Potent 1,3-disubstituted-9H-pyrido[3,4-b]indoles as new lead compounds in antifilarial chemotherapy

Article abstract of DOI:10.1016/S0968-0896(99)00050-4

Substituted 9H-pyrido[3,4-b]indoles (β-carbolines) identified in our laboratory as potential pharmacophore for designing macrofilaricidal agents, have been explored further for identifying the pharmacophore responsible for high order of adulticidal activity. This has led to syntheses and macrofilaricidal evaluations of a number of 1-aryl-9H-pyrido[3,4-b]indole-3-carboxylate derivatives (3-7). The macrofilarical activity was initially evaluated in vivo against Acanthoeilonema viteae. Amongst all the synthesized compounds, only twelve compounds namely 3a, 3c, 3d, 3f, 4c, 4d, 4f, 5a, 6f, 6h, 6i and 7h have exhibited either >90% micro- or macrofilaricidal activity or sterilization of female worms. These compounds have also been screened against Litomosoides carinii and of these only 3f and 5a have also been found to be active. Finally these two compounds have been evaluated against Brugia malayi. The structure activity relationship (SAR) associated with position-1 and 3 substituents in β-carbolines have been discussed. It has been observed that the presence of carbomethoxy at position-3 and an aryl substituent at position-1 in β-carbolines effectively enhance antifilarial activity particularly against A. viteae. Amongst the various compounds screened, methyl 1-(4-methylphenyl)-9H-pyrido[3,4-b]indole-3-carboxylate (4c) has shown highest adulticidal activity and methyl 1-(4-chlorophenyl)-1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indole-3-carboxylate (3a) has shown highest microfilaricidal action against A. viteae at 50mg/kgx5 days (ip). Another derivative of this compound namely 1-(4-chlorophenyl)-3-hydroxymethyl-9H-pyrido[3,4-b]indole (5a) exhibited highest activity against L. carinii at 30mg/kgx5 days (ip) and against B. malayi at 50mg/kgx5 days (ip) or at 200mg/kgx5 days (po). Copyright (C) 1999 Elsevier Science Ltd.

Full text of DOI:10.1016/S0968-0896(99)00050-4

Bioorganic & Medicinal Chemistry 7 (1999) 1223±1236
Potent 1,3-Disubstituted-9H-pyrido[3,4-b]indoles as New Lead
Compounds in Anti®larial Chemotherapyy
Sanjay K. Srivastava,a Alka Agarwal,a Prem M.S. Chauhan,a,* Shiv K. Agarwal,{
Amiya P. Bhaduri,a Som N. Singh,x Nigar Fatimab and Ranjit K. Chatterjeeb
aDivision of Medicinal Chemistry, Central Drug Research Institute, Lucknow 226001, India
bDivision of Parasitology, Central Drug Research Institute, Lucknow 226001, India
Received 10 November 1998; accepted 29 January 1999
AbstractÐSubstituted 9H-pyrido[3,4-b]indoles (b-carbolines) identi®ed in our laboratory as potential pharmacophore for designing
macro®laricidal agents, have been explored further for identifying the pharmacophore responsible for high order of adulticidal
activity. This has led to syntheses and macro®laricidal evaluations of a number of 1-aryl-9H-pyrido[3,4-b]indole-3-carboxylate
derivatives (3±7). The macro®larical activity was initially evaluated in vivo against Acanthoeilonema viteae. Amongst all the syn-
thesized compounds, only twelve compounds namely 3a, 3c, 3d, 3f, 4c, 4d, 4f, 5a, 6f, 6h, 6i and 7h have exhibited either >90%
micro- or macro®laricidal activity or sterilization of female worms. These compounds have also been screened against Litomosoides
carinii and of these only 3f and 5a have also been found to be active. Finally these two compounds have been evaluated against
Brugia malayi. The structure activity relationship (SAR) associated with position-1 and 3 substituents in b-carbolines have been
discussed. It has been observed that the presence of carbomethoxy at position-3 and an aryl substituent at position-1 in b-carbolines
e€ectively enhance anti®larial activity particularly against A. viteae. Amongst the various compounds screened, methyl 1-(4-
methylphenyl)-9H-pyrido[3,4-b]indole-3-carboxylate (4c) has shown highest adulticidal activity and methyl 1-(4-chlorophenyl)-
1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indole-3-carboxylate (3a) has shown highest micro®laricidal action against A. viteae at 50 mg/
kgÂ5 days (ip). Another derivative of this compound namely 1-(4-chlorophenyl)-3-hydroxymethyl-9H-pyrido[3,4-b]indole (5a)
exhibited highest activity against L. carinii at 30 mg/kgÂ5 days (ip) and against B. malayi at 50 mg/kgÂ5 days (ip) or at 200 mg/
kgÂ5 days (po). # 1999 Elsevier Science Ltd. All rights reserved.
Introduction
derivatives11 and 1,10-dicyano-2-substituted ethylenes12
were identi®ed as potential ®laricides but most of the
compounds exhibited very poor adulticidal response.
Benzimidazole group of anthelmintics exhibit high
order of activity against intestinal helminths but have
not found application for the treatment of tissue dwell-
ing helminths.13,14 Therefore the need arose to identify
structural prototypes associated with macro®laricidal
activity.
The successful treatment of ®lariasis, a disease of many
tropical and subtropical areas, is not possible because of
the nonavailability of macro®laricidal drugs.1±3 The age
old drug diethyl carbamazine (DEC) continues to be the
mainstay of clinical practice despite its well known
de®ciencies.4,5 Ivermectin, a semisynthetic macrocyclic
lactone antibiotic, may take an impact as micro®laricide
for onchocerciasis but it did not irreversibly damage the
adult ®larial worms.6 Although organic arsenical com-
pounds have long been known as good macro-
®laricides,7 their potential toxicity to the host has
prevented their development as useful anti®larial drugs.
Besides these anti®larials, a number of phenoxy-
cyclohexane derivatives,8 2,4,6-substituted triazines,9
5-amino and 5,8-diaminoisoquinolines,10 aplysinoposin
In earlier communications,15±24 the macro®laricidal
activities of 1-substituted and 1,5-/1,6-/1,7- and 1,8-dis-
ubstituted-9H-pyrido[3,4-b]indoles, (III-VII, Fig. 2) and
representatives of pyrido[3,4-b]imidazo[1,2-c0]quin-
azolo[4,5-e] and [4,5-g]indoles (Fig. 1) were reported.
These research activities did not reveal the optimal
structural requirements to evoke very high order of
macro®laricidal activity. In continuation of this work, it
was considered essential to evaluate 1,3-disubstituted-
9H-pyrido[3,4-b]indoles (Fig. 3) because of the reasons
stated later.
Key words: b-Carboline; macro®laricidal; sterilization.
*Corresponding author.
CDRI Communication No. 5795.
Present address: Wochkaradt Research Centre, D-4, MIDC, Chi-
y
{
kalthana Aurangabad, India.
x
Centrally acting agents known to interact with benzo-
diazepine and g-aminobutyric acid (GABA) receptors
Present address: Department of Physiology, DIPAS, Timarpur,
Delhi-54, India.
0968-0896/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved.
PII: S0968-0896(99)00050-4

