Search of antimycobacterial activities in hybrid molecules with benzopyran skeleton

Article abstract of DOI:10.1007/s00044-010-9402-6

A series of hybrid molecules (7-9, 12, 13, and 14-18) consisting of chromans and pyrolidines or cyclic amines were prepared either by (3 + 2) cycloaddition of nitrostyrenes and azomethine ylide or by three component reactions of chromanyl aldehydes, acetylenes, and cyclic amines. All the synthesized compounds were evaluated against both avirulent (H37Ra) and virulent (H37Rv) strains of Mycobacterium tuberculosis. Out of all the compounds screened, compounds 16, 17, and 18 were found to be active against the virulent strain M. tubercolosis H37Rv displaying MIC in the range of 6.25-1.56 μg/ml against. Springer Science+Business Media, LLC 2010.

Full text of DOI:10.1007/s00044-010-9402-6

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2011) 20:1515–1522
DOI 10.1007/s00044-010-9402-6
ORIGINAL RESEARCH
Search of antimycobacterial activities in hybrid molecules
with benzopyran skeleton
•
Rama P. Tripathi Surendra Singh Bisht
•
•
Vivek Parashar Pandey Sarvesh K. Pandey
•
•
Shubhra Singh Sudhir Kumar Sinha
•
Vinita Chaturvedi
Received: 9 March 2010 / Accepted: 26 July 2010 / Published online: 6 August 2010
Ó Springer Science+Business Media, LLC 2010
Abstract A series of hybrid molecules (7–9, 12, 13, and
14–18) consisting of chromans and pyrolidines or cyclic
amines were prepared either by (3 ? 2) cycloaddition of
nitrostyrenes and azomethine ylide or by three component
reactions of chromanyl aldehydes, acetylenes, and cyclic
amines. All the synthesized compounds were evaluated
against both avirulent (H37Ra) and virulent (H37Rv)
strains of Mycobacterium tuberculosis. Out of all the
compounds screened, compounds 16, 17, and 18 were
found to be active against the virulent strain M. tuberco-
losis H37Rv displaying MIC in the range of 6.25–1.56 lg/ml
against.
synergy with the HIV/AIDS pandemic, and the emergence
of multidrug resistant (MDR) and extensively drug-resis-
tant (XDR) strains of M. tuberculosis. Moreover, nowadays
more people die from TB (Spigelman, 2007); therefore, the
present scenario involves the development of new drugs
regimens which are effective against MDR and XDR TB
and latent TB. New chemotherapeutic agents that will
shorten the duration of current chemotherapy are also
needed as the treatment schedule of the disease is
6–12 months. Although some recent progresses have been
made due to 10 potent leads in antiTB drug pipeline, yet
none of them are expected to hit the market before 2012,
the stipulated time. Therefore, extensive efforts are being
made globally to develop new chemical entities against this
devastating pathogen taking into account both the seren-
dipitous and rational drug design approach. Very recently
compounds with chromeno and chromano dibenzofurans
(A and B) skeletons were shown to posses’ potent antitu-
bercular activity in vitro (Prado et al., 2006; Prado et al.,
2007). To establish structure activity relationship, a num-
ber of other derivatives of benzofuran having fused benz-
opyran were prepared, but the compounds had lower
antitubercular activity and they were also cytotoxic. Apart
from this, certain chromene-based compounds have also
shown antibacterial activities (Fukushima et al., 2000;
Nicolaou et al., 2001; Babu et al., 2003; Prado et al., 2006;
Prado et al., 2007; Brown et al., 2004) (Fig. 1).
Keywords Mycobacterium tuberculosis Á Tuberculosis Á
Benzopyran Á (3 ? 2) Cycloaddition Á
Multi-component reaction
Introduction
Mycobacterium tuberculosis, responsible for tuberculosis
(TB) in human, causes the death of almost 3 million people
annually, and it is positioned as the leading bacterial
infectious agent (Tripathi et al., 2005; Dwivedi et al., 2008;
Cegielski et al., 2002; Spigelman, 2007). Despite the
availability of four drug regimens to treat TB, loss of
human lives is essentially unabated as a result of poverty,
Pyrrolidine derivatives on the other hand showed a wide
range of biological activities (Pandey et al., 2007; Tsou,
et al., 2008) including the noteworthy antitubercular
activities (He Xin et al., 2006). Receiving impetus from
above reports and guided by the principle that the combi-
nation of two or more biologically versatile moieties in a
single molecular frame often enhances the biological pro-
file of molecule many folds (Morphy et al., 2004),
R. P. Tripathi (&) Á S. S. Bisht Á V. P. Pandey Á S. K. Pandey
Medicinal and Process Chemistry Division, Central Drug
Research Institute, CSIR, Lucknow 226001, India
e-mail: rpt.cdri@gmail.com
S. Singh Á S. K. Sinha Á V. Chaturvedi
Drug Target Discovery and Development Division, Central Drug
Research Institute, CSIR, Lucknow 226001, India
123

1516
Med Chem Res (2011) 20:1515–1522
Thus, cycloaddition of the above nitrostyrene 6 with [(4-
methoxybenzylidene)-amino]-acetic acid ethyl ester (1) in
acetonitrile in the presence of DBU–LiBr as a catalyst led
to the formation of the expected ethyl-3-(2,2-dimethylch-
roman-6-yl)-4-nitro-5-(4-methoxyphenyl)pyrrolidine-2-
carboxylate (7) as a major compound along with small
amount of other products as observed on TLC (Scheme 3)
¨
(Annunziata et al., 1991; Galley et al., 1995; Patzel et al.,
Fig. 1 Antitubercular chromeno and chromano benzofurans A and B
1993). The compound 7 was isolated by column chroma-
tography and characterized on the basis of its spectroscopic
data. The relative stereochemistry in compound 7 was
speculated on the basis of literature precedents and the
mechanism (Annunziata et al., 1991; Galley et al., 1995). It
has earlier been reported that in such cycloaddition reac-
tions involving a chiral dienophile and azomethine ylide,
the relative orientation of substituents in major isomer at
C2/C3 and C3/C4 is anti and at C4/C5 is syn. Furthermore,
the relative stereochemistry is attained via regiospecific
endo cycloaddition of the W-shaped dipole to the E con-
figured dipolarophiles in the ester series.
