Synthesis and antidepressant evaluation of five novel heterocyclic tryptophan-hybrid derivatives

Article abstract of DOI:10.1002/ardp.200900244

This study aimed at evaluating the reactivity of L-Tryptophan (TRP) 1 towards various chemical reagents to produce new bi- and tri-heterocyclic systems providing basic pharmacological activities. Indol-3-yl hydroxyoxazol-2-yl acetonitrile derivatives 5 and 6, indol-3-yl-hydroxyoxazol-2- yl-1,2,4-triazine derivatives 8 and 9, indol-3-yl-hydroxyoxazol-2-yl- aminopyrazole derivatives 11a, b, and indol-3-yl-hydroxyoxazol-2-yl- aminoisoxazole derivative 12 were synthesized via straightforward and efficient methods. The structures were characterized by spectral data (IR, ¹H-NMR, ¹³C-NMR, and MS) and the purity was ascertained by microanalysis. Also, this work was extended to study the potential role of the novel synthesized TRP derivatives 5, 6, 9, 11a, and 12 as antidepressant and sedative agents in comparison with TRP. All compounds showed significant antidepressant activity in the forced-swimming test at two doses (50 or 100 mg/kg). Also, all tested compounds (at 50 or 100 mg/kg) produced a significant decrease in locomotor activity of mice during a 30 min observation period. The most potent antidepressant and sedative effect was produced by the tri-heterocyclic compounds 9 and 12, followed by 11a and TRP.

Full text of DOI:10.1002/ardp.200900244

Arch. Pharm. Chem. Life Sci. 2010, 343, 261–267
G. A. Elmegeed et al.
261
Full Paper
Synthesis and Antidepressant Evaluation of Five Novel
Heterocyclic Tryptophan-Hybrid Derivatives
Gamal A. Elmegeed1, Ayman R. Baiuomy2,3, Mervat M. Abdelhalim1, and Hanaa Y. Hana1
1 Hormones Department, National Research Centre, Dokki, Cairo, Egypt
2 Pharmacology Department, National Research Centre, Dokki, Cairo, Egypt
3 Faculty of Medical Sciences, Taif University, Taif, USA
This study aimed at evaluating the reactivity of L-Tryptophan (TRP) 1 towards various chemical
reagents to produce new bi- and tri-heterocyclic systems providing basic pharmacological activ-
ities. Indol-3-yl hydroxyoxazol-2-yl acetonitrile derivatives 5 and 6, indol-3-yl-hydroxyoxazol-2-yl-
1,2,4-triazine derivatives 8 and 9, indol-3-yl-hydroxyoxazol-2-yl-aminopyrazole derivatives 11a, b,
and indol-3-yl-hydroxyoxazol-2-yl-aminoisoxazole derivative 12 were synthesized via straightfor-
ward and efficient methods. The structures were characterized by spectral data (IR, 1H-NMR, 13C-
NMR, and MS) and the purity was ascertained by microanalysis. Also, this work was extended to
study the potential role of the novel synthesized TRP derivatives 5, 6, 9, 11a, and 12 as antide-
pressant and sedative agents in comparison with TRP. All compounds showed significant antide-
pressant activity in the forced-swimming test at two doses (50 or 100 mg/kg). Also, all tested com-
pounds (at 50 or 100 mg/kg) produced a significant decrease in locomotor activity of mice dur-
ing a 30 min observation period. The most potent antidepressant and sedative effect was pro-
duced by the tri-heterocyclic compounds 9 and 12, followed by 11a and TRP.
Keywords: Antidepressant / Oxazole / Pyrazole / Sedative / Tryptophan /
Received: October 11, 2009; Accepted: December 11, 2009
DOI 10.1002/ardp.200900244
studies agree that the sedative-hypnotic action of TRP is
moderate [6]. However, TRP is able to give therapeutic
improvement in cases of chronic and severe insomniacs
characterized by both sleep-onset and sleep-maintenance
problems only after several days to weeks of therapy [7].
The heterocyclic antidepressants are the mainstay of
antidepressant treatment and the development of new
synthetic heterocyclic compounds as antidepressant, sed-
ative, or analgesic agents has progressed considerably
during the past decade [8–10]. In the scope of a research
program aimed at the development of new alternatives
to treat neurological disorders [11–13], in the present
study, we describe the synthesis of new functionalized
bi-heterocyclic or tri-heterocyclic compounds (Fig. 1)
attached to the essential pharmacophoric features of the
TRP molecule. The heterocycles have been constructed
using the amino group of TRP as a ring nitrogen or amino
substituent. Also the systemic antidepressant and seda-
tive activity of the newly synthesized compounds were
investigated in comparison with TRP.
Introduction
Antidepressant drugs have greatly improved the out-
come of depression. However, a considerable proportion
of patients show only partial or no response, regardless
of the treatment received [1]. As an essential amino acid,
L-tryptophan (TRP) is the precursor of the neurotransmit-
ter 5-hydroxy tryptamine (5HT, serotonin) [2]. TRP admin-
istration is known to elevate mood in healthy subject [3],
while depletion of TRP caused a rapid lowering of mood
[4]. Although TRP is not used clinically against depression
for a general lack of efficacy, there is much evidence that
it has a detectable antidepressant effect and enhances
the effects of other antidepressive therapies [5]. Most
Correspondence: Gamal A. Elmegeed, Department of Chemistry and
Biochemistry, Texas Tech University, Lubbock, TX 79409-1061, USA.
