Isovanillin derived N-(un)substituted hydroxylamines possessing an ortho-allylic group: Valuable precursors to bioactive N-heterocycles

Article abstract of DOI:10.1039/c3ob42460j

The intramolecular 1,3-dipolar cycloaddition of isovanillin derived N-aryl hydroxylamines possessing ortho-allylic dipolarophiles affords novel benzo analogues of tricyclic isoxazolidines that can be readily transformed into functionalized lactams, γ-amin

Full text of DOI:10.1039/c3ob42460j

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Isovanillin derived N-(un)substituted
hydroxylamines possessing an ortho-allylic group:
valuable precursors to bioactive N-heterocycles†
Cite this: DOI: 10.1039/c3ob42460j
Balakrishna Dulla,a,b Neelima D. Tangellamudi,*a Sridhar Balasubramanian,c
Swapna Yellanki,a,d Raghavender Medishetti,a,d Rakesh Kumar Banote,a,d
Girish Hari Chaudhari,a,d Pushkar Kulkarni,*a,d Javed Iqbal,*a Oliver Reiser*b and
Manojit Pal*a
The intramolecular 1,3-dipolar cycloaddition of isovanillin derived N-aryl hydroxylamines possessing
ortho-allylic dipolarophiles affords novel benzo analogues of tricyclic isoxazolidines that can be readily
transformed into functionalized lactams, γ-aminoalcohols and oxazepines. The corresponding N-unsub-
stituted hydroxylamines give rise to tetrahydroisoquinolines. Anxiogenic properties of these compounds
are tested in zebra fish.
Received 10th December 2013,
Accepted 29th January 2014
DOI: 10.1039/c3ob42460j
www.rsc.org/obc
The development of operationally simple strategies that allow
direct and fast access to an array of densely functionalized
small molecules of potential pharmacological interest is the
central focus of modern organic synthesis. The search for pri-
vileged building blocks that allows their broad diversification
into pharmacologically relevant scaffolds is therefore of
immense importance, and accordingly, we identified isovanil-
lin derived N-hydroxylamines as key precursors to hybrid struc-
tures combining vanillyl and N-heterocyclic moieties.
Fig. 1 Design of C by combining A and B.
Isoxazolidines (A, Fig. 1) are important heterocycles1 com-
monly found in a diverse array of bioactive natural products
(e.g. cycloserin, acivicine). They are also valuable intermediates
in organic synthesis.2 Compounds such as capsaicin, the main
capsaicinoid in chili peppers containing a vanillyl moiety (B,
Fig. 1), on the other hand have attracted considerable interest
as they target TRPV1 (transient receptor potential vanilloid 1),
a molecular integrator for a broad variety of seemingly un-
related noxious stimuli.3 A few small molecule based TRPV1
antagonists and agonists have been advanced into clinical
trials for pain relief.3 This and our long-standing interest in
bioactive fused heterocycles prompted us to design novel mole-
cular scaffolds by combining the isovanillyl moiety and the
isoxazolidine ring in a single framework C (Fig. 1). We antici-
pated that isovanilloid based tricyclic drug-like molecules
derived from
C might show pharmacological properties
similar to capsaicin. While several methods have been
reported for the synthesis of isoxazolidines, the dipolar cyclo-
addition of nitrile oxides/hydroxylamines to allyl dipolaro-
philes appears to be attractive.4,5 The intramolecular version of
1,3-dipolar cycloadditions6–8 of hydroxylamines to simple
allylic or N/O-allylic dipolarophiles has also been reported.6
For example, benzo analogues of tricyclic isoxazolidines have
been prepared by using this strategy7 (Scheme 1). While all
these methods were not precisely suitable for our purpose
these findings however provided a valuable lead to develop a
strategically related but unique approach to C (Scheme 1).
