Azachalcone derivatives and their bis substituted analogs as novel antimycobacterial agents

Article abstract of DOI:10.1135/cccc19980698

Fifteen novel substituted azachalcone derivatives and their bis substituted analogs were prepared from 3,5-diacetyl-2,6-dimethylpyridine by the Claisen-Schmidt condensation. The influence of the reaction conditions on the yield of mono- and bischalcones was studied to optimize the reaction. Spectral characteristics along with preliminary results of antimycobacterial activity of selected compounds are given.

Full text of DOI:10.1135/cccc19980698

698
Kozmik, Lhotak, Odlerova, Palecek:
AZACHALCONE DERIVATIVES AND THEIR BIS SUBSTITUTED ANALOGS
AS NOVEL ANTIMYCOBACTERIAL AGENTS
a1
a2
b
a3
Vaclav KOZMIK , Pavel LHOTAK , Zelmira ODLEROVA and Jaroslav PALECEK
a Department of Organic Chemistry, Prague Institute of Chemical Technology, 166 28 Prague 6,
Czech Republic; e-mail: 1 vaclav.kozmik@vscht.cz, 2 pavel.lhotak@vscht.cz,
3 jaroslav.palecek@vscht.cz
b Institute of Preventive and Clinical Medicine, 833 01 Bratislava, Slovak Republic
Received January 21, 1998
Accepted April 10, 1998
Fifteen novel substituted azachalcone derivatives and their bis substituted analogs were prepared
from 3,5-diacetyl-2,6-dimethylpyridine by the Claisen–Schmidt condensation. The influence of the
reaction conditions on the yield of mono- and bischalcones was studied to optimize the reaction.
Spectral characteristics along with preliminary results of antimycobacterial activity of selected com-
pounds are given.
Key words: Azachalcones; Pyridines; 1,1′-(Pyridine-3,5-diyl)bis(3-arylprop-2-en-1-ones); Antimyco-
bacterial activity; Antituberculotics.
It is well known that the patients with immunosuppressive disorders (including AIDS)
are highly sensitive towards a broad range of protozoal, fungal, viral and bacterial in-
fections1,2. Among these pathogenic microorganisms one can find extremely “multi-
drug” resistant strains, such as Mycobacteria tuberculosis that represents potential
danger for the mankind due to the possibility of world-wide expansion of tuberculosis3–5
noncurable by standard antituberculotics. Recently, many new chalcone derivatives
with antiviral6, antimitotic7, anti-inflammatory8, antimalarial9 and antibacterial10 acti-
vities have been described. Medvecky et al.11 showed azachalcone derivatives exhibit-
ing the same efficiency as a generally accepted standard isoniazid12 (INH), however,
with much higher toxicity. The above-mentioned work11 together with our own promis-
ing results13 of the testing of 1a for antimycobacterial activity focused our interest on
new synthetic research in the family of substituted azabischalcones. Our aim was to
prepare new chalcone derivatives based on the pyridine moiety (Scheme 1, Table I) and
evaluate their activity towards various mycobacterial strains.
As we have mentioned in our previous publication14, the yield of the Claisen–
Schmidt condensation (i.e., reaction of methyl aryl ketones with arenaldehydes)
strongly depends on the reaction conditions and also on the presence of some substi-
tuents in the reactants14–17
.
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Azachalcone Derivatives
699
To optimize the above described condensation, we have focused our interest on a
more detailed study of the influence of the reaction conditions (reactant ratio, solvent,
catalyst, temperature, reaction time) on the yield of azamonochalcones 2a and similar
bis substituted derivatives 1a. The course of the reactions was monitored by TLC and
the reaction was stopped either after disappearing of 3,5-diacetyl-2,6-dimethylpyridine (3)
or when polymeric compounds were produced in higher yields.
