Synthesis and biological evaluation of nitric oxide-releasing derivatives of capsaicin as analgesia drugs

Article abstract of DOI:10.2174/157018011793663831

TRPV1 is a ligand-gated non-selective cation channel that is considered to be an important pain integrator. Capsaicin, the prototypical TRPV1 agonist, has a clear therapeutic potential. In this letter, for lowering its pungency, a series of nitric oxide-releasing derivatives of capsaicin were designed and synthesized, including 10 compounds which were the direct combination of capsaicin and dihydro capsaicin with various nitric oxide donors. Preliminary biological tests suggested the compounds had both TRPV1 agonist activity and nitric oxide release activity. Compound B2, B5, B8 had better analgesic activity than capsaicin. Based on these results, Compound B2, B5, B8 can be considered as lead candidates for the further development of analgesic drugs.

Full text of DOI:10.2174/157018011793663831

76
Letters in Drug Design & Discovery, 2011, 8, 76-81
Synthesis and Biological Evaluation of Nitric Oxide-releasing Derivatives
of Capsaicin as Analgesia Drugs
Liang Ge, jingjie Wang#, Xiaoyan Zhang, Huibin Zhang, Hai Qian*, Wenlong Huang and
Jinpei Zhou*
School of Pharmacy, China Pharmaceutical University, 24 Tongjiaxiang, Nanjing 210009, China
Received May 10, 2010: Revised September 14, 2010: Accepted September 20, 2010
Abstract: TRPV1 is a ligand-gated non-selective cation channel that is considered to be an important pain integrator.
Capsaicin, the prototypical TRPV1 agonist, has a clear therapeutic potential. In this letter, for lowering its pungency, a se-
ries of nitric oxide-releasing derivatives of capsaicin were designed and synthesized, including 10 compounds which were
the direct combination of capsaicin and dihydro capsaicin with various nitric oxide donors. Preliminary biological tests
suggested the compounds had both TRPV1 agonist activity and nitric oxide release activity. Compound B2, B5, B8 had
better analgesic activity than capsaicin. Based on these results, Compound B2, B5, B8 can be considered as lead candidates
for the further development of analgesic drugs.
Keywords: Analgesia Drugs, Nitric Oxide-Releasing, Capsaicin Derivatives, TRPV1 Agonist.
INTRODUCTION
Capsaicin and dihydro capsaicin were combined with the NO
donors, to form a new class of potent TRPV1 agonist. As a
result, 10 capsaicin derivatives were synthesized and their
activities were evaluated.
Pain is a complex perceptual experience that can have a
profound impact on the quality of a person’s life [1]. Cur-
rently, due to its complicated pathological mechanism, all
marketed drugs against pain have their deficiencies
[2].Transient receptor vanilloid type-1 (TRPV1), formerly
known as the vanilloid receptor (VR1), is a ligand-gated
non-selective cation channel that is considered to be an im-
portant pain integrator [3]. It has been shown to be important
in both nociception and the inflammatory response, and
hence has rapidly become a significant therapeutic target [4].
METHODS
Evaluation of TRPV1 Agonist Activity
The TRPV1 agonist activity assays were performed using
the method reported by the reference [6]. Human embryonic
kidney (HEK)-293 cells overexpressing the human TRPV1
were grown as monolayers in minimum essential medium
supplemented with nonessential amino acids, 10% fetal calf
serum, and 0.2 mM glutamine and maintained under 5% CO2
at 37°C. The effect of the compounds on [Ca2+]i was deter-
mined by using Fura-2, a selective intracellular fluorescent
probe for Ca2+. Prior to Ca2+ measurements the cells were
seeded at a cell density of 20,000 cells/well 3–4 days from
measurements to yield 90% confluence in 96-well plates.
Acute intracellular increase in Ca2+ levels was measured in a
fluorescence reader using the cell permeable fluores-cent
probe Fura-2/AM, dissolved in DMSO to 2 mM. The cells
were incubated in cell medium with 2μM Fura-2/AM for 30
min in 37 ˚C followed by two washings in Krebs–Ringer–
Hepes (KRH) buffer, incubation in KRH buffer for 30 min in
darkness. The ratio of 340 /380nm excitatory wavelengths
was measured without interruption before (basal level) and
during the 2 min exposure to the test compounds or cap-
saicin. All compounds used were diluted to homogenous
solutions in KRH buffer in 10 ꢀM. The ratio values after
addition of the chemicals was gotten within the two minutes
of registration.