Herein we report the intramolecular 1,3-dipolar cycloaddition
of isovanillin derived N-substituted hydroxylamines possessing
allylic dipolarophiles at the o-position. In an extension of this
approach the corresponding N-unsubstituted hydroxylamines
aDr Reddy’s Institute of Life Sciences, University of Hyderabad Campus, Gachibowli,
Hyderabad 500 046, India. E-mail: jiqbal@ilsresearch.org,
manojitpal@rediffmail.com, neelimadt@ilsresearch.org; Tel: +91 40 6657 1500
bInstitut fur Organische Chemie, Universität Regensburg, Universitätsstr. 31, 93053
Regensburg, Germany. E-mail: Oliver.Reiser@chemie.uni-regensburg.de
cLaboratory of X-ray Crystallography, Indian Institute of Chemical Technology,
Uppal Road, Hyderabad 500607, India
dZephase Therapeutics, University of Hyderabad Campus, Gachibowli, Hyderabad
500046, India. E-mail: pushkark@drils.org
†Electronic supplementary information (ESI) available: Experimental pro-
cedures, spectral data for all new compounds, copies of NMR spectra and results
of in vitro study. CCDC 909838. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c3ob42460j
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Table 1 The reactions of 1a–b with various N-aryl hydroxylaminesa
Entry 6; Ar=
1; Z=
Products
Yieldb (%)
96
1
2
3
4
5
6
7
6a; Ph
6b; 4-MeC6H4
6c; 4-NCC6H4
6d; 3-(MeSO2NH)C6H4 1a
6e; 2-NCC6H4
1a; H
1a
1a
8a : 9a (1 : 2)c
8b : 9b (1 : 2)c 100
8c : 9c (1 : 2)c
8d : 9d (1 : 2)c
7e
94
95
88
78
58
1a
1b; CO2Et 8f
1b 10
Scheme 1 Synthesis of benzo analogues of tricyclic isoxazolidine.
6a;
6e
a Reactions were performed using 1a–b (1 mmol) and 6 (2 mmol) in
EtOH (5 mL) at 80 °C for 3–5 h under nitrogen. b Isolated overall yield.
c Ratio was changed to 2 : 1 when the reaction was performed in the
absence of any solvent at 130 °C.
Scheme 2 Preparation of 1a–b and their reaction with NH2OH·HCl.
Further chemical transformations of nitrone 3 obtained from 1b.
Fig. 2 ORTEP representation of 8a. Thermal ellipsoids are drawn at the
give rise to tetrahydroisoquinolines. Further synthetic appli-
cations and pharmacological properties of some of these com-
pounds synthesized are presented.
50% probability level.
undergo intermolecular [3 + 2] cycloaddition with ethyl acry-
late or to tetrahydroisoquinoline 5 upon reduction with Zn/
AcOH (Scheme 2).
As the starting point, o-substituted allyl isovanillins 1a and
1b were prepared via sequential O-allylation of isovanillin
followed by Claisen rearrangement and cross metathesis
(Scheme 2).9 However, neither 1a nor 1b afforded the expected
isoxazolidines when reacted with NH2OH·HCl. While oxime 2a
was obtained from 1a, the acceptor substituted 1b reacted
further to yield 3 via an intramolecular aza-Michael addition
of the hydroxylamine nitrogen, being apparently favored over
the expected [3 + 2] cycloaddition. Notably, the conversion of
1b to 3 was not affected significantly by additives like NaOAc
or Et3N or by the reaction temperature. The nitrone 3 can be
further transformed, e.g. to the regioisomeric tetrahydro-1H-
isoxazolo[3,2-a]isoquinolines 4a and 4b when allowed to
We then focused on the reaction of N-aryl hydroxylamines 6
with 1a–b (Table 1), affording a mixture of two regioisomers 8
and 9 (1 : 2 at 80 °C or 2 : 1 at 130 °C, Table 1) via an apparent
formation of a Z-nitrone10 7. The 2 : 1 mixture of 8 and 9
observed at 130 °C was perhaps due to the reversible formation
of 7 from 9 and then to the thermally stable product 8.6a The
regioisomers 8 and 9 were separated by column chromato-
graphy on silica gel using EtOAc–hexane as an eluant.