O
O
H C
CH
3
3
Ar
CHO
+
+
H C
3
N
CH
O
3
4a-4p
3
O
O
O
Ar
Ar
Ar
CH
3
H C
3
N
CH
H C
3
N
CH
3
3
1a-1p
2a-2g
Ar
Ar
Ar
1,2
a
1,2
f
1,2
l
Ph
4-ClC H
2-Furyl
6
4
4-(CH ) NC H
4-BrC H
6 4
2-Thienyl
3-Thienyl
3-Pyridyl
4-Pyridyl
b
g
h
i
m
n
3 2
6
4
4-HOC H
4-CH OC H
c
6
4
3
6
4
4
4-CH C H
4-NCC H
6
d
o
3
6
4
4-FC H
6
4-O NC H
2 6 4
e
j
p
4
4-CH OCOC H
6 4
k
3
SCHEME 1
The results are collected in Table II. It is obvious (see Table II, entries 1–3) that the
ratio of bischalcone : monochalcone derivatives (1a : 2a) in the acid-catalyzed reaction
depends on the amount of sulfuric acid. At a low concentration of H2SO4 in acetic acid
(1 : 40, v/v), used as a solvent (Table II, entry 2), the reaction did not occur at all, while
a higher concentration of sulfuric acid (2 : 40) led to the isolation of compound 2a in
58% yield (Table II, entry 1). It is interesting that a slightly higher concentration (3 : 40)
gave the bis substituted derivative 1a (59%) as a main product (Table II, entry 3) while
the overall yield of the condensation (1a + 2a) remained approximately the same.
Recently, the base-catalyzed condensation of 2,6-diacetylpyridine with 4-substituted
benzaldehydes has been described18. Based on these results, we have attempted using
various bases, such as KOH, CH3COOK, piperidine, diethylamine and Ba(OH)2, in our
reaction system using methanol as a solvent. As follows from Table II, the reaction
carried out at low temperature (entry 5) afforded only low yields of products. On the
other hand, the same reaction mixture at higher temperature (60 °C) gave mainly
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

700
Kozmik, Lhotak, Odlerova, Palecek:
Calculated/Found
TABLE I
Characteristics of compounds 1, 2 and 5
Yield, %
Method
M.p., °C
Formula
M.w.
Compound
Solventa
% C
% H
% N
1a
1b
1c
74
88–90
C25H21NO2
367.4
81.72
81.57
5.76
5.76
3.81
3.81
A
MeOH
51
229–232
C29H31N3O2
453.6
76.79
76.64
6.89
6.72
9.26
9.41
A
Ac–MeOH
12
215–217
C
25H21NO4
399.4
75.17
74.78
5.30
5.50
3.51
3.35
A
Ch–MeOH
1d
1eb
1fc
1gd
1h
1i
62
122–123
MeOH
C
27H25NO2
395.5
82.00
81.75
6.37
6.52
3.54
3.54
A
70
168–169
C25H19F2NO2
403.4
74.43
74.38
4.75
4.97
3.47
3.35
A
Ch–MeOH
68
175–177
C25H19Cl2NO2
436.3
68.82
68.79
4.39
4.46
3.21
3.11
A
Ch–MeOH
64
191–193
EA–Hex
C25H19Br2NO2
525.2
57.17
56.87
3.65
3.70
2.67
2.63
A
66
130–131
C
27H25NO4
427.4
75.86
75.72
5.89
6.00
3.28
3.28
A
Ch–MeOH
37
230–232
C27H19N3O2
417.5
77.68
77.55
4.59
4.72
10.07
10.07
A
Ch–MeOH
1j
12
260–262
Ch–Py
C25H19N3O6
457.4
65.64
65.61
4.19
4.21
9.19
9.02
A
1k
1l
16
176–177
EA–Hex
C
29H25NO6
483.5
72.04
71.84
5.21
5.09
2.90
2.69
A
59
130–131
EA–Hex
C
21H17NO4
347.4
72.61
72.49
4.93
4.67
4.03
3.87
A
1me
1nf
62
137–139
EA–Hex
C21H17NO2S2
379.5
66.46
67.06
4.52
4.57
3.69
3.75
A
46
112–114
EA–Hex
C21H17NO2S2
379.5
66.46
66.64
4.52
4.62
3.69
3.79
A
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Azachalcone Derivatives
701
TABLE I
(Continued)
Calculated/Found
Yield, %
Method
M.p., °C
Formula
M.w.
