Molecular recognition of carbohydrates by zinc porphyrins: Lewis acid/Lewis base combinations as a dominant factor for their selectivity

Article abstract of DOI:10.1021/ja9713183

A systematic study of the binding of carbohydrates by functionalized zinc porphyrins indicated that [5,15-bis(8-quinolyl)porphyrinato]zinc(II) (1) showed marked affinity for octyl glucoside and mannoside in CHCl₃ (-ΔG°= 4.5-6.3 kcal mol^-1<

Full text of DOI:10.1021/ja9713183

J. Am. Chem. Soc. 1997, 119, 8991-9001
8991
Molecular Recognition of Carbohydrates by Zinc Porphyrins:
Lewis Acid/Lewis Base Combinations as a Dominant Factor for
Their Selectivity
Tadashi Mizutani,* Takuya Kurahashi, Takeshi Murakami,
Noriyoshi Matsumi, and Hisanobu Ogoshi*
Contribution from the Department of Synthetic Chemistry and Biological Chemistry,
Graduate School of Engineering, Kyoto UniVersity, Sakyo-ku, Kyoto 606-01, Japan
ReceiVed April 25, 1997. ReVised Manuscript ReceiVed July 8, 1997X
Abstract: A systematic study of the binding of carbohydrates by functionalized zinc porphyrins indicated that [5,
15-bis(8-quinolyl)porphyrinato]zinc(II) (1) showed marked affinity for octyl glucoside and mannoside in CHCl3
(-∆G° ) 4.5-6.3 kcal mol-1). Analysis of the complexation-induced shifts of the carbohydrate OH protons in the
1H NMR revealed that receptor 1 bound the 4-OH group of mannoside and glucoside by coordination to the zinc and
the 6-OH and 3-OH groups by hydrogen bonding to the quinolyl nitrogen atoms. These NMR results and comparison
of binding affinity with reference receptors and ligands indicated that receptor 1 recognized the trans,trans-1,2-
dihydroxy-3-(hydroxymethyl) moiety of carbohydrates by the combination of Lewis acid (zinc) and Lewis bases
(quinolyl nitrogens). Poor affinities of 1 to octyl galactosides and octyl 2-O-methyl-R-mannoside were ascribed to
neighboring group effects, where a neighboring group in ligands not directly involved in the receptor-ligand
interactions had considerable influence on the affinity through destabilizing the hydrogen-bonding-network(s) in the
receptor-ligand complex. The circular dichroism induced in the porphyrin Soret band by complexation with the
carbohydrates displayed characteristic patterns, which parallel the patterns of the complexation-induced shifts in the
1H NMR. The CD patterns sensitively reflected the receptor-ligand interaction modes, particularly ligand orientation
and fluctuation in the complex. Variable-temperature CD revealed that glucoside was fluctuating on 1 while mannoside
was rigidly fixed on 1 at room temperature. Addition of alcohols to CHCl3 suppressed the binding by 1, while
addition of polar additives such as water, alcohols, phenols, and ethers assisted the binding by 3 and 4 (-∆∆G° )
0.2-0.4 kcal mol-1) in a low concentration range (0-1.5 mol %).
Among a number of carbohydrates, glucose, galactose,
mannose, fucose, N-acetylglucosamine, N-acetylgalactosamine,
and sialic acids are known to play key roles in the cell
recognition. Precise molecular recognition of these carbohy-
drates by a synthetic receptor is a challenging goal in artificial
receptor chemistry. Considerable efforts have been done to
construct model receptors of sugars, including resorcinolalde-
hyde cyclotetramer,1 tetrahydroxycholaphane,2 C3 macrocyclic
receptor,3 boronic-acid-based receptors,4 polyaza cleft,5 ami-
nocyclodextrins,6 phosphonates,7 capped porphyrin,8 glyco-
phane,9 and polypyridine macrocycle.10 These studies focused
on diverse aspects of carbohydrate recognition such as diaste-
reoselectivity, enantioselectivity, binding in polar solvents, and
facile detection of the binding events, particularly by taking
advantage of the chirality of carbohydrates. Owing to the
structural similarity of carbohydrates and their highly polar
nature, we are still far from the goal, particularly specific
carbohydrate recognition in water via noncovalent interactions.
Another important aspect of carbohydrate recognition chemistry
is that carbohydrates are poor substrates for spectroscopic
investigations. Therefore, it is desired to develop a sensitive
spectroscopic method to probe the carbohydrate binding.