The structure of 8a was unequivocally characterized by
single crystal X-ray diffraction studies11 (Fig. 2) that indicated
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Scheme 4 Synthesis of γ-aminoalcohol 13 and oxazepine 14 from 8a.
Fig. 3 Endo approach of the CvC moiety to the Z-nitrone leading to
8f with trans-relationship of HC with HA and HB (from NOESY spectrum).
Scheme 3 Synthesis of γ-aminoalcohol 11 and lactam 12 from 8f.
the cis-fusion (HA and HB) of rings A and B. The reaction of 6e
with 1a however stopped at the stage of the nitrone 7a (entry 5,
Table 1). While the reason for this observation was not clear,
an intramolecular interaction between the –N+–O− moiety and
–CN group could prevent the reaction from proceeding further.
Notably, the aldehyde 1b afforded 8f (entry 6, Table 1) as an
isolable major product under the same reaction conditions. 1H
NMR analysis of 8f (the NOESY spectrum) revealed the coup-
ling of HC with the vicinal proton HB but not with the HA (long
range coupling) indicating the relative trans-relationship of HC
with HA and HB (Fig. 3). An endo approach of the CvC moiety
to the Z-nitrone aided by the secondary orbital interactions
between the nitrone nitrogen p orbitals and the –CvO group10
possibly favored the formation of this particular diastereomer
(Fig. 3). The reaction of 1b with 6e was also successful but
afforded a 1,2,3,4-tetrahydronaphthalene 1012 possibly via the
formation of an isomeric bridged cycloadduct (e.g. 9) followed
by cleavage of its N–O bond in a single pot. To demonstrate
the utility of the present isoxazolidine synthesis, 8f was con-
verted to a γ-aminoalcohol 11 and densely functionalized
lactam 12 separately (Scheme 3). Similarly, 8a was also con-
verted to another γ-aminoalcohol 13 and then to the oxazepine
derivative 14 (Scheme 4).
Fig. 4 Structures of compounds 15–17 and 19–28.
of invasive procedures or euthanasia.14 We first tested
the hypothesis that capsaicin administration should result
in anxiogenic behaviour in adult zebrafish. Thereafter, com-
pounds were tested in this model to identify the most potent
anxiogenic compounds (Fig. 6). Capsaicin when tested in this
model showed clear anxiogenic behaviour, which was evident
from the fact that the % time spent in the light box was signifi-
cantly lower in the capsaicin treated fish as compared to the
control at 10 µg kg−1 dose and the effect was dose dependent
(Fig. 7A). Erratic movements (number and duration) were also
observed and they increased in a dose dependent manner in
capsaicin treated fish (Fig. 7B & 7C). This suggested that
Based on capsaicin’s known anxiogenic activity in various
animal models,13 compounds 15–17 and 19–28 (Fig. 4, see
ESI† for compound 18) obtained after removal of the TBS pro-
tecting group (see ESI†) of various previously synthesized com-
pounds e.g. 3, 8, 9, 10, 11, 12, 13 and 14 along with a positive
control clonidine (a known anxiolytic agent) were tested in the
zebrafish model of anxiety14 (Fig. 5). We used the adult zebra-
fish model of the light/dark box anxiety test to assess our com-
pounds as this method is simple and does not require the use
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Fig. 5 The figure shows the evaluation of anxiety like behaviour in the
adult zebrafish using the light/dark box paradigm. Normal fish move
across freely in both light and dark environments; however, when
anxious their movements are higher in the dark environment as com-
pared to light.
Fig. 6 Screening of compounds for anxiolytic activity. The effect of
compounds was assessed at 10 mg kg−1 in the light/dark box paradigm
to evaluate the parameter of percentage time spent in light. Com-
pound-15 was found to have the maximum effect in this study.
Fig. 7 Multi-dose evaluation of capsaicin and 15 in the adult zebrafish
model of anxiety for (A) percentage time spent in light, (B) duration of
erratic movements, and (C) the number of erratic movements using the
light/dark box paradigm.
capsaicin showed an anxiogenic effect in adult zebrafish that
was similar to the effect seen in other mammalian species.
