Synthesis and Characterization of 5-Hydroxy-2-(2-phenylethyl)chromone (5-HPEC) and Its Analogues as Non-nitrogenous 5-HT2B Ligands

Article abstract of DOI:10.1021/acs.jnatprod.5b00118

The involvement of the neurotransmitter serotonin (5-HT) in numerous physiological functions is often attributed to the diversity of receptors with which it interacts. Ligands targeting serotonin receptor 2B (5-HT_2B) have received renewed interest for their potential to help understand the role of 5-HT_2B in migraines, drug abuse, neurodegenerative diseases, and irritable bowel syndrome. To date, most of the ligands targeting 5-HT_2B have been nitrogen-containing compounds. The natural product 5-hydroxy-2-(2-phenylethyl)chromone (5-HPEC, 5) has been shown previously to act as a non-nitrogenous antagonist for the 5-HT_2B receptor (pK_i = 5.6). This report describes further progress on the study of the structure-activity relationship of both naturally occurring and synthetic compounds bearing the 2-(2-phenylethyl)chromone scaffold at the 5-HT_2B receptor. The inhibitory activity of the newly synthesized compounds (at 10 μM) was tested against each of the 5-HT₂ receptors. Following this assay, the binding affinity and antagonism of the most promising compounds were then evaluated at 5-HT_2B. Among all the analogues, 5-hydroxy-2-(2-phenylpropyl)chromone (5-HPPC, 22h) emerged as a new lead compound, showing a 10-fold improvement in affinity (pK_i = 6.6) over 5-HPEC with reasonable antagonist properties at 5-HT_2B. Additionally, ligand docking studies have identified a putative binding pocket for 5-HPPC and have helped understand its improved affinity. (Figure Presented).

Full text of DOI:10.1021/acs.jnatprod.5b00118

Article
pubs.acs.org/jnp
Synthesis and Characterization of 5‑Hydroxy-2-(2-
phenylethyl)chromone (5-HPEC) and Its Analogues as Non-
nitrogenous 5‑HT2B Ligands
Dwight A. Williams,*,† Saheem A. Zaidi,‡ and Yan Zhang*,‡
†Department of Pharmacology and Toxicology, Virginia Commonwealth University, 410 North 12th Street, P.O. Box 980613,
Richmond, Virginia 23298-0613, United States
‡Department of Medicinal Chemistry, Virginia Commonwealth University, BioTech One, Suite 205, 800 E. Leigh Street, P.O. Box
980540, Richmond, Virginia 23298-0540, United States
S
* Supporting Information
ABSTRACT: The involvement of the neurotransmitter serotonin (5-HT) in
numerous physiological functions is often attributed to the diversity of
receptors with which it interacts. Ligands targeting serotonin receptor 2B (5-
HT2B) have received renewed interest for their potential to help understand
the role of 5-HT2B in migraines, drug abuse, neurodegenerative diseases, and
irritable bowel syndrome. To date, most of the ligands targeting 5-HT2B have
been nitrogen-containing compounds. The natural product 5-hydroxy-2-(2-
phenylethyl)chromone (5-HPEC, 5) has been shown previously to act as a non-nitrogenous antagonist for the 5-HT2B receptor
(pKi = 5.6). This report describes further progress on the study of the structure−activity relationship of both naturally occurring
and synthetic compounds bearing the 2-(2-phenylethyl)chromone scaffold at the 5-HT2B receptor. The inhibitory activity of the
newly synthesized compounds (at 10 μM) was tested against each of the 5-HT2 receptors. Following this assay, the binding
affinity and antagonism of the most promising compounds were then evaluated at 5-HT2B. Among all the analogues, 5-hydroxy-2-
(2-phenylpropyl)chromone (5-HPPC, 22h) emerged as a new lead compound, showing a 10-fold improvement in affinity (pKi =
6.6) over 5-HPEC with reasonable antagonist properties at 5-HT2B. Additionally, ligand docking studies have identified a putative
binding pocket for 5-HPPC and have helped understand its improved affinity.
hromones (1) are heterocyclic compounds identified by
their benzoannelated γ-pyrone core. They can be found
C
throughout Nature and have been isolated from both terrestrial
and marine sources. Naturally occurring chromones are often
divided into subfamilies depending upon the position and type
of substituent on the A ring.1,2 Examples of such subfamilies are
the well-known flavones (2) and isoflavones (3) (Figure 1).1
Flavones and isoflavones have been of interest for many years,
as they have shown a broad range of biological activities, which
include but are not limited to antioxidant,3 anti-inflammatory,4
and antiviral effects.5 Recently, a relatively new class of naturally
occurring chromones, the 2-(2-phenylethyl)chromones (4),
have begun to receive growing attention. 2-(2-Phenylethyl)-
chromones were first described in 1978 and have a rare
phenylethyl substituent at the C-2 position.6 Since their initial
discovery, less than 100 naturally occurring 2-(2-phenylethyl)-
chromones have been isolated and characterized.7 Accordingly,
there are very limited reports related to the biological activity of
2-(2-phenylethyl)chromones.7−11 Of interest is 5-hydroxy-2-(2-
phenylethyl)chromone (5-HPEC, 5), which was isolated from
Imperata cylindrica P. Beauv. (Poaceae) by Yoon et al.9 The
impetus for isolating and characterizing 5-HPEC (5) was its
neuroprotective activity against glutamate excitotoxicity in
primary cultures of rat cortical cells. Glutamate excitotoxicity
describes the process of neuronal cell death that occurs when
ionotropic glutamate receptors (iGluR) are overstimulated due
Figure 1. Chromone core (1), flavone (2), isoflavone (3), 2-(2-
phenylethyl)chromone (4), and 5-hydroxy-2-(2-phenylethyl)-
chromone (5).
to disruptions in glutamate homeostasis that increase
extracellular glutamate concentrations.12 Glutamate excitotox-
Received: February 4, 2015
© XXXX American Chemical Society and
American Society of Pharmacognosy
A
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Figure 2. Structural scaffolds of known 5-HT2B antagonists.
icity has been proposed as a common end point for neuronal
cell loss in glaucoma, retinal ischemia, Alzheimer’s disease,
stroke, and HIV-associated neurocognitive disorder. Despite
years of intense research developing iGluR antagonists to treat
excitotoxicity, this approach has had little success, as prolonged
antagonism of iGluRs is also neurotoxic. Therefore, alternative
strategies are being sought to mediate the effects of glutamate
excitotoxicity.
differ structurally, a unifying feature of the aforementioned
ligands is the presence of at least one basic nitrogen atom. A
long-standing hypothesis has been that ligands targeting the 5-
HT receptors or transporter should contain a basic nitrogen
atom in order to facilitate ligand binding and pharmacological
action.29 Challenging this idea, Madras and associates have
demonstrated that non-nitrogenous compounds maintained
not only the pharmacological profile of their nitrogenous
counterparts but also equipotent-binding affinities at the
monoamine transporters.30−33 Thus, it is interesting that 5-
HPEC (5), which lacks a basic nitrogen atom, can target the 5-
HT2B receptor with moderate affinity and selectivity. This could
suggest that 2-(2-phenylethyl)chromones such as 5 may
represent a novel class of naturally occurring non-nitrogenous
ligands for the 5-HT2B receptor.
