Synthesis and antibacterial activity of C2-symmetric binaphthyl scaffolded amino acid derivatives

Article abstract of DOI:10.1016/j.ejmech.2011.06.024

The synthesis of eleven novel antibacterial agents is reported. The structures are based on a C₂-symmetric binaphthyl scaffold which holds two identical chains consisting of a short linker, a basic amino acid and a small hydrophobic side chain.

Full text of DOI:10.1016/j.ejmech.2011.06.024

European Journal of Medicinal Chemistry 46 (2011) 4201e4211
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and antibacterial activity of C2-symmetric binaphthyl scaffolded
amino acid derivatives
,
b
,
,
,
Mark Robertson a, John B. Bremner a , Jonathan Coates 1, John Deadman b 1, Paul A. Keller a
*
*
,
Stephen G. Pyne a , Kittiya Somphol , David I. Rhodes
a School of Chemistry, University of Wollongong, Wollongong, NSW 2522, Australia
,
a
b,1
*
b Avexa Ltd, 576 Swan St, Richmond, Vic 3121, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of eleven novel antibacterial agents is reported. The structures are based on a C2-
symmetric binaphthyl scaffold which holds two identical chains consisting of a short linker, a basic
amino acid and a small hydrophobic side chain. Antibacterial activity is revealed for a number of
Received 26 October 2010
Received in revised form
7 May 2011
Accepted 18 June 2011
Available online 25 June 2011
derivatives down to an MIC of 2
m
g/mL (2
mM) against Staphylococcus aureus e comparable to vanco-
mycin, and an MIC of 31 g/mL (31
m
m
M) against some vancomycin-resistant enterococcal strains.
Crown Copyright Ó 2011 Published by Elsevier Masson SAS. All rights reserved.
Keywords:
Antibacterial
Peptides
Binaphthyl scaffolds
VRE
S. aureus
Resistant bacteria
1. Introduction
workers with respect to other cationic peptidomimetics based on
dipeptides which contain two cationic charges and two sterically
bulky hydrophobic units [9e11]. Subsequently cationic tripeptide
analogues were also developed [12,13]. The compounds have good
activity against both Gram-positive (including MRSA) and Gram-
negative bacteria, but activity against vancomycin-resistant
strains was not assessed [12,13].
In our research the design principles we adopted [14] for the
scaffolded amino acids included: 1) the presence of a basic amino
acid residue to engage in an ionic interaction with the terminal
The emergence of resistance to vancomycin in Gram-positive
staphylococci and enterococci presents a serious health care chal-
lenge [1e5]. This challenge is heightened by cross-resistance to
other antibacterials including linezolid [6]. In an attempt to over-
come this resistance, high molecular weight cyclic peptides like
oritavancin [7] or large vancomycin dimers linked via a rigid acti-
nocin group [8] have been developed. Another strategy is to reduce
molecular size with a view to the design of simpler cationic amino
acids that possess additional features related to vancomycin. Such
analogues could act in a similar fashion to vancomycin while
concurrently maintaining the capability to bind strongly with the
altered peptido-glycan cell wall moiety in vancomycin-resistant
strains [3]. The same structural entity in sensitive strains would
also be susceptible and thus inhibition by the same molecule would
broaden the antibacterial spectrum. A similar structural mini-
misation strategy has been effectively pursued by Svendsen and co-
carboxylate group of
D-Ala or D-Lac in the cell wall peptide-glycan
unit; 2) amino acid moieties for H-bond interactions with either
of these two terminal groups; and 3) a 1,10-binaphthyl system (or
heteroaryl [15,16] or phenyl [17] systems) to enable hydrophobic
interactions with the D-Ala methyl group or with other hydro-
phobic regions; such a system also offered the potential, through
the atropisomers, for further stereochemical refinements if
required. The initial exploration of these design principles involved
amino acids contained within a scaffolded cyclic structure on the
2,20-dimethoxy-1,10-binaphthyl system with the macrocyclic ring
connected via the 3,30-positions of the binaphthyl core and a
D-
lysine as the basic amino acid residue. This produced a derivative
with good antibacterial activity (Minimum Inhibitory Concentra-
* Corresponding authors. Tel.: þ61 2 4221 4692; fax: þ61 2 4221 4287.
E-mail addresses: jbremner@uow.edu.au (J.B. Bremner), keller@uow.edu.au (P.A.
Keller), spyne@uow.edu.au (S.G. Pyne).
1
tion; MIC) of 15 mg/mL (16 mM) against Staphylococcus aureus [14].
Tel.: þ61 3 9208 4094; fax: þ61 3 9208 4100.
0223-5234/$ e see front matter Crown Copyright Ó 2011 Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2011.06.024

4202
M. Robertson et al. / European Journal of Medicinal Chemistry 46 (2011) 4201e4211
HN
NH3Cl
NH
.
NH2 HCl
NH
HN
O
O
O
H
N
H
N
(S)
CO2Me
O
O
3
O
O
Ph
N
H
(S)
O
O
H
N
H
N
NHAc
O
OMe
OMe
N
H
O
O
O
Ph
(R,S)
(S)
O
NH
HN
NH3Cl
.
NH2 HCl
3 MIC 2 µg/mL (2 µM)
1 MIC 2 - 4 µg/mL (2 - 5 µM)
2 MIC 4 µg/mL (5 µM)
Fig. 1. Cyclic and acyclic hydrophobic scaffolded antibacterial agents containing amino acid moieties with MIC values against S. aureus [23].
Testing of the deprotected acyclic precursors of these macrocycles,
e.g. 1 (Fig. 1), revealed significant activities (e.g. 1, MIC ¼ 2e4 g/mL,
2e5 M, against S. aureus) [18]. Further development of this class of
molecule [21]. However, the relative position of these amino acids
has yet to be confirmed. The presence of the allyloxy substituent in
2 and 3 is a remnant of its requirement for use in a metathesis
reaction to produce cyclic structures [14], and hence it could be
replaced by additional basic amino acid units. The necessity of the
binaphthyl aromatic unit in our acyclic antibacterial agents has
been previously established e if the binaphthyl scaffold is replaced
with an indole [15], carbazole [16], or a simple benzene unit [17], no
significant antibacterial activity was found. We recently reported
m
m
compounds revealed that moving the aryl substituents from the
binaphthyl 3,30-positions to the 2,20-aryloxy positions maintained
activity (e.g. 2 (MIC ¼ 4
m
g/mL, 5
m
M) and 3 (MIC ¼ 2
mg/mL, 2 mM)
while allowing for a significantly easier synthetic access [19,20].
Our structure activity relationship (SAR) studies have already
revealed the importance of the basic side chains within the
P
X
P
P
X
X
O
Fmoc
OH
Fmoc
X
O
a
b
N
H
N
H
H2N
Y
Y
O
O
O
X
P
P
Y
% Yield
75
93
82
X
P
Y
%Yield
73
4
5
Arg Pmc
Lys Boc
6
7
8
Arg Pmc Bn
Arg Pmc Me
9
Arg Pmc Bn
10 Arg Pmc Me 80
11 Lys Boc Me 100
Lys
Boc Me
O
O
OH
O
O
R
R
O
O
NH2CH(XP)CO2Y, e
c
OH
(
)-binaphthyl
( )-binaphthyl
R
S
12
13
R = ethyl
15 R = ethyl
d
d
14
16
R = H
R = H
P
X
H.HCl
O
X
O
NH
NH
Y
Y
Y
Y
O
O
O
O
O
O
O
O
O
O
O
f
O
NH
NH
O
O
X
X
P
H.HCl
Binaph
X
P
Y
%Yield
59
Binaph
X
Y
%Yield
73
17
18
19
20
( )
Arg Pmc Bn
Arg Pmc Bn
Arg Pmc Me
Lys Boc Me
21
22
23
24
( )
Arg Bn
Arg Bn
Arg Me
Lys Me
S
S
(
)
86
(
)
86
R
R
( )
S
31
87
( )
S
64
76
( )
S
( )
S
Scheme 1. Synthesis of compounds 21e24. Reagents and conditions: a) for 6 and 7: BnOH or MeOH, SOCl2, 0e70 ꢀC, overnight, for 8: MeOH, EDCI, HOBt, CH3CN, RT, 3 h; b)
piperidine, CH3CN, RT, 3 h; c) ethyl 4-bromobutyrate, K2CO3, acetone, reflux, 24 h; d) LiOH, H2O, THF, RT, 4 h; e) EDCI, HOBt, CH3CN, RT, 3 h; f) TFA, CH2Cl2, RT, 3 h to overnight, then
1 M HCleEt2O.

M. Robertson et al. / European Journal of Medicinal Chemistry 46 (2011) 4201e4211
4203
H
H
N
HN
N
HN
R2
Pmc
NH
NH
(R)
R1
(R)
OH
NH
NH
O
O
O
O
O
O
O
O
(S)
(S)
O
O
b
a
O
O
19
NH
NH
R1
(R)
OH
NH
(R)
NH
R2
Pmc
HN
N
HN
N
H
H
26 R1 = NHBn, R2 = Pmc
R
25
1 = O-pyridin-2-ylmethyl, R2 = Pmc
27
c
28 R1 = NHBn, R2 = H.HCl
1 = O-pyridin-2-ylmethyl, R2 = H.HCl
29
R
Scheme 2. Synthesis of compounds 28 and 29. Reagents and conditions: a) LiOH, H2O, THF, RT, 90 min, 74%; b) BnNH2 or 2-pyridinecarbinol, EDCI, HOBt, CH3CN, RT, 3 h; 27% (26),
64% (27); c) TFA, CH2Cl2, RT, overnight, then 1 M HCleEt2O, 75% (28), 90% (29).
