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

Article abstract of DOI:10.1021/jm9800705

Substituted 9H-pyrido[3,4-b]indoles (β-carbolines), identified in our laboratory as potential pharmacophores for designing macrofilaricidal agents, have been explored further for identifying the pharmacophore responsible for the high order of adulticidal

Full text of DOI:10.1021/jm9800705

J . Med. Chem. 1999, 42, 1667-1672
1667
Brief Articles
P oten t 1,3-Disu bstitu ted -9H-p yr id o[3,4-b]in d oles a s New Lea d Com p ou n d s in
An tifila r ia l Ch em oth er a p y†,‡
Sanjay K. Srivastava,| Alka Agarwal,| Prem M. S. Chauhan,*,| Shiv K. Agarwal,§ Amiya P. Bhaduri,|
Som N. Singh,∇ Nigar Fatima, and Ranjit K. Chatterjee
Divisions of Medicinal Chemistry and Parasitology, Central Drug Research Institute, Lucknow 226001, India
Received J anuary 29, 1998
Substituted 9H-pyrido[3,4-b]indoles (â-carbolines), identified in our laboratory as potential
pharmacophores for designing macrofilaricidal agents, have been explored further for identifying
the pharmacophore responsible for the 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 macrofilaricidal activity was initially evaluated in vivo
against Acanthoeilonema viteae. Among all the synthesized compounds, only 12 compounds,
namely 3a , 3c, 3d , 3f, 4c, 4d , 4f, 5a , 6f, 6h , 6i, and 7h , have exhibited either >90% micro- or
macrofilaricidal activity or sterlization 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 â-carbolines has
been discussed. It has been observed that the presence of a carbomethoxy at position 3 and an
aryl substituent at position 1 in â-carbolines effectively enhances antifilarial activity particularly
against A. viteae. Among the various compounds screened, methyl 1-(4-methylphenyl)-9H-
pyrido[3,4-b]indole-3-carboxylate (4c) has shown the highest adulticidal activity and methyl
1-(4-chlorophenyl)-1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indole-3-carboxylate (3a ) has shown the
highest microfilaricidal action against A. viteae at 50 mg/kg × 5 days (ip). Another derivative
of this compound, namely 1-(4-chlorophenyl)-3-(hydroxymethyl)-9H-pyrido[3,4-b]indole (5a ),
exhibited the highest activity against L. carinii at 30 mg/kg × 5 days (ip) and against B. malayi
at 50 mg/kg × 5 days (ip) or at 200 mg/kg × 5 days (po).
In tr od u ction
rivatives,11 and 1,1′-dicyano-2-substituted-ethylenes12
were identified as potential filaricides, but most of the
compounds exhibited very poor adulticidal response. The
benzimidazole group of anthelmintics exhibits high
order of activity against intestinal helminths but has
not found application for the treatment of tissue-
dwelling helminths.13,14 Therefore the need arose to
identify structural prototypes associated with macro-
filaricidal activity.
In earlier communications,15-24 the macrofilaricidal
activities of 1-substituted- and 1,5-, 1,6-, 1,7-, and 1,8-
disubstituted-9H-pyrido[3,4-b]indoles and representa-
tives of pyrido[3,4-b]imidazo[1,2-c]quinazolo[4,5-e]- and
-[4,5-g]indoles were reported. These research activities
did not reveal the optimal structural requirements to
evoke a very high order of macrofilaricidal activity. In
continuation of this work, it was considered essential
to evaluate 1,3-disubstituted-9H-pyrido[3,4-b]indoles
because of reasons stated later.
The successful treatment of filariasis, a disease of
many tropical and subtropical areas, is not possible
because of the nonavailability of macrofilaricidal drugs.1-3
The age old drug diethylcarbamazine (DEC) continues
to be the mainstay of clinical practice despite its well-
known deficiencies.4,5 Ivermectin, a semisynthetic mac-
rocyclic lactone antibiotic, may take impact as a mi-
crofilaricide for onchocerciasis, but it did not irreversibly
damage the adult filarial worms.6 Although organic
arsenical compounds have long been known as good
macrofilaricides,7 their potential toxicity to the host has
prevented their development as useful antifilarial drugs.
Besides these antifilarials, a number of phenoxycyclo-
hexane derivatives,8 2,4,6-substituted-triazines,9 5-ami-
no- and 5,8-diaminoisoquinolines,10 aplysinoposin de-
† CDRI Communication No. 5795.