Given the interesting biological activity and binding profile of
5-HPEC (5), the goal of the current study was to explore the
affinity, selectivity, and functional activity of other naturally
occurring and non-natural 2-(2-phenylethyl)chromones at the
5-HT2B receptor. Such a systematic study would be useful for
increasing the structural diversity of ligands targeting the 5-
HT2B receptor families and could also provide insight into how
non-nitrogenous ligands interact with the 5-HT2B receptor to
induce selectivity. Such compounds may also present unique
pharmacological profiles. The structural features investigated
included alkyl chain length and composition at C-2, the nature
of the aromatic C ring, and substitution patterns of the B and C
rings. Following their synthesis, each compound was screened
for inhibition of radioligand binding at all three 5-HT2
receptors. Compounds showing significant inhibition were
further evaluated for their binding affinity at the appropriate
receptor. Compounds showing significant improvements in
affinity over 5-HPEC (5) were then screened for their
functional activity at the 5-HT2B. Finally, molecular modeling
studies were performed to examine potential correlations
between the structural modifications and the ligands’ 5-HT2B
affinity.
As stated, 5-HPEC (5) showed neuroprotective activity
against glutamate excitotoxicity; however, the potential
mechanisms of action leading to the protective activity of 5-
HPEC are not fully known. Through a series of biological
screening experiments, it was possible to show that 5-HPEC
(5) can act as a selective serotonin receptor 2B (5-HT2B)
antagonist with reasonable affinity (pKi = 5.6).13 The biological
activity of chromones has largely been attributed to their
antioxidative properties, and only recently have they been
considered as potential ligands for G-protein coupled receptors
like 5-HT2B.14−16 The 5-HT2B receptor is one of three subtypes
found in the serotonin receptor 2 (5-HT2) family of receptors,
with the others being 5-HT2A and 5-HT2C.17 Studies have
shown that 5-HT2B is involved in the development of
migraine,18 modulating the 5-HT transport system,19 and the
rewarding and reinforcing effects of the abused drug 3,4-
methylenedioxymethamphetamine (MDMA).20,21 The endog-
enous ligand serotonin (5-HT) and selective ligands targeting
the 5-HT2A receptor have been shown to be protective against
glutamate neurotoxicity, but the potential role of 5-HT2B in
protection against glutamate excitotoxicity has yet to be fully
determined.22−25 This could be in part due to the notable
challenge in developing ligands specific for subtypes within the
5-HT2 family.26
5-HT2B shares approximately 46−50% sequence identity with
5-HT2A and 5-HT2C. The homology within the transmembrane
domain of the 5-HT2 receptors (which contains the 5-HT
binding pocket) is higher than 70%.17 Thus, the design of
selective ligands targeting 5-HT2B over 5-HT2A/2C presents a
considerable obstacle. Among the available 5-HT2B selective
ligands, commonly used structural scaffolds are arylureas (6),
arylpiperazines (7), indolonapthyridines (8), pyrimidines (9),
and tetrahydro-β-carbolines (10) (Figure 2).27,28 Although they
RESULTS AND DISCUSSION
■
Chemistry. The synthesis of the 5-HPEC analogues in this
study was based on a previous route established for the
B
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synthesis of 2-(2-phenylethyl)chromones.34 The first step was
to synthesize the esters needed to explore changes in C-2
substitution (Scheme 1). Several approaches were employed for
(benzyloxy)acetate (19) was synthesized by reaction of benzyl
alcohol with sodium hydride at 0 °C followed by the addition
of ethyl 2-bromoacetate.
In the previous report on the synthesis of 5-HPEC (5), it was
determined that monoprotection of the starting dihydroxyace-
tophenone (20a) is required to give high yields of the target
chromone via a direct Claisen condensation approach.34
Accordingly, the same strategy was employed in the synthesis
of the proposed analogues (Scheme 2). The appropriate
acetophenone (20) was protected with MOM as previously
described to give 21.36 The protected acetophenone was then
refluxed with sodium hydride to generate the needed enolate.
Following enolate formation the prepared ester (12, 15, 17, or
19) was added and the mixture was refluxed further for 4 h.
Upon workup, the crude condensation product was dissolved in
MeOH with catalytic hydrochloric acid and refluxed for 45 min
to give the desired analogues in good to excellent yields after
purification (5, 22a−n, Table 1).
a
Scheme 1. Synthesis of Esters for Claisen Condensation
Biological Testing. The goal of this study was to
investigate the affinity, selectivity, and functional activity of
naturally occurring and synthetic compounds bearing the 2-(2-
phenylethyl)chromone scaffold at the 5-HT2B receptor. Screen-
ing of these analogues was done in three phases.13 The initial
screening measured the inhibition of radioligand binding at
each of the 5-HT2 receptors by the newly synthesized
analogues at 10 μM. Those compounds showing greater that
50% inhibition at this concentration were further tested for
their affinity at the designated receptor. Analogues demonstrat-
ing significant improvement in 5-HT2B binding affinity over 5-
HPEC (5) were then screened for their functional activity.
The results of the initial screening are shown in Table 1. 5-
HPEC (5) showed only significant inhibitory activity (62.6%)
for the 5-HT2B receptor. Replacement of C-7′ with an oxygen
atom (22a) maintained significant inhibitory activity at 5-HT2B
(50.0%) as well the apparent selectivity over 5-HT2A/2C. Several
naturally occurring 2-(2-phenylethyl)chromones contain hy-
droxy group substituents on the C ring. Substitution at C-3′
with a hydroxy group (22c) increased inhibitory activity at 5-
HT2B to 76.3% and maintained selectivity to some degree.
Hydroxy group substitution at C-4′ (22d) maintained
inhibitory activity at 5-HT2B (70.9%); however, selectivity to
5-HT2B was reduced as the inhibitory activity at 5-HT2C was
increased to 56.6%. This observation suggested that the C-4′
position is important for 5-HT2B/2C selectivity over 5-HT2A.
Replacement of the phenyl ring with a thiophene (22e) or
furan (22f) ring system maintained significant inhibitory
activity and selectivity for 5-HT2B.
a
Reagents and conditions: (a) H2SO4 (cat.), EtOH, reflux, 24 h. (b)
CH2Cl2, DIPEA, MOMCl, rt, 3 h. (c) 1. DBU, triethyl
phosphonoacetate, rt, 4 h. 2. H2, Pd/C (10 mol %), 60 atm, 2 h.
(d) 1. 1,1′-Carbonyldimidazole, THF, rt, 30 min. 2. EtOH, rt, 16 h. (e)
1. NaH, THF, 0 °C 1 h. 2. Ethyl 2-bromoacetate, 0 °C, 16 h.
ester synthesis depending upon the available starting materials.
The synthesis of ethyl 2-phenylacetate (12a), ethyl 3-
phenylpropanoate (12b), ethyl 4-phenylbutanoate (12c),
ethyl 5-phenylpentanoate (12d), and ethyl 3-(thiophen-2-
yl)propanoate (12e) was accomplished via Fischer esterifica-
tion.35 Refluxing the appropriate carboxylic acid in ethanol with
catalytic sulfuric acid produced the desired ester in quantitative
yield, which after workup was used without further purification.
