Investigation of the structural requirements for N-methyl-D-aspartate receptor positive and negative allosteric modulators based on 2-naphthoic acid

Article abstract of DOI:10.1016/j.ejmech.2018.12.054

The N-methyl-D-aspartate receptor (NMDAR), a ligand-gated ion channel activated by L-glutamate and glycine, plays a major role in the synaptic plasticity underlying learning and memory. NMDARs are involved in neurodegenerative disorders such as Alzheimer's and Parkinson's disease and NMDAR hypofunction is implicated in schizophrenia. Herein we describe structure-activity relationship (SAR) studies on 2-naphthoic acid derivatives to investigate structural requirements for positive and negative allosteric modulation of NMDARs. These studies identified compounds such as UBP684 (14b), which act as pan potentiators by enhancing NMDAR currents in diheteromeric NMDAR tetramers containing GluN1 and GluN2A-D subunits. 14b and derivatives thereof are useful tools to study synaptic function and have potential as leads for the development of drugs to treat schizophrenia and disorders that lead to a loss of cognitive function. In addition, SAR studies have identified a series of styryl substituted compounds with partial NAM activity and a preference for inhibition of GluN2D versus the other GluN2 subunits. In particular, the 3-and 2-nitrostyryl derivatives UBP783 (79i) and UBP792 (79h) had IC₅₀s of 1.4 μM and 2.9 μM, respectively, for inhibition of GluN2D but showed only 70–80% maximal inhibition. GluN2D has been shown to play a role in excessive pain transmission due to nerve injury and potentially in neurodegenerative disorders. Partial GluN2D inhibitors may be leads for the development of drugs to treat these disorders without the adverse effects observed with full NMDAR antagonists.

Full text of DOI:10.1016/j.ejmech.2018.12.054

Accepted Manuscript
Investigation of the structural requirements for N-methyl-D-Aspartate receptor positive
and negative allosteric modulators based on 2-naphthoic acid
Mark W. Irvine, Guangyu Fang, Kiran Sapkota, Erica S. Burnell, Arturas Volianskis,
Blaise M. Costa, Georgia Culley, Graham L. Collingridge, Daniel T. Monaghan, David
E. Jane
PII:
S0223-5234(18)31097-3
DOI:
https://doi.org/10.1016/j.ejmech.2018.12.054
EJMECH 10988
Reference:
To appear in: European Journal of Medicinal Chemistry
Received Date: 17 October 2018
Revised Date: 5 December 2018
Accepted Date: 22 December 2018
Please cite this article as: M.W. Irvine, G. Fang, K. Sapkota, E.S. Burnell, A. Volianskis, B.M. Costa,
G. Culley, G.L. Collingridge, D.T. Monaghan, D.E. Jane, Investigation of the structural requirements for
N-methyl-D-Aspartate receptor positive and negative allosteric modulators based on 2-naphthoic acid,
European Journal of Medicinal Chemistry (2019), doi: https://doi.org/10.1016/j.ejmech.2018.12.054.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Investigation of the Structural Requirements for N-Methyl-D-
Aspartate Receptor Positive and Negative Allosteric Modulators Based
on 2-Naphthoic Acid
#
#
#
2,
1
,
1,
1,3
Mark W. Irvine , Guangyu Fang , Kiran Sapkota , Erica S. Burnell , Arturas
4
,6
2,5
1
6,7
Volianskis , Blaise M. Costa , Georgia Culley , Graham L. Collingridge , Daniel T.
#
#
1,
2
,
Monaghan and David E. Jane *
1
Centre for Synaptic Plasticity, School of Physiology, Pharmacology and Neuroscience,
University of Bristol, Biomedical Sciences Building, University Walk, Bristol, BS8 1TD,
2
UK, Department of Pharmacology and Experimental Neuroscience, University of Nebraska
3
Medical Center, Omaha, Nebraska 68198-5800 U.S.A., School of Chemistry, National
4
University of Ireland Galway, Galway H91TK33, Ireland, Centre for Neuroscience and
Trauma, Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen
5
Mary University of London, UK, Pharmacology Division, Virginia College of Osteopathic
6
Medicine, Blacksburg, VA 24060, U.S.A., Centre for Synaptic Plasticity, School of
Physiology, Pharmacology and Neuroscience, Dorothy Hodgkin Building, University of
7
Bristol, Bristol, BS1 3NY, UK, Lunenfeld-Tanenbaum Research Institute, Mount Sinai
Hospital, Toronto, Ontario M5G 1X5, Canada.
#
MI, GF and KS contributed equally as first authors and DEJ and DTM as senior authors.
*
To whom correspondence should be addressed. Phone: +44 (0)117 3311409. Fax: +44
(0)1173312288. E-mail: david.jane@bristol.ac.uk
1

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Abstract
The N-methyl-D-aspartate receptor (NMDAR), a ligand-gated ion channel activated by L-
glutamate and glycine, plays a major role in the synaptic plasticity underlying learning and
memory. NMDARs are involved in neurodegenerative disorders such as Alzheimer’s and
Parkinson’s disease and NMDAR hypofunction is implicated in schizophrenia. Herein we
describe structure-activity relationship (SAR) studies on 2-naphthoic acid derivatives to
investigate structural requirements for positive and negative allosteric modulation of
NMDARs. These studies identified compounds such as UBP684 (14b), which act as pan
potentiators by enhancing NMDAR currents in diheteromeric NMDAR tetramers containing
GluN1 and GluN2A-D subunits. 14b and derivatives thereof are useful tools to study synaptic
function and have potential as leads for the development of drugs to treat schizophrenia and
disorders that lead to a loss of cognitive function. In addition, SAR studies have identified a
series of styryl substituted compounds with partial NAM activity and a preference for
inhibition of GluN2D versus the other GluN2 subunits. In particular, the 3-and 2-nitrostyryl
derivatives UBP783 (79i) and UBP792 (79h) had IC s of 1.4 µM and 2.9 µM, respectively,
5
0
for inhibition of GluN2D but showed only 70-80% maximal inhibition. GluN2D has been
shown to play a role in excessive pain transmission due to nerve injury and potentially in
neurodegenerative disorders. Partial GluN2D inhibitors may be leads for the development of
drugs to treat these disorders without the adverse effects observed with full NMDAR
antagonists.
Keywords: N-Methyl-D-aspartate receptor; NMDA; GluN2; positive allosteric modulator;
negative allosteric modulator; 2-naphthoic acid
2