hybridization of two or more than two pharmacophores was
envisaged. Herein, we have synthesized certain hybrid
molecules consisting of chromans, chromenes, cyclic
amines, and pyrrolidine and evaluated them for their anti-
tubercular profiles against M. tuberculosis.
Results and discussion
In the first set of 3 ? 2 cycloaddition reactions to access
chromanyl and chromenyl pyrrolidines, we have carried
out reactions of (benzylidene) amino acetic acid ethyl
esters with different nitrostyrenes. The (benzylidene)
amino acetic acid ethyl esters 1–4 were prepared
(Scheme 1) by reaction of different aromatic aldehydes and
ethylglycinate hydrochlorides by our earlier reported
method (Pandey et al., 2007) and used as such for further
reaction. The starting nitrostyrene (6) was prepared
(Scheme 2) by reaction of preformed 2,2-dimethyl-chro-
man-6-carbaldehyde (5) (obtained by the reaction of 4-
hydroxy benzaldehyde with isoprene in the presence of
ortho-phosphoric acid, Ahluwalia and Arora 1981) with
nitromethane in the presence of ammonium acetate in
acetic acid (Cheng et al., 2009) (Scheme 2).
Similarly, 3 ? 2 cycloaddition of reaction of the in situ
generated azomethine ylides from the [(benzylidene)-
amino]-acetic acid ethyl ester (2) and [(3-nitrobenzyli-
dene)-amino]-acetic acid ethyl ester (3) with the above
nitrostyrene derivative 6 led to the formation of respective
chromanyl pryrrolidine derivatives 8 and 9 in good yields
(Scheme 3).
In yet another attempt to prepare fused chromanyl pyr-
rolidines, the 3 ? 2 cycloaddition of azomethine ylide of
[(4-methoxybenzylidene)-amino]-acetic acid ethyl ester 1
and [(4-nitrobenzylidene)-amino]-acetic acid ethyl ester 4
with 3-nitrochromene derivative 11 was carried out.
Compound 11, in turn, was prepared by recently reported
reaction of 4-methoxy nitrostyrene 10 and salicylaldehyde
Scheme 1 Synthesis of
(benzylidene) amino acetic acid
ethyl esters (1–4)
Scheme 2 Synthesis of (E)-2,
2-dimethyl-6-(2-
nitrovinyl)chroman (6)
123

Med Chem Res (2011) 20:1515–1522
1517
Scheme 3 Synthesis of
chromanyl pryrrolidine
derivatives (7, 8, and 9)
Scheme 4 Synthesis of fused
chromanyl pyrrolidines (12 and
13)
(Viranyi et al., 2006). Thus, 3 ? 2 cycloaddition of 1 and 4
separately with 11 in acetonitrile in the presence of DBU–
LiBr led to the formation of respective ethyl-4-(4-
methoxyphenyl)-3a-nitro-3-(4-methoxyphenyl)-1,2,3,3a,4,
9b-hexahydrochromeno[3,4-c]pyrrole-1-carboxylates (12)
and ethyl-4-(4-nitrophenyl)-3a-nitro-3-(4-methoxyphenyl)-
1,2,3,3a,4,9b-hexahydrochromeno[3,4-c]pyrrole-1-carbox-
ylates (13), respectively in good yields (Scheme 4). The
structures of the compounds 12 and 13 were in full agree-
ment with the spectroscopic data.
Biological activity
The above synthesized compounds 7–9, 12, 13, and 14–18
were evaluated against M. tuberculosis H37Ra and M.
tuberculosis H37Rv strains following earlier protocols
(Collins and Franzblan, 1997; Saito et al., 1991). The
results are depicted in Table 1. As evident from Table 1
among all the compounds screened, except compounds 7
and 12, all were active against the virulent strain, M.
tuberculosis H37Rv with MIC values ranging from
12.5–1.56 lg/ml, while these compounds were inactive
against the avirulent strain, indicating the selectivity of
these compounds toward virulent strain only. Among the
active compounds, only three compounds 15, 16, and
17 from 4-(1-(2,2-dimethylchroman-6-yl)-3-phenylprop-2-
ynyl) cyclic amines series showed potent antitubercular
activity with MIC of 6.12, 1.56, and 3.12, respectively.
Thus, the most potent compound of the series, compound
16 (MIC 1.56 lg/ml) opens up new door to optimize this
Further, in order to see the antitubercular activity pro-
files in the hybrid compounds of three moieties the acety-
lenes, chroman, and cyclic amines, a three component
reactions of the above chromanyl carbaldehyde 5 with
different acetylenes and cyclic amines in the presence of
zinc(II) acetate (Ramu et al., 2007) were carried out sep-
arately to get the desired 4-(1-(2,2-dimethylchroman-6-yl)-
3-phenylprop-2-ynyl) cyclic amines (14–18) in good yields
(Scheme 5).