the importance of the presence of two basic amino acid side chains
for activity across a broad spectrum of bacterial strains [20,22],
however these reported analogues positioned these amino acids
sequentially pendant from one of the naphthyl units of the
hydrophobic scaffold. We describe here the synthesis and anti-
bacterial results for significantly different derivatives which
maintain the binaphthyl hydrophobic scaffold but have incorpo-
rated the required basic amino acid moieties in chains attached to
both binaphthyl 2,20-oxy positions.
binaphthyl units for any potential binding with the peptide side
chain to its targets. Both Arg and Lys side chains were used together
with either the R- or S-binaphthyl anchors and a butanoic acid-
based linking group. The amino acid chain was initially termi-
nated by a benzyl ester as in one of our previous examples (3, Fig.1).
However, we also further investigated a variety of ester and amide
units to cap the chain.
The facile synthesis of the first target structures 21e24 is out-
lined in Scheme 1. The protected Lys and Arg derivatives were
esterified with either a methyl or benzyl moiety (6e8) before
deprotection of the
a-amino group in these esters to give the
2. Results and discussion
amines (9e11). These amino esters were then added to the (R)- [24]
or (S)-binaphthyl scaffold, which had been chain extended at the
2,20-positions with an oxybutanoic acid moiety (14 and 16), to yield
derivatives 17e20. Deprotection of 17e20 gave the binaphthyl
amino acid derivatives 21e24 respectively, after conversion to their
hydrochloride salts.
The arginine derivative 19 was also used to vary the ester
terminus in the corresponding N-benzyl amide 28 and 2-
pyridylmethyl ester 29 (Scheme 2). Similarly, the lysine derivative
2.1. Chemistry
Our target compounds are of the type exemplified by
compounds 21e24 (Scheme 1). We incorporated a linker between
the naphthyl and amino acid units as previous studies have shown
that the presence of three contiguous methylene units can be
tolerated within the structure (e.g. 2, MIC 5
further ensured there was no steric interference from the
mM, S. aureus) e this
R2
Boc
HN
HN
(R)
O
(R)
OH
OH
R1
NH
NH
O
O
O
O
O
O
O
(S)
O
O
a
b
(S)
O
O
20
O
R1
NH
NH
(R)
O
(R)
HN
R2
HN
Boc
30
31 R1 = Bn, R2 = Boc
32 R1 = 2-pyridylmethyl, R2 = Boc
R
1 = 1-naphthyl, R2 = Boc
c
33
1 = Bn, R2 = H.HCl
1 = 2-pyridylmethyl, R2 = H.HCl
34
R
R
35
36 R1 = 1-naphthyl, R2 = H.HCl
Scheme 3. Synthesis of compounds 34e36. Reagents and conditions: a) LiOH, H2O, THF, RT, 90 min, 92%; b) PPh3, DIAD, THF, benzyl alcohol (for 31), 2-pyridinecarbinol (for 32), 1-
naphthalene methanol (for 33), 0 ꢀC to RT, overnight; c) TFA, CH2Cl2, RT, 3 h, then 1 M HCleEt2O, 80% (34, 2 steps), 54% (35, 2 steps), 83% (36, 2 steps).

4204
M. Robertson et al. / European Journal of Medicinal Chemistry 46 (2011) 4201e4211
R2
In addition, this activity was not sensitive to the binaphthyl
HN
stereochemistry with similar activity being observed for the cor-
responding (R)-binaphthyl isomer 22. This result is not inconsis-
tent with the binaphthyl scaffold having a general hydrophobic
interaction role. The terminal ester appears to require a reason-
able degree of hydrophobic steric bulk with the smaller methyl
diester 23 showing notably less activity than 21 or 22. However,
the introduction of a heteroatom into the terminal aryl ester, e.g.
the corresponding 2-pyridylmethyl diester 29 with the potential
for hydrogen-bonding interaction in this region, was detrimental
with the compound showing very poor activity. This trend is
emulated with the dilysine series with 34 (dibenzyl ester)
showing the best activity, with both the larger dinaphthyl diester
36 and the 2-pyridylmethyl diester 35 showing poorer activity. By
extending the length of the basic amino acid side chains, we
produced the homoarginine derivatives 39 and 40 with terminal
benzyl and naphthyl esters respectively. The extra length in the
side chains showed no advantage, with respect to antibacterial
activity.
R2
N
N
H
(R)
O
R1
R1
NH
O
O
O
O
a
(S)
O
O
34, 36
NH
(R)
O
N
H
N
R2
HN
R2
1 = Bn, R2 = Boc
37
R
38 R1 = 1-naphthyl, R2 = Boc
With E. faecium, compounds 21 and 22 showed the best activity,
b
a highlight being the moderate activity (MICs 31
the vancomycin-resistant strains VRE449 and VRE820 in comparison
to vancomycin which was completely ineffective (MIC >86 M,
mM) shown against
39
R
1 = Bn, R2 = H.HCl
40 R1 = 1-naphthyl, R2 = H.HCl
m
Scheme 4. Synthesis of compounds 39 and 40. Reagents and conditions: a) Et3N, N,N0-
bis(tert-butoxycarbonyl)-N00-triflyl guanidine, CH2Cl2, RT, overnight, 79% (37), 61% (38);
b) TFA, CH2Cl2, RT, overnight, then 1 M HCleEt2O, 86% (39), 61% (40).
VRE820). Interestingly, a direct comparison between 21 and 28,
where the only difference is the replacement of the terminal
dibenzyl ester with a N,N-dibenzyl amide showed a similar trend
for the vancomycin sensitive enterococcal strains, however the
amide 28 was significantly less potent against the resistant strains
compared to the corresponding ester derivative. A comparison
between the activities shown for S. aureus and VRE987, which were
both vancomycin sensitive strains, showed our derivatives to be
essentially ineffective against the latter. Indeed, generally the
trends in activities against E. faecium were poor, with decreasing
activity observed when the terminal ester was reduced in size (e.g.
to a methyl ester), and when an aryl heteroatom was incorporated
into the terminal ester.
In general, the use of C2-symmetric systems of the type illus-
trated in Table 1 showed no particular advantage or insight into the
antibacterial activities of our scaffolded amino acid molecules.
Although the structures 21 and 22 showed equivalent activity to
our previous acyclic lead compounds 2 and 3, this study was unable
to improve antibacterial activities against E. faecium. We have since
further developed our acyclic binaphthyl scaffolded amino acids
and have shown that they possess consistently good activities,
including against S. aureus and resistant strains of bacteria [20].
This current study has highlighted that the repositioning of the
20 was used to generate the analogues 34, 35 and 36 where the
terminal methyl ester was replaced with a benzyl, 2-pyridylmethyl
and 1-naphthyl ester respectively (Scheme 3). Finally, a guanylation
reaction of the lysine benzyl ester 34 and the lysine 1-naphthyl
ester 36 provided the corresponding homoarginyl derivatives, 39
and 40, respectively (Scheme 4).
In all the reactions to produce the derivatives, there was no
evidence for racemisation of the binaphthyl unit occurring. This is
consistent with our previous results [14,18e22] and experience
with this moiety during the synthesis of such antibacterial agents.
2.2. Evaluation of antibacterial activities
The results from the antibacterial testing of these compounds
against S. aureus (ATCC6538P; vancomycin sensitive) and vanco-
mycin sensitive and resistant strains of Enterococcus faecium (#243,
449, 820, 987; clinical isolates) are summarised in Table 1. The most
active compound against S. aureus was the (S)-diarginine-based
structure 21 with an MIC of 2 mg/mL, equipotent with vancomycin.