Compound
Solventa
% C
% H
% N
1o
1p
2a
2b
2c
22
159–160
C23H19N3O2
369.4
74.78
74.55
5.18
4.99
11.37
B
Ch–MeOH
11.05
12
166–168
C23H19N3O2
369.4
74.78
74.63
5.18
5.08
11.37
11.11
B
Ch–MeOH
2
78–84
C
18H17NO2
279.3
77.40
77.22
6.13
6.10
5.01
4.72
A
MeOH
4
128–130
EA–Hex
C20H22N2O2
322.4
74.51
74.80
6.88
6.97
8.69
8.75
A
1
190–195
EA–Hex
C
18H17NO3
295.3
73.20
72.98
5.80
5.90
4.74
4.58
A
2d
2eg
2fh
2gi
5a
5
106–108
EA–Hex
C
19H19NO2
293.4
77.79
77.80
6.53
6.69
4.77
4.85
A
5
105–107
C18H16FNO2
297.3
72.71
72.78
5.42
5.57
4.71
4.65
A
Ch–MeOH
6
123–125
C18H16ClNO2
313.8
68.90
68.65
6.14
5.17
4.46
4.24
A
Ch–MeOH
4
135–137
EA–Hex
C18H16BrNO2
358.2
60.35
60.03
4.50
4.68
3.91
4.00
A
87
85–87
C
25H25NO2
371.5
80.83
80.67
6.78
6.59
3.77
3.66
EA–Hex
a
Crystallization solvents: MeOH methanol, EA ethyl acetate, Ch chloroform, Hex hexane, Ac
b
c
d
acetone; % F calculated: 9.42, found: 9.54; % Cl calculated: 16.25, found: 16.56; % Br calcu-
lated: 30.43, found: 30.15; % S calculated: 16.90, found: 16.67; % S calculated: 16.90, found:
16.71; % F calculated: 6.39, found: 6.68; % Cl calculated: 11.30, found: 11.56; % Br calculated:
22.30, found: 22.19.
e
f
g
h
i
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

702
Kozmik, Lhotak, Odlerova, Palecek:
polymeric products (entries 6, 7). The highest yields of 1a (70–74%) were achieved
with the reactant molar ratio 10 : 40 in methanol at room temperature (entries 4, 8, 9).
In all these cases the yield of monoderivative 2a was very low (<5%). Contrary to our
expectations, the condensation accomplished at higher temperature (80–130 °C) and
catalyzed with potassium acetate, piperidine or diethylamine gave mixtures of mono-
and bischalcones with predominant derivative 2a in 26, 29 and 22% yields, respec-
tively.
As a result of this study, the conditions described in entries 1 (method B) and 9
(method A) (see Experimental) were used for preparation of compounds 1a–1p and
2a–2g.
Compound 1a was then subjected to catalytic hydrogenation to confirm the influence
of 2-oxopropenyl moiety on the antimycobacterial activity of the studied compounds.
The reaction was carried out using Pd/C in ethyl acetate and compound 5a was isolated
in an almost quantitative yield (Scheme 2).
