Boronic acid based photoinduced electron transfer (PET) fluorescence sensors for saccharides

Article abstract of DOI:10.1039/c0nj00578a

A simple three step synthesis was developed to provide six novel modular sensors, consisting of three para sensors, and three meta sensors with naphthalene, anthracene and pyrene fluorophores. The interaction of the six sensors with the saccharides: d-glu

Full text of DOI:10.1039/c0nj00578a

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PAPER
www.rsc.org/njc | New Journal of Chemistry
Boronic acid based photoinduced electron transfer (PET) fluorescence
sensors for saccharidesw
Joseph D. Larkin,a Karine A. Frimat,b Thomas M. Fyles,c Stephen E. Flowerb and
Tony D. James*b
Received (in Montpellier, France) 23rd July 2010, Accepted 16th August 2010
DOI: 10.1039/c0nj00578a
A simple three step synthesis was developed to provide six novel modular sensors, consisting of
three para sensors, and three meta sensors with naphthalene, anthracene and pyrene fluorophores.
The interaction of the six sensors with the saccharides: D-glucose, D-fructose, D-galactose, and
D-mannose, were evaluated. All sensors displayed increasing fluorescence intensity upon the
addition of these saccharides, with all of the sensors showing enhanced selectivity for D-glucose
over D-galactose, D-fructose and D-mannose. High affinity (Kobs) was also observed for the meta
sensors with respect to the para sensors. The naphthalene and anthracene meta sensors showed
particularly high affinity (Kobs) for D-galactose. Circular dichroism spectroscopy was used to
probe the structures of the complexes formed. Cyclic complexes were formed between all six
sensors and D-glucose. Whilst naphthalene and anthracene meta sensors which displayed high
affinity for D-galactose also formed cyclic complexes with that saccharide.
glycosuria,7,8 but by far the most prevalent condition resulting
from ineffective D-glucose transport is diabetes mellitus.9
Introduction
‘‘A sensor is a device that interacts with matter or energy and
yields a measurable signal in response’’.1 This definition bears
Diabetes presents one of the largest health challenges to face
us in the 21st century. Current reports indicate that diabetes
affects 5% of the global population.10 In the UK the increase
witness to the extensive range of applications possible with
sensors. We can distinguish biosensors, which utilise a biological
in obesity, population age and a progressively more sedentary
element for analyte recognition, from chemosensors, in which
lifestyle has seen the prevalence of Type 1 diabetes double
every 20 years since 1945.11 Diabetes is associated with chronic
the analyte interacts with a synthetically prepared entity.
In keeping with convention the term saccharide is used
to refer broadly to polyhydroxylated carbohydrates.2 The
logical perspective the debilitating long-term complications
ill health, disability and premature mortality. From a physio-
include heart disease,12 blindness,13 kidney failure,14 stroke15
product of photosynthesis, carbohydrates single-handedly
and nerve damage leading to amputation.16
account for the most prolific class of organic compounds that
can be found on the surface of the Earth. Within biology they
At an economic level the repercussions are also serious.
are of fundamental significance. In their most ubiquitous roles
Within the UK 5% of the National Health Service’s budget is
spent on treating diabetes and its complications.17 This
they endow Nature with structural rigidity, in the form of
cellulose, and function as the energy store that sustains life, in
the forms of starch and glycogen.3
equates to d3.5 billion per year or d9.6 million per day.
Following extensive and widespread trials, unequivocal
Not only are these compounds abundant they are also
evidence exists that monitoring and adjusting diabetic blood-
incredibly versatile. Oligo-saccharides are involved in protein
dramatically reduces the health risks faced by diabetics.18–20
targeting and folding, as well as controlling the cell recognition
sugar levels to maintain them within tight boundariesz
events for infection, inflammation and immunity.4 From a
Since continuous and noninvasive systems are critical for
medicinal perspective the monitoring of D-glucose has proved
the control of the disease status. Glucose chemosensors have
of particular importance. D-Glucose provides the metabolic
become the focus of intense research, the ultimate aim is to
energy for most cells of higher organisms. In humans a
provide diabetics simple more robust and less invasive
breakdown in the transport pathways of D-glucose has been
methods of measuring blood glucose levels important for the
linked to conditions such as cancer,5 cystic fibrosis6 and renal
long-term management of the disease. Towards that end one
area of research of particular focus has been the development
of boronic acid based saccharide receptors.21–39
a The National Institutes of Health, National Heart, Lung,
and Blood Institute, Bldg. 50, Bethesda, MD 20851, USA
With this research we set out to construct modular
diboronic acid fluorescent photo induced electron transfer
b Department of Chemistry, University of Bath, Bath BA2 7AY, UK.
(PET) sensors for saccharides. The recognition of saccharides
using the esterification with boronic acids is facilitated by the
interaction with a proximal tertiary amine. The precise nature
E-mail: t.d.james@bath.ac.uk; Tel: +44 (0)1225 383810
c Department of Chemistry, University of Victoria, Victoria,
BC V8W 3V6, Canada
w Electronic supplementary information (ESI) available: Synthesis of
1, 13 and 27. Also: titration curves of sensors 1, and 3 to 8,
fluorescence spectra and CD spectra of sensors 3 to 8 with selected
saccharides. See DOI: 10.1039/c0nj00578a
z Non-diabetic blood glucose concentrations are usually in the range
4 mM to 7 mM.18
c
2922 New J. Chem., 2010, 34, 2922–2931 This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010

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Results and discussion
The target sensors 3–8 can be prepared by dividing the
synthesis into 3 different steps: the initial formation of the
core unit, followed by the addition of the fluorophore and
subsequent addition of the boronic acid units in the last stage
of the synthesis. Therefore, one unique synthetic route to make
a core molecule (the linker in this case) can be used to
synthesise a variety of sensors with different fluorophores.
The para or meta diaminomethyl-benzyl represents the core
unit of the sensors. Both boronic acid groups and fluorophore
unit are added to this core structure via an amine group.
Changing the nature of the fluorophore (naphthalene, anthracene,
pyrene) and the position of the two aminomethyl groups (para
for sensors 3–5 and meta for sensors 6–8) quickly allows the
synthesis of six sensors.
Fig. 1 Schematic representation of PET sensors 1 and 2.
of the Lewis acid–base interaction (Nꢀ ꢀ ꢀB) has been the subject
of some controversy.40–42 However, the fact that the proximal
amine has a positive effect on the binding efficiency of boronic
acids is not in debate. The interaction of the boron atom
(Lewis acid) and neighboring nitrogen atom (Lewis base) is
strengthened on saccharide binding, thus the photo induced
electron transfer (PET) process, from nitrogen to the attached
fluorophore is suppressed and the fluorescence of the fluorophore
is switched on.43
The synthesis of compounds 3, 4 and 5 uses core unit 17 as a
starting material. Synthesis of core unit 17 was achieved
starting from commercial 4-cyanobenzaldehyde 14 Scheme 1.