E-mail: gamalae@hotmail.com
Fax: +1 806 742-1289
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Arch. Pharm. Chem. Life Sci. 2010, 343, 261–267
Figure 1. Structures of compounds 9, 11a, and 12.
Results and discussion
Chemistry
It was described that the benzoylation of TRP 1 afforded
the corresponding tryptophan phenyl ester 2 through a
two-step reaction [14]. Compound 2 reacted with ethyl
cyanoacetate in refluxing dimethylformamide (DMF) to
give the Nb-acetonitrilocarbonyltryptophan phenyl ester
derivative 3 via elimination of ethanol (Scheme 1). The
mass spectrum (EI-MS) of compound 3 showed the molec-
ular ion peak at m/z 346 [M+ – 1] (65%). The IR spectrum of
compound 3 revealed the presence of two NH groups at
m = 3410 to 3365 cm–1, a CN group at m = 2220 cm–1, and
two C=O groups at m = 1730 and 1680 cm–1. Also, the 1H-
NMR spectrum of compound 3 showed two multiplets at
d = 6.92–7.14 ppm (5H, C6H5) and d = 7.26 ppm (4H, C6H4),
and showed two D2O-exchangeable singlets at d = 8.78
and 10.02 ppm for the two NH groups. The 13C-NMR spec-
trum showed the presence of d = 25.9, 30.2 (2 CH2), 116.7
(CN), 121.8, 126.5, 127.5, 129.1, 152.0 (C-phenyl), 169.6,
171.8 (2C=O) ppm.
Therapeutic agents containing an oxazole moiety have
attracted the attention of researchers in the pharmaceut-
ical chemistry; derivatives of oxazole proved to be suit-
able as antidepressant agents [15, 16]. In view of this
information, here, we would like to report on the forma-
tion and characterization of novel indolyl oxazole deriv-
atives. Compound 3 seemed to be an interesting candi-
date for further chemical transformations; the reaction
of compound 3 with benzenediazonium chloride gave
the hydrazone derivative 4. Heating of compound 4 in
acetic acid solution gave the phenylhydrazonoindol-3-yl-
hydroxyoxazol-2-yl acetonitrile derivative 5 (Scheme 1).
The structures of the latter products were based on the
analytical and spectral data (cf. Experimental Section).
The structure of compound 5 was supported by its inde-
pendent synthesis, heating of compound 3 in acetic acid
solution to give a single product with the molecular for-
mula C14H11N3O2: The structure of indol-3-yl-hydroxyox-
azol-2-yl acetonitrile derivative 6 is considered as the
Scheme 1. Synthesis of compounds 3–6.
reaction product on the basis of the IR spectrum which
showed the presence of OH and NH stretching at m =
3745–3476 cm–1 and CN stretching at m = 2223 cm–1. The
1H-NMR spectrum showed the presence of two CH2 groups
at d = 3.62 and 3.78 ppm and a broad singlet at d = 5.47
ppm for the OH group in addition to the disappearance
of the benzoate-group signals. The coupling of com-
pound 6 with benzenediazonium chloride gave the same
phenylhydrazonoindol-3-yl-hydroxyoxazol-2-yl acetoni-
trile derivative 5 (Scheme 1) which was confirmed via the
mixed m.p. and fingerprint IR.
Taking into account the structural requirements for
antidepressant agents, several new triazine, pyrazole and
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Arch. Pharm. Chem. Life Sci. 2010, 343, 261–267
Five Novel Heterocyclic Tryptophan-Hybrid Derivatives
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Scheme 2. Synthesis of compounds 7–9.
Scheme 3. Synthesis of compounds 10–12.
isoxazole derivatives have been prepared and evaluated
for their antidepressant activity [9, 10, 17]. The reaction
of compound 5 with phenylisothiocyanate in refluxing
DMF/Et3N solution gave the corresponding indol-3-yl-
hydroxyoxazol-2-yl-5-imino-1,2,4-triazine derivative 8.
The formation of compound 8 was assumed to proceed
via the non-isolable adduct intermediate 7 followed by
intermolecular cyclization (Scheme 2). Heating of com-
pound 8 in absolute ethanol/NaOH solution gave the
Pharmacology
The antidepressant and sedative activity of the novel syn-
thesized bi-heterocyclic or tri-heterocyclic compounds 5,
6, 9, 11a, and 12 were investigated individually in com-
parison with TRP.
