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Discovery of a Remarkable Methyl Shift Effect in the Vanilloid
Activity of Triterpene Amides
Rosa Maria Vitale,⊥ Cristina Avonto,⊥ Danilo Del Prete, Aniello Schiano Moriello, Pietro Amodeo,
Giovanni Appendino,* and Luciano De Petrocellis*
Cite This: J. Nat. Prod. 2020, 83, 3476−3481
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sı Supporting Information
*
ABSTRACT: As part of a study on triterpenoid conjugates, the
dietary pentacyclic triterpenoids oleanolic (2a) and ursolic acids
(3a) were coupled with vanillamine, and the resulting amides (2b
and 3b, respectively) were assayed for activity on the vanilloid
receptor TRPV1. Despite a structural difference limited to the
location of a methyl group in their conformationally rigid
pentacyclic core, oleanoloyl vanillamide dramatically outperformed
ursoloyl vanillamide in terms of potency (EC50 = 35 ± 2 nM for 2b
and 5.4 ± 2.3 μM for 3b). Using molecular docking and dynamics,
this difference was translated into distinct accommodation modes
at the TRPV1 vanillyl ligand pocket, suggesting a critical role of a
C−H πphenyl interaction between the triterpenoid C-29 methyl and
Phe591 of TRPV1. Because the molecular mechanisms underlying
the activation process of transient receptor channels (TRPs) remain to be fully elucidated, the observation of spatially restricted
structure−activity information is of significant relevance to identify the molecular detail of TRPV1 ligand gating.
T
inflammation, pain, and metabolic syndrome, but their
insolubility and dismally low oral absorption have so far
prevented pharmaceutical advancement.9 Derivatization of the
carboxylate function, as in bardoxolone methyl,11 is known to
improve the pharmacokinetic profile of oleanolic and ursolic
acids,11 and provided a rationale for the synthesis of conjugates
of the natural compounds. Biogenic amines seemed an
attractive class of conjugation candidates, as lipophilic acids
like fatty acids can be converted in vivo in amide conjugates.12
Since oleanolic and ursolic acid show an intrinsic modest
antagonist activity on TRPV1,13,14 conjugation with vanillamines seemed, in the context of control of pain and
inflammation, a rational strategy to improve both the
pharmacodynamic and the pharmacokinetic properties of the
natural products.
The neopentylic C-28 carboxylic group of triterpenoid acids
is poorly reactive and requires forced conditions for its
esterification and amidation, with additional complications
observed for phenolic amines due to competition with the
formation of phenolic esters.15 We previously developed a
RPV1, a member of the vanilloid subfamily of transient
potential receptor channels (TRPs), is critically involved
in the transduction of nociceptive stimuli and is responsible for
the irritant and burning sensation of capsaicin (1), the active
ingredient of hot chili pepper.1 Structure−activity studies have
identified the critical structural determinants for TRPV1
activation by capsaicinoids,2 and cryo-EM studies of this ion
channel bound to a set of ligands (the plant diterpenoid
resiniferatoxin, the tarantula toxin DkTx, the synthetic
antagonist capsazepine) have provided insights into protein−
ligand interactions in the TRPV1 vanillyl pocket.3−5 However,
given the complexity and multimodal action of this class of
receptors, the molecular details of the ligand−channel
interactions have largely remained elusive, in particular, and
paradoxically, for the archetypal ligand capsaicin (1).6 To this
aim, data that translate into unambiguous and spatially
restricted structure−activity information are of considerable
relevance. In this context, we report the discovery of a “magic”
methyl shift effect7,8 in the activity of the vanillamides of
oleanolic (2a) and ursolic acid (3a) and its rationalization in
terms of docking and molecular dynamics (MD) experiments
in the TRPV1 ligand pocket.