Scheme 5 Synthesis of 4-(1-
(2,2-dimethylchroman-6-yl)-3-
phenylprop-2-ynyl) cyclic
amines (14–18)
123

1518
Med Chem Res (2011) 20:1515–1522
General procedure for preparation of benzylidene ethyl
Table 1 Antitubercular activity of synthesized compounds 7–9, 12,
13, and 14–18 against M. tuberculosis H37Ra and M. tuberculosis
H37Rv
glycinates (1–4)
S. No. Compound
MIC (lg/ml) against MIC (lg/ml) against
To a solution of ethyl glycinate hydrochloride salt (2 eq.)
and anhydrous MgSO4 in dry CH2Cl2 was added aromatic
aldehydes (1 eq.), and the reaction was stirred for 3–4 h at
ambient temperature. After the completion of the reaction,
the reaction mixture was filtered and concentrated under
reduced pressure to get the desired benzylidene ethyl gly-
cinates (1–4). The freshly prepared benzylidine ethyl gly-
cinates (1–4) were used as such.
M. tuberculosis
H37Rv
M. tuberculosis
H37Ra
1
7
[12.5
12.5
12.5
[12.5
12.5
12.5
6.25
1.56
3.12
NDa
0.75
[12.5
[12.5
[12.5
[12.5
[12.5
[12.5
[12.5
[12.5
[12.5
[12.5
–
2
8
3
9
4
12
5
13
6
14
Preparation of 2,2-di-methyl chroman-6-
7
15
carbaldehyde (5)
8
16
9
17
To a stirring solution of 4-hydroxybenzaldehyde (1 g,
8.19 mmol), orthophosphoric acid (0.94 ml, 16.39 mmol)
in petroleum ether (10 ml) was added isoprene (1.64 ml,
16.39 mmol) at 0°C. The reaction mixture was stirred at
room temperature for 16 h. After completion of reaction
(TLC), the reaction mixture was poured into beaker con-
taining crushed ice and sodium bicarbonate and extracted
with ethyl acetate. The organic layer was dried over
sodium sulfate then concentrate under reduced pressure.
Purification of the residue by silica gel chromatography
(EtOAc/n-hexane, 1:3) provided 2,2-di-methyl chroman-6-
10
11
12
a
18
Isoniazid
Ethambutol 3.25
–
ND not done, MIC minimum inhibitory concentration
series for new class of antituberculars. Further, the com-
pounds being specific to the virulent strains only, also point
out the target important for infective mycobacteria, which
is yet to be determined.
In conclusion, we have synthesized hybrid molecules
with chroman, pyrrolidine, and cyclic amines as combina-
tion of pharmacophores using either (3 ? 2) cycloaddition
or three component reaction. The compounds were screened
against avirulent and virulent strains of M. tuberculosis.
Three of the compounds 15, 16, and 17 displayed MIC in
the range of 6.25–1.56 lg/ml, a criterion for further opti-
mization of the series for new antitubercular agents.
1
carbaldehyde 5 as liquid, 0.8 g, 51.3%. H NMR (CDCl3,
300 MHz): d 1.35 (s, 6H, CH392), 1.81–1.85 (m, 2H,
CH2), 2.82 (t, 2H, J = 6.7 Hz, OCH2), 6.85 (d, 1H,
J = 9.0 Hz, ArH), 7.58–7.61(m, 2H, ArH), 9.80 (s, 1H,
CHO).
Preparation of (E)-2,2-dimethyl-6-(2-nitrovinyl)
chroman (6)
Experimental section
To a stirred solution of 2,2-dimethylchroman-6-carbalde-
hyde 5 (1 g, 5.26 mmol), nitromethane (5 ml, as reagent
and as solvent), ammonium acetate (0.41 g, 5.26 mmol),
and acetic acid (1 ml) were heated at 80°C for 4 h. After
completion of reaction (TLC), the reaction mixture was
poured onto ice; excess of acetic acid was neutralized by
sodium bicarbonate extracted with ethyl acetate. The
organic layer was dried (Na2SO4) and concentrated under
reduced pressure to get compound 6 as syrup. Yield 0.8 g
(65.23%). FT-IR (KBr, cm-1) 1657, 1256; 1H NMR
(200 MHz, CDCl3) d 1.35 (s, 6H, C(CH3)2), 1.86 (t, 2H,
J = 6.4 Hz, CH2), 2.82 (t, 2H, J = 6.4 Hz, CH2), 6.80 (d,
1H, J = 8.3 Hz, ArH), 7.25–7.29 (m, 2H, ArH), 7.42 (d,
1H, J = 13.4 Hz, =CH), 7.85 (d, 1H, J = 13.4 Hz, =CH);
13C NMR (50 MHz, CDCl3) d 22.6 (CH2), 27.3 (CH3),
32.8 (CH2), 118.9 (ArCH), 122.1 (ArC), 129.0 (ArCH),
131.7, 135.0, 139.4 (ArCH), 158.4 (ArC); ESMS (m/z):
234 [M ? H]?.
Chemistry
Commercially available reagent grade chemicals were used
as received. All the reaction were followed by TLC on E.
Merck Kieselgel 60 F254, with detection by UV light,
spraying a 20% KMnO4 aq solution. Column chromatogra-
phy was performed on silica gel (60–120 mesh and 100–200
mesh, E. Merck). IR spectra were recorded as thin films or in
KBr soln with
a Perkin Elmer Spectrum RX—1
(4000–450 cm-1) spectrophotometer. 1H and 13C NMR
spectra were recorded on a Brucker DRX-300 in CDCl3.