Spectral characteristics of all new compounds correspond to the proposed structures. In IR
spectra (Table III) of 1 and 2, characteristic vibrations can be found in the 1 623–1 674 cm–1
TABLE II
The influence of reaction conditions on the yield of derivatives 1a and 2a (10 mmol of compound 3
have been used in all experiments)
Yield, %
4a
mmol
Time
h
Entry
Agents
T, °C
1a
2a
1
2
32
32
32
40
40
40
40
40
40
40
23
40
30
2 ml H2SO4/40 ml CH3COOH
1 ml H2SO4/40 ml CH3COOH
3 ml H2SO4/40 ml CH3COOH
1 mmol KOH/1 ml H2O/12 ml CH3OH
1 mmol KOH/15 ml CH3OH
25
25
25
25
5
336
96
240
3
17
–
58
–
3
59
70
5
12
4
4
5
8
10
3
6
1 mmol KOH/15 ml CH3OH
60
60
25
25
25
130
80
100
3
8
7
1 mmol Ba(OH)2/15 ml CH3OH
1 mmol Ba(OH)2/15 ml CH3OH
1 mmol KOH/15 ml CH3OH
3
11
72
74
30
22
12
11
4
8
4
2
9
5
3
10
11
12
13
10 mmol KOH/15 ml CH3OH
30 mmol CH3COOK/20 ml (CH3CO)2O
1 mmol piperidine/20 ml CH3OH
3 mmol diethylamine/6 ml pyridine
2
8
2
26
29
22
28
20
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Azachalcone Derivatives
703
region proving thus the presence of carbonyl group in the –CH=CH–CO– moiety. In addi-
tion, an intensive absorption band exhibiting minimal variability is present in the spec-
tra of 2, at 1 690 cm–1 corresponding to the C=O vibration of acetyl group directly
bonded to a pyridine ring.
O
O
O
O
Pd/C
H C
3
N
CH
H C
3
N
CH
3
3
1a
5a
SCHEME 2
The UV-VIS spectra of compounds 1 and 2 are summarized in Table III. The
presence of two distinct maxima at 220 and 320 nm indicates typical π→π* transitions
of the conjugated system19, which is corroborated by relatively high values of log ε. In
accordance with literature data20, the substitution of the para-position in phenyl ring by
electron-donating groups leads to a considerable bathochromic shift; at the same time,
the electron-withdrawing substituents cause only minimal hypsochromic changes21.
The MS spectra of compounds 1 and 2 are very similar (Tables IV and V). Neverthe-
less, their fragmentation is not fully identical. The characteristic fragmentation mode of
these compounds has been already described22–28 in the basic chalcone series. MS spectra
of azachalcones 2 (Scheme 3) consist of molecular ion a and additional peak b [M – H]+.
+
+
X - C H
7
Ar
CH
2
6
f
g
+
+
O
O
Ar
Ar
O
O
H C
3
N
N
CH
3
3
Ar
CH
3
h
H
N
CH
3
O
M
a
H C
3
CH
+
i
M - H
b
+
O
+
+
- CO
- C H
2 2
Ar
CH
Ar
e
Ar
c
d
SCHEME 3
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

704
Kozmik, Lhotak, Odlerova, Palecek:
TABLE III
Characteristic IR and UV-VIS data of compounds 1, 2 and 5
Compound
ν, cm–1
λmax, nm
log εa
1a
1b
1c
3 015, 1 642, 1 601, 1 576
3 023, 1 652, 1 590, 1 525
225, 304
258, 414
4.54, 4.70
4.46, 4.87
4.22, 4.53
3 632, 3 412, 3 019, 1 729, 1 688, 1 600, 1 585, 240, 343
1 514, 1 252
1d
1e
1f
3 024, 1 665, 1 639, 1 598
228, 316
222, 307
224, 311
228, 310
239, 337
221, 295
215, 308
227, 301
