First immobilization of a glycoluril-derived molecular clip on Merrifield resin: facile separation of dihydroxybenzenes by affinity chromatography

Article abstract of DOI:10.1016/j.tetlet.2010.02.154

A practical method for the separation and purification of dihydroxybenzenes from phenol-dihydroxybenzene, methoxyphenol-dihydroxybenzene, and isomeric dihydroxybenzene mixtures was developed on the basis of affinity chromatography using a functionalized M

Full text of DOI:10.1016/j.tetlet.2010.02.154

Tetrahedron Letters 51 (2010) 2473–2476
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
First immobilization of a glycoluril-derived molecular clip on Merrifield
resin: facile separation of dihydroxybenzenes by affinity chromatography
*
Esmail Rezaei-Seresht , Fahimeh Hokmabadi
Department of Chemistry, Faculty of Sciences, Sabzevar Tarbiat Moallem University, Towhidshahr, Sabzevar 96179-76487, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A practical method for the separation and purification of dihydroxybenzenes from phenol-dihydroxyben-
zene, methoxyphenol-dihydroxybenzene, and isomeric dihydroxybenzene mixtures was developed on
the basis of affinity chromatography using a functionalized Merrifield resin. The resin was obtained by
immobilization of a glycoluril-derived clip on Merrifield resin. This recyclable resin was repeatedly used
for convenient and rapid separation of dihydroxybenzenes from the above-mentioned mixtures.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 28 January 2010
Revised 17 February 2010
Accepted 26 February 2010
Available online 3 March 2010
Keywords:
Glycoluril clip
Immobilization
Merrifield resin
Dihydroxybenzenes
Affinity chromatography
Affinity chromatography, as a powerful method for probing
small molecule biomacromolecule interactions by immobilizing
either on a solid support, has been applied successfully in rapid
selection and purification of compounds from complex mixtures.1
Although this technique is primarily intended for isolation and
purification of complex biological mixtures,2 it has also been
shown to be a very powerful and predictive technique to monitor
ligand–protein, substrate–enzyme, inhibitor–enzyme, and ligand–
receptor interactions.3–7 Therefore, continued efforts to develop
novel receptors to meet the demand of high selectivity and good
versatility are important.
In recent years, a series of organic receptors based on diphenyl-
glycoluril, commonly referred to as ‘molecular clips’ have been
introduced and developed by Nolte’s group.8 These molecules pos-
sess a well-defined and rigid U-shaped cavity, which is formed by
the glycoluril framework and two aromatic side-walls. With their
preorganized clefts, they are excellent receptors for dihydroxyben-
The new functionalized resin is able to separate isomeric dihy-
droxybenzenes, phenol-dihydroxybenzene, and methoxyphenol-
dihydroxybenzene mixtures efficiently and rapidly.
The synthesis of the functionalized resin 5 was achieved as de-
picted in Scheme 1. Following a published procedure, we prepared
the clip molecule 3 in two steps via TFA-catalyzed condensation of
the commercially available 4,40-dimethoxybenzil (1) with urea fol-
lowed by amidoalkylation of the resulting 4,40-bis(methoxyphenyl)
glycoluril (2) with 1,2-bis(bromomethyl)benzene in DMSO.14 The
resulting clip 3 was then demethylated with pyridineꢁHCl according
to a procedure developed in our laboratory to yield the hydroxy-con-
taining clip 4.15
Compound 4 was immobilized on Merrifield resin (Fluka, cross-
linked with 2% divinylbenzene, ꢂ1.4 mmol/g Cl loading, 200–
400 mesh) by agitating a mixture of 4 and the resin in the presence
of pyridine in DMF at 60 °C for 7 days.16 Extensive washing of 5
was then performed to remove physisorbed species. The beads of 5
were washed with DMF, water, MeOH, and CH2Cl2, and then dried
in vacuo. Elemental analysis (C, 85.87; H, 7.01; N, 1.48) indicated a
loading of 0.28 mmol of 4 per 1 g of resin. IR (KBr, cmꢀ1): 2940,
1715, 1610, 1496, 1460, 1455, 1262, 752, 685.
We initially demonstrated the affinity chromatography ap-
proach by separating phenol from a mixture containing a dihy-
droxybenzene compound (catechol, resorcinol, or hydroquinone).
Considering the high affinity of glycoluril clips for dihydroxyben-
zenes, we expected to separate the dihydroxybenzene compound
(DHB) from the mixture via its host–guest complexation with the
immobilized clip. Separation was achieved by packing 5 (10 g) in
a 2 ꢃ 25 cm column, loading the mixture as a methanolic solution
zene guest molecules through hydrogen bonds, p–p stacking inter-
actions, and a so-called ‘cavity effect’.9–12 The binding strength of
these types of guests within the host can span a wide range
(Ka = 0–105 Mꢀ1), which vary with a simple modification of either
the host or guest molecule.13
Here we report the first immobilization of a glycoluril-derived
molecular clip on Merrifield resin. Bearing in mind the strong bind-
ing interactions between dihydroxybenzenes and the glycoluril
clips, we designed an affinity chromatography separation strategy.
* Corresponding author. Tel.: +98 571 400 3267; fax: +98 571 441 1611.
E-mail address: rezaei_seresht@yahoo.com (E. Rezaei-Seresht).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.02.154