‡ Presented at the 33rd Annual Convention of Chemists organized
by the Indian Chemical Society at PSG College of Technology,
Coimbatore, India.
Centrally acting agents known to interact with ben-
zodiazepine and γ-aminobutyric acid (GABA) receptors
also exhibit anthelmintic activity,25-28 and since 3-car-
boxy-â-carbolines also exhibit a high order of affinity
for the benzodiazepine receptor,29,30 it was considered
desirble to evaluate the macrofilaricidal activities of
* Corresponding author.
| Division of Medicinal Chemistry.
Division of Parasitology.
§ Present address: Wochkaradt Research Centre, D-4, MIDC,
Chikalthana Aurangabad, India.
∇ Present address: Department of Physiology, DIPAS, Timarpur,
Delhi 54, India.
10.1021/jm9800705 CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/17/1999

1668 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 9
Brief Articles
Ta ble 1. Antifilarial Activity (%) of 1-Aryl-3-substituted-
Sch em e 1a
9H-pyrido[3,4-b]indoles (3-7) against A. viteae at 50 mg/kg × 5
days (ip)a
antifilarial activityb
antifilarial activityb
compd mif maf sterl of ?
compd
mif maf sterl of ?
3a
3b
3c
3d
3e
3f
94
0
0
90
0
0
91
0
0
0
0
39
25
90
0
50
93
0
57
56
100
84
81
94
44
100
0
0
0
0
0
0
0
67
0
4h
4i
0
60
0
0
75
0
62 45
76 56
0
0
0
0
0
84
44 86
5a
5a c
5b
5c
6a
6d
6e
6f
94
75
0
0
69
0
0
40
60
0
50
100
0
0
0
0
3fc
3h
4b
4c
4d
4e
4f
a
Reagents: (i) MeOH, SOCl2; (ii) R1CHO, MeOH, 10% aq
Na2CO3; (iii) sulfur, xylene, reflux.
Sch em e 2a
100
0
0
6h
6i
7h
0
93
91
89
0
0
0
0
0
4g
0
DECd citratee 90
0
a
Intraperitoneal route. Compounds 3g, 3i, 4a , 5d -i, 6b, 6c,
6g, 7a , 7c, 7d , 7f, and 7i are inactive and are not described here.
b
O, inactive; ?, female worms; mif, microfilariae; maf, macro-
filariae. c At 200 mg/kg × 5 days (oral). DEC, diethylcarbam-
d
azine. e At 350 mg/kg × 5 days (ip).
hydride (LiAIH4) in dry THF;33 in the second, the ester
was reacted with aqueous ammonia in a steel bomb to
provide the respective amides34 (6a -i); in the third,
compounds 4a , 4c, 4d , 4f, 4h , and 4i were reacted with
hydrazine hydrate in ethanol to furnish their corre-
sponding carboxylic acid hydrazides32 (7a , 7c, 7d , 7f,
7h , and 7i).
An tifila r ia l Activity
a
Reagents: (i) LiAlH4, dry THF, reflux, 10% aq NaOH; (ii) aq
The micro- and macrofilaricidal activities of the
synthesized compounds (3-7) were evaluated against L.
carinii in cotton rats (Sigmodon hispidus) and A. viteae
and B. Malayi in Mastomys coucha as described ear-
lier.35,36
ammonia, MeOH, 80 °C; (iii) hydrazine hydrate, EtOH, reflux.
esters of 1-substituted-3-carboxy-9H-pyrido[3,4-b]in-
doles as macrofilaricidal agents. The details of this study
are presented here.
Compounds being insoluble in water were made as
fine suspensions within 1% Tween 80. Two to three
animals were used for each dose level study, and at least
two replicates were used for confirmation of activity.
The design of 1,3-disubstituted-9H-pyrido[3,4-b]in-
doles (hereafter called â-carbolines for the sake of
convenience) was based on earlier experience.15-24 It
was observed that a phenyl or thiophene ring at position
1 in â-carboline was necessary for evoking weak mac-
rofilaricidal activity. The choice of substituents at
position 3 was limited to ester, amide, and hydroxy-
methyl groups, and for specific structure-activity re-
lationship studies, the corresponding hydrazides were
also prepared.
Resu lts a n d Discu ssion
All the synthesized compounds (3-7) were evaluated
for their antifilarial activity in vivo against A. viteae at
50 mg/kg × 5 days by intraperitoneal route (ip) and/or
200 mg/kg × 5 days through oral route (po) in M.
coucha. The antifilarial activity against A. viteae is given
in Table 1. Compounds which do not exhibit micro- or
macrofilaricidal activity are not described in Table 1.