Oleanolic and ursolic acids (2a and 3a, respectively) are
pentacyclic triterpenoids with a broad distribution in Nature
and with a significant human dietary exposure due to their
occurrence in edible plants (olives), herbs (sage), fruits
(apple),9 and caffeinated spices (mate).10 Their profile of
bioactivity is of considerable interest in the realm of
© 2020 American Chemical Society and
American Society of Pharmacognosy
Received: June 9, 2020
Published: November 2, 2020
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Note
subunit.10 The two best not-redundant poses in terms of
binding energy value for each compound (Figures 1 and 2,
panel B) only differed in the orientation of the vanillyl moiety
(hereinafter referred to as OMe-in when the methoxy group
points toward the cleft between helices S3 and S4 and OMeout when it is rotated by 180°).
protocol for the amidation of triterpenoid acids with phenolic
amines based on the activation of the carboxylic group by in
situ formation of a mixed phosphoric anhydride.15 However,
modest yields were obtained with ursolic acid, and yield further
dropped with oleanolic acid, presumably because the gemdimethyl substitution further encumbers the C-28 carboxylic
group. Much better yields could, however, be obtained by ex
situ activation with hydroxysuccinimide and reaction with an
excess of free amine. In this way, improved yields (20−30%)
were obtained for various amino alcohols and aminophenols,
including vanillamine.
Vanilloid activity was evaluated in HEK-293 cells overexpressing hTRPV1. Despite the consistent tendency for
compounds of the ursolic acid series to outperform those from
the corresponding oleanolic series,9 about 2 orders of
magnitude greater potency for the vanillamide of oleanolic
acid was observed compared to that of ursolic acid (EC50 = 35
± 2 nM for 2b vs 5.4 ± 2.3 μM for 3b, Table 1).
Table 1. TRPV1 Activity Data for the Vanillamides 2b and
3b Compared to the Activity of Capsaicin (1)
compound
2b (oleanoyl
vanillamide)
3b (ursoloyl
vanillamide)
1 (capsaicin)
efficacy (relative to
ionomycin 4 μM)
potency EC50
IC50 (capsaicin
0.1 μM)
72 ± 1
35 ± 2 nM
50 ± 2 nM
16 ± 1
5.4 ± 2.3 μM
7.5 ± 0.7 μM
79 ± 1
5.3 ± 0.4 nM
8.0 ± 0.3 nM
a
Data were obtained in HEK-293 cells, stably transfected with
recombinant human TRPV1 (hTRPV1).
The pentacyclic triterpenoid scaffold of oleanolic and ursolic
acid is devoid of conformational mobility, and the two
compounds only differ in the location of a methyl group,
making it possible that the presence of a substitution at C-19
interferes, by steric hindrance, with the fitting of 3b into the
ligand binding site of TRPV1. However, a docking study by
using the available structure of TRPV1 in its activated state
(PDB id: 5IRX) suggested a more complex and different
scenario. In fact, both compounds docked into the vanilloidbinding pocket, as defined by the S3−S4 helices, S4−S5 linker
of one subunit, and the S5−S6 helices of the adjacent
Figure 1. Representative energy-minimized OMe-in docking poses of
2b and 3b (tan and olive drab, respectively, panel A) and capsaicin
(salmon, panel B) after best fit of the protein backbone. Ligands are
shown in ball-and-stick representation, whereas protein residues
within 4.5 Å from the ligand are shown in stick representation.
Ribbons and selected side chain stick bonds of TRPV1 monomers A
and B are colored in dark gray and sky blue, respectively. Oxygen,
nitrogen, and sulfur atoms are colored in red, blue, and yellow,
respectively. Only polar hydrogens are shown and colored white.
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Phe591 (S5 helix-B monomer) side chain, which pushes down
the terpenoid scaffold. Conversely, the lack of this methyl in 3b
induces a shift of the terpenoid scaffold toward Phe591,
resulting in a looser binding of the vanillyl group in the ligand
pocket. In the OMe-in orientation, both vanillamides are
engaged in H-bonds between the hydroxyl group and both the
Ser512 (S3) and Arg557 (S4) side chains, whereas in the
OMe-out orientation only the phenolic hydroxy of 2b can form
a H-bond with the Ser512 side chain, whereas the methoxy
groups of both isomers are H-bonded to the Arg557 side chain.