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Introduction
N-Methyl-
D
-aspartic acid receptors (NMDARs) are members of the ionotropic glutamate
receptor family, which are L-glutamate-gated ion channels that mediate fast excitatory
synaptic transmission in the central nervous system (CNS). NMDARs are tetramers
assembled from two GluN1 subunits, each containing a binding site for the co-agonist glycine
and two GluN2A-D subunits, containing a binding site for L-glutamate in the ligand binding
domain (LBD) region on each subunit. In some areas of the CNS, GluN3A and GluN3B
subunits are incorporated into the tetramer [1-3]. An important function of NMDARs is to
initiate the synaptic plasticity that occurs during CNS development and in learning and
memory [4].
NMDARs have been the subject of intense investigations into the development of drugs
that can modulate their activity. This is due to the involvement of these receptors in
neurological disorders such as epilepsy, chronic pain, depression and schizophrenia and
neurodegenerative disorders such as ischemia, Alzheimer’s and Parkinson’s diseases [5].
Very few compounds have made it into the clinic, with low affinity channel blockers such as
memantine, which is used to treat moderate to severe Alzheimer’s disease, being the
exception. Antagonists interacting with the glutamate binding site on GluN2 subunits, the
glycine binding site on GluN1 subunits, the ion channel with high affinity and the N-terminal
domain of the GluN2B subunit have so far failed in clinical trials for stroke, head injury and
epilepsy [1,5,6]. This is largely due to lack of efficacy and/or intolerable side effects such as
amnesia, ataxia and psychotomimetic effects. More recently, attention has focused on the
development of allosteric modulators, which may be able to treat neurological disorders
without interfering with the normal physiological functions of NMDARs, thereby reducing
side effects [6]. Furthermore, most efforts in NMDAR drug development have focused on
inhibitors of activity. However, for treating schizophrenia, which is associated with NMDAR
hypofunction, NMDAR positive allosteric modulators (PAMs) may have therapeutic benefits
6
over currently available antipsychotics [6]. NMDAR PAMs may also have a role in treating
the cognitive deficits observed in patients with other disorders such as Alzheimer’s and
Parkinson’s disease [6].
We have reported a series of phenanthrene derivatives that can act as negative allosteric
modulators (NAMs) and/or PAMs by binding to a site(s) distinct from those known for
previous NMDAR ligands [7]. For example, UBP512 (1) (Figure 1) potentiated NMDARs
containing GluN2A, had no effect on GluN2B and inhibited GluN2C and GluN2D in an
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electrophysiological assay. Others have reported compounds that potentiate GluN2C and
GluN2D (2, CIQ) [8] or specifically potentiate GluN2C (3) [9] (Figure 1). Recently, a
GluN2A selective PAM (6) has been reported, which was developed from the lead
compounds GNE-6901 (4) and GNE-8324 (5) (Figure 1) [10]. X-ray crystallography has
revealed that these compounds bind at the dimer interface of the ligand binding domains
(
LBDs) of GluN1 and GluN2A [10]. Endogenous neurosteroids such as pregnenolone sulfate
and synthetic derivatives thereof also potentiate NMDAR responses [11,12].
Removal of the terminal aromatic ring in 1 and modification of the resultant 2-naphthoic
acid core afforded a series of derivatives, such as UBP617 (7) (Figure 1), which non-
selectively inhibited receptors containing different GluN2 subunits [13]. Interestingly, 7 and
several structurally realated analogues showed submaximal inhibition of NMDARs making
them potential leads for neurological conditions associated with overactivation of the
receptor, such as neuropathic pain, where a complete block of activity could have adverse
effects due to inhibition of essential brain functions. Others have reported compounds that
selectively antagonise GluN2C and GluN2D (QNZ46, 8, Figure 1) [14] and a series of
compounds that act as partial negative allosteric modulators (NAMs) [15]. NAMs that
specifically inhibit GluN2A (TCN-201, MPX-004, 9, Figure 1) have been reported [16,17].
Inhibition of GluN1/GluN2A by 9 has been shown to be dependent on the glycine
concentration and X-ray crystallography has revealed that it binds to the dimer interface of
the ligand binding domains of GluN1 and GluN2A [17].
Herein we describe structure-activity relationship (SAR) studies on 2-naphthoic acid
derivatives as analogues of our previously reported phenanthrene [7] and naphthalene series
[
7a,13] with the aim of understanding the structural requirements for NMDAR NAMs and
PAMs.
Results
Chemistry
The synthesis of the naphthalene derivatives described in this report is outlined in
Schemes 1-10. Heck coupling between methyl 6-bromo-2-naphthoate (10) and the
appropriate alkene afforded 11a-b (Scheme 1). To aid SAR studies, a small amount of the
trans-alkene (11a-b) was hydrolysed to its corresponding acid (12a-b) using base. However,
the majority was taken forward and hydrogenated before being hydrolysed with base to yield
saturated acids 14a-b. The 6-cyclopropyl derivative (17) was synthesized from 10 in three
steps (Scheme 1). Firstly, Stille coupling between 10 and tri-n-butyl(vinyl)tin afforded 15.
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The cyclopropyl ring was then formed via a Simmons-Smith reaction and the resultant ester
(16) hydrolysed to the desired acid (17) using base.
In order to gather SAR information, several analogues of 14a were synthesized (Scheme
2
). Reduction of the 3-carboxy moiety using LiAlH proceeded smoothly, giving the 3-
4
hydroxymethyl derivative 18 in good yield. Reaction of 18 with PBr afforded 3-
3
bromomethyl derivative 19 which was in turn converted to nitrile 20 by reaction with NaCN
under phase transfer conditions. Acidic hydrolysis of the nitrile yielded the corresponding 3-
acetic acid derivative 21. The 5-bromo analogue 22 was readily synthesized by reacting 14a
with a solution of bromine in glacial acetic acid (Scheme 2). Alkylation of 6-hydroxy-2-
naphthoic acid (23) with 1-bromobutane afforded the 6-butoxy derivative 24 in good yield
(Scheme 2).
Methyl 6-bromo-2-naphthoate (10) was utilised as a starting material in the synthesis of
various analogues of 14b (Schemes 3 and 4). Heck coupling between 10 and the appropriate
alkene led to the synthesis of trans alkene intermediates 25a-b and 30 (Scheme 3). To aid
SAR studies, a sample of 30 was hydrolysed using base to yield unsaturated acid 31.
Hydrogenation of 25a-b and 30 gave the corresponding alkyl esters which were subjected to
base hydrolysis to give acids 27a-b and 33 (Scheme 3). Sonogashira coupling between 10
and 4-methylpent-1-yne afforded ester 28 which was readily hydrolysed to acid 29 (Scheme
3
). Using transesterification under acidic conditions, 10 was converted to isobutyl ester 34 in
reasonable yield. Palladium catalysed carboxylation using carbon monoxide subsequently
afforded acid 35 (Scheme 4). A Claisen condensation between 10 and ethyl 4-methylvalerate
followed by intramolecular decarboxylation yielded ketone 36. Palladium catalysed
carboxylation using carbon monoxide gave ester 37 which was hydrolysed using base to
afford acid 38 (Scheme 4). Sonogashira coupling between 10 and 4-pentyn-2-ol led to the
synthesis of alcohol 39. Hydrogenation of the alkyne bond followed by oxidation of the
alcohol using Dess-Martin periodinane (DMP) afforded ketone 40 in good yield (Scheme 4).
The introduction of a carboxymethyl group was achieved by reacting ketone 40 with methyl
diethylphosphonoacetate under Wittig reaction conditions. Hydrogenation of the resultant
alkene gave ester (41) which was readily hydrolysed to di-acid 42 using base (Scheme 4).
To gather additional SAR information, ketone 37 was subjected to further chemical
modification (Scheme 4). Using Wittig reaction chemistry, methylenation of ketone 37
afforded alkene 43 in good yield. Although the majority of alkene 43 was taken forward and
hydrogenated to give ester 45, some was held back and hydrolysed using base to give
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unsaturated acid 44. Ester 45 was hydrolysed to acid 46 in good yield under basic conditions
(Scheme 4).
Thioether, amide and ester analogues of 14b were also synthesised during the course of
SAR studies (Scheme 5). The reaction between 6-bromomethyl derivative 47 and 2-
methylpropan-1-thiol in the presence of sodium yielded thioether 48 which was readily
converted to corresponding acid 49 by base hydrolysis (Scheme 5). Coupling of acid chloride
5
0 with isobutylamine under standard conditions afforded amide 51 which was hydrolysed to
acid 52 using base (Scheme 5). Using identical conditions, 6-hydroxymethyl 53 and
isobutyryl chloride were coupled to yield ester 54 (Scheme 5).
Further modifications to the 6-isohexyl side chain in 14b were investigated using 6-
bromomethyl derivative 55 as a starting material (Scheme 6). The reaction between 55 and 2-
methylpropan-1-ol in the presence of sodium yielded ether 56. Palladium catalysed
carboxylation using carbon monoxide subsequently afforded acid 57 (Scheme 6). Base
promoted nucleophilic substitution between 55 and ethyl 4-methylvalerate generated ester 58.
Palladium catalysed carboxylation using carbon monoxide yielded di-ester 59. Base
hydrolysis subsequently afforded di-acid 60 (Scheme 6).
3
-Hydroxy-2-naphthoic acid derivatives of 14b were also the subject of investigation
(Schemes 7). The starting material required for these compounds (63) was synthesised in two
steps from 7-bromo-3-hydroxy-2-naphthoic acid 69. Firstly, the 2-carboxy group was
esterified using K CO and methyl iodide to afford methyl ester 62. The 3-hydroxy group
2
3
was in turn acetylated using acetic anhydride to afford 63 (Scheme 7). Heck coupling
between 63 and 4-methylpent-1-ene and hydrogenation of the resulting alkene yielded 64.
Base hydrolysis was used to deprotect a sample of this compound giving 65 (Scheme 7). The
majority of 64 was deprotected at the 3-position using dimethylamine to afford phenol 66
which was in turn reacted with triflic anhydride under classical conditions to give triflate 67.
Removal of the triflate group using formic acid and Pd(PPh ) yielded ester 68 which was
3
4
subsequently hydrolysed in the presence of base to acid 69 (Scheme 7).
Swapping the respective positions of the carboxy and hydroxy groups in compound 65
was desirable for investigating the SAR surrounding this compound (Scheme 8). Sonogashira
coupling between triflate 70 and 4-methylpent-1-yne led to the synthesis of alkyne 71.
Hydrogenation of the triple bond followed by t-BuLi promoted carboxylation afforded ester
7
2. Acidic deprotection of the 3-hydroxy group yielded 73 which was readily hydrolysed
using base to give acid 74 (Scheme 8). Replacing the hydroxy group in 65 with a carboxy
moiety was also of interest for SAR studies (Scheme 8). Heck coupling between
6

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commercially available 75 and 4-methylpent-1-ene afforded alkene 76. Subsequent
hydrolysis of the nitrile groups under acidic conditions and hydrogenation of the alkene bond
afforded di-acid 77 (Scheme 8).
Heck coupling between 63 and the appropriately substituted styrene afforded a series of 7-
substituted styryl derivatives (78a-j) (Scheme 9). The majority of these compounds were
taken forward and de-protected under basic conditions to give 79a-j. However, to gather
additional SAR information, 78a, 78b and 78d were hydrogenated to their saturated
counterparts (80a-c) and then hydrolysed using base to afford phenethyl derivatives 81a-c
(Scheme 9). In order to investigate it’s importance, the 3-hydroxy moiety of 79a was
subjected to modification. De-acetylation of 78a using dimethylamine afforded phenol 82
which was in turn reacted with triflic anhydride under classical conditions to give triflate 83
(Scheme 9). Palladium catalysed carboxylation using carbon monoxide gave di-ester 84
which was hydrolysed using base to afford di-acid 85 in moderate yield (Scheme 9).
The coumarin UBP608 has previously been reported as a moderately potent NAM that
fully inhibited GluN2A responses with an IC of 18.6 ± 1.4 µM and 23-fold selectivity over
5
0
GluN2D [7a]. It was thought, given styryl group addition to the naphthalene series (see 78a-j
in Table 5) gave a series of interesting NMDAR NAMs, that the same strategy could be
applied to create the coumarin analogue of 78a. It was hoped that by using commercially
available ethyl 6-bromo-3-coumarincarboxylate (86), a range of analogues could be accessed
in a similar way to the naphthalene series, through palladium catalysed cross-coupling with a
variety of substituted benzene derivatives. In our hands, however, negligible yields of the
desired styryl-coupled coumarin (88) were achieved under standard Heck and Suzuki
conditions (Scheme 10). Instead of attempting to functionalise an existing coumarin, the next
strategy was to synthesise a coumarin with the desired functional groups in place, in this case,
a styryl group. A Knoevenagel condensation of Meldrum’s acid [18] with known
intermediate (E)-2-hydroxy-5-styrylbenzaldehyde (87) (synthesised using a literature
procedure [19]) gave the desired coumarin 88 in a moderate yield (Scheme 10).
Biological evaluation and SAR studies
Compounds were initially evaluated at a concentration of 100 µM for their effects on
agonist-induced NMDAR currents using a two-electrode voltage clamp (TEVC)
electrophysiological assay [7]. Although the test concentration is high even for screening it
allowed us to detect any weak NMDAR PAM effects. Compounds with significant activity
7

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were investigated more thoroughly using full concentration response curves. cRNA coding
for the four GluN1/GluN2A-D diheteromeric NMDARs were individually injected into
Xenopus laevis oocytes. After 2 to 5 days, NMDAR currents were induced by L-glutamate
(
Glu) (10 µM) and glycine (Gly) (10 µM) and after a steady-state response was obtained, the
test compounds were co-applied with agonist. Data from these studies are shown in Tables 1-
and 5. Full concentration-response curves (Figures 2 and 3) and EC or IC values across
3
5
0
50
GluN2A-D were then generated for compounds with significant NMDAR potentiating or
inhibitory activity identified in the initial screen (Tables 4 and 6). All compounds were
soluble and showed no visible signs of precipitation at the concentrations tested in these
assays. The origianlly described compounds (e.g. 1 and 7, Figure 1) did not display
glutamate-site or glycine-site NMDAR agonist activity nor were they active in the absence of
agonists [7,13]. In this study, compounds with the greatest PAM activity (14b and 46, Tables
1
, 2 and 4) were similarly evaluated and found to have no NMDAR agonist activity or effect
on the holding current (Saptoka et al., 2017).
SAR studies to identify novel NMDAR positive allosteric modualtors.
SAR studies were focused on identifying novel NMDAR PAMs and investigating their
structural requirements. The following structural changes were investigated: 1. Effect of
removing the unsubstituted aromatic ring from the phenanthrene based compounds such as
UBP512 (1) to form naphthalene derivatives, 2. Effect of changing the 6-substituent on the
naphthyl ring, 3. Effect of changing the position of the carboxylic acid group attached to the
naphthalene ring, 4. Effect of adding substituents to the naphthyl ring system, 5. Effect of
adding substituents to the alkyl chain attached to the 6-position of the naphthalene ring, 6.
Effect of adding heteroatoms to the alkyl chain attached to the 6-position of the naphthalene
ring.
Effect of removing unsubstitued aromatic ring from phenanthrene lead compounds.
Previous studies have shown that 9-substituted phenanthrene-3-carboxylic acids such
as UBP512 (1, Figure 1) and 9-alkyl derivatives have potentiating effects on NMDARs [7].
The 9-iodo derivative (1) weakly potentiated the GluN2A response, had no effect on GluN2B
and inhibited GluN2C/GluN2D [7] (Table 1).
Removal of the unsubstituted aromatic ring from 1 (Figure 1) to afford 6-iodo-2-naphthoic
acid eliminated NMDAR PAM activity on GluN2A (at 100 µM it inhibited the agonist
response on GluN2A by 26 ± 2% and had 9-12% inhibitory activity on GluN2B-D). 2-
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Naphthoic acid analogues with short chain alkyl substituents at the 6-position (e.g. ethyl or n-
propyl) were found to have no NMDAR PAM activity. The 6-ethyl derivative (100 µM)
instead inhbited GluN2A-D with perecentage values in the range of 17-52%, while the 6-n-
propyl derivative (100 µM) had percentage inhibition values on GluN2A-D in the range of 0-
1
4%). A similar outcome was observed for the 6-cyclopropyl derivative (17, Table 1). In
contrast, the corresponding 9-ethyl, 9-n-propyl and 9-cyclopropyl phenanthrene-3-carboxylic
acid derivatives showed weak to moderate NMDAR PAM activity [7]. Like the parent
phenanthrenes [7], the 6-n-pentyl (14a) and 6-isohexyl (14b, UBP684) derivatives of 2-
naphthoic acid showed potentiating effects on NMDARs. The 6-n-pentyl derivative (14a)
showed potentiating activity on NMDARs containing GluN2A, GluN2C and GluN2D
(Tables 1 and 4) but not GluN2B. When tested at a concentration of 100 µM, the 6-isohexyl
naphthyl derivative (14b) showed potentiation in excess of 170% across GluN2A-D. This
was higher than that of the 6-n-pentyl derivative (14a) (Table 1), suggesting that 14b was
better at increasing the efficacy of L-glutamate/and or glycine. The pan-potentiator 14b (EC50
values ranging from 28.0-37.2 µM across GluN2A-D) had similar potency to that of 14a on
GluN2A but was a more potent PAM on GluN2B-D (Tables 1 and 4, Figure 2). These data
suggest that the unsubstituted aromatic ring of the phenanthrene series is not needed for
NMDAR PAM activity when long chain alkyl substituents are present at the 6-position of the
naphthalene ring.
Effect of changes to the 6-alkyl substituent on the naphthalene ring.
Conformational restriction of the isohexyl side chain in 14b by incorporation of a trans
double bond gave 12b, which displayed an increase in potentiation of agonist response on
GluN2C and GluN2D compared to 14b (Table 1). However, a similar conformational
restriction of the n-pentyl side chain of 14a to give 12a resulted in weak inhibitory activity
across the GluN2 subunits (Table 1). Incorporation of a triple bond into the isohexyl side
chain to give 29, led to the loss of the potentiating effect on GluN2A and GluN2B and a
much reduced potentiating effect on GluN2C and GluN2D compared to 14b (Table 1).
Although restricting conformational freedom by incorporating a double or triple bond was
detrimental for PAM activity on GluN2A and GluN2B, adding a trans double bond into the
side chain of 14b can be used to increase selectivity for GluN2C/GluN2D versus
GluN2A/GluN2B.
Adding a 4-phenylbut-1-yl substituent to the 6-position of the naphthalene ring (Figure 2,
Table 1) to give 27a reduced potentiation compared to 14b. Adding a 3-cyclopentylprop-1-yl
9