During the course of discussion if the route of admin-
istration has not been described, the mode of adminis-
tration of test compounds should be treated as intra-
peritoneal.
The other test models used in the present study for
evaluation of antifilarial activity were L. carinii in
cotton rats and Brugia malayi in M. coucha. A. viteae
is metabolically similar to human filarial parasites
which are anaerobic in nature, and therefore, A. viteae
in Mastomys was used for evaluation of efficacy for
antifilarial activity of all newly synthesized compounds.
This model has also been recommended by WHO for the
experimental chemotherapy of filariasis.37 L. carinii, a
metabolically facultative filarial species maintained in
cotton rats was earlier used for efficacy evaluation of
Ch em istr y
Our synthetic approach was focused on the prepara-
tion of the key compounds 1-aryl-1,2,3,4-tetrahydro-9H-
pyrido[3,4-b]indoles 3a -i in order to allow easy elabo-
ration of the functional group attached to position 3.
Pictet-Spengler cyclization31 of L-tryptophan methyl
ester hydrochloride (2) in the presence of the appropri-
ate aldehyes (R1CHO) furnished the corresponding
methyl l-aryl-1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indole-
3-carboxylates 3a -i. Dehydrogenation32 of 3a -i over
sulfur in xylene yielded the respective methyl 1-aryl-
9H-pyrido[3,4-b]indole-3-carboxylates 4a -i as described
in Scheme 1.
Methyl esters 4a -i, chosen as convenient intermedi-
ates, were elaborated in three ways (Scheme 2). In the
first, the ester group at position 3 was reduced to its
corresponding alcohol (5a -i) by lithium aluminium

Brief Articles
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 9 1669
DEC38 and was subsequently tested in human filarials
with success. B. malayi is target human filarial parasite,
and therefore, the use of experimental model for evalu-
ating efficacy of this parasite is obvious. Besides these
reasons, the use of three different models was consid-
ered necessary because of the envisaged intractions of
the synthesized compounds with GABA receptors. A
precise comment on this subject has been made later.
against A. viteae. The most potent compound, methyl
1-(4-methylphenyl)-9H-pyrido[3,4-b]indole-3-carboxy-
late (4c), caused the highest macrofilaricidal activity
(100%), while its tetrahydro compound (3c) showed low
but significant adulticidal response (90%). However, the
antifialrial activity of the correspondirng hydroxymethyl
derivative (5c) was limited to sterilization of only 40%
of the surviving female worms. Compared to these
compounds, variations at position 3 in â-carboline with
a 4-halophenyl substituent at position 1 by incorporat-
ing amide (6c) or hydrazide (7c) group made the
compounds ineffective against filarial infection.
The micro- and macrofilaricidal activities in com-
pounds with various substituents at positions 1 and 3
in â-carbolines were monitored as follows: With a
particular substituent at position 1, the effect of sub-
stituents such as ester, amide, and hydroxymethyl
group at position 3 was monitored. Along with this study
the effect of the ester group at position 3 with and
without a tetrahydropyridine ring on the antifilarial
activity was also monitored. In situations where the
activity was significantly high, the effect of hydrazide
at position 3 was also monitored. The active compounds
(with at least 90% micro- and/or macrofilaricidal activity
or sterilization of female worms) were short-listed and
were subjected for evaluation against L. carinii infec-
tion. The best compound from this short-listed one was
finally evaluated against B. malayi infection. The
structure-activity relationship, therefore, relates to
activity against A. viteae infection only.
Unlike 4-substituted-phenyl substituents at position-1
in â-carbolines, compounds with a 3-halophenyl sub-
stituent at position 1 exhibited a distinct type of
antifilarial action. In this class of compounds, it was
interesting to note the effect of the pyridine ring on
antifilarial activity. For example, the tetrahydro com-
pound 3d , possessing 3-bromophenyl at position 1 in
â-carboline, exhibited significant microfilaricidal activity
(90%) which after aromatization (4d ) led to enhanced
adulticidal activity (84%) with complete loss of microfi-
laricidal activity and in addition made all the surviving
female worms sterile. The adulticidal activity decreased
up to 69% or completely disappeared after converting
4d into its amide (6d ) and hydrazide (7d ) derivatives,
respectively. The tetrahydro compound 3e, having a
3-fluorophenyl substituent at position 1 in- â-carboline,
exhibited only weak macrofilaricidal 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 â-carbolines,
compounds in which the ester was reduced to the
corresponding hydroxymethyl (5e) group, led to com-
plete loss of biological response, while an amide function
at position 3 (6e), unlike 6d , predominantly evoked
microfilaricidal activity (84%) with 50% sterilization of
surviving female worms. However, none of the com-
pounds having a 3-halo substituent at position 1 in
â-carboline exerted significant adulticidal response
(>90%) against A. viteae.