Chemical shift values are reported in ppm relative to TMS
(tetramethylsilane) as internal reference, unless otherwise
stated, s (singlet), d (doublet), t (triplet), m (multiplet); J in
hertz. ESI mass spectra were performed using Quattro II
(Micromass).
123

Med Chem Res (2011) 20:1515–1522
1519
Preparation of 2-(4-methoxyphenyl)-3-nitro-2H-
Ethyl-3-(2,2-dimethylchroman-6-yl)-4-nitro-5-
chromene (11)
phenylpyrrolidine-2-carboxylate (8)
To a stirred solution of (E)-1-methoxy-4-(2-nitrovinyl)
benzene 10 (1 g, 5.58 mmol), salicylaldehyde (0.88 g,
6.13 mmol), 0.242 ml of DBU (30 mol %) was added at
room temperature. After completion of reaction (TLC), the
reaction mixture was extracted with ethyl acetate. The
organic layer was dried (Na2SO4) and concentrated under
reduced pressure to get compound 11 as yellow solid. Yield
It was obtained by the reaction of compound 6 (0.5 g,
2.14 mmol), [(benzylidene) amino]-acetic acid ethyl ester
2 (0.41 g, 2.14 mmol) and DBU–LiBr (1:1, 10 mol%) as
liquid, 0.40 g, in 43.9% yield. FT-IR (KBr, cm-1) 3401,
1
1728, 1603; H NMR (200 MHz, CDCl3) d 0.82–1.34 (m,
9H, OCH2CH3 and C(CH3)2), 1.84 (t, J = 7.6 Hz, 2H,
CH2), 2.73 (t, 2H, J = 7.7 Hz, CH2), 3.98–4.06 (m, 2H),
4.24–4.32 (m, 2H, OCH2), 4.67 (m, 1H, CH), 5.17 (d, 1H,
J = 2.6 Hz, CH), 6.75 (d, 1H, J = 8.2 Hz, ArH), 6.96 (d,
2H, J = 9.2 Hz, ArH), 7.25–7.43 (m, 5H, ArH); 13C NMR
(50 MHz, CDCl3) d 13.92, 14.68 (CH3), 22.9 (CH2), 27.3,
(CH3), 33.07 (CH2), 61.93 (OCH2), 68.04 (CH), 80.18 (C),
97.58 (CH), 118.44 (ArCH), 121.80 (ArC), 126.58 (ArCH),
128.44, 128.11 (ArC), 128.80, 129.09, 129.20 (ArCH),
130.01, 135.08, 139.09 (ArC), 154.31 (ArC), 171.8
(COOEt); ESMS (m/z): 425 [M ? H]?.
1
1.3 g (82.2%). FT-IR (KBr, cm-1) 1657, 1256; H NMR
(200 MHz, CDCl3) d 3.75 (s, 3H, OCH3), 6.51 (s, 1H, H-
2), 6.79–6.85 (m, 3H, ArH), 6.98–7.02 (m, 1H, ArH),
7.25–7.34 (m, 4H, ArH), 8.03 (s, 1H, H-4); ESMS (m/z):
234 [M ? H]?.
General procedure for preparation of compounds (7, 8,
9, 12, and 13)
To a stirring solution of DBU (10 mol%) and LiBr
(10 mol%) in acetonitrile was added [(benzylidene)amino]-
acetic acid ethyl ester (1–4, 1 eq.) at 0°C and stirring con-
tinued for further 30 min and followed by addition of
compound 3 or compound 8 (1 eq.). After complete addi-
tion, the reaction mixture was stirred at room temperature
for further 1 h. After completion of the reaction (TLC), the
reaction mixture was extracted with ethyl acetate
(29 70 ml); the organic layer was dried (anh. Na2SO4) and
evaporated under reduced pressure to get a crude product.
The latter was chromatographed (SiO2 column, 60–120
mesh) using a gradient of hexane: ethyl acetate (6:4) to give
the desired compounds (7, 8, 9, 12, and 13).
Ethyl-3-(2,2-dimethylchroman-6-yl)-4-nitro-5-
(3-nitrophenyl)pyrrolidine-2-carboxylate (9)
It was obtained by the reaction of compound 6 (0.5 g,
2.14 mmol), [(3-nitrobenzylidene)-amino]-acetic acid ethyl
ester 3 (0511 g, 2.14 mmol), and DBU–LiBr (1:1,
10 mol%) as liquid, 0.42 g, in 42.2% yield. FT-IR (KBr,
1
cm-1) 3422, 1727, 1609; H NMR (200 MHz, CDCl3) d
1.26–1.34 (m, 9H, OCH2CH3 and C(CH3)2), 1.77 (t,
J = 6.6 Hz, 2H, CH2), 2.74 (t, 2H, J = 6.6 Hz, CH2),
4.09–4.11 (m, 2H), 4.25–4.32 (m, 2H, OCH2), 4.99 (d, 1H,
CH), 5.24 (d, 1H, J = 3.7 Hz, CH), 6.74 (d, 1H,
J = 8.1 Hz, ArH), 6.96 (m, 2H, ArH), 7.54–7.58 (d, 1H,
J = 7.9 Hz, ArH), 7.70 (d, 1H, J = 8.14 Hz, ArH), 8.16
(d, 1H, J = 8.17 Hz, ArH), 8.28 (s, 1H, ArH); 13C NMR
(50 MHz, CDCl3) d 14.61 (CH3), 22.92 (CH2), 27.30,
27.34 (CH3), 33.03 (CH2), 62.02 (OCH2), 66.42, 67.33,
74.84 (CH), 96.76 (CH), 118.53 (ArCH), 121.94 (ArC),
122.67, 124.00, 126.55 (ArCH), 130.07, 132.78 (ArCH),
138.02, 148.70, 154.44 (ArC), 171.49 (COOEt); ESMS (m/
z): 470 [M ? H]?.