The C-3 hydroxy of the cyclic scaffold of both isomers is close
to the sulfur atom of the Met581 (S4−S5 linker) side chain in
both the OMe-in and OMe-out orientation. Because in rigid
systems the effect of substitution can be directly translated into
the occupancy of a specific area of the ligand-binding space, it
was interesting to investigate if the site of the C−H πphenyl
interaction of the C-29 oleanoyl methyl was also occupied by
capsaicin. When this archetypal vanilloid ligand was docked
into the vanilloid-binding pocket, one of the ω-methyls was
indeed spatially close to Phe591 (S5-B), with two orientations
of the vanillyl group of the same OMe-in and OMe-out type
being observed, in accordance to the binding mode of 2b and
3b (Figures 1 and 2, panel B). On account of a major
conformational mobility and a slender carbon−carbon
connectivity, the branched acyl tail of capsaicin allows two
H-bonds of its amide group with either both the Thr550 (S4)
and the Tyr511 (S3) side chains (OMe-out orientation) or,
alternatively, Tyr511 (S3) (OMe-in orientation), rationalizing
the higher potency of capsaicin compared to 2b (EC50 = 5.3
and 35 nM, respectively). For comparison purposes, we also
evaluated the activity of the corresponding acidic parent
triterpenoids (oleanolic and ursolic acids, 2a and 3a,
respectively), previously reported to act as weak antagonists
at TRPV1.13,14 We confirmed that both compounds behave as
weak antagonists, inhibiting the capsaicin response by 20 ± 3%
and 30 ± 1% at 25 μM, respectively. The corresponding
docking complexes are reported in Figure S1. Ursolic acid (2a)
engages a H-bond between its carboxylate and the Thr550 side
chain, while the arrangement of the polycyclic moiety is
substantially preserved in comparison to its vanillamideconjugated derivative. Conversely, oleanolic acid adopts a
completely different orientation, engaging Ser512 with a Hbond with its hydroxy group. A hypothetical corresponding
pose of ursolic acid, with the carboxylate group forming a Hbond with Thr550, is prevented by a steric clash between the
C-29 methyl group and Phe591. Thus, since both acidic
precursors are endowed with a weak and comparable inhibitory
activity, the dramatic difference in the activity profile between
2b and 3b can be ascribed to the introduction of a vanillamide
group. To confirm and further explore the better accommodation of 2b vs 3b within the site emerging from the
docking, we carried out 100 ns of molecular dynamics in the
membrane environment for both OMe-in complexes. The root
mean square deviation (rmsd) of both protein and ligands,
shown in Figure 3, shows smaller fluctuations in both protein
and ligands for the 2b complex in comparison with those of 3b.
In fact, the latter is characterized by both a drift in protein
backbone and a higher mobility of the ligand in the four
binding sites of the tetramer. Thus, MD calculations show a
relative structural destabilization on going from 2b to 3b of the
active form of TRPV1 used to derive the theoretical
complexes, corresponding to the cryo-EM structure in complex
with resiniferatoxin. The greater structural stability of 2b is also
Figure 2. Representative energy-minimized OMe-out docking poses
of 2b and 3b (tan and olive drab, respectively, panel A) and capsaicin
(salmon, panel B) after best fit of the protein backbone. Ligands are
shown in ball-and-stick representation, whereas protein residues
within 4.5 Å from the ligand are shown in stick representation.
Ribbons and selected side chain stick bonds of TRPV1 monomers A
and B are colored in dark gray and sky blue, respectively. Oxygen,
nitrogen, and sulfur atoms are colored in red, blue, and yellow,
respectively. Only polar hydrogen are shown and colored white.
At odds with the starting hypothesis, in the emerging
scenario the β-oriented methyl on C-19 does not prevent
accommodation of 3b in the binding site, but its translocation
on C-20 rather induces a better fit of 2b in the binding site. In
fact, in both poses, the vanillyl group of 2b is deeper inside the
pocket than in 3b, and this arrangement is promoted by a C−
H πphenyl interaction16,17 between the C-29 methyl group and
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Figure 3. Root mean square deviation (rmsd) of protein backbone
atoms (panels A, C) and the respective ligands (B, D) after protein
best fit. Plot lines were smoothed with a five-point window running
average.
Figure 4. Representative frames from MD of 2b (A) and 3b (B)
complexes with TRPV1. The color code is the same used for Figure 2.