Evaluation of the test compound at a single dose was
performed and compound 15 obtained from 8c was identified
as most active when tested initially at 10 mg kg−1 (Fig. 6).
compared to control fish (Fig. 7A).15 Erratic movements (dur-
ation and number) were also observed and there was a dose-
dependent increase in the compound 15 group (Fig. 7B & 7C).
In conclusion, isovanillin derived N-(un)substituted hydroxyl-
amines possessing an o-allylic group have been identified as
valuable precursors to bioactive N-heterocycles. Thus novel
benzo analogues of tricyclic isoxazolidine possessing potential
A
multi-dose evaluation of 15 confirmed its capsaicin
like anxiogenic activity as fish administered 15 showed a sig-
nificant reduction in the % time spent in the light as
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anxiogenic properties were synthesized for the first time via an 379.19 (100%); HRMS (ESI): calcd for C26H37NO5SiNa (M + Na)+
intramolecular 1,3-dipolar cycloaddition of N-aryl hydroxyl- 494.2338 found 494.2341.
amines possessing activated/unactivated allylic dipolarophiles
at the o-position. The corresponding N-unsubstituted hydroxyl-
amine afforded tetrahydroisoquinoline. The one-pot
methodology presented here is amenable to the synthesis of
functionalized lactams, γ-aminoalcohols, oxazepines, etc. and
may find wide applications in organic synthesis/medicinal
chemistry.
Preparation
of
5-(tert-butyldimethylsilyloxy)-3-hydroxy-6-
methoxy-1-phenyl-1,3a,4,8b-tetrahydroindeno[1,2-b]pyrrol-2(3H)-
one (12). To a solution of 8f (0.470 g, 1.0 mmol) in AcOH–
THF–H2O (2 : 1 : 1, 40 mL) was added Zn dust (0.4 g,
6.1 mmol) at 60 °C. The reaction mixture was stirred for 5 h.
After completion of the reaction the mixture was cooled to
room temperature and Zn was filtered off. The filtrate was con-
centrated to remove THF, and neutralized with saturated
NaHCO3 solution. The reaction mixture was extracted with
CH2Cl2 (2 × 20 mL). The combined organic layer was washed
with brine (5 mL), dried over anhydrous Na2SO4, filtered and
concentrated. The residue was purified by column chromato-
graphy using EtOAc–hexane (3 : 7) as an eluent to yield a color-
less solid (0.255 g, 60%); mp: 160–163 °C Rf = 0.4 (3 : 7 EtOAc–
Experimental
Chemistry
Representative experimental procedures
Hex); IR (cm−1): 3450, 3088, 2965, 2874, 1700, 1630, 1565; H
1
1,3-Dipolar addition of 3 with ethyl acrylate. To a solution of
5-(tert-butyldimethylsilyloxy)-3-(2-ethoxy-2-oxoethyl)-6-methoxy-
3,4 dihydroisoquinoline 2-oxide (3, 0.393 g, 1 mmol) in
ethanol (5 mL) was added ethylacrylate (0.5 g, 5 mmol) and
the mixture was refluxed for 3.5 h. After completion of the
reaction, the solvent was removed under high vacuum and the
residue was purified by column chromatography on silica gel
(eluting with 10% EtOAc–hexane) to afford the desired product(s).