The X-ray crystallographic structure of the mannose-binding
protein-mannose complex showed that calcium and carboxyl-
ates of the amino acid side chains form hydrogen-bonding-
networks with mannose.11 To mimic such hydrogen-bonding-
networks, we designed receptors bearing two hydrogen-bonding
sites and one Lewis acid site fixed on porphyrins.12 We aim to
address the following two issues: (1) the structural motif of
receptors required for carbohydrate recognition and structural
features of carbohydrates to be recognized by the receptors and
(2) roles of polar additives in energetics and selectivity of
carbohydrate recognition, based on the comparative studies of
binding affinity, 1H NMR, and induced circular dichroism
studies of the relative orientation of ligands in the receptor-
ligand complexes.
X Abstract published in AdVance ACS Abstracts, September 15, 1997.
(1) (a) Aoyama, Y.; Tanaka, Y.; Sugahara, S. J. Am. Chem. Soc. 1989,
111, 5397. (b) Kurihara, K.; Ohto, K.; Tanaka, Y.; Aoyama, Y.; Kunitake,
T. J. Am. Chem. Soc. 1991, 113, 444.
(2) Bhattarai, K. M.; Bonar-Law, R. P.; Davis, A. P.; Murray, B. A. J.
Chem. Soc., Chem. Commun. 1992, 752.
(3) Liu, R.; Still, W. C. Tetrahedron Lett. 1993, 34, 2573.
(4) (a) Murakami, H.; Nagasaki, T.; Hamachi, I.; Shinkai, S. Tetrahedron
Lett. 1993, 34, 6273. (b) James, T. D.; Sandanayake, K. R. A. S.; Shinkai,
S. Nature 1995, 374, 345. (c) James, T. D.; Sandanayake, K. R. A. S.;
Iguchi, R.; Shinkai, S. J. Am. Chem. Soc. 1995, 117, 8982. (d) Takeuchi,
M.; Imada, T.; Shinkai, S. J. Am. Chem. Soc. 1996, 118, 10658.
(5) Huang, C.-Y.; Cabell, L. A.; Anslyn, E. V. J. Am. Chem. Soc. 1994,
116, 2778.
(6) Eliseev, A. V.; Schneider, H.-J. J. Am. Chem. Soc. 1994, 116, 6081.
(7) Das, G.; Hamilton, A. D. J. Am. Chem. Soc. 1994, 116, 11139.
(8) Bonar-Law, R. P.; Sanders, J. K. M. J. Am. Chem. Soc. 1995, 117,
259.
Results
Five zinc porphyrins were prepared, and their affinities for
carbohydrate derivatives were investigated. Receptor 1 has two
(11) Weis, W. I.; Drickamer, K.; Hendrickson, W. A. Nature 1992, 360,
(9) Jimenez-Barbero, J.; Junquera, E.; Martin-Pastor, M.; Sharma, S.;
Vicent, C.; Penades, S. J. Am. Chem. Soc. 1995, 117, 11198.
(10) Inouye, M.; Miyake, T.; Furusyo, M.; Nakazumi, H. J. Am. Chem.
Soc. 1995, 117, 12416.
127.
(12) For preliminary accounts of this work, see: Mizutani, T.; Murakami,
T.; Matsumi, N.; Kurahashi, T.; Ogoshi, H. J. Chem. Soc., Chem. Commun.
1995, 1257.
S0002-7863(97)01318-8 CCC: $14.00 © 1997 American Chemical Society

8992 J. Am. Chem. Soc., Vol. 119, No. 38, 1997
Mizutani et al.
Table 1. Binding Constants (K) and Free Energy Changes (∆G°) of Receptor-Carbohydrate Complex Formation in Chloroform at 15 °Ca
K/M-1 (-∆G°/(kcal mol-1))
ligand
receptor 1
receptor 2
receptor 3
receptor 4
receptor 5
R-Glc
7 570 (5.11)
41 400 (6.09)
1 870 (4.31)
3 840 (4.73)
15 500 (5.52)
61 700 (6.31)
380 (3.40)
2 530 (4.49)
6 360 (5.01)
1 030 (3.97)
1 620 (4.23)
8 220 (5.16)
23 300 (5.76)
250 (3.16)
2060 (4.37)
b
320 (3.30)
570 (3.63)
650 (3.70)
690 (3.74)
810 (3.83)
250 (3.16)
400 (3.43)
530 (3.59)
600 (3.66)
3 670 (4.70)
2 090 (4.38)
2 240 (4.42)
1 710 (4.26)
3 860 (4.73)
2 970 (4.58)
2 550 (4.49)
b
<10 (<1.3)
440 (3.49)
14 (1.51)
<10 (<1.3)
695 (3.75)
78 (2.49)
b
â-Glc
R-Gal
â-Gal
R-Man
â-Man
2-O-Me-R-Man
6-O-Ac-â-Glc
6-O-Bz-â-Glc
6800 (5.05)
7300 (5.09)
b
b
b
a Standard deviations in K are about 5-10%. b Not determined.