Capsaicin, the prototypical TRPV1 agonist, which is re-
sponsible for the piquancy of hot-chilli peppers, is a versatile
natural compound, the biological use of which is covered by
more than 900 patents [5]. Its effect, traditionally referred to
as desensitization, has a clear therapeutic potential. In fact,
capsaicin-containing creams have been in clinical use for
decades to relieve painful conditions such as diabetic neu-
ropathy. Though the highly pungency limited its use, cap-
saicin has great value for further research [6].
Nitric oxide (NO) is naturally generated from L-arginine
by the action of NO synthase (NOS) and a key signaling
molecule involved in regulating the numerous physiologic
and pathologic processes [7]. NO can increase gastric blood
flow and inhibit neutrophil adherence as well as protect the
gastric mucosa against damage induced by irritants [8]. In
particular, the NO-naproxen derivative has displayed an en-
hanced analgesic activity [9].
In this letter, according to the molecular structure of cap-
saicin, intended for lowering its pungency, a series of nitric
oxide-releasing derivatives of capsaicin were designed.
Evaluation of Nitric Oxide Release Activity
*Address correspondence to these authors at the School of Pharmacy, China
Pharmaceutical University, Nanjing 210009, People’s Republic of China;
Tel: +86-(0)25-83271302; Fax: +86-(0)25-83271297;
E-mail: qianhai24@163.com; Tel: +86-(0)25- 85230904;
Fax: +86-(0)25-83271480; E-mail: jpzhou668@163.com
The nitric oxide release activity in vitro were determined
by Greiss assay. Briefly, MDA-MB-231 cells (5ꢁ106/well)
were treated in triplicate with 100 ꢀM of one of the com-
pounds for 24h. The cells were harvested lyzed. The cell
#Contributed equally to the first author.
1570-1808/11 $58.00+.00
© 2011 Bentham Science Publishers Ltd.

Synthesis and Biological Evaluation of Nitric Oxide-Releasing Derivatives of Capsaicin
Letters in Drug Design & Discovery, 2011, Vol. 8, No. 1 77
Table 1. The Structures of the Target Compounds B1-B10
O
R2
H
N
R1
O
O
R1
R2
Compound
B1
PhO2S
N
N
O
O
B2
B3
PhO2S
N
N
O
O
O
PhO2S
O
O
O
N
N
O
O
B4
O
PhO2S
O
O
O
N
N
O
O
B5
B6
O
PhO2S
O
O
N
O
N
O
O
O
PhO2S
O
O
N
O
N
O
O
B7
B8
O
O2NO
O
O2NO
B9
O2NO
B10
O2NO
lysates were mixed with Griess for 30-300 min, followed by
measuring at 540 nm. The cells treated with diluent were
used as negative controls for the background levels of ni-
trate/nitrite production, while with sodium nitrate at different
concentrations was used as positive controls for the standard
curve [10]. According to the determined levels of ni-
trate/nitrite formed from individual compounds in the cells,
the nitric oxide release activity of the compounds was ob-
tained.
Evaluation of Analgesic Activity
According to the method of tail-immersion test [10], an-
algesic activity was carried out in 14 groups (buprofen
group, capsaicin group, dihydro capsaicin group, ten com-
pounds synthesized groups and blank group) with 112 mice
(half male and half female mice, 8 mice for each group).
Ibuprofen, capsaicin, dihydro capsaicin and ten compounds
synthesized were dissolved by 0.5% CMC-Na aqueous solu-
tion. The Compounds (30 mg/kg) was orally admin-

78 Letters in Drug Design & Discovery, 2011, Vol. 8, No. 1
Ge et al.
istered by gastric intubation once a day for 4 days (ibupro-
fen, capsaicin, dihydro capsaicin and vehicle administered as
control). In the last day, baseline latency of each mouse in
each group was determined twice, 5 min apart and averaged
to give a single pre-drug latency. The pre-drug latency is
presented as the mean (±SE) latency in second. Determine
the post-drug latency of pain response of the mice at 30min
after administration, according to the method mentioned
above. Analgesia data are expressed as the increased per-
centage of pain threshold.
mouse’s tail-immersion reaction and B2, B5, B8 show better
than capsaicin, which means that the compounds have potent
analgesic activity.