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substituent to the 6-position of the naphthalene ring to give 27b (Tables 1 and 4) led to a
similar level of potentiating activity on GluN2A-D to that of 14b, with the former being more
potent on GluN2A (Table 4). Thus, incorporating the two methyl groups at the end of the
isohexyl chain of 14b into a cyclopentyl ring enhances PAM potency and selectivity for
GluN2A.
Effect of changing the nature and position of the carboxylic acid group attached to the
naphthalene ring.
Reduction of the carboxylic acid group in 14a to give the corresponding hydroxymethyl
derivative 18 replaced potentiating activity with weak inhibitory activity at GluN2A-D (Table
1
). A similar observation was made when a CH linker was introduced between the
2
naphthalene ring and the carboxylic acid group in 14a. The resultant acetic acid derivative,
1, had weak to moderate inhibitory activity at GluN2A-D (Table 1). Taken together, the
2
activities of 18 and 21 suggest that the carboxylic acid group is necessary for potentiating
activity and that this group must be directly attached to the naphthalene ring. Furthermore,
moving the carboxylic acid of 14b to an adjacent position on the naphthalene ring to give 7-
isohexyl-2-naphthoic acid (69) resulted in weak inhibitory activity at GluN2D and a weaker
potentiating effect on GluN2A-C compared to the parent compound (Table 1). Thus,
switching the position of the carboxylic acid group relative to the alkyl substituent is
detrimental for NMDAR PAM activity, especially for GluN2D.
Effect of adding substituents to the naphthalene ring.
Adding a bromo substituent to the 5-position of the naphthalene ring of 14a to give 22
(Table 1) resulted in weak inhibitory activity on GluN2A and GluN2B and no activity on
GluN2C and GluN2D, suggesting the bromo group is in an area of excluded volume in the
NMDAR PAM binding site or that this addition prevents the PAM’s allosteric action. The
2
,3-dicarboxy analogue (77) of 14b resulted in little or no activity on GluN2A and GluN2B
but weak to moderate inhibitory activity on GluN2C and GluN2D (Table 1).
Adding a hydroxyl group to the 3-position of the naphthalene ring of 14b to give 74
produced a pan-potentiator with similar, or possibly enhanced activity on GluN2B-D
compared to 14b (Table 1). Thus, it may be possible to reduce the hydrophobicity and
increase water solubility of the NMDAR PAMs described here by adding a hydroxyl group to
the 3-position of the 2-naphthoic acid derivatives. Switching the placement of the hydroxyl
and carboxyl groups on the naphthalene ring of 74 to give 65 resulted in weak inhibitory
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activity on GluN2A and weaker potentiating activity on GluN2B-D compared to that
observed for 14b and 74 (Table 1). However, unlike the 7-isohexyl derivative 69, which
showed weak inhibitory activity on GluN2D, 65 potentiated GluN2D activity (Table 1),
suggesting that the 3-hydroxyl group is required for this activity. Interestingly, replacing the
isohexyl group of 65 with a bromo [13], phenyl (7, Figure 1) [13], styryl (79a, Table 5) or
phenethyl (81a, Table 5) group leads to moderate NMDAR NAM activity on GluN2A-D.
Effect of adding substituents to the 6-alkyl chain.
Substitution at the 1-position of the isohexyl side chain of 14b with a methyl group to give
4
6 resulted in a pan-potentiator with similar potency on GluN2A-D (EC values ranged from
50
2
5.0 to 39.4 µM) to that of 14b (Tables 2 and 4, Figure 2). However, the maximum
potentiating effect of 46 across GluN2A-D was greater than that observed for 14b (Figure 2).
Conformational restriction of 46 by incorporating a double bond to give 44 (Table 3)
produced a pan-potentiator with similar potency to its parent compound on GluN2C but
weaker potency on the other GluN2 subunits (EC values ranged from 26.1 to 116.4 µM
5
0
across GluN2A-D, Table 4). Interestingly, 44 showed different degrees of maximal
potentiation across GluN2A-D and the value for GluN2B was higher than for any other
compound that was tested (Figure 2E, Table 4). Adding a carboxylic acid at the 4-position of
the n-pent-1-yl side chain of 14a to give 33 resulted in little or no activity at GluN2B or
GluN2C and very weak potentiating activity on GluN2A and GluN2D (Table 2).
Conformational restriction of 33 by including a trans double bond to give 31 (Table 2)
resulted in little or no activity across GluN2A-D. Furthermore, adding a CH CO H group to
2
2
the 4-position of the n-pent-1-yl side chain of 14a to give 42 removed potentiating activity
and instead weak inhibition was observed on GluN2A, GluN2B and GluN2D (Table 2).
Adding a carboxylic acid at the 2-position of the isohexyl side chain of 14b to give 60
resulted in selective weak potentiation of GluN2C with little or no activity on GluN2A and
weak inhibition of GluN2B and GluN2D (Table 2). Thus, it appears that polar substituents on
the alkyl chain cannot be accommodated, while methylene substitution (44) at the 1-position
of the alkyl chain of 14b reduces PAM potency on GluN2A and GluN2B but increases
agonist efficacy to a greater degree than 14b.
Effect of adding heteroatoms to the 6-alkyl chain.
A SAR study was undertaken to investigate the effect of adding heteroatoms to the
isohexyl side chain of 14b, with the aim of reducing hydrophobicity. Adding a ketone group
1
1

ACCEPTED MANUSCRIPT
to the isohexyl chain of 14b to produce 38 (Table 3) led to a loss of potentiating activity on
GluN2B-D and a weak potentiating effect on GluN2A. Replacing the CH group adjacent to
2
the naphthalene ring of 14a with an oxygen atom to give 24 (Table 1) resulted in inhibitory
activity across GluN2A-D. Similarly, replacing the second CH group in the isohexyl chain
2
of 14b with either a sulphur atom (49) or an oxygen atom (57) resulted in either loss of
potentiating activity or weak inhibitory effects (Table 3). Incorporating either an amide or
ester group into the isohexyl chain of 14b to give 52 and 54 respectively, led to either
inhibitory effects or loss of activity on GluN2A-D. However, incorporating an ester group at
a different position in the isohexyl chain of 14b to give 35 resulted in a pan-potentiator with
similar levels of activity across GluN2A-D to that observed with 14b (Table 3). The
potentiating activity of the ester 35 was unexpected given that the ketone 38 and the ether
derivative 57 lacked potentiating activity. A possible explanation is that both oxygen atoms
of the ester group are required for potentiating activity.
SAR studies on 2-naphthoic acid derivatives as NMDAR negative allosteric modulators
In the preceding SAR studies, NMDAR NAM activity was observed for some 2-naphthoic
acid derivatives. For example, the 6-pentyl compound (21, Table 1) and 6-isohexyl
derivatives with heteroatoms in the side chain (24 Table 1, 52, 54 and 57 Table 3) showed
5
0% or greater inhibition on at least one of the GluN1/GluN2 subtypes when tested at a
concentration of 100 µM. These data show that inserting heteroatoms into the 6-alkyl chain
such as an O atom (24 and 57), a carboxamide (52) or an ester (54) converts PAMs into
NMDAR NAMs. This suggests that the PAM and NAM binding sites for 6-substituted 2-
naphthoic acid derivatives differ in that the NAM binding site appears to be much more polar
in the area where the 6-substituent binds. Chain extension of the carboxylic acid in 14a by
insertion of a CH group leads to preferential GluN2D NAM activity for compound 21, while
2
adding a carboxy group to the 3-position of 14b leads to preferential GluN2C and GluN2D
NAM activity for compound 77 (Table 1). Thus, while acidic group chain extension and 2,3-
dicarboxy substitution is acceptable for NMDAR NAMs it is detrimental to PAM activity.
The 7-styryl substituted 2-naphthoic acid 79a (Tables 5 and 6) showed greater NMDAR
NAM activity than any of the 6-substituted 2-naphthoic acid derivatives. This 2,7 relationship
between the carboxy group and styryl side chain favours NAM activity but the 2,7
relationship of the 7-alkyl derivatives 65 and 69 was detrimental to PAM activity (Table 1).
Compound 79a is structurally similar to the previously reported NMDAR NAM 7, (Figure 1)
[
13], which has a phenyl substituent at the position occupied by the styryl group. Compared
1
2

ACCEPTED MANUSCRIPT
to 7, (Figure 1), the parent styryl-substituted compound, 79a was found to have similar
activity on GluN2A, ~10-fold greater inhibitory activity on GluN2B and 3-5 fold greater
inhibitory on GluN2C and GluN2D (Table 6). In addition, 79a showed 83-94% maximal
inhibition across GluN2A-D, whereas 7 showed only 57-72% maximal inhibition of GluN2A
and GluN2B (Table 6) [13].
Given that 79a showed interesting NMDAR NAM activity, a SAR study was undertaken
with the aim of improving NAM potency and GluN2 subunit selectivity. When the hydroxyl
group of 79a was replaced by a carboxyl group to give compound 85 (formula C, Table 5)
inhibitory activity was reduced. Similarly, replacement of the naphthalene ring of 79a with a
coumarin ring to give compound 88 (formula D, Table 5) dramatically reduced inhibitory
activity and indeed led to potentiating activity on GluN2C and GluN2D. This suggests that
the hydroxyl group of 79a is necessary for optimal NAM activity. Next, the effect of
saturating the double bond linking the phenyl ring of 79a to the naphthalene ring was studied.
The saturated analogue, compound 81a (Table 5) had weaker inhibitory activity than the
parent compound 79a, suggesting a degree of conformational restriction is necessary for
optimal NMDAR NAM activity.
Having established that the core structure was necessary for NMDAR NAM activity of
7
9a, a study was undertaken to investigate the effect of substitutions on the phenyl ring.
Carboxyl group substitution at the ortho, meta or para positions (compounds 79b, 79c and
9d, Table 5) led to much reduced inhibitory activity compared to the parent compound.
Saturation of the double bond in the ortho and para carboxy derivatives to give compounds
1b and 81c, respectively, did not improve upon the already weak inhibitory activity of the
7
8
parent compounds. Interestingly, ortho methoxy substitution (compound 79e, Table 5) led to
weak potentiation of GluN2A responses and weak inhibition of GluN2B-D. Either meta or
para methoxy substitution to give compounds 79f and 79g (Table 5), respectively, led to
improved inhibitory activity compared to the ortho derivative. Ortho nitro substitution (79h,
Table 5) improved inhibitory activity compared to the corresponding methoxy derivative,
especially on GluN2C and GluN2D. Meta and para nitro substitution (79i and 79j, Table 5)
had a similar effect on inhibitory activity to that observed with the corresponding methoxy
substituted compounds.
Full concentration response curves were obtained for the inhibitory activity of 79h, 79i
and 79j across GluN1/GluN2A-D (Figure 3B-D). Surprisingly, unlike the parent compound
7
9a (Figure 3A), all three compounds failed to produce 100% maximal inhibition of
GluN2A-D responses. The ortho nitro derivative 79h only maximally inhibited GluN2A by
1
3