For the spectral data of the compounds synthesized e.g. 4a and
4b, see ESI.†
The reaction of 1a–b with various N-aryl hydroxylamines. To a
solution of aldehyde (1a–b, 1.0 mmol) in ethanol (5 mL) was
added aryl hydroxyl amine (6, 2 mmol) and MgSO4 (5 mmol)
under a nitrogen atmosphere. The reaction mixture was
refluxed for 3–5 h (for inversion in the yields of regio isomers
the reaction mixture was heated at 130 °C for 12 h). After com-
pletion of the reaction, ethanol was removed under vacuum
and the residue was purified by column chromatography on
silica gel to give the desired product. For the spectral data of
the compounds synthesized e.g. 8, 9, 10 etc., see ESI.†
NMR (400 MHz, CDCl3) δ 7.40–7.33 (m, 2H), 7.26–7.20 (m, 3H),
6.46 (q, J = 8.2 Hz, 2H), 5.30 (d, J = 6.30 Hz, 1H), 4.73 (d, J =
8.3 Hz, 1H), 3.70 (s, 3H), 3.59–3.50 (m, 1H), 3.30 (s, 1H),
3.24–3.03 (m, 2H), 1.00 (s, 9H), 0.15 (d, J = 1.5 Hz, 6H); 13C
NMR (100 MHz, CDCl3) δ 173.3, 150.7, 141.2, 136.6, 132.8,
128.8 (2C), 126.7, 125.4 (2C), 118.7, 109.9, 71.0, 65.6, 55.1,
42.6, 28.3, 26.0 (3C), 18.6, −4.04, −4.07; mass (ES): m/z 448.19
(M + Na, 20%), 371.23 (40%), 313.19 (100%); HRMS (ESI):
calcd for C24H31NO4SiNa (M + Na)+ 448.1920, found 448.1909.
Preparation of (4-(tert-butyldimethylsilyloxy)-5-methoxy-1-(phe-
nylamino)-2,3-dihydro-1H-inden-2-yl)methanol (13). The title
compound was synthesized from 8a by using a procedure
similar to the synthesis of 11; brown viscous oil, yield (88%),
Rf = 0.4 (1 : 9 EtOAc–Hex); IR (cm−1): 3373, 3079, 2930, 2854,
1
1600, 1494, 1443; H NMR (400 MHz, CDCl3) δ 7.27–7.22 (m,
2H), 6.89–6.80 (m, 3H), 6.73 (q, J = 8.1 Hz, 2H), 5.06 (d, J =
6.6 Hz, 1H), 3.84–3.77 (m, 4H), 3.72 (dd, J = 11.2, 4.6 Hz, 1H),
3.40–3.27 (bs, 1H), 3.05–2.86 (m, 3H), 1.02 (s, 9H), 0.19 (d, J =
12.2 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ 150.1, 148.0, 141.1,
137.3, 133.1, 129.4 (2C), 118.1, 116.1, 113.6 (2C), 110.8, 63.4,
Preparation of (4-(tert-butyldimethylsilyloxy)-5-methoxy-1-(phe-
nylamino)-2,3-dihydro-1H-inden-2-yl)-2-hydroxyacetate (11). To a 61.0, 55.3, 44.5, 31.1, 25.9 (3C), 18.6, −4.0, −4.2; mass (ES): m/z
solution of (3R,3aR,8bR)-ethyl-5-(tert-butyldimethylsilyloxy)-6- 422.21 (M + H, 40%), 400.23 (35%), 307.17 (100%); HRMS
methoxy-1-phenyl-3,3a,4,8b-tetrahydro-1H-indeno[1,2-c]isoxazole- (ESI): calcd for C23H34NO3Si (M
3-carboxylate (8f) (0.470 g, 1.0 mmol) in MeOH (5 mL) was 400.2313.
+
H)+ 400.2307 found
added 5% Pd/C (47 mg) under balloon pressure of H2. TLC
shows completion of reaction after 6 h. The Pd was filtered
Preparation of 7-(tert-butyldimethylsilyloxy)-8-methoxy-1-phenyl-
5,5a,6,10b-tetrahydro-1H-indeno[1,2-e][1,4]oxazepin-2(3H)-one
through celite, and the filtrate was concentrated under high (14). To a solution of (4-(tert-butyldimethylsilyloxy)-5-methoxy-
vacuum. The residue was purified by column chromatography 1-(phenylamino)-2,3-dihydro-1H-inden-2-yl)methanol
(13)
with EtOAc–hexane (2 : 8) as an eluent to yield the desired (0.422 g, 1.0 mmol) in dry DMF (10 mL) were added ethyl-
product; yield (80%). Rf = 0.4 (2 : 8 EtOAc–Hex); IR (cm−1): bromo acetate (0.2 g, 1.2 mmol) and oven dried K2CO3
1
3340, 3079, 2930, 2847, 1681, 1650, 1585; H NMR (400 MHz, (0.548 g, 4.0 mmol). The mixture was refluxed for 36 h.