1224
S. K. Srivastava et al. / Bioorg. Med. Chem. 7 (1999) 1223±1236
structure to activity relationship studies, the corres-
ponding hydrazides were also prepared (Fig. 5).
Chemistry
Our synthetic approach was focused on the preparation
of the key compounds 1-aryl-1,2,3,4-tetrahydro-9H-
pyrido[3,4-b]indoles (3a±i) in order to allow easy ela-
boration of the functional group attached to position 3.
Pictet±Spengler cyclisation31 of l-tryptophan methyl
ester hydrochloride (2) in the presence of the appro-
priate aldehydes (R1CHO) furnished the corresponding
methyl-1-aryl-1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indole-
3-carboxylates (3a±i). Dehydrogenation32 of 3a±i over
sulphur in xylene yielded the respective methyl-1-aryl-
9H-pyrido[3,4-b]indole-3-carboxylates (4a±i) as descri-
bed in Scheme 1.
Figure 1.
Methyl esters (4a±i), chosen as convenient inter-
mediates, were elaborated in three ways (Scheme 2). In
the ®rst, the ester group at position-3 was reduced to its
corresponding alcohol (5a±i) by lithium aluminium hy-
dride (LiAlH4) in dry THF;33 in the second, the ester
was reacted with aqueous ammonia in steel bomb to
provide the respective amides34 (6a±i) and in the third,
compounds 4a, 4c, 4d, 4f, 4h and 4i were reacted with
hydrazine hydrate in ethanol to furnish their corres-
ponding carboxylic acid hydrazides32 (7a, 7c, 7d, 7f, 7h
and 7i).
Figure 2.
Figure 3.
Anti®larial activity
also exhibit anthelmintic activity25±28 and since 3-car-
boxy-b-carbolines (Fig. 4) also exhibit high order of
anity for benzodiazepine receptor,29,30 it was con-
sidered desirable to evaluate the macro®laricidal activ-
ities of esters of 1-substituted-3-carboxy-9H-pyrido-
[3,4-b]indoles as macro®laricidal agents. The details of
this study are presented here. The design of 1,3-di-
substituted-9H-pyrido[3,4-b]indoles (hereafter called
b-carbolines for the sake of convenience) was based on
the earlier experience.15±24 It was observed that phenyl
or thiophene ring at position-1 in b-carboline was
necessary for evoking weak macro®laricidal activity.
The choice of substitutents at position-3 was limited to
ester, amide and hydroxymethyl groups and for speci®c
The micro- and macro®laricidal activities of the synthe-
sized compounds (3±7) were evaluated against L. carinii
in cotton rats (Sigmodon hispidus), A. viteae and B.
malayi in Mastomys coucha as described earlier.35,36
Compounds being insoluble in water were made ®ne
suspensions within 1% Tween 80. Two to three animals
were used for each dose level study and at least two
replicates were used for con®rmation of activity.
Results and Discussion
All the synthesized compounds (3±7) were evaluated for
their anti®larial activity in vivo against A. viteae at
50 mg/kgÂ5 days by intraperitoneal (ip) route and/or
200 mg/kgÂ5 days through oral (po) route in Mast-
omys coucha. The anti®larial activity against A. viteae
are given in Table 1. Compounds, which do not exhibit
micro- or macro®laricidal activity are not described in
Table 1. During the course of discussion if the route of
administration has not been described, the mode of
Figure 4.
Figure 5.

S. K. Srivastava et al. / Bioorg. Med. Chem. 7 (1999) 1223±1236
1225
Scheme 1. Reagents: (i) MeOH, SOCl2; (ii) R1CHO, MeOH, 10% aq Na2CO3; sulpher, xylene re¯ux.
Scheme 2. Reagents: (i) LiAlH4 dry THF, re¯ux, 10% aq NaOH; (ii) aq ammonia, MeOH, 80 ꢀC; (iii) hydrazine hydrate, EtOH, re¯ux.
administration of test compounds should be treated as
intraperitoneal.
also monitored. In situations where the activity was
signi®cantly high, the e€ect of hydrazide at position-3
was also monitored. The active compounds (with at
least 90% micro- and/or macro®laricidal activity or
sterilization of female worms) were short listed and were
subjected for evaluation against L. carinii infection. The
best compound from this short list was ®nally evaluated
against B. malayi infection. The structure to activity
relationship, therefore, relates to activity against A.
viteae infection only.
The other test models used in the present study for eval-
uation of anti®larial activity were L. carinii in cotton
rats and Brugia malayi in M. coucha. A. viteae is meta-
bolically similar to human ®larial parasites which are
anaerobic in nature and therefore, A. viteae in Mast-
omys was used for evaluation of ecacy for anti®larial
activity of all newly synthesized compounds. This model
has also been recommended by WHO for the experi-
mental chemotherapy of ®lariasis.37 L. carinii, a meta-
bolically facultative ®larial species maintained in cotton
rats was earlier used for ecacy evaluation of diethyl-
carbamazine (DEC)38 and was subsequently tested in
human ®larials with success. B. malayi is a target human
®larial parasite and therefore, the use of an experimental
model for evaluating ecacy of this parasite is obvious.
Besides these reasons, the use of three di€erent models
was considered necessary because of the envisaged inter-
actions of the synthesized compounds with GABA recep-
tors. A precise comment on this subject is made later.
Amongst the 4-halosubstituents at position-1 in b-car-
boline, 4-chlorophenyl substituent plays a signi®cant
role in eliciting anti®larial response and particularly,
the tetrahydro pyridine ring along with the ester func-
tion at position-3 was found e€ective. For example,
methyl 1-(4-chlorophenyl)-1,2,3,4-tetrahydro-9H-pyr-
ido[3,4-b]indole-3-carboxylate (3a) exhibited highest
micro®laricidal (94%) and 39% macro®laricidal activity
along with the sterilization of all the surviving female
worms but after its aromatization, the compound (4a)
was found to be devoid of any ®laricidal activity. The
hydroxymethyl derivative (5a) of this compound
showed a wide range of activity by di€erent routes of
administration. For example, it exhibited 76% micro-
and 56% adulticidal activity along with sterilization
of 75% of surviving female worms by ip administra-
tion but by po route it was predominantly macro-
®laricidal (94%) without micro®laricidal activity. The
amide and hydrazide functions (6a and 7a respectively)
at position-3 in b-carboline of this class of compound
The micro and macro®laricidal activities in compounds
with various substituents at position-1 and position-3 in
b-carbolines were monitored as follows: with a parti-
cular substituent at position-1, the e€ect of substituents
such as ester, amide and hydroxymethyl group at
position-3 was monitored. Along with this study the
e€ect of the ester group at position-3 with and without a
tetrahydro pyridine ring on the anti®larial activity was

1226
S. K. Srivastava et al. / Bioorg. Med. Chem. 7 (1999) 1223±1236
Table 1. Anti®larial activity (in %) of 1-aryl-3-substituted-9H-
pyrido[3,4-b]indoles (3±7) against A. viteae at 50 mg/kgÂ5 days ipa
surviving female worms. Compared to these com-
pounds, variations at position-3 in b-carboline with 4-
halophenyl substituent at position-1 by incorporating
amide (6c) or hydrazide (7c) group made the com-
pounds ine€ective against ®larial infection.
Compoundb
Anti®larial activity
mif
maf
Sterl. of ,
3a
3b
3c
3d
3e
3f
3fc
3h
4b
4c
4d
4e
4f
4g
4h
4i
5a
5ac
5b
5c
6a
6d
6e
6f
6h
6i
7h
94
0
0
90
0
0
91
0
0
0
0
0
0
0
0
62
76
0
0
0
39
25
90
0
50
93
0
57
56
100
84
81
94
44
60
45
56
94
75
0
100
0
0
0
0
0
0
0
67
0
100
0
0
0
0
0
75
0
Unlike 4-substituted phenyl substituents at position-1 in
b-carbolines, compounds with 3-halophenyl substituent
at position-1, exhibited distinct type of anti®larial
action. In this class of compounds, it was interesting to
note the e€ect of pyridine ring on anti®larial activity.
For example, the tetrahydro compound 3d, possessing
3-bromophenyl at position-1 in b-carboline, exhibited
signi®cant micro®laricidal activity (90%) which after
aromatization (4d) led to enhanced adulticidal activity
(84%) with complete loss of micro®laricidal activity and
in addition made all the surviving female worms sterile.
The adulticidal activity decreased up to 69% or com-
pletely disappeared after converting 4d into its amide
(6d) and to the hydrazide (7d) derivatives, respectively.
The tetrahydro compound 3e, having 3-¯uorophenyl
substituent at position-1 in b-carboline, exhibited only
weak macro®laricidal activity (50%) but unlike 3d,
adulticidal activity was not only retained but also
increased to 81% after its aromatization to 4e. The 3-
chlorophenyl substituent at position-1 in b-carbolines,
compounds in which the ester was reduced to the cor-
responding hydroxymethyl (5e) group led to complete
loss of biological response while an amide function at
position-3 (6e), unlike 6d, predominantly evoked micro-
®laricidal activity (84%) with 50% sterilization of
surviving female worms. However, none of the com-
pounds, having 3-halosubstituent at position-1 in b-
carboline exerted signi®cant adulticidal response
(>90%) against A. viteae.
0
40
60
0
50
100
0
0
0
0
0
0
0
69
0
86
89
0
84
44
0
93
91
90
0
0
DECd citratee
aIntraperitoneal route.
bCompound numbers 3g, 3i, 4a, 5d±5i, 6b, 6c, 6g, 7a, 7c, 7d, 7f and 7i
are inactive and are not described here; `O'Ðinactive; `,'Ðfemale
worms; mifÐmicro®lariae; mafÐmacro®lariae.
cAt 200 mg/kgÂ5 days po.
dDECÐDiethylcarbamazine.
eAt 350 mg/kgÂ5 days ip.
Amongst the compounds with 2-halophenyl substituent
at position-1 in b-carboline, the 2-chlorophenyl sub-
stituent at position-1 and an ester function at position-3
elicit interesting adulticidal response against A. viteae
and was better than the one with 3-halophenyl sub-
stituent at position-1. In this group of compounds the
role of pyridine ring in b-carboline was not very sig-
ni®cant. For example methyl 1-(2-chlorophenyl)-1,2,3,4-
tetrahydro-9H-pyrido[3,4-b]indole-3-carboxylate (3f)
showed signi®cant adulticidal activity (93%) through
ip route while, by po route, it was micro®laricidal
(91%) with complete loss of adulticidal activity. Aro-
matisation of 3f led to the compound 4f, which exhibi-
ted 94% adulticidal activity and was equipotent to its
parent compound 3f. Its amide derivative, 6f, showed
86% macro- and 44% micro®laricidal activities with
100% sterilization of survived female worms. The
hydroxymethyl compound (5f) and the hydrazide (7f)
were inactive as anti®larial agent. Compounds with 2-
¯uorophenyl substituent at position-1 were inactive
except aromatised drivative 4g which showed 44%
adulticidal activity.
did not exert any signi®cant role. For example, com-
pound 6a exhibited only sterilization of 60% female
worms whereas 7a failed to show any anti®larial
response. On the other hand incorporation of 4-¯uoro-
phenyl substituent at position-1 in b-carboline, irre-
spective of the nature of group present at position-3 led
to low order of anti®larial activity in comparison to
compounds with 4-chlorophenyl substituent at position-
1. The tetrahydro compound 3b showed insigni®cant
macro®laricidal (25%) activity whereas its aromatised
congener 4b caused 56% adulticidal with 67% steriliza-
tion of the surviving female worms. The hydroxymethyl
derivative (5b) exerted 75% adulticidal activity but the
compound with an amide function at position-3 in b-
carboline (6b) failed to show any response.
The ester group at position-3 with 4-methylphenyl sub-
stituent at position-1 in 9H-pyrido[3,4-b]indole, played
a major role for evoking adulticidal activity against A.
viteae. The most potent compound methyl 1-(4-meth-
ylphenyl)-9H-pyrido[3,4-b]indole-3-carboxylate (4c)
caused highest macro®laricidal activity (100%) while its
tetrahydro compound (3c) showed low but signi®cant
adulticidal response (90%). However, the anti®larial
activity of the corresponding hydroxymethyl deriva-
tive (5c) was limited to sterilization of only 40% of the
An overview of the activity data of compounds with
thienyl substituent at position-1 in b-carboline clearly
indicated that unlike the 1-halophenyl substituent, a
thienyl group played a signi®cant role for evoking