Ethyl-3-(2,2-dimethylchroman-6-yl)-4-nitro-5-
(4-methoxyphenyl)pyrrolidine-2-carboxylate (7)
It was obtained by the reaction of compound 6 (0.5 g,
2.14 mmol), [(4-methoxybenzylidene) amino]-acetic acid
ethyl ester 1 (0.47 g, 2.14 mmol), and DBU–LiBr (1:1,
10 mol%) as liquid, 0.65 g, in 66.6% yield. FT-IR (KBr,
cm-1) 1657, 1730, 3402; 1H NMR (200 MHz, CDCl3) d 0.87
(t, 3H, J = 7.1 Hz, OCH2CH3), 1.22–1.33 (m, 6H,
C(CH3)2), 1.79 (m, 2H, CH2), 2.16 (bs, 1H, NH), 2.75 (t, 2H,
J = 6.7 Hz, CH2), 3.75–3.82 (m, 5H, OCH3 and CH92),
4.27–4.32 (m, 2H, OCH2), 4.65 (d, 1H, J = 8.5 Hz, CH),
5.11 (m, 1H, CH), 6.70 (d, 1H, J = 8.2 Hz, ArH), 6.89–6.96
(m, 4H, ArH), 7.48 (d, 2H, J = 8.7 Hz); 13C NMR (50 MHz,
CDCl3) d 14.68 (CH3), 22.8 (CH2), 27.3, 27.2 (CH3), 33.14
(CH2), 55.4 (OCH3), 61.28 (OCH2), 64.36, 67.53 (CH),
95.30 (C), 114.50, 114.80 (ArC), 117.98 (ArCH), 121.13
(ArC), 127.20 (ArCH), 128.31 (ArC), 128.53, 129.30
(ArCH), 129.96 (ArC), 154.31, 160.42 (ArC), 172.11
(COOEt); ESMS (m/z): 455 [M ? H]?.
Ethyl-4-(4-methoxyphenyl)-3a-nitro-3-
(4-methoxyphenyl)-1,2,3,3a,4,9b-hexahydrochromeno
[3,4-c]pyrrole-1-carboxylate (12)
It was obtained by the reaction of compound 11 (0.5 g,
1.76 mmol), [(4-methoxybenzylidene) amino]-acetic acid
ethyl ester (0.39 g, 1.76 mmol), and DBU–LiBr (1:1,
10 mol%) as white solid, m. p. 125°C, 0.54 g, in 60.8%
yield. FT-IR (KBr, cm-1) 3431, 1729, 1596; 1H NMR
(200 MHz, CDCl3) d 1.29 (t, 3H, J = 7.2 Hz, CH3),
3.72–3.79 (m, 7H, OCH392 and CH), 4.22–4.32 (q, 2H,
123

1520
Med Chem Res (2011) 20:1515–1522
J = 7.14 Hz, OCH2CH3), 5.38–5.41 (m, 2H, CH92), 6.01
(s, 1H, CH), 6.67–7.12 (m, 11H, ArH), 8.16 (d,
J = 8.0 Hz, ArH); ESMS (m/z): 505 [M ? H]?.
4.65 (s, 1H, CH), 6.71 (d, 1H, J = 8.2 Hz, ArH), 7.25–7.32
(m, 5H, ArH), 7.46–7.51 (m, 2H, ArH); 13C NMR
(50 MHz, CDCl3) d 23.00 (CH2), 27.36 (CH3), 32.24
(CH2), 50.29 (NCH2), 62.03 (CH), 67.52 (OCH2), 86.07,
88.48 (C:C), 117.38 (ArCH),120.71, 123.59 (ArC),
128.08, 128.64, 129.06, 129.96, 132.21 (ArCH), 154.04
(ArC); ESMS (m/z): 361 [M ? H]?.
Ethyl-4-(4-methoxyphenyl)-3a-nitro-3-(4-nitrophenyl)-
1,2,3,3a,4,9b-hexahydrochromeno[3,4-c]pyrrole-1-
carboxylate (13)
It was obtained by the reaction of compound 11 (0.5 g,
1.76 mmol), [(4-nitrobenzylidene)amino]-acetic acid ethyl
1-(1-(2,2-dimethylchroman-6-yl)-3-phenylprop-2-
ynyl)piperidine (15)
ester
4 (0.41 g, 1.76 mmol), and DBU–LiBr (1:1,
10 mol%) as white solid, m. p. 179–180°C, 0.49 g, in
54.5% yield. FT-IR (KBr, cm-1) 3385, 1740, 1602, 1545;
1H NMR (200 MHz, CDCl3) d 1.50 (t, 3H, J = 7.1 Hz,
CH3), 2.91 (m, 1H, NH), 3.70 (s, 3H, OCH3), 4.06 (d, 1H,
J = 3.7 Hz, CH), 4.35 (q, 2H, J = 7.08 Hz, OCH2CH3),
4.98 (s, 1H, CH), 5.41 (s, 1H, CH), 6.60 (d, 2H,
J = 8.6 Hz, ArH), 6.76 (d, 1H, J = 7.9 Hz, ArH),
6.96–7.19 (m, 5H, ArH), 7.46–7.55 (m, 2H, ArH), 8.19 (d,
2H, J = 8.6 Hz, ArH); 13C NMR (50 MHz, CDCl3) d
14.76 (CH3), 45.34, 55.55, 55.54 (OCH3), 62.69 (OCH2),
68.95, 75.58 (CH), 114.40, 118.77 (ArCH), 123.82, 124.42,
128.65, 129.22, 129.56, 129.98 (ArCH), 142.42, 149.03,
150.30, 160.44 (ArC), 172.68 (COOEt); ESMS (m/z): 520
[M ? H]?.