Screening for antidepressant activity
The effects of the tested compounds at two doses (50 or
100 mg/kg, administered i.p. in Swiss albino mice of
either sex) as antidepressants were studied using Por-
solt's forced-swimming test in comparison with TRP and
using the tricyclic antidepressant drug, imipramine (15
mg/kg, i.p.) as a reference drug. 60 min after the i.p.-
administration, all tested compounds displayed a signifi-
cant antidepressant effect compared with the control
group. The tricycles, indol-3-yl-hydroxyoxazol-2-yl-1,2,4-
triazine derivative 9 at 50 mg/kg and the indol-3-yl-
hydroxyoxazol-2-yl-aminoisoxazole derivative 12 at 100
mg/kg were more potent than compounds 5 (100 mg/kg),
12 (50 mg/kg), and 11a (50 mg/kg) as well as the parent
compound TRP (100 mg/kg). The effect of compounds 6,
11a (100 mg/kg), and TRP (50 mg/kg) was comparable to
that of imipramine (15 mg/kg; Table 1).
indol-3-yl-hydroxyoxazol-2-yl-1,2,4-triazin-5-one
deriv-
ative 9 (Fig. 1). Elucidation of the proposed structures 8
and 9 was based on their correct elemental analyses and
1
compatible IR, H-NMR, 13C-NMR, and mass spectral data
(Experimental Section).
The acetonitrile moiety in compound 6 showed pro-
nounced activity towards several chemical reagents.
Compound 6 reacts with benzaldehyde in dioxane/piper-
idine solution to give the benzal derivative (indol-3-yl-
hydroxyoxazol-2-yl-phenylacrylonitrile derivative) 10
(Scheme 3). The behavior of compound 10 towards some
nitrogen nucleophiles was investigated. Thus, it reacted
with either hydrazine hydrate or phenyl hydrazine in
refluxing absolute ethanol to afford the corresponding
indol-3-yl-hydroxyoxazol-2-yl-aminopyrazole derivatives
11a (Fig. 1) and 11b, respectively (Scheme 3). Formation of
the latter products is explained in terms of the first addi-
tion of the hydrazine to the a,b-unsaturated nitrile moi-
ety followed by auto-dehydrogenation. Compound 10
also reacted with hydroxylamine hydrochloride in
refluxing ethanolic sodium acetate solution to afford the
indol-3-yl-hydroxyoxazol-2-yl-aminoisoxazole derivative
12 (Fig. 1, Scheme 3). The analytical and spectral data of
the latter products are in agreement with the proposed
structures (Experimental Section).
Screening for sedative activity
The effects of the tested compounds at two doses (50 or
100 mg/kg, i.p.) as sedative agents were studied compared
with the saline-treated group of mice (Table 2). All tested
compounds produced a significant decrease in locomo-
tor activity of mice during a 30-min observation period.
The sedative effect of all the tested compounds was dose-
dependent. The most potent effect was produced by com-
pounds 9 and 12, followed by 11a and TRP. Compound 12
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Arch. Pharm. Chem. Life Sci. 2010, 343, 261–267
Table 1. Effect of tested compounds on the duration of immobil-
ity in Porsolt's forced-swimming test (n = 6).
heterocyclic moiety. The tri-heterocyclic derivatives 9
and 12 are more effective than the bi-heterocyclic deriv-
atives 5 and 6, this may be attributed to the addition of
triazine and isoxazole rings to the indolyloxazole moiety.
Also, the addition of a pyrazole ring to the indolyloxazole
moiety to form compound 11a increases the antidepres-
sant and sedative activity, but triazine and isoxazole
rings are more potent in this respect. The results verified
the importance of the presence of indole, oxazole, pyra-
zole, triazine, and isoxazole moieties as pharmacophores
for the antidepressant and sedative activities. Directed by
the structure of the tested compounds it is likely that
these compounds have a dual mechanism-of-action for
their antidepressant and sedative activities. Further stud-
ies should be made to establish the mechanism-of-action
with the possibility to formulate a potent antidepressant
and sedative prescription.
Treatment
Dose
(mg/kg)
Duration of immobil-
ity € SEM (s)
Saline
Imipramine
Compound 5
295.35 € 1.21
236.00 € 14.0*
237.74 € 7.8*
254.52 € 5.5*
248.75 € 7.2*
235.66 € 7.1*
224.05 € 12.2*
240.41 € 3.1*
252.98 € 5.6*
236.26 € 6.4*
251.70 € 7.5*
220.38 € 12.4*
237.14 € 7.6*
253.72 € 5.0*
15
50
100
50
100
50
100
50
100
50
100
50
Compound 6
Compound 9
Compound 11a
Compound 12
TRP
100
* Significant difference compared to saline-treated control
group (p 0.05). Compounds 9 (at 50 mg/kg) and 12 (at 100 mg/
kg), were more potent than compounds 5 (100 mg/kg), 12 (50
mg/kg), and 11a (50 mg/kg) as well as TRP (100 mg/kg). The
effect of compounds 6, 11a (100 mg/kg), and TRP (50 mg/kg) was
similar in efficacy compared to that of imipramine (15 mg/kg)
(ANOVA and Duncan's multiple range test).