Red dotted lines represent the distance between C29 and both Ala549
and Phe591 in complex 2b.
confirmed by the network of H-bonds engaged within each
binding site in comparison to that of 3b, as shown in Table 2,
reporting H-bond occurrences greater than 10% over the
simulated 100 ns of production run. In fact, while 3b forms
only one H-bond with Ser152 with an occurrence of ∼40% in
three sites out of four, 2b forms additional H-bonds with
Arg557 and/or Glu570, with an overall occurrence of H-bonds
well above 50%, up to ∼74%. Moreover, methyl C29 forms
stable hydrophobic interactions with both Phe591 and Ala549
during the whole simulated period, as shown in Figure S2. The
representative frames from molecular dynamics are shown in
Figure 4. The greater capability of 2b to stabilize the active
form of TRPV1 is fully consistent with the higher agonist
efficacy observed for this compound in comparison with 3b.
In conclusion, a comparative analysis of bioactivity data,
docking experiments, and MD simulations has highlighted the
critical role of the C-29 methyl of triterpenoids for significant
and effective binding to TRPV1, with only the oleanane
skeleton having this methyl in the correct location for the
interaction. As the rigid ring system of both triterpenoid
vanillamides encompasses conformationally constrained versions of the side chain of capsaicin, it is not unrealistic that a
similar interaction may occur between Phe591 and one of the
ω-methyls of capsaicin, thus disclosing a role for this residue in
agonist binding and receptor activation.
■
MHz) NMR spectra were measured on a Bruker spectrometer. 1H
(500 MHz) and 13C (126 MHz) NMR spectra were measured on an
Agilent spectrometer. Chemical shifts were referenced to the residual
solvent signal (CDCl3, δH = 7.26, δC = 77.16, or DMSO-d6, δH = 2.50,
δC = 39.52, hept). Low- and high-resolution ESIMS spectra were
obtained on an LTQ OrbitrapXL (Thermo Scientific) mass
spectrometer. Silica gel 60 (63−200 mesh) used for gravity column
chromatography was purchased from Merck. Reactions were
monitored by TLC on silica gel Merck 60 F254 (0,25 μm) plates
and neutral alumina Macherey-Nagel ALUGRAM (0,20 μm) plates
that were visualized by UV inspection (254 and 365 nm) and/or
staining with 5% H2SO4 in EtOH and heating. Organic phases were
dried with anhydrous Na2SO4 before evaporation. Chemical reagents
and solvents were from Sigma-Aldrich.
Synthesis of Triterpenoid Vanillamides. Synthesis of
Oleanoyl Vanillamide (2b) as Representative. (a) Carboxylate
activation: To a stirred solution of N-hydroxysuccinimide (1.51 g;
13.1 mmol) in EtOAc (50 mL) were added oleanolic acid (2.05 g; 4.5
mmol) and dicyclohexylcarbodiimde (DCC, 4.58 g; 22.2 mmol). The
suspension was stirred at room temperature (rt) for 16 h and then
worked up by filtration and evaporation. The residue was purified by
gravity column chromatography using petroleum ether/EtOAc (8:2)
as mobile phase, to give the hydroxysuccinimide ester as a white
powder (1.32 g, 52% yield): 1H NMR (300 MHz, CDCl3) δ 5.31
(1H, brt), 3.46 (1H, m), 3.20 (1H, m), 2.79 (4H, m), 1.15 (3H, s),
0.98 (3H, s), 0.92 (3H, s), 0.91 (3H, s), 0.90 (3H, s), 0.80 (3H, s),
0.76 (3H, s). (b) Amidation: To a stirred solution of oleanoyl
EXPERIMENTAL SECTION
General Experimental Procedures. IR spectra were obtained on
an Avatar 370 FT-IR Thermo Nicolet. 1H (300 MHz) and 13C (75
Table 2. Occurrence of Ligand−Protein H-Bonds for TRPV1 in Complex with Compounds 3b and 2b during 100 ns of MD
protein binding
site
compound 3b (HB
occurrence)
compound 3b (frames with
≥1 HB)
1
2
3
OH···Ser512 (36.8%)
OH···Ser512 (34.8%)
OH···Ser512 (40.8%)
42.42%
44.28%
40.99%
4
OH···Ser512 (58.7%)
58.7%
compound 2b (HB occurrence)
OH···Ser512 (51.2%)
OH···Ser512 (64.2%); OH···Glu570 (50%)
OH···Ser512 (41.0%); OH···Arg557 (39.7%);
CO···Tyr511 (33%)
OH···Ser512 (57.6%)
3479
compound 2b (frames with
≥1 HB)
52.80%
73.8%
66.80%
57.6%
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Note
hydrogens, calculate Gasteiger charges, and select rotatable side chain
bonds. Grid dimensions of 60 × 50 × 60, respectively, centered in the
binding pocket, were generated with the program AutoGrid 4.2
included in the Autodock 4.2 distribution, with a spacing of 0.375 Å.