This involved the addition of methylamine to 4-cyanobenz-
aldehyde 14 to form 4-cyanomethylamine 16, which can be
reduced to the diamine 17 by treatment with LiAlH4
(Scheme 1).
The modular concept for the design of saccharide selective
boronic acid sensors has been championed by us44–52 and
others.53–59 A modular approach allows the linker and fluoro-
phore units of a sensor to be varied independently. That way
the dimensions of the binding pocket and emission wavelength
could be altered in a controlled manner. We used the structure
of sensors 1 as blue print for our design, schematically
represented in Fig. 1.
Treatment of the commercially available 4-cyanobenzaldehyde
14 with a solution of 6 equivalents of methylamine in
methanol gave the intermediate imine 15, which was not
isolated. This was reduced in situ with sodium borohydride
(5 equivalents) in methanol to give the amine 16 in 84% yield.
The amine 16 was then treated with 5 equivalents of lithium
aluminium hydride in dry THF to reduce the nitrile group to a
primary amine.63 This afforded the target amine 17 in a yield
of 70% over 2 steps. The fluorophore and the two boronic acid
groups are consecutively added onto the core unit 17, as
shown in Scheme 2.
Sensor 1 consists of a fluorophore (an anthracene unit)
which is at the centre of the molecule and also acts as the
linker, the two receptors (phenyl boronic acid units) are then
arranged symmetrically either side of the anthracene unit.60–62
The modular system 2 consists of a fluorophore, linker
(hexamethylene) and two boronic acid receptors.45–50 Sensor
2 is one of a series of modular sensors prepared by our group,
this sensor with a hexamethylene linker and pyrene fluorophore
had the largest observed binding constant amongst the sensors
prepared for D-glucose with an observed binding constant of
962 dm3 molꢁ1. However, sensor 1 has an observed binding
constant of 4000 dm3 molꢁ1 61,62
Here, we propose that the
.
Scheme 1 Synthetic route to core unit 17. Reagents and conditions:
(i) CH3NH2/methanol, rt; (ii) NaBH4/methanol, rt; (iii) LiAlH4/dry
THF, D.
larger binding constant observed for sensor 1 may be due in
part to the greater rigidity of the linker connecting the two
boronic acid receptor units as well as a stacking interaction
between D-glucose and the extended aromatic surface of
the anthracene unit. In order to explore the effect of linker
rigidity on the saccharide selectivity we designed sensors 3–5
(para series) and 6–8 (meta series) (Fig. 2).
Scheme 2 Addition of fluorophores and boronic acid receptors to
core unit 17. Reagents and conditions: (i) a, fluorophore/methanol,
rt; b, NaBH4/methanol, rt; (ii) 13, K2CO3/dry acetonitrile, D.
Fig. 2 Six target sensors.
c
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The fluorophore is added to diamine 17 via the reaction
between the primary amine group of 17 and the
aldehyde group of naphthalen-2-carbaldehyde, anthracen-9-
carbaldehyde or pyren-1-carbaldehyde. The two boronic acid
groups are finally added to the diamine compounds 10, 11 and
12 by using a nucleophilic substitution with cyclic boronate
ester 13.
The addition of the fluorophores as arylaldehydes gave
diamines 10, 11 and 12 in 73%, 59% and 90% yield
respectively. The addition of the two boronic acids by
treatment with bromide 13 afforded the para series of sensors
3, 4 and 5 in 82%, 81% and 82% yield, respectively, after
purification (trituration with hexane and chloroform).
Core unit 21 was synthesised in a similar manner to core
unit 17, using 3-cyanobenzaldehyde 18 as starting material,
Scheme 3.
Scheme
5
Synthesis of sensor 1. Reagents and conditions: (i)
CH3NH2/methanol, rt; (ii) NaBH4/methanol, rt; (iii) bromide 13,
K2CO3/dry CH3CN, D.
Core unit 21 was then used for the synthesis of the meta
sensors (6–8) in a similar manner to the way that core unit 17
was used for the preparation of sensors 3–5. Accordingly
diamines 22, 23 and 24 were obtained in 86, 92 and 78% yield
respectively. Treatment of 22–24 with cyclic boronate ester 13
gave the meta sensors 6, 7 and 8 in 85%, 91% and 78% yield
respectively (Scheme 4).
Fig. 3 Structures of D-glucose, D-galactose, D-mannose and D-fructose.
Fluorescence titrations of sensors 1 and 3–8 with D-glucose,
D-fructose, D-galactose, and D-mannose (Fig. 3) were carried
out in an aqueous methanolic buffer solution [52.1 wt%
methanol at pH 8.21 (KCl, 0.01000 mol dmꢁ3; KH2PO4,
0.002752 mol dmꢁ3; Na2HPO4, 0.002757 mol dmꢁ3)].64 The
fluorescence intensity of the sensors 1 and 3–8 increased with
increasing saccharide concentration. The observed stability
constants (Kobs) of sensors 1 and 3–8 were calculated by the
fitting of emission intensity versus saccharide concentration
curves using a 1 : 1 binding model (1 : 2 complexes were
not needed to reproduce the data). The observed stability
constants (Kobs) are shown in Table 1.
Sensor 1 was also synthesised in order to make it possible to
directly compare all the sensors under identical conditions.
The route used to prepare sensor 1 is different to the originally
published method and is shown in Scheme 5. 9,10-Dialdehyde
anthracene 25 was treated with a solution of methylamine
(6 equivalents) in methanol at room temperature to give the
intermediate imine 26 which was not isolated. The imine was
then reduced in situ with sodium borohydride (5 equivalents)
in methanol at room temperature to form the diamine 27.
Treatment of diamine 27 with 3 equivalents of aryl bromide 13
in alkaline dry acetonitrile afforded sensor 1 in 28% yield
(23% over the two steps) (Scheme 5).
To help visualize the trends of the observed stability
constants (Kobs) in Table 1, the stability constants of the
diboronic acid sensors 3–8 are reported in Fig. 4 and 5.
From Table 1 and Fig. 4 and 5 it is clear that the observed
stability constants are generally larger for the meta sensors
(6–8) than for the para sensors (3–5). Also, increasing the size
of the fluorophore for both the para and meta sensors in
general reduces the observed stability constants; for the para
sensors 4 (naphthalene) 4 5 (anthracene) 4 6 (pyrene) and
for the meta sensors 6 (naphthalene) 4 7 (anthracene) 4 8
(pyrene). From Table 1 it is also apparent that the original
sensor 1 has the highest observed stability constant for
D-glucose. However, when we consider the observed stability
constants for D-galactose the meta sensors (6–8) and para
sensor 3 (naphthalene) all have a higher binding constant with
that saccharide than sensor 1. Clearly a smaller fluorophore
and meta spacer favours the formation of a complex with
D-galactose.