245, 337
285, 340
4.41, 4.69
4.50, 4.63
4.47, 4.70
4.45, 4.40
4.40, 4.65
3.88, 3.91
3.71, 3.74
4.40, 4.58
4.41, 4.77
4.37, 4.65
3 023, 1 644, 1 600, 1 508, 1 239
3 024, 1 644, 1 591, 1 401
1g
1h
1i
3 016, 1 645, 1 603, 1 586, 1 488
3 023, 1 636, 1 598, 1 513, 1 254
3 024, 2 232, 1 671, 1 650, 1 606
3 018, 1 673, 1 597, 1 525, 1 347
3 025, 1 721, 1 647, 1 605, 1 284
3 015, 1 623, 1 599, 1 552
1j
1k
1l
1m
1n
1o
1p
2a
2b
2c
2d
2e
2f
3 014, 1 638, 1 608, 1 588
3 014, 1 639, 1 617, 1 595
213, 238, 316 4.58, 4.32, 4.66
2 979, 1 689, 1 648, 1 607, 1 588
2 960, 1 672, 1 659, 1 614, 1 585
3 024, 1 690, 1 670, 1 646, 1 597
3 011, 1 688, 1 590, 1 526
300
4.74
280
4.68
228, 304
259, 416
235, 342
233, 318
229, 308
231, 312
231, 312
246, 278
4.34, 4.33
4.07, 4.44
3.90, 3.96
4.36, 4.47
4.29, 4.37
4.35, 4.42
4.38, 4.38
4.16, 3.95
3 587, 3 350, 3 025, 1 691, 1 595, 1 514
3 016, 1 689, 1 641, 1 596
3 022, 1 690, 1 600, 1 500
3 012, 1 690, 1 645, 1 591, 1 492
3 016, 1 690, 1 644, 1 590, 1 488
3 028, 3 013, 1 688, 1 590
2g
5a
a
ε is given in m2/mol.
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Azachalcone Derivatives
705
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

706
Kozmik, Lhotak, Odlerova, Palecek:
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Azachalcone Derivatives
707
During the following fragmentation of a, the major part of ions is created by the direct
bond cleavage, the most important fragmentation mode being the cleavage of the bond
adjacent to carbonyl group giving ions c and d. Another possible explanation of the
presence of ion d could be elimination of CO from fragment c. The presence of ion e
can be explained by elimination of ethyne molecule from ion d, although the presence
of [M – e]+ ion does not exclude the possibility of its direct formation. Ion f, possessing
low relative intensity, is formed by hydrogen transfer from methyl group in position 2
of the pyridine ring. This so called ortho effect24 proceeds via a six-membered cyclic
mechanism in which hydrogen is transferred to a double bond of the chalcone moiety.
Easy and unexpected formation of ion c (25–87% rel. int.) could be rationalized by the
breaking of the bond between the 2-oxopropenyl and pyridine moieties. The less intens-
ive h and i ions have their origin in elimination of methyl or acetyl radical from mole-
cular ion a, which proves the presence of an acetyl group in compounds 2. The very
intensive fragmentation mode (26–100% rel. int.) is characterized by the formation of
substituted tropylium ion g in the spectra of azamonochalcones 2a–2b. Elimination of
carbon monoxide from molecular ion (Table IV), which was observed in simple chal-
cone derivatives25,28, is not so intensive in this series (1–3% rel. int.).
The fragmentation mechanism in symmetrical bis substituted compounds 1 is clearly