SYNTHESIS EXPERIMENTAL SECTION
All reagents were of commercial quality and were used
as received. Solvents were dried and purified by using stan-
dard techniques. Reactions were monitored by TLC. Melting
1
points were uncorrected. H NMR spectra were recorded on
a Brucker ACF-300 MHz spectrometer with TMS as the
internal standard in CDCl3. Mass Spectra were made with
HP1100 analyzer. Element analyses were performed on
Carlo Erba 1106 instrument.
Increased percentage of pain threshold (%) = [(Post-drug
latency- pre-drug latency)/ pre-drug latency]*100.
In the equation, pre-drug latency and post-drug latency
are represented the mean value of each group.
General Procedure for the Preparation of B1-B10
RESULTS AND DISCUSSION
Synthesis
(a) Capsaicin or dihydro capsaicin 0.50g (1.64mmol),
NaOH 0.26g(6.5mmol) and different derivatives of furazan
(1.97mmol), dissolved in 35ml dry CH2Cl2.The mixture was
stirred at 30-35 ˚C for 0.5 h. Added 0.47g
(2.3mmol)DCC/5ml CH2Cl2 solution under ice bath and the
mixture was stirred at 30-35 ˚C. The reaction was monitored
by TLC and filtrated. The filtrate was concentrated under
reduced pressure to give a residue which was partitioned
between ethyl acetate and water. The ethyl acetate extract
was washed with saturated brine, dried over Na2SO4. After
evaporation of solvent, the crude product was subjected to
silica gel column, and chromatographed with eluent (petro-
leum ether /ethyl acetate 1:2) to yield the desired product B1,
B2.
We designed and synthesized a series of nitric oxide-
releasing derivatives of capsaicin, including 10 compounds
which were the direct combination of capsaicin and dihydro
capsaicin with various NO donors. The target compounds
were shown in the Table 1.
Biological Activity
The new compounds were tested for TRPV1 agonist ac-
tivity, nitric oxide release activity and analgesic activity. The
results of primary pharmacological test are as followed: In
the TRPV1 agonist high throughput screening model (Table
2), all the compounds enhance Ca2+ inflow, among which
compound show better than capsaicin. The NO release activ-
ity in vitro was determined by Greiss assay (Table 2). The
result showed that these compounds all have NO release. In
the model of mouse tail-immersion test (Table 3), compound
B2, B3, B4, B5, B6, B7, B8, B9 can significantly inhibit
(b) Capsaicin or dihydro capsaicin 0.50g (1.64mmol),
DMAP 0.02g(0.16mmol) and different derivatives of furazan
(1.97mmol), dissolved in 35ml dry CH2Cl2.The mixture was
stirred at 30-35 ˚C for 0.5 h. The reaction was monitored by
TLC and filtrated. The filtrate was concentrated under re-
duced pressure to give a residue which was partitioned be-
Table 2. The TRPV1 Agonist Activity and the Nitric Oxide Release Activity of the Synthesized Compounds
Compound
R340/R380*
NO(+/-)**
blank
0.999
1.885
1.996
1.771
1.683
1.711
1.695
1.546
1.584
1.772
1.554
2.103
1.953
-
capsaicin
-
dihydro capsaicin
-
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
+
+
+
+
+
+
+
+
+
+
*The ratio of 340 /380nm excitatory wavelengths which means the intracellular increase in Ca2+ levels.
**The “+/ –” means whether there is nitric oxide releasing.

Synthesis and Biological Evaluation of Nitric Oxide-Releasing Derivatives of Capsaicin
Letters in Drug Design & Discovery, 2011, Vol. 8, No. 1 79
Table 3. The Analgesic Activity of the Synthesized Compounds
Compound
Increased of Pain Threshold (%)
Compound
Increased of Pain Threshold (%)
blank
20.19
78.66**
258.74**
94.07**
66.05
B4
B5
B6
B7
B8
B9
B10
147.93*
259.97**
162.33*
195.90**
282.96**
58.34*
ibuprofen
capsaicin
dihydro capsaicin
B1
B2
B3
307.17**
157.16*
74.47*
*Statistically significant between pre-drug latency and the post-drug latency in the same group by paired t-test, P<0.05.