Scheme 3 Formation of core unit 21. Reagents and conditions: (i)
CH3NH2/methanol, rt; (ii) NaBH4/methanol, rt; (iii) LiAlH4/dry
THF, D.
In order to probe the nature of the differences in observed
stability constants we carried out circular dichroism (CD)
spectroscopic analysis of the complexes, since it will be
possible to gain information about the structure of the
sensor:saccharide complexes. CD spectroscopy has been used
with diboronic acid sensors to show the formation of cyclic
complexes with certain saccharides. For example compound 1,
forms a cyclic complex with D-glucose Fig. 6.61,62
Scheme 4 Addition of the fluorophore and the two boronic acid
receptors to core unit 21. Reagents and conditions: (i) a, fluorophores/
methanol, rt; b, NaBH4/methanol; (ii) bromide 13, K2CO3/dry
acetonitrile, D.
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Table 1 Observed stability constants (Kobs) (coefficient of determination; r2) for the saccharide complexes of sensors 1 and 3–8
Sensor
D-Glucose Kobs/dm3 molꢁ1
D-Galactose Kobs/dm3 molꢁ1
D-Fructose Kobs/dm3 molꢁ1
D-Mannose Kobs/dm3 molꢁ1
3
4
5
6
7
8
1
320 ꢂ 13 (0.99)
282 ꢂ 42 (0.98)
157 ꢂ 7 (0.99)
452 ꢂ 38 (0.99)
428 ꢂ 67 (0.97)
299 ꢂ 15 (0.99)
1972 ꢂ 176 (0.99)
168 ꢂ 22 (0.98)
18 ꢂ 7 (0.94)
154 ꢂ 10 (0.99)
112 ꢂ 24 (0.96)
84 ꢂ 4 (0.99)
11 ꢂ 2 (0.99)
9 ꢂ 3 (0.98)
9 ꢂ 1 (0.99)
10 ꢂ 2 (0.99)
24 ꢂ 6 (0.97)
36 ꢂ 5 (0.99)
19 ꢂ 2 (0.99)
71 ꢂ 3 (0.99)
330 ꢂ 26 (0.99)
299 ꢂ 25 (0.99)
171 ꢂ 14 (0.99)
114 ꢂ 14 (0.99)
124 ꢂ 5 (0.99)
107 ꢂ 19 (0.98)
131 ꢂ 10 (0.99)
132 ꢂ 7 (0.99)
Table 2 Absorption and CD maximum of 3–5 (para series) and its
saccharide complexes
CD maximum
wavelength(l)/ellipticity
Sensor
Absorption
(para series) Saccharide maximum/nm (y) (nm/deg cm2 dmolꢁ1
)
3
D-Glucose
L-Glucose
D-Galactose 274
D-Fructose 273
275
275
289/ꢁ452
289/+390
Silent
Silent
4
5
D-Glucose
L-Glucose
D-Galactose 378
D-Fructose 379
D-Glucose
L-Glucose
D-Galactose 345
D-Fructose 345
380
380
393/+713
393/ꢁ944
Silent
Silent
349
349
356/ꢁ329
356/+352
Silent
Silent
Fig.
4
Observed stability constants (Kobs) for the saccharide
complexes of the para sensors 3–5.
Table 3 Absorption and CD maximum of 6–8 (meta series) and their
saccharide complexes
CD maximum
wavelength (l)/ellipticity
Sensors
Absorption
(meta series) Saccharides maximum/nm (y) (nm/deg cm2 dmolꢁ1
)
6
7
8
D-Glucose
L-Glucose
D-Galactose 273
D-Fructose 275
D-Glucose
L-Glucose
D-Galactose 383
D-Fructose 384
D-Glucose
L-Glucose
D-Galactose 344
D-Fructose 349
273
273
289/+905
290/ꢁ967
290/ꢁ1052
Silent
395/ꢁ948
395/+806
394/+824
Silent
384
384
349
349
357/ꢁ934
357/+496
Silent
Silent
compound
1 and D- and L-glucose produce mirrored
symmetrical absorptions with opposite signs. The results of
the CD spectroscopic measurements performed on sensors 3–8
are given in Tables 2 and 3. Fig. 8 shows the CD spectra of 7 in
the presence of D-glucose and L-glucose and Fig. 9 represents
the CD activity of 7 in the presence of D-galactose.
Fig.
5 Observed stability constants (Kobs) for the saccharide
complexes of the meta sensors 6–8.
The results should help elucidate the structure of the
complexes formed between sensors 3–8 and the saccharides
D-glucose, D-galactose, D-mannose and D-fructose.
From Tables 2 and 3, we can see that all of the sensors
produce CD-active complexes with D-glucose, but are
CD-silent with D-fructose. This result indicates that all the
sensors form a cyclic complex with D-glucose and a non-cyclic
complex with D-fructose. However, D-galactose gave different
results dependent on the structure of the diboronic acid sensor.
Sensors 3, 4, 5 and 8 form CD-silent complexes with D-galactose,
Fig. 6 Cyclic complex formed between sensor 1 and saccharides.
The formation of the cyclic complex between compound 1
and D-glucose produces a rigid structure freezing the molecular
motion of the chromophoric anthracene unit and as a result a
CD active species is formed. The complexes formed between
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Fig. 8 CD spectra of sensor 7 in the presence of L- or D-glucose.
Fig. 7 Cyclic complexes for D-galactose and D-glucose bound to para
and meta linkers in their furanose or pyranose forms.
Table 4 Relative energies of D-galactose and D-glucose bound to
para- and meta-linkers in their furanose or pyranose forms
Basis set
cc-pVDZ
Linker
Furanose
Pyranose
D-Galactose
D-Glucose
D-Galactose
D-Glucose
meta
para
meta
para
meta
para
meta
para
0.0
+11.9
0.0
+2.4
0.0
+10.5
0.0
+1.9
0.0
+11.0
0.0
+5.4
0.0
+8.7
0.0
+5.3
Fig. 9 CD spectra of sensor 7 in the presence of D-galactose.
cc-pVDZ
6-31G(d)
6-31G(d)
while sensors 6 and 7 form a cyclic CD-active complex with
D-galactose. This observation may help explain why sensors 6
and 7 gave higher Kobs values with D-galactose than sensors 3,
4, 5 and 8.
From the CD data sensors 6 and 7 are able to form cyclic
complexes with D-glucose and D-galactose. However, sensor 8
has the same basic structure as sensors 6 and 7 and the fact
that it does not form the same complex is somewhat surprising.
However, this could be due to the bulk of the fluorophore
(pyrene unit), which could make the rotation of the C–N
bonds difficult. The lack of flexibility may make it difficult for
the two boronic acid groups to rearrange easily and form
a cyclic complex. As expected, all of the sensors showed
fluorescence enhancement on saccharide addition, with sensors
belonging to the meta series (6–8) having larger observed
stability constants Kobs than sensors of the para series (3–5).