S. K. Srivastava et al. / Bioorg. Med. Chem. 7 (1999) 1223±1236
Table 3. Anti®larial activity (in %) of 5a against B. malayi
1227
micro®laricidal response. In general, it was interesting to
note in this class of compounds the insigni®cant role of
either pyridine ring or an ester function at position-3 in
b-carboline for evoking anti®larial activity. The other
derivatives such as hydrazide (7h) and amide (6i) exhib-
ited interesting micro®laricidal response. The tetrahydro
compound having thien-3-yl substituent at position-1
(3h) showed 57% adulticidal activity which remained
almost equipotent (60%) after its aromatisation (4h) but
the hydroxymethyl derivative (5h) did not evoke any
anti®larial response. A major improvement in macro-
®laricidal activity (89%) was recorded for the amide 6h
whereas the hydrazide derivative 7h was only micro-
®laricidal (91%) without the adulticidal activity.
Amongst the compounds with thien-2-yl substituent at
position-1 in b-carboline, the tetrahydro compound (3i)
was inactive while its aromatic congener 4i exhibited
45% adulticidal and 62% micro®laricidal activity. The
hydroxymethyl derivative (5i) of this series of compound
failed to show any biological response but the amide (6i)
exhibited signi®cant micro®laricidal activity (93%). The
hydrazide 7i was devoid of any anti®larial activity.
Dose mg/kgÂ5 days
Route
Anti®larial activity
mif maf Sterl. of ,
50
250
DEC Citrate
ip
po
ip
0
62
56
50
85
69
0
0
90a
aAt 100 mg/kgÂ5 days ip.
activity by ip as well as by po route. At 50 mg/kg Â5
days ip, 5a showed 62% adulticidal activity and 85% of
the surviving female worms were found sterile while at
250 mg/kgÂ5 days po, activities of 5a somewhat
decreased since it exhibited only 56% macro®laricidal
activity and caused 69% sterilization of the surviving
female worms.
A total analysis of the anti®larial activities of b-carbo-
line derivatives reported earlier15±24 and of the present
study clearly indicate two results:
Those compounds which showed signi®cant ®laricidal
action (>90% micro- or macro®laricidal response or
sterilization of female worms), were next examined
against L. carinii in cotton rats at 30 mg/kgÂ5 days
ip. On the basis of this consideration compounds 3a, 3c,
3d, 3f, 4c, 4d, 4f, 5a, 6f, 6h, 6i and 7h were chosen for
testing their anti®larial response against L. carinii and
the results are summarized in Table 2.
(i) b-carboline framework is a pharmacophore for
macro®laricidal activity; and
(ii) the nature of substituents specially at positions-1
and 3 signi®cantly contribute towards the mac-
ro®laricidal ecacy.
The present work also reveals that absorption, distribu-
tion and bioclearance of b-carboline derivatives by po
of administration are substituent dependant. The results
of parallel anti®larial evaluations in vivo against A.
viteae, L. carinii and B. malayi evoke certain specula-
tions which may provide a basis for future study. Ade-
quate evidence25,26 exists that b-carboline-3-carboxylic
acid derivatives interact with GABA receptors and it is
also known27 that GABA receptor is a biochemical tar-
get site for anti®larial compounds. In the light of these
observations, it would be reasonable to presume that
compounds evaluated in the present study also interact
with GABA receptors, which in A. viteae, L. carinii and
B. malayi are either di€erent or have signi®cant di€er-
ence in their population.
Amongst all the twelve compounds screened, only 3f
and 5a were found active and of the two 5a exhibited
more pronounced e€ect against L. carinii than 3f. The
compound 5a, having hydroxymethyl at position-3 and
4-chlorophenyl at position-1 in b-carboline exhibited
95% adulticidal along with 29% micro®laricidal
response and the tetrahydro compound 3f, possessing 2-
chlorophenyl substituent at position-1, showed insignif-
iant macro®laricidal activity (20%) but caused steriliza-
tion of 88% surviving female worms.
Since, 1-(4-chlorophenyl)-3-hydroxymethyl-9H-pyrido-
[3,4-b]indole (5a) and methyl 1-(2-chlorophenyl)-9H-
pyrido[3,4-b]indole-3-carboxylate (3f) showed anti-
®larial activity against L. carinii, they were, therefore,
evaluated for their ecacy against B. malayi by ip and
po route of administrations (Table 3).
The logical next step of the future study would be to
look into the GABA receptors of di€erent human and
experimental ®larial worms. The experimental receptor
model which will be very near to the human parasites
(Brugia malayi and Wuchereria bancrofti) would be of
great value for developing target sites of quick biologi-
cal screening and the results of this study may give
valuable inputs for high throughput screening.
Compound 3f failed to show any activity at 50 mg/kgÂ5
days ip against B. malayi whereas 5a exhibited anti®larial
Table 2. Anti®larial activity (in %) of 3f and 5a against L. carinii at
30 mg/kgÂ5 days ip
Experimental
Chemistry
Compound
Anti®larial activity
mif
maf
Sterl. of ,
The compounds were routinely checked for their purity
by thin layer chromatography (TLC) on silica gel G
and column chromatography separations were carried
out on Merck silica gel (230±400 mesh). Melting point
(mp) were determined in capillary tubes on an electro-
3f
5a
0
29
90a
20
95
0
88
0
0
DEC Citrate
aAt 75 mg/kgÂ5 days ip.