**Statistically significant between pre-drug latency and the post-drug latency in the same group by paired t-test, P<0.01.
tween ethyl acetate and water. The ethyl acetate extract was
washed with saturated brine, dried over Na2SO4. After
evaporation of solvent, the crude product was subjected to
silica gel column, and chromatographed with eluent (petro-
leum ether /ethyl acetate 1:1) to yield the desired product
B3-B6.
Ar-H), 6.87-7.24(m, 3H, Ar-H), 5.75(bs, 1H, N-H), 5.37(m,
2H, CH=CH), 4.46(t, 2H, J=5.3Hz, ArCH2NH), 3.70(s, 3H,
OCH3), 2.24(m, 3H, NHCOCH2,CH(CH3)2), 2.0(m, 2H,
CH2CH=CH), 1.38-1.71(m, 4H, CH2CH2CH2CH=CH),
0.96(d, 6H, J=6.7Hz, CH(CH3)2); MS(ESI, m/z)
:
552.2(M+Na+, base peak); Anal. Calcd. for C26H31N3O7S:C
58.96, H 5.90, N 7.93; Found C 58.91, H 5.89, N 7.89.
(c) Capsaicin or dihydro capsaicin 1.0g (3.3mmol),
chloroacetic
acid
0.37g(3.96mmol)
and
DMAP
N-[[3-methoxy-4-(3-benzenesulfonyl-1,2,5-oxadiazole-2-
oxide-4-yloxy)-phenyl]-methyl]-8-methyl-nonanoylamine
(B2)
0.04g(0.33mmol), dissolved in 50ml dry CH2Cl2 .The mix-
ture was stirred at 30-35 ˚C for 0.5 h, added 0.94g
DCC/10ml CH2Cl2 with the ice bath and reacted over night.
The filtrate was concentrated under reduced pressure and
dissolved in 30ml dry acetone with KI 0.85g.The reaction
was under refluxing and in the darkness for 2 h. Then added
ethyl acetate, washed with water, and dried over MgSO4 .
After evaporation of solvent, the solid dissolved in 25ml dry
CH3CN and reacted with AgNO3 0.84g under refluxing and
in the darkness for 48 h. Added CH2Cl2 and 2N HCl after
evaporation of CH3CN. The filtrate was washed with water,
dried over Na2SO4. After evaporation of solvent, the crude
product was subjected to silica gel column, and chroma-
tographed with eluent(petroleum ether / acetone 3:1) to yield
the desired product B7, B8.
Yield 35.6％; white crystal 0.31g; m.p. 124-
126ꢀ;IR(KBr,ꢀ) : 3309, 1649, 1625, 1542, 1510, 1452,
1164, 600cm-1; 1HNMR(CDCl3, 300Hz, ꢀppm): 7.64-8.19(m,
5H, Ar-H), 6.90-7.25(m, 3H, Ar-H), 5.76(bs, 1H, N-H),
4.47(d, 2H, J=6.0Hz, ArCH2NH), 3.70(s, 3H, OCH3), 2.24(t,
2H, J=7.6Hz, NHCOCH2), 1.17-1.70(m, 11H, CH2CH2CH2
CH2CH2CH(CH3)2), 0.87(d, 6H, J=6.7Hz, CH(CH3)2);
(ESI,m/z): 554.1(M+Na+, base peak ); Anal. Calcd. for
C26H33N3O7S:C 58.74, H 6.26, N 7.90; Found C 58.69, H
6.23, N 7.89.
3- [[2-(3- Benzenesulfonyl-1,2,5-oxadiazole-2-oxide-4-
yloxy)ethyl]oxyformyl] propionic acid 2-methoxy-4-[(8-
methyl-non-6-enoylamino)methyl] phenyl ester(B3)
(d) Capsaicin or dihydro capsaicin 1.0g (3.3mmol), 1,4-
dibromo
Yield 90.9%; white crystal 1.0 g; m.p. 88-
butane
1.16ml(9.9mmol)
and
K2CO3
89ꢀ;IR(KBr,ꢀ) : 3263, 1762, 1748, 1641, 1619, 1555, 1510,
0.9g(6.6mmol), dissolved in 50ml dry ethyl acetate .The re-
action was under refluxing and in the darkness for 24 h. The
filtrate was washed with water, dried over Na2SO4. After
evaporation of solvent, the solid and AgNO3 0.59g
(3.45mmol), dissolved in 25ml dry CH3CN, under refluxing
and in the darkness for 3 h. The reaction was monitored by
TLC and filtrated. After evaporation of CH3CN, added
CH2Cl2 and filtrated. After evaporation of solvent, the crude
product was subjected to silica gel column, and chroma-
tographed with eluent(petroleum ether / acetone 3:1) to yield
the desired product B9, B10.