Table 2. Binding Constants (K) and Free Energy Changes (∆G°)
for Complexation of Porphyrin Receptors 1 (or 3) with Reference
Ligands in Chloroform at 15 °Ca
quinolyl groups fixed at the 5- and 15-positions of porphyrin
with a cis configuration, receptor 3 has two 2-hydroxynaphthyl
groups with a cis configuration, and receptor 4 has two 2,7-
dihydroxynaphthyl groups with a trans configuration. All these
K/M-1 (-∆G°/(kcal mol-1))
ligand
receptor 1
receptor 3
6
7
8
3 (0.63)
3 (0.63)
5 (0.92)
3 (0.63)
19 (1.68)
17 (1.62)
5 (0.92)
9
7 (1.11)
10
11
12
13
210 (3.05)
60 (2.32)
2600 (4.50)
560 (3.62)
140 (2.80)
43 (2.15)
320 (3.29)
88 (2.56)
a In amylene-containing CHCl3. [1] ) 5.4 × 10-6 to 7.4 × 10-6 M,
[3] ) 4.6 × 10-6 to 5.8 × 10-6 M, [6-9] ) 0-3.4 × 10-1 M, [10-
13] ) 0-9.6 × 10-3 M.
Among the receptors investigated, receptor 1 showed the highest
affinity for the ligands, especially for â-Man and â-Glc. A
porphyrins have one Lewis acid site and two hydrogen-bonding
sites arranged in a similar manner to form a recognition pocket
above the porphyrin plane. Receptor 2 is the trans isomer of
receptor 1, serving one Lewis acid site and one hydrogen-
bonding site for carbohydrate binding. Receptor 5, ZnTPP (TPP
) 5,10,15,20-tetraphenylporphyrinato anion), has only one
Lewis acid site. Receptor 2 and receptor 5 were used in control
experiments to reveal the influence of the quinolyl hydrogen-
bonding sites.
We used chloroform as a solvent for the binding studies to
mimic the relatively nonpolar environment of the binding pocket
of sugar-binding proteins. The effects of polar additives were
examined by adding them to the chloroform. To solubilize the
carbohydrates in organic solvents, we prepared octyl pyranosides
according to reported procedures. Four octyl glycopyranosides,
namely, R- and â-octyl galactopyranoside (R- and â-Gal), R-
and â-octyl mannopyranoside (R- and â-Man) thus prepared
and two commercially available octyl pyranosides, R- and
â-octyl glucopyranoside (R- and â-Glc), were used as ligands.
As reference ligands, octyl 2-O-R-D-methylmannopyranoside (2-
O-Me-R-Man), octyl 6-O-â-D-acetylglucopyranoside (6-O-Ac-
â-Glc), and octyl 6-O-â-D-benzoylglucopyranoside (6-O-Bz-â-
Glc) were prepared.
similar trend was found for the affinity of 2, even though the
affinity was reduced for all of the ligands compared to that of
1. Binding by receptor 4 was moderate, and that by receptor 3
was weak. Comparison of the binding constants of R-Man with
those of 2-O-Me-R-Man indicated that the 2-O-methyl group
of 2-O-Me-R-Man markedly inhibited the binding by receptors
1 and 2 while it hardly influenced that by receptors 3 and 4.
1H NMR Study of Binding. The complexation-induced
shifts (CIS) of the 1-H, 2-OH, 3-OH, 4-OH, and 6-OH
resonances of R- and â-anomers of Glc, Man, and Gal were
determined in CDCl3 in the low-concentration range of receptor
1. The assignments of the resonances of the four hydroxy
Binding Constants Determinations by UV-Vis Titration.
The binding constants were determined by UV-vis titration,
in which the absorbance changes in the Soret band owing to
the increased ligand concentration were monitored and analyzed
by least-squares curve fitting, assuming a 1:1 complex forma-
tion. In all cases, the Soret peak maxima were red-shifted by
ca. 5 nm, and the difference spectra showed isosbestic points.
The curve fitting to 1:1 complexation was satisfactory (standard
deviations for the binding constants were ca. 5%).