Conclusion
In conclusion, we have described a facile synthesis of
novel promising antidepressant and sedative agents, and
we also investigated the importance of incorporating a
(50 mg/kg) displayed a significant sedative effect com- bi-heterocyclic moiety to the TRP nucleus to form new
pared with 11a (50 mg/kg) and TRP (50 mg/kg). TRP is effective hybrid molecules. All compounds showed signif-
more potent than the bi-heterocyclic derivatives 5 and 6 icant antidepressant and sedative activity at two doses
(Table 2).
(50 or 100 mg/kg). The three tri-heterocyclic compounds
namely 9, 11a, and 12 showed even better antidepressant
and sedative activity which exceed that of the parent
Structure-activity relationship
Analysis of the structure-activity relationship indicates reference TRP. Finally, the encouraging result of the anti-
that the antidepressant and sedative activity of the tested depressant and sedative activity displayed by these com-
compounds seems to be linked to the presence of a tri- pounds may be of interest for further derivatization and
Table 2. Influence of the tested compounds on spontaneous locomotor activity and exploratory movements in mice (n = 6).
Treatment
Dose (mg/kg)
Number of movements € SEM % inhibition of locomotor
during 30 min
activity
Saline
Compound 5
478.8 € 56.3
269.7 € 75.6*
212.3 € 45.9*
254.0 € 57.9*
208.5 € 37.2*
223.6 € 44.6*
153.2 € 38.4*
243.0 € 23.4*
190.7 € 25.7*
162.7 € 8.5*
138.4 € 25.6*
248.3 € 9.2*
198.5 € 20.2*
50
100
50
100
50
100
50
100
50
43.6
55.6
46.9
56.4
53.2
68.0
49.2
60.1
66.0
71.0
48.1
58.5
Compound 6
Compound 9
Compound 11a
Compound 12
TRP
100
50
100
* Significant difference compared to saline-treated control group (p a 0.05). The sedative effect of all the tested compounds was
dose-dependent. Compound 12 (50 mg/kg) displayed a significant sedative effect compared with 11a (50 mg/kg) and TRP (50 mg/kg)
(ANOVA and Duncan's multiple range test).
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Arch. Pharm. Chem. Life Sci. 2010, 343, 261–267
Five Novel Heterocyclic Tryptophan-Hybrid Derivatives
265
further studies in the hope of finding a new potent anti- Phenyl 2-(2-cyano-2-phenylhydrazonoacetamido)-3-(1H-
depressant and sedative prescription.
indol-3-yl)propanoate 4
A solution of compound 3 (1.73 g, 5 mmol) in absolute ethanol
(30 mL) containing sodium acetate (0.5 g) was cooled to 0–58C,
then treated gradually under continuous stirring with a cold sol-
ution of benzenediazonium chloride salt (5 mmol; prepared by
the addition of sodium nitrite solution (0.34 g, 5 mmol) to a cold
solution of aniline (0.46 g, 5 mmol) in concentrate hydrochloric
acid (3 mL)). After the addition of the diazonium salt was com-
pleted, the reaction mixture was stirred at room temperature
for 1 h. The precipitated product, separated upon dilution with
cold water, was filtered off, washed several times with water,
dried, and recrystallized from ethanol to yield 1.62 g (72%) of
compound 4. Orange powder, m.p.: 169–1718C, IR (KBr, cm–1) m:
3463–3375 (3 NH), 3050 (CH-aromatic), 2956–2878 (CH-ali-
phatic), 2225 (CN), 1735, 1682 (2 C=O), 1670 (C=N), 1576 (C=C);1H-
NMR (DMSO-d6, ppm) d: 3.06 (m, 2H, CH2), 4.86 (m, 1H, CH), 6.80
(s, 1H, C-2 indole), 6.78–7.02 (m, 5H, C6H5), 6.78–7.10 (m, 5H,
C6H5), 7.28 (m, 4H, C6H4), 7.75, 8.38, 10.12 (3s, 3H, 3 NH, D2O-
exchangeable); EI-MS m/z (%): 451 [M+9] (35), 345 (24), 130 (54), 106
(100), 77 (37). Anal. calcd. for C26H21N5O3 (451.477): C, 69.17; H,
4.69; N, 15.51. Found: C, 68.94; H, 4.87; N, 15.38.
Experimental
Synthetic methods, analytical and spectral data
All chemicals were purchased from commercials suppliers and
used directly without further purification. The appropriate pre-
cautions in handling moisture-sensitive compounds were under-
taken. All melting points were measured using an electro-ther-
mal capillary melting point apparatus (Bꢀchi 535; Bꢀchi, Flawil,
Switzerland) and were uncorrected; the IR spectra are expressed
in cm–1 and recorded using KBr pellets in a Pa-9721 IR spectrome-
ter (Shimadzu, Japan). 1H-NMR and 13C-NMR spectra were
recorded with Jeol instrument (Jeol, Japan), at 270 and 125 MHz,
respectively, in DMSO-d6 or CDCl3 as solvents. The chemical shifts
(d) were recorded in ppm relative to TMS. Mass spectra were
recorded on a GCMS-QP 1000 Ex spectra mass spectrometer (Shi-
madzu) operating at 70 eV. Elemental analyses were carried by
the Micro-analytical Data Unit at the National Research Center,
Giza, Egypt and the Micro-analytical data Unit at Cairo Univer-
sity. The reactions were monitored by thin layer chromatogra-
phy (TLC) which was carried out using Merck 60 F254 aluminum
sheets (Merck, Germany) and visualized by UV light (254 nm).