The esters adopted to examine effects of substitution on the C
ring were synthesized in three steps. First, the hydroxy group of
13 was protected with methoxylmethyl (MOM) by reaction
with methyoxymethyl chloride (MOMCl) in dichloromethane
(CH2Cl2).36 The protected aldehyde (14) was then reacted in a
modified Horner−Wadsworth−Emmons reaction with triethyl
phosphonoacetate to yield the α,β-unsaturated ester that was
immediately reduced to afford the substituted alkanes 15a−c.37
Ethyl 2-phenoxyacetate (17) was synthesized by activation of
phenoxyacetic acid (16) with 1,1′-carbonyldiimidazole (CDI)
followed by the addition of absolute ethanol.38 Finally, ethyl 2-
In addition to the above structural changes, the length of the
C-2 alkyl chain was also explored. Decreasing the C-2 alkyl
chain length (22g) decreased inhibitory activity at the 5-HT2B
receptor. Conversely, when the alkyl spacer was extended to
a
Scheme 2. Synthesis of 2-(2-Phenylethyl)chromones via Claisen Condensation and Cyclization
a
Reagents and conditions: (a) CH2Cl2, DIPEA, MOMCl, rt, 1 h. (b) 1. NaH, THF, reflux 1 h. 2. Ester, THF, reflux, 4 h. (c) MeOH, HCl (12
drops), reflux, 45 min.
C
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Table 1. Percent Inhibition of Radioligand Binding at 5-HT2 Receptors by Compounds 5 and 22a−n at 10 μM (Inhibition
≥50% Is Deemed Significant)
a
Denotes compound previously isolated from natural sources.
give 5-hydroxy-2-(3-phenylpropyl)chromone (5-HPPC, 22h),
inhibitory activity at 5-HT2B was increased and selectivity was
maintained. 2-[(Benzyloxy)methyl]-5-hydroxychromone (22i),
in which C-8′ is replaced with an oxygen atom, also showed
significant inhibitory activity (77.7%) at the 5-HT2B receptor,
although selectivity over the 5-HT2C receptor appeared to be
diminished. Further extension of the alkyl chain (22j)
decreased inhibitory activity.
In the initial isolation of 5-HPEC (5) it was noted that
removal of the C-5 hydroxy group dramatically reduced
neuroprotective activity.9 Therefore, the necessity of the C-5
hydroxy substituent for inhibitory activity at 5-HT2 receptors
was investigated by examining the activity of other 2-(2-
phenylethyl)chromone types. Although naturally occurring, no
biological investigations of 7-hydroxy-2-(2-phenylethyl)-
chromone (22k, 7-HPEC) have been reported. In the testing
performed, none of the 7-HPEC analogues (22k−n) showed
significant inhibitory activity at 5-HT2B. This suggested that the
C-5 hydroxy group may be critical for activity at the 5-HT2B
receptor. Moreover, the selectivity for these 7-HPEC analogues
was reduced. Interestingly, compound 22n, carrying a hydroxy
group at the C-4′ position, showed significant inhibitory activity
(53.1%) for the 5-HT2C receptor. Compound 22d, which also
has a hydroxy group at C-4′, showed higher inhibitory activity
D
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toward the 5-HT2C receptor as well. Such results lend further
support to the hypothesis that the C-4′ hydroxy group may be
favorable for 5-HT2C receptor selectivity.
HT2C = 5.9). Substitution of the phenyl ring with a thiophene
(22e) or furan (22f) gave a 2-fold improvement in affinity (pKi
= 5.9 and 5.7, respectively) over 5-HPEC (5).
Following the inhibition studies, analogues showing greater
than 50% inhibitory activity at 5-HT2B were examined for their
binding affinity toward this receptor. These data are shown in
Table 2. While having inhibitory activity at 5-HT2B in the
The most dramatic improvement in affinity was observed
with 5-HPPC (22h). 5-HPPC showed a 10-fold (pKi = 6.6)
increase in 5-HT2B affinity, suggesting that a propyl chain at C-
2 may be optimal. The replacement of C-8′ to give the
benzyloxy derivative 22i maintained the relative chain length;
however, a 6-fold decrease in 5-HT2B affinity compared to that
of 5-HPPC (22h) was observed. This, in conjunction with the
inhibition data, suggested that nonpolar moieties at C-2 would
be preferred. Encouraged by the improvement in affinity with
5-HPPC (22h), the functional activity of 5-HPPC was
investigated.
Table 2. pKi Values for Analogues Showing ≥50% Inhibitory
Activity in the Primary Assay
Presently, only 5-HT2B receptor antagonists are clinically
beneficial, as agonists of this receptor have been shown to
increase significantly the risk of developing valvular heart
disease.39,40 Our group determined previously that 5-HPEC (5)
behaves functionally as a 5-HT2B antagonist.13 Given this
increase in affinity, 5-HPPC (22h) was tested to determine if
antagonist activity at 5-HT2B was maintained. As conducted
earlier, a calcium mobilization assay in Flp-In HEK cells was
performed to investigate the functional activity of 5-HPPC
(22h) at 10 μM. At this concentration, 5-HPPC (22h) showed
negligible efficacy (0.23% of the maximal response of 5-HT)
when compared to the endogenous agonist 5-HT. Conversely,
when challenged with an EC50 dose (1.6 nM) of 5-HT, 5-
HPPC (22h) demonstrated improved antagonist activity
(20.5% inhibition) compared to 5-HPEC (5) (6.9% inhibition).
Taken together, these results suggest that 5-HPPC maintains
antagonist activity at the 5-HT2B receptor.
Ligand Docking. To gain further insight into plausible
reasons for the changes seen in the inhibitory activity and
affinity upon structural modification, ligand docking experi-
ments on the 5-HT2B receptor crystal structure (PDB ID-4IB4)
were undertaken. A generic algorithm docking program
(GOLDv51) was used to explore docking poses for each of
the synthesized analogues. The generated binding modes were
then scored using the Hydropathic INTeraction (HINT)
scoring function.41 The highest scored poses for 5-HPEC (5)
and 5-HPPC (22h) inside the 5-HT2B receptor are shown in
Figure 3, with the associated HINT scores shown in Table 3.
The chromone ring in each compound occupied a hydrophobic
pocket formed by Val136, Phe217, Phe340, Phe341, and
Val336. Within this pocket, the C-5 hydroxy group is able to
participate in hydrogen-bonding interactions with Asp135 and
Ser139. Compounds 22k−n would be unable to participate in
the described hydrogen-bonding interaction due to the lack of a
hydroxy group at C-5, and this could explain their decreased 5-
HT2B inhibitory activities. In addition to the importance of the
C-5 hydroxy group observed from the inhibitory activity data,
the affinity data showed that the length and composition of the
C-2 alkyl chain may also be important.