1228
S. K. Srivastava et al. / Bioorg. Med. Chem. 7 (1999) 1223±1236
thermal melting point Toshiniwal CL-03001 apparatus
and are uncorrected. Infrared (IR) spectra were run
on a Backman±Acculab-10 spectrophotometer (nmax in
cm 1). Nuclear magnetic resonance (NMR) spectra
were recorded on a Bruker-400-FT instrument, and
chemical shifts (d in ppm) were reported relative to the
solvent peak (CHCl3 in CDCl3 at 7.23 ppm CH3OH in
CD3OD at 3.4 ppm and DMSO in DMSO-d6 at
2.49 ppm) or TMS. Signals were designated as follows;
s, singlet; bs, broad signal; d, doublet; dd, doublet of
doublet; t, triplet; m, multiplet. EI mass spectra were
recorded on a Jeol-JMS-D-300 spectrometer. Chemical
analyses were carried out on a Carlo±Erba EA 1108
elemental analyzer. Reagents and solvents were pur-
chased from common commercial suppliers and used as
received. Organic solutions were dried over anhydrous
Na2SO4 and concentrated with a Buchi rotary evap-
orator at low pressure. Yields were of puri®ed product
and were not optimized. The physical properties for
compounds are sumarized in Tables 4 and 5.
Table 4. Physico±chemical properties for the methyl 1-aryl-1,2,3,4-
tetrahydro-9H-pyrido[3,4-b]indole-3-carboxylates tested in this study
Compounda
R1
%
mp
Solvent
Formulad
Yieldb ꢀC crystallizationc
3a
90
211
152
A
C19H17N2O2Cl
3b
78
B
C19H17N2O2F
Methyl-1-(4-chlorophenyl)-9H-pyrido[3,4-b]indole-3-car-
boxylate (4a): method A. A suspension of 3a (1.56 g,
4.58 mmol) and sulphur (0.29 g, 9.16 mmol) in xylene
(30 mL) was heated at re¯ux for 8 h; allowed to cool to
room temperature, excess sulphur was ®ltered o€ and
the ®ltrate was concentrated in vacuo. The residue was
crystallized to a€ord 4a, 0.36 g (37%). IR (KBr): 3236,
3010, 2822, 1716, 1600, 1362, 1250 cm 1; MS: m/z
(relative intensity) 338 (M, Cl37, 14.8), 336 (M, Cl35,
3c
87
160
B
C20H20N2O2
3d
3e
98
76
156
106
A
A
C19H17N2O2Br
1
39.9), 278 (100), 214 (20); H NMR (400 MHz, CDCl3):
d 8.9 (s, 1H, H-4), 8.8(bs, 1H, indole NH), 8.25 (d, 1H,
ArH, J=8 Hz), 7.9 (d, 2H, ArH, J=8 Hz), 7.64±7.50 (m,
4H, ArH), 7.4 (t, 1H, ArH, J=8 Hz), 4.06 (s, 3H, OCH3).
C19H17N2O2Cl
Methyl-1-(4-¯uorophenyl)-9H-pyrido[3,4-b]indole-3-car-
boxylate (4b). A suspension of 3b (1.96 g, 6.06 mmol)
and sulphur (0.39 g, 12.12 mmol) in xylene (35 mL) were
reacted in a manner similar to that described for 4a
to a€ord 4b, 1.16 g (81%). IR (KBr): 3320, 3040, 2960,
1720, 1620, 1350, 1250 cm 1; MS: m/z (relative inten-
sity): 320 (M, 1.2), 260 (100), 180 (23.7); 1H NMR
(400 MHz, CDCl3): d 8.88 (s, 1H, H-4), 8.74 (bs, 1H,
indole NH), 8.24 (d, 1H, ArH, J=7 Hz), 8.0±7.9 (m,
2H, ArH), 7.82±7.52 (m, 2H, ArH), 7.4 (t, 1H, ArH,
J=6.67 Hz), 7.3±7.2 (m, 2H, ArH), 4.08 (s, 3H, OCH3).
3f
32
80
209
97
A
B
C19H17N2O2Cl
3g
C19H17N2O2F
Methyl-1-(4-methylphenyl)-9H-pyrido[3,4-b]indole-3-car-
boxylate (4c). Compound (4c) was prepared from 3c
(4.0 g, 12.6 mmol) and sulphur (0.8 g, 25.2 mmol) in xy-
lene (80 mL) by following the method described for 4a,
3.53 g (97.1%), IR (KBr): 3220, 3040, 2980, 1720, 1620,
1340, 1240 cm 1: MS m/z (relative intensity): 318
(M+2, 4.0), 255 (37.4), 160 (53.3); 1H NMR (400 MHz,
CDCl3): d 8.88 (s, 1H, H-4), 8.72 (bs, 1H, indole NH),
8.2 (d, 1H, ArH, J=8 Hz), 7.86 (d, 2H, ArH, J=8 Hz),
7.64±7.52 (m, 2H, ArH), 7.46±7.36 (m, 3H, ArH), 4.06
(s, 3H, OCH3), 2.46 (s, 3H, CH3).
3h
3i
75
57
140
135
C
C
C17H16N2O2S
C17H16N2O2S
aSee ref 9 for method.
Methyl-1-(3-bromophenyl)-9H-pyrido[3,4-b]indole-3-car-
boxylate (4d). Compound 3d (1.20 g, 3.12 mmol) and
sulphur (0.20 g, 6.24 mmol) in xylene (25 mL) was reac-
ted as described for 4a to provide 4d, 0.90 g (76%),
bYield is that obtained from neutralisation step as a ®nal step.
cA=MeOH; B=EtOAc:hexane (7:3); C=EtOH:acetone (2:8).
dAll compounds had elemental analyses within ‹0.4% of theoretical
values.

S. K. Srivastava et al. / Bioorg. Med. Chem. 7 (1999) 1223±1236
1229
Table 5. Physico-chemical properties for the 1-aryl-9H-pyrido[3,4-b]indole-3-carboxylate/hydroxymethyl/carboxamide/carboxylic acid hydrazide
tested in this study
Compounda
R1
R3
% Yieldb
37
mp ꢀ
C
Solvent crystallizationc
A
Formulad
4a
270
C19H13N2O2Cl
4b
4c
81
271
B
B
C19H13N2O2F
97.1
>300
C20H16N2O2
4d
4e
4f
76
80
104
285
249
262
B
A
A
B
C19H13N2O2Br
C19H13N2O2Cl
C19H13N2O2Cl
C19H13N2O2F
99
4g
75.1
4h
4i
95
85
80
210
195
220
A
A
C
C17H12N2O2S
C17H12N2O2S
C18H13N2OCl
5a
(continued)

1230
S. K. Srivastava et al. / Bioorg. Med. Chem. 7 (1999) 1223±1236
Table 5Ðcontd
Compounda
R1
R3
% Yieldb
46.8
mp ꢀ
C
Solvent crystallizationc
D
Formulad
5b
218
C18H13N2OF
5c
56.6
208
C
C19H16N2O
5d
5e
51.3
58.3
176
195
E
C
C18H13N2OBr
C18H13N2OCl
5f
63.1
46.4
165
300
C
C18H13N2OCl
5g
D
C18H13N2OF
5h
5i
56
71
37
102
79
E
E
C
C16H12N2OS
C16H12N2OS
C18H12N3OCl
6a
270
6b
6c
70
38
246
285
F
B
C18H12N3OF
C19H15N3O
(continued)

S. K. Srivastava et al. / Bioorg. Med. Chem. 7 (1999) 1223±1236
1231
Table 5Ðcontd
6d
6e
97
189
B
B
C18H12N3OBr
65
260
C18H12N3OCl
6f
80
81
299
251
B
B
C18H12N3OCl
6g
C18H12N3OF
6h
6i
49
82
72
300
300
235
A
A
G
C16H11N3OS
C16H11N3OS
C18H13N4OCl
7a
7c
40
70
242
135
H
C19H16N4O
7d
G
H
H
C18H13N4OBr
7f
7h
7i
86.6
52
193
250
225
C18H13N4OCl
C16H12N4OS
C16H12N4OS
93.7
H
aSee Experimental for method (A for 4a±i; B for 5a±i; C for 6a±i; D for 7a±i).
bYield is referred to a ®nal step.
cA=acetone:chloroform (8:2), B=hexane:ethanol (8:2), C=acetone, D=EtOAc:hexane (3:7), E=hexane:ethanol (1:9), F=acetone:hexane (5:5),
G=ethanol, H=methanol.
dAll compounds had elemental analyses within ‹0.4% of theoretical values.