ACCEPTED MANUSCRIPT
3
0% and GluN2B-D by 60-80% (Table 6). Similar findings were observed with the meta
(79i) and para (79j) nitro derivatives in terms of their maximal inhibition. Regarding
inhibitory activity, IC values for 79h were 3-fold lower on GluN2A and GluN2D and 4-fold
5
0
higher on GluN2B compared to 79a (Table 6). A similar trend was observed for 79i and 79j,
with the former having the most potent inhibitory activity on GluN2D of all the analogues
tested (IC value 1.4 µM). Compared to the previously reported 7-phenyl derivative UBP617
5
0
(7, Table 6) (Costa et al., 2012), the meta-nitrostyryl derivative 79i had similar activity on
GluN2A and 10-fold, 5-fold and 35-fold higher inhibitory activity on GluN2B, GluN2C and
GluN2D, respectively (Table 6). Thus, meta-nitrostyryl substitution produced a NAM that
was more potent than the parent compound 79a and was selective for inhibiting NMDARs
containing GluN2D. In addition, unlike 79a, 79i was a partial NAM on GluN2D.
Testing 79h at two different agonist concentrations (10/10 µM Glu/Gly and 300/300 µM
Glu/Gly) showed that the degree of inhibition of the agonist response was not reduced at
higher agonist concentrations (Figure 4). This suggests that 79h is not competing with either
Glu or Gly for their binding sites on the GluN1 or GluN2 LBD, respectively.
Discussion
Structure-activity relationship studies on 2-naphthoic acid derivatives based on the
lead phenanthrene UBP512 (1, Table 1) [7] have led to the discovery of novel series of both
NMDAR PAMs and NAMs. We have shown that 6-alkyl substitued 2-naphthoic acid
derivatives such as 14b (UBP684) can act as pan potentiators of agonist-induced currents
through NMDARs (i.e. they potentiate regardless of the type of GluN2 subunit incorporated
into the NMDAR). The NMDAR PAM 27b (Table 1) showed a preference for the GluN2A
subunit and further modification of this compound may lead to GluN2A selective NMDAR
potentiators. In contrast to 6-alkyl derivatives such as 14b, the 7-styryl derivative 79a and
analogues thereof were found to be NMDAR NAMs. NAM activity and selectivity for
GluN2D could be enhanced by 3-nitro substitution to produce 79i (Table 6), which unlike the
parent compound 79a, was a partial NAM.
Our SAR studies revealed different structural requirements for NMDAR NAMs and
PAMs based on 2-naphthoic acid. Whilst 6-alkyl substituents were required for optimal
PAM activity, NAM activity was predominantly observed when heteroatoms were added to
the 6-alkyl chain. In addition, with regards to relative positioning of the carboxy and alkyl or
alkenyl groups, a 2,6-substitution pattern favours PAM activity (e.g. 14a and 14b, Table 1),
whereas a 2,7-substitution pattern was either detrimental for PAM activity (e.g. 65 and 69) or
1
4

ACCEPTED MANUSCRIPT
produced moderately potent NAM activity (e.g. 79a, Table 5). These differences in the
structural requirements suggest that either there are distinct binding sites for PAMs and
NAMs or that they contact different areas within the same binding site on the NMDAR
complex.
Experiments with structurally related analogues of the NMDAR PAM 14b (Table 1)
and the NAM 79a showed that they are not binding to the known sites for glutamate
antagonists, glycine site antagonists, channel blockers or at the N-terminal domain site where
NMDAR NAMs such as ifenprodil bind [7,13]. The NMDAR PAM 14b (UBP684) has been
shown to slow deactivation upon glutamate removal and increases open channel probability
by stabilizing the NMDAR LBDs in an active conformation [20,21]. It has been proposed
that 14b may be binding at the LBD dimer interface [6d,20,21], as has been observed for the
GluN2A selective PAM GNE-6901 (4, Figure 1) [10a] or at the LBD/transmembrane domain
linker region as proposed for neurosteroids that act as NMDAR PAMs [22]. A feasible
binding mode for 14b was observed when it was docked into the GluN1/GluN2A LBD dimer
interface using the Induced Fit module in Maestro (Schrodinger LLC) [21]. The 6-isohexyl
side chain of 14b interacts with a number of hydrophobic residues in the dimer interface in
agreement with the current SAR study, which showed that a 6-alkyl substituent is preferred
for NMDAR PAM activity. However, structural studies are required to definitively show that
1
4b is binding to the LBD dimer interface.
It has been reported that the GluN2A selective NAM MPX-004 (9, Figure 1) binds at
a similar site to the GluN2A PAM GNE-6901 at the dimer interface of the LBDs of
GluN1/GluN2A. The major diffrences between these two binding sites is the conformation of
Y535 in GluN1 and the position of V783 in GluN2A, which is displaced upon MPX-004 but
not PAM binding [10a,17]. It is possible that the 2-naphthoic acid based NAMs and PAMs
bind at these sites. However, the inhibitory activity of NMDAR NAMs structurally related to
7
9h were not dependent on glycine concentration [13] in the same way as MPX-004 [17]. In
the case of 79h it did not show dependence on glycine concentration for its inhibitory activity
Figure 4) and so it is unlikely that 79h and derivatives thereof are binding to the NMDAR
(
LBD dimer interface or the glycine binding site on the GluN1 LBD. Further studies are
needed to definitively identify the binding sites on the NMDAR for the NAMs based on 2-
naphthoic acid. This will enable computer modelling studies to gain an understanding of the
binding modes of the NMDAR NAMs we have identified.
The NMDAR PAMs described herein are useful tools to study synaptic function and
represent possible leads for the development of drugs for disorders that involve NMDAR
1
5

ACCEPTED MANUSCRIPT
hypofunction, such as schizophrenia. Since NMDARs are involved in mechanisms that have
been proposed to underlie learning and memory processes in the hippocampus, NMDAR
potentiators may have application in the treatment of disorders that involve a loss of cognitive
function, such as Alzheimer’s disease.
A new class of partial NMDAR NAMs that show some selectivity for GluN2D has been
identified. NMDAR inhibitors have been proposed as treatments for disorders which arise
from NMDAR overactivation such as neuropathic pain, epilepsy, depression and for
neurodegenerative disorders such as ischaemia. However, inhibition of NMDARs involved in
normal CNS activity causes adverse effects such as psychotomimetic effects, ataxia and
cognitive dysfunction. The use of partial NAMs, together with improved subtype-selectivity,
may be a way of counteracting overactivation of NMDARs in CNS disorders whilst allowing
essential physiological signalling, thus avoiding adverse CNS effects.
Acknowledgements
Research reported in this publication was supported by the National Institute of Mental
Health of the National Institutes of Health under Award Number R01MH060252, the MRC
(Grants G0601509, G0601812) and the BBSRC (grant BB/L001977/1).
Abbreviations
AMPAR, (S)-2-amino-3-hydroxy-5-methyl-4-isoxazolepropanoic acid receptor; CNS,
central nervous system; GFP, green fluorescent protein; HEK, human embryonic kidney;
HEPES, 4-(2-hydroxethyl)-1-piperazineethanesulfonic acid); LBD, ligand binding domain;
LTP, long-term potentiation; NAM, negative allosteric modulator; NMDAR, N-methyl-D-
aspartic acid receptor; PAM, positive allosteric modulator; STP, short-term potentiation;
TEVC, two electrode voltage clamp
Experimental Methods
Chemistry experimental
General Procedures
Melting points were determined using an Electrothermal IA9100 capillary apparatus and are
1
uncorrected. H-NMR spectra were measured on either a Jeol JNM-LA300 spectrometer at
3
00.53 MHz, a Jeol JNM-ECP400 spectrometer at 400.18 MHz, a Varian 400MR
1
6

ACCEPTED MANUSCRIPT
1
3
spectrometer at 399.77 MHz, or a Varian 500 spectrometer at 500 MHz. C-NMR spectra
were recorded on either a Jeol JNM-LA300 spectrometer at 75.57 MHz, a Jeol JNM-ECP400
spectrometer at 100.63 MHz, a Varian 400MR spectrometer at 100.52 MHz or a Varian 500
spectrometer at 125 MHz. Chemical shifts (δ) are reported in parts per million (ppm) with
tetramethylsilane in CDCl or DMSO-d used as internal standards. Mass spectrometry was
3
6
performed in the mass spectroscopy laboratories of the School of Chemistry, University of
Bristol, UK. Elemental analyses were performed in the microanalytical laboratories of the
School of Chemistry, University of Bristol, UK. The purity of all compounds sent for
biological testing was determined by combustion analysis, which confirmed that there were ≥
9
5% pure. Thin layer chromatography was performed on Merck silica gel 60 F254 plastic
sheets. Flash chromatography was performed on Merck silica gel 60 (220-440 mesh) from
Fisher. All anhydrous reactions were conducted under argon. All anhydrous solvents were
obtained from Sigma-Aldrich, UK or Acros Organics, UK. 47 [23] (methyl 6-(bromomethyl)-
2
-naphthoate), 50 [24] (methyl 6-(chlorocarbonyl)-2-naphthoate), 53 [25] (6-
(
hydroxymethyl)-2-naphthoic acid), 55 [26] (2-bromo-6-(bromomethyl)naphthalene), 61 [27]
7-bromo-3-hydroxy-2-naphthoic acid) and 70 [28,29] (6-(methoxymethoxy)naphthalen-2-yl
(
trifluoromethane-sulfonate) were synthesized according to literature procedures.
(E)-Methyl 6-(pent-1-en-1-yl)-2-naphthoate (11a). A flask was charged with 10 (3.00 g,
1
1.3 mmol), palladium acetate (25 mg, 1 mol%) and tri-o-tolylphosphine (138 mg, 4 mol%).
The flask was then briefly evacuated and backfilled with argon three times. Degassed
anhydrous DMF (100 mL) was added followed by pent-1-ene (1.55 mL, 14.1 mmol) and
triethylamine (1.97 mL, 14.1 mmol). The resultant mixture was heated at 100 °C overnight.
After being allowed to cool to room temperature the reaction mixture was filtered through a
celite pad to remove any precipitated Pd(0) and then poured into a stirred solution of EtOAc
(100 mL), water (100 mL) and aqueous 1 M HCl (10 mL). The organic layer was
subsequently isolated and the aqueous phase further extracted with EtOAc (2 × 50 mL). The
organic extracts were pooled, washed with water (5 × 100 mL), brine (100 mL) and dried
over MgSO . Concentration in vacuo afforded a light brown solid which was purified by
4
flash chromatography (2 → 5% EtOAc in hexane) to afford 11a as a clear oil (2.62 g, 91%);
1
H NMR (400 MHz, CDCl ) δ 8.54 (s, 1H), 8.02 (dd, J = 8.4 & 1.6 Hz, 1H), 7.86 (d, J = 8.8
3
Hz, 1H, ArH), 7.81 (d, J = 8.4 Hz, 1H, ArH), 7.70 (s, 1H, ArH), 7.63 (dd, J = 8.8 & 2.0 Hz,
1
H, ArH), 6.56 (d, J = 16.0 Hz, 1H, ArCH=CH-), 6.42 (dt, J = 16.0 & 6.8 Hz, 1H,
1
7