A total of 100 molecular docking runs for each docking calculation
were performed adopting a Lamarckian Genetic Algorithm (LGA)
and the protocol already published.23 Flexibility was used for all
rotatable bonds of the docked ligands. For each docking run, the best
not-redundant poses in terms of binding energy values were selected
as representatives and underwent energy minimization with the
Amber16 package24 using the ff14SB version of AMBER ff14SB force
field for the protein and gaff parameters for the ligand. UCSF
Chimera 1.1425 was used for figures of the molecular complexes. The
energy-minimized complexes were embedded in a POPC bilayer using
the charmmgui web-interface, and then MD simulations in the
membrane environment were carried out with the pmemd.cuda
module of the Amber16 package, using lipid 14 (lipids), ff14SB force
(protein), and gaff (ligand) force field parametrization. MD
production runs were carried out for 100 ns. The Cpptraj module
of AmberTools16 was used for trajectory analysis. The full MD
protocol has been published elsewhere.27
TRPV1 Channel Assay. Compound effects on intracellular Ca2+
concentration ([Ca2+]i) were determined using the selective intracellular fluorescent probe for Ca2+ Fluo-4, and assays were performed
as described.26 Briefly, HEK-293 cells, stably transfected with
recombinant human TRPV1 (selected by Geneticin 600 μg mL−1)
or not transfected were cultured in EMEM + 2 mM glutamine +1%
nonessential amino acids + 10% FBS and maintained at 37 °C with
5% CO2. The day of the experiment the cells were loaded in the dark
at rt for 1 h with Fluo-4 AM (4 μM in DMSO containing 0.02%
Pluronic F-127). After that, the cells were rinsed and resuspended in
Tyrode’s solution (145 mM NaCl, 2.5 mM KCl, 1.5 mM CaCl2, 1.2
mM MgCl2, 10 mM D-glucose, and 10 mM HEPES, pH 7.4), then
transferred to a quartz cuvette of a spectrofluorimeter (PerkinElmer
LS50B; λEX = 488 nm, λEM = 516 nm) under continuous stirring. Cell
fluorescence before and after the addition of various concentrations of
test compounds was measured normalizing the effects against the
response to ionomycin (4 μM). The potency of the compounds (EC50
values) is determined as the concentration required to produce halfmaximal increases in [Ca2+]i. Antagonist behavior is evaluated against
the agonist of the TRPV1 capsaicin (100 nM) and analyzed by adding
the compounds directly in the quartz cuvette 5 min before stimulation
of cells with the agonist. IC50 is expressed as the concentration
exerting a half-maximal inhibition of agonist effect, taking as 100% the
effect on [Ca2+]i exerted by capsaicin (100 nM) alone. Dose−
response curve fitting (sigmoidal dose−response variable slope) and
parameter estimation were performed with Graph-Pad Prism8
(GraphPad Software Inc.). All determinations were performed at
least in triplicate.
hydroxysuccinimide (300 mg, 0.54 mmol) in CH2Cl2 (4 mL) was
added vanillamine (150 mg, 1.1 mmol). The mixture was stirred at rt
for 24 h and then worked up by dilution with brine and extraction
with CH2Cl2. The organic phase was treated with Na2SO4 and
filtered, and the solvent evaporated. The residue was purified by
gravity column chromatography using petroleum ether/EtOAc (3:7)
to give 2b as a white powder (66 mg, 20% yield).