1
protons were made on the basis of H-1H COSY or PDQF
experiments. The observed chemical shifts were the average
values of the free and the complexed ligand in the limit of fast
1
chemical exchange. Figure 1 shows the H NMR spectra of
â-Man in the presence of varying amounts of receptor 1 in
CDCl3. Upon addition of 1, the resonance for the 6-OH proton
moved downfield and those for the 1-H, 3-OH, and 4-OH
protons moved upfield. The signal for the 2-OH proton was
hardly influenced at all upon complexation. The spectral
changes in the resonances of the â-Glc protons were similar to
The binding constants of octyl pyranosides and those of the
reference ligands 6-13 are listed in Tables 1 and 2, respectively.

Molecular Recognition of Carbohydrates
J. Am. Chem. Soc., Vol. 119, No. 38, 1997 8993
Table 4. 1H NMR Complexation-Induced Shifts (CIS, ∆δ/ppm) of
R-Man, R-Glc, and R-Gal upon Addition of 1 in CDCl3 at 25 °Ca
∆δ/ppm (δ of free ligand/ppm)
R-Man
R-Glc
R-Gal
1-H
-1.6 (4.83)
+0.9 (2.20)
-1.8 (2.40)
-2.4 (2.36)
+1.4 (1.99)
-1.5 (4.85)
+0.3 (1.96)
-2.2 (2.52)
-2.0 (2.44)
+0.4 (1.88)
-2.2 (4.94)
+0.6 (1.88)
-3.4 (2.52)
-1.7 (2.79)
+0.5 (2.20)
2-OH
3-OH
4-OH
6-OH
a Extrapolated to 100% complex from the CIS values at 0-25%
complexation. Signal assignments were made on the basis of the 1H-
1H COSY or PDQF experiments.
Table 5. 1H NMR Complexation-Induced Shifts (CIS, ∆δ/ppm) of
â-Man, â-Glc, and â-Gal upon Addition of 2 in CDCl3 at 25 °Ca
∆δ/ppm (δ of free ligand/ppm)
â-Man
â-Glc
â-Gal
1-H
-1.0 (4.53)
-0.3 (2.38)
-0.3 (2.47)
-2.0 (2.42)
+0.3 (2.03)
-1.2 (4.29)
-0.4 (2.36)
-1.4 (2.60)
-2.2 (2.48)
+0.2 (1.95)
-1.5 (4.24)
-1.3 (2.35)
-0.8 (2.58)
-0.6 (2.75)
+0.1 (2.06)
2-OH
3-OH
4-OH
6-OH
a Extrapolated to 100% complex from the CIS values at 0-25%
1
complexation. Signal assignments were made on the basis of H-1H
COSY experiments.
receptor was complexed and the values of ∆ꢀ were corrected
for the fractions of complexed porphyrin receptors. The ICD
patterns induced in 1-3 by R-anomers were similar to those
by â-anomers for Glc, Man, and Gal. The signal intensities of
the ICD of 1 decrease in the order, Man . Gal ≈ Glc. High
affinity for Glc and the very small Cotton effects induced by it
are indications that the intensity of Cotton effects is not related
to the binding affinity. The different ICD between Man and
Glc indicates that the stereochemistry at C-2 carbon has
significant effects on the ICD. In order to further investigate
the effects of substituents at C-2 on the ICD, the CD spectrum
of the 2-O-Me-R-Man was recorded. Interestingly, the Cotton
effects were nearly diminished (|∆ꢀ| < 5). Although receptors
3 and 4 showed weak affinity for the ligand, some complexes
showed Cotton effects with comparable intensity to those of
the 1-Man complex. For instance, the receptor 3-Glc complex
showed distinct Cotton effects even though the binding was
weak.
The CD spectra were also recorded for some of the complexes
at low temperatures, to -60 °C, in CHCl3. The Cotton effects
for both the receptor 1-R-Man complex and the receptor 1-R-
Glc complex were increased with lower temperatures. The CD
spectra for these complexes are shown in Figure 3. The 1-R-
Glc complex exhibited biphasic Cotton effects at -60 °C similar
to those of the 1-R-Man complex. The 1-â-Glc complex also
exhibited similar biphasic ICD at -60 °C (data not shown).
Both the 1-R-Gal complex and the 1-â-Gal complex showed
biphasic Cotton effects at -60 °C with an opposite sign
(negative Cotton effects at 414 nm and positive Cotton effects
at 421 nm).