The mixtures were separated by preparative TLC and gravity
chromatography.
General procedure for 2-(phenylhydrazono)-2-[4-(1H-
indol-3-yl)methyl-5-hydroxyoxazol-2-yl]acetonitrile 5 and
2-[4-(1H-indol-3-yl)methyl-5-hydroxyoxazol-2-
yl]acetonitrile 6
A solution of either compound 4 (2.25 g, 5 mmol) or compound
3 (1.73 g, 5 mmol) in acetic acid was heated under reflux for 4–5
h until all the reactants had disappeared as indicated by TLC.
The reaction mixture was poured over an ice/water mixture and
the resulting semisolid was subjected to extraction with chloro-
form (2630 mL). The organic layer was dried over magnesium
sulfate and then filtrated. The solid product that formed in each
case on removal of the solvent under vacuum was collected,
dried, and recrystallized from the appropriate solvent.
Compound 5 was also synthesized from compound 6 using
the same synthetic method for compound 4 and confirmed via
the mixed m.p. and fingerprint IR.
Phenyl 2-amino-3-(1H-indol-3-yl)propanoate 2
The starting compound 2 was prepared according to the pub-
lished procedure [14]. Yield: 3.47 g (62%), IR (KBr, cm–1) m: 3445–
3265 (NH2, NH), 3035 (CH-aromatic), 2945–2865 (CH-aliphatic),
1734 (C=O), 1593 (C=C); 1H-NMR (CDCl3, ppm) d: 2.44 (s, 2H, NH2,
D2O-exchangeable), 3.23 (m, 2H, CH2), 4.25 (m, 1H, CH), 6.78 (s,
1H, C-2 indole), 6.78–7.04 (m, 5H, C6H5), 7.18 (m, 4H, C6H4), 9.92
(s, 1H, NH, D2O-exchangeable); EI-MS m/z (%): 280 [M+9] (45), 130
(100), 116 (34), 77 (67). Anal. calcd. for C17H16N2O2 (280.321): C,
72.84; H, 5.75; N, 9.99; O, 11.42. Found: C, 72.75; H, 6.05; N,
10.22.
Phenyl 2-(2-cyanoacetamido)-3-(1H-indol-3-
yl)propanoate 3
Compound 5
Yellow crystals from ethanol, yield: 1.19 g (67%), m.p.: 188–
1908C, IR (KBr, cm–1) m: 3760–3456 (OH, 2 NH), 3035 (CH-aro-
matic), 2976–2886 (CH-aliphatic), 2227 (CN), 1678 (C=N), 1546
(C=C); 1H-NMR (CDCl3, ppm) d: 3.46 (m, 2H, CH2), 6.83 (s, 1H, C-2
indole), 6.69–7.02 (m, 5H, C6H5), 7.19 (m, 4H, C6H4), 5.75 (brs, 1H,
OH, D2O-exchangeable), 7.38, 10.02 (2s, 2H, 2 NH, D2O-exchange-
able); 13C-NMR (DMSO-d6, ppm) d: 24.9 (CH2), 119.3, 122.2, 120.5,
111.6, 137.1, 122.9, 110.4, 127.3 (C-indole), 150.7, 138.6, 124.3 (C-
oxazole), 143.2, 116.5, 128.5, 118.7 (C-phenyl), 155.8 (C=N), 118.3
(CN); EI-MS m/z (%): 357 [M+9]( 42), 227 (100), 130 (43), 107 (100), 77
(32). Anal. calcd. for C20H15N5O2 (357.356): C, 67.22; H, 4.23; N,
19.60. Found: C, 66.98; H, 4.50; N, 19.33.
To a solution of 2 (1.09 g, 5 mmol) in dry DMF (20 mL), an equiva-
lent amount of ethyl cyanoacetate (0.56 g, 5 mmol) was added.
The reaction contents were heated under reflux for 4 h and
monitored by TLC. Then, the solvent was removed under
reduced pressure and the residue was treated with ethyl acetate.
The solid product so separated was filtered, dried, and recrystal-
lized from absolute ethanol to give the yellow crystals of com-
pound 3. Yield: 1.25 g (72%), m. p.: 138–1408C; IR (KBr, cm–1) m:
3410–3365 (2 NH), 3053 (CH-aromatic), 2934–2864 (CH-ali-
phatic), 2220 (CN), 1730, 1680 (2 C=O), 1590 (C=C); 1H-NMR
(DMSO-d6, ppm) d: 2.89 (m, 2H, CH2), 3.36 (s, 2H, CH2CN), 4.65 (m,
1H, CH), 6.82 (s, 1H, C-2 indole), 6.92–7.14 (m, 5H, C6H5), 7.26 (m,
4H, C6H4), 8.78, 10.02 (2s, 2H, 2NH, D2O-exchangeable); 13C-NMR
(DMSO-d6, ppm) d: 25.9, 30.2 (2 CH2), 53.2 (CH), 112.1, 119.7,
120.4, 121.6, 122.3, 122.8, 129.4, 136.5 (C-indole), 116.7 (CN),
121.8, 126.5, 127.5, 129.1, 152.0 (C-phenyl), 169.6, 171.8 (2C=O);