ACCEPTED MANUSCRIPT
ArCH=CH-), 3.97 (s, 3H, -CO CH ), 2.32-2.23 (m, 2H, -CH CH CH ), 1.55 (sex, J = 7.2
2
3
2
2
3
13
Hz, 2H, -CH CH CH ), 0.99 (t, J = 7.2 Hz, 3H, -CH CH CH ); C NMR (100 MHz, CDCl )
2
2
3
2
2
3
3
δ 167.3, 137.8, 135.9, 133.1, 131.6, 130.7, 129.7, 129.4, 127.9, 126.8, 125.6, 125.0, 124.4,
+
5
2.2, 35.3, 22.5, 13.8; HRMS-ESI calcd for C H O [M + H] 255.1385; found 255.1392.
1
7
18
2
(E)-Methyl 6-(4-methylpent-1-en-1-yl)-2-naphthoate (11b). Method identical to that
described for 11a. 10 (4.00 g, 15.1 mmol), palladium acetate (34 mg, 1 mol%), tri-o-
tolylphosphine (184 mg, 4 mol%), 4-methylpent-1-ene (2.39 mL, 18.9 mmol) and
triethylamine (2.63 mL, 18.9 mmol) afforded a light brown solid which was purified by flash
chromatography (2 → 5% EtOAc in hexane) to afford 11b as a as a clear oil (3.61 g, 89%);
1
H NMR (400 MHz, CDCl ) δ 8.54 (s, 1H, ArH), 8.02 (dd, J = 8.8 & 2.0 Hz, 1H, ArH), 7.87
3
(
d, J = 8.8 Hz, 1H, ArH), 7.81 (d, J = 8.4 Hz, 1H, ArH), 7.70 (s, 1H, ArH), 7.64 (dd, J = 8.4
1.6 Hz, 1H, ArH), 6.54 (d, J = 15.6 Hz, 1H, ArCH=CH-), 6.42 (dt, J = 15.6 & 7.2 Hz, 1H,
ArCH=CH-), 3.97 (s, 3H, -CO CH ), 2.20-2.15 (m, 2H, -CH CH(CH ) ), 1.84-1.70 (m, 1H,
&
2
3
2
3 2
1
3
-
CH CH(CH ) ), 0.98 (d, J = 6.8 Hz, 6H, -CH CH(CH ) ); C NMR (100 MHz, CDCl ) δ
2 3 2 2 3 2 3
1
5
67.3, 137.8, 135.9, 132.0, 131.6, 130.7, 130.6, 129.4, 128.0, 126.8, 125.6, 125.0, 124.4,
+
2.2, 42.6, 28.6, 22.4; HRMS-ESI calcd for C H O [M + H] 269.1536; found 269.1540.
1
8
20
2
(E)-6-(Pent-1-en-1-yl)-2-naphthoic acid (12a). To a stirring solution of 11a (1.29 g, 5.1
mmol) in a THF/water mix (3:1, 100 mL) was added LiOH (486 mg, 20.3 mmol) dissolved in
water (10 mL). The resultant mixture was stirred at room temperature overnight. In the
morning, TLC indicated incomplete hydrolysis so the mixture was heated at 65 °C until all
the ester had been consumed. After 2 h the mixture was allowed to cool to room temperature
before the THF was removed in vacuo. The resultant aqueous solution was topped up with
water (40 mL) and then acidified to pH 1 using aqueous 2 M HCl. The solid which
precipitated out of solution was filtered off, washed copiously with water and then dried over
P O overnight. Recrystallisation from toluene (twice) afforded 12a as a white solid (507 mg,
2
5
o
1
4
1
8
2%); mp: 157-160 C; H NMR (500 MHz, DMSO-d ) δ 13.00 (br s, 1H, -CO H), 8.53 (s,
6 2
H, ArH), 8.02 (d, J = 8.5 Hz, 1H, ArH), 7.94 (dd, J = 8.5 & 1.5 Hz, 1H, ArH), 7.92 (d, J =
.5 Hz, 1H, ArH), 7.86 (s, 1H, ArH), 7.74 (dd, J = 8.5 & 1.5 Hz, 1H, ArH), 6.59 (d, J = 16.0
Hz, 1H, ArCH=CH-), 6.53 (dt, J = 16.0 & 6.5 Hz, 1H, ArCH=CH-), 2.23 (q, J = 7.0 Hz, 2H,
CH CH CH ), 1.50 (sex, J = 7.5 Hz, 2H, -CH CH CH ), 0.94 (d, J = 7.5 Hz, 3H, -
-
2
2
3
2
2
3
13
CH CH CH ); C NMR (100 MHz, DMSO-d ) δ 167.3, 137.1, 135.3, 132.7, 131.2, 130.1,
2
2
3
6
1
8

ACCEPTED MANUSCRIPT
1
29.4, 129.4, 127.9, 127.5, 125.4, 124.6, 124.3, 34.6, 21.8, 13.5; HRMS-ESI calcd for
-
C H O [M - H] 239.1078; found 239.1081; Anal. (C H O ) C, H.
16
16
2
16 16
2
(E)-6-(4-Methylpent-1-en-1-yl)-2-naphthoic acid (12b). To a stirring solution of 11b (889
mg, 3.31 mmol) in a dioxane/water mix (3:1, 80 mL) was added aqueous 1 M NaOH (13.2
mL, 13.2 mmol). The resultant mixture was stirred at 80 °C until TLC indicated complete
hydrolysis of the ester. The mixture was then allowed to cool to room temperature before the
dioxane was removed in vacuo. The resultant aqueous solution was topped up with water (40
mL), extracted with diethyl ether (25 mL), and then acidified to pH 1 using aqueous 2 M
HCl. The solid which precipitated out of solution was filtered off, washed copiously with
water and then dried over P O overnight. Recrystallisation from toluene afforded 12b as a
2
5
o
1
white solid (376 mg, 45%); mp: 178-182 C; H NMR (400 MHz, DMSO-d ) δ 13.01 (br s,
6
1
1
H, -CO H), 8.54 (s, 1H, ArH), 8.03 (d, J = 8.8 Hz, 1H, ArH), 7.95 (dd, J = 8.8 & 1.6 Hz,
2
H, ArH), 7.92 (d, J = 8.8 Hz, 1H, ArH), 7.87 (s, 1H, ArH), 7.76 (dd, J = 8.8 & 1.6 Hz, 1H,
ArH), 6.58 (d, J = 16.0 Hz, 1H, ArCH=CH-), 6.52 (dt, J = 16.0 & 6.4 Hz, 1H, ArCH=CH-),
.14 (t, J = 6.4 Hz, 2H, -CH CH(CH ) ), 1.75 (sep, J = 6.8 Hz, 1H, -CH CH(CH ) ), 0.94 (d,
2
2
3 2
2
3 2
13
J = 6.8 Hz, 6H, -CH CH(CH ) ); C NMR (100 MHz, DMSO-d ) δ 167.3, 137.1, 135.3,
2
3 2
6
1
31.7,131.2, 130.4, 130.1, 129.4, 127.9, 127.5, 125.5, 124.7, 124.4, 41.9, 27.9, 22.2; HRMS-
-
ESI calcd for C H O [M - H] 253.1234; found 253.1235; Anal. (C H O ·0.34C H ) C,
17
18
2
17 18
2
7
8
H.
Methyl 6-n-pent-1-yl-2-naphthoate (13a). A solution of 11a (1.30 g, 5.1 mmol) in EtOAc
100 mL) was hydrogenated under 3 bar of hydrogen in the presence of 10 wt % palladium
(
on activated carbon (50 mg) for 18 h. The reaction mixture was then filtered through a celite
1
pad before being concentrated in vacuo to afford 13a as a clear oil (1.28 g, 98%); H NMR
(
400 MHz, CDCl ) δ 8.57 (s, 1H, ArH), 8.03 (dd, J = 8.8 & 1.6 Hz, 1H, ArH), 7.87 (d, J =
3
8
.4 Hz, 1H, ArH), 7.81 (d, J = 8.4 Hz, 1H, ArH), 6.64 (s, 1H, ArH), 7.40 (dd, J = 8.4 & 2.0
Hz, 1H, ArH), 3.98 (s, 3H, -CO CH ), 2.79 (t, J = 7.6 Hz, 2H, ArCH -), 1.76-1.67 (m, 2H, -
2
3
2
1
3
CH CH CH -), 1.38-1.31 (m, 4H, -CH CH CH -), 0.90 (t, J = 7.2 Hz, 3H, -CH ); C NMR
2
2
2
2
2
2
3
(
100 MHz, CDCl ) δ 167.4, 143.4, 135.8, 130.9, 130.8, 129.2, 128.3, 127.6, 126.5, 126.2,
3
+
1
25.2, 52.1, 36.2, 31.5, 30.9, 22.5, 14.0; HRMS-CI calcd for C H O [M + H] 257.1542;
1
7
20
2
found 257.1550.
1
9

ACCEPTED MANUSCRIPT
Methyl 6-(4-methylpent-1-yl)-2-naphthoate (13b). Method identical to that described for
1
1
3a. 11b (2.70 g, 10.1 mmol) and 10 wt % palladium on activated carbon (100 mg) afforded
1
3b as a clear oil (2.68 g, 98%); H NMR (400 MHz, CDCl ) δ 8.57 (s, 1H, ArH,), 8.03 (dd,
3
J = 8.8 & 1.6 Hz, 1H, ArH), 7.87 (d, J = 8.8 Hz, 1H, ArH), 7.81 (d, J = 8.8 Hz, 1H, ArH),
6
7
1
.55 (s, 1H, ArH), 7.40 (dd, J = 8.8 & 1.6 Hz, 1H, ArH), 3.98 (s, 3H, -CO CH ), 2.77 (t, J =
2 3
.6 Hz, 2H, ArCH -), 1.76-1.67 (m, 2H, -CH CH -), 1.64-1.55 (m, 1H, -CH(CH ) ), 1.32-
2
2
2
3 2
13
.23 (m, 2H, -CH CH -), 0.89 (d, J = 6.8 Hz, 6H, -CH(CH ) ); C NMR (100 MHz, CDCl )
2
2
3 2
3
δ 167.4, 143.4, 135.8, 130.9, 130.8, 129.2, 128.3, 127.6, 126.6, 126.2, 125.3, 52.1, 38.6, 36.5,
+
2
9.1, 27.9, 22.6; HRMS-CI calcd for C H O [M + H] 271.1698; found 271.1703.
1
8
22
2
6
-n-Pent-1-yl-2-naphthoic acid (14a). To a stirring solution of 13a (1.14 g, 4.5 mmol) in a
THF/water mix (3:1, 80 mL) was added aqueous 1 M NaOH (22.5 mL, 22.5 mmol). The
resultant mixture was stirred at 65 °C until TLC indicated complete hydrolysis of the ester.
The mixture was then allowed to cool to room temperature before the THF was removed in
vacuo. The resultant aqueous solution was topped up with water (40 mL) and then acidified
to pH 1 using aqueous 2 M HCl. The solid which precipitated out of solution was filtered off,
washed copiously with water and then dried over P O overnight to afford 13a as an off-
2
5
o
1
white solid (913 mg, 84%); mp: 128-132 C; H NMR (500 MHz, DMSO-d ) δ 13.00 (br s,
6
1
H, -CO H), 8.54 (s, 1H, ArH), 8.01 (d, J = 9.0 Hz, 1H, ArH), 7.94 (dd, J = 9.0 & 1.5 Hz,
2
1
H, ArH), 7.91 (d, J = 8.5 Hz, 1H, ArH), 7.76 (s, 1H, ArH), 7.46 (dd, J = 8.5 & 1.5 Hz, 1H,
ArH), 2.76 (t, J = 7.5 Hz, 2H, ArCH -), 1.66 (pent, J = 7.5 Hz, 2H, -CH CH CH -), 1.37-
2
2
2
2
1
3
1
.25 (m, 4H, -CH CH CH -), 0.86 (t, J = 7.0 Hz, 3H, -CH ); C NMR (100 MHz, DMSO-
2 2 2 3
d6) δ 167.5, 142.8, 135.1, 130.6, 130.2, 129.1, 128.2, 127.6, 127.2, 125.9, 125.1, 35.3, 30.9,
-
3
0.3, 21.9, 13.9; HRMS-ESI calcd for C H O [M - H] 241.1234; found 241.1235; Anal.
1
6
18
2
(
C H O ·0.2H O) C, H.
16 18 2 2
6
-(4-Methylpent-1-yl)-2-naphthoic acid (14b). To a stirring solution of 13b (2.66 g, 9.84
mmol) in a dioxane/water mix (3:1, 80 mL) was added NaOH (1.58 g, 39.5 mmol) dissolved
in water (20 mL). The resultant mixture was stirred at 80 °C until TLC indicated complete
hydrolysis of the ester. The mixture was then allowed to cool to room temperature before the
dioxane was removed in vacuo. The resultant aqueous solution was topped up with water (40
mL) and then acidified to pH 1 using aqueous 2 M HCl. The solid which precipitated out of
solution was filtered off, washed copiously with water and then dried over P O overnight.
2
5
2
0