Also, all six sensors are D-glucose selective with the highest
observed stability constants Kobs obtained with D-glucose.
Sensors 6 and 7 have particularly high observed stability
constants Kobs with D-galactose when compared with the other
sensors.
optimized the geometries of both the pyranose and furanose
forms of D-galactose and D-glucose with meta and para
benzene linkers. In Table 4 the relative energies of two
D-galactose and two D-glucose conformers with meta- and
para-linkers are listed. In all instances, the meta-linked
conformer is much lower in energy than the para-counterpart
for D-galactose. The corresponding relative energies for glucose
with both meta and para linkers show a much smaller difference,
see Table 4. These differences in the relative energies help
explain why the meta sensors 6 and 7 are CD active with
D-galactose, while the para sensors 3–5 are CD silent with
D-galactose. The energy differences also explain why both the
meta and para sensors are CD active with D-glucose.
Conclusions
To help explain the experimental CD spectra we have
carried out calculations on model systems. In our computations
an anthracene linker segment is represented by a phenyl group
to reduce computational cost, however the remainder of the
bound saccharide to the boron sensor is unchanged, see Fig. 7.
The density functional PBE1PBE65–67 was used in conjunction
with Dunning–Woon cc-pVDZ68–71 and Pople-type 6-31G(d)
and 6-31+G(d)72 basis sets. This method in conjunction with
these basis sets have been shown previously to be efficient
alternatives to more rigorous methods when studying boronic
acid compounds.73–76 All computations were performed with
the GAUSSIAN 03 program.77
This research has shown that it is possible to synthesise
modular PET fluorescent saccharide sensors using quick, easy
and mild reaction conditions. Two series of sensors para 3–5
and meta series 6–8 were synthesised. The six sensors (3–8)
prepared are different in the nature of the fluorophore
(naphthalene, anthracene or pyrene) and/or geometry of the
two boronic acids units (spacer), allowing us to investigate
systematically the effect of the fluorophore and the spacer on
the selectivity of the sensors. Previous research has shown that
the selectivity of a sensor toward one particular saccharide can
be explained by the formation of a cyclic complex between the
sensor and that saccharide.61,62 This was the case for the cyclic
complex formed between sensor 1 and D-glucose. Here, the six
sensors 3–8 showed selectivity towards D-glucose and form
In order to explain why galactose is CD silent with para-
sensors 3–5 and CD active with meta sensors 6 and 7, we
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cyclic complexes with D-glucose. Two meta sensors 6 and 7
showed particularly strong affinity for D-galactose, with Kobs
of 330 dm3 molꢁ1 and 299 dm3 molꢁ1 respectively. This may
suggest that the spacer used in the meta series of sensors was
favourable for interactions with D-galactose. Although, meta
sensor 8 did not seem to form a cyclic complex with
D-galactose the Kobs of 171 dm3 molꢁ1 was higher than that
for sensor 1 which has a Kobs of 114 dm3 molꢁ1. Therefore the
choice of the spacer is important for the selectivity of the
sensor, but, structural factors can handicap the formation of
the cyclic complex, for example the presence of sterically bulky
groups.
samples were prepared as Nujol mulls, solutions in chloroform
or as neat samples. The frequencies (n) as absorption maxima
are given in wavenumbers (cmꢁ1).
Elemental analyses were performed at the University
of North London, the University of Birmingham and the
University of Bath.
Melting points were determined using a Gallenkamp
melting point apparatus and are reported uncorrected.
Thin layer chromatography (TLC)
Precoated aluminium-backed silica plates were supplied by
Fluka Chemie (Silica gel with fluorescent indicator 254 nm,
thickness 0.2 mm). Ultraviolet light was employed for
visualisation.
It has also been shown that there is substantial variation in
the values of the observed stability constants Kobs. Sensors 1
and 3–8 are all glucose selective. However, they all have very
different stability constant Kobs values. The highest stability
constant is seen for sensor 1 with Kobs of 1972 dm3 molꢁ1, the
meta series of sensors 6–8 have a Kobs varying between
299 dm3 molꢁ1 (8) and 452 dm3 molꢁ1 (6). Whilst the para
series of sensors have observed stability constant Kobs values
varying between 157 dm3 molꢁ1 (5) and 320 dm3 molꢁ1 (3).
The results presented here have confirmed that PET
diboronic acid sensors represent a powerful tool for the
detection of saccharides. We believe that these results will
aid further research in the development of saccharide selective
sensors. For example, sensors 6 and 7 could be used as models
for the design of D-galactose selective fluorescent sensors. We
are currently exploring the development of these sensors
incorporated into polymers and attached to fibre-optic
devices, to facilitate continuous in vivo monitoring of saccharides
for a variety of industrial and medicinal applications.
Column chromatography
Column chromatography was performed using silica gel
60 (0.063–0.200 mm) (E. Merck, 64 271 Darstadt, Germany)
and the column fractions were collected and monitored
by TLC.
Fluorescence experiments
Fluorescence measurements were recorded on a Perkin Elmer
LS 50 B Fluorimeter using quartz cuvets with 10 mm path
length.
Synthesis
4-Methylaminomethyl-benzonitrile
(16).
Methylamine
(45.7 cm3 of a 2.0 mol dmꢁ3 solution in methanol, 91.4 mmol)
was added under argon atmosphere to 4-cyanobenzaldehyde
(2.00 g, 15.25 mmol) 14 in a stirred round-bottomed flask at
room temperature. The reaction was left stirring overnight. A
solution of sodium borohydride (5.64 g, 152.50 mmol) in dry
methanol (100 cm3) was added in one portion to the reaction
mixture and the reaction mixture was stirred for 4 h and then
concentrated under reduced pressure. Then water (50 cm3) was
added to the solution and the aqueous layer was extracted with
dichloromethane (3 ꢃ 50 cm3). The combined organic extracts
were dried (MgSO4), filtered and concentrated under reduced
pressure to give the amine 16 as a yellow oil (1.88 g, 84.4%)
(found: M+, 146.0835. C9H10N2 requires 146.0843); nmax
(Neat)/cmꢁ1 2229 (CN nitrile). dH(300 MHz; CDCl3) 2.29
(3H, s, CH3), 3.67 (2H, s, CH2), 7.30 (2H, d, J2,3 8.1 Hz,
2-ArCH and 6-ArCH), 7.45 (2H, d, J3,2 8.1 Hz, 3-ArCH and
5-ArCH); dC(75 MHz; CDCl3) 36.05 (CH3), 55.43 (CH2),
110.52 (4-ArC), 119.09 (CN), 128.66 (2-ArCH and 6-ArCH),
132.13 (3-ArCH and 5-ArCH) and 145.17 (1-ArC); m/z (EI+)
146 (66%, M+) and 44 (100, [CH3NHCH2]+).