Table 1
Antibacterial activities of our synthesised compounds.
MIC Values
S. aureus
VRE243
VRE449
VRE820
VRE987
m
g/mL
mM
m
g/mL
mM
m
g/mL
mM
m
g/mL
mM
mg/mL
m
M
21
22
2
4
2
4
63
31
61
31
31
31
31
31
31
31
31
31
33
31
31
31
23
24
16
>125
18
>153
e
e
e
e
>125
e
>143
e
>125
e
>143
e
e
e
e
e
28
29
34
2
16
4
2
15
4
63
>125
125
61
>122
129
63
>125
83
61
>122
65
125
>125
63
122
>122
65
125
>125
125
122
>122
129
35
36
39
125
8
4
129
7
4
>125
>125
83
>129
>117
59
>125
125
63
>129
117
59
>125
63
63
>129
59
59
>125
125
104
>129
117
119
40
8
2
7
1
>125
2
>109
1
125
63
109
43
63
>125
54
>86
>125
<1
>108
<1
Vancomycin
S. aureus (ATCC 6538P), E. faecium #243, E. faecium #449, E. faecium #820, E. faecium #987. Note: MIC values reported are medium have been rounded.

M. Robertson et al. / European Journal of Medicinal Chemistry 46 (2011) 4201e4211
4205
amino acid basic side chains relative to the scaffold and the
4.2.2. Protocol 2: N-fmoc deprotection
terminal esters was particularly detrimental to the activity against
the resistant strains tested and these results have assisted with the
SAR picture developing for this class of inhibitors.
To a stirred solution of the Fmoc-protected peptide in dry
acetonitrile (5e10 mL) was added piperidine (0.1 mL). The resultant
solution was then stirred at room temperature for 3 h. The solvent
was then removed under reduced pressure and the resultant
residue subjected to flash silica gel chromatography using a short
column with 2% MeOH/CH2Cl2 then 5% MeOH/CH2Cl2) upon
removal of Fmoc by-products to afford the desired compound.
3. Conclusion
In conclusion, some of the C2-symmetric scaffolded cationic
amino acid derivatives synthesised here showed good activity
against S. aureus, and in selected cases equalled the activity shown
by our lead compounds and vancomycin. However, further devel-
opment of this series was curtailed in the light of better activities
shown by simpler compounds with just one side chain attached to
the binaphthyl scaffold.
4.2.3. Protocol 3: N-boc and Pmc/Pbf-deprotection
To a stirred solution of the protected peptide in CH2Cl2 (2 mL)
was added TFA (2 mL). The reaction mixture was stirred at room
temperature for 3 h before the solvent was removed under reduced
pressure. After triturating twice more with CH2Cl2 (2 mL), the
residue was taken up in CH2Cl2 (2 mL) and treated with a 1 M HCl/
diethyl ether solution (2 mL), stirred for 1 min and then evaporated
to dryness. This treatment with HCl was repeated twice more. For
Boc-deprotection this is the final step, for Pmc/Pbf-deprotection the
following is completed. The residue was taken up in the minimum
required CH2Cl2 (or dry MeOH if insoluble in CH2Cl2), precipitated
by the addition of diethyl ether and the solid collected by centri-
fugation. This step is repeated once more to remove the protecting
group by product. The resultant solid was then dried to yield the
desired compound as its hydrochloride salt.
4. Experimental protocols
4.1. General notes
Melting point determinations were carried out on a Gallen-
kamp melting point apparatus and are uncorrected. Chemical
ionization (CI) and electron impact (EI) mass spectra were
obtained on a Shimadzu QP-5000 mass spectrometer by a direct
insertion technique with an electron beam energy of 70 eV.
Electrospray ionization (ESI) mass spectra were obtained on a VG
Autospec spectrometer. High-resolution mass spectra (HRMS)
were determined on a micromass QTof2 spectrometer using
polyethylene glycol or polypropylene glycol as the internal stan-
dard. The m/z values are stated with their peak intensity as
a percentage in parentheses. Proton and carbon nuclear magnetic
resonance (NMR) spectra were obtained as specified on a Varian
Mercury 300 MHz or Varian Inova 500 MHz spectrometer. Spectra
were recorded in the specified deuterated solvent, and referenced
4.2.4. Protocol 4: esterification
To an ice cold solution of an acid (1 equiv.) in dry THF (30 mL)
was added DIAD (2.1 equiv.) and PPh3 (2.1 equiv.) under a nitrogen
atmosphere. The alcohol (2.1 equiv.) was then added and the
solution was allowed to warm to room temperature and was then
stirred overnight. The solvent was then evaporated under reduced
pressure and the crude product was purified by flash column
chromatography with 0e5% MeOH/CH2Cl2 to yield an ester
product.
to the residual non-deuterated solvent signal. Chemical shifts (
d)
4.3. Preparation of derivatives
in ppm were measured relative to the internal standard. Multiplet
(m) signals are reported as ranges; ‘app’ refers to apparent when
describing some multiplets. Analytical thin layer chromatography
(TLC) was carried out on Merck silica gel 60 F254 pre-coated
aluminium plates with a thickness of 0.2 mm. All column chro-
matography was performed under ‘flash’ conditions on Merck
silica gel 60 (230e400 mesh). Chromatography solvent mixtures
were measured by volume. All compounds were judged to be of
greater than 95% purity based upon 1H NMR and TLC analysis.
Starting materials and reagents were purchased from Sigma-
eAldrich Pty Ltd or Auspep Pty Ltd and were used as received.
Solvent extracts were dried over magnesium sulfate.
4.3.1. Methyl (2R)-2-(9H-9-fluorenylmethoxycarboxamido)-5-{3-
[(2,3-dihydro-2,2,5,7,8-pentamethyl-2H-1-benzopyran-6-yl)sulfo-
nyl]guanidino}pentanoate (7)
All final tested compounds are fully characterized with the
exception where LRMS revealed only an m/2 peak due to instru-
mentation limitations, the HRMS measurements on m/2 ions was
not possible.
To Fmoc-(R)-Arg(Pmc)-OH (1.00 g, 1.51 mmol) dissolved in dry
MeOH (5 mL) was added thionyl chloride (0.2 mL). The solution was
then heated at reflux overnight before being evaporated to dryness.
Water (20 mL) was then added and the solution was extracted with
CH2Cl2 (3 ꢁ 30 mL). The combined organic extracts were dried and
evaporated to dryness to yield the desired product (952 mg, 93%) as
a foamy white solid which was of sufficient purity to carry onto the
4.2. General protocols
4.2.1. Protocol 1: peptide coupling
To a stirred solution of an acid (1 equiv.) and an amine (1 equiv.)
in dry acetonitrile or DMF (5e10 mL) was added EDCI (1.2 equiv.)
and HOBt (1.2 equiv.). If the amine was an HCl salt then 1 equiv. of
DIPEA was also added. The reaction mixture was stirred overnight
before the solvent was removed under reduced pressure and the
resultant residue subjected to flash silica gel column chromatog-
raphy (normally using 2% MeOH/CH2Cl2 as the eluant) to afford the
desired compound.
next step. 1H NMR (300 MHz, CDCl3)
d 1.27 (s, 6H), 1.51e1.63 (m,
2H), 1.72e1.76 (m, 2H), 1.80 (t, J ¼ 6.9 Hz, 2H), 2.10 (s, 3H),
2.54e2.64 (m, 2H), 2.56 (s, 3H), 2.60 (s, 3H), 3.63 (s, 3H, OCH3),
4.12e4.16 (m, 1H), 4.27e4.35 (m, 3H), 5.95 (d, J ¼ 8.4 Hz, 1H, NH),
6.30 (br s, 1H, NH), 6.35 (br s, 2H, NH), 7.26 (t, J ¼ 7.4 Hz, 2H), 7.36 (t,
J ¼ 7.4 Hz, 2H), 7.57 (d, J ¼ 7.5 Hz, 2H), 7.73 (d, J ¼ 7.5 Hz, 2H); 13C
NMR (75 MHz, CDCl3)
d 12.0, 17.4, 18.5, 21.3, 24.9, 26.6, 29.3, 32.6,

4206
M. Robertson et al. / European Journal of Medicinal Chemistry 46 (2011) 4201e4211
36.4, 40.5, 46.9, 52.2, 66.9, 73.4, 117.7, 119.6, 123.7, 124.9, 126.8,
127.4,133.1,134.5,135.1,140.9,143.4,143.5,153.2,156.0,157.2,162.3,
172.4. MS (ESI þ ve) m/z: 677 (100%) [M þ H]þ.
stirring at RT for 4 h, diethyl ether was added and the layers were
separated. The aqueous layer was then acidified with diluted HCl
solution. This was then extracted with diethyl ether (3 ꢁ 20 mL).