1
Figure 1. The H NMR spectra of CDCl3 solutions of â-Man in the
presence of receptor 1 at 25 °C. (a) 0%, (b) 0.4%, (c) 2.5%, (d) 4.7%,
(e) 6.8%, and (f) 8.9% of â-Man was complexed with receptor 1.
Table 3. 1H NMR Complexation-Induced Shifts (CIS, ∆δ/ppm) of
â-Man, â-Glc, and â-Gal upon Addition of 1 in CDCl3 at 25 °Ca
∆δ/ppm (δ of free ligand/ppm)
â-Man
â-Glc
â-Gal
1-H
-2.1 (4.53)
0.0 (2.38)
-0.3 (2.50)
-2.7 (2.45)
+1.6 (2.06)
-1.8 (4.29)
-0.1 (2.38)
-1.5 (2.63)
-2.2 (2.52)
+1.2 (1.97)
-3.8 (4.25)
-0.9 (2.37)
-2.6 (2.60)
-0.5 (2.76)
-0.5 (2.08)
2-OH
3-OH
4-OH
6-OH
a Extrapolated to 100% complex from the CIS values at 0-25%
complexation. Signal assignments were made on the basis of the 1H-
1H COSY or PDQF experiments.
those of the â-Man protons. For â-Gal, the resonances
associated with all these protons were shifted upfield. The
values of CIS were linearly increased as the fraction of the ligand
complexed with the receptor was increased, and the CIS values
for the complex are determined by extrapolation to 100%
complexation and listed in Tables 3 and 4. Similarly, the values
of CIS of â-Glc, â-Man, and â-Gal by receptor 2 were
determined and are listed in Table 5.
Induced Circular Dichroism (ICD) Study of Binding.
Induced circular dichroism was observed in the Soret band of
porphyrin receptors for some combinations of receptors and
ligands. In Figure 2, the CD spectra of the 1-â-Man complex
and the 1-â-Glc complex are shown. Although both â-Glc
and â-Man were strongly bound to receptor 1, the two ICD
spectra were quite different. The 1-â-Man complex showed
biphasic Cotton effects (Figure 2a) while the 1-â-Glc complex
showed very weak Cotton effects (Figure 2b). Table 6
summarizes the values of ∆ꢀ for each complex, where the CD
spectra were recorded under the conditions that 30-95% of the
Solvent Effects on the Binding. Sanders et al.8 reported
that the addition of water and methanol to the chloroform
solution assists the binding of carbohydrate derivatives by the
capped zinc porphyrin. We also examined the effects of polar
additives on the binding of carbohydrates. The free energy
changes of binding of â-Glc, -∆G°, are plotted against the mole
fractions of added alcohols in Figures 4 and 5. For receptor 1,
the binding was simply inhibited as the concentration of alcohols
in CHCl3 was higher. On the other hand, for receptor 4, the
values of -∆G° increased in the range of the low alcohol

8994 J. Am. Chem. Soc., Vol. 119, No. 38, 1997
Mizutani et al.
Figure 2. Circular dichroism induced in receptor 1 by (a) â-Man and
(b) â-Glc in CHCl3 at 15 °C. [1] ) 6.51 × 10-6 M, [â-Man] ) 5.36
× 10-3 M, [â-Glc] ) 1.22 × 10-2 M.
Figure 3. Circular dichroism induced in receptor 1 by (a) R-Man and
(b) R-Glc at 10, -40, and -60 °C in CHCl3. (a) [1] ) 5.21 × 10-6 M,
[R-Man] ) 6.31 × 10-3 M, (b) [1] ) 5.21 × 10-6 M, [R-Glc] ) 1.87
× 10-3 M.
Table 6. Differential Dichroic Absorption (∆ꢀ) of
Receptor-Carbohydrate Complexes in Chloroform at 15 °C
concentration range. Other phenols showed moderate effects.
In contrast, addition of pyridine simply suppressed the binding.
The effects of added alcohols on the induced CD of the
receptor-ligand complexes were examined. For most of the
complexes examined, effects of the additives on the ICD were
too small to observe. In the complex between 3 and â-Glc,
however, the values of |∆ꢀ| at 427 nm distinctly increased with
increasing the tert-butyl alcohol concentrations up to 7 mol %:
∆ꢀ, cm-1 M-1(tBuOH, mol %) -10 (0), -15 (0.75), -21 (2.2),
-25 (7.1) at 427 nm. Since the binding constants were
decreased beyond 1.5 mol % of tert-butyl alcohol, the signal
intensity of ICD was increased in the concentration range where
the binding constants were decreasing. These results indicate
that tert-butyl alcohol did interact with the receptor-ligand
complex and altered the interaction modes to some extent.