simpler (Scheme 4) with a fragmentation pattern typical of chalcones, i.e., cleavage of
α bonds linked to carbonyl group. The most intensive mode is again the formation of a
substituted tropylium cation g or its heteroanalogs, such as pyrylium (C5H5O+) (1l),
thiapyrylium (C5H5S+) (1m, 1n), and azepinium (C6H5N+) (1o, 1p). The formation of
intensive ions c, d, e, and f from molecular ion a is the same as described above for
+
+
X - C H
7
and its heteroanalogs
6
Ar
CH
2
g
f
O
O
+
Ar
Ar
M
a
M - H
b
H
N
CH
3
+
+
O
+
- C H
2
2
- CO
Ar
e
Ar
CH
Ar
d
c
SCHEME 4
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

708
Kozmik, Lhotak, Odlerova, Palecek:
TABLE VI
1H NMR data (δ, ppm; J, Hz) of compounds 1, 2 and 5
Pyridine
Compound
Benzene
CH=CH (d)
Other
CH3 (s)
H-4 (s)
1a
1b
1c
1d
1e
1f
2.71
2.67
2.69
2.70
2.71
2.71
2.71
2.69
2.73
2.75
2.73
2.71
2.70
2.69
2.73
2.74
7.90
7.80
7.84
7.88
7.88
7.89
7.89
7.85
7.95
7.96
7.94
7.92
7.86
7.83
7.94
7.95
8.07
8.01
8.05
7.39–7.44 m, 6 H;
7.56–7.59 m, 4 H
7.13; 7.51
J = 16.06
–
6.66 d, 4 H; 7.45 d, 4 H
6.86 d, 4 H; 7.48 d, 4 H
7.21 d, 4 H; 7.47 d, 4 H
7.09–7.13 m, 4 H; 7.55 m, 4 H
7.38 d, 4 H; 7.51 d, 4 H
7.43 d, 4 H; 7.55 d, 4 H
6.92 d, 4 H; 7.52 d, 4 H
7.68 d, 4 H; 7.72 d, 4 H
7.74 d, 4 H; 8.28 d, 4 H
7.64 d, 4 H; 8.07 d, 4 H
6.89; 7.40
J = 15.85
3.04a
6.98; 7.43
J = 16.50
3.54b
7.08; 7.48
J = 16.07
2.39c
7.05; 7.48
J = 16.04
–
7.09; 7.47
J = 16.08
–
1g
1h
1i
7.11; 7.45
J = 16.04
–
6.99; 7.45
J = 16.01
3.85d
7.22; 7.54
J = 16.06
–
1j
7.25; 7.59
J = 16.02
–
1k
1l
7.20; 7.55
J = 16.08
3.94e
6.53 dd, 2 H; 6.74 d, 2 H;
7.55 d, 2 H
7.03; 7.32
J = 15.65
–
–
–
–
–
1m
1n
1o
1p
2a
2b
2c
7.10 dd, 2 H; 7.34 d, 2 H;
7.47 d, 2 H
6.91; 7.64
J = 15.66
7.35–7.39 m, 4 H;
7.58 d, 2 H
6.92; 7.47
J = 15.94
7.36 dd, 2 H; 7.90 ddd, 2 H;
8.65 dd, 2 H; 8.79 d, 2 H
7.21; 7.54
J = 16.08
7.42 dd, 4 H; 8.70 dd, 4 H
7.28; 7.47
J = 16.06
2.61
2.68
7.42–7.46 m, 3 H;
7.58–7.60 m, 2 H
7.13; 7.50
J = 16.09
–
2.81f
2.60
2.64
6.67 d, 2 H; 7.46 d, 2 H
6.89; 7.38
J = 15.85
3.06a
2.80f
2.62
2.65
6.88 d, 2 H; 7.48 d, 2 H
6.97; 7.41
J = 16.00
6.60b
2.81f
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Azachalcone Derivatives
709
TABLE VI
(Continued)
Pyridine
Compound
Benzene
CH=CH (d)
Other
CH3 (s)
H-4 (s)
2d
2e
2f
2.61
2.66
8.05
8.05
8.06
8.06
7.85
7.24 d, 2 H; 7.48 d, 2 H
7.08; 7.46
J = 16.04
2.40c
2.80f
2.62
2.67
7.10–7.15 m, 2 H;
7.57–7.60 m, 2 H
7.05; 7.47
J = 16.06
–
2.80f
2.62
2.67
7.41 d, 2 H; 7.52 d, 2 H
7.10; 7.46
J = 16.04
–
2.80f
2g
5a
2.62
2.67
7.45 d, 2 H; 7.57 d, 2 H
7.11; 7.45
J = 16.03
–
2.80f
2.68
7.17–7.22 m, 6 H;
7.26–7.30 m, 4 H
–
3.02–3.06 m, 4 Hg;
3.12–3.16 m, 4 Hg
a
b
c
d
e
f
g
–(CH3)2N–; –HO–; –CH3–; H3O–; –CH3OOC–; CH3CO–; CH2–CH2–.
azachalcones 2. A molecular rearrangement25,28 accompanied by extrusion of CO is
observable in derivatives 1l–1p, whereas compounds 1b–1k do not show this behaviour
under the measuring conditions.