The combined extracts were dried and the solvent was evaporated
under reduced pressure to yield 16 (342 mg, 64%) as a white foam.
4.3.2. Methyl (2R)-2-amino-5-{3-[(2,3-dihydro-2,2,5,7,8-pentam-
ethyl-2H-1-benzopyran-6-yl)sulfonyl]guanidino}pentanoate (10)
1H NMR (300 MHz, CDCl3)
d 1.52e2.00 (m, 8H), 3.81e4.05 (m, 4H),
7.14e7.20 (m, 4H), 7.25e7.30 (m, 2H), 7.35 (d, J ¼ 9.1 Hz, 2H), 7.81 (d,
J ¼ 8.2 Hz, 2H), 7.90 (d, J ¼ 8.8 Hz, 2H), 11.84 (br s, 2H, 2 ꢁ OH); 13C
NMR (75 MHz, CDCl3)
d 24.1, 29.6, 68.1, 115.6, 120.4, 123.7, 125.2,
126.3, 127.9, 129.30, 129.32, 133.9, 153.9, 179.8. MS (ESI þ ve) m/z
458 [M þ H]þ, 372, 286 (100%).
4.3.5. Dibenzyl (2R)-7,70-((S)-1,10-binaphthyl-2,20-bisoxy)-2,20-di
{3-[(2,3-dihydro-2,2,4,6,7-pentamethyl-2H-1-benzofuran-5-yl)
sulfonyl]guanidinopropyl}-3,30-diaza-4,40-dioxodiheptanoate (17)
The title compound was prepared via protocol 2, using Fmoc-
(R)-Arg(Pmc)-OMe (7) (356 mg, 0.53 mmol) to yield the desired
product (186 mg, 80%) as a white foam [25]. 1H NMR (300 MHz,
CDCl3) d 1.30 (s, 6H), 1.46e1.62 (m, 3H), 1.66e1.76 (m, 1H), 1.74 (br s,
2H, NH2), 1.80 (t, J ¼ 6.8 Hz, 2H), 2.10 (s, 3H), 2.54 (s, 3H), 2.55 (s,
3H), 2.62 (t, J ¼ 6.8 Hz, 2H), 3.12e3.21 (m, 2H), 3.38e3.45 (m, 1H),
3.67 (s, 3H, OCH3), 6.41 (s, 1H, NH); 13C NMR (75 MHz, CDCl3)
d 12.0,
17.4, 18.4, 21.3, 25.5, 26.7, 32.7, 40.6, 61.9, 53.8, 73.5, 117.8, 123.9,
133.3, 134.7, 135.3, 153.4, 156.2, 176.1.
4.3.3. Diethyl (S)-4,40-(1,10-binaphthyl-2,20-bisoxy)dibutanoate (15)
The title compound was prepared via protocol 1, using 9 [21]
(159 mg, 0.30 mmol; prepared via 4 and 6) and 16 (68.7 mg,
0.15 mmol) to yield 17 as a white solid (124 mg, 59%). 1H NMR
(300 MHz, CDCl3)
d 1.25 (s, 12H), 1.32e1.39 (m, 4H), 1.54e1.81 (m,
16H), 2.06 (s, 6H), 2.42e2.60 (m, 4H), 2.50 (s, 6H), 2.53 (s, 6H),
2.94e3.15 (m, 4H), 3.74e3.78 (m, 2H), 3.94e3.97 (m, 2H),
4.29e4.40 (m, 2H), 5.04 (s, 4H) 6.12 (br s, 2H, NH), 6.23 (br s, 4H,
NH), 6.43 (d, J ¼ 7.2 Hz, 2H, NH), 7.08 (d, J ¼ 8.4 Hz, 2H), 7.16 (dist t,
2H), 7.18e7.28 (m, 12H), 7.32 (d, J ¼ 9.0 Hz, 2H), 7.80 (d, J ¼ 8.4 Hz,
2H), 7.86 (d, J ¼ 9.0 Hz, 2H); 13C NMR (75 MHz, CDCl3)
d
12.0, 17.4,
To
a
suspension of (S)-1,10-binaphthalene-2,20-diol (5.0 g,
17.5 mmol) and anhydrous potassium carbonate (12.0 g, 87.6 mmol)
dissolved in acetone (200 mL), was added ethyl bromobutyrate
(6.0 mL, 2.2 equiv.) under a nitrogen atmosphere. The mixture was
then heated at reflux for 24 h before being evaporated to dryness
and the residue partitioned between ethyl acetate (100 mL) and
water (100 mL). The organic layer was then washed with water
(2 ꢁ 50 mL) before being dried and evaporated to yield an oil
(7.56 g, 85%) which was used in the next step without further
18.5, 21.3, 25.1, 25.3, 26.7, 29.1, 31.7, 32.6, 40.5, 51.9, 67.0, 68.2, 73.6,
115.7,117.9,120.3,123.7,124.0, 125.2, 126.3, 127.9,128.1, 128.3, 128.5,
129.2, 129.4, 133.2, 134.0, 134.7, 135.2, 135.3, 153.5, 153.8, 156.1171.8,
173.2. MS (ESI þve) m/z 742.7 (100%) [M þ H]þ.
4.3.6. Dibenzyl (2R)-7,70-((R)-1,10-binaphthyl-2,20-bisoxy)-2,20-di
{3-[(2,3-dihydro-2,2,4,6,7-pentamethyl-2H-1-benzofuran-5-yl)
sulfonyl]guanidinopropyl}-3,30-diaza-4,40-dioxodiheptanoate (18)
purification. 1H NMR (300 MHz, CDCl3)
d
1.17 (t, J ¼ 7.2 Hz, 6H),
1.73e1.79 (m, 4H), 1.87e1.94 (m, 4H), 3.97e4.08 (m, 8H), 7.18e7.26
(m, 4H), 7.31e7.36 (m, 2H), 7.39 (d, J ¼ 8.8 Hz, 2H), 7.84 (d,
J ¼ 8.0 Hz, 2H), 7.92 (d, J ¼ 8.8 Hz); 13C NMR (75 MHz, CDCl3)
d 14.0,
24.5, 29.9, 59.9, 68.3, 115.5, 120.4, 123.5, 125.2, 126.1, 127.7, 129.15,
129.20, 133.9, 153.9, 173.1. MS (EI, þve) m/z 514 (100%) [M]. HRMS
(ESI, þve) calcd for C32H35O6 515.2434, found 515.2434.
4.3.4. (S)-4,40-(1,10-Binaphthyl-2,20-bisoxy)dibutanoic acid (16)
The title compound was prepared via protocol 1, using 9 [21]
(125 mg, 0.236 mmol) and 14 [24] (45 mg, 0.098 mmol) to yield
18 as a white solid (123 mg, 86%). 1H NMR (300 MHz, CDCl3)
d 1.25
(s, 12H), 1.28e1.35 (m, 4H), 1.43e1.75 (m, 16H), 2.07 (s, 6H), 2.52 (s,
6H), 2.53e2.57 (m, 4H), 2.54 (s, 6H), 2.95e3.14 (m, 4H), 3.77e3.82
(m, 2H), 3.94e3.99 (m, 2H), 4.34e4.41 (m, 2H), 5.04 (s, 4H), 6.05 br
To 15 (598 mg, 1.52 mmol) dissolved in THF (30 mL) was added
a solution of LiOH (250 mg, 10.50 mmol) in water (20 mL). After

M. Robertson et al. / European Journal of Medicinal Chemistry 46 (2011) 4201e4211
4207
s, 2H, NH), 6.19 (br s, 2H, NH), 6. 21 (s, 4H, NH), 7.10, d, J ¼ 8.5 Hz,
4.3.9. Dibenzyl (2R)-7,70-((S)-1,10-binaphthyl-2,20-bisoxy)-2,20-di(3-
2H), 7.15e7.20 (m, 2H), 7.22e7.31 (m, 12H), 7.33 (d, J ¼ 9.1 Hz, 2H),
guanidinopropyl)-3,30-diaza-4,40-dioxodiheptanoate dihydrochloride
7.80 (d, J ¼ 7.9 Hz, 2H), 7.87 (d, J ¼ 9.1 Hz, 2H). 13C NMR (75 MHz,
(21)
CDCl3)
d 12.0, 17.4, 18.5, 21.3, 24.9, 25.2, 26.7, 29.2, 31.5, 32.6, 40.5,
51.7, 67.0, 73.5, 76.6, 115.4, 117.9, 120.2, 123.7, 124.0, 125.3, 126.3,
127.9, 128.1, 128.4, 128.5, 129.1, 129.4, 133.3, 134.0, 134.7, 135.2,
135.3, 153.5, 153.7, 156.1171.7, 173.1. MS (ESI þve) m/z 1483.4 (10%)
[M þ H]þ; 742.4 (20) [M þ H]2þ
.