∆ꢀ/(cm-1 M-1), (wavelength/nm)
receptor
receptor
receptor
receptor receptor
ligand
R-Glc
1
2
3
4
5b
a
a
-8 (423) 18 (418) 18 (418)
-18 (428) -9 (433)
a
â-Glc
-8 (425) 20 (420)
5 (420)
a
-10 (430) -3 (435)
R-Gal
â-Gal
R-Man
a
a
a
a
a
a
11 (420)
-5 (420)
a
a
a
22 (420)
6 (416) 18 (418) -13 (428)
-26 (426) -13 (427) -24 (438)
â-Man
18 (422)
7 (416) 17 (418) -5 (420)
a
-6 (432) -6 (427) -12 (436)
2-O-Me-R-Man
a
a
-10 (410) -19 (417)
13 (421)
|∆ꢀ| < 5 in 400-450 nm. b ZnTPP.
a
concentration and decreased upon further addition of alcohol.
In Figure 6, the similar plots are shown for complexation of
â-Glc to 3 for the various additives such as water, phenol,
p-nitrophenol, p-methoxyphenol, p-dimethoxybenzene, and py-
ridine. Water showed very distinct effects: the binding constant
increased rapidly in the low concentration range of water until
the chloroform became saturated. p-Dimethoxybenzene and
p-methoxyphenol also showed distinct effects in the low-
Discussion
Receptor Design. Receptors 1, 3, and 4 all have three
interaction sites for carbohydrates, one Lewis acid site (Zn) in
common, and two hydrogen-bonding sites, namely, hydrogen
acceptors (N) in 1 and hydrogen donors (OH) in 3 and 4. We
reported previously that 3 and 4 selectively bound amino acid
esters with a polar side chain, dimethyl aspartate, and dimethyl

Molecular Recognition of Carbohydrates
J. Am. Chem. Soc., Vol. 119, No. 38, 1997 8995
Figure 6. Plot of the free energy changes for complexation between
receptor 3 and â-Glc in CHCl3 at 15 °C (-∆G°) against concentrations
of water, phenol, p-nitrophenol, p-methoxyphenol, p-dimethoxybenzene,
and pyridine.
Figure 4. Plot of the free energy changes for complexation between
receptor 1 and â-Glc in CHCl3 at 15 °C (-∆G°) against alcohol
concentrations.
receptor 1. Receptor 2, the trans isomer of 1, showed a similar
pattern of binding affinity but weaker in magnitude. Therefore,
the two quinolyl groups with the cis configuration in 1
cooperatively assisted the binding of the ligands. When the
zinc of receptor 1 was replaced with two protons, the free base
of 1 showed much reduced affinity for carbohydrates. For
instance, the binding constant for â-Glc was ca. 600 M-1 14
.
This confirms the important role of the zinc. Both the Lewis
acid site and the Lewis base sites are needed to bind carbohy-
drates strongly.
Carbohydrate Selectivity of Receptors 1 and 2. Receptor
1 showed high affinity for both mannosides and glucosides
rather than galactosides. The stereochemical arrangement of
C-5, C-4, and C-3 of Glc is the same as that of Man, and this
arrangement was particularly well recognized by receptor 1. Gal,
the epimer of Glc at C4, was weakly bound, indicating that the
stereochemistry at C4 was crucial. In contrast, the stereochem-
istry at C2 was less important. For the stereochemistry at C1,
â-anomers were bound more strongly to receptor 1 than the
corresponding R-anomers of Man, Glc, and Gal. The trend of
these affinities suggests that, in the 1-Man complex and the
1-Glc complex, the 4-OH group was directly involved in the
receptor-ligand interaction, while the 2-OH group was not.
As simpler analogs of carbohydrates, the affinities for
cyclohexanediols 10-13 were determined (Table 2). Compari-
son between the binding constant of 10 and that of 11 indicates
that the trans vicinal dihydroxy configuration was favored over
the cis configuration by receptor 1. Similarly, comparison of
the binding constant between 12 and 13 indicates that the trans
vicinal hydroxy hydroxymethyl configuration was favored over
the cis configuration.