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E. Rezaei-Seresht, F. Hokmabadi / Tetrahedron Letters 51 (2010) 2473–2476
O
O
O
O
HN
HN
NH
NH
O
i
ii
MeO
OMe
3
N
N
N
N
MeO
OMe
O
1
2
OMe
MeO
iii
O
O
O
O
N
N
N
N
N
N
iv
N
N
5
4
O
O
OH
HO
Scheme 1. Reagents and conditions: (i) urea, TFA, toluene, Dean-Stark apparatus; (ii) KOH, DMSO, 1,2-bis(bromomethyl)benzene, 120 °C, 2 h; (iii) pyridineꢁHCl, 180–190 °C,
4 h; (iv)
, pyridine, DMF, 60 °C, 7 d.
OH
OMe
Table 1
The solvent systems for elution of the components of the phenol–DHB mixtures
NaOH (aq)
reflux, 1 h
1/2 (Me)2SO4
+
Mixture
Eluted components
MeOH/CHCl3 MeOH/CHCl3 MeOH/CHCl3 MeOH/CHCl3
(5:95, v/v) (10:90, v/v) (12:88, v/v) (15:85, v/v)
OH
DHB
OH
6
Phenol, catechol
Phenol, resorcinol
Phenol
Phenol
—
—
Catechol
—
—
Resorcinol
—
Phenol, hydroquinone Phenol
Hydroquinone —
Scheme 2.
To check the scope of the molecular clip in the affinity chroma-
tography of various DHB mixtures, we loaded a methanolic sample
(1 mL) containing two isomeric DHBs (concentration was 0.005 M
for each solute) on the modified resin 5. Separation was performed
using a suitable eluent as described above (Table 2).
We also investigated the separation of these mixtures using a
traditional column containing Silica Gel 60 (0.040–0.063 mm,
Merck) as a stationary phase. The results indicated that the iso-
meric DHBs could not be separated from each other.
Table 2
The solvent systems for elution of the components of the isomeric DHB mixtures
Mixture
Eluted components
MeOH/CHCl3
(10:90, v/v)
MeOH/CHCl3
(12:88, v/v)
MeOH/CHCl3
(15:85, v/v)
Catechol, resorcinol
Catechol, hydroquinone
Resorcinol, hydroquinone
—
Catechol
Catechol
—
Resorcinol
—
Resorcinol
Hydroquinone
Hydroquinone
In a subsequent series of experiments, we examined the perfor-
mance of our column in a practical situation. Therefore, we mono-
methylated DHBs as follows: at 10 °C dimethyl sulfate (0.64 mL,
7.0 mmol) was added dropwise to a solution containing the DHB
(1.5 g, 13.6 mmol), sodium hydroxide (0.54 g, 13.5 mmol), and
water (5 mL). The reaction mixture was refluxed for 1 h with
(1 mL, 0.005 M for each of the solutes), and washing the column
with MeOH–CHCl3 solution (5:95, v/v) at a flow rate of 1.5 mL/
min. Next, the resin-bound DHB was released from the column
by elution with the more polar eluent (Table 1). After each separa-
tion, the column was regenerated by washing with methanol.

E. Rezaei-Seresht, F. Hokmabadi / Tetrahedron Letters 51 (2010) 2473–2476
2475
4.004
mAU
A
70
60
50
40
30
20
10
0
7.513
0
1
2
3
4
5
6
7
8
9
min.
7.478
mAU
B
250
200
150
100
50
0
0
1
2
3
4
5
6
7
8
9
min.
4.012
mAU
C
350
300
250
200
150
100
50
3.593
2.633
2.028
7.433
5.119
6.253
4.755
5
9.280
0
min.
0
1
2
3
4
6
7
8
9
Figure 1. HPLC chromatograms of (A) the reaction mixture of 3-methoxyphenol and resorcinol before separation, (B) the recovered component (3-methoxyphenol) of the
mixture by elution with MeOH/CHCl3 (5:95, v/v), (C) the recovered component (resorcinol) of the mixture by elution with MeOH/CHCl3 (15:85, v/v), (D) a standard sample of
3-methoxyphenol, and (E) a standard sample of resorcinol.
stirring. After removal of the solvent under reduced pressure, a
crude residue that contained mainly methoxyphenol 6, and the
unreacted DHB was obtained (Scheme 2). A small amount of this
residue was dissolved in MeOH (1 mL), loaded onto the column,
and eluted with the appropriate solvent (Table 3).
All the collected fractions were analyzed by HPLC and/or TLC. As
an example, the HPLC chromatogramsof the reaction mixture for the
mono-methylation of resorcinol before and after separation indi-
cated that pure 3-methoxyphenol and unreacted starting material
(resorcinol) were recovered from the reaction mixture (Fig. 1).