As shown in this model, the C-2 alkyl chain units of 5-HPEC
(5) and 5-HPPC (22h) are directed toward the cytoplasmic
surface of the receptor. The phenyl ring substituents of 5-
HPEC (5) and 5-HPPC (22h) can be positioned toward one of
the two possible hydrophobic pockets: one may be formed
between helices 5, 6, and 7 (Met218, Leu347, Leu348, and
Leu362) and the other formed between extracellular loop 2 and
helix 3 (Trp131, Leu132, Val208, and Leu209) (Figure S15,
Supporting Information). Overlapping of 5-HPPC (22h) and
5-HPEC (5) showed that the extended nonpolar phenyl ring of
primary assay at 10 μM, 5-hydroxy-2-(phenoxymethyl)-
chromone (22a) showed insignificant binding affinity at this
receptor (pKi < 5). Hydroxy group substitution at C-3′ (22c)
provided a 2-fold improvement in affinity over 5-HPEC (5)
(pKi = 5.9). The C-4′ hydroxy group (22d) also improved 5-
HT2B affinity (pKi = 6.0); however, as was observed in the
inhibition assay, selectivity over 5-HT2C was lost (pKi at 5-
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activity at 5-HT2B. To understand the basis for this improved
affinity, ligand docking studies were conducted. These results
were consistent with the observed biological data and revealed a
primarily hydrophobic binding pocket with significant hydro-
gen-bonding contribution by the Asp135 and Ser139 residues
with the C-5 hydroxy group. Extension of the C-2 alkyl chain
allowed 5-HPPC (22h) to take greater advantage of this
hydrophobic pocket. Accordingly, these data support an initial
hypothesis that the natural product 5-HPEC (5) can serve as a
novel scaffold to design and develop novel non-nitrogenous 5-
HT2B antagonists. These new ligands are anticipated to help
shed new light on understanding the correlation of the
neuroprotective properties of 2-(2-phenylethyl)chromones
and their antagonism at the 5-HT2B receptor.
EXPERIMENTAL SECTION
■
General Experimental Procedures. Chemical reagents were
purchased from Sigma-Aldrich, Alfa Aesar, Combi-blocks, or AK
Scientific and used without further purification. TLC analyses were
carried out on Analtech Uniplate F254 plates. Chromatographic
purification was accomplished on silica gel columns (230−400 mesh,
Bodman). IR spectra were recorded on a Nicolet Avatar 360 FT-IR
instrument with ATR attachment. 1H (400 MHz) and 13C (100 MHz)
NMR spectra were acquired at 30 °C on a Bruker Ultrashield 400 Plus
spectrometer. HRMS analysis was performed on a Quattro II triple
quadrupole mass spectrometer, a Waters Micromass QTOF-II
instrument (ESI source), or an Applied Bio Systems 3200 Q trap
with a turbo V source for TurbolonSpray.
Figure 3. Plausible ligand binding modes for 5-HPEC (5) and 5-
HPPC (22h) inside the 5-HT2B receptor. Cartoon representation of
the 5-HT2B receptor in cyan. Ligands are shown as ball-and-stick
representations: 5-HPEC (green), 5-HPPC (orange). Amino acid
residues involved in interactions are shown in stick representation
(cyan).
Fischer Esterification. Sulfuric acid (4.0 mL, 122 mmol) was
slowly added to a solution of the carboxylic acid (122 mmol) in
ethanol (150 mL) previously cooled to 0 °C on an ice bath. After
warming to room temperature, the mixture was heated to reflux and
allowed to stir for 16 h. On cooling to room temperature, the mixture
was concentrated by rotary evaporation at room temperature. The
residue was then dissolved in EtOAc. The organic layer was washed
three times with half the volume of saturated NaHCO3 solution. The
organic layer was then washed with brine and dried over MgSO4. The
organic layer was then evaporated to dryness to afford the desired ester
(in >90% yield), which was used in the Claisen condensation without
further purification.
Table 3. Optimal Docking Scores of 5-HPEC (5) and 5-
HPPC (22h) in the 5-HT2B Receptor Crystal Structure
compound
HINT score
5-HPEC (5)
507
777
5-HPPC (22h)
5-HPPC (22h) reached further into the first hydrophobic
pocket. This difference was perceived as a favorable interaction
and was reflected by an increased HINT score, and it could
provide an explanation for the increased affinity of 5-HPPC
(22h) over 5-HPEC (5). Taken together, these docking studies
were consistent with the observed biological data and may be
applied to guide future molecular design to further improve the
affinity of this scaffold for the 5-HT2B receptor.
To summarize, previous work from this laboratory has
demonstrated that the naturally occurring 2-(2-phenylethyl)-
chromone 5-HPEC (5) has the potential to serve as a scaffold
for the development of non-nitrogenous ligands at the 5-HT2B
receptor. The focus of the present study was to examine
structural features of the 2-(2-phenylethyl)chromone scaffold
required to improve affinity and maintain selectivity toward 5-
HT2B. A series of naturally occurring and synthetic 2-(2-
phenylethyl)chromones bearing the 5-HPEC scaffold was
synthesized and screened for this purpose. Key observations
from these studies include the following: the C-5 hydroxy
group is required for affinity at 5-HT2B; substitution at C-3′ is
tolerated, while substitution at C-4′ decreases selectivity over 5-
HT2C; replacing the phenyl C ring with smaller aromatic
moieties is well tolerated; and hydrocarbon alkyl chains of three
carbons at C-2 may be preferred. Among all the analogues
synthesized so far, 5-HPPC (22h) has emerged as a new lead
compound, showing a 10-fold improvement in 5-HT2B affinity
over 5-HPEC (5). 5-HPPC (22h) also maintained antagonist
1
Ethyl 2-phenylacetate (12a): colorless oil; H NMR (CDCl3, 400
MHz) δ 7.33−7.23 (5H, m), 4.14 (2H, q, J = 7.14 Hz), 3.59 (2H, s),
1.24 (3H, t, J = 7.14 Hz); 13C NMR (CDCl3, 100 MHz) δ 171.6,
134.2, 129.3, 128.5, 127.1, 60.8, 41.5, 14.2.
1
Ethyl 3-phenylpropanoate (12b): colorless oil; H NMR (CDCl3,
400 MHz) δ 7.29−7.18 (5H, m), 4.12 (2H, q, J = 7.14 Hz), 2.94 (2H,
t, J = 7.60 Hz), 2.61 (2H, t, J = 7.56 Hz), 1.22 (3H, t, J = 7.12 Hz); 13C
NMR (CDCl3, 100 MHz) δ 172.9, 140.6, 128.5, 128.3, 126.2, 60.4,
35.9, 31.0, 14.2.
1
Ethyl 4-phenylbutanoate (12c): colorless oil; H NMR (CDCl3,
400 MHz) δ 7.29−7.17 (5H, m), 4.12 (2H, q, J = 7.13 Hz), 2.65 (2H,
t, J = 7.60 Hz), 2.32 (2H, t, J = 7.5 Hz), 1.95 (2H, p, J = 7.54 Hz), 1.25
(3H, t, J = 7.08 Hz); 13C NMR (CDCl3, 100 MHz) δ 173.5, 141.5,
128.5, 128.4, 125.9, 60.3, 35.2, 33.7, 26.6, 14.3.
1
Ethyl 5-phenylpentanoate (12d): colorless oil; H NMR (CDCl3,
400 MHz) δ 7.29−7.15 (5H, m), 4.11 (2H, q, J = 7.13 Hz), 2.62 (2H,
t, J = 7.10 Hz), 2.31 (2H, t, J = 7.16 Hz), 1.66 (4H, m), 1.24 (3H, t, J =
7.14 Hz); 13C NMR (CDCl3, 100 MHz) δ 173.7, 142.2, 128.4, 128.3,
125.8, 60.2, 35.6, 34.2, 30.9, 24.6, 14.3.