ACCEPTED MANUSCRIPT
Recrystallisation from acetonitrile afforded 14b as a fluffy white solid (1.67 g, 66%); mp:
o
1
1
8
49-153 C; H NMR (400 MHz, DMSO-d ) δ 13.05 (br s, 1H, -CO H), 8.55 (s, 1H, ArH),
6 2
.02 (d, J = 8.4 Hz, 1H, ArH), 7.95 (dd, J = 8.4 & 2.0 Hz, 1H, ArH), 7.91 (d, J = 8.4 Hz, 1H,
ArH), 7.76 (s, 1H, ArH), 7.47 (dd, J = 8.4 & 2.0 Hz, 1H, ArH), 2.74 (t, J = 7.6 Hz, 2H,
ArCH -), 1.71-1.61 (m, 2H, -CH CH -), 1.56 (sep, J = 6.8 Hz, 1H, -CH(CH ) ), 1.24-1.17
2
2
2
3 2
1
3
(
m, 2H, CH CH -), 0.85 (d, J = 6.8 Hz, 6H, -CH(CH ) ); C NMR (100 MHz, DMSO-d ) δ
2 2 3 2 6
1
2
67.4, 142.7, 135.1, 130.5, 130.2, 129.1, 128.2, 127.5, 127.2, 125.9, 125.1, 38.0, 35.5, 28.4,
-
7.2, 22.4; HRMS-ESI calcd for C H O [M - H] 255.1391; found 255.1396; Anal.
1
7
20
2
(
C H O ·0.13H O) C, H.
17 20 2 2
Methyl 6-vinyl-2-naphthoate (15). A flask containing 10 (2.00 g, 7.6 mmol) was
evacuated and backfilled with argon three times. Anhydrous toluene (50 mL) was cannulated
into the flask and the resultant solution de-gassed with argon for approx. 30 mins. Pd(PPh3)4
(
266 mg, 3 mol%) was then added and the mixture de-gassed for a further 10 mins before
vinyl(tri-n-butyl)tin (2.55 mL, 8.7 mmol) was added. The resultant mixture was refluxed for
h before being allowed to cool to room temperature and filtered through celite to remove
4
any precipitated Pd(0). The filtrate was then poured into a stirring mixture of EtOAc and
saturated aqueous NH Cl (50 mL each). The organic layer was isolated and washed with
4
aqueous 1M KF (2 × 50 mL) to remove any tin by-products. The white solid (Bu SnF) which
3
precipitated from solution after the first wash was removed via filtration through celite. The
organic layer was then isolated, washed with water (50 mL), brine (50 mL), dried over
MgSO and concentrated in vacuo to yield a light peach coloured residue. Purification by
4
flash chromatography (5% EtOAc in hexane) afforded 15 as a viscous clear oil which
1
partially solidified on standing to a white solid (1.01 g, 63%); H NMR (300 MHz, CDCl ) δ
3
8
.56 (s, 1H, ArH), 8.05 (d, J = 8.7 & 1.8 Hz, 1H, ArH), 7.90 (d, J = 8.7 Hz, 1H, ArH), 7.85
d, J = 8.7 Hz, 1H, ArH), 7.78 (s, 1H, ArH), 7.69 (dd, J = 8.7 & 1.8 Hz, 1H, ArH), 6.89 (dd, J
17.4 & 10.8 Hz, 1H, ArCH=CH ), 5.93 (d, J = 17.4 Hz, 1H, ArCH=CH ), 5.41 (d, J = 10.8
(
=
2
2
13
Hz, 1H, ArCH=CH ), 3.98 (s, 3H, -CO CH ); C NMR (100 MHz, CDCl ) δ 167.2, 137.3,
2
2
3
3
1
36.5, 135.8, 132.2, 130.7, 129.6, 128.2, 127.3, 126.0, 125.7, 124.0, 115.6, 52.2; HRMS-ESI
+
calcd for C H O [M + H] 213.0910; found 213.0915.
1
4
12
2
Methyl 6-cyclopropyl-2-naphthoic acid (17). Diiodomethane (0.91 mL, 11.32 mmol) was
dissolved in anhydrous DCM (30 mL) and ZnEt (1.0 M solution in hexane, 5.66 mL, 5.66
2
mmol) added to this solution at 0 °C followed by a solution of 15 in DCM (600 mg, 2.83
2
1

ACCEPTED MANUSCRIPT
mmol in 10 mL). The reaction mixture was then stirred vigorously overnight before being
quenched with aqueous saturated NH Cl. The mixture was diluted with diethyl ether (50 mL)
4
and the organic layer isolated, washed with water (25 mL), brine (25 mL), dried over MgSO4
and concentrated in vacuo. The resultant residue was purified by flash chromatography (5%
EtOAc in hexane) to afford the ester (16) as a viscous clear oil (465 mg, 73%) which was
taken forward and hydrolysed without further characterisation. To a mixture of the 16 (465
mg, 2.05 mmol) in a THF/water mix (3:1, 40 mL) was added aqueous 1 M NaOH (8.2 mL,
8
.2 mmol). The resultant mixture was stirred at 65 °C until TLC indicated complete
hydrolysis of the ester. The mixture was then allowed to cool to room temperature before the
THF was removed in vacuo. The resultant aqueous solution was topped up with water (40
mL), extracted with diethyl ether (25 mL) and then acidified to pH 1 using aqueous 2 M HCl.
The solid which precipitated out of solution was filtered off, washed copiously with water
and then dried over P O overnight to yield a white solid. Recrystallisation from toluene
2
5
o
1
afforded 17 as a white solid (179 mg, 41%); mp: 125-129 C; H NMR (400 MHz, DMSO-
d ) δ 12.96 (br s, 1H, -CO H), 8.52 (s, 1H, ArH), 7.98 (d, J = 8.4 Hz, 1H, ArH), 7.92 (dd, J =
6
2
8
1
0
1
.4 & 1.6 Hz, 1H, ArH), 7.87 (d, J = 8.4 Hz, 1H, ArH), 7.68 (s, 1H, ArH), 7.31 (dd, J = 8.4 &
.6 Hz, 1H, ArH), 2.16-2.08 (m, 1H, ArCH(CH ) ), 1.09-1.03 (m, 2H, ArCH(CH ) ), 0.87-
2
2
2 2
1
3
.81 (m, 2H, ArCH(CH ) ); C NMR (100 MHz, DMSO-d ) δ 167.9, 144.8, 135.6, 130.9,
2
2
6
30.7, 129.7, 127.8, 127.4, 125.8, 125.6, 123.5, 16.0, 10.4; HRMS-ESI calcd for C H O
2
1
4
12
-
[
M - H] 211.0765; found 211.0770; Anal. (C H O ) C, H.
14 12 2
2
-Hydroxymethyl-6-n-pent-1-yl-naphthalene (18). A flask was charged with 14a (4.50 g,
1
8.6 mmol) before being briefly evacuated and backfilled with argon. Anhydrous THF (100
mL) was cannulated into the flask and the resultant solution cooled to 0 °C. A 1 M LiAlH4
solution in THF (27.9 mL, 27.9 mmol) was then added dropwise with care. After complete
addition the solution was allowed to warm to room temperature before being refluxed for 4 h.
After being allowed to cool to room temperature the solution was further cooled to 0 °C and
excess LiAlH destroyed via the dropwise addition of saturated aqueous NH Cl. The THF
4
4
was then removed in vacuo and the resultant residue partitioned between EtOAc and water
100 mL each). The organic layer was isolated, dried over MgSO and concentrated in vacuo
(
4
to yield a cream coloured solid which was purified by flash chromatography (20 → 30%
o
1
EtOAc in hexane) to afford 18 as a white solid (3.20 g, 75%); mp: 72-76 C; H NMR (400
MHz, CDCl ) δ 7.80-7.73 (m, 3H, ArH), 7.61 (s, 1H, ArH), 7.45 (dd, J = 8.4 & 2.0 Hz, 1H,
3
2
2