Among the compounds with a 2-halophenyl substitu-
ent at position 1 in â-carboline, the 2-chlorophenyl
substituent at position 1 and an ester function at
position 3 elicit interesting adulticidal response against
A. viteae and were better than a 3-halophenyl substitu-
ent at position 1. In this group of compounds the role of
the pyridine ring in â-carboline was not very significant.
For example, methyl 1-(2-chlorophenyl)-1,2,3,4-tetrahy-
dro-9H-pyrido[3,4-b]indole-3-carboxylate (3f) showed
significant adulticidal activity (93%) through ip route,
while by oral route, it was microfilaricidal (91%) with
complete loss of adulticidal activity. Aromatization of
3f led to the compound 4f, which exhibited 94% adul-
ticidal activity and was equipotent to its parent com-
pound 3f. Its amide derivative 6f showed 86% macro-
and 44% microfilaricidal activities with 100% steriliza-
tion of surviving female worms. The hydroxymethyl
compound 5f and the hydrazide 7f were inactive as
antifilarial agents. Compounds with a 2-fluorophenyl
substituent at position 1 were inactive except aroma-
tized drivative 4g which showed 44% adulticidal activ-
ity.
Among the 4-halo substituents at position 1 in â-car-
boline, the 4-chlorophenyl substituent plays a significant
role in eliciting antifilarial response, and particularly,
the tetrahydropyridine ring along with the ester func-
tion at position 3 was found effective. For example,
methyl 1-(4-chlorophenyl)-1,2,3,4-tetrahydro-9H-pyrido-
[3,4-b]indole-3-carboxylate (3a ) exhibited highest mi-
crofilaricidal (94%) and 39% macrofilaricidal 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 filaricidal activity. The
hydroxymethyl derivative (5a ) of this compound showed
a wide range of activity by different routes of adminis-
tration. For example, it exhibited 76% micro- and 56%
adulticidal activity along with sterilzation of 75% of
surviving female worms by ip administration, but by
oral route it was predominantly macrofilaricidal (94%)
without microfilaricidal activity. The amide and hy-
drazide functions (6a and 7a , respectively) at position
3 in â-carboline of this class of compounds did not exert
any significant role. For example, compound 6a exhib-
ited only sterilization of 60% female worms, whereas
7a failed to show any antifilarial response. On the other
hand incorporation of a 4-fluorophenyl substituent at
position 1 in â-carboline, irrespective of the nature of
the group present at position 3, led to a low order of
antifilarial activity in comparison to compounds with a
4-chlorophenyl substituent at position 1. The tetrahydro
compound 3b showed insignificant macrofilaricidal
(25%) activity, whereas its aromatized congener 4b
caused 56% adulticidal activity with 67% sterilization
of the surviving female worms. The hydroxymethyl
derivative (5b) exerted 75% adulticidal activity, but the
compound with an amide function at position 3 in
â-carboline (6b) failed to show any response.
The ester group at position 3 with a 4-methylphenyl
substituent at position 1 in 9H-pyrido[3,4-b]indole
played a major role for evoking adulticidal activity

1670 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 9
Brief Articles
Ta ble 3. Antifilarial Activity (%) of 5a against B. malayi
Ta ble 2. Antifilarial Activity (%) of 3f and 5a against L.
carinii at 30 mg/kg × 5 days (ip)
antifilarial activity
dose (mg/kg
antifilarial activity
× 5 days)
route
mif
maf
sterl of ?
compd
mif
maf
sterl of ?
50
ip
po
ip
0
0
62
56
50
85
69
0
250
DEC citrate
3f
5a
0
20
95
0
88
0
0
90a
29
DEC citrate
90a
a
At 100 mg/kg × 5 days (ip).
a
At 75 mg/kg × 5 days (ip).
adulticidal activity and 85% of the surviving female
worms were found sterile, while at 250 mg/kg × 5 days
(po), activities of 5a somewhat decreased since it
exhibited only 56% macrofilaricidal activity and caused
69% sterilization of the surviving female worms.