Figure 5. Plot of the free energy changes for complexation between
receptor 4 and â-Glc in CHCl3 at 15 °C (-∆G°) against alcohol
concentrations.
glutamate.13 For carbohydrates, however, receptors 1 and 2
showed better affinity and selectivity than 3 and 4, showing
the importance of the hydrogen acceptor/donor combinations
for carbohydrate recognition. The Lewis base/Lewis acid/Lewis
base combination in 1 formed a better binding site than the
Lewis acid/Lewis acid/Lewis acid combination in 3 and 4. For
comparison of selectivity, the differences in -∆G° between the
most strongly bound pyranoside ligand and the most weakly
bound ligand are 2.9 kcal/mol for 1, 0.6 kcal/mol for 3, and 0.4
kcal/mol for 4, confirming that the selectivity is highest for
NMR Study for Determination of Interacting Hydroxy
Groups. Since receptor 1 has three interaction sites while the
pyranoside ligands have four OH groups, it is important to
determine which OH groups directly interact with the receptor.
The 1H NMR chemical shift displacements for carbohydrate OH
(13) Mizutani, T.; Murakami, T.; Kurahashi, T.; Ogoshi, H. J. Org. Chem.
1996, 61, 539.
(14) Owing to the small changes in absorbance in visible spectra, the
precise determination of binding constants was difficult.

8996 J. Am. Chem. Soc., Vol. 119, No. 38, 1997
Mizutani et al.
and the magnitude of CIS of the 4-OH resonance. The axial
4-OH in Gal should make the hydrogen-bonding-network shown
in Figure 7 unfeasible. The upfield shift of the 6-OH group of
galactose indicates that there was no strong hydrogen bonding
between the 6-OH group and the quinolyl nitrogen in the
complex. Among the OH protons of Gal, the greatest upfield
shift was observed for the resonance of the 3-OH proton, rather
than that of the 4-OH proton. This suggests that the 3-OH group
was coordinated to the Zn.
Comparison of binding affinities to reference ligands 10-13
indicates that trans-1,2-dihydroxy moiety was favored over the
cis moiety, and trans-1,2-(hydroxymethyl)hydroxy moiety
favored over the cis moiety. The high affinity to Man and Glc
with the 4-OH coordination to the zinc of receptor 1 and the
low affinity to Gal with the 3-OH coordination to the zinc are
thus consistent with the affinity of 1 to the reference ligands.
Figure 7. Schematic representation of hydrogen-bonding-networks of
the receptor 1-Man complex based on the H NMR CIS values.
1
protons induced by complexation with porphyrin receptors were
found to provide valuable information. Two opposing aniso-
tropic effects should be taken into account to interpret the CIS
values of ligand upon complexation with porphyrin receptors:
an upfield shift due to the ring current of porphyrin when the
ligand proton is located above the porphyrin plane in the center
and a downfield shift of the OH protons upon hydrogen bonding.
Effects of the ring current of quinolyl groups were estimated to
be small except for the hydrogen-bonding protons to the quinolyl
nitrogen, based on the isoshielding map.15
Table 3 indicates that Man and Glc show similar patterns of
the sign of the CIS values, while Gal shows a different trend.
The resonance for the 6-OH proton was shifted downfield, and
that for the 4-OH proton was shifted upfield for both Man and
Glc. These CIS values indicate that it is indeed the 4-OH group
that is coordinated to the zinc and the 6-OH group that is
hydrogen bonded to the quinolyl nitrogen (see Figure 7). In
this hydrogen-bonding-network, an alternating charge arrange-
ment, Zn(δ+)-4O(δ-)-4-O-H(δ+)-6O(δ-)-6-O-H(δ+)-
N(δ-), is achieved, which, we suggest, particularly stabilizes
the 1-Man complex and the 1-Glc complex. The X-ray
crystallographic study of Ca2+-dependent lectin showed that
mannoside was bound via a hydrogen-bonding-network involv-
ing calcium, glutamate, and aspartate.16 The binding mode of
receptor 1 toward mannoside was thus similar, zinc in place of
calcium and quinolyl groups in place of carboxylates.
If the receptor 1-Man (Glc) complexes adopt this bidentate
binding mode, then the 3-OH group is located close to the other
quinolyl nitrogen and can form a hydrogen bond to it. For Man,
the 2-OH group can assist the intermolecular hydrogen bonding
between the 3-OH group and the quinolyl nitrogen by the
intramolecular hydrogen bonding to the 3-OH group as shown
in Figure 7. Anslyn et al.5 demonstrated the importance of
intramolecular hydrogen bonding in polyols recognition and
pointed out that cis-cyclohexanediol forms stronger intramo-
lecular hydrogen bonding than the trans diol. Therefore, the
intramolecular hydrogen bonding between the 2-OH group and
the 3-OH group of Man should be stronger than that of Glc.