1232
S. K. Srivastava et al. / Bioorg. Med. Chem. 7 (1999) 1223±1236
1
IR(KBr): 3320, 3082, 2940, 1740, 1620, 1340, 1240 cm
;
and NH), 8.22 (d, 1H, ArH, J=8 Hz), 7.82 (d, 1H, ArH,
J=4.0 MHz), 7.7±7.52 (m, 4H, ArH), 7.4 (m, 1H, ArH),
4.08 (s, 3H, OCH3).
MS m/z (relative intensity): 382 (M, Br81, 6.1), 380 (M,
Br79, 5.2), 323(64.9), 241(58.4); 1H NMR (400 MHz,
CDCl3): d 8.9 (s, 1H, H-4), 8.72 (bs, 1H, indole NH),
8.24 (d, 1H, ArH, J=8 Hz), 8.12 (s, 1H, ArH), 7.9 (d,
1H, ArH, J=8 Hz), 7.68±7.56 (m, 3H, ArH), 7.48±7.38
(m, 2H, ArH), 4.08 (s, 3H, OCH3).
1-(4-Chlorophenyl)-3-hydroxymethyl-9H-pyrido[3,4-b]-
indole (5a): method B. A solution of 4a (0.4 g, 1.18 mmol)
in dry THF (8 mL) was added dropwise to the stirred
solution of LiAlH4 (0.09 g, 2.37 mmol) in dry THF
(20 mL) at ambient temperature. The reaction mixture
was re¯uxed for 8 h and was allowed to maintain at
room temperature. The complex was decomposed by
10% aq NaOH solution and solid separated was ®lt-
erated, washed with water and then ®lterate was con-
centrated in vacuo. The residue thus obtained was
®ltered, washed with water and crystallized to provide
the 5a, 0.29 g (80%). IR (KBr): 3180, 3060, 2800, 1630,
1490, 1240, 1010, 720 cm 1; MS: m/z (relative intensity):
310 (M, Cl37, 4.5), 308(M, Cl35, 54.9), 306(100),
Methyl-1-(3-chlorophenyl)-9H-pyrido[3,4-b]indole-3-car-
boxylate (4e). Dehydrogenation of 3e (0.86 g, 2.53 mmol)
with sulphur (0.16 g, 5.06 mmol) in xylene (15 mL) using
identical procedure as described for 4a furnished 4e,
0.79 g (80%). IR (KBr): 3340, 3082, 2940, 1760, 1640,
1350, 1250 cm 1: MS: m/z (relative intensity): 338 (M,
Cl37, 1.6), 336(M, Cl35, 5.4), 256(56), 64(100); H NMR
1
(400 MHz, CDCl3): d 8.9 (s, 1H, H-4), 8.72 (bs, 1H, in-
dole NH), 8.24 (d, 1H, ArH, J=8 Hz), 8.1 (s, 1H, ArH),
7.88 (d, 1H, ArH, J=8 Hz), 7.68±7.56 (m, 3H, ArH),
7.5±7.38 (m, 2H, ArH), 4.08 (s, 3H, OCH3).
1
278(47.5); H NMR (400 MHz, CDCl3+DMSO-d6): d
8.46 (bs, 1H, indole NH), 8.12 (d, 1H, ArH, J=8 Hz),
8.1±8.0 (m, 3H, ArH), 7.7±7.49 (m, 4H, ArH), 7.24 (t,
1H, ArH, J=8 Hz), 4.96 (s, 2H, CH2), 3.7 (s, 1H, OH).
Methyl-1-(2-chlorophenyl)-9H-pyrido[3,4-b]indole-3-car-
boxylate (4f). Compound 4f was synthesized from 3f
(1.0 g, 2.94 mmol) and sulphur (0.19 g, 5.88 mmol) in
xylene (18 mL) as described for 4a, 0.98 g (99%). IR
1
1-(4-Fluorophenyl)-3-hydroxymethyl-9H-pyrido[3,4-b]-
indole (5b). Compound 4b (0.38 g, 1.19 mmol) in dry
THF (10 mL) and LiAlH4 (0.09 g, 2.37 mmol) in dry
THF (20 mL) were treated as for 5a to provide 5b, 0.16 g
(46.8%). IR (KBr): 3220, 3040, 2780, 1610, 1500, 1400,
1220, 1040, 740 cm 1; MS m/z (relative intensity): 293
(M+1, 100), 292 (M, 2.0), 122(34.6); 1H NMR
(400 MHz, CDCl3): d 8.42 (bs, 1H, indole NH), 8.14 (d,
1H, ArH, J=8 Hz), 8.04±7.36 (m, 3H, ArH), 7.68±7.46
(m, 3H, ArH), 7.4±7.28 (m, 2H, ArH), 4.48 (s, 2H,
CH2), 3.78 (s, 1H, OH).
(KBr): 3360, 3020, 2940, 1740, 1640, 1340, 1250 cm
;
MS: m/z (relative intensity): 338 (M, Cl37, 4.6), 336 (M,
Cl35, 3.1), 279(70.9), 217(100); 1H NMR (400 MHz,
CDCl3): d 8.9 (s, 1H, H-4), 8.84 (bs, 1H, indole NH),
8.24 (d, 1H, ArH, J=7 Hz), 7.94 (m, 1H, ArH), 7.8 (m,
1H, ArH), 7.7±7.56 (m, 2H, ArH), 7.52±7.38 (m, 3H,
ArH), 4.06 (s, 3H, OCH3).
Methyl-1-(2-¯uorophenyl)-9H-pyrido[3,4-b]indole-3-car-
boxylate (4g). A suspension of 3g (1.45 g, 4.48 mmol) in
xylene (25 mL) was reacted with sulphur (0.29 g,
8.96 mmol) as described for 4a to a€ord 4g, 1.07 g
(75.1%). IR (KBr): 3300, 3040, 2960, 1740, 1660, 1360,
1260 cm 1; MS: m/z (relative intensity): 320 (M, 1.5),
1-(4-Methylphenyl)-3-hydroxymethyl-9H-pyrido[3,4-b]-
indole (5c). Compound 4c (0.51 g, 1.62 mmol) in dry
THF (10 mL) and LiAlH4 (0.13 g, 3.23 mmol) in dry
THF (25 mL) were reacted in a similar manner to that
described for 5a to a€ord 5c, 0.26 g (56.6%). IR
(KBr): 3160, 3040, 2770, 1620, 1500, 1240, 1010,
700 cm 1; MS: m/z (relative intensity): 288(M, 100),
273(50.5), 133(65.3); 1H NMR (400 MHz, CDCl3): d
8.46 (bs, 1H, indole NH), 8.14 (d, 1H, ArH, J=8 Hz),
7.92±7.78 (m, 3H, ArH), 7.6±7.36 (m, 4H, ArH), 7.3 (t,
1H, ArH, J=8 Hz), 4.88 (d, 2H, CH2, J=5 Hz), 3.92 (t,
1H, OH, J=5 Hz), 2.48 (s, 3H, CH3).
1
261 (100), 129 (10.9); H NMR (400 MHz, CDCl3): d
8.94 (s, 1H, H-4), 8.68 (bs, 1H, indole NH), 8.22 (d, 1H,
ArH, J=7.9 Hz), 7.88 (t, 1H, ArH, J=7.5 Hz), 7.56±
7.52 (m, 2H, ArH), 7.5±7.42 (m, 1H, ArH), 7.4±7.3 (m,
3H, ArH), 4.04 (s, 3H, OCH3).
Methyl-1-(3-thienyl)-9H-pyrido[3,4-b]indole-3-carboxyl-
ate (4h). By a similar procedure as described for 4a,
compound 4h was obtained from 3h (2.3 g, 7.37 mmol)
in xylene (45 mL) and sulphur (0.47 g, 14.74 mmol), 1.8 g
(95%). IR (KBr): 3320, 3080, 2980, 1720, 1440, 1340,
1290, 1080 cm 1; MS: m/z (relative intensity): 308 (M,
1-(3-Bromophenyl)-3-hydroxymethyl-9H-pyrido[3,4-b]-
indole (5d). In a manner similar to the preparation of
5a, compound 5d was obtained from 4d (0.36 g, 0.95 mmol)
in dry THF (10 mL) and LiAlH4 (0.07 g, 1.89 mmol) in
dry THF (20 mL) to 0.17 g (51.3%). IR (KBr): 3220,
3060, 2950, 1640, 1430, 1250, 1050, 730 cm 1; MS m/z
(relative intensity): 355 (M+2, 1.55), 276 (100), 245
(61.8); 1H NMR (400 MHz, CD3OD): (8.24±8.1 (m, 2H,
indole NH and ArH), 7.9 (d, 2H, ArH, J=6 Hz), 7.68±
7.46 (m, 4H, ArH), 7.24 (t, 1H, ArH, J=6 Hz), 3.56 (s,
1H, CH2), 3.56 (s, 1H, OH), 3.3 (s, 2H, CH2).
1
1.8), 255(52.4), 160(54.9); H NMR (400 Mhz, CDCl3):
d 8.88 (m, 2H, H-4 indole and NH), 8.22 (d, 1H, ArH,
J=8 Hz), 7.92 (m, 1H, ArH), 7.74 (d, 1H, ArH, J=
4.5 Hz), 7.66±7.5 (m, 3H, ArH), 7.38 (t, 1H, ArH,
J=7 Hz), 4.06 (s, 3H, OCH3).
Methyl-1-(2-thienyl)-9H-pyrido[3,4-b]indole-3-carboxyl-
ate (4i). Compound 3i (1.9 g, 6.09 mmol) in xylene
(35 mL) was dehydrogenated over sulphur (0.39 g,
12.18 mmol) to furnish 4i, 1.6 g (85%). IR (KBr): 3340,
3100, 2980, 1740, 1420, 130, 1250, 1010 cm 1; MS: m/z
(relative intensity): 308 (M, 47.7), 250(100), 160(21.5);
1H NMR (400 MHz, CDCl3): d 8.86 (m, 2H, H-4 indole
1-(3-Chlorophenyl)-3-hydroxymethyl-9H-pyrido[3,4-b]-
indole (5e). Compound 5e was prepared from 4e (0.25 g,
0.74 mmol) in dry THF (12 mL) and LiAlH4 (0.06 g,