Experimental section
NMR spectroscopy
NMR spectra were recorded on a Bruker AC-300 or AM-300,
a Varian Gemini 500, a Jeol 270-EX or a Jeol 400-EX spectro-
meter. All chemical shifts (d) are described in parts per million
relative to tetramethylsilane as the internal standard. The
multiplicities of the spectroscopic data are presented in the
following manner: s = singlet; d = doublet; t = triplet;
m = multiplet and the values of the coupling constants
J are given in Hz.
Mass spectrometry
Mass spectra and accurate mass were recorded on a Kratos
Profile or VG ProSpec for Electron Impact (E.I.), a VG
ProSpec for Chemical Ionisation (C.I.), a VG ZabSpec for
Fast Atom Bombardment (F.A.B.), a micromass LCT for
Electrospray Ionisation (E.I.) or a Micromass Autospec
spectrometer with E.I., C.I., F.A.B. and Electrospray sources.
Electrospray samples were prepared in a CH3OH/H2O 1 : 1
solution and F.A.B. spectra were recorded using m-nitrobenzyl
alcohol or glycerol as a matrix.
4-Methylaminomethyl-benzylamine (17). To a solution of
4-methylaminomethyl-benzonitrile 16 (1.22 g, 8.35 mmol) in
dry THF (30 cm3) at 0 1C was added LiAlH4 (40 cm3 of a
1.0 mol dmꢁ3 solution in dry diethylether, 40.00 mmol) and
the resultant reaction mixture heated under reflux for 3 h.
After cooling, the solvent was removed under reduced pressure
and water (50 cm3) was added drop wise. The organic phase
was extracted with DCM (3 ꢃ 50 cm3) and dried (MgSO4).
The solvent was removed under reduced pressure to afford the
diamine 17 as a yellow oil (1.04 g, 83.0%).
Infrared spectra
Infrared spectra were recorded on a Perkin-Elmer Paragon
1000 FT-IR or a Perkin-Elmer 1600 FT-IR spectrometer. The
c
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(Found: M+, 150.1148. C9H14N2 requires 150.1156).
dH(300 MHz; CDCl3) 36.05 (3H, s), 3.71 and 3.82 (4H, s)
and 7.20–7.30 (4H, m); dC(75 MHz; CDCl3) 36.0, 46.2, 55.8,
127.2, 128.4, 138.7, 142.1; m/z (EI+) 149 (28%, [M ꢁ H]+),
133 (20, [M ꢁ NH3]+) and 120 (100, [M ꢁ CH3NH]+).
130.9, 131.3, 133.9, 138.9, 139.1; m/z (ES+) 365 (100%,
[M + H]+) and 334 (43, [M ꢁ CH3NH]+).
(2-Boronobenzyl)-(4-{[(2-boronobenzyl)-methyl
amino]
methyl}-benzyl)-naphthalen-2-ylmethyl-amine (3). To a stirred
solution of diamine 10 (0.58 g, 2.00 mmol) in 50 cm3 of dry
acetonitrile was added 2-(2-bromomethyl-phenyl)-[1,3,2]-
dioxaborinane 13 (1.52 g, 6.00 mmol), followed by K2CO3
(1.10 g, 8.00 mmol). The reaction mixture was heated and
stirred under reflux for 5 h. The acetonitrile was then removed
under reduced pressure and water (50 cm3) was added. The
aqueous phase was extracted with DCM (3 ꢃ 50 cm3) and the
combined organic extracts were dried (MgSO4). After filtration,
the solvent was removed under reduced pressure to afford the
crude product as a dark yellow solid. Recrystallisation from
CHCl3/hexane afforded the boronic acid 3 as a pale yellow
powder (0.92 g, 82.4%), mp 134–136 1C (decomp.). dH(300 MHz;
CHCl3/CD3OD 1 : 1) 2.13 (3H, s), 3.42 (2H, s), 3.47 (2H, s),
3.49 (2H, s), 3.52 (2H, s, 4), 3.60 (2H, s), 7.06–7.60 (19H, m);
dC(75 MHz; CHCl3/CD3OD 1 : 1) 39.6, 56.6, 56.8, 57.9, 58.2,
65.7, 125.5, 125.6, 126.5, 126.8, 127.1, 127.1, 127.3, 127.6,
127.8, 128.3, 128.97, 129.6, 130.5, 132.5, 132.5, 132.8,
138.8, 141.0, 142.9; m/z (ES+) 633 (40%, [M ꢁ 3 ꢃ
H2O + 4 ꢃ CH3OH + H]+ and 619 (100, [M ꢁ 2 ꢃ H2O +
3 ꢃ CH3OH + H]+).
(4-Methylaminomethyl-benzyl)-naphthalen-2-ylmethyl-amine
(10). To a solution of the diamine 17 (0.92 g, 6.10 mmol) in
methanol (50 cm3) was added 2-naphthaldehyde (0.95 g,
6.10 mmol). After 5 h stirring at room temperature, a solution
of NaBH4 (1.11 g, 30.00 mmol) in methanol (20 cm3) was
added and the reaction mixture was stirred for 4 h and then
concentrated under reduced pressure. Water (50 cm3) was
added carefully and the organic phase was extracted with
DCM (3 ꢃ 50 cm3) and dried (MgSO4). The solvent was
removed under reduced pressure to afford the diamine 10 as a
yellow oil (1.30 g, 73.5%) (found: M+, 290.1780. C20H22N2
requires 290.1782). dH(300 MHz; CDCl3) 2.43 (3H, s), 3.72
(2H, s), 3.81 (2H, s), 3.94 (2H, s), 7.29–7.76 (11H, m); dC(75
MHz; CHCl3) 36.0, 53.0, 53.3, 55.8, 125.6, 125.9, 126.0, 126.5,
126.7, 127.3, 127.4, 127.7, 127.9, 128.2, 129.1, 132.7, 133.6,
137.9, 138.8, 139.1; m/z (EI+) 289 (36%, [M ꢁ H]+), 260
(9, [M ꢁ (CH3NH)]+), 170 (10, [NaphCH2NHCH2]+) and
141 (100, [NaphCH2]+).