It was obtained by the reaction of compound 5 (0.5 g,
2.63 mmol), piperidine (0.34 ml, 3.42 mmol), phenylacet-
ylene (0.43 ml, 3.9 mmol), and Zn(OAc)2Á2H2O (0.057 g,
0.263 mmol) as yellow liquid, 0.79 g, in 84.6% yield. FT-
1
IR (KBr, cm-1) 2972, 2932, 2854, 1588, 1492; H NMR
(200 MHz, CDCl3) d 1.32 (s, 6H, C(CH3)2), 1.40–1.48 (m,
6H, CH2 piperidine ring) 1.75 (t, 2H, J = 6.7 Hz, CH2),
2.53–2.55 (m, 4H, –CH2NCH2–), 2.74 (t, 2H, J = 6.7 Hz,
CH2), 4.66 (s, 1H, CH), 6.70 (d, 1H, J = 8.3 Hz, ArH),
7.24–7.31 (m, 5H, ArH), 7.46–7.51 (m, 2H, ArH); 13C
NMR (50 MHz, CDCl3) d 23.00, 24.96, 26.61 (CH2), 27.41
(CH3), 33.33 (CH2), 51.04 (NCH2), 62.34 (CH), 74.44,
87.04, 87.91 (C:C), 117.18 (ArCH), 120.47, 123.99
(ArC), 127.98, 128.25, 28.59, 129.84, 129.91,132.21
(ArCH), 153.79 (ArC); ESMS (m/z): 362 [M ? H]?.
General procedure for preparation
of compound (14–18)
1-(1-(2,2-dimethylchroman-6-yl)non-2-ynyl)piperidine
(16)
A
solution of alkyne (1.5 mmol), Zn(OAc)2Á2H2O
(0.1 mmol), aldehyde (1.0 mmol), and amine (1.3 mmol)
in toluene was taken in a round-bottomed flask and inserted
into a preheated oil bath (120°C bath temperature) and
stirring continued for given time. After completion of the
reaction (as monitored by TLC), the reaction mixture was
diluted with aq NH4Cl (2.5 ml) and stirred for 5 min. The
aqueous layers were extracted with diethyl ether, dried over
Na2SO4 and concentrated to give the crude product which
was further purified by column chromatography on silica
gel (ethylacetate/hexane = 1:6) to afford the correspond-
ing pure propargylamine.
It was obtained by the reaction of compound 5 (0.5 g,
2.63 mmol), piperidine (0.297 ml, 3.42 mmol), octyne
(0.58 ml, 3.9 mmol), and Zn(OAc)2Á2H2O (0.057 g,
0.263 mmol) as yellow liquid, 0.84 g, in 88.0% yield. FT-
IR (KBr, cm-1) 2931, 2856, 1656, 1584; 1H NMR
(200 MHz, CDCl3) d 0.86 (t, 3H, J = 6.5 Hz, CH3), 1.32
(s, 6H, C(CH3)2), 1.38–1.45 (m, 14H), 1.75 (t, 2H,
J = 6.6 Hz, CH2), 2.26 (m, 2H, CH2), 2.44 (m, 4H,
–CH2NCH2–), 2.73 (t, 2H, J = 6.6 Hz, CH2), 4.40 (s, 1H,
CH), 6.66 (d, 1H, J = 8.2 Hz, ArH), 7.17–7.18 (m, 2H,
ArH); 13C NMR (50 MHz, CDCl3) d 14.51 (CH3), 19.27,
22.99, 23.04, 25.00, 29.02, 29.49, 31.79, 33.33, 50.86
(CH2), 26.57 (CH3), 61.91(CH), 74.35, 87.75 (C:C),
116.98 (ArCH), 120.24 (ArC), 127.97, 129.81 (ArCH),
130.53, 153.56 (ArC). ESMS (m/z): 368 [M ? H]?.
4-(1-(2,2-dimethylchroman-6-yl)-3-phenylprop-2-
ynyl)morpholine (14)
It was obtained by the reaction of compound 5 (0.5 g,
2.63 mmol), morpholine (0.297 ml, 3.42 mmol), phenyl-
acetylene (0.43 ml, 3.9 mmol), and Zn(OAc)2Á2H2O
(0.057 g, 0.263 mmol) as yellow liquid, 0.79 g, in 84.2%
yield. FT-IR (KBr, cm-1) 2927, 1697, 1618, 1533; 1H
NMR (200 MHz, CDCl3) d 1.33 (s, 6H, C(CH3)2), 1.83 (t,
2H, J = 6.6 Hz, CH2), 2.57–2.65 (m, 4H, –CH2NCH2–),
2.75 (t, 2H, J = 6.7 Hz, CH2), 3.69 (t, 4H, –CH2OCH2–),
4-(1-(2,2-dimethylchroman-6-yl)oct-
2-ynyl)morpholine (17)
It was obtained by the reaction of compound 5 (0.5 g,
2.63 mmol), morpholine (0.297 ml, 3.42 mmol), heptyne
(0.52 ml, 3.9 mmol), and Zn(OAc)2Á2H2O (0.057 g,
0.263 mmol) as yellow liquid, 0.75 g, in 80.8% yield.