S. K. Srivastava et al. / Bioorg. Med. Chem. 7 (1999) 1223±1236
1233
1.48 mmol) in dry THF (15 mL) to 0.14 g (58.3%). IR
(KBr): 3140, 3020, 2920, 1620, 1430, 1230, 1000,
710 cm 1; MS m/z (relative intensity): 310 (M, Cl37,
42.9), 308 (M, Cl35, 100), 280(40.5), 243 (24.5); 1H
NMR (400 MHz, CDCl3): d 8.44 (bs, 1H, indole NH),
8.26 (d, 1H, ArH, J=8 Hz), 8.0±7.86 (m, 3H, ArH),
7.62±7.46 (m, 4H, ArH), 7.34 (t, 1H, ArH, J=8 Hz),
4.48 (d, 2H, CH2, J=5 Hz), 3.7 (t, 1H, OH, J=5 Hz).
(37%). IR (KBr): 3442, 3366, 3220, 1664, 1386,
742 cm 1; MS m/z (relative intensity): 323 (M, Cl37, 9.5),
321 (M, Cl35, 25.7), 278 (100), 242(51.1); 1H NMR
(400 Mhz, CDCl3): d 8.94 (s, 1H, H-4), 8.74 (bs, 1H, in-
dole NH), 8.22 (d, 1H, ArH, J=8 Hz), 8.04 (bs, 1H, NH
of NH2), 7.95 (d, 2H, ArH, J=8 Hz), 7.7±7.5 (m, 4H,
ArH), 7.38 (t, 1H, ArH, J=8 Hz), 5.62 (bs, 1H, NH of
NH2).
1-(2-Chlorophenyl)-3-hydroxymethyl-9H-pyrido[3,4-b]-
indole (5f). In a manner similar to the preparation of
5a, compound 5f was obtained from 4f (0.35 g,
1.04 mmol) in dry THF (15 mL) and LiAlH4 (0.08 g,
2.08 mmol) in dry THF (20 mL) to 0.2 g (63.1%). IR
(KBr): 3220, 3020, 2960, 1620, 1420, 1230, 1040,
710 cm 1; MS m/z (relative intensity): 310 (M, Cl37,
1-(4-Fluorophenyl)-9H-pyrido[3,4-b]indole-3-carboxamide
(6b). Compound 4b (1.4 g, 4.38 mmol) and aq ammonia
(14 mL) in methanol (16 mL) were reacted in a manner
similar to that described for 6a to a€ord 6b, 0.93 g
(70%). IR (KBr): 3420, 3300, 1660, 1370, 720 cm 1; MS
m/z (relative intensity): 305 (M, 5.5), 256 (37), 64(100);
1H NMR (400 MHz, CDCl3): d 8.96 (s, 1H, H-4), 8.66
(bs, 1H, indole NH), 8.22 (d, 1H, ArH, J=8 Hz), 8.04
(bs, 1H, NH of NH2), 8.02±7.94 (m, 2H, ArH), 7.88 (d,
1H, ArH, J=8 Hz), 7.66±7.52 (m, 2H, ArH), 7.48±7.3
(m, 2H, ArH), 5.6 (bs, 1H, NH of NH2).
1
45.3), 308 (M, Cl35, 100), 280(39), 243(27); H NMR
(400 MHz, CDCl3): d 8.52 (bs, 1H, indole NH), 8.48 (d,
1H, ArH, J=8 Hz), 8.26±8.2 (m, 3H, ArH), 8.0±7.9 (m,
2H, ArH), 7.54±7.46 (m, 3H, ArH), 4.88 (s, 2H, CH2),
3.88 (s, 1H, OH).
1-(4-Methylphenyl)-9H-pyrido[3,4-b]indole-3-carboxamide
(6c). By an analogous procedure as described for 6a,
compound 6c was obtained from 4c (1.0 g, 3.16 mmol)
and aq ammonia (10 mL) in methanol (12 mL), 0.36 g
(38%). IR (KBr): 3480, 3380, 3220, 1660, 1370,
740 cm 1; MS m/z (relative intensity): 301 (M, 69.3), 270
1-(2-Fluorophenyl)-3-hydroxymethyl-9H-pyrido[3,4-b]-
indole (5g). Compound 4g (0.20 g, 0.63 mmol) in dry
THF (10 mL) were treated with LiAlH4 (0.05 g,
1.25 mmol) in dry THF (10 mL) as described for 5a
to furnish 5g, 0.08 g (46.4%). IR (KBr): 3398, 2883,
1624, 1560, 1388, 1217, 1024, 748 cm 1; MS m/z (rela-
1
(100), 181 (21.3); H NMR (400 MHz, CDCl3): d 8.92
1
(relative intensity): 292 (M, 1.9), 242 (3.0), 55(100): H
(s, 1H, H-4), 8.7 (bs, 1H, indole NH), 8.22 (d, 1H, ArH,
J=8 Hz), 8.1 (bs, 1H, NH of NH2), 7.9 (d, 2H, ArH,
J=8 Hz), 7.66±7.52 (m, 2H, ArH), 7.48±7.42 (m, 2H,
ArH), 7.38 (t, 1H, ArH, J=8 Hz), 5.6 (bs, 1H, NH of
NH2), 2.5 (s, 3H, CH3).
NMR (400 MHz, CDCl3): d 8.4 (bs, 1H, indole NH),
8.14 (d, 1H, ArH, J=8 Hz), 8.04±7.88 (m, 3H, ArH),
7.56±7.48 (m, 3H, ArH), 7.38±7.24 (m, 2H, ArH), 4.8 (s,
2H, CH2), 3.74 (s, 1H, OH).
1-(3-Thienyl)-3-hydroxymethyl-9H-pyrido[3,4-b]indole
(5h). A solution of 4h (0.23 g, 0.75 mmol) in dry THF
(15 mL) was reacted with LiAlH4 (0.06 g, 1.49 mmol) in
dry THF (15 mL) as for 5a to a€ord 5h, 0.12 g (56%).
IR (KBr): 3240, 2923, 2862, 1625, 1452, 1244, 1645,
746 cm 1; MS m/z (relative intensity): 280 (M, 32.1), 219
(77.4), 42(100); 1H NMR (400 MHz, CDCl3): d 8.2±8.02
(m, 2H, indole NH and ArH), 7.9±7.8 (m, 2H, ArH),
7.7±7.44 (m, 5H, ArH), 4.88 (m, 2H, CH2, J=8 Hz), 3.8
(m, 1H, OH).
1-(3-Bromophenyl)-9H-pyrido[3,4-b]indole-3-carboxamide
(6d). In a manner similar to the preparation of 6a,
compound 6d was synthesized from 4d (1 g, 2.63 mmol)
and aq ammonia (10 mL) in methanol (13 mL), 0.93 g,
(97%). IR (KBr): 3496, 3253, 1678, 1369, 732 cm 1; MS
m/z (relative intensity): 368 (M, Br81, 10.8), 366 (M,
Br79, 12.5), 323(100), 242(98.9); 1H NMR (400 MHz,
CDCl3+CD3OD): d 8.94 (s, 1H, H-4), 8.76 (bs, 1H, in-
dole NH), 8.3±8.2 (m, 1H, ArH), 8.12 (d, 1H, ArH,
J=8 Hz), 8.04 (bs, 1H, NH of NH2), 7.96±7.86 (m, 1H,
ArH), 7.84±7.54 (m, 3H, ArH), 7.5 (t, 1H, ArH,
J=8 Hz), 7.46±7.36 (m, 1H, ArH), 5.62 (bs, 1H, NH of
NH2).
1-(2-Thienyl)-3-hydroxymethyl-9H-pyrido[3,4-b]indole
(5i). In an analogous procedure as described for 5a,
compound 5h was synthesized from 4i (0.18 g,
0.60 mmol) in dry THF (8 mL) and LiAlH4 (0.05 g,
1.20 mmol) in dry THF (15 mL) to 0.12 g (71%). IR
(KBr) 3269, 2923, 2860, 1625, 1448, 1049, 744 cm 1; MS
m/z (relative intensity); 280 (M, 10.1), 266(100),
1-(3-Chlorophenyl)-9H-pyrido[3,4-b]indole-3-carboxamide
(6e). Compound 4e (0.78 g, 2.32 mmol) and aq ammo-
nia (8 mL) in methanol (10 mL) were treated as for 6a to
provide 6e, 0.48 g (65%). IR (KBr): 3500, 3080, 3240,
1660, 1360, 710 cm 1; MS m/z (relative intensity): 323
(M, Cl37, 5.5), 321 (M, Cl35, 15.1), 278 (36.4), 203 (68.2);
1H NMR (400 MHz, CDCl3): d 8.97 (s, 1H, H-4), 8.72
(bs, 1H, indole NH), 8.3±8.2 (m, 1H, ArH), 8.05 (bs,
1H, NH of NH2), 8.0±7.8 (m, 2H, ArH), 7.7±7.42 (m,
4H, ArH), 7.38 (t, 1H, ArH, J=8 Hz), 5.65 (bs, 1H, NH
of NH2).
1
184(76.5); H NMR (400 Mhz, CDCl3): d 8.18±8.0 (m,
2H, indole NH and ArH), 7.86±7.72 (m, 3H, ArH), 7.7±
7.62 (m, 2H, ArH), 7.58±7.46 (m, 2H, ArH), 4.8 (m, 2H,
CH2), 3.7 (m, 1H, OH).
1-(4-Chlorophenyl)-9H-pyrido[3,4-b]indole-3-carboxamide
(6a): method C. A solution of 4a (0.93 g, 2.75 mmol) in
aq ammonia solution (8 mL) and methanol (10 mL)
was heated 80 ꢀC under pressure in steel bomb for 8 h.
The reaction mixture was concentrated and separated
solid was ®ltered and on crystallization gave 6a, 0.33 g
1-(2-Chlorophenyl)-9H-pyrido[3,4-b]indole-3-carboxamide
(6f). By a similar procedure as described for 6a, com-
pound 4f (0.63 g, 1.87 mmol) and aq ammonia (6 mL)