4.3.7. Dimethyl (2R)-7,70-((S)-1,10-binaphthyl-2,20-bisoxy)-2,20-di
{3-[(2,3-dihydro-2,2,4,6,7-pentamethyl-2H-1-benzofuran-5-yl)
sulfonyl]guanidinopropyl}-3,30-diaza-4,40-dioxodiheptanoate (19)
The title compound was prepared via protocol 3, using 17
(124 mg, 0.089 mmol) to yield 21 as a white solid (65.9 mg, 73%). 1H
NMR (300 MHz, CD3OD)
d 1.42e2.00 (m, 16H), 3.00e3.17 (m, 4H),
3.90e3.97 (m, 4H), 4.23e4.35 (m, 2H), 5.02e5.12 (m, 4H),
6.96e6.99 (m, 2H), 7.04e7.15 (m, 2H), 7.16e7.34 (m,12H), 7.37e7.49
(m, 2H), 7.80 (d, J ¼ 7.8 Hz, 2H), 7.89 (d, J ¼ 8.7 Hz, 2H); 13C NMR
(75 MHz, CD3OD)
d 26.3, 26.7, 29.4, 31.7, 32.8, 41.8, 53.4, 67.9, 69.6,
116.7, 121.4, 124.6, 126.2, 127.2, 129.1, 129.3, 129.4, 129.6, 130.5,
130.8, 135.3, 137.0, 155.4, 158.4173.0, 173.2. MS (ESI þve) m/z 951
(5%) [M þ H]þ; 476 (100) [M þ H]2þ. HRMS (ESI, þve) calcd for
C54H63N8O8 951.4769, found 951.4805.
4.3.10. Dibenzyl (2R)-7,70-((R)-1,10-binaphthyl-2,20-bisoxy)-2,20-
di(3-guanidinopropyl)-3,30-diaza-4,40-dioxodiheptanoate dihydr-
ochloride (22)
The title compound was prepared via protocol 1, using (R)-
Arg(Pmc)-OMe (10) (40 mg, 0.088 mmol) and 16 (20 mg,
0.044 mmol) to yield 19 as a white solid (18 mg, 31%). 1H NMR
(300 MHz, CDCl3)
d 1.28 (s, 12H), 1.35e1.40 (m, 4H), 1.48e1.55 (m,
2H),1.60e1.78 (m,14H), 2.09 (s, 6H), 2.53 (s, 6H), 2.54e3.61 (m, 4H),
2.56 (s, 6H), 3.03e3.18 (m, 4H), 3.64 (s, 6H), 3.83e3.89 (m, 2H),
4.00e4.05 (m, 2H), 4.32e4.39 (m, 2H), 6.06 (br s, 2H, NH), 6.18e6.29
(m, 6H, NH), 7.13 (d, J ¼ 8.7 Hz, 2H), 7.21 (app t, 2H), 7.32 (app t, 2H),
7.39 (d, J ¼ 9.0 Hz, 2H), 7.84 (d, J ¼ 8.1 Hz, 2H), 7.92 (d, J ¼ 9.3 Hz, 2H).
4.3.8. Dimethyl (2R)-7,70-((S)-1,10-binaphthyl-2,20-bisoxy)-2,20-di
[(1,10-dimethylethoxycarbonylamino)butyl]-3,30-diaza-4,40-
dioxodiheptanoate (20)
The title compound was prepared via protocol 3, using 18
(120 mg, 0.081 mmol) to yield 22 as a white solid (71 mg, 86%). 1H
NMR (300 MHz, CD3OD)
d 1.54e1.61 (m, 4H), 1.63e1.70 (m, 6H),
1.78e1.87 (m, 2H), 1.90e1.95 (m, 4H), 3.10e3.15 (m, 4H), 3.90e4.04
(m, 4H), 4.31e4.36 (m, 2H), 5.10 (ABq, J ¼ 12.3 Hz, 4H), 7.00e7.03 (m,
2H), 7.10e7.15 (m, 2H), 7.23e7.32 (m, 12H), 7.45 (d, J ¼ 9.0 Hz, 2H),
7.83 (d, J ¼ 7.9 Hz, 2H), 7.93 (d, J ¼ 9.1 Hz, 2H); 13C NMR (75 MHz,
CD3OD) d 26.3, 26.7, 29.4, 31.7, 32.8, 41.8, 53.4, 67.9, 69.6,116.7,121.4,
124.6,126.2,127.2,129.1,129.3,129.4,129.6,130.5,130.8,135.3,137.0,
155.4, 158.4, 173.0, 173.2. MS (ESI þve) m/z 476 (100%) [M þ H]2þ
.
4.3.11. Dimethyl (2R)-7,70-((S)-1,10-binaphthyl-2,20-bisoxy)-2,20-
di(3-guanidinopropyl)-3,30-diaza-4,40-dioxodiheptanoate dihyd-
rochloride (23)
The title compound was prepared via protocol 1, using 16
(50 mg, 0.11 mmol) and (R)-Lys(BOC)-OMe (11) (68 mg, 0.23 mmol)
to yield the desired product 20 as an off white solid (90 mg, 87%).
Rf ¼ 0.44 (5% MeOH/CH2Cl2). 1H NMR (300 MHz, CDCl3)
d 1.15e1.26
(m, 4H), 1.30e1.55 (m, 6H), 1.43 (s, 18H), 1.59e1.76 (m, 10H),
2.97e3.02 (m, 4H), 3.73 (s, 6H), 3.84e3.91 (m, 2H), 4.11e4.18 (m, 2H),
4.42e4.49 (m, 2H), 4.53 (br s, 2H, 2 ꢁ NHBoc), 5.62 (d, J ¼ 8.2 Hz, NH),
7.16e7.19 (m, 2H), 7.23e7.58 (m, 2H), 7.33e7.38 (m, 2H), 7.45 (d,
J ¼ 9.1 Hz, 2H), 7.91 (d, J ¼ 8.2 Hz, 2H), 7.99 (d, J ¼ 8.8 Hz, 2H); 13C NMR
(75 MHz, CDCl3)
d 22.4, 24.9, 28.4, 29.4, 31.7, 32.0, 33.9, 40.1, 51.6,
52.2, 68.1, 79.0, 115.6, 120.4, 123.6, 125.2, 126.2, 127.8, 127.9, 129.2,
129.3, 134.0, 153.7, 155.8, 172.1, 172.6. MS (ESI þve) m/z 981.5 (30%)
[M þ K]þ; 968.6 (100) [M þ Na]þ; 943.6 (10) [M þ H]þ.

4208
M. Robertson et al. / European Journal of Medicinal Chemistry 46 (2011) 4201e4211
The title compound was prepared via protocol 3, using 19
2H); 13C NMR (75 MHz, CDCl3)
d 12.1, 17.4, 18.5, 21.3, 25.2, 26.7, 28.7,
(20 mg, 0.015 mmol) to yield 23 as a white solid (9 mg, 64%). 1H
31.6, 40.5, 52.5, 67.9, 68.1, 73.7, 112.0, 115.6, 118.1, 120.3, 123.6, 124.1,
125.2, 126.4, 127.9, 128.4, 129.2, 133.9, 134.9, 135.4, 138.1, 153.8, 156.2,
174.3, 175.2. MS (ESI þve) m/z 1326 (80%) [M þ Na]þ; 1304 (100)
[M þ H]þ. HRMS (ESI, þve) calcd for C68H87N8O14S2 1303.5789, found
1303.5783.
NMR (300 MHz, CD3OD)
d 1.54e1.63 (m, 10H), 1.73e1.95 (m, 6H),
3.07e3.23 (m, 4H), 3.69 (s, 6H), 3.78e3.91 (m, 2H), 3.92e4.06 (m,
2H), 4.25e4.29 (m, 2H), 6.69e6.82 (m, 2H), 6.93e7.00 (m, 4H), 7.38
(d, J ¼ 8.8 Hz, 2H), 7.64 (d, J ¼ 7.7 Hz, 2H), 7.81 (d, J ¼ 8.3 Hz, 2H). 13C
NMR (75 MHz, CD3OD)
d 26.3, 26.7, 29.8, 32.9, 41.9, 52.9, 55.1, 69.7,
116.8,121.7,124.7, 126.3, 127.3,129.1, 130.5, 130.9,135.4,155.6, 158.6,
174.9, 175.7. MS (ESI þve) m/z: 401 (100%) [M þ 2H]2þ. HRMS
(ESI þve) calcd for C42H55N8O8 799.4143, found 799.4133.