123

Med Chem Res (2011) 20:1515–1522
1521
FT-IR (KBr, cm-1) 2934, 2864, 1670, 1576; 1H NMR
(200 MHz, CDCl3) d 0.88 (t, 3H, J = 7.0 Hz, CH3),
1.32–1.58 (m, 12H, C(CH3)2, CH293), 1.75 (t, 2H,
J = 6.6 Hz, CH2), 2.26 (m, 2H, CH2), 2.49 (m, 4H,
–CH2NCH2–), 2.73 (t, 2H, J = 6.6 Hz, CH2), 3.66 (m, 4H,
–CH2OCH2), 4.39 (s, 1H, CH), 6.67 (d, 1H, J = 8.1 Hz,
ArH), 7.18–7.22 (m, 2H, ArH); 13C NMR (50 MHz,
CDCl3) d 14.44 (CH3), 19.19, 22.59, 22.97, 29.13, 30.09,
31.56, 33.28, 50.14 (CH2), 27.35 (CH3), 61.64 (CH), 67.47
(CH2), 74.44, 76.37 (C:C), 117.19 (ArCH), 120.47 (ArC),
128.00, 129.89 (ArCH), 153.86 (ArC). ESMS (m/z): 356
[M ? H]?.
inhibition as compared with control) at this concentration
are then tested at six serial dilutions starting from 50 to
1.56 lg/ml.
Activity against M. tuberculosis H37Rv strain
Drug susceptibility and determination of MIC of the test
compounds/drugs against M. tuberculosis H37Rv were
performed by agar microdilution method where twofold
dilutions of each test compound were added into 7H10 agar
supplemented with OADC and organism. A culture of M.
tuberculosis H37Rv growing on L–J medium was har-
vested in 0.85% saline with 0.05% Tween-80. A suspen-
sion of 1 mg/ml concentration of extracts/compounds was
prepared in DMSO. This suspension was added to (in
tubes) 7H10 Middle Brook’s medium (containing 1.7 ml
medium and 0.2 ml OADC supplement) at different con-
centrations of compound keeping the volume constant, i.e.,
0.1 ml. Medium was allowed to cool by keeping the tubes
in slanting position. These tubes were then incubated at
37°C for 24 h followed by streaking of M. tuberculosis
H37Rv (5–104 bacilli per tube). These tubes were then
incubated at 37°C. Growth of bacilli was seen after 30 days
of incubation. Tubes having the compounds were com-
pared with control tubes where medium alone was incu-
bated with H37Rv. The concentration at which complete
inhibition of colonies occurred was taken as active con-
centration of test compound.
4-(1-(2,2-dimethylchroman-6-yl)non-
2-ynyl)morpholine (18)
It was obtained by the reaction of compound 5 (0.5 g,
2.63 mmol), morpholine (0.297 ml, 3.42 mmol), octyne
(0.58 ml, 3.9 mmol), and Zn(OAc)2Á2H2O (0.057 g,
0.263 mmol) as yellow liquid, 0.74 g, in 76.5% yield. FT-IR
(KBr, cm-1) 2931, 2857, 1585, 1494; 1H NMR (200 MHz,
CDCl3) d 0.86 (t, 3H, J = 6.6 Hz, CH3), 1.32–1.57 (m, 14H,
C(CH3)2, CH294), 1.75 (t, 2H, J = 6.6 Hz, CH2), 2.26 (m,
2H, CH2), 2.49 (m, 4H, –CH2NCH2–), 2.73 (t, 2H,
J = 6.6 Hz, CH2), 3.66 (t, 4H, J = 4.22 Hz, –CH2OCH2–),
4.39 (s, 1H, CH), 6.67 (d, 1H, J = 8.2 Hz, ArH), 7.17–7.18
(m, 2H, ArH); 13C NMR (50 MHz, CDCl3) d 14.51 (CH3),
19.24, 23.00, 29.04, 29.41, 31.75, 33.27, 50.14 (CH2), 27.35
(CH3), 61.63 (CH), 67.47 (CH2), 74.35 (C:C), 117.19,
128.01; ESMS (m/z): 370 [M ? H]?.
Acknowledgments Surendra, Vivek, and Sarvesh are thankful to
CSIR New Delhi for award of SRF and RA, respectively. We sin-
cerely acknowledge the financial assistance from DRDO New Delhi.
This is CDRI communication No. 7853.
Biological activity
Activity against M. tuberculosis H37Ra strain
References
Ahluwalia VK, Arora KK (1981) Nuclear isoprenylation of polyhy-
droxy acetophenones: acid catalysed condensation with isoprene.
Tetrahedron 37:1437–1439
Annunziata R, Clinquini M, Cozzi F, Raimondi L, Pilati T (1991)
1,3-dipolar cycloaddition reactions of azomethine ylides on
enantiomerically pure (E)-c-alkoxy-a,b-unsaturated esters. Tet-
rahedron Asymmetry 2:1329–1342
Babu KS, Raju BC, Praveen B, Kishore KH, Murty US, Rao JM
(2003) Microwave assisted synthesis and antimicrobial activity
of 2,2-dimethylchromenes. Heterocycl Commun 9:519–526
Brown CW, Shengquan L, Klucik J, Berlin KD, Brennan PJ, Kaur D,
Benbrook DM (2004) Novel heteroarotinoids as potential
All of the synthesized compounds were evaluated for their
efficacy against M. tuberculosis H37Ra at active concen-
tration ranging from 50 lg/ml to MIC using twofold
dilutions in the initial screen. Log phase culture of M.
tuberculosis H37Ra is diluted so as to give final OD
550 nm of 0.05 in Sauton’s medium. In 96-well white
plates, 190 ml of culture is dispensed in each well. A
dimethyl sulfoxide (DMSO) solution of test compounds is
dispensed into 96-well plates so as to make final test
concentration of 25 mg/ml (5 mg test compound is dis-
pensed into 10 ml of DMSO). Then, the plate is incubated
at 37°C/5% CO2 for 5 days. On 5th day, 15 ml Alamar
Blue solution is added to each well of the plate. The plate is
again incubated overnight at 37°C/5% CO2 incubator. The
fluorescence is read on BMG polar star with excitation
frequency at 544 nm and emission frequency at 590 nm.