1
1450, 1360, 1140, 600cm-1; HNMR(CDCl3,300Hz,ꢀppm):
7.59-8.05(m, 5H, Ar-H), 6.81-6.97(m, 3H, Ar-H), 5.70(bs,
1H, N-H), 5.35(m, 2H, CH=CH), 4.54-4.63(m, 4H,
OCH2CH2O), 4.41(d, 2H, J=5.5Hz, ArCH2NH), 3.81(s, 3H,
OCH3), 2.96(t, 2H, J=6.7Hz, CH2COOAr), 2.81(t, 2H,
J=6.7Hz, CH2COO), 2.22(m, 3H, CH2CONH,CH(CH3)2),
1.99(m, 2H, CH2CH=CH), 1.40-1.69(m, 4H, CH2CH2CH2
CH=CH), 0.90(d, 6H, J=6.7Hz, CH(CH3)2); MS(ESI,m/z):
696.1(M+Na+, base peak );Anal. Calcd. for C32H39N3SO11:C
57.06, H 5.79, N 6.24 ; Found C 56.97, H 5.79, N 6.28.
3-[[2-(3-Benzenesulfonyl-1,2,5-oxadiazole-2-oxide-4-
yloxy)ethyl]oxyformyl] propionic acid 2-methoxy-4-[(8-
methyl-nonanoylamino)methyl] phenyl ester(B4)
Spectra Data
N-[[3-methoxy-4-(3-benzenesulfonyl-1,2,5-oxadiazole-2-
oxide-4-yloxy)-phenyl]-methyl]-8-methyl-non-6-enoyl-
amine(B1)
Yield 80.9%; white crystal 0.89g; m.p. 91-
92ꢀ;IR(KBr,ꢀ):3314, 1754, 1734, 1626, 1556, 1512, 1464,
1143, 601cm-1; 1HNMR(CDCl3,300Hz,ꢀppm): 7.73-
8.07(m,5H,Ar-H), 6.81-6.97(m, 3H, Ar-H), 5.74(bs, 1H, N-
H), 4.63(t, 2H, J=3.1Hz, OCH2), 4.54(t, 2H, J=4.6Hz,
Yield 41.5%; white crystal 0.36g; m.p. 134-136ꢀ;
IR(KBr,ꢀ):3308, 1649, 1624, 1542, 1509, 1452, 1165,
600cm-1; 1HNMR(CDCl3,300Hz,ꢀppm): 7.64-8.20(m, 5H,

80 Letters in Drug Design & Discovery, 2011, Vol. 8, No. 1
Ge et al.
CH2O), 4.41(d, 2H, J=5.6Hz, ArCH2NH), 3.81(s, 3H,
OCH3), 2.96(t, 2H, J=6.7Hz, CH2COOAr), 2.80(t, 2H,
J=6.7Hz, CH2COO), 2.21(t,2H, J=7.6Hz, CH2CONH), 1.13-
1.69(m, 11H, CH2CH2CH2CH2CH2CH(CH3)2), 0.85(d, 6H,
2H, J=7.6Hz, CH2CONH), 1.17-1.70(m, 11H, CH2CH2CH2
CH2CH2CH(CH3)2), 0.89(d, 6H, J=6.7Hz, CH(CH3)2);
MS(ESI,m/z) :411.3(M+H+); Anal. Calcd. for C20H30N2O7:C
58.52, H 7.37, N 6.82; Found C 58.47, H 7.29, N 6.77.
J=6.7Hz,
CH(CH3)2);
MS(ESI,m/z):
698.2(M+Na+,
N-(3-methoxy-4-nitroxy-butyoxy-benzyl)-8-methyl-non-6-
enoylanine(B9)
basepeak); Anal.Calcd. for C32H41N3SO11:C 56.89, H 6.07, N
6.22 ; Found C 56.70, H 6.22, N 6.17.