4.3.14. (2R)-7,70-((S)-1,10-Binaphthyl-2,20-bisoxy)-N,N’-dibenzyl-
2,20-di(3-guanidinopropyl)-3,30-diaza-4,40-dioxodiheptanamide (28)
4.3.12. Dimethyl (2R)-7,70-((S)-1,10-binaphthyl-2,20-bisoxy)-2,20-
dibutylamino-3,30-diaza-4,40-dioxodiheptanoate dihydrochloride (24)
The title compound was prepared via protocol 1 using 25
(70 mg, 0.054 mmol) and benzylamine (0.1 mL, 0.92 mmol) to yield
the coupled product 26 (21.4 mg, 27%). This was then deprotected
directly via protocol 3 to yield 28 (10 mg, 75%). 1H NMR (300 MHz,
The title compound was prepared via protocol 3, using 20
(88 mg, 0.093 mmol) to yield the desired product 24 as an off white
CD3OD) d 1.51e1.85 (m, 12H), 1.95e2.02 (m, 4H), 3.09e3.22 (m, 4H,
solid (50 mg, 76%). 1H NMR (300 MHz, CD3OD)
d 1.22e1.52 (m, 4H),
2 ꢁ CH2N), 3.92e4.08 (m, 4H, 2 ꢁ CH2O), 4.30e4.35 (m, 6H, 2 ꢁ (CH
(Arg) and CH2Ph)), 7.03 (d, J ¼ 8.4 Hz, 2H, ArH), 7.16e7.33 (m, 14H,
ArH), 7.49 (d, J ¼ 9.0 Hz, 2H, ArH), 7.88 (d, J ¼ 8.1 Hz, 2H, ArH), 7.97
(d, J ¼ 9.0 Hz, 2H, ArH), 8.47 (app t, 2H, NH); 13C NMR (75 MHz,
1.53e1.89 (m, 12H), 1.90e2.14 (m, 4H), 2.64e3.00 (m, 4H), 3.69 (s,
6H), 3.90e4.19 (m, 4H), 4.22e4.40 (m, 2H), 7.04 (dist d, J ¼ 8.0 Hz,
2H), 7.16e7.21 (m, 2H), 7.23e7.39 (m, 2H), 7.48e7.61 (m, 2H),
7.88e7.90 (m, 2H), 7.94e8.08 (m, 2H); 13C NMR (75 MHz, CD3OD)
CD3OD)
d 26.3, 30.3, 32.9, 41.9, 44.0, 54.3, 69.7, 116.8, 121.6, 124.7,
d
23.8, 26.7, 27.9, 31.8, 32.8, 40.5, 52.8, 53.3, 69.7, 116.8, 124.5, 124.7,
126.3, 127.2, 128.2, 128.4, 129.1, 129.6, 130.5, 130.9, 135.4, 139.7,
135.5, 158.5, 174.0, 175.7. MS (ESI þve) m/z 949 ([M þ H]þ, 10%), 475
([M þ 2H]2þ, 100). HRMS (ESI þve) calcd for C54H65N10O6 949.5089,
found 949.5071.
126.2, 127.2, 129.1, 130.5, 130.8, 135.4, 155.5, 173.8, 175.6. MS
(ESI þve) m/z 743.3 (10%) [M þ H] þ; 372.6 (100) [M þ 2H]2þ. HRMS
(ESI þve) calcd for C42H55N4O8 743.4020, found 743.4033.
4.3.13. (2R)-7,70-((S)-1,10-binaphthyl-2,20-bisoxy)-2,20-di{3-[(2,3-
dihydro-2,2,4,6,7-pentamethyl-2H-1-benzofuran-5-yl)sulfonyl]
guanidinopropyl}-3,30-diaza-4,40-dioxodiheptanoic acid (25)
4.3.15. Di(1-methylpyridyl) (2R)-7,70-((S)-1,10-binaphthyl-2,20-bis-
oxy)-2,20-di(3-guanidinopropyl)-3,30-diaza-4,40-dioxodiheptanoate
dihydrochloride (29)
To a soln of 19 (200 mg) in THF (20 mL), was added a solution
of LiOH (75 mg, 3.1 mmol) in water (10 mL). After stirring at room
temperature for 90 min, ethyl acetate was added and the layers
were separated. The aqueous layer was then acidified with
a diluted potassium bisulphate solution. This was then extracted
with CH2Cl2 (3 ꢁ 20 mL) and then the solvent was removed
under reduced pressure to yield 25 (145 mg, 74%) as a white
The protected precursor was prepared via protocol 1 using 25
(60 mg, 0.046 mmol) and 2-pyridinemethanol (0.02 mL) to yield 27
as an impure light brown solid (44 mg, 64%, MS (ESI þve) m/z
1485.5 (10%) [M þ H]þ; 743.3 (20) [M þ 2H]2þ). This was then
deprotected directly via protocol 3 to yield 29 as an off white solid
(28 mg, 90%). 1H NMR (300 MHz, CD3OD)
d 1.47e1.84 (m, 10H),
foam. 1H NMR (300 MHz, CD3OD)
d 1.23 (s,12H),1.35e1.97 (m, 20H),
1.85e2.04 (m, 6H), 3.05e3.23 (m, 4H), 3.85e4.09 (m, 4H),
4.30e4.42 (m, 2H), 5.44 (ABq, J ¼ 14.9 Hz, 4H), 6.94e6.96 (m, 2H),
7.09e7.14 (m, 2H), 7.21e7.26 (m, 2H), 7.43e7.46 (m, 2H), 7.80e7.98
(m, 8H), 8.41e8.46 (m, 2H), 8.68e8.80 (m, 2H); 13C NMR (75 MHz,
2.03 (s, 6H), 2.30e2.63 (m, 10H), 2.94e3.22 (m, 4H), 3.66e3.86 (m,
2H), 3.89e4.09 (m, 2H), 4.20e4.42 (m, 2H), 6.15e6.62 (m, 6H),
7.01e7.11 (m, 4H), 7.22e7.32 (m, 4H), 7.68e7.81 (m, 4H), 8.51 (br s,

M. Robertson et al. / European Journal of Medicinal Chemistry 46 (2011) 4201e4211
4209
CD3OD)
d
26.3, 26.7, 29.0, 32.7, 41.9, 53.5, 63.6, 69.9, 116.7, 121.4,
129.7, 131.8, 132.0, 132.7, 134.2, 136.1, 154.3, 172.0, 174.6. MS
(ESI þve) m/z 895.5 (10%) [M þ H]þ; 825.4 (40) [M ꢂ lys]þ; 448.7
(100) [M þ 2H]2þ. HRMS (ESI þve) calcd for C54H63N4O8 895.4646,
found 895.4670.
124.7, 126.2, 127.2, 127.2, 127.5, 129.0, 130.5, 130.8, 135.3, 143.7,
147.5, 152.2, 155.5, 158.5, 172.5, 176.0. MS (ESI þve) m/z 477.5 (100%)
[M þ 2H]2þ
.
