 8.32 (1H, s, purine ring)
4.79 (2H, br. s, N(6)СН2); 5.83 (2H, s, СН2); 6.19 (2H, m, furan ring);
7.05-7.45 (4H, m, Рh, furan ring); 7.60 (s); 7.96 (s) (2Н, purine ring)
12
13
4.80 (2H, br. s, N(6)СН2); 5.62 (2H, s, СН2); 6.20 (2H, m, furan ring);
7.04-7.46 (5H, m, Рh, furan ring); 7.60 (s), 7.96 (s) (2H, purine ring)
_______
* In DMSO-d6.
EXPERIMENTAL
1H NMR spectra were taken on a Bruker WH-90 spectrometer using TMS as internal standard. Melting
points were determined on a Boetius apparatus and are not corrected. The ultraviolet spectra were recorded on a
UNICAM UV-vis spectrophotometer. TLC analysis was carried out on Silufol UV-254 plates in the systems A:
chloroform–ethyl acetate, 1:1 and B: chloroform–ethyl acetate–ethanol, 2: 2: 1. The column chromatography
was performed on L40/100 grade silica gel in the same systems.
The synthesis of the purines 7 and 15 has been reported in the study [3] and of compound 14 in [4].
The antitubercular activity for the compounds prepared was studied in the culture Mycobacterium
tuberculosis H37Rv in the medium BACTEC 12B with the radiometric system BACTEC 460.
9-(2,6-Dichlorobenzyl)-6-diethylaminopurine (1) and 3-(2,6-Dichlorobenzyl)-6-diethylaminopurine
(6). A mixture of 6-diethylaminopurine 5 (1.91 g, 10 mmol), benzene (20 ml), aqueous NaOH solution (50%,
8 ml), tetrabutylammonium bromide (0.32 g, 1 mmol), and 2,6-dichlorobenzyl chloride (2.14 g, 11 mmol) was
heated at 80°C until solution of the suspension of the purine sodium salt (30-45 min). The mixture was cooled,
water (100 ml) added, and twice extracted with chloroform (50 ml). The chloroform extracts were dried over
anhydrous sodium sulfate and evaporated to dryness and the dry residue was separated on a silica column
(30 × 2 cm) using system A. Following chromatography, crystallization from hexane gave compound 1 (2.48 g,
71%) and compound 6 (0.63 g, 18%); mp 201-202°C,
309 nm (methanol). Compound 1. Found, %:
λmax
N 20.08; C 54.93; H 4.88. C16H17Cl2N5. Calculated, %: N 20.00; C 54.86; H 4.86. Compound 6. Found, %:
N 20.17; C 55.11; H 4.86. C16H17Cl2N5. Calculated, %: N 20.00; C 54.86; H 4.86.
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6-Piperidino-9-(2,6-dichlorobenzyl)purine (8). 6-Chloro-9-(2,6-dichlorobenzyl)purine 7 (0.32 g,
1 mmol) and piperidine (2.55 g, 30 mmol) were heated at 100°C for 2 h. The solution was poured into water
(50 ml) and after 2 h it was filtered, washed with water, and crystallized from ethanol to give compound 8
(0.15 g, 41%); mp 191-192°C,
= 280 nm (methanol). Found, %: N 19.42; C 56.45; H 4.77. C17H17Cl2N5.
λmax
Calculated, %: N 19.32; C 56.37; H 4.74.
3-(2,6-Dichlorobenzyl)-6-dimethylaminopurine (11), 3-(2,6-dichlorobenzyl)-6-furfurylaminopurine
(12), and 3-(2-chlorobenzyl)-6-furfurylaminopurine (13). (General Method). A suspension containing the
aminopurine (10 mmol), benzyl chloride (10 mmol), and dimethylformamide (10 ml) was heated at 110°C for
2 h. Water (10 ml) was added and the product was neutralized with concentrated ammonia solution. NaOH
solution (1N, 50 ml) was added and the product was twice extracted with chloroform. The chloroform extracts
were dried over anhydrous sodium sulfate and evaporated. The dried residue was chromatographed on a silica
gel column (30 × 4 cm, system A, then B). After chromatography the products were crystallized from ether to
give compound 11 (1.96 g, 61%); mp 212-213°C,
309 nm (methanol), compound 12 (1.83 g, 49%);
λmax
mp 171-173°C,
294 nm (methanol), and compound 13 (1.80 g, 53%); mp 191-193°C,
294 nm
λmax
λmax
(methanol). Compound 11. Found, %: N 21.58; C 54.20; H 4.11. C14H13Cl2N5. Calculated, %: N 21.74;
C 52.19; H 4.07. Compound 12. Found, %: N 18.55; C 54.62; H 3.50. C17H13Cl2N5O. Calculated, %: N 18.71;
C 54.56; H 3.51. Compound 13. Found, %: N 20.45; C 60.28; H 4.19. C17H14ClN5O. Calculated, %: N 20.61;
C 60.28; H 4.15.
5-Fluoro-1-(2,6-dichlorobenzyl)uracil (2). A suspension containing 5-fluorouracil (1.3 g, 10 mmol),
powdered KOH (0.56 g, 10 mmol), benzene (10 ml), and trioctylmethylammonium bromide (0.4 g) was stirred
for 1 h at 80°C. 2,6-Dichlorobenzyl chloride (1.95 g, 10 mmol) was added and the product was heated and
stirred for a further 2 h. The mixture was cooled and washed with benzene. The residue was twice extracted
with hot chloroform (50 ml). The chloroform extracts were evaporated and the residue was crystallized from
butanol to give compound 2 (0.6 g, 21%); mp 253-255°C, λmax 273 nm (methanol). Found, %: N 9.69; C 45.70;
H 2.44. C11H7Cl2FN2O2. Calculated, %: N 9.61; C 45.63; H 2.46.
1,3-Di(3,4-dichlorobenzyl)-5-fluorouracil (4). A two phase system containing 5-fluorouracil (1.3 g,
10 mmol), sodium hydroxide (0.8 g, 20 mmol), water (8 ml), tetrabutylammonium bromide (0.64 g, 2 mmol),
and 3,4-dichlorobenzyl chloride (3.9 g, 20 mmol), heated at 60°C, was stirred for 1.5 h. Sodium hydroxide
solution (1 N, 50 ml) was added and the product was twice extracted with chloroform (50 ml). The chloroform
extracts were dried over anhydrous sodium sulfate, filtered, and evaporated to dryness. Recrystallization from
acetonitrile gave compound 4 (2.3 g, 52%); mp 142-144°C, λmax 273 nm (methanol). Found, %: N 6.36; C 48.00;
H 2.52. C18H11Cl4FN2O2. Calculated, %: N 6.25; C 48.25; H 2.47.
REFERENCES
1.
2.
S. L. Dax, Antibacterial Chemotherapeutic Agents, Blackie Academic and Professional, London (1997).
M. E. Wolf (editor), Burger's Medicinal Chemistry and Drug Discovery, 5th Edition, Vol. 2, Wiley
Interscience (1996), p. 575.
3.
4.
N. Ramzaeva, Yu. Gol'dberg, E. Alksnis, M. Lidak, and M. Shimanskaya, Zh. Org. Khim., 25, 1783
(1989).
N. Ramzaeva, Yu. Gol'dberg, E. Alksnis, M. Lidak, M. Yure, and E. Gudriniece, Zh. Org. Khim., 25,
1780 (1989).
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