The MS spectrum of saturated derivative 5a corresponds with the well-known frag-
mentation of carbonyl compounds (see Experimental).
1H NMR spectra of symmetrical compounds 1b–1k (Table VI) exhibit typical
AA′XX′ or AA′BB′ splitting pattern for para-substituted phenyl rings in the region
6.66–8.28 ppm depending on the substitution. All derivatives 1a–1p show a signal of
position 4 of the pyridine ring, which can be found as a singlet at 7.83–7.96 ppm. The
doublets of the CH=CH–CO moiety are situated in the 6.89–7.64 ppm region with
typical coupling constants 15.6–16.1 Hz proving trans-configuration of the double
bond. Methyl groups in 2 and 6 positions of the pyridine ring give a singlet at 2.7 ppm.
1
In addition, the H NMR spectra of non-symmetrical azachalcones 2 also contain a
singlet at about 2.80 ppm due to the acetyl group.
Preliminary Results of Biological Activity Studies
Substituted chalcones exhibit a distinct antimycobacterial in vitro efficiency measured
on a suitable cultivating medium by the dilution method29. Activity of compound 1a
against Mycobacterium tuberculosis H37Rv (minimum inhibition concentration (MIC)
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710
Kozmik, Lhotak, Odlerova, Palecek:
0.25 µg/ml), M. kansassi PKG8 (MIC 5 µg/ml), and M. avium 80/72 (MIC 50 µg/ml) is
comparable with that of isoniazide (INH), and is better than activity of ethionamide
(2-ethylisonicotinthioamide), PAS (4-amino-2-hydroxybenzoic acid) or conteben (4-acet-
amidobenzaldehyde thiosemicarbazone). In vivo experiments in mice showed acute toxicity
(dosis tolerata maxima) of approximately 2 000 mg/kg while the published value for
INH is 125 mg/kg (ref.30). A detailed study of the antimycobacterial activity of all
compounds 1 and 2 has been published separately31.
EXPERIMENTAL
Temperature data were not corrected. The melting points were determined on a Boetius block (Zeiss,
Jena, Germany). The IR spectra were measured on an FT-IR spectrometer Nicolet 740 in chloroform.
1H NMR spectra were obtained with a Bruker 400 spectrometer in deuteriochloroform; chemical
shifts are reported in δ (ppm) with TMS as an internal standard, the coupling constants J are given
in Hz. Mass spectra were measured on a Varian MAT 44S instrument with ionization energy 70 eV.
The UV-VIS spectra were collected on an Otsuka MCPD 1100 spectrophotometer in ethanol. The
purity of the substances and the course of reactions were monitored by TLC using Silufol and Alufol
plates (Kavalier, Votice, Czech Republic). Column preparative chromatography was carried out on
silica gel Merck (40/100).
3,5-Diacetyl-2,6-dimethyl-1,4-dihydropyridine
A mixture of aqueous formaldehyde (36%; 13.6 ml, 0.4 mol), pentane-2,4-dione (26.2 g, 0.29 mol),
and aqueous solution of ammonium carbonate (10%; 600 ml, 0.62 mol) was allowed to stay for 48 h
at room temperature with intermittent stirring. The yellow precipitate was collected by suction and
dried at room temperature to yield 26.7 g (95%) of yellow crystals with m.p. 195–208 °C. The pure
product was obtained by crystallization from aqueous ethanol, m.p. 213–215 °C (ref.32 gives m.p.
207–208 °C).