4.3.16. (2R)-7,70-((S)-1,10-binaphthyl-2,20-bisoxy)-2,20-di[(1,10-dim-
ethylethoxycarbonylamino)butyl]-3,30-diaza-4,40-dioxodiheptanoic
acid (30)
4.3.18. Di(2-methylpyridyl) (2R)-7,70-((S)-1,10-binaphthyl-2,2-
bisoxy)-2,20-dibutyl-3,30-diaza-4,40-dioxodiheptanoate
dihydrochloride (35)
The crude Pmc protected precursor 32 was prepared via
protocol 4, using 30 (120 mg, 0.131 mmol) and 2-pyridinemethanol
(0.026 mL) to yield an impure light brown solid. This was then
deprotected via protocol 3 to yield 35 as an off white solid (68 mg,
To a soln of 20 (200 mg, 0.212 mmol) in THF (20 mL), was added
a solution of LiOH (75 mg, 3.14 mmol) in water (10 mL). After
stirring at room temperature for 90 min, ethyl acetate was added
and the layers were separated. The aqueous layer was then acidified
with a dilute potassium bisulfate solution. This was then extracted
with CH2Cl2 (3 ꢁ 20 mL) and then the solvent was removed under
reduced pressure to yield 30 (178 mg, 92%) as a white foam. 1H NMR
54%). 1H NMR (300 MHz, CD3OD)
d 1.28e1.51 (m, 4H), 1.52e1.79 (m,
8H), 1.80e2.03 (m, 4H), 2.78e2.94 (m, 4H), 3.94e3.98 (m, 4H),
4.25e4.38 (m, 2H), 5.45 (ABq, J ¼ 14.4 Hz, 4H), 6.94e6.97 (m, 2H),
7.11e7.16 (m, 2H), 7.25 (t, 2H), 7.44e7.47 (m, 2H), 7.82 (d, J ¼ 7.9 Hz,
2H), 7.86e7.96 (m, 4H), 7.99e8.01 (m, 2H), 8.41e8.52 (m 2H),
(300 MHz, CDCl3)
d 1.21e1.26 (m, 4H), 1.30e1.62 (m, 4H), 1.40 (s,
8.74e8.75 (m, 2H); 13C NMR (75 MHz, CDCl3)
d 26.3, 26.7, 29.4, 31.7,
18H), 1.62e1.86 (m, 12H), 2.90e3.11 (m, 4H), 3.89e3.91 (m, 2H),
4.01e4.15 (m, 2H), 4.38e4.54 (m, 2H), 4.79e4.81 (m, 2H,
2 ꢁ NHBoc), 6.20e6.40 (m, 2H, 2 ꢁ NH), 7.12 (d, J ¼ 8.1 Hz, 2H), 7.19
(app t, 2H), 7.30 (t, J ¼ 7.2 Hz, 2H), 7.41 (d, J ¼ 9.0 Hz, 2H), 7.84 (d,
J ¼ 7.8 Hz, 2H), 7.92 (d, J ¼ 8.7 Hz, 2H), 10.51 (br s, 2H, 2 ꢁ OH);13C
32.8, 41.8, 53.4, 67.9, 69.6, 116.7, 121.4, 124.6, 126.2, 127.2, 129.1,
129.3, 129.4, 129.6,130.5,130.8,135.3,137.0,155.4, 158.4173.0,173.2.
MS (ESI þve) m/z 449.4 (100%) [M þ 2H]2þ
.
4.3.19. Di(1-naphthalenylmethyl) (2R)-7,70-((S)-1,10-binaphthyl-2,20-
bisoxy)-2,20-dibutylamino-3,30-diaza-4,40-dioxodiheptanoate
dihydrochloride (36)
NMR (75 MHz, CDCl3)
d 20.7, 22.4, 25.0, 29.2, 31.3, 31.5, 40.0, 51.7,
68.1, 79.2, 115.8, 120.5, 123.7, 125.2, 126.3, 127.8, 129.2, 129.3, 134.0,
153.7, 156.2, 158.0, 173.5, 175.5. MS (ESI þve) m/z 937 (80%)
[M þ Na]þ; 915 (100) [M þ H]þ.
4.3.17. Dibenzyl (2R)-7,70-((S)-1,10-binaphthyl-2,20-bisoxy)-2,20-di-
butylamino-3,30-diaza-4,40-dioxodiheptanoate dihydrochloride (34)
The title compound was prepared via protocol 4, using 30
(60 mg, 0.066 mmol), triphenylphosphine (73 mg, 278 mmol),
DIAD (0.055 mL, 0.275 mmol) and 1-naphthalene methanol (45 mg,
0.028 mmol). The Boc-protected intermediate 33 eluted at the same
time as a reaction by product, and so this material was then
deprotected via protocol 3 to yield the desired product 36 as a pale
yellow hydrochloride salt (58 mg, 83%). 1H NMR (500 MHz, CDCl3)
The title compound was prepared via protocol 4, using 30
(120 mg, 0.131 mmol), triphenylphosphine (73 mg, 0.278 mmol),
DIAD (0.055 mL, 0.275 mmol) and BnOH (0.05 mL, 0.275 mmol).
The Boc-protected intermediate 31 eluted at the same time as
a reaction by product, and so this material was then deprotected via
protocol 3 to yield the desired product 34 as a pale yellow hydro-
d
1.19e1.25 (m, 4H), 1.48e1.72 (m, 12H), 1.78e1.94 (m, 4H),
2.64e2.68 (m, 4H), 3.80e3.93 (m, 4H), 4.22e4.45 (m, 2H), 5.54
(ABq, J ¼ 12.3 Hz, 4H), 6.96e7.00 (m, 2H), 7.11 (app t, 2H), 7.23 (app
t, 2H), 7.32e7.50 (m, 10H), 7.73e7.90 (m, 8H), 7.95 (d J ¼ 8.4 Hz, 2H);
chloride salt (101 mg, 80%). 1H NMR (300 MHz, CD3OD)
d 1.20e1.40
(m, 4H), 1.49e1.72 (m, 10H), 1.67e1.84 (m, 2H), 1.85e2.01 (m, 4H),
2.70e2.87 (m, 4H), 3.82e4.06 (m, 4H), 4.27e4.32 (m, 2H), 5.08
(ABq, J ¼ 12.3 Hz, 4H), 6.98 (dist d, J ¼ 8.5 Hz, 2H), 7.11 (app t, 2H),
7.21e7.36 (m, 10H), 7.41e7.50 (m, 2H), 7.55e7.61 (m, 2H), 7.81 (d,
J ¼ 7.9 Hz, 2H), 7.91 (d, J ¼ 8.8 Hz, 2H); 13C NMR (75 MHz, CD3OD)
13C NMR (125 MHz, CDCl3)
d 23.6, 26.5, 27.8, 31.6, 32.7, 40.3, 53.6,
66.3, 69.5, 116.7, 121.4, 124.6, 126.2, 126.3, 127.1, 127.2, 127.7128.9,
129.0, 129.7, 130.5, 130.7, 132.4, 132.8, 132.9, 135.1, 135.3, 142.9,
155.3, 173.1, 175.6. MS (ESI þve) m/z 995.5 (10%) [M þ H]þ; 825.4
(40) [M ꢂ lys]þ; 448.7 (100) [M þ 2H]2þ. HRMS (ESI þve) calcd for
C62H67N4O8 995.4959, found 995.4990.
d
21.2, 22.6, 25.6, 26.8, 30.6, 31.7, 39.3, 52.4, 66.8, 68.5, 115.6, 120.4,
123.6, 125.1, 126.1, 128.0, 128.2, 128.3, 218.5, 128.8, 129.0, 129.4,

4210
M. Robertson et al. / European Journal of Medicinal Chemistry 46 (2011) 4201e4211
4.3.20. Dibenzyl (2R)-7,70-((S)-1,10-binaphthyl-2,2-bisoxy)-2,20-di
[4-(1,10-dimethylcarbonylbutyl)guanidinobutyl]-3,30-diaza-4,40-
dioxodiheptanoate (37)
134.0, 153.2, 153.6, 156.1, 163.3, 172.0, 172.9. MS (ESI þve) m/z 1501.8
(10%) [M þ Na]þ; 1479.7 (10) [M þ H]þ; 740.5 (20) [M þ 2H]2þ
.
4.3.22. Dibenzyl (2R)-7,70-((S)-1,10-binaphthyl-2,20-bisoxy)-2,20-
di(3-guanidinobutyl)-3,30-diaza-4,40-dioxodiheptanoate dihydro-
chloride (39)
To a soln of 34 (20 mg, 0.021 mmol) in CH2Cl2 (2 mL) was added
triethylamine (0.09 mL) and N,N0-bis(tert-butoxycarbonyl)-N00-tri-
flylguanidine (25 mg, 0.062 mmol) under nitrogen. The solution
was allowed to stir overnight before being evaporated to dryness.
The resultant residue was then subjected to flash column chro-
matography using 2% MeOH/CH2Cl2 as the eluant to yield the
desired compound 37 as a pale yellow oil (23 mg, 79%). 1H NMR
The title compound was prepared via protocol 3, using 37 (20 mg,
0.014 mmol) to yield the desired product 39 as a light brown solid
(15 mg, 86%). 1H NMR (300 MHz, CDCl3)
d 1.16e1.31 (m, 4H),
1.41e1.32 (m,12H),1.36e1.49 (m, 4H), 3.06e3.09 (m, 4H), 3.96e4.04
(m, 4H), 4.24e4.36 (m, 2H), 5.06e5.16 (m, 4H), 7.01 (dist d, J ¼ 8.1 Hz,
2H), 7.17e7.20 (m, 2H), 7.30e7.31 (m, 9H), 7.44e7.55 (m, 3H),
7.58e7.65 (m, 2H), 7.85 (t, J ¼ 6.9 Hz, 2H), 7.93e7.99 (m, 2H); 13C NMR
(300 MHz, CDCl3)
d 1.11e1.23 (m, 4H), 1.38e1.61 (m, 10H), 1.48 (s,
18H), 1.49 (s, 18H), 1.65e1.80 (m, 6H), 3.20e3.32 (m, 4H), 3.79e3.86
(m, 2H), 4.06e4.11 (m, 2H), 4.41e4.48 (m, 2H), 5.16 (ABq,
J ¼ 12.3 Hz, 4H), 5.54 (d, J ¼ 8.2 Hz, 2H, 2 ꢁ NH), 7.16 (dist d,
J ¼ 8.2 Hz, 2H), 7.23e7.27 (m, 2H), 7.31e7.40 (m, 15H), 7.44e7.52 (m,
1H), 7.53e7.78 (m, 2H), 7.87 (d, J ¼ 7.9 Hz, 2H), 7.94 (d, J ¼ 9.1 Hz,
(75 MHz, CDCl3)
d 23.9, 26.7, 29.3, 32.0, 32.1, 32.8, 42.2, 67.9, 69.7
(CH2), 53.4 (CH), 116.8, 124.7, 126.3, 127.3, 129.1, 129.3, 129.4, 129.6,
130.5 (ArCH),121.6,130.9,135.4,137.2,155.5 (ArC),158.6 (CN3),173.3,
175.7 (CO). MS (ESI þve) m/z 490.5 (60%) [M þ 2H]2þ; 452.4 (100)
[M þ H ꢂ Ph]2þ; 414.5 (80) [M þ 2H ꢂ 2Ph]2þ. HRMS (ESI þve) calcd
for C56H67N8O8 979.5082, found 979.5044.