Yield 52％; white crystal 0.5g; m.p. 69-71ꢀ;IR(KBr,
ꢀ):3305, 1635, 1546, 1518, 1464, 1282, 1238, 1138cm-1;
1HNMR(CDCl3,300Hz,ꢀppm):6.81(m, 3H, Ar-H), 5.66(bs,
1H, NH), 5.34(m, 2H, CH=CH), 4.56(t, 2H, J=6.0Hz,
OCH2CH2), 4.38(t, 2H, J=5.7Hz, CH2CH2ONO2), 4.04(t,
2H, J=5.7Hz, ArCH2NH), 3.84(s, 3H, OCH3), 2.21(m, 3H,
CH2CONH,CH(CH3)2), 1.94(m, 4H, OCH2CH2CH2CH2
ONO2), 1.39-1.69(m, 6H, CH2CH2CH2CH=CH), 0.95(d, 6H,
J=6.7Hz, CH(CH3)2); MS(ESI,m/z) : 445.2(M+Na+, base
peak );Anal. Calcd. for C22H34N2O6:C 62.56, H 8.06, N 6.64
; Found C 62.40, H8.43, N 6.46.
3-[[6-(3-benzenesulfonyl-1,2,5-oxadiazole-2-oxide-4-
yloxy)hexyl]oxyformyl] propionic acid 2-methoxy-4-[(8-
methyl-non-6-enoylamino)methyl] phenyl ester (B5)
Yield 74.6%; white crystal 0.89g; m.p. 73-
75ꢀ;IR(KBr,ꢀ):3316, 1765, 1759, 1638, 1621, 1556, 1451,
1377, 1145, 605cm-1; 1HNMR(CDCl3,300Hz,ꢀppm): 7.60-
8.06(m,5H,Ar-H), 6.82-7.0(m,3H, Ar-H), 5.74(bs,1H,N-H),
5.35(m,2H,CH=CH),
4.13(t,2H, J=3.3Hz,
4.40(m,4H,OCH2C4H8CH2O),
ArCH2NH), 3.80(s,3H,OCH3),
2.92(t,2H, J=6.9Hz, CH2COOAr), 2.76(t, 2H, J=6.9Hz,
CH2COO), 2.21(m, 3H, CH2CONH, CH(CH3)2), 2.05(m, 2H,
CH2CH=CH), 1.26-1.69(m, 12H, CH2CH2CH2 CH=CH,
N-(3-methoxy-4-nitroxy-butyoxy-benzyl)-8-methyl-
nonanoylanine(B10)
OCH2CH2CH2CH2CH2CH2O),
0.89(d,6H,
J=6.6Hz,
CH(CH3)2); MS(ESI,m/z): 752.3(M+Na+, base peak); Anal.
C36H47N3SO11: C 59.26, H 6.45, N 5.76; Found C 59.34, H
6.71, N 5.55
Yield 69％; white crystal 0.72g; m.p. 73-
74ꢀ;IR(KBr,ꢀ):3307, 1635, 1544, 1518, 1466, 1297, 1237,
1
1138cm-1; HNMR(CDCl3,300Hz,ꢀppm):6.81(m, 3H, Ar-H),
5.65(bs, 1H, NH), 4.57(t, 2H, J=6.0Hz, OCH2CH2), 4.38(t,
2H, J=6.0Hz, CH2CH2ONO2), 4.04(t, 2H, J=5.7Hz,
ArCH2NH), 3.85(s, 3H, OCH3), 2.21(t, 2H, J=7.6Hz,
CH2CONH), 1.94(m, 4H, OCH2CH2CH2CH2ONO2), 1.13-
1.66(m, 11H, CH2CH2CH2CH2CH2CH(CH3)2), 0.86(d, 6H,
J=6.7Hz, CH(CH3)2); MS(ESI,m/z):425.3(M+H+, base
peak);Anal. Calcd. for C22H36N2O6:C 62.26,H 8.49,N
6.60;Found C 62.10, H8.84, N 6.41.