Oleanoyl vanillamide (2b): white powder; IR νmax (KBr) 3544,
3465, 3158, 1770, 1653, 1515, 1455, 1379, 1235, 1205, 1034, 854,
816, 739, cm−1; 1H NMR (500 MHz, CDCl3) δ 6.76 (1H, d, J = 8.0
Hz, H-5′), 6.73 (1H, d, J = 2.0 Hz, H-2’), 6.68 (1H, dd, J = 8.0, 2.0
Hz, H-6’), 5.24 (1H, t, J = 3.6 Hz, H-12), 4.24 (2H, s, H-7’), 3.81
(3H, s, H-8’), 3.13 (1H, dd, J = 10.7, 5.3 Hz, H-3), 2.81 (1H, dd, J =
14.0, 4.6 Hz, H-18), 2.00 (1H, td, J = 14.7, 5.4 Hz, H16-a), 1.82 (1H,
m, H-11), 1.81 (1H, m, H-22a), 1.70 (1H, m, H-15a), 1.68 (1H, m,
H-16b), 1.64 (1H, m, H-22b), 1.62 (1H, m, H-19a), 1.56 (1H, m, H1a), 1.53 (2H, m, H-2), 1.48 (1H, m, H-6a), 1.47 (1H, m, H-9), 1.38
(1H, dd, J = 12.4, 3.3 Hz, H-7a), 1.31 (2H, m, H-6b and H-21a), 1.26
(1H, m, H-7b), 1.19 (1H, m, H-21b), 1.11 (1H, m, H-19b), 1.09
(3H, s, H-27), 1.07 (1H, m, H-15b), 0.91 (3H, s, H-23), 0.89 (1H, m,
H-1b), 0.87 (3H, s, H-30), 0.85 (3H, s, H-29), 0.83 (3H, s, H-25),
0.71 (3H, s, H-24), 0.69 (3H, s, H-26), 0.66 (1H, dd, J = 11.7, 1.6 Hz,
H-5); 13C NMR (CDCl3, 126 MHz) δ 175.6 (C, C-28), 147.1 (C, C3′), 145.1 (C, C-4′), 143.0 (C, C-13), 129.6 (C, C-1′), 122.9 (CH, C12), 120.5 (CH, C-6′), 114.7 (CH, C-5′), 110.9 (CH, C-2′), 78.8
(CH, C-3), 55.8 (CH3, C-8′), 55.2 (CH, C-5), 47.5 (CH, C-9), 46.8
(C, C-17), 45.7 (CH2, C-19), 43.4 (CH2, C-7′), 41.7 (C, C-14), 41.2
(CH, C-18), 39.3 (C, C-8), 38.7 (C, C-4), 38.5 (CH2, C-1), 37.0 (C,
C-10), 33.7 (CH2, C-21), 32.9 (CH3, C-29), 32.7 (CH2, C-7), 32.4
(CH2, C-22), 30.6 (C, C-20), 28.0 (CH3, C-23), 27.7 (CH2, C-15),
26.7 (CH2, C-2), 25.6 (CH2, C-27), 23.4 (CH3, C-30), 23.4 (CH2, C11), 23.0 (CH2, C-16), 18.3 (CH2, C-6), 16.8 (CH3, C-26), 15.6
(CH3, C-24), 15.3 (CH3, C-25); HR-ESIMS m/z 591.4273 [M + H]+
(calcd for C38H57NO4 591.4288).