2H), 8.28 (br s, NH); 13C NMR (75 MHz, CDCl3)
d 22.5, 24.8, 28.0,
28.2, 28.4, 31.6, 31.8, 40.5, 51.7, 67.1, 68.0, 79.4, 83.2, 107.8, 115.6,
120.4, 121.5, 123.8, 125.4, 126.4, 128.0, 128.3, 128.5, 128.6, 129.2,
4.3.23. Dibenzyl (2R)-7,70-((S)-1,10-binaphthyl-2,2-bis(oxy)-2,20-
di(4-guanidinobutyl)-3,30-diaza-4,40-dioxodiheptanoate dihydr-
ochloride (40)
129.4, 132.0, 132.1, 134.1, 135.2, 153.2, 153.8, 156.1, 163.4, 172.0, 172.7.
þ
MS (ESI þve) m/z 1401.7 (40%) [M þ Na]þ; 1379 (100) [M þ H]
.
4.3.21. Di(1-naphthalenemethyl) (2R)-7,70-((S)-1,10-binaphthyl-
2,2-bisoxy)-2,20-di[4-(1,10-dimethylcarbonylbutyl)guanidinobutyl]-
3,30-diaza-4,40-dioxodiheptanoate (38)
The title compound was prepared via protocol 3, using 38 (38 mg,
0.026 mmol) to yield the desired product 40 as a light brown solid
(18 mg, 61%). 1H NMR (300 MHz, CDCl3)
d 1.09e1.45 (m, 6H),
1.46e1.80 (m,10H),1.81e1.98 (m, 4H), 2.85e3.00 (m, 2H), 3.02e3.15
(m, 2H), 3.83e4.04 (m, 4H), 4.20e4.35 (m, 2H), 5.49e5.37 (m, 4H),
6.98e7.02 (m, 2H), 7.13e7.18 (m, 2H), 7.22e7.30 (m, 2H), 7.33e7.51
To a soln of 36 (47 mg, 0.044 mmol) in CH2Cl2 (2 mL) was added
triethylamine (0.19 mL) and N,N’-bis(tert-butoxycarbonyl)-N’’-tri-
flylguanidine (53 mg, 0.13 mmol) under nitrogen. The solution was
allowed to stir overnight before being evaporated to dryness. The
resultant residue was then subjected to flash column chromatog-
raphy eluting with 2% MeOH/CH2Cl2 to yield the desired compound
38 as an off white solid (40 mg, 61%). 1H NMR (300 MHz, CDCl3)
(m, 10H), 7.79e7.98 (m, 10H); 13C NMR (75 MHz, CDCl3)
d 22.7, 22.8,
25.5, 25.55, 28.0, 28.1, 30.7, 30.8, 31.55, 31.6, 40.95, 41.0, 52.2, 52.5,
65.2, 68.3, 68.5, 115,5, 115.6, 120.35, 120.4, 123.5, 125.1, 125.2, 125.5,
126.0, 126.1, 126.5, 127.8, 127.9, 128.6, 129.3, 129.4, 129.65, 129.7,
131.4, 131.8, 134.1, 134.2, 154.25, 154.3, 157.4, 172.1, 172.8, 174.5. MS
(ESI þve) m/z 540.4 (20%) [M þ 2H]2þ; 477.3 (95) [M þ H-naph-
thyl]2þ; 414.4 (100) [M þ H ꢂ 2 ꢁ naphthyl]2þ. HRMS (ESI þve) calcd
for C64H71N8O8 1079.5395, found 1079.5409.
d
0.99e1.57 (m, 14H), 1.47 (s, 18H), 1.48 (s, 18H), 1.63e1.71 (m, 6H),
3.11e3.18 (m, 4H), 3.70e3.77 (m, 2H), 3.97e4.03 (m, 2H), 4.38e4.45
(m, 2H), 5.51 (d, J ¼ 7.9 Hz, 2H, NH), 5.61 (ABq, J ¼ 12.3 Hz, 4H), 7.12
(dist d, J ¼ 7.9 Hz, 2H), 7.18e7.32 (m, 6H), 7.44e7.60 (m, 8H), 7.78e7.82
(m, 4H), 7.87e7.92 (m, 4H), 7.97 (dist d, J ¼ 7.9 Hz, 2H), 8.24 (br s, 2H,
4.4. Determination of Minimum Inhibitory Concentration (MIC)
NH); 13C NMR (75 MHz, CDCl3)
d
22.4, 24.8, 28.0, 28.2, 28.3, 31.6, 40.5,
MIC studies were performed on S. aureus wild type (ATCC 6538P)
in Luria Broth. MIC determinations for wild type and clinical isolates
of E. faecium were conducted by growth in Enterococcosal broth
51.8, 53.4, 65.6, 67.9, 79.5, 83.2, 115.5, 120.4, 121.5, 123.4, 123.8, 125.2,
126.1, 126.4, 126.7, 128.0, 128.8, 129.2, 129.4, 129.7, 130.7, 131.5, 133.7,

M. Robertson et al. / European Journal of Medicinal Chemistry 46 (2011) 4201e4211
4211
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(2008) 4306e4314.
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Chem. 26 (2002) 1549e1552.
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Plates were incubated overnight at 37 ꢀC and the MIC recorded as the
highest concentration at which bacterial growth was observed.
Dilution factors give rise to concentrations of 125, 62.5, 31.3,15.6, 7.8,
3.9 and 1.95 mg/mL which are subsequently rounded off.
[15] V.S. Au, J.B. Bremner, J.A. Coates, P.A. Keller, S.G. Pyne, Tetrahedron 62 (2006)
9373e9382.
[16] J.B. Bremner, J.A. Coates, P.A. Keller, S.G. Pyne, H.M. Witchard, Tetrahedron 59
(2003) 8741e8755.
Acknowledgements
[17] T.P. Boyle, J.B. Bremner, J.A. Coates, J. Deadman, P.A. Keller, S.G. Pyne,
D. Rhodes, Tetrahedron 64 (2008) 11270e11290.
[18] J.B.Bremner,S.G.Pyne,P.A.Keller,D.R.Coghlan,A.Garas,H.M.Witchard,T.P.Boyle,
J.A. Coates, WO 03/002545 A1, Peptoid Compounds, AU2002/00850 (2003).
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Bioorg. Med. Chem. Lett. 19 (2009) 3010e3013.
We thank Avexa Limited, the University of Wollongong and the
National Health and Medical Research Council (Development
Grants 303415 and 404528) for their support and Dr Susan Cox for
her support in the initial development of this project.
[20] J.B. Bremner, P.A. Keller, S.G. Pyne, T.P. Boyle, Z. Brkic, D.M. David, J. Morgan,
M. Robertson, K. Somphol, P. Ambrose, S. Bhavnani, T.R. Fritsche,
D.J. Biedenbach, R.N. Jones, M.H. Miller, R.W. Buckheit Jr., K.M. Watson,
D. Baylis, J.A. Coates, J. Deadman, D. Jeevarajah, A. McCracken, D.I. Rhodes,
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[21] J.B. Bremner, P.A. Keller, S.G. Pyne, T.P. Boyle, Z. Brkic, D.M. David,
M. Robertson, K. Somphol, D. Baylis, J.A. Coates, J. Deadman, Da. Jeevarajah,
D.I. Rhodes, Bioorg. Med. Chem. 18 (2010) 2611e2620.
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