CDCl3) δ 7.18 (t, J = 7.93 Hz, 2H), 6.82–6.65 (m, 5H), 5.15 (d, J = After completion of the reaction, the mixture was diluted with
7.3 Hz, 1H), 4.34 (d, J = 4.7 Hz, 1H), 3.96 (q, J = 10.7, 7.2 Hz, saturated NH4Cl solution (20 mL) and extracted with CH2Cl2
2H), 3.77 (s, 3H), 3.63 (dd, J = 10.7, 7.1 Hz, 1H), 3.28 (bs, 1H), (2 × 25 mL). The combined organic layer was collected, washed
3.26–2.96 (m, 2H), 1.11 (t, J = 7.1 Hz, 3H), 1.01 (s, 9H), 0.17 with 2 N HCl and water, then dried over anhydrous Na2SO4,
(d, J = 6.3 Hz); 13C NMR (100 MHz, CDCl3) δ 172.7, 150.8, filtered and concentrated. The residue was purified by column
141.2, 136.6, 135.9, 132.7, 128.8 (2C), 126.7, 125.3 (2C), chromatography on silica gel using EtOAc–hexane (3 : 7) as an
118.7, 109.9 (2C), 71.1, 65.6, 55.1, 42.7, 28.2, 25.9 (3C), eluent to afford the desired product as a brown solid (0.228 g,
18.6, 14.4, −4.1 (2C); Mass (ES): m/z 494.23 (M + Na, 100%), 60%); mp: 280–282 °C; yield (60%), Rf = 0.4 (3 : 7 EtOAc–Hex);
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IR (cm−1): 3021, 2973, 2877, 1720, 1615, 1585; 1H NMR and standard error of the mean ( SEM). Data were analysed
(400 MHz, CDCl3) δ 7.41 (t, J = 7.7 Hz, 2H), 7.34 (d, J = 7.3 Hz, using analysis of variance (ANOVA) followed by Tukey’s
2H), 7.31–7.23 (m, 1H), 6.92 (d, J = 8.0 Hz, 1H), 6.75 (d, J = 8.0 multiple comparative test. Statistical significance was set at the
Hz, 1H), 5.30 (d, J = 7.1 Hz, 1H), 4.34 (d, J = 15.5 Hz, 1H), 4.11 p < 0.05 level.
(dd, J = 12.6, 3.9 Hz, 1H), 3.91 (d, J = 15.5 Hz, 1H), 3.79 (s, 3H),
3.72 (dd, J = 12.7, 4.8 Hz, 1H), 2.94 (dd, J = 20.0, 13.3 Hz, 3H),
1.00 (s, 9H), 0.20 (s, 3H), 0.13 (s, 3H); 13C NMR (100 MHz,
CDCl3) 172.6, 150.2, 144.5, 141.3, 134.8, 131.8, 129.2 (2C),
Acknowledgements
126.9, 126.5 (2C), 114.7, 110.5, 72.5, 71.7, 68.8, 55.2, 43.5, 32.0, NDT thanks DST, New Delhi, India (fast-track grant no. SR/FT/
25.8 (3C), 18.5, −4.2, −4.4; mass (ES): m/z 462.20 (M + Na, CS-005/2010) for financial support. The authors thank DRILS
100%), 440.22 (M + H, 10%), 289.16 (80%); HRMS (ESI): calcd for analytical support.
for C25H33NO4 NaSi (M + Na)+ 462.2076, found 462.2060.