(4-{[(Anthracen-9-ylmethyl)-amino]-methyl}-benzyl)-methyl-
amine (11). To a solution of diamine 17 (0.65 g, 4.30 mmol) in
methanol (50 cm3) was added 9-anthraldehyde (0.89 g,
4.30 mmol). After 5 h stirring, a solution of NaBH4 (0.75 g,
20.00 mmol) in methanol (20 cm3) was added. The reaction
mixture was stirred for 4 h at room temperature and then
concentrated under reduced pressure. Water (50 cm3) was
added carefully and the aqueous layer was extracted with
DCM (3 ꢃ 50 cm3). The combined organic layers were dried
(MgSO4), filtered and concentrated under reduced pressure to
afford the diamine 11 as a yellow-orange oil (0.86 g, 58.8%)
(found: M+, 340.1995. C24H24N2 requires 340.1992).
dH(300 MHz; CDCl3) 2.47 (3H, s), 3.77 (2H, s), 4.02 (2H, s),
4.68 (2H, s), 7.25–7.51 (8H, m), 7.99 (2H, d, J 7.5 Hz), 8.21
(2H, d, J 7.5 Hz), 8.39 (1H, s); dC(75 MHz; CDCl3) 36.0, 44.9,
54.1, 55.8, 124.2, 124.9, 126.0, 127.2, 127.8, 128.3, 128.4, 128.6,
129.1, 129.3, 130.3, 131.5, 131.7, 138.9, 139.1; m/z (ES+)
363 (100%, [M + Na]+), 341 (49, [M + H]+) and 310
(47, [M ꢁ CH3NH]+).
Anthracen-9-ylmethyl-(2-boronobenzyl)-(4-{[(2-boronobenzyl)-
methyl-amino] methyl}-benzyl)-amine (4). To a stirred solution
of diamine 11 (0.34 g, 1.00 mmol) in dry acetonitrile (40 cm3) was
added 2-(2-bromomethyl-phenyl)-[1,3,2]dioxaborinane 13 (0.76 g,
3.00 mmol), followed by K2CO3 (0.55 g, 4.00 mmol). The
reaction mixture was then heated and stirred under reflux for
5 h. The acetonitrile was removed under reduced pressure and
water (50 cm3) was added. The aqueous phase was extracted with
DCM (3 ꢃ 50 cm3) and the combined organic extracts were dried
(MgSO4), filtered and removed under reduced pressure to afford
the crude product as a yellow-orange solid. Recrystallisation
from chloroform/hexane afforded the boronic acid 4 as a pale
yellow powder (0.49 g, 80.5%), mp 154–155 1C (decomp.).
dH(300 MHz; CDCl3/CD3OD 1 : 1) 2.06 (3H, s), 3.49 (2H, s),
3.58 (2H, s), 3.74 (4H, s), 4.47 (2H, s), 7.05–8.37 (21H, m); dC(125
MHz; CDCl3/CD3OD 1 : 1) 40.2, 59.2, 59.4, 59.8, 124.6, 124.7,
124.8, 124.9, 131.2, 131.5; m/z (ES+) 727 (46%, [M ꢁ 4 ꢃ
H2O + 2 ꢃ HO(CH2)3OH + K]+) and 799 (92%, [M + 2 ꢃ
HO(CH2)3OH + K]+).
(4-Methylaminomethyl-benzyl)-pyren-1-ylmethyl-amine (12).
To a stirred solution of diamine 17 (0.72 g, 4.80 mmol) in
methanol (50 cm3) was added 1-pyrenecarboxaldehyde (1.10 g,
4.80 mmol). After 5 h stirring, a solution of NaBH4 (0.94 g,
25.00 mmol) in methanol (20 cm3) was added, and the reaction
mixture was stirred for 4 h at room temperature. The reaction
mixture was concentrated under reduced pressure and water
(50 cm3) was added carefully. The aqueous phase was extracted
with DCM (3 ꢃ 50 cm3) and the combined DCM extracts were
dried (MgSO4), filtered and concentrated under reduced pressure
to afford the diamine 12 as a yellow oil (1.57 g, 89.8%) (found:
[M + H]+, 365.1999. C26H25N2 requires 365.2017). dH(300 MHz;
CDCl3) 2.44 (3H, s), 3.73 (2H, s), 3.91 (2H, s), 4.44 (2H, s),
7.23–8.09 (13H, m); dC(75 MHz; CDCl3) 36.1, 51.1, 53.5, 55.9,
123.3, 124.7, 125.0, 125.1, 125.9, 127.1, 128.3, 128.5, 129.2, 130.7,
(2-Boronobenzyl)-(4-{[(2-boronobenzyl)-methyl-amino]-
methyl}-benzyl)-pyren-1-ylmethyl-amine (5). To
a stirred
solution of diamine 12 (0.72 g, 2.00 mmol) in dry acetonitrile
(40 cm3) was added 2-(2-bromomethyl-phenyl)-[1,3,2]dioxa-
borinane 13 (1.52 g, 6.00 mmol), followed by K2CO3 (1.10 g,
8.00 mmol). The reaction mixture was then stirred and heated
under reflux for 5 h. The acetonitrile was removed under
reduced pressure and water (50 cm3) was added. The aqueous
phase was extracted with DCM (3 ꢃ 50 cm3) and the
combined organic extracts were dried (MgSO4). After filtration,
the filtrate was concentrated under reduced pressure to afford
the crude product as a dark yellow solid. Recrystallisation
from chloroform/hexane afforded the boronic acid 5 as a pale
yellow powder (1.04 g, 82.3%), mp 174–175 1C (decomp.)
c
2928 New J. Chem., 2010, 34, 2922–2931 This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010

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(found: C, 77.3; H, 6.2; N, 3.9%. Calc. for C46H46B2N2O4
(protected compound): C, 77.5; H, 6.5; N, 3.9%).
dH(300 MHz; CDCl3/CD3OD 1 : 1) 1.79 (3H, s), 3.25
(2H, s), 3.46 (2H, s) 3.63 (4H, s), 4.05 (2H, s), 6.74–7.93
(21H, m); dC(125 MHz; CDCl3/CD3OD 1 : 1) 40.2, 52.9, 54.9,
57.9, 58.0, 59.49, 123.1, 124.3, 124.7, 125.1, 125.8, 127.2, 127.3,
130.6, 131.1, 131.1; m/z (ES+) 711 (100%, [M ꢁ 4 ꢃ H2O +
4 ꢃ CH3OH + Na]+).
3-Methylaminomethyl-benzonitrile (20). Methylamine (60 cm3
of a 2.0 mol dmꢁ3 solution in CH3OH, 120 mmol) was added
under an argon atmosphere to a solution of 3-cyanobenzaldehyde
18 (2.62 g, 20.00 mmol) in methanol CH3OH (30 cm3). After 5 h
stirring at room temperature, the reaction was complete as
judged by TLC. A solution of NaBH4 (3.78 g, 100 mmol) in
methanol (30 cm3) was then added in one portion, the reaction
mixture stirred for 4 h at room temperature and then concen-
trated under reduced pressure. Water (50 cm3) was then added
and the aqueous layer was extracted with DCM (3 ꢃ 50 cm3).