Ethyl 3-(thiophen-2-yl)propanoate (12e): pale yellow oil; 1H
NMR (CDCl3, 400 MHz) δ 7.11 (1H, d, J = 5.2 Hz), 6.91 (1H, dd, J =
5.2, 3.4 Hz), 6.81 (1H, d, J = 3.4 Hz), 4.14 (2H, q, J = 7.13 Hz), 3.16
(2H, t, J = 7.62 Hz), 2.67 (2H, t, J = 7.62 Hz), 1.25 (3H, t, J = 7.16
Hz); 13C NMR (CDCl3, 100 MHz) δ 172.5, 143.1, 126.8, 124.6, 123.5,
60.6, 36.2, 25.2, 14.2.
General Procedure for Protection with MOM.36 To a solution
of phenol (4.0 g, 32.8 mmol) and DIPEA (17.1 mL, 98.2 mmol) in
CH2Cl2 (45 mL) was added MOMCl (4.1 g, 50.5 mmol) at room
F
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Article
temperature. This solution was stirred at room temperature for 1−2 h.
After the allotted time, water was added to the mixture and the
aqueous layer was extracted with CH2Cl2. The organic layer was dried
over Na2SO4 and concentrated. The residue was purified by
chromatography over silica gel eluted with 1:1 CH2Cl2−hexanes.
For 2-methoxymethoxybenzaldehyde (13a), 3-methoxymethoxy-
benzaldehyde (13b), 4-methoxymethoxybenzaldehyde (13a), 2-
hydroxy-4-methoxymethoxyacetophenone (20a), and 2-hydroxy-6-
methoxymethoxyacetophenone (20b), all spectroscopic data and
yields were consistent with those previously reported.36
= 7.13 Hz), 4.08 (2H, s), 1.28 (3H, t, J = 7.16 Hz); 13C NMR (CDCl3,
100 MHz) δ 170.3, 137.2, 128.5, 128.1, 128.0, 73.3, 67.3, 60.8, 14.2.
General Procedure for the Preparation of Hydroxychro-
mones (22a−n). To a slurry of sodium hydride (4.0 mmol) at reflux
in THF was added dropwise over 10 min the acetophenone 21 (1.0
mmol), which was dissolved in 10 mL of THF. The solution was then
allowed to reflux for 1 h past the addition of the last drop. While still at
reflux, the appropriate ester (12, 15, 17, or 19) (1.5 mmol) was then
added dropwise over 15 min, and the resulting solution stirred at reflux
for 4 h. The reaction mixture was then poured over 50 mL of saturated
NH4Cl while still hot and extracted three times with EtOAc. The
combined organic layers were dried over Na2SO4 and concentrated to
yield the crude Claisen product. Without purification, the Claisen
product was then dissolved in 20 mL of MeOH. While vigorously
stirring, 15 drops of concentrated HCl were added, and the solution
was placed in an oil bath that was preheated to 90 °C and was refluxed
for 45 min. On cooling to room temperature, saturated Na2CO3 was
added until neutral. Next, 50 mL of EtOAc was added. The organic
layer was washed with H2O (25 mL) and brine (25 mL), dried over
Na2SO4, and concentrated to give the crude hydroxychromone
products (22), which were purified by the appropriate measure to
give the desired product in fair to excellent yield (20−90%).
Ethyl 3-(2-(methoxymethoxy)phenyl)propanoate (15a). To a
mixture of 13 (6.6 mmol) and triethyl phosphonoacetate (6.0
mmol) was added DBU (8.2 mmol). The resulting mixture was
stirred for 4 h at room temperature. The reaction was quenched with
H2O (25 mL), and the aqueous layer was extracted with EtOAc (20
mL, 3×). The organic layer was washed with brine, dried over Na2SO4,
and concentrated to give a crude reddish-brown oil. This crude oil was
filtered over a silica gel pad with 1:1 CH2Cl2−hexanes to remove the
baseline residue. The filtrate was then concentrated to give a light-
colored oil. This oil was then redissolved in ethanol (30 mL), and Pd/
C (10% wt) was added. The mixture was then hydrogenated at 60 psi
for 2 h. The reaction was then filtered over Celite, and the Celite layer
was washed with ethanol. After the filtrate was concentrated down, the
resulting oil was purified on silica gel with 4:1 hexanes−EtOAC to give
5-Hydroxy-2-(2-phenylethyl)chromone (5): purified by column
chromatography by gradient elution from 1:1 CH2Cl2−hexanes to
100% CH2Cl2; IR (diamond) νmax 2934, 1653, 1616, 1480, 1409, 1258,
1
the desired product as a colorless oil: H NMR (CDCl3, 400 MHz) δ
1
845, 802 cm−1; H NMR (CDCl3, 400 MHz) δ 12.51 (1H, s, OH-5),
7.16 (2H, m), 7.05 (1H), 6.62 (1H), 5.29 (2H, s), 4.1 (2H, q, J = 7.16
Hz), 3.48 (3H, s), 2.96 (2H, t, J = 7.56 Hz), 2.61 (2H, t, J = 7.56 Hz),
1.23 (3H, t, J = 7.12 Hz); 13C NMR (CDCl3, 100 MHz) δ 173.3,
155.1, 130.0, 129.4, 127.6, 121.6, 113.7, 94.2, 60.3, 56.0, 34.4, 26.1,
14.2.
7.44 (1H, t, J = 8.32 Hz), 7.18−7.32 (5H, m), 6.85 (1H, dd, J = 8.4,
0.80 Hz), 6.76 (1H, dd, J = 8.4, 0.80 Hz), 6.06 (1H, s), 3.05 (2H, t, J =
7.0 Hz), 2.92 (2H, t, J = 6.8 Hz); 13C NMR (CDCl3, 100 MHz) δ
183.5, 169.8, 160.8, 156.7, 139.4, 135.1, 128.7, 128.2, 126.6, 111.2,
110.6, 108.8, 106.6, 36.0, 32.8; HRMS m/z 265.0909 (calcd for
C17H14O3, 265.0870).
5-Hydroxy-2-(phenoxymethyl)chromone (22a): purified by col-
umn chromatography eluting with 3:1 CH2Cl2−hexanes and
precipitation from acetone; IR (diamond) νm1ax 3082, 2903, 1655,
1628, 1497, 1431, 1384, 1240, 863, 803 cm−1; H NMR (DMSO-d6,
400 MHz) δ 12.47 (1H, s), 7.67 (1H, t, J = 8.36 Hz), 7.34 (2H, dt, J =
2.04, 8.72 Hz), 7.11−6.99 (4H, m), 6.84 (1H, dd J = 7.6, 8.24 Hz),
6.54 (1H, s), 5.17 (2H, s); 13C NMR (DMSO-d6, 100 MHz) δ 182.8,
166.1, 159.9, 157.3, 156.0, 136.1, 129.6, 121.6, 114.8, 111.1, 110.1,
108.1, 107.3, 65.3; HRMS m/z 267.0664 (calcd for C16H12O4,
267.0663).