A typical procedure for the removal of tert-butyldimethylsilyloxy
group of compound 8c. To a solution of 4-(5-(tert-butyldimethyl-
silyloxy)-6-methoxy-3,3a,4,8b-tetrahydro-1H-indeno[1,2-c]isoxazol-
Notes and references
1-yl) benzonitrile (8c) (1 mmol) in dry THF (5 mL) was added
tetra-butyl ammonium iodide (1.5 mmol) at 0 °C. The reaction
mixture was stirred at the same temperature for 0.5 h, and
THF was removed under high vacuum followed by extraction
with DCM (2 × 10 mL). The combined DCM layer was
collected, dried over anhydrous Na2SO4, filtered and concen-
trated. The residue was purified using column chromatography
over silica gel to give the product 4-(5-hydroxy-6-methoxy-
3,3a,4,8b-tetrahydro-1H-indeno[1,2-c]isoxazol-1-yl)benzonitrile
(15) as a white solid; mp 180 °C; yield (88%), Rf = 0.2 (1 : 9
EtOAc–Hex); IR (cm−1): 3430, 3256, 3060, 2973, 2868, 2205,
1 M. Sutharchanadevi and R. Muragan, in Comprehensive
Heterocyclic Chemistry II, ed. A. R. Katritzky, C. W. Rees and
E. F. V. Scriven, Pergamon Press, Oxford, UK, 1996, vol. 3,
pp. 221–260.
2 For selected examples, see: (a) J. W. Bode, N. Fraefel,
D. Muri and E. M. Carreira, Angew. Chem., Int. Ed., 2001,
40, 2082; (b) A. R. Minter, A. A. Fuller and A. K. Mapp,
J. Am. Chem. Soc., 2003, 125, 6846; (c) A. A. Fuller, B. Chen,
A. R. Minter and A. K. Mapp, J. Am. Chem. Soc., 2005, 127,
5376; (d) T. J. Maimone, J. Shi, S. Ashida and P. S. Baran,
J. Am. Chem. Soc., 2009, 131, 17066.
3 M. Pal, S. Angaru, A. Kodimuthali and N. Dhingra, Curr.
Pharm. Des., 2009, 15, 1008.
4 A. Padwa, in Comprehensive Organic Synthesis, ed.
B. M. Trost and I. Fleming, Pergamon Press, Oxford, UK,
1991, vol. 4, pp. 1069–1168.
5 (a) G. S. Lemen, N. C. Giampietro, M. B. Hay and
J. P. Wolfe, J. Org. Chem., 2009, 74, 2533; (b) D. Bonne,
L. Salat, J.-P. Dulcère and J. Rodriguez, Org. Lett., 2008, 10,
5409; (c) J. Peng, D. Jiang, W. Lin and Y. Chen, Org. Biomol.
Chem., 2007, 5, 1391; (d) M. B. Hay and J. P. Wolfe, Angew.
Chem., Int. Ed., 2007, 46, 6492; (e) D. A. Evans, H. J. Song
and K. R. Fandrick, Org. Lett., 2006, 8, 335.
1
1620, 1555, 1486, 1276; H NMR (400 MHz, CDCl3) δ 7.58 (d,
J = 8.9 Hz, 2H), 7.19 (d, J = 8.9 Hz, 2H), 6.93 (d, J = 8.1 Hz, 1H),
6.84 (d, J = 8.2 Hz, 1H), 5.67 (s, 1H), 5.35 (d, J = 7.6 Hz, 1H),
4.10–4.05 (m, 1H), 3.98–3.85 (m, 4H), 3.56–3.48 (m, 1H),
3.30–3.22 (m, 1H), 3.03 (dd, J = 16.9, 3.1 Hz, 1H); 13C NMR
(100 MHz, CDCl3) δ 154.0, 146.6, 141.4, 134.5 (2C), 133.4,
128.6, 119.5, 116.1, 114.0 (2C), 110.7, 103.8, 75.0, 74.6, 56.4,
46.7, 34.2, 29.7; Mass (ES): m/z 309.13 (M + H 100%).
For the spectral data of other compounds synthesized e.g.