Ursoloyl vanillamide (3b): white powder; IR νmax (KBr) 3574,
3465, 3180, 1770, 1660, 1520, 1405, 1365, 1260, 1215, 1043, 859
cm−1; 1H NMR (500 MHz, CDCl3) δ 6.80 (1H, d, J = 2.0 Hz, H-2′),
6.69 (1H, d, J = 8.0 Hz, H-5′), 6.63 (1H, dd, J = 8.0, 1.9 Hz, H-6′),
5.18 (1H, t, J = 3.8 Hz, H-12), 4.14 (2H, d, J = 5.8 Hz, C-7′), 3.74
(3H, s, H-8′), 3.00 (1H, dt, J = 10.6, 5.3 Hz, H-3), 2.16 (1H, d, J =
11.2 Hz, H-18), 2.07 (2H, td, J = 13.4, 4.1 Hz, H-16a), 1.84 (2H, m,
H-11), 1.80 (1H, m, H-15a), 1.70 (2H, m, H-22), 1.63 (1H, bd, J =
13.5 Hz, H-16b), 1.53 (1H, dd, J = 12.7, 3.4 Hz, H-1a), 1.46 (5H, m,
H-9, 21-a, 6-a, H-7a, H-2), 1.37 (1H, m, H-19), 1.30 (1H, m, H-6b,
H-7b), 1.25 (1H, m, H-21b), 1.04 (3H, s, H-27), 1.04 (1H, m, H15b), 0.95 (1H, m, H-20), 0.92 (3H, d, J = 5.6 Hz, H-29), 0.90 (3H,
s, H-23), 0.90 (1H, m, H-1b), 0.87 (3H, s, H-25), 0.82 (3H, d, J = 6.3
Hz, H-30), 0.73 (3H, s, H-26), 0.68 (3H, s, H-24), 0.67 (1H, m, H5). 13C NMR (DMSO-d6, 126 MHz) δ 174.4 (C, C-28), 147.4 (C, C3′), 145.3 (C, C-4′), 137.4 (C, C-13), 130.2 (C, C-1′), 125.3 (CH, C12), 119.6 (CH, C-6′), 115.1 (CH, C-5′), 111.6 (CH, C-2′), 76.8
(CH, C-3), 55.5 (CH3, C-8′), 54.8 (CH, C-5), 52.3 (CH, C-18), 47.5
(C, C-17), 47.0 (CH, C-9), 41.9 (CH2, C-7′), 41.7 (C, C-14), 40.0
(C, C-8), 39.1 (C, C-4), 38.4 (CH2, C-1), 38.3 (C, C-10), 38.3 (2
CH, C-20 and C-19), 36.5 (CH2, C-22), 32.7 (CH2, C-21), 30.0
(CH2, C-7), 28.2 (CH3, C-23), 27.5 (CH2, C-15), 27.0 (CH2, C-2),
23.8 (CH2, C-16), 23.1 (CH3, C-27), 22.9 (CH2, C-11), 20.9 (CH3,
C-29), 18.0 (CH2, C-6), 17.1 (CH3, C-26), 16.9 (CH3, C-30), 16.1
(CH3, C-24), 15.3 (CH3, C-25); HR-ESIMS m/z 591.4293 [M + H]+
(calcd for C38H57NO4 591.4288).
Molecular Docking and Molecular Dynamics Studies. The
starting ligand geometry of the ligands was built with Ghemical 2.9918
and energy minimized at molecular mechanics level first, using Tripos
5.2 force field parametrization19 and then optimized using the
GAMESS program20 at the Hartree−Fock level with the STO-3G
basis set, followed by a single-point HF energy evaluation at the 631G* level to derive the partial atomic charges for the ligand by the
RESP procedure.21 Docking studies were performed with AutoDock
4.2.22 hTRPV1 (PDB id: 5IRX) and the ligands were processed with
AutoDock Tools (ADT) package version 1.5.6rc1 to merge nonpolar
■
ASSOCIATED CONTENT
* Supporting Information
sı
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.jnatprod.0c00639.
1
H and 13C NMR spectra of oleoylvanillamide (2b) and
Figure S1 (best docking poses of 2a and 3a) and Figure
S2 (distances between the centers of mass of methyl C29 and monomers A and B) (PDF)
■
AUTHOR INFORMATION
Corresponding Authors
Luciano De Petrocellis − Endocannabinoid Research Group
(ERG), Institute of Biomolecular Chemistry, National
Research Council (ICB-CNR), 80078 Pozzuoli, NA, Italy;
Phone: +39-081-8675173; Email: luciano.depetrocellis@
icb.cnr.it; Fax: +39-081-8041770
3480
https://dx.doi.org/10.1021/acs.jnatprod.0c00639
J. Nat. Prod. 2020, 83, 3476−3481
Journal of Natural Products
pubs.acs.org/jnp
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C.; Walker, J. M.; Di Marzo, V. Br. J. Pharmacol. 2004, 143, 251−256.