The combined organic extracts were dried (MgSO4), filtered and
concentrated under reduced pressure to afford the amine 20 as a
yellow oil (2.69 g, 92.1%) (found: M+, 146.0837. C9H10N2
requires 146.0843); nmax (CHCl3)/cmꢁ1 2232 (CN nitrile).
dH(270 MHz; CDCl3) 2.38 (3H, s), 3.72 (2H, s) and 7.34–7.57
(4H, m); dC(67.5 MHz; CDCl3) 35.9, 55.9, 112.0, 118.6, 128.81,
130.30, 131.24, 132.3, 141.5; m/z (EI+) 145 (77%, [M ꢁ H]+),
116 (49, [M ꢁ CH3NH]+) and 44 (100, [CH3NHCH2]+).
(3-{[(Anthracen-9-ylmethyl)-amino]-methyl}-benzyl)-methyl-
amine (23). To a stirred solution of diamine 21 (0.45 g,
3.00 mmol) in methanol (50 cm3) was added 9-anthraldehyde
(0.61 g, 3.00 mmol). After 5 h stirring, a solution of NaBH4
(0.56 g, 15.00 mmol) in methanol (20 cm3) was added and the
reaction mixture was stirred for 4 h and then concentrated
under reduced pressure. Water (50 cm3) was added carefully
and the aqueous phase was extracted with DCM (3 ꢃ 50 cm3).
The combined DCM extracts were dried (MgSO4), filtered and
concentrated under reduced pressure to afford the diamine 23
as a yellow-orange oil (0.94 g, 92.2%) (found: [M + H]+,
341.2010. C24H25N2 requires 341.2017). dH(400 MHz; CDCl3)
2.46 (3H, s), 3.77 (2H, s), 4.02 (2H, s), 4.69 (2H, s), 7.33–7.51
(8H, m), 7.99 (2H, d, J 8.0 Hz), 8.22 (2H, d, J 8.0 Hz), 8.39
(1H, s); dC(100 MHz; CDCl3) 36.0, 45.0, 54.3, 56.0, 124.1,
124.8, 125.9, 126.9, 126.9, 127.1, 128.0, 128.4 and 129.0, 130.2,
131.4, 131.5, 140.0, 140.4; m/z (ES+) 341 (100%, [M + H]+).
Methyl-(3-{[(pyren-1-ylmethyl)-amino]-methyl}-benzyl)-
amine (24). To a stirred solution of diamine 21 (0.45 g,
3.00 mmol) in methanol (50 cm3) was added 1-pyrenecarbox-
aldehyde (0.69 g, 3.00 mmol). After 5 h stirring, a solution of
NaBH4 (0.55 g, 15.00 mmol) in methanol (20 cm3) was added.
The reaction mixture was stirred for 4 h and then concentrated
under reduced pressure. Water (50 cm3) was added carefully
and the aqueous phase was extracted with DCM (3 ꢃ 50 cm3).
The combined DCM extracts were dried (MgSO4), filtered and
concentrated under reduced pressure to afford the diamine 24
as a yellow oil (0.85 g, 77.8%) (found: [M + H]+, 365.2008.
C26H25N2 requires 365.2017). dH(400 MHz; CDCl3) 2.46 (3H, s),
3.76 (2H, s), 3.96 (2H, s), 4.47 (2H, s), 7.20–8.31 (13H, m);
dC(100 MHz; CDCl3) 35.9, 51.1, 53.7, 55.9, 123.1, 124.5, 124.8,
124.9, 125.7, 126.8, 126.8, 126.9, 127.2, 127.3, 127.9, 128.3,
128.9, 130.5, 130.6, 131.1, 133.6, 139.8, 140.3; m/z (ES+)
365 (100%, [M + H]+) and 334 (43, [M ꢁ CH3NH]+).
3-Methylaminomethyl-benzylamine (21). To a solution of
3-methylaminomethyl-benzonitrile 20 (0.73 g, 5.00 mmol) in
dry THF (30 cm3) at 0 1C was added LiAlH4 (25.0 cm3 of a
1.0 mol dmꢁ3 solution in dry diethylether, 25.00 mmol) and
the resultant reaction mixture heated under reflux for 3 h.
After cooling, the solvent was removed under reduced pressure
and water (50 cm3) was added drop wise. The aqueous phase
was extracted with DCM (3 ꢃ 50 cm3) and dried (MgSO4).
The solvent was removed under reduced pressure, to afford the
diamine 21 as a yellow oil (0.59 g, 79.0%) (found: M+,
150.1147. C9H14N2 requires 150.1156). dH(270 MHz; CDCl3)
2.45 (3H, s), 3.74 (2H, s), 3.85 (2H, s) and 7.18–7.38 (4H, m);
dC(100 MHz; CDCl3) 36.0, 46.3, 55.9, 125.5, 126.5, 126.7,
128.4, 140.1, 143.1; m/z (EI+) 149 (34%, [M ꢁ H]+), 133 (90,
[M ꢁ NH3]+) and 120 (100, [M ꢁ CH3NH]+).
(2-Boronobenzyl)-(3-{[(2-boronobenzyl)naphthalen-2-ylmethyl-
amino]-methyl}-benzyl)-methyl-amine (6). To a stirred solution
of diamine 22 (0.58 g, 2.00 mmol) in dry acetonitrile (40 cm3) was
added 2-(2-bromomethyl-phenyl)-[1,3,2]dioxaborinane 13 (1.52 g,
6.00 mmol), followed by K2CO3 (1.10 g, 8.00 mmol). The
reaction mixture was then stirred and heated under reflux for
5 h. After cooling, the acetonitrile was removed under reduced
pressure and water (50 cm3) was added. The aqueous phase was
extracted with DCM (3 ꢃ 50 cm3) and the combined organic
extracts were dried (MgSO4). After filtration, they were concen-
trated until dryness to afford the crude product as a dark yellow
solid. Recrystallisation from chloroform/hexane afforded the
boronic acid 6 as a pale yellow powder (0.95 g, 85.1%), mp
147–150 1C (decomp.). dH(300 MHz; CDCl3/CD3OD 1 : 1) 2.28
(3H, s), 3.80 (2H, s), 3.83 (2H, s), 3.87 (2H, s), 3.92 (2H, s), 4.56
(2H, s), 7.06–7.81 (19H, m); dC(75 MHz; CDCl3/CD3OD 1 : 1)
40.6, 57.1, 58.1, 60.6, 66.4, 124.6, 125.1, 125.2, 126.0, 126.2,
126.3, 126.7, 126.8, 126.9, 127.0, 127.3, 127.4, 128.0, 128.1, 128.4,
132.2, 136.5, 137.4; m/z (ES+) 615 (30%, [M ꢁ 4 ꢃ H2O +
4 ꢃ CH3OH + H]+) and 777 (100%, [M ꢁ 2 ꢃ H2O + 2 ꢃ
HO(CH2)3OH + 2 ꢃ CH3OH + K]+).