16–17 and 19–28, see ESI.†
Biology
6 (a) V. Nair and T. D. Suja, Tetrahedron, 2007, 63, 12247;
(b) K. P. Kaliappan, P. Das and N. Kumar, Tetrahedron Lett.,
2005, 46, 3037; (c) F. Heaney, J. Fenlon, P. McArdle and
D. Cunningham, Org. Biomol. Chem., 2003, 1122;
(d) E. Frank, J. Wölfling, B. Aukszi, V. König,
T. R. Schneider and G. Schneider, Tetrahedron, 2002, 58,
6843; (e) G. Broggini, C. L. Rosa, T. Pilati, A. Terraneo and
G. Zecchi, Tetrahedron, 2001, 57, 8323; (f) T. K. M. Shing
and Y. L. Zhong, Tetrahedron, 2001, 57, 1573.
7 (a) J. H. Jeong and S. M. Weinreb, Org. Lett., 2006, 8, 2309;
(b) P. J. Chua, B. Tan, L. Yang, X. Zeng, D. Zhu and
G. Zhong, Chem. Commun., 2010, 46, 7611.
8 (a) S. Moutel, M. Shipman, O. R. Martin, K. Ikeda and
N. Asano, Tetrahedron: Asymmetry, 2005, 16, 487;
(b) P. J. Dransfield, S. Moutel, M. Shipman and V. Sik,
J. Chem. Soc., Perkin Trans. 1, 1999, 3349; (c) P. Pádár,
A. Bokros, G. Paragi, P. Forgo, Z. Kele, N. M. Howarth and
L. Kovács, J. Org. Chem., 2006, 71, 8669.
Evaluation of test compounds in the zebrafish model of
anxiety
Materials and methods. Wild type zebrafish (Danio rerio)
were maintained as per the procedure reported earlier.16 The
studies on anxiety assessment using the light/dark box para-
digm were conducted based on the parameters of percentage
time spent in light, duration of erratic movements and the
number of erratic movements from the published protocol.14
Drug administration was carried out by a procedure reported
earlier.17 Clonidine, an anxiolytic agent, was used as a positive
control to ascertain the validity of the experiments. Evaluation
was conducted in three parts: (a) screening of capsaicin for
assessment of its anxiogenic activity in adult zebrafish, (b)
screening of test compounds at a single dose to identify the
most potent anxiogenic agent, and (c) multi-dose studies on
the most potent agent to verify anxiogenic activity.
Statistical analysis. Statistical analysis was performed using
GraphPad Prism software. Data were represented using mean
Org. Biomol. Chem.
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Paper
9 (a) J. P. Freeman, Chem. Rev., 1983, 83, 241; (b) K. S. Huang 13 S. S. Manna and S. N. Umathe, Brain Res., 2011, 1425, 75.
and E. C. Wang, Tetrahedron Lett., 2001, 42, 6155; 14 A. Stewart, C. Maximino and T. Marques de Brito, in
(c) K. Voigtritter, S. Ghorai and B. H. Lipshutz, J. Org.
Chem., 2011, 76, 4697.
Zebrafish Neurobehavioral Protocols, ed. A. V. Kalueff and
M. Cachat, Neuromethods, 2011, vol. 51, pp. 157–167.
10 T. Tejero, A. Dondoni, I. Rojo, F. L. Merchan and P. Merino, 15 For a video showing the effect of clonidine, capsaicin and
Tetrahedron Lett., 1997, 53, 3301.
11 CCDC 909838.
12 While a particular diastereomer was isolated after routine
work-up and purification of the reaction mixture (see ESI†)
compound 15 on adult zebrafish, see: ESI.†
16 G. H. Chaudhari, K. S. Chennubhotla, K. Chatti and
P. Kulkarni, J. Pharmacol. Toxicol. Methods, 2013, 67,
115.
in this case the formation of other diastereomer(s) cannot 17 R. K. Banote, S. Koutarapu, K. S. Chennubhotla, K. Chatti
be ruled out completely.
and P. Kulkarni, Epilepsy Behav., 2013, 27, 212.
This journal is © The Royal Society of Chemistry 2014
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