Ethyl 3-(3-(methoxymethoxy)phenyl)propanoate (15b): prepared
in the same manner as 15a; colorless oil; 1H NMR (CDCl3, 400 MHz)
δ 7.17 (1H, m), 6.87 (3H, m), 5.15 (2H, s), 4.13 (2H, q, J = 7.12 Hz),
3.47 (3H, s), 2.92 (2H, t, J = 7.60 Hz), 2.61 (2H, t, J = 7.52 Hz), 1.23
(3H, t, J = 7.12 Hz); 13C NMR (CDCl3, 100 MHz) δ 172.8, 157.4,
142.2, 129.4, 121.8, 116.3, 114.0, 94.5, 60.4, 55.9, 35.8, 30.9, 14.2.
Ethyl 3-(4-(methoxymethoxy)phenyl)propanoate (15c): prepared
in the same manner as 15a; colorless oil; 1H NMR (CDCl3, 400 MHz)
δ 7.12 (2H, d, J = 8.5 Hz), 6.96 (2H, d, J = 8.6 Hz), 5.14 (2H, s), 4.13
(2H, q, J = 7.16 Hz), 3.46 (3H, s), 2.89 (2H, t, J = 7.6 Hz), 2.58 (2H,
t, J = 7.52 Hz), 1.23 (3H, t, J = 7.12 Hz); 13C NMR (CDCl3, 100
MHz) δ 172.9, 155.6, 134.0, 129.2, 116.3, 94.5, 60.3, 55.9, 36.1, 30.1,
14.2.
Ethyl 2-phenoxyacetate (17). To a slurry of 1,1′-carbon-
yldimidazole in anhydrous THF was added a solution of phenoxyacetic
acid 16 (anhydrous). Upon addition, rapid effervescence was observed.
This solution was allowed to stir for 30 min past the end of
effervescence. At this time, absolute ethanol was added, and the
mixture was allowed to stir at room temperature for 16 h. The mixture
was then concentrated, and the residue was taken up in dichloro-
methane. The organic layer was washed three times with half the
volume of saturated NaHCO3, then washed with brine, dried over
MgSO4, and concentrated to give the desired product as a colorless oil:
1H NMR (CDCl3, 400 MHz) δ 7.28 (2H, dd, J = 3.0, 1.8 Hz), 6.97
(1H, t, J = 3.1 Hz), 6.89 (2H, d, J = 2.0 Hz), 4.61 (2H, s), 4.26 (2H, q,
J = 7.15 Hz), 1.29 (3H, t, J = 7.13 Hz); 13C NMR (CDCl3, 100 MHz)
δ 168.9, 157.8, 129.6, 121.7, 114.7, 65.4, 61.3, 14.2.
Ethyl 2-(benzyloxy)acetate (19). To a slurry of sodium hydride
(60% dispersion, 17.8 mmol) cooled to −10 °C was added benzyl
alcohol (13.7 mmol) dropwise over 5 min. This solution was allowed
to stir at this temperature for 1 h. Following this, ethyl 2-bromoacetate
(13.7 mmol) was added. The solution was then allowed to come to
room temperature and stirred at room temperature for 20 h. The
reaction mixture was then concentrated. The residue was taken up in
EtOAc. The organic layer was washed with NaHCO3 and brine. After
drying over Na2SO4, the organic layer was concentrated to give a crude
pale yellow oil. The oil was purified over silica gel by eluting with 1:1
CH2Cl2−hexanes to give the pure product as a colorless oil: 1H NMR
(CDCl3, 400 MHz) δ 7.36−7.33 (5H, m), 4.63 (2H, s), 4.22 (2H, t, J
5-Hydroxy-2-(2′-hydroxy-2-phenylethyl)chromone (22b): purified
by stirring the crude solid in minimal CH2Cl2 and collecting the
undissolved solid; IR (diamond) νmax 3153, 2944, 1650, 1618, 1583,
1
1487, 1259, 845, 801 cm−1; H NMR (DMSO-d6, 400 MHz) δ 12.63
(1H, br s, OH-5), 9.48 (1H, br s, OH-2′), 7.62 (1H, t, J = 8.32 Hz),
7.08−6.99 (3H, m), 6.78 (2H, t, J = 8.4 Hz), 6.69 (1H, t, J = 7.4 Hz),
6.23 (1H, s), 2.95 (4H, s); 13C NMR (DMSO-d6, 100 MHz) δ 182.9,
171.4, 159.9, 156.2, 155.2, 135.6, 129.8, 127.4, 125.8, 118.8, 114.9,
110.7, 109.8, 108.1, 107.0, 33.5, 27.0; HRMS m/z 281.0854 (calcd for
C17H14O4, 281.0819).
5-Hydroxy-2-(3′-hydroxy-2-phenylethyl)chromone (22c): purified
by stirring the crude solid in minimal CH2Cl2 and collecting the
undissolved solid; IR (diamond) νmax 3220, 2947, 1654, 1614, 1578,
1
1565, 1245, 843, 801 cm−1; H NMR (CDCl3, 400 MHz) δ 12.67
(1H, s, OH-5), 7.61 (1H, t, J = 8.32 Hz), 7.09 (1H, t, J = 7.4 Hz), 6.98
(1H, dt, J = 2.4, 8.4 Hz), 6.69 (3H, m), 6.65 (1H, dt, J = 2.4, 0.84 Hz),
6.18 (1H, s), 3.05 (4H, m); 13C NMR (CDCl3 100 MHz) δ 183.6,
170.1, 160.7, 156.7 156.1, 141.2, 135.3 129.9, 120.4, 115.2, 113.7,
111.3, 110.5, 108.7, 106.9, 53.8, 32.6; HRMS m/z 283.0985 (calcd for
C17H14O4, 283.0971).
5-Hydroxy-2-(4′-hydroxy-2-phenylethyl)chromone (22d): purified
by stirring the crude solid in minimal CH2Cl2 and collecting the
undissolved solid; IR (diamond) νmax 3381, 2947, 1650, 1616, 1579,
1
1569, 1250, 845, 800 cm−1; H NMR (DMSO-d6, 400 MHz) δ 12.62
(1H, s, OH-5), 7.64 (1H, t, J = 8.32 Hz), 7.03 (3H, d, J = 8.44 Hz),
6.78 (1H, d, J = 8.2 Hz), 6.65 (2H, d, J = 8.44 Hz), 6.27 (1H, s), 2.93
(4H, m); 13C NMR (DMSO-d6, 100 MHz) δ 182.8, 171.1, 159.5,
G
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Journal of Natural Products
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156.2, 155.4, 135.7, 129.9, 129.2, 115.0, 110.7, 109.7, 108.4, 107.3,
35.5, 31.1; HRMS m/z 283.0998 (calcd for C17H14O4, 283.0971).