The compounds, which were found to be active ([90%
antagonists of Mycobacterium bovis BCG.
47:1008–1017
J Med Chem
Cegielski JP, Chin DP, Espinal MA, Frieden TR, Rodriquez Cruz R,
Talbot EA, Weil DE, Zaleskis R, Raviglione MC (2002) The
global tuberculosis situation: progress and problems in the 20th
century, prospects for the 21st century. Infect Dis Clin N Am
16:1–58
Cheng P, Chen JJ, Huang N, Wang RR, Zheng YT, Liang YZ (2009)
Synthesis and anti-human immunodeficiency virus type
1
123

1522
Med Chem Res (2011) 20:1515–1522
activity of (E)-N-phenylstyryl-N-alkylacetamide derivatives.
Molecules 14:3176–3186
Prado S, Ledeit H, Michel S, Koch M, Darbord JC, Cole ST, Tillequin
F, Brodin P (2006) Benzofuro[3,2-f][1]benzopyrans: a new class
of antitubercular agents. Bioorg Med Chem 14:5423–5428
Prado S, Janin YL, Joanis BS, Brodin P, Michel S, Koch M, Cole ST,
Tillequinc F, Bost PE (2007) Synthesis and antimycobacterial
evaluation of benzofurobenzopyran analogues. Bioorg Med
Chem 15:2177–2186
Ramu E, Varala R, Sreelatha N, Adapaa SR (2007) Zn(OAc)2Á2H2O:
a versatile catalyst for the one-pot synthesis of propargylamines.
Tetrahedron Lett 48:7184–7190
Collins LA, Franzblan SG (1997) Microplate alamar blue assay
versus BACTEC 460 system for high-throughput screening of
compounds against Mycobacterium tuberculosis and Mycobac-
terium avium. Antimicrob Agents Chemother 41:1004–1009
Dwivedi N, Dube D, Kukshal V, Srivastava SK, Ramachandran R,
Tripathi RP (2008) NAD? dependent DNA ligase (Rv3014c)
from M tuberculosis: strategies for inhibitor design. Med Chem
Res 17:189–198
Fukushima T, Tanaka M, Gohara M (2000) Benzophenone deriva-
tives, their manufacture with exserohilum & their agricultural
uses. US Patent JP 63, 376, see Chem Abstr 2000, 132, 179673r
Saito H, Tomioka H, Sato K, Emori M, Yamane T, Yamashita K
(1991) In vitro antimycobacterial activities of newly synthesized
benzoxazinorifamycins. Antimicrob Agents Chemother 35:
542–547
¨
Galley G, Liebscher J, Patzel M (1995) Polyfuntionalized pyrrolidines
by stereoslective 1,3-dipolar cycloaddition of azomethine ylides
to chiral enones. J Org Chem 60:5005–5010
Spigelman MK (2007) New tuberculosis therapeutics: a growing
pipeline. J Infect Dis 196:S28–S34
Morphy R, Kay C, Rankovic Z (2004) From magic bullets to designed
multiple ligands. Drug Discov Today 9:641–651
Nicolaou KC, Roecker AJ, Barluenga S, Pfefferkorn JA, Cao GQ
(2001) Discovery of novel antibacterial agents active against
methicillin-resistant Staphylococcus aureus from combinatorial
benzopyran libraries. Chem Bio Chem 2:460–465
Tripathi RP, Tewari N, Dwivedi N, Tiwari VK (2005) Fightingtu-
berculosis: an old disease with new challenges. Med Res Rev
25:93–131
Tsou EL, Chen SY, Yang MH, Wang SC, Cheng TRR, Cheng WC
(2008) Synthesis and biological evaluation of a 2-aryl polyhydr-
oxylated pyrrolidine alkaloid-based library. Bioorg Med Chem
16:10198–10204
¨
Patzel M, Galley G, Jones PG, Charapkowsky A (1993) Synthesis of
enantiomerically pure pyrrolidines by stereospecific cycloaddi-
tion of azomethine ylides with enones. Tetrahedron Lett
34:5707–5710
Viranyi A, Marth G, Dancso A, Blasko G, TTke L, Nyerges M (2006)
3-Nitrochromene derivatives as 2p components in 1,3-dipolar
cycloadditions of azomethine ylides. Tetrahedron 62:8720–8730
Xin He et al (2006) Pyrrolidine carboxamides as a novel class of
inhibitors of enoyl acyl carrier protein reductase from Myco-
bacterium tuberculosis. J Med Chem 49:6308–6323
Pandey J, Dwivedi N, Singh N, Srivastava AK, Tamarkar A, Tripathi
RP (2007) Diastereoselective synthesis of glycosylated prolines
as a-glucosidase inhibitors and organocatalyst in asymmetric
aldol reaction. Bioorg Med Chem Lett 17:1321–1325
123