ACCEPTED MANUSCRIPT
ArH), 7.35 (dd, J = 8.4 & 2.0 Hz, 1H, ArH), 4.84 (s, 2H, -CH OH), 2.77 (t, J = 7.6 Hz, 2H,
2
ArCH -), 1.77-1.67 (m, 2H, -CH CH CH -), 1.39-1.32 (m, 4H, CH CH CH -), 0.91 (t, J =
2
2
2
2
2
2
2
1
3
7
.2 Hz, 3H, -CH ); C NMR (100 MHz, CDCl ) δ 140.6, 137.4, 133.1, 131.8, 127.9, 127.8,
3 3
1
27.7, 126.1, 125.3, 125.2, 65.6, 36.1, 31.5, 31.0, 22.6, 14.0; HRMS-CI calcd for C H O
1
6
20
+
[
M] 228.1514; found 228.1516; Anal. (C H O) C, H.
16 20
2
-Bromomethyl-6-n-pent-1-yl-naphthalene (19). A flask containing 18 (3.00 g, 13.1 mmol)
was briefly evacuated and backfilled with argon. Anhydrous DCM (100 mL) was then
cannulated into the flask and the resultant solution cooled to 0 °C. PBr (4.92 mL, 52.4
3
mmol) was added dropwise and after complete addition the solution was allowed to warm to
room temperature and stirred until TLC showed complete conversion. After 1 h the solution
was cooled to 0 °C and excess PBr destroyed via the dropwise addition of saturated aqueous
3
NaHCO . The DCM was removed in vacuo to afford an oily residue which was diluted with
3
diethyl ether (100 mL). The organic layer was isolated, dried over MgSO and concentrated
4
in vacuo to yield an amber oil which solidified on standing. Dissolving the crude product in
hexane and passing it through a short silica plug (10 cm) afforded 19 as an oil which partially
1
solidified on standing to a light brown solid (2.98 g, 78%); H NMR (400 MHz, CDCl ) δ
3
7
.79 (s, 1H, ArH), 7.76 (d, J = 8.4 Hz, 1H, ArH), 7.73 (d, J = 8.4 Hz, 1H, ArH), 7.59 (s, 1H,
ArH), 7.47 (dd, J = 8.4 & 2.0 Hz, 1H, ArH), 7.35 (dd, J = 8.4 & 2.0 Hz, 1H, ArH), 4.67 (s,
H, -CH Br), 2.76 (t, J = 7.6 Hz, 2H, ArCH -), 1.74-1.66 (m, 2H, -CH CH CH -), 1.38-1.31
2
2
2
2
2
2
1
3
(
m, 4H, -CH CH CH -), 0.90 (t, J = 7.2 Hz, 3H, -CH ); C NMR (100 MHz, CDCl ) δ
2 2 2 3 3
1
2
41.4, 134.2, 133.3, 131.6, 128.3, 128.1, 127.8, 127.6, 126.7, 126.2, 36.1, 34.3, 31.5, 31.0,
+
2.6, 14.0; HRMS-CI calcd for C H Br [M + H] 291.0748; found 291.0746.
1
6
19
(
6-n-Pent-1-ylnapthalen-2-yl)acetonitrile (20). 19 (1.90 g, 6.5 mmol) was dissolved in
anhydrous DCM (25 mL) and stirred vigorously with a solution of sodium cyanide (480 mg,
.8 mmol) and tetra-n-butylammonium bromide (316 mg, 0.98 mmol) in water (25 mL).
9
After 48 hours TLC indicated complete conversion. The organic layer was subsequently
isolated and the aqueous phase extracted with DCM (2 × 20 mL). The organic layers were
combined, dried over MgSO and concentrated in vacuo to afford a golden brown oil.
4
Purification by flash chromatography (10% EtOAc in hexane) yielded 20 as a yellow oil
1
(
1.20 g, 78%); H NMR (400 MHz, CDCl ) δ 7.81-7.77 (m, 2H, ArH), 7.75 (d, J = 8.4 Hz,
3
1
H, ArH), 7.61 (s, 1H, ArH), 7.38 (dd, J = 8.4 & 2.0, 1H, ArH), 7.35 (dd, J = 8.0 & 2.0 Hz,
2
3

ACCEPTED MANUSCRIPT
1
H, ArH), 3.90 (s, 2H, -CH CN), 2.77 (t, J = 7.6 Hz, 2H, ArCH -), 1.71 (pent, J = 7.6 Hz,
2
2
1
3
2
H, -CH CH CH -), 1.40-1.30 (m, 4H, -CH CH CH -), 0.90 (t, J = 7.2 Hz, 3H, -CH ); C
2
2
2
2
2
2
3
NMR (100 MHz, CDCl ) δ 141.3, 132.9, 131.8, 128.6, 128.4, 127.5, 126.6, 126.2, 126.2,
3
+
1
2
25.4, 118.0, 36.1, 31.5, 31.0, 23.8, 22.6, 14.0; HRMS-ESI cald for C H N [M + Na]
17 19
60.1410; found 260.1420.
(6-n-Pent-1-ylnaphthalen-2-yl)acetic acid (21). A stirring mixture of 20 (1.17 g, 4.9 mmol)
in glacial acetic acid (20 mL), conc H SO (10 mL) and water (10 mL) was heated under
2
4
reflux for 18 h. The mixture was then allowed to cool to room temperature before being
diluted with water (100 mL). The aqueous mixture was extracted with EtOAc (100 mL then 2
×
50 mL) and the organic layers pooled, washed with water (3 × 100 mL), brine (100 mL),
dried over Na SO and concentrated in vacuo to afford a light brown solid. The crude product
2
4
was dissolved in diethyl ether (100 mL) and the resultant organic solution extracted with
aqueous 2 M NaOH (30 mL). The sodium salt which formed had poor solubility so additional
water (approximately 150 mL) was added in order to get it fully into solution. The aqueous
phase was isolated and the organic solution further extracted with aqueous 2 M NaOH (2 ×
3
0 mL). The alkaline phases were combined and acidified to pH 1 using aqueous 2 M HCl.
The aqueous solution was then extracted with diethyl ether (2 × 100 mL) and the organic
layers pooled, washed with water (4 × 100 mL), brine (100 mL), dried over MgSO and
4
o
1
concentrated in vacuo to afford 21 as a light brown solid (994 mg, 79%); mp: 120-124 C; H
NMR (400 MHz, DMSO-d ) δ 12.36 (br s, 1H, -CH CO H), 7.79 (d, J = 6.0 Hz, 1H, ArH),
6
2
2
7
.77 (d, J = 6.0 Hz, 1H, ArH), 7.71 (s, 1H, ArH), 7.65 (s, 1H, ArH), 7.38 (dd, J = 6.0 & 2.0
Hz, 1H, ArH), 7.36 (dd, J = 6.0 & 2.0 Hz, 1H, ArH), 3.71 (s, 2H, -CH CO H), 2.73 (d, J =
2
2
7
.2 Hz, 2H, ArCH -), 1.66 (pent, J = 7.2 Hz, 2H, -CH CH CH -), 1.39-1.25 (m, 4H, -
2 2 2 2
1
3
CH CH CH -), 0.86 (t, J = 7.2 Hz, 3H, -CH ); C NMR (100 MHz, DMSO-d ) δ 172.7,
2
2
2
3
6
1
2
39.6, 131.9, 131.7, 131.4, 127.8, 127.4, 127.3, 127.2, 127.1, 125.7, 40.7, 35.1, 30.8, 30.4,
+
1.9, 13.8; HRMS-ESI cald for C H O [M + Na] 279.1356; found 279.1360; Anal.
1
7
20
2
(
C H O ) C, H.
17 20 2
5
-Bromo-6-n-pent-1-yl-2-naphthoic acid (22). To a stirring solution of 14a (1.00 g, 4.1
mmol) in glacial acetic acid (65 mL) at 50 °C was added dropwise a solution of bromine
0.21 mL, 4.1 mmol) in glacial acetic acid (5 mL). The resultant mixture was stirred at 50 °C
until TLC showed complete consumption of the starting material. The mixture was then
(
2
4

ACCEPTED MANUSCRIPT
allowed to cool to room temperature before being diluted with water (100 mL), causing
precipitation of a solid. Excess bromine was destroyed via the dropwise addition of a
saturated aqueous Na SO solution. Filtration of the suspension afforded an off-white solid
2
3
which was washed copiously with water and then dried over P O overnight. Re-
2
5
crystallisation from glacial acetic acid (three times) afforded 22 as a white solid (293 mg,
o
1
2
2%); mp: 193-196 C; H NMR (400 MHz, DMSO-d ) δ 13.18 (br s, 1H, -CO H), 8.61 (d, J
6 2
=
1.6 Hz, 1H, ArH), 8.27 (d, J = 8.8 Hz, 1H, ArH), 8.12-8.08 (m, 2H, ArH), 7.58 (d, J = 8.4
Hz, 1H, ArH), 2.95 (t, J = 7.2 Hz, 2H, ArCH -), 1.65 (pent, J = 7.2 Hz, 2H, -CH CH CH -),
2
2
2
2
1
3
1
.40-1.29 (m, 4H, -CH CH CH -), 0.88 (t, J = 7.2 Hz, 3H, -CH ); C NMR (100 MHz,
2 2 2 3
DMSO-d ) δ 167.5, 143.1, 134.1, 132.5, 131.2, 129.7, 129.6, 128.6, 127.4, 127.4, 122.8,
6
+
3
7.1, 31.5, 29.7, 22.4, 14.3; HRMS-ESI calcd for C H O Br [M + Na] 343.0304; found
1
6
17
2
3
43.0312; Anal. (C H O Br) C, H.
1
6
17
2
3
0
6
-Butoxy-2-naphthoic acid (24). Method adapted from the literature. To a stirring solution
of 23 (1.00 g, 5.3 mmol) in an EtOH/water mix (3:1, 40 mL) was added 1-bromobutane (0.86
mL, 8.0 mmol). The resultant mixture was refluxed for 18 h and then allowed to cool to room
temperature before a 10% aqueous NaOH solution (10 mL) was added. The mixture was then
refluxed for a further 2 h before being allowed to cool to room temperature. After being
diluted with water (150 mL) the solution was acidified to pH 1 using aqueous 2 M HCl. The
solid which precipitated out of solution was filtered off, washed copiously with water and
o
then dried over P O overnight to afford 24 as a white solid (1.10 g, 85%); mp: 188-192 C
2
5
30
o
1
(
lit : 198 C); H NMR (400 MHz, DMSO-d ) δ 12.93 (br s, 1H, -CO H), 8.51 (s, 1H, ArH),
6 2
8
.00 (d, J = 8.8 Hz, 1H, ArH), 7.92 (dd, J = 8.8 & 2.0 Hz, 1H, ArH), 7.86 (d, J = 8.8 Hz, 1H,
ArH), 7.39 (d, J = 2.4 Hz, 1H, ArH), 7.23 (dd, J = 8.8 & 2.4 Hz, 1H, ArH), 4.12 (t, J = 6.4
Hz, 2H, ArOCH -), 1.81-1.73 (m, 2H, -CH CH CH ), 1.48 (sex, J = 7.2 Hz, 2H, -
2
2
2
3
13
CH CH CH ), 0.96 (t, J = 7.2 Hz, 3H, -CH CH CH ); C NMR (100 MHz, DMSO-d ) δ
2
2
3
2
2
3
6
1
1
67.5, 158.4, 136.7, 130.8, 130.3, 127.3, 126.8, 125.6, 125.5, 119.6, 106.5, 67.4, 30.6, 18.7,
3.6.
(E)-Methyl 6-(4-phenylbut-1-en-1-yl)-2-naphthoate (25a). Method identical to that
described for 11a. 10 (1.50 g, 5.7 mmol), palladium acetate (13 mg, 1 mol%), tri-o-
tolylphosphine (70 mg, 4 mol%), 4-phenylbut-1-ene (1.06 mL, 7.1 mmol) and triethylamine
2
5