EI-MS m/z (%): 346 [M+9 – 1] (65), 264 (34), 130 (100), 116 (36), 77
(46). Anal. calcd. for C20H17N3O3 (347.367): C, 69.15; H, 4.93; N,
12.10. Found: C, 68.75; H, 5.15; N, 11.82.
Compound 6
Brown crystals from methanol, yield: 0.89 g (71%), m.p.: 206–
2078C, IR (KBr, cm–1) m: 3745–3476 (OH, NH), 3035 (CH-aromatic),
2986–2887 (CH-aliphatic), 2223 (CN), 1672 (C=N), 1564 (C=C); 1H-
NMR (CDCl3, ppm) d: 3.62 (m, 2H, CH2), 3.78 (s, 2H, CH2CN), 6.88
(s, 1H, C-2 indole), 7.16 (m, 4H, C6H4), 5.47 (brs, 1H, OH, D2O-
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exchangeable), 10.12 (s, 1H, NH, D2O-exchangeable); 13C-NMR
(DMSO-d6, ppm) d: 18.4, 23.2 (2 CH2), 119.7, 123.2, 120.6, 112.0,
136.6, 123.4, 111.0, 127.5 (C-indole), 150.7, 139.0, 125.2 (C-oxa-
zole), 117.9 (CN); EI-MS m/z (%): 253 [M+9] (35), 130 (23), 123 (100),
116 (52). Anal. calcd. for C14H11N3O2 (253.256): C, 66.40; H, 4.38;
N, 16.59. Found: C, 66.59; H, 4.62; N, 16.73.
tography over alumina. Elution with n-hexane removed side
products and further elution with ethyl acetate gave the pure
product 10. Yield: 0.50 g (74%), m.p.: 231–2338C; IR (KBr, cm–1) m:
3728–3487 (OH, NH), 3035 (CH-aromatic), 2983–2880 (CH-ali-
1
phatic), 2225 (CN), 1659 (C=N), 1554 (C=C); H-NMR (DMSO-d6,
ppm) d: 3.72 (m, 2H, CH2), 5.64 (brs, 1H, OH, D2O-exchangeable),
6.72 (s, 1H, C-2 indole), 7.13 (s, 1H, CH), 7.18–7.30 (m, 5H, C6H5),
7.39 (m, 4H, C6H4), 10.25 (s, H, NH, D2O-exchangeable); EI-MS m/z
(%): 341 [M+9] (27), 211 (100), 130 (28), 90 (76). Anal. calcd. for
C21H15N3O2 (341.363): C, 73.89; H, 4.43; N, 12.31. Found: C, 74.09;
H, 4.62; N, 12.57.
6-[4-(1H-Indol-3-yl)methyl-5-hydroxyoxazol-2-yl]-5-imino-
2,4-diphenyl-1,2,4-triazine-3-thione 8
To a solution of compound 5 (0.71 g, 2 mmol) in dimethylforma-
mide (20 mL) containing a catalytic amount of triethylamine (0.5
mL), phenylisothiocyanate (0.26 g, 2 mmol) was added. The reac-
tion mixture was refluxed for 4 h until all starting material had
disappeared as indicated by TLC. The reaction mixture was left to
cool at room temperature, poured into an ice/water mixture and
neutralized with dilute hydrochloric acid. The obtained solid
product was collected by filtration, dried, and recrystallized from
methanol to yield 0.61 g (62%) of compound 8, pale brown crys-
tals, m. p.: 242–2438C; IR (KBr, cm–1) m: 3695–3456 (OH, 2 NH),
3032 (CH-aromatic), 2975–2867 (CH-aliphatic), 1672 (C=N), 1568
(C=C), 1195 (C=S); 1H-NMR(CDCl3, ppm)d: 3.71(m, 2H, CH2), 5.35(s,
1H, OH, D2O-exchangeable), 6.55 (s, 1H, C-2 indole), 6.57–7.02 (m,
10H, 2 C6H5), 7.12 (m, 4H, C6H4), 8.94, 10.12 (2s, 2H, 2 NH, D2O-
exchangeable); 13C-NMR (DMSO-d6, ppm) d: 24.7 (CH2), 119.8,
121.0, 122.3, 111.3, 136.9, 122.5, 111.3, 127.5 (C-indole), 151.5,
138.4, 125.4 (C-oxazole), 155.3, 162.4, 180.3 (C-triazine), 127.0,
128.9, 124.8, 138.2 (C-phenyl), 122.3, 129.2, 125.6, 133.6 (C-phe-
nyl); EI-MS m/z (%): 492 [M+9] (29), 362 (35), 279 (100), 130 (43), 77
(52). Anal. calcd. for C27H20N6O2S (492.552): C, 65.84; H, 4.09; N,
17.06; S, 6.51. Found: C, 66.08;H, 4.33; N, 17.30; S, 6.29.