5-Hydroxy-2-(2-(thiophen-2-yl)ethyl)chromone (22e): purified by
column chromatography eluting with 1:1 CH2Cl2−hexanes; IR
(diamond) νmax 3103, 3066, 2913, 1645, 1613, 1474, 1439, 1379,
1357, 1239, 840, 807 cm−1; 1H NMR (acetone-d6, 400 MHz) δ 12.64
(1H, s), 7.61 (1H, t, J = 8.36 Hz), 7.25 (1H, dd, J = 2.16, 4.2 Hz), 6.99
(1H, dd, J = 0.72, 8.44 Hz), 6.93−6.91 (2H, m), 6.75 (1H, dd, J =
0.60, 8.28 Hz), 6.22 (1H, s), 3.35 (2H, t, J = 7.24 Hz), 3.09 (2H, t, J =
7.64 Hz); 13C NMR (acetone-d6, 100 MHz) δ 184.3, 170.9, 161.8,
157.7, 143.1, 136.3, 127.8, 126.0, 124.7 111.7, 111.1, 109.6, 107.8, 36.7,
27.4; HRMS m/z 271.0436 (calcd for C15H12O3S, 271.0434).
7-Hydroxy-2-(2′-hydroxy-2-phenylethyl)chromone (22l): purified
by stirring the crude solid in acetone for 24 h and then filtering the
precipitate; IR (diamond) νmax 3176, 2945, 1626, 1546, 1443, 1227,
842, 818 cm−1; 1H NMR (DMSO-d6, 400 MHz) δ 10.69 (1H, s), 9.38
(1H, s), 7.94 (1H, d, J = 8.72 Hz), 7.06 (1H, dd, J = 7.44, 1.44 Hz),
6.99 (1H, dt, J = 1.64, 7.9 Hz), 6.86 (1H, dd, J = 8.7, 2.2 Hz), 6.79−
6.78 (2H, m), 6.68 (1H, t, J = 7.4 Hz), 2.90 (4H, m); 13C NMR
(DMSO-d6, 100 MHz) δ 176.4, 168.6, 162.3, 157.7, 154.9, 129.8,
127.3, 126.5, 125.9, 118.9, 115.8, 114.8, 114.7, 108.9, 102.1, 33.3, 27.0;
HRMS m/z 283.0946 (calcd for C17H14O4, 283.0971).
7-Hydroxy-2-(3′-hydroxy-2-phenylethyl)chromone (22m): puri-
fied by stirring the crude solid in CH2Cl2 and collecting the
precipitate; IR (diamond) νmax 3145, 2926, 1626, 1590, 1558, 1402,
5-Hydroxy-2-(2-(furan-2-yl)ethyl)chromone (22f): Purified by
column chromatography eluting with 4:1 hexanes−EtOAc; IR
(diamond) νmax 3144, 3121, 2917, 1645, 1615, 1593, 1581, 1313,
1295, 1262, 838, 808 cm−1; 1H NMR (acetone-d6, 400 MHz) δ 12.65
(1H, s, OH-5), 7.61 (1H, t, J = 8.32 Hz), 7.43 (1H, d, J = 1.68 Hz),
6.96 (1H, d, J = 8.4 Hz), 6.74 (1H, d, J = 8.24 Hz), 6.31 (1H, dd, 1.92,
8.4 Hz), 6.23 (1H, s), 6.15 (1H, d, J = 3.2 Hz), 3.13 (2H, t, 7.0 Hz),
3.03 (2H, t, 7.0 Hz); 13C NMR (acetone-d6, 100 MHz) δ 182.3, 171.1,
161.7, 157.7, 154.5, 142.5, 136.3, 111.7, 111.2, 109.3, 107.6, 106.8,
33.4, 25.7; HRMS m/z 255.0675 (calcd for C15H12O4, 255.0663).
5-Hydroxy-2-benzylchromone (22g): purified by column chroma-
tography eluting with 4:1 hexanes−EtOAc; IR (diamond) νmax 3098,
1
1250, 1225, 856, 834 cm−1; H NMR (acetone-d6, 400 MHz) δ 9.89
(1H, br s), 8.56 (1H, br s), 7.91 (1H, d, J = 8.68 Hz), 7.09 (1H, t, J =
7.8 Hz), 6.93 (1H, dd, J = 8.72, 2.28 Hz), 6.87 (1H, d, J = 2.24 Hz),
6.68 (2H, m), 6.66 (1H, m), 6.00 (1H, s), 3.00 (4H, m); 13C NMR
(acetone-d6, 100 MHz) δ 177.2, 168.7, 163.1, 159.1, 158.4, 142.8,
130.3, 127.7, 120.4, 117.9, 116.2, 115.2, 114.1, 110.4, 103.3, 36.2, 33.4;
HRMS m/z 283.0957 (calcd for C17H14O4, 283.0971).
7-Hydroxy-2-(4′-hydroxy-2-phenylethyl)chromone (22n): purified
by column chromatography eluting with 7:3 hexanes−EtOAc; IR
(diamond) νmax 3181, 2942, 1622, 1596, 1547, 1256, 848, 808 cm−1;
1H NMR (acetone-d6, 400 MHz) δ 9.49 (1H, s), 8.11 (1H, s), 7.92
(1H, d, J = 8.68 Hz), 7.11 (2H, d, J = 8.48 Hz), 6.94 (1H, dd, J = 8.7,
2.24 Hz), 6.89 (1H, d, J = 2.24 Hz), 6.77 (2H, d, J = 8.48 Hz), 5.99
(1H, m), 3.01 (2H, t, J = 8.36 Hz), 2.89 (2H, t, J = 8.4 Hz); 13C NMR
(acetone-d6, 100 MHz) δ 177.1, 168.8, 159.1, 131.9, 130.2, 127.7,
117.9, 116.0, 115.1, 110.4, 103.2, 36.7, 32.7; HRMS m/z 305.0787
(calcd for C17H14O4Na, 305.0790).
Biological Testing. Percentage inhibition studies, Ki determi-
nations, receptor binding profiles, and agonist and/or antagonist
functional data were conducted by the National Institute of Mental
Health’s Psychoactive Drug Screening Program (PDSP), contract
number HHSN-271-2008-00025-C (NIMH PDSP). This facility is
directed by Dr. Bryan L. Roth at the University of North Carolina at
Chapel Hill, NC, and Project Officer Dr. Jamie Driscol at NIMH,
Bethesda, MD. For experimental details please refer to the PDSP Web
site http://pdsp.med.unc.edu/ and click on “Binding Assay” or
“Functional Assay” on the menu bar.
1
3055, 2788, 1667, 1618, 1482, 1434, 1372, 1263, 864, 820 cm−1; H
NMR (acetone-d6, 400 MHz) δ 12.62 (1H, s), 7.57 (1H, t, J = 8.4 Hz),
7.43- 7.28 (5H, m), 6.89 (1H, dd, J = 0.68, 8.48 Hz), 6.72 (1H, dd, J =
0.52, 8.24 Hz), 6.16 (1H, s), 4.05 (1H, s); 13C NMR (acetone-d6, 100
MHz) δ 184.4, 171.2, 161.8, 157.7, 136.4, 136.2, 130.1, 129.7, 128.2,
111.7, 111.1, 109.6, 107.7, 40.8; HRMS m/z 251.0747 (calcd for
C16H12O3, 251.0714).