Methyl-(3-{[(naphthalene-2ylmethyl)amino]-methyl}-benzyl)-
amine (22). To a stirred solution of diamine 21 (0.45 g,
3.00 mmol) in methanol (50 cm3) was added 2-naphthaldehyde
(0.47 g, 3.00 mmol). After 5 h stirring, a solution of NaBH4
(0.56 g, 15.00 mmol) in methanol (20 cm3) was then added and
the reaction mixture stirred for 4 h, then concentrated under
reduced pressure. Water (50 cm3) was added carefully and the
aqueous phase was extracted with DCM (3 ꢃ 50 cm3). The
combined DCM extracts were dried (MgSO4), filtered and
concentrated under reduced pressure to afford the diamine 22
as a yellow oil (0.75 g, 85.9%) (found: [M + H]+, 291.1863.
C20H23N2 requires 291.1861). dH(270 MHz; CDCl3) 2.40 (3H,
s), 3.69 (2H, s), 3.79 (2H, s), 3.92 (2H, s), 7.14–7.79 (11H, m);
dC(100 MHz; CDCl3) 36.3, 53.5, 53.7, 56.3, 125.7, 126.2, 126.7,
126.8, 127.1, 127.1, 127.9, 127.9, 128.2, 128.3, 128.7, 132.9,
133.6, 137.9, 140.2, 140.6; m/z (ES+) 291 (100%, [M + H]+).
(3-{[Anthracen-9-ylmethyl-(2-boronobenzyl)-amino]-methyl}-
benzyl)-(2-borono benzyl)-methyl-amine (7). To a stirred
c
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solution of diamine 19 (0.68 g, 2.00 mmol) in dry acetonitrile
(40 cm3) was added 2-(2-bromomethyl-phenyl)-[1,3,2]-
dioxaborinane 13 (1.52 g, 6.00 mmol), followed by K2CO3
(1.10 g, 8.00 mmol). The reaction mixture was then stirred and
heated under reflux for 5 h. After cooling, the acetonitrile was
removed under reduced pressure and water (50 cm3) was
added. The aqueous phase was extracted with DCM
(3 ꢃ 50 cm3) and the combined organic extracts were dried
(MgSO4). After filtration, the filtrate was concentrated until
dryness to afford the crude product as a dark yellow solid.
Recrystallisation from chloroform/hexane afforded the
boronic acid 7 as a pale yellow powder (1.11 g, 91.3%), mp
179–180 1C (decomp.). dH(300 MHz; CDCl3/CD3OD 1 : 1)
2.21 (3H, s), 3.66 (2H, s), 3.68 (2H, s), 3.70 (2H, s), 3.73
(2H, s), 4.57 (2H, s), 6.99–8.38 (21H, m); m/z (ES+) 665
(50%, [M ꢁ 4 ꢃ H2O + 4 ꢃ CH3OH + H]+).
Notes and references
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(2-Boronobenzyl)-(3-{[(2-boronobenzyl)-pyren-1-yl methyl-
amino]-methyl}-benzyl)-methyl-amine (8). To a stirred solution
of diamine 24 (0.72 g, 2.00 mmol) in dry acetonitrile (40 cm3) was
added 2-(2-bromomethyl-phenyl)-[1,3,2]dioxaborinane 13 (1.52 g,
6.00 mmol), followed by K2CO3 (1.10 g, 8.00 mmol). The
reaction mixture was then stirred and heated under reflux for
5 h. After cooling, the acetonitrile was removed under reduced
pressure and water (50 cm3) was added. The aqueous phase was
extracted with DCM (3 ꢃ 50 cm3) and the combined organic
extracts were dried (MgSO4). After filtration, the filtrate was
concentrated until dryness to afford the crude product as a dark
yellow solid. Recrystallisation from chloroform/hexane afforded
the boronic acid 8 as a pale yellow powder (0.99 g, 78.3%), mp
173–174 1C (decomp.). dH(300 MHz; CDCl3/CD3OD 1 : 1) 2.18
(3H, s), 3.69 (2H, s), 3.72 (2H, s), 3.82 (2H, s), 3.85 (2H, s), 4.30
(2H, s), 6.70–8.30 (21H, m); m/z (ES+) 837 (90%, [M ꢁ H2O +
2 ꢃ HO(CH2)3OH + CH3OH + K]+) and 851 (100%,
[M ꢁ 2 ꢃ H2O + 2 ꢃ HO(CH2)3OH + 2 ꢃ CH3OH + K]+).
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17 Department of Health: London, 2004.
18 H. M. Colhoun, D. J. Betteridge, P. N. Durrington, G. A. Hitman,
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19 D. M. Nathan, The Epidemiology of Diabetes Interventions and
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Fluorescence measurements. The fluorescence spectra of 1
(1 ꢃ 10ꢁ7 mol dmꢁ3), 3 (5 ꢃ 10ꢁ6 mol dmꢁ3), 4 (1 ꢃ
20 The Diabetes Control and Complications Trial Research Group,
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10ꢁ7 mol dmꢁ3),
5
(1
ꢃ
10ꢁ7 mol dmꢁ3),
6
(5
ꢃ
10ꢁ6 mol dmꢁ3), 7 (1 ꢃ 10ꢁ7 mol dmꢁ3) and 8 (1 ꢃ 10ꢁ7
mol dmꢁ3) in a pH 8.21 buffer [0.01000 mol dmꢁ3 KCl,
0.002752 mol dmꢁ3 KH2PO4 and 0.002757 mol dmꢁ3 Na2HPO4,
in 52.1% methanol–47.9% water (w/w)]64 were recorded
as increasing amounts of various saccharides (D-glucose,
D-galactose, D-mannose and D-fructose) were added to the
solution.
CD measurements. The CD spectra of 3 (1 ꢃ 10ꢁ3 mol dmꢁ3),
4 (1 ꢃ 10ꢁ3 mol dmꢁ3), 5 (1 ꢃ 10ꢁ3 mol dmꢁ3), 6
(1 ꢃ 10ꢁ3 mol dmꢁ3), 7 (1 ꢃ 10ꢁ3 mol dmꢁ3) and 8 (1 ꢃ
10ꢁ3 mol dmꢁ3) in a 90% methanol–10% water (v/v) were
recorded in the presence of D-glucose (1 ꢃ 10ꢁ2 mol dmꢁ3),
29 T. D. James and S. Shinkai, Advanced Concepts in Fluorescence
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2795–2804.
L-glucose (1 ꢃ 10ꢁ2 mol dmꢁ3), D-mannose (1 ꢃ 10ꢁ2 mol dmꢁ3
)
and D-fructose (1 ꢃ 10ꢁ2 mol dmꢁ3).
Acknowledgements
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TDJ thanks the EPRSC for a Research Grant (GR/M15217)
and the University of Bath for support.
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2930 New J. Chem., 2010, 34, 2922–2931 This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010

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