1234
S. K. Srivastava et al. / Bioorg. Med. Chem. 7 (1999) 1223±1236
in methanol (8 mL) were reacted to furnish 6f, 0.48 g
(80%). IR (KBr): 3388, 3210, 1668, 1382, 748 cm 1; MS
m/z (relative intensity): 323 (M, Cl37, 5.1), 321 (M, Cl35,
12.3), 256 (30.9), 160 (46.6); 1H NMR (400 MHz,
CDCl3): d 9.04 (s, 1H, H-4), 8.38 (bs, 1H, indole NH),
8.26 (d, 1H, ArH, J=8 Hz), 8.2 (bs, 1H, NH of NH2),
7.7±7.58 (m, 3H, ArH), 7.56±7.46 (m, 3H, ArH), 7.38 (t,
1H, ArH, J=8 Hz), 5.64 (bs, 1H, NH of NH2).
3.16 mmol) and hydrazine hydrate (2.8 mL, 84.6 mmol)
in ethanol (20 mL), 0.4 g (40%). IR (KBr): 3279, 1666,
1618, 1557, 1347, 962 cm 1; MS m/z (relative intensity):
1
316 (M 6.9), 257 (14.8), 64 (100). H NMR (400 MHz,
CDCl3+DMSO-d6): d 8.6 (s, 1H, H-4), 8.01 (bs, 1H,
indole NH), 7.91 (m, 1H, ArH), 7.81 (m, 1H, ArH), 7.55
(m, 2H, ArH), 7.35 (m, 2H, ArH), 7.17 (m, 2H, ArH),
3.7 (bs, 3H, NH and NH2), 2.3 (s, 3H, CH3).
1-(2-Fluorophenyl)-9H-pyrido[3,4-b]indole-3-carboxamide
(6g). By an analogous procedure as described for 6a,
compound 6g was prepared from 4g (0.87 g, 2.72 mmol)
and aq ammonia (10 mL) in methanol (14 mL), 0.67 g
(81%). IR (KBr): 3380, 3202, 1666, 1384, 748 cm 1; MS
m/z (relative intensity): 305 (M, 15.4), 262 (100), 139
1-(3-Bromophenyl)-9H-pyrido[3,4-b]indole-3-carboxylic
acid hydrazide (7d). In an analogous procedure as
described for 7a, compound 8d was synthesized from 4d
(1 g, 2.62 mmol), hydrazine hydrate (1 mL, 32.1 mmol)
in ethanol (5 mL) 0.7 g (70%). IR (KBr): 3350, 1643,
1278, 1074, 793 cm 1, MS m/z (relative intensity), 381
(M, 1.2) 322 (1.9), 130 (100) 1H NMR (400 MHz,
CDCl3+DMSO-d6): d 8.65 (s, 1H, H-4), 8.51 (bs, 1H,
indole NH), 8.1±7.8 (m, 2H, ArH), 7.6±7.1 (m, 6H,
ArH), 4.2±3.6 (bs, 3H, NH and NH2).
1
(79.2); H NMR (400 MHz, CDCl3): d 8.9 (s, 1H, H-4),
8.62 (bs, 1H, indole NH), 8.22 (d, 1H, ArH, J=8 Hz),
8.08 (bs, 1H, NH of NH2), 7.88 (d, 2H, ArH, J=8 Hz),
7.7±7.5 (m, 2H, ArH), 7.44 (m, 2H, ArH), 7.38 (t, 1H,
ArH, J=8 Hz), 5.58 (bs, 1H, NH of NH2).
1-(2-Chlorophenyl)-9H-pyrido[3,4-b]indole-3-carboxylic
acid hydrazide (7f). By a similar procedure as described
for 7a, compound 7f was obtained from 4f (1 g,
1.78 mmol) and hydrazine hydrate (1.5 mL, 48.2 mmol)
in ethanol (50 mL), 0.52 g (86.6%), IR (KBr): 3940,
3780, 2360, 1630, 1320, 836 cm 1, MS m/z: 338 (M, Cl37,
15.3), 336 (M, Cl35, 65.8), 279 (52.6), 278 (44.6), 242
(69.4); 1H NMR (400 MHz, CDCl3+DMSO-d6): d
9.25±9.12 (m, 2H, H-4 and indole NH), 8.56±8.2 (m,
4H, ArH), 8.18±7.7 (m, 4H, ArH), 4.2±3.25 (bs, 3H, NH
and NH2).
1-(3-Thienyl)-9H-pyrido[3,4-b]indole-3-carboxamide (6h).
In a manner similar to the preparation of 6a, com-
pound 6h was prepared from 4h (1.2 g, 3.89 mmol) and
aq ammonia (11 mL) in methanol (15 mL) to 0.56 g
(49%). IR (KBr): 3420, 3320, 1660, 1370, 730 cm 1; MS
m/z (relative intensity); 294 (M+1, 21.9), 293 (M, 100),
1
250 (80.8); H NMR (400 MHz, CDCl3+CD3OD): d
8.92 (s, 1H, H-4), 8.7 (bs, 1H, indole NH), 8.22 (d, 1H,
ArH, J=8 Hz), 8.06 (bs, 1H, NH of NH2), 7.96±7.92
(m, 1H, ArH), 7.78 (d, 1H, ArH, J=8 Hz), 7.66±7.54
(m, 3H, ArH), 7.38 (t, 1H, ArH, J=8 Hz), 5.6 (bs, 1H,
NH of NH2).
1-(3-Thienyl)-9H-pyrido[3,4-b]indole-3-carboxylic acid
hydrazide (7h). In a similar manner to the preparation
of 7a compound 7h was obtained from 4h (0.5 g,
1.62 mmol) and hydrazine hydrate (1.5 mL, 48.2 mmol)
in ethanol (50 mL), 0.26 g (52%), IR (KBr): 3279, 3199,
1645, 1364, 828 cm 1, MS m/z: 308 (M, 35.5), 277
(17.0), 255 (24.9), 249 (48.9); 1H NMR (400 MHz,
CDCl3+DMSO-d6): d 8.85 (s, 1H, H-4), 8.4±8.1 (m,
2H, indole NH and ArH), 8.0 (m, 1H, ArH), 7.8 (m,
1H, ArH), 7.7±7.3 (m, 4H, ArH), 4.9±4.2 (bs, 3H, NH
and NH2).
1-(2-Thienyl)-9H-pyrido[3,4-b]indole-3-carboxamide (6i).
Compound 4i (0.98 g, 3.18 mmol) and aq ammonia
(10 mL) in methanol (13 mL) were treated in a manner
similar to that described under 6a to a€ord 6i, 0.77 g
(82%). IR (KBr): 3440, 3240, 1662, 1384, 746 cm 1; MS
m/z (relative intensity); 294 (M+1, 19.1), 293 (M, 100),
250 (17.2); 1H NMR (400 MH, CDCl3+CD3OD): d
8.85 (s, 1H, H-4), 8.79 (bs, 1H, indole NH), 8.22 (d, 1H,
ArH, J=8 Hz), 8.02 (bs, 1H, NH of NH2), 7.84±7.74
(m, 2H, ArH), 7.68±7.58 (m, 2H, ArH), 7.56 (d, 1H, ArH,
J=8 Hz), 7.4 (m, 1H, ArH), 5.62 (bs, 1H, NH of NH2).
1-(2-Thienyl)-9H-pyrido[3,4-b]indole-3-carboxylic acid
hydrazide (7i). A solution of 4i (0.8 g, 2.59 mmol) and
hydrazine hydrate (1.5 mL, 48.2 mmol) was re¯uxed in
ethanol (50 mL) in a similar manner as described in 7a,
0.75 g (93.7%); IR (KBr): 3945, 3906, 1630, 1357,
904 cm 1; MS m/z (relative intensity): 308 (M, 35.5), 255
(24.9), 249 (48.9), 160 (28.9); 1H NMR (400 MHz,
CDCl3+DMSO-d6): d 8.8 (s, 1H, H-4), 8.25±8.1 (m,
2H, indole NH and ArH), 7.8 (m, 1H, ArH), 7.6±7.4 (m,
5H, ArH), 4.8±4.3 (bs, 3H, NH and NH2).
1-(4-Chlorophenyl)-9H-pyrido[3,4-b]indole-3-carboxylic
acid hydrazide (7a): method D. Compound 4a (1 g,
2.97 mmol) and hydrazine hydrate (1.5 mL, 48.2 mmol)
was re¯uxed in ethanol (50 mL) for 4 h. The reaction
mixture was concentrated and solid thus separated was
®ltered and on crystallization gave 7a, 0.72 g (72%);
IR (KBr): 3930, 3886, 2369, 1623, 1320, 836 cm 1; MS
m/z (relative intensity): 338 (M, Cl37, 10.0), 336 (M,
1
Cl35, 26.9), 277 (29.3), 130 (100), H NMR (400 MHz,
CDCl3+DMSO-d6): d 8.83 (s, 1H, H-4), 8.75 (bs, 1H,
indole NH), 8.3±8.15 (m, 2H, ArH), 7.8±7.5 (m, 4H,
ArH), 7.4±7.2 (m, 2H, ArH), 4.2±3.5 (bs, 3H, NH and
NH2).
Materials and Methods for Biological Evaluation
1. Acanthocheilonema viteae: A. viteae infection was
transmitted to 6 weeks old male M. coucha
through the vector Ornithodorus moubata by the
method as reported in literature.39 The micro- and
macro®laricidal activities of the compounds were
1-(4-Methylphenyl)-9H-pyrido[3,4-b]indole-3-carboxylic
acid hydrazide (7c). By a similar procedure as described
for 7a, compound 7c was obtained from 4c (1 g,