General procedure for 4-(1H-Indol-3-yl)methyl-2-(3-
amino-5-phenyl-1H-pyrazol-4-yl)oxazol-5-ol 11a and 4-
(1H-indol-3-yl)methyl-2-(3-amino-1,5-diphenylpyrazol-4-
yl)oxazol-5-ol 11b
To a solution of compound 10 (1.70 g, 5 mmol) in absolute etha-
nol (30 mL), either hydrazine hydrate (0.25 g, 5 mmol) or phenyl
hydrazine (0.54 g, 5 mmol) was added. The reaction mixture, in
each case, was heated under reflux for 4 to 6 h until all the reac-
tion material had disappeared as indicated by TLC. The reaction
mixture was left to cool at room temperature, poured into an
ice/water mixture. The solid that formed in each case, was fil-
tered off, dried, and recrystallized from the appropriate solvent.
Compound 11a
Pale brown crystals from ethanol, yield: 1.20 g (65%), m. p.: 183–
1848C; IR (KBr, cm–1) m: 3760–3455 (OH, 2 NH, NH2), 3032 (CH-aro-
matic), 2976–2886 (CH-aliphatic), 1673 (C=N), 1546 (C=C); 1H-
NMR (CDCl3, ppm) d: 3.64 (m, 2H, CH2), 4.23 (s, 2H, NH2, D2O-
exchangeable), 5.75 (s, 1H, OH, D2O-exchangeable), 6.72 (s, 1H, C-
2 indole), 6.88–7.04 (m, 5H, C6H5), 7.18 (m, 4H, C6H4), 10.08, 11.32
(2s, 2H, 2 NH, D2O-exchangeable); 13C-NMR (CDCl3, ppm) d: 23.2
(CH2), 119.7, 122.0, 120.5, 111.8, 136.5, 123.6, 109.4, 127.5 (C-
indole), 160.2, 138.2, 125.3 (C-oxazole), 154.2, 93.7, 145.3 (C-pyra-
zole), 133.2, 126.5, 129.5, 128.0 (C-phenyl); EI-MS m/z (%): 371
[M+9] (55), 213 (72), 158 (100), 130 (73), 77 (56). Anal. calcd. for
C21H17N5O2 (371.392): C, 67.91; H, 4.61; N, 18.86. Found: C, 68.19;
H, 4.40; N, 19.13.
6-[4-(1H-Indol-3-yl)methyl-5-hydroxyoxazol-2-yl]-2,4-
diphenyl-3-thioxo-1,2,4-triazin-5-one 9
Compound 8 (0.98 g, 2 mmol) was taken in absolute ethanol (30
mL) containing sodium hydroxide (5.0 mL, 10%). The reaction
mixture was heated under reflux for 3 h. Then, the solvent was
removed under reduced pressure. The semisolid residue, which
formed, was subjected to column chromatography over silica
gel. Elution with ethyl acetate/chloroform mixture (1:1) gave yel-
low crystals from product 9. Yield: 0.75 g (76%), m. p.: 214–
2168C; IR (KBr, cm–1) m: 3698–3457 (OH, NH), 3030 (CH-aromatic),
2984–2873 (CH-aliphatic), 1710 (C=O), 1668 (C=N), 1562 (C=C),
1193 (C=S); 1H-NMR (CDCl3, ppm) d: 3.67 (m, 2H, CH2), 5.32 (s, 1H,
OH, D2O-exchangeable), 6.46 (s, 1H, C-2 indole), 6.58–7.13 (m,
10H, 2 C6H5), 7.22 (m, 4H, C6H4), 9.24 (s, H, NH, D2O-exchange-
able); 13C-NMR (DMSO-d6, ppm) d: 23.4 (CH2), 119.3, 120.2, 122.6,
111.6, 137.2, 122.4, 110.7, 127.8 (C-indole), 150.6, 138.3, 125.4 (C-
oxazole), 155.9, 161.4, 180.0 (C-triazine), 126.2, 129.5, 125.5,
138.7 (C-phenyl), 121.3, 128.2, 124.8, 132.7 (C-phenyl); EI-MS m/z
(%): 493 [M+9] (34), 363 (45), 280 (100), 130 (23), 77 (40). Anal. calcd.
for C27H19N5O3S (493.536): C, 65.71; H, 3.88; N, 14.19; S, 6.50.
Found: C, 65.94; H, 4.05; N, 14.33; S, 6.27.