A total analysis of the antifilarial activities of â-car-
boline derivatives reported earlier15-24 and of the present
study clearly indicate two results: (i) â-carboline frame-
work is a pharmacophore for macrofilaricidal activity
and (ii) the nature of the substituents especially at
positions 1 and 3 significantly contributes toward the
macrofilaricidal efficacy. The present work also reveals
that absorption, distribution, and bioclearence of â-car-
boline derivatives by oral route of administration are
substituent-dependent. The results of parallel antifi-
larial evaluations in vivo against A. viteae, L. carinii,
and B. malayi evoke certain speculations which may
provide a basis for future study. Adequate evidence25,26
exists that â-carboline-3-carboxylic acid derivatives
interact with GABA receptors, and it is also known27
that GABA receptor is a biochemical target site for anti-
filarial compounds. In light of these observations, it
would be reasonable to presume that compounds evalu-
ated in the present study also interact with GABA
receptors, which in A. viteae, L. carinii, and B. malayi
are either different or have significant difference in their
population.
An overview of the activity data of compounds with a
thienyl substituent at position 1 in â-carboline clearly
indicated that unlike the l-halophenyl substituent, a
thienyl group played significant role for evoking a
microfilaricidal response. In general, it was interesting
to note in this class of compounds the insignificant role
of either a pyridine ring or an ester function at position
3 in â-carboline for evoking antifialrial activity. The
other derivatives such as hydrazide (7h ) and amide (6i)
exhibited interesting microfilaricidal responses. The
tetrahydro compound having a thien-3-yl substituent at
position 1 (3h ) showed 57% adulticidal activity which
remained almost equipotent (60%) after its aromatiza-
tion (4h ), but the hydroxymethyl derivative (5h ) did not
evoke any antifilarial response. A major improvement
in macrofilaricidal activity (89%) was recorded for the
amide 6h , whereas the hydrazide derivative 7h was only
microfilaricidal (91%) without the adulticidal activity.
Among the compounds with a thien-2-yl substituent at
position 1 in â-carboline, the tetrahydro compound (3i)
was inactive, while its aromatic congener 4i exhibited
45% adulticidal and 62% microfilaricidal activity. The
hydroxymethyl derivative (5i) of this series of com-
pounds failed to show any biological response, but the
amide 6i exhibited significant microfilaricidal activity
(93%). The hydrazide 7i was devoid of any antifilarial
activity.
Those compounds which showed significant filaricidal
action (>90% micro- or macrofilaricidal response or
sterilization of female worms) were next examined
against L. carinii in cotton rats at 30 mg/kg × 5 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 antifilarial response against L. carinii,
and the results are summarized in Table 2.
Among all 12 compounds screened, only 3f and 5a
were found active, and of the two 5a exhibited a more
pronounced effect against L. carinii than 3f. The
compound 5a , having a hydroxymethyl at position 3 and
a 4-chlorophenyl at position l in â-carboline, exhibited
95% adulticidal along with 29% microfilaricidal re-
sponse, and the tetrahydro compound 3f, possessing a
2-chlorophenyl substituent at position 1, showed insig-
nificant macrofilaricidal activity (20%) but caused ster-
ilization of 88% surviving female worms.
The next logical step of a future study would be to
look into the GABA receptors of different human and
experimental filarial worms. The experimental receptor
model which will be very near to the human parasites
(Brugia malayi and Wuchereria bancrofti) would be at
great value for developing target sites of quick biological
screening, and the results of this study may give
valuable inputs for high-throughput screening.
Exp er im en ta l Section
Ch em istr y. The compounds were routinely checked for
their purity by thin layer chromatography (TLC) on silica gel
G, and column chromatography seprations were carried out
on Merk silica gel (230-400 mesh). Melting point (mp) were
determined in capillary tubes on an Electrothermal melting
point Toshiniwal CL-03001 apparatus and are uncorrected.
Infrared (IR) spectra were run on a Backman-Acculab-10
spectrophotometer (νmax in cm-1). Nuclear magnetic resonance
(NMR) spectra were recorded on a Bruker-400-FT instrument,
and chemical shifts (δ in ppm) are 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 are 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 J eol-J MS-D-300 spectrom-
eter. 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 Na2-
SO4 and concentrated with a Buchi rotary evaporator at low
pressure. Yields were of purified product and were not
optimized.
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 antifilarial
activity against L. carinii, they were, therefore, evalu-
ated for their efficacy against B. malayi by intraperi-
toneal and oral route of administrations (Table 3).