ACCEPTED MANUSCRIPT
(0.99 mL, 7.1 mmol) afforded 25a as a light brown solid (1.75 g, 98%) which was utilised
immediately in the next step.
(E)-Methyl 6-(3-cyclopentylprop-1-en-1-yl)naphthalene-2-carboxylate (25b). Method
identical to that described for 11a. 10 (1.50 g, 5.7 mmol), palladium acetate (13 mg, 1 mol%),
tri-o-tolylphosphine (70 mg, 4 mol%), allyl cyclopentane (0.99 mL, 7.1 mmol) and
triethylamine (0.99 mL, 7.1 mmol) afforded 25b as a light brown solid (1.60 g, 96%) which
was utilised immediately in the next step.
Methyl 6-(4-phenylbut-1-yl)-2-naphthoate (26a). Method identical to that described for
1
3a. 25a (1.75 g, 5.5 mmol) and 10 wt % palladium on activated carbon (100 mg) yielded a
viscous golden coloured oil which was purified by flash chromatography (5% EtOAc in
1
hexane) to afford 26a as a viscous clear oil (1.29 g, 73%); H NMR (400 MHz, CDCl ) δ
3
8
.57 (s, 1H, ArH), 8.03 (dd, J = 8.4 & 1.6 Hz, 1H, ArH), 7.87 (d, J = 8.4 Hz, 1H, ArH), 7.80
(
d, J = 8.4 Hz, 1H, ArH), 7.63 (s, 1H, ArH), 7.38 (dd, J = 8.4 & 2.0 Hz, 1H, ArH), 7.31-7.25
m, 2H, ArH), 7.21-7.15 (m, 3H, ArH), 3.98 (s, 3H, -CO CH ), 2.83 (t, J = 7.2 Hz, 2H,
(
2
3
13
ArCH -), 2.67 (m, 2H, -CH CH CH Ph), 1.82-1.67 (m, 4H, -CH CH CH Ph); C NMR (100
2
2
2
2
2
2
2
MHz, CDCl ) δ 167.4, 142.9, 142.4, 135.8, 131.0, 130.8, 129.2, 128.4, 128.3, 128.2, 127.6,
3
1
26.6, 126.2, 125.7, 125.3, 52.1, 36.1, 35.8, 31.1, 30.7; HRMS-CI calcd for C H O [M +
22 22 2
+
H] 319.1698; found 319.1705; Anal. (C H O ) C, H.
2
2
22
2
Methyl 6-(3-cyclopentylprop-1-yl)naphthalene-2-carboxylate (26b). Method identical to
that described for 13a. 25b (1.60 g, 5.4 mmol) and 10 wt % palladium on activated carbon
(100 mg) yielded a golden coloured oil which was purified by flash chromatography (1 →
1
5
% EtOAc in hexane) to afford 26b as a viscous clear oil (1.10 g, 68%); H NMR (400 MHz,
CDCl ) δ 8.57 (s, 1H, ArH), 8.03 (dd, J = 8.8 & 2.0 Hz, 1H, ArH), 7.87 (d, J = 8.4 Hz, 1H,
3
ArH), 7.81 (d, J = 8.8 Hz, 1H, ArH), 7.44 (s, 1H, ArH), 7.40 (dd, J = 8.4 & 1.6 Hz, 1H,
ArH), 3.98 (s, 3H, -CO CH ), 2.79 (t, J = 7.6 Hz, 2H, ArCH -), 1.84-1.68 (m, 5H, -
2
3
2
CH CH cPe), 1.65-1.45 (m, 4H, CH CH cPe), 1.43-1.34 (m, 2H, CH CH cPe), 1.13-1.02 (m,
2
2
2
2
2
2
1
3
2
1
H, CH CH cPe); C NMR (100 MHz, CDCl ) δ 167.4, 143.4, 135.8, 130.9, 130.8, 129.2,
2 2 3
28.3, 127.6, 126.5, 126.2, 125.2, 52.1, 40.1, 36.5, 35.9, 32.7, 30.4, 25.2; HRMS-ESI calcd
+
for C H O [M + Na] 319.1669; found 319.1674.
2
0
24
2
2
6

ACCEPTED MANUSCRIPT
6
-(4-Phenylbut-1-yl)naphthalene-2-carboxylic acid (27a). Method identical to that
described for 14a. 26a (1.29 g, 4.1 mmol) and aqueous 1 M NaOH (12.3 mL, 12.3 mmol)
o
1
afforded 27a as a white solid (1.17 g, 95%); mp: 151-155 C; H NMR (400 MHz, DMSO-
d ) δ 12.91 (br s, 1H, -CO H), 8.53 (s, 1H, ArH), 8.00 (d, J = 8.4 Hz, 1H, ArH), 7.94 (dd, J =
6
2
8
.4 & 1.6 Hz, 1H, ArH), 7.89 (d, J = 8.4 Hz, 1H, ArH), 7.74 (s, 1H, ArH), 7.44 (dd, J = 8.4 &
.6 Hz, 1H, ArH), 7.28-7.22 (m, 2H, ArH), 7.19-7.12 (m, 3H, ArH), 2.79 (d, J = 7.2 Hz, 2H,
1
13
ArCH CH -), 2.61 (d, J = 7.2 Hz, 2H, ArCH CH -), 1.73-1.56 (m, 4H, -CH CH Ph); C
2
2
2
2
2
2
NMR (100 MHz, DMSO-d ) δ 167.6, 142.4, 142.1, 135.0, 130.6, 130.0, 129.1, 128.2, 128.2,
6
1
28.1, 127.4, 125.9, 125.6, 125.3, 35.1, 34.9, 30.6, 30.2; HRMS-ESI calcd for C H O [M -
21 20 2
-
H] 303.1385; found 303.1393; Anal. (C H O ) C, H.
2
1
20
2
6
1
-(3-Cyclopentylprop-1-yl)-2-naphthoic acid (27b). Method identical to that described for
4a. 26b (1.10 g, 3.7 mmol) and aqueous 1 M NaOH (11.1 mL, 11.1 mmol) yielded a white
solid which was recrystallised from acetonitrile to afford 27b as an off-white solid (476 mg,
o
1
4
1
8
5%); mp: 147-150 C; H NMR (400 MHz, DMSO-d ) δ 13.00 (br s, 1H, -CO H), 8.53 (s,
6 2
H, ArH), 8.01 (d, J = 8.4 Hz, 1H, ArH), 7.94 (dd, J = 8.4 & 1.6 Hz, 1H, ArH), 7.91 (d, J =
.4 Hz, 1H, ArH), 7.75 (s, 1H, ArH), 7.46 (dd, J = 8.4 & 1.6 Hz, 1H, ArH), 2.75 (t, J = 7.6
Hz, 2H, ArCH -), 1.81-1.61 (m, 5H, -CH CH cPe), 1.57-1.41 (m, 4H, CH CH cPe), 1.36-
2
2
2
2
2
1
3
1
.27 (m, 2H, CH CH cPe), 1.08-0.97 (m, 2H, CH CH cPe); C NMR (100 MHz, DMSO-d )
2 2 2 2 6
δ 167.4, 142.8, 135.1, 130.5, 130.2, 129.1, 128.2, 127.5, 127.2, 125.9, 125.1, 39.4, 35.6, 35.2,
-
3
2.1, 29.8, 24.6; HRMS-ESI calcd for C H O [M - H] 281.1547; found 281.1552; Anal.
1
9
22
2
(
C H O ) C, H.
19 22 2
Methyl 6-(4-methylpent-1-yn-1-yl)-2-naphthoate (28). A stirring solution of 10 (1.32g, 5.0
mmol), PdCl (Ph ) (211 mg, 0.3 mmol) and CuI (57 mg, 0.3 mmol) in anhydrous THF (15
2
3 2
mL) was briefly evacuated and backfilled with argon. An identical procedure was conducted
on a solution of 4-methylpent-1-yne (0.71 mL, 6.0 mmol) and diethylamine (1.0 mL, 10
mmol) in anhydrous THF (5 mL). The alkyne solution was then added to the bromide
o
solution and the resultant mixture stirred at 50 C overnight. The reaction was then quenched
with saturated NH Cl (10 mL) and extracted with diethyl ether (2 × 40 mL). The organic
4
extracts were combined, dried over MgSO and concentrated in vacuo. The resultant residue
4
was purified by flash chromatography (10% EtOAc in hexane) to afford 28 as a clear oil
1
(
1.25 g, 94%); H NMR (400 MHz, CDCl ) δ 8.51 (s, 1H, ArH), 8.01 (d, J = 8.2 Hz, 1H,
3
ArH), 7.90 (s, 1H, ArH), 7.82 (d, J = 8.2 Hz, 1H, ArH), 7.76 (d, J = 8.2 Hz, 1H, ArH), 7.49
2
7

ACCEPTED MANUSCRIPT
(
d, J = 8.2 Hz, 1H, ArH), 3.95 (s, 3H, -CO CH ), 2.34 (d, J = 6.4 Hz, 2H, -CH CH(CH ) ),
2
3
2
3 2
13
1
.99-1.89 (m, 1H, -CH CH(CH ) ), 1.07 (d, J = 6.4 Hz, 6H, -CH CH(CH ) ); C NMR (100
2 3 2 2 3 2
MHz, CDCl ) δ 167.0, 135.1, 131.4, 130.7, 129.6, 129.1, 127.7, 125.8, 124.1, 91.5, 81.6,
3
+
5
2.2, 28.7, 28.2, 22.1; HRMS-ESI calcd for C H O [M + H] 267.1386; found 267.1380.
1
8
19
2
6
-(4-Methylpent-1-yn-1-yl)-2-naphthoic acid (29). To a stirring solution of 28 (1.25 g, 4.7
mmol) in dioxane (10 mL) was added LiOH (562 mg, 23.5 mmol) dissolved in a few mL of
water. The resultant mixture was stirred at room temperature until TLC indicated complete
hydrolysis. The dioxane was then removed in vacuo and the resultant residue dissolved in
water (40 mL), extracted with diethyl ether (10 mL), and acidified to pH 1 using aqueous 2 M
HCl. The solid which precipitated from solution was filtered off, washed copiously with
water and then dried over P O overnight to afford 29 as white solid (1.05 g, 88%); mp: 125-
2
5
o
1
1
29 C; H NMR (300 MHz, DMSO-d ) δ 8.54 (s, 1H, ArH), 8.06-8.03 (m, 2H, ArH), 7.95-
6
7
.94 (m, 2H, ArH), 7.49 (dd, J = 7.6 & 1.5 Hz, 1H, ArH), 2.36 (d, J = 6.5 Hz, 2H, -
CH CH(CH ) ), 1.92-1.79 (m, 1H, -CH CH(CH ) ), 1.01 (d, J = 6.6 Hz, 6H, -
2
3 2
2
3 2
13
CH CH(CH ) ); C NMR (75 MHz, DMSO-d ) δ 167.8, 135.1, 131.7, 131.0, 130.8, 130.1,
2
3 2
6
1
29.6, 129.1, 128.4, 126.4, 123.5, 92.0, 82.1, 28.3, 28.2, 22.4; HRMS-ESI calcd for C H O
17 15 2
-
[
M-H] 251.1074; found 251.1077; Anal. (C H O ) C, H.
17 16 2
(RS)-(E)-Ethyl 6-(4-ethylcarbonylpent-1-en-1-yl)-2-naphthoate (30). Method identical to
that described for 11a. 10 (3.00 g, 11.3 mmol), palladium acetate (25 mg, 1 mol%), tri-o-
tolylphosphine (138 mg, 4 mol%), ethyl 2-methyl-4-pentenoate (2.28 mL, 14.1 mmol) and
triethylamine (1.97 mL, 14.1 mmol) yielded a dark orange oil which was purified by flash
chromatography (5 → 20% EtOAc in hexane) to afford 30 as a viscous light yellow oil (3.35
1
g, 91%); H NMR (400 MHz, CDCl ) δ 8.54 (s, 1H, ArH), 8.03 (dd, J = 8.4 & 2.0 Hz, 1H,
3
ArH), 7.86 (d, J = 8.4 Hz, 1H, ArH), 7.81 (d, J = 8.8 Hz, 1H, ArH), 7.70 (s, 1H, ArH), 7.61
(
dd, J = 8.8 & 1.6 Hz, 1H, ArH), 6.60 (d, J = 15.6 Hz, 1H, -CH=CHCH -), 6.35 (dt, J = 15.6
2
&
7.2Hz, 1H, -CH=CHCH -), 4.15 (q, J = 7.2 Hz, 2H, -CH(CH )CO CH CH ), 3.97 (s, 3H, -
2 3 2 2 3
CO CH ), 2.69-2.58 (m, 2H, -CH=CHCH -), 2.47-2.37 (m, 1H, -CH(CH )CO CH CH ),
2
3
2
3
2
2
3
1
3
1
1
3
.28-1.22 (m, 6H, -CH(CH )CO CH CH ); C NMR (100 MHz, CDCl ) δ 175.9, 167.2,
3 2 2 3 3
37.2, 135.8, 131.8, 131.8, 130.7, 129.5, 129.3, 128.0, 127.0, 125.6, 125.3, 124.4, 60.4, 52.2,
+
9.6, 37.2, 16.8, 14.3; HRMS-ESI calcd for C H O [M + Na] 349.1410; found 349.1423.
2
0
22
4
2
8