S. K. Srivastava et al. / Bioorg. Med. Chem. 7 (1999) 1223±1236
1235
assessed against A. viteae in M. coucha at 50 mg/kg
ip and/or 200 mg/kg po for 5 consecutive days
according to literature methods.40,41
Bose, C.; Srivastava, V. M. L. Syntheses and anti®larial pro®le
of 5-amino and 5,8-diamino isoquinoline derivatives: a new
class of anti®larial agents. Bioorg. Med. Chem. Lett. 1996, 6,
2623±2628.
2. Litomosoides carinii: The infection was transmitted
to 6 weeks old cotton rats (Sigmodon hispidus)
through the vector Liponyssus bacoti by the litera-
ture method.42 Animals showing 250 or more
micro®lariae per 5 mm of blood were chosen for
screening. Blood samples of experimental and
control animals were examined for micro®lariae
before starting the treatment and thereafter at
weekly interval until day 42. All the compounds
were given 30 mg/kg ip for 5 consecutive days. On
day 42, all the treated and control animals were
sacri®ed and the condition of adult male and
female worms observed. The micro- and macro-
®laricidal action were assessed as described for
A. viteae.
3. Brugia malayi: The 6 weeks old male mastomys
were infected by inoculum of 50 infective larvae of
Brugia malayi recovered from infected mosquitoes
(Aedes aegybti).36 Method of screening of com-
pounds were similar to those of A. viteae except
blood was examined up to day 92 post treatment.
Animals were sacri®ced on day 92 for adult worm
recovery.
11. Singh, S. N.; Bhatnagar, S.; Fatma, N.; Chauhan, P. M.
S.; Chatterjee, R. K. Anti®larial activity of a synthetic marine
alkaloid, aplysinopsin (CDRI Compound 92/138). Tropical
Medicine and International Health 1997, 2, 535±543.
12. Tewari, S.; Chauhan, P. M. S.; Bhaduri, A. P.; Singh, S.
N.; Fatma, N.; Chatterjee, R. K.; Srivastava, V. M. L. 1,10-
Dicyano-2-substituted ethylenes: A new class of glucose
uptake inhibitors in anti®larial chemotherapy. Bioorg. Med.
Chem. Lett. 1997, 7, 1891±1896.
13. Sharma, S. Design of new drugs for helminth diseases:
lead optimization in benzimidozole. Adv. Drug Res. 1994, 25,
103±172.
14. Townsend, L. B.; Wise D. S. The synthesis and chemistry
of certain anthelmintic benzimidazoles. Parasitology Today
1990, 6, 107±112.
15. Agarwal, A.; Agarwal, S. K.; Bhakuni, D. S.; Gupta, S.;
Katiyar, J. C. Antiparasitic agents: Part VIIIÐSynthesis of
1,6- and 1,8-disubstituted-9H-pyrido[3,4-b]indoles and 2-sub-
stituted-1(3),10-dihydro-9-phenylpyrido[3,4-b]imidazo[4,5-b]-
indoles and their anthelmintic activity. Indian J. Chem. 1989,
28B, 943±949.
16. Agarwal, A.; Agarwal, S. K.; Bhakuni, D. S. Antiparasitic
agents: Part XÐSynthesis of 2,7-disubstituted-1,6-dihydro-
pyrido[3,4-b]imidazo[4,5-e]indoles as anthelmintic agents.
Indian J. Chem. 1990, 29B, 843±847.
17. Agarwal, A.; Agarwal, S. K.; Bhakuni, D. S.; Gupta, S.;
Katiyar, J. C. Antiparasitic agents: Part XIIIÐSynthesis and
anthelmintic activity of 6- and 8-(2,4-dioxoquinazolin-3-yl)-1-
substituted-9H-pyrido[3,4-b]indoles, 6- and 8-(2-methyl-5-acet-
amidobenzimidazol-1-yl)-1-substituted-9H-pyrido[3,4-b]-indoles
and 6-[2-carbomethoxyamino-5-N,N0-dicarbo-methoxyquan-
idino)benzimidazol-1-yl]-1-phenyl-9H-pyrido[3,4-b]indole. Indian
J. Chem. 1990, 29B, 848±854.
18. Kumar, P.; Agarwal, S. K.; Bhakuni, D. S. Antiparasitic
agents: Part XIÐSynthesis and anthelmintic activity of 6-/8-
[(2-carbomethoxyamino)benzimidazole]-5-carbonylamino-1-
substituted-9H-pyrido[3,4-b]indoles. Indian J. Chem. 1990, 29B,
1077±1088.
19. Agarwal, A.; Agarwal, S. K.; Bhakuni, D. S.; Singh, S. N.;
Chatterjee, R. K. Antiparasitic agents: Part XVIÐSynthesis of
5(6)-substituted benzimidazole-2-carbamates as anthelmintic
agents. Indian J. Chem. 1993, 32B, 453±456.
20. Agarwal, A.; Agarwal, S. K.; Singh, S. N.; Fatma, N.;
Murthy, P. K.; Chatterjee, R. K. Synthesis and anti®larial
activity of pyrido[3,4-b]imidazo[1,2-c0]quinazolo[4,5-e]/[4,5-g]-
indoles. Med. Chem. Res. 1994, 3, 523±530.
21. Bose, C.; Agarwal, S. K.; Chatterjee, R. K.; Srivastava, V.
M. L. Carboline anti®larials: e€ects on carbohydrate metabo-
lizing enzymes in Litomosides carinii female. Indian J. Exp.
Bio. 1994, 32, 431±434.
22. Agarwal, A.; Agarwal, S. K.; Singh S. N.; Fatima N.;
Chatterjee, R. K., Structure±anti®larial activity relationship of
5/6/7/8-mono or disubstituted 1H/1-phenyl-9H-pyrdo[3,4-b]-
indolesÐa new class of potential ®laricides. Z. Naturforsch
1994, 49c, 526±529.
23. Agarwal A; Agarwal S. K. Antiparasitic agents: Part
XVII. Synthesis of 2-methylmercapto-7-H/phenyl-1H,6H-pyr-
ido[3,4-b]imidazo[4,5-e]indoles, 6-/8-(4-oxo-2-thioxoquinazo-
line-3-yl)-1-H/phenyl-9H-pyrido[3,4-b]indoles and 6-/8-(2,4-
dioxo-1,3-benzoxazin-3-yl)-1-phenyl-9H-pyrido[3,4-b]indoles as
anthelmintic agents. Indian J. Chem. 1995, 34B, 323.
24. Agarwal, A.; Agarwal, S. K.; Singh S. N.; Fatima N.;
Chatterjee, R. K. Synthesis of neoeudistomin analoguesÐAs
potential ®laricides. Bioorg. Med. Chem. Lett. 1995, 5, 1545±
1548.
Acknowledgements
We are indebted to RSIC, Lucknow for providing
spectroscopic and analytical data. One of us (S.K.S.) is
grateful to CSIR for the award of a Senior Research Fel-
lowship and A.A. and N.F. are thankful to CSIR and
ICMR for the award of Research Associate.
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