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Hassinen, T.; Heikkilä, V.; Hutchison, G.; Huuskonen, J.; Jensen, J.;
Liboska, R.; Rowley, C. http://www.uku.fi/-thassine/projects/
GHEMICAL.
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(20) Schmidt, M. W.; Baldridge, K. K.; Boatz, J. A.; Elbert, S. T.;
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R. K.; Goodsell, D. S.; Olson, A. J. J. Comput. Chem. 2009, 30, 2785−
2791.
(23) Iannotti, F. A.; De Maio, F.; Panza, E.; Appendino, G.;
Taglialatela-Scafati, O.; De Petrocellis, L.; Amodeo, P.; Vitale, R. M.
Molecules 2020, 25, 1119.
(24) Case, D. A.; Betz, R. M.; Cerutti, D. S.; Cheatham, III, T. E.;
Darden, T. A.; Duke, R. E.; Giese, T. J.; Gohlke, H.; Goetz, A. W.;
Homeyer, N.; Izadi, S.; Janowski, P.; Kaus, J.; Kovalenko, A.; Lee, T.
S.; LeGrand, S.; Li, P.; Lin, C.; Luchko, T.; Luo, R.; Madej, B.;
Mermelstein, D.; Merz, K. M.; Monard, G.; Nguyen, H.; Nguyen, H.
T.; Omelyan, I.; Onufriev, A.; Roe, D. R.; Roitberg, A.; Sagui, C.;
Simmerling, C. L.; Botello-Smith, W. M.; Swails, J.; Walker, R. C.;
Wang, J.; Wolf, R. M.; Wu, X.; Xiao, L.; Kollman, P. A. AMBER 2016;
University of California: San Francisco, 2016.
(25) Pettersen, E. F.; Goddard, T. D.; Huang, C. C.; Couch, G. S.;
Greenblatt, D. M.; Meng, E. C.; Ferrin, T. E. J. Comput. Chem. 2004,
25, 1605−1612.
(26) Schiano-Moriello, A.; De Petrocellis, L. Methods Mol. Biol.
2016, 1412, 65−76.
(27) Chianese, G.; Lopatriello, A.; Schiano-Moriello, A.; Caprioglio,
D.; Mattoteia, D.; Benetti, E.; Ciceri, D.; Arnoldi, L.; De Combarieu,
E.; Vitale, R. M.; Amodeo, P.; Appendino, G.; De Petrocellis, L.;
Taglialatela-Scafati, O. J. Nat. Prod. 2020, 83, 2727−2736.
Giovanni Appendino − Dipartimento di Scienze del Farmaco,
Università del Piemonte Orientale, 28100 Novara, Italy;
orcid.org/0000-0002-4170-9919; Phone: +39-0321375744; Email: giovanni.appendino@uniupo.it; Fax: +390321-37564
Authors
Rosa Maria Vitale − Institute of Biomolecular Chemistry,
National Research Council (ICB-CNR), 80078 Pozzuoli,
NA, Italy; orcid.org/0000-0001-9243-1307
Cristina Avonto − National Center for Natural Products
Research, Research Institute of Pharmaceutical Science,
School of Pharmacy, The University of Mississippi, University,
Mississippi 38677, United States
Danilo Del Prete − Dipartimento di Scienze del Farmaco,
Università del Piemonte Orientale, 28100 Novara, Italy;
orcid.org/0000-0002-2161-8980
Aniello Schiano Moriello − Endocannabinoid Research
Group (ERG), Institute of Biomolecular Chemistry, National
Research Council (ICB-CNR), 80078 Pozzuoli, NA, Italy;
Epitech Group SpA, Saccolongo, Padova, Italy
Pietro Amodeo − Institute of Biomolecular Chemistry,
National Research Council (ICB-CNR), 80078 Pozzuoli,
NA, Italy; orcid.org/0000-0002-6439-7575
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.jnatprod.0c00639
Author Contributions
⊥
R. M. Vitale and C. Avonto share first author status.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank MIUR for financial support to the groups in Novara
and Naples (PRIN2017, Project 2017WN73PL, Bioactivitydirected exploration of the phytocannabinoid chemical space).
We thank Mr. S. Donadio for the technical support.
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Note
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