Compound 11b
Brown crystals from dioxane, yield: 1.15 g (68%), m. p.: 200–
2028C; IR (KBr, cm–1) m: 3783–3425 (OH, NH, NH2), 3028 (CH-aro-
1
matic), 2983–2889 (CH-aliphatic), 1668 (C=N), 1564 (C=C); H-
NMR (CDCl3, ppm) d: 3.70 (m, 2H, CH2), 4.03 (s, 2H, NH2, D2O-
exchangeable), 5.37 (s, 1H, OH, D2O-exchangeable), 6.74 (s, 1H, C-
2 indole), 6.82–7.15 (m, 10H, 2 C6H5), 7.21 (m, 4H, C6H4), 10.28 (s,
1H, NH, D2O-exchangeable); 13C-NMR (CDCl3, ppm) d: 23.7 (CH2),
118.9, 122.3, 121.2, 111.3, 136.8, 122.8, 110.2, 127.5 (C-indole),
159.4, 138.4, 125.4 (C-oxazole), 153.7, 93.3, 143.4 (C-pyrazole),
133.2, 127.5, 129.8, 128.3 (C-phenyl), 139.3, 120.5, 129.8, 126.7
(C-phenyl); EI-MS m/z (%): 447 [M+9] (46), 317 (23), 213 (84), 234
(100), 130 (47), 77 (37). Anal. calcd. for C27H21N5O2 (447.488): C,
72.47; H, 4.73; N, 15.65. Found: C, 72.29; H, 4.92; N, 15.83.
2-[4-(1H-Indol-3-yl)methyl-5-hydroxyoxazol-2-yl]-3-
phenylacrylonitrile 10
To a solution of compound 6 (0.50 g, 2 mmol) in dioxane (30 mL)
containing a catalytic amount of piperidine (0.5 mL), benzalde-
hyde (0.21 g, 2 mmol) was added. The reaction mixture was
refluxed for 3 h until all starting material had disappeared as
indicated by TLC; then, the solvent was removed under vacuum.
The crude product so obtained was purified by column chroma-
4-(1H-Indol-3-yl)methyl-2-(3-amino-5-phenylisoxazol-4-
yl)oxazol-5-ol 12
To a solution of compound 10 (1.70 g, 5 mmol) in absolute etha-
nol (30 mL) containing anhydrous sodium acetate (1 g), hydrox-
ylamine hydrochloride (0.41 g, 5 mmol) was added. The reaction
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Arch. Pharm. Chem. Life Sci. 2010, 343, 261–267
Five Novel Heterocyclic Tryptophan-Hybrid Derivatives
267
mixture was heated under reflux for 4 h and monitored by TLC.
After cooling, the reaction mixture was evaporated under vac-
uum. The resulting solid was dissolved in diethyl ether and fil-
trated to remove any unreacted hydroxylamine hydrochloride.
The solvent was allowed to evaporate at room temperature and
the semisolid residue, which had formed, was scratched with
chilled ethyl acetate. The solid separated out was filtered and
washed with chilled ethyl acetate to give a white powder from
compound 12. Yield: 1.40 g (75%), m.p.: 163–1658C; IR (KBr, cm–1)
m: 3732–3450 (OH, NH, NH2), 3030 (CH-aromatic), 2975–2879 (CH-
aliphatic), 1670 (C=N), 1540 (C=C); 1H-NMR (DMSO-d6, ppm) d:
3.60 (m, 2H, CH2), 4.03 (s, 2H, NH2, D2O-exchangeable), 5.60 (brs,
1H, OH, D2O-exchangeable), 6.75 (s, 1H, C-2 indole), 6.83–7.02 (m,
5H, C6H5), 7.20 (m, 4H, C6H4), 10.28 (s, H, NH, D2O-exchangeable);
13C-NMR (DMSO-d6, ppm) d: 23.0 (CH2), 118.0, 121.6, 120.5, 111.3,
136.5, 123.2, 110.2, 127.6 (C-indole), 161.5, 138.5, 124.5 (C-oxa-
zole), 150.2, 100.3, 158.7 (C-isoxazole), 130.0, 127.2, 129.6, 128.7
(C-phenyl); EI-MS m/z (%): 372 [M+9] (28), 213 (47), 159 (100), 130
(53), 77 (46). Anal. calcd. for C21H16N4O3 (372.377): C, 67.73; H,
4.33; N, 15.05. Found: C, 67.50; H, 4.59; N, 14.83.
Screening for sedative effect
Spontaneous locomotor activity and exploratory movements in
mice was measured in the commercially available motor-activity
apparatus (Ugo Basile, Italy). The investigated compounds 5, 6, 9,
11a, 12, and TRP were injected i.p. at a dose 50 or 100 mg/kg.
Thirty minutes after the injection, mice were placed in the activ-
ity monitor, in which the activity was monitored for 30 min.
Statistical Analyses
Data are expressed as mean € S.E. Differences between vehicle
control and treatment groups were tested using one-way ANOVA
followed by multiple comparisons by the Duncan's multiple
comparison test. A probability value less than 0.05 was consid-
ered statistically significant.
The authors acknowledge the financial support of the National
Research Center, Egypt (grant no.: E-8040505- 2008/2009).
The authors have declared no conflict of interest.
Pharmacological assay
Animals
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Swiss albino mice of either sex, weighing 20–25 g (body weight),
aged 6 to 8 weeks, were supplied by the Animal House at
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12 h light/dark cycle at 20 € 28C and fed with standard labora-
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formed after approval from the Ethics Committee of the
National Research Centre and in accordance with the recom-
mendations for the proper care and use of laboratory animals
(NIH publication No. 85-23, revised 1985). Equal groups of six
mice per group were used in all experiments.
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