2476
E. Rezaei-Seresht, F. Hokmabadi / Tetrahedron Letters 51 (2010) 2473–2476
7.535
mAU
60
D
50
40
30
20
10
0
min.
0
1
2
3
4
5
6
7
8
9
4.012
mAU
E
80
60
40
20
0
min.
0
1
2
3
4
5
6
7
Fig. 1 (continued)
Table 3
The solvent systems for elution of the components of the reaction mixtures
Reaction mixture
Eluted components
MeOH/CHCl3 (5:95, v/v)
MeOH/CHCl3 (10:90, v/v)
MeOH/CHCl3 (12:88, v/v)
MeOH/CHCl3 (15:85, v/v)
Catechol, 2-methoxyphenol
Resorcinol, 3-methoxyphenol
Hydroquinone, 4-methoxyphenol
2-Methoxyphenol
3-Methoxyphenol
4-Methoxyphenol
—
—
Catechol
—
—
—
Resorcinol
—
Hydroquinone
6. Bom, A.; Bradley, M.; Cameron, K.; Clark, J. K.; van Egmond, J.; Feilden, H.;
MacLean, E. J.; Muir, A. W.; Palin, R.; Rees, D. C.; Zhang, M. Angew. Chem., Int. Ed.
2002, 41, 265.
7. Sasmal, S.; Sinha, M. K.; Keinan, E. Org. Lett. 2004, 6, 1225.
8. Smeets, J. W. H.; Sijbesma, R. P.; Niele, F. G. M.; Spek, A. L.; Smeets, W. J. J.;
Nolte, R. J. M. J. Am. Chem. Soc. 1987, 109, 928.
9. Sijbesma, R. P.; Kentgens, A. P. M.; Nolte, R. J. M. J. Org. Chem. 1991, 56, 3199.
10. Sijbesma, R. P.; Kentgens, A. P. M.; Lutz, E. T. G.; Van der Maas, J. H.; Nolte, R. J.
M. J. Am. Chem. Soc. 1993, 115, 8999.
11. Reek, J. N. H.; Priem, A. H.; Engelkamp, H.; Rowan, A. E.; Elemans, J. A. A. W.;
Nolte, R. J. M. J. Am. Chem. Soc. 1997, 119, 9956.
In conclusion, a practical method for the separation and purifi-
cation of dihydroxybenzene compounds has been developed. The
approach is based on affinity chromatography using a recyclable
glycoluril clip-functionalized Merrifield resin. Current work in
our laboratory is directed toward the application of this function-
alized resin (or Merrifield resins with higher density of the immo-
bilized clip) for the separation and purification of naturally
occurring and biologically important dihydroxybenzenes.
12. Gieling, G. T. W.; Scheeren, H. W.; Israel, R.; Nolte, R. J. M. Chem. Commun. 1996, 241.
13. Rowan, A. E.; Elemans, J. A. A. W.; Nolte, R. J. M. Acc. Chem. Res. 1999, 32, 995.
14. Creaven, B. S.; Gallagher, J. F.; McDonagh, J. P.; McGinley, J.; Murray, B. A.;
Whelan, G. S. Tetrahedron 2004, 60, 137.
References and notes
15. Rahimizadeh, M.; Rezaei-Seresht, E.; Bakavoli, M.; Pordel, M. Can. J. Chem. 2007,
85, 964.
16. A mixture of Merrifield resin (10 g), compound 4 (3.52 g, 6.64 mmol), and
pyridine (2.2 mL) in DMF (70 mL) was heated at 60 °C for 7 d. After cooling, the
brown solid was filtered and washed sequentially with DMF (50 mL), H2O
(50 mL), MeOH (50 mL), and CH2Cl2 (50 mL), and finally dried in voccuo.
1. Tian, R. J.; Xu, S. Y.; Lei, X. Y.; Jin, W. H.; Ye, M. L.; Zou, H. F. Trends Anal. Chem.
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5. Bertucci, C.; Domenici, E. Curr. Med. Chem. 2002, 9, 1463.