Antitubercular agents. Part 1: Synthesis of phthalimido- and naphthalimido-linked phenazines as new prototype antitubercular agents

Article abstract of DOI:10.1016/j.bmcl.2005.01.085

The preparation and antitubercular properties of a series of phthalimido- and naphthalimido-linked phenazines are described. Some of these new compounds inhibited the growth of Mycobacterium tuberculosis ATCC 27294, Mycobacterium avium ATCC 49601, Mycobacterium intracellulare ATCC 13950 and some clinical isolates.

Full text of DOI:10.1016/j.bmcl.2005.01.085

Bioorganic & Medicinal Chemistry Letters 15 (2005) 1923–1926
Antitubercular agents. Part 1: Synthesis of phthalimido- and
naphthalimido-linked phenazines as new prototype
antitubercular agents
Ahmed Kamal,a,* A. Hari Babu,a A. Venkata Ramana,a Rakesh Sinha,b
J. S. Yadava and Sudarshan K. Arorab
aDivision of Organic Chemistry-I, Indian Institute of Chemical Technology, Hyderabad 500007, India
bLupin Laboratories Limited, Lupin Research Park, Pune 411042, India
Received 10 December 2004; accepted 29 January 2005
Abstract—The preparation and antitubercular properties of a series of phthalimido- and naphthalimido-linked phenazines are
described. Some of these new compounds inhibited the growth of Mycobacterium tuberculosis ATCC 27294, Mycobacterium avium
ATCC 49601, Mycobacterium intracellulare ATCC 13950 and some clinical isolates.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Tuberculosis is generally considered as the most impor-
tant chronic communicable disease in the world.1 The
disease continues to be one of the major health problems
not only in India but also in other South Asian coun-
tries.2 In the last decade the increase of tuberculosis
coinciding with the AIDS epidemic has resulted in addi-
tional drug resistant isolates of Mycobacterium tubercu-
losis.3 The researchers of drug resistant tuberculosis
have generated a renewal of interest in a strategic search
for prototype leads.4,5
pigmentation, which is the main drawback of these com-
pounds.9,10 In this context a programme was launched
in this laboratory to synthesize new analogues of phen-
azines by linking them to phthalimido and naphtha-
limido moieties through bis alkyl piperazines. The
piperazine system has been incorporated in the linker
spacer keeping in mind the need to improve the solubi-
lity of such new analogues. Phthalimido and naphtha-
limido type of compounds have been reported in the
literature to possess antimicrobial activity.11
Many studies have attempted in the past to develop new
antitubercular compounds to resolve some of the
problems with the currently available antitubercular
drugs. Phenazines have been initially developed as drugs
for mycobacterial infections like tuberculosis and lep-
rosy.6 Clofazimine, the lead compound in this series
has contributed significantly towards the control of
leprosy, particularly for dapsone-resistant bacteria.7,8
Clofazimine has also shown chemical efficacy in tuber-
culosis that is caused by multiple drug resistant strains
in particular. Some of the newer phenazine analogues
such as B746 and B4157 have not only showed increased
antimycobacterial activity but also produced less skin
These new conjugates of phenazine with phthalimido
and naphthalimido moieties have been evaluated for
their in vitro antitubercular activity. There are some re-
ports on the synthesis of the phenazine analogues in the
literature.12 However, the method employing 2-chloro-
nitrobenzene as the starting material has been utilized
for the preparation of piperazine linked phenazine ring
system (6) by a modified procedure.
Synthesis of phthalimido- and naphthalimido-linked
phenazine conjugates 8a–h has been carried out by
employing N-(p-chlorophenyl)-o-phenylenediamine 4,
which has been obtained by reacting o-chloronitrobenz-
ene 1 with p-chloroaniline 2 in presence of K2CO3 in
DMF, the product 3 obtained is then reduced to 4 using
SnCl2Æ2H2O in methanol. The oxidation of 4 in presence
of FeCl3Æ6H2O gave the product 5, which on refluxing
*
Corresponding author. Tel.: +91 40 2719 3157; fax: +91 40 2719
3189; e-mail addresses: ahmedkamal@iict.res.in; ahmedkamal@ins.
iictnet.com
0960-894X/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.01.085