3-[[6-(3-benzenesulfonyl-1,2,5-oxadiazole-2-oxide-4-
yloxy)hexyl]oxyformyl] propionic acid 2-methoxy-4-[(8-
methyl-nonanoylamino)methyl] phenyl ester (B6)
Yield 77.3%; white solid 0.92g; m.p. 45-47ꢀ;IR(KBr,
ꢀ):3311, 1761, 1733, 1644, 1618, 1557, 1511, 1455, 1167,
605cm-1; 1HNMR(CDCl3,300Hz,ꢀppm): 7.60-8.06(m, 5H,
Ar-H), 6.82-7.0(m, 3H, Ar-H), 5.75(bs, 1H, N-H), 4.40(m,
4H, OCH2CH2CH2CH2CH2CH2O), 4.14(t, 2H, J=6.6Hz,
ArCH2NH), 3.81(s,3H,OCH3), 2.93(t, 2H, J=6.6Hz,
CH2COOAr), 2.76(t, 2H, J=6.9Hz, CH2COO), 2.20(t, 2H,
CONCLUSION
J=7.5Hz,
CH2CH2CH2CH2CH2CH(CH3)2,
CH2CH2CH2CH2O), 0.85(d, 6H, J=6.6Hz, CH(CH3)2);
MS(ESI, m/z): 732.3(M+H+); Anal. Calcd. for
C36H49N3SO11:C 59.08, H 6.75, N 5.74; Found C 59.04, H
6.52, N 5.66.
CH2CONH),
1.15-1.87(m,
19H,
OCH2CH2
In conclusion, we have synthesized a new series of nitric
oxide-releasing derivatives of capsaicin and evaluated them
for their TRPV1 agonist activity, nitric oxide release activity
and analgesic activity. These compounds showed TRPV1
agonist activity as compared with capsaicin and their nitric
oxide release activity was identified. Compare the analgesic
activity of compounds, and we found that Among the com-
pounds with furazan ring (B3, B4, B5, B6), the length of the
linker between furan ring and capsaicin core is related to the
analgesic activity. The length of linker in B5 or B6 is longer
than it in B3 or B4 .And the analgesic activity of B5 or B6 is
better than B3 or B4. As a NO donor, 2-oxopropyl nitrate is
better than butyl nitrate, because among the compounds with
nitric acid ester portion (B7, B8, B9, B10), the analgesic activ-
ity of compounds(B7, B8) with 2-oxopropyl nitrate portion is
better than the compounds (B9, B10) with butyl nitrate por-
tion. B2, B5, B8 show better potent analgesic activity than
capsaicin. Based on these results, some of these molecules
and NO donors can be considered as lead candidates for the
further development of nitric oxide-releasing derivatives of
capsaicin as analgesic drugs.
1-Nitroxy-acetic
enoylamino)–methyl] phenyl ester(B7)
acid
2-methoxy-4-[(8-methyl-non-6-
Yield 44.7%; white crystal 0.6g; m.p.76-78ꢀ;
IR(KBr,ꢀ): 3312, 1779, 1641, 1514, 1464, 1278, 1212,
848cm-1; 1HNMR(CDCl3,300Hz,ꢀppm):6.84-7.27(m, 3H,
Ar-H), 5.75(bs, 1H, N-H), 5.33(m, 2H, CH=CH), 5.17(s, 2H,
OCOCH2ONO2), 4.43(d, 2H, J=5.7Hz, ArCH2NH), 3.81(s,
3H, OCH3), 2.22(m, 3H, CH2CONH, CH(CH3)2), 1.98(m,
2H, CH2CH=CH), 1.37-1.69(m, 4H, CH2CH2CH2CH=CH),
0.95(d, 6H, J=6.7Hz, CH(CH3)2); MS(ESI, m/z):
447.1(M+K+, base peak ); Anal. Calcd. for C20H28N2O7:C
58.82, H 6.86, N 6.86; Found C 58.65, H 7.13, N 6.52.
1-Nitroxy-acetic acid 2-methoxy-4-[(8-methyl-nonanoyl-
amino)-methyl] phenyl ester(B8)
Yield 32.3％; white crystal 0.43g; m.p. 78-80ꢀ;
IR(KBr,ꢀ): 3311, 1777, 1640, 1544, 1470, 1288, 1210,
845cm-1; 1HNMR(CDCl3,300Hz,ꢀppm):6.86-7.05(m, 3H,
Ar-H), 5.73(bs, 1H, NH), 5.18(s, 2H, OCOCH2ONO2),
4.44(d, 2H, J=6.0Hz, ArCH2NH), 3.84(s, 3H, OCH3), 2.22(t,
ACKNOWLEDGEMENTS
The work was supported by the key project of Chinese
Ministry of Education (No. 109086) and Specialized Re-

Synthesis and Biological Evaluation of Nitric Oxide-Releasing Derivatives of Capsaicin
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