Compound 3f failed to show any activity at 50 mg/kg
× 5 days (ip) against B. malayi, whereas 5a exhibited
antifilarial activity by intraperitoneal as well as by oral
route. At 50 mg/kg × 5 days (ip), 5a showed 62%

Brief Articles
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 9 1671
Meth yl 1-(4-Ch lor op h en yl)-9H-p yr id o[3,4-b]in d ole-3-
ca r boxyla te (4a ). A suspension of 3a (1.56 g, 4.58 mmol) and
sulfur (0.29 g, 9.16 mmol) in xylene (30 mL) was heated at
reflux for 8 h and allowed to cool to room temprature, excess
sulfur was filtered off, and the filtrate was concentrated in
vacuo. The residue was crystallized to afford 4a , 0.36 g (37%).
conditions of adult male and female worms observed. The
micro- and macrofilaricidal actions were assessed as described
for A. viteae.
3. B. m a la yi: The 6-week-old male Mastomys were infected
by inoculum of 50 infective larvae of B. malayi recovered from
infected mosquitoes (Aedes aegybti).36 Method of screening of
compounds was similar to that of A. viteae except blood was
examined up to day 92 posttreatment. Animals were sacrificed
on day 92 for adult worm recovery.
IR (KBr): 3236, 3010, 2822, 1716, 1600, 1362, 1250 cm-1
.
,
MS: m/z (relative intensity) 338 (M, Cl37, 14.8), 336 (M, Cl35
1
39.9), 278 (100), 214 (20). H NMR (400 MHz, CDCl3): δ 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). Similarly,
compounds 4b-i were synthesized.
Ack n ow led gm en t. We are indebted to RSIC, Luc-
know, for providing spectroscopic and analytical data.
One of us (S.K.S.) is grateful to CSIR for the award of
Senior Research Fellowship, and A.A. and N.F. thank
CSIR and ICMR for the award of Research Associate,
respectively.
1-(4-Ch lor op h en yl)-3-(h yd r oxym eth yl)-9H-p yr id o[3,4-
b]in d ole (5a ). 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 temper-
ature. The reaction mixture was refluxed for 8 h and was
allowed to remain at room temperature. The complex was
decomposed by 10% aqueous NaOH solution, solid that sepa-
rated was filterated and washed with water, and then filterate
was concentrated in vacuo. The residue thus obtained was
filtered, washed with water, and crystallized to provide 5a ,
0.29 g (80%). IR (KBr): 3180, 3060, 2800, 1630, 1490, 1240,
Refer en ces
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1010, 720 cm-1. MS: m/z (relative intensity): 310 (M, Cl37
,
4.5), 308 (M, Cl35, 54.9), 306 (100), 278 (47.5). H NMR (400
MHz, CDCl3 + DMSO-d6): δ 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). Compounds 5b-i were synthesized using a
similar procedure.
1
1-(4-Ch lor op h en yl)-9H -p yr id o[3,4-b]in d ole-3-ca r b ox-
a m id e (6a ). A solution of 4a (0.93 g, 2.75 mmol) in aqueous
ammonia solution (8 mL) and methanol (10 mL) was heated
at 80 °C under pressure in a steel bomb for 8 h. The reaction
mixture was concentrated, and solid thus separated was
filtered and on crystallization gave 6a , 0.33 g (37%). IR
(KBr): 3442, 3366, 3220, 1664, 1386, 742 cm-1. MS m/z
(relative intensity): 323 (M, Cl37, 9.5), 321 (M, C135, 25.7), 278
1
(100), 242 (51.1). H NMR (400 MHz, CDCl3): δ 8.94 (s, 1H,
H-4), 8.74 (bs, 1H, indole 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). Compounds 6b-i were obtained by using the
same method.
1-(4-Ch lor op h en yl)-9H-p yr id o[3,4-b]in d ole-3-ca r boxy-
lic Acid Hyd r a zid e (7a ). Compound 4a (1 g, 2.97 mmol) and
hydrazine hydrate (1.5 mL, 48.2 mmol) were refluxed in
ethanol (50 mL) for 4 h. The reaction mixture was concen-
trated, and solid thus separated was filtered and on crystal-
lization gave 7a , 0.72 g (72%). IR (KBr): 3930, 3886, 2369,
1623, 1320, 836 cm-1. MS m/z (relative intensity): 338 (M, Cl37,
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1
10.0), 336 (M, Cl35, 26.9), 277 (29.3), 130 (100). H NMR (400
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1672 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 9
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