1924
A. Kamal et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1923–1926
Cl
Cl
C2H5
N
N
CH(CH3)2
Cl
N
N
Cl
N
N
H
N
N
H
B746
Clofazimine
CF3
N
Cl
N
C2H5
N
N
CF3
H
B4157
Cl
O
N
N
N
(CH2)2
N
N
()n
N
N
H
Cl
O
n = 0,1,2,3
8a-d
Cl
O
(CH2)2
N
N
N
N
N
()n
N
N
H
Cl
O
n = 0,1,2,3
8e-h
with 1-(2-aminoethyl)piperazine in dioxane gave
the product 6, this upon refluxing with 7a–h in aceto-
nitrile in presence of K2CO3 gave the desired products
8a–h13–15 as illustrated in Scheme 1.
dilution of the compounds that completely inhibited
the growth.
Compounds 8c and 8d having phthalimide linked phen-
azines were the most active compounds with an MIC va-
lue of 1.0 lg/mL against the sensitive strain of M.
tuberculosis and an MIC value of 1.0–4.0 lg/mL against
drug resistant clinical isolates of M. tuberculosis. Com-
pound 8h having naphthalimide linked phenazines dem-
onstrated poor activity (MIC 8.0–16.0 lg/mL) against
sensitive and resistant strains of M. tuberculosis. None
of the compounds were found to have significant activity
against M. avium and M. intracellulare cultures.
All the compounds (8a–h) were evaluated for antimyco-
bacterial activity against three different mycobacteria
(M. tuberculosis ATCC 27294, M. avium ATCC 49601
and M. intracellulare ATCC 13950) species at a concen-
tration of 50, 25 and 12.5 lg by diffusion assay (Table
1). Compounds 8c, 8d and 8h demonstrated good to
mild inhibition of the mycobacterium cultures. The ac-
tive compounds were then assayed for determination
of minimum inhibitory concentration (MIC) against a
variety of M. tuberculosis clinical isolates (drug sensitive
and resistant) in agar dilution assay as per the NCCLS-
M24-T2 recommendations. Briefly, 10 serial twofold
dilutions of the compound/standard drug were prepared
in DMSO and incorporated into Middlebrook7H10
agar medium. Individual M. tuberculosis isolates at
concentration of 1 · 107 CFU/mL were spotted (3–
5 lL/spot) on to the media plates. The plates were sealed
and incubated at 37 ꢁC for 3–4 weeks. Minimum inhibi-
tory concentration (MIC) was recorded as the highest
In conclusion, a novel series of antimycobacterial com-
pounds have been designed and synthesized that demon-
strated significant activity (8c and 8d) against drug
sensitive and resistant M. tuberculosis cultures. The anti-
mycobacterial activity of these two compounds were
better than isoniazid on drug resistant clinical isolates
of M. tuberculosis. These findings clearly indicate that
phthalimide–phenazine conjugates linked through piper-
azine moiety side-armed with alkane spacers exhibit
good antimycobacterial activity compared to their

A. Kamal et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1923–1926
1925
NH
NH
H2N
Cl
NO2
Cl
NO2
Cl
NH2
4
2
Cl
(ii)
(i)
3
1
(iii)
H
N
H
N
NH -(CH ) -
N
2 2
NH
N
N
Cl
2
N
N
Cl
(iv)
NH.HCl
N
(CH2)2
N
NH
O
Cl
Cl
Br-(CH2)n-
N
5
6
(v)
7a-d
O
H
N
N
N
Cl
O
N
O
Br-(CH2)n-
N
(v)
N
N
(CH2)2
()n
N
O
7e-h
O
8a, n=0
8b, n=1
8c, n=2
8d, n=3
H
N
N
N
Cl
N
Cl
O
N
N
(CH2)2
N
()n
8e, n=0
8f, n=1
8g,n=2
8h, n=3
O
Cl
Scheme 1. Reagents and conditions: (i) K2CO3, DMF, reflux, 24 h; (ii) SnCl2, MeOH, reflux, 2 h; (iii) FeCl3Æ6H2O, HCl; (iv) dioxane, reflux, 5 h; (v)
K2CO3, CH3CN, reflux, 48 h.
Table 1. Antimycobacterial activity of compounds 8a–h
Phenazine hybrid
MIC (lg/mL)
M.tuberculosis H37Rv ATCC 27294 M. tuberculosis clinical M. avium ATCC 49601 M. intracellulare ATCC 13950
isolates
Sensitive
Resistant
8a
8b
>16.0
>16.0
1.0
>16.0
>16.0
>16.0
>16.0
>16.0
>16.0
16.0
>16.0
>16.0
8.0
8c
8d
1.0–4.0
1.0–2.0
>16.0
1.0–4.0
1.0–4.0
>16.0
1.0
16.0
8.0
8e
>16.0
>16.0
>16.0
16.0
>16.0
>16.0
>16.0
>16
>16.0
>16.0
>16.0
>16
8f
8g
>16.0
>16.0
8.0–16.0
>16.0
>16.0
8.0–16.0
8h
Isoniazid
0.25
0.125–0.25 8.0–>16.0 >16.0
8.0
naphthalimido counterparts. Additionally, as the alkane
spacer between the piperazine and phthalimide moieties
increase from three to five and six there is enhance-
ment in the activity. This investigation indicates that
there is potential to design and synthesize such type of
hybrids for the development of new antitubercular
compounds.
Acknowledgements
This work was financially supported by the Department
of Science and Technology, New Delhi, India, under the
drugs and pharmaceutical research programme. The
authors A.H.B. and A.V.R. thank CSIR, New Delhi
for the award of research fellowships.

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A. Kamal et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1923–1926
Kazimierczuk, Z. Acta Biochim. Pol. 2000, 47, 87; (d)
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(300 MHz CDCl3) d 1.44–1.55 (m, 4H), 1.7–1.8 (m, 2H),
2.2–2.5 (m, 8H), 2.8–3.0 (m, 4H), 3.62–3.65 (m, 2H), 3.75–
3.80 (m, 2H), 5.6 (s, 1H), 6.3 (s, 1H), 6.8–7.1 (m, 4H), 7.25
(d, J = 7.4Hz, 2H), 7.45 (d, J = 6.9 Hz, 2H), 7.6–7.8 (m,
4H), 7.95–8.20 (m, 4H), 9.5 (br s, 1H); MS (FAB) 759
[M]+.
15. Selected spectral data for compound 8h: 1H NMR
(300 MHz CDCl3) d 1.42–1.53 (m, 2H), 1.6–1.8 (m, 6H),
2.3–2.6 (m, 8H), 2.9–3.0 (m, 2H), 3.45–3.55 (m, 2H), 3.8–3.9
(m, 2H), 5.56 (s, 1H), 6.22 (s, 1H), 6.55–6.65 (m, 4H), 6.92–
7.15 (m, 4H), 7.44–7.55 (m, 4H), 8.23 (d, J = 7.8 Hz, 2H),
8.56 (d, J = 7.0 Hz, 2H), 9.5 (br s, 1H); MS (FAB) 823 [M]+.