5-Hydroxy-2-(3-phenylpropyl)chromone (22h): purified by col-
umn chromatography eluting with 4:1 hexanes−EtOAc; IR (diamond)
νmax 3025, 2930, 1652, 1618, 1475, 1459, 1367, 1252, 845, 802 cm−1;
1H NMR (CDCl3, 400 MHz) δ 12.54 (1H, s), 7.47 (1H, t, J = 8.32
Hz), 7.31−7.17 (5H, m), 6.83 (1H, dd, J = 0.64, 8.4 Hz), 6.77 (1H, d,
J = 8.24 Hz), 6.09 (1H, s), 2.72 (2H, t, J = 7.4 Hz), 2.62 (2H, t, J =
7.32 Hz), 2.07 (2H, t, J = 7.72 Hz); 13C NMR (CDCl3, 100 MHz) δ
184.5, 170.6, 160.8, 156.7, 140.7, 135.0, 128.5, 128.4, 126.2 111.1,
110.6, 108.5, 106.8, 34.9, 33.6, 28.2; HRMS m/z 279.1040 (calcd for
C18H16O3, 279.1023).
Molecular Modeling Studies. The chemical structures of ligands
5-HPEC (5) and 5-HPPC (22h) were sketched within SYBYL-X2.0,
5-Hydroxy-2-((benzyloxy)methyl)chromone (22i): purified by
column chromatography eluting with 7:3 hexanes−EtOAc; IR
(diamond) νmax 3030, 2951, 2871, 1649, 1585, 1480, 1457, 1420,
1255, 1220, 853, 802 cm−1; 1H NMR (acetone-d6, 400 MHz) δ 12.60
(1H, s), 7.57 (1H, t, J = 8.32 Hz), 7.43−7.28 (5H, m), 6.90 (1H, dd, J
= 0.52, 8.48 Hz), 6.73 (1H, d, J = 8.28 Hz), 6.34 (1H, s), 4.71 (2H, s),
4.52 (2H, s); 13C NMR (acetone-d6, 100 MHz) δ 184.2, 168.5, 161.8,
157.4, 138.6, 136.5, 129.3, 128.7, 111.9, 111.5, 109.5, 108.5, 107.9,
73.8, 68.6, 38.7; HRMS m/z 281.0827 (calcd for C17H14O4, 281.0819).
5-Hydroxy-2-(4-phenylbutyl)chromone (22j): purified by column
chromatography eluting with 7:3 hexanes−EtOAc; IR (diamond) νmax
3061, 2933, 2852, 1650, 1621, 1478, 1459, 1382, 1366, 1258, 873, 803
cm−1; 1H NMR (acetone-d6, 400 MHz) δ 12.70 (1H, s), 7.59 (1H, t, J
= 8.32 Hz), 7.28−7.14 (5H, m), 6.95 (1H, dd, J = 0.68, 8.4 Hz), 6.74
(1H, d, J = 8.28 Hz), 6.20 (1H, s), 2.77−2.67 (4H, m), 1.83−1.74
(4H, m); 13C NMR (acetone-d6, 100 MHz) δ 184.5, 172.6, 161.8,
157.7, 143.0, 136.2, 129.2, 129.1, 126.6, 111.6, 111.1, 109.0, 107.7,
36.0, 34.5, 31.5, 27.0; HRMS m/z 293.1196 (calcd for C19H18O3,
293.1183).
and their Gasteiger−Huckel charges were assigned before energy
̈
minimization (10 000 iterations) under the TAFF. The generic
algorithm docking program GOLD42 was used to perform the docking
studies with standard default settings unless otherwise specified. The
binding site was defined to include all atoms within 10 Å of the α-
carbon atom of Asp135 for the 5-HT2B crystal structure (PDB ID
4IB4).43 The obtained GOLD-docked solutions were merged into the
receptor and the combined receptor−ligand structures were energy-
minimized using the parameters described above in order to remove
clashes and minimize strain energy, thus optimizing the interactions
between ligand and receptor within the binding pocket. These models
were then subjected to hydropathic analysis with the HINT41 program,
and best-scored HINT solutions were obtained. The pictures shown
were generated using the PyMOL Molecular Graphics System, version
1.5.0.4, Schrodinger, LLC.
̈
ASSOCIATED CONTENT
■
S
* Supporting Information
7-Hydroxy-2-(2-phenylethyl)chromone (22k): purified by column
chromatography eluting with 19:1 CH2Cl2−MeOH; IR (diamond)
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jnat-
prod.5b00118.
1
νmax 3026, 1621, 1548, 1495, 1421, 1256, 852, 823 cm−1; H NMR
(acetone-d6, 400 MHz) δ 9.45 (1H, s, OH-7), 7.96−7.90 (1H, m),
7.28−7.18 (5H, m), 6.94 (1H, d, J = 8.68 Hz), 6.87 (1H, s), 6.00 (1H,
s), 3.08 (2H, t, J = 7.76 Hz), 2.95 (2H, t, J = 6.08 Hz); 13C NMR
(acetone-d6, 100 MHz) δ 177.2, 168.7, 163.1, 159.1, 141.2, 129.3,
129.3, 127.7, 127.1, 117.8, 115.2, 110.3, 103.3, 36.2, 33.4; HRMS m/z
265.0890 (calcd for C17H14O3, 265.0870).
1H and 13C spectra for all previously unreported
compounds and alternative docking poses of 5-HPEC
(5) and 5-HPPC (22h) in the 5-HT2B crystal structure
(PDF)
H
DOI: 10.1021/acs.jnatprod.5b00118
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
Article
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AUTHOR INFORMATION
■
Corresponding Authors
(25) Kamei, J.; Igarashi, H.; Kasuya, Y. Res. Commun. Chem. Pathol.
Pharmacol. 1991, 74, 167−184.
*E-mail: williamsda2@vcu.edu (D. Williams).
*Tel: +1 804 828 0021. Fax: +1 804 828 7625. E-mail:
yzhang2@vcu.edu (Y. Zhang).
(26) Kwon, Y. J.; Saubern, S.; Macdonald, J. M.; Huang, X. P.; Setola,
V.; Roth, B. L. Bioorg. Med. Chem. Lett. 2010, 20, 5488−5490.
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Dominguez, E.; Loza, M. I. Curr. Top. Med. Chem. 2010, 10, 493−503.
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Mini-Rev. Med. Chem. 2004, 4, 325−330.
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Blundell, P.; Gonzalez, M. D.; Meltzer, P. C. Synapse 1996, 24, 340−
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(30) Goulet, M.; Miller, G. M.; Bendor, J.; Liu, S. H.; Meltzer, P. C.;
Madras, B. K. Synapse 2001, 42, 129−140.
(31) Madras, B. K.; Fahey, M. A.; Miller, G. M.; De La Garza, R.;
Goulet, M.; Spealman, R. D.; Meltzer, P. C.; George, S. R.; O’Dowd, B.
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors thank Dr. Y. Yuan for helpful discussions in
preparing the data for this article. This work was supported by a
NIH/NIDA training grant (DA007027) (D.A.W.) and PHS
Research Funds (DA024022) (Y.Z.). Ki determinations,
receptor binding profiles, and agonist and/or antagonist
functional data were generously provided by the National
Institute of Mental Health’s Psychoactive Drug Screening
Program, contract number HHSN-271-2008-00025-C (NIMH
PDSP).
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DOI: 10.1021/acs.jnatprod.5b00118
J. Nat. Prod. XXXX, XXX, XXX−XXX