3,5-Diacetyl-2,6-dimethylpyridine (3)
Aqueous H2SO4 (20%, 199 ml) was added dropwise during 2 h to an ice cool (0–5 °C), vigorously
stirred mixture of 3,5-diacetyl-2,6-dimethyl-1,4-dihydropyridine (30.6 g, 0.16 mol), diethyl ether
(800 ml), sodium nitrite (61.2 g, 0.89 mol) and water (300 ml). The reaction mixture was stirred for
additional 6 h at the same temperature and then for 15 h at room temperature. The content was alka-
linized with 20% aqueous NaOH solution (220 ml) and the mixture was extracted with diethyl ether
(4 × 200 ml). The combined organic layers were washed with brine (100 ml), dried over potassium
carbonate and evaporated to dryness. The crude product (15.8 g, 52%) was crystallized from cyclohex-
ane to yield 3 (13.8 g, 46%), m.p. 66–69 °C (ref.32 gives m.p. 69–70 °C (petroleum ether)).
1,1′-(2,6-Dimethyl-3,5-pyridinediyl)bis(3-phenyl-(E)-prop-2-en-1-one) (1a)
and 1-(5-Acetyl-2,6-dimethylpyridin-3-yl)-3-phenyl-(E)-prop-2-en-1-one (2a)
Method A. To an ice cool solution of 3,5-diacetyl-2,6-dimethylpyridine (3) (1.92 g, 10.0 mmol) in
methanol (40 ml), benzaldehyde (4a) (4.24 g, 40 mmol) and powdered potassium hydroxide (50 mg,
0.89 mmol) were gradually added. The reaction mixture was stirred for 30 min at 5 °C and then for
5 h at room temperature. The mixture was diluted with 15 ml of water and extracted with dichloro-
methane (3 × 30 ml). The combined organic layers were washed with water (20 ml), brine (20 ml)
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Azachalcone Derivatives
711
and dried over MgSO4. The solvent was evaporated and the residue was purified by column chroma-
tography on silica gel (350 g SiO2, hexane–t-butyl methyl ether). The corresponding fractions were
collected, evaporated and crystallized from methanol to yield 1a (2.7 g, 74%) as yellowish crystals,
m.p. 88–90 °C, and 2a (56 mg, 2%), m.p. 78–84 °C.
Method B. To a solution of 3,5-diacetyl-2,6-dimethylpyridine (3) (1.92 g, 10 mmol) and benzalde-
hyde (4a) (3.2 ml, 32 mmol) in glacial acetic acid (40 ml), concentrated H2SO4 (2 ml, 38 mmol) was
added and the mixture was stirred for 14 days at room temperature. The reaction mixture was then
diluted with water (200 ml) and extracted with dichloromethane (3 × 40 ml). The combined extracts
were washed consecutively with water (30 ml), a saturated aqueous solution of Na2S2O5 (30 ml), and
brine (30 ml). The product was then isolated in a similar manner as described above in method A to
yield azachalcone 1a (0.63 g, 17%), m.p. 88–90 °C, and 2a (1.62 g, 58%), m.p. 78–84 °C.
1,1′-(2,6-Dimethyl-3,5-pyridinediyl)bis(3-phenylpropan-1-one) (5a)
A mixture of compound 1a (1.0 g, 2.7 mmol), 10% Pd/C (100 mg), and ethyl acetate (25 ml) was
hydrogenated at room temperature under a common pressure. The reaction was stopped after con-
sumption of 2 equivalents of hydrogen, the catalyst was filtered off and the solvent was evaporated.
The residue (1.02 g) was purified by column chromatography on silica gel (35 g SiO2, hexane–t-butyl
methyl ether 3 : 1) and subsequently by crystallization from an ethyl acetate–hexane mixture to yield 5a
(877 mg, 87%) as white crystals, m.p. 85–87 °C. MS spectrum, m/z (rel.%): [M]+• = 371 (34 rel.%);
[M – C6H6]+ = 293 (2.5); [M – (Ph–CH2)]+ = 280 (2.6); [M – (Ph–CH2CH2)]+ = 266 (100); [M –
(Ph–CH2CH2CO)]+ = 238 (16); [Ph–CH2CH2CO]+ = 133 (8); [Ph–CH2CH2]+ = 105 (43); [Ph–CH2]+ = 91 (65);
[Ph]+ = 71 (26).
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