The resonance for the 3-OH proton of Man appeared downfield
from that of Glc in the complex (Table 3). This is consistent
with the intramolecular hydrogen-bonding-network shown in
Figure 7, because the stronger hydrogen bonding between the
3-OH group of Man and the quinolyl nitrogen should cause
greater downfield shift of this proton than the 3-OH proton of
Glc. The CD spectroscopic studies at low temperatures also
support the above discussion as described later in this paper.
The higher affinity for Man than Glc can also be accounted for
by this intramolecular hydrogen bonding.
Receptor 2, the trans isomer of 1, also showed characteristic
CIS patterns. For both â-Man and â-Glc, the greatest upfield
shifts were observed for the 4-OH resonances, thus suggesting
that the 4-OH group was coordinated to the Zn. The difference
in the CIS patterns of 2 from those of receptor 1 was that the
downfield shifts of the 6-OH resonance were almost diminished
and the shifts of the 2-OH resonance and of the 3-OH resonance
remained unchanged. Thus, the quinolyl nitrogen of 2 chose
the 3-OH group rather than the 6-OH group of Man and Glc as
a hydrogen-bond donor.
Lewis Acid/Lewis Base Arrangements in Receptors and
Ligands and Neighboring Group Participation. The binding
constants of 2-O-Me-R-Man for receptor 1 and receptor 2 were
reduced by a factor of 30-40 compared to R-Man. The
alkylation of the 2-OH group not directly involved in the
hydrogen-bonding interaction between receptor 1 and Man
dramatically suppressed the binding. One can explain, however,
this trend by assuming that the methoxy group prevents the
original intramolecular hydrogen donation from the 2-OH group
to the 3-OH group, and rather, the lone-pair electrons of the
2-methoxy group have repulsive interaction with the developing
negative charge on the 3-OH group upon hydrogen bonding to
the quinolyl nitrogen. For receptors 3 and 4, which have acidic
OH groups in place of basic quinolyl nitrogen, the binding of
2-O-Me-R-Man was reduced only by a factor of at most 2
compared with that of R-Man. This different behavior of
receptor 3 and receptor 4 also supports the above mechanism,
that is, for receptor 1, the combination of basic nitrogen and
the 2-methoxy group adjacent to the hydrogen-bonding hydroxy
group leads to significant destabilization of the complex.
A similar explanation is possible for the low affinity of 1 to
1
galactosides. The H NMR study showed that 1 recognized
the trans vicinal hydroxy groups of Gal, i.e., the 2-OH and 3-OH
groups, by binding the 3-OH group via the zinc and the 2-OH
group via the quinolyl nitrogen. The 1-octyloxy group then
comes next to the hydrogen-bonding 2-OH group. The repul-
sion between this alkoxy group and the 2-OH group hydrogen
bonded to the quinolyl nitrogen would lead to the low affinity
for galactosides. These neighboring group effects are sum-
marized in Figure 8. The OH group R to the hydrogen-donating
OH group assists the binding by neutralizing the negative charge
on the oxygen upon hydrogen bonding, while the alkoxy group
at the same position inhibits it by destroying the hydrogen-
bonding-network.
The CIS patterns for Gal were different from those of Man
and Glc with respect to the signs of CIS of the 6-OH resonance
The upfield shift of the 2-OH proton of â-Gal upon addition
of 2 indicated that the 2-OH group was coordinated to the Zn.
The 2-OH coordination of â-Gal rather than the 3-OH coordina-
tion can be ascribed to the neighboring group inhibition shown
in Figure 8, where the 3-OH coordination would lead to the
(15) Johnson, C. E. J.; Bovey, F. A. J. Chem. Phys. 1958, 29, 1012.
(16) Weis, W. I.; Drickamer, K.; Hendrickson, W. A. Nature 1992, 360,
127.

Molecular Recognition of Carbohydrates
J. Am. Chem. Soc., Vol. 119, No. 38, 1997 8997
Figure 8. Common structural motif of Man, Gal, and 2-O-Me-R-Man
interacting receptors 1 and 2. Left: neighboring OH group assists the
binding by neutralizing the negative charge on the oxygen of the OH
group hydrogen bonded to the quinolyl nitrogen. Right: neighboring
alkoxy group inhibits the binding by the negative charge repulsion
between the lone pair electrons of the alkoxy group and the hydrogen-
bonding OH group.
unfavorable geometry. These results suggest that Lewis acid/
Lewis base combinations of receptors and ligands involving both
directly interacting substituents and their neighboring substit-
uents are important for the binding selectivity.
Figure 9. Directions of the C-O bonds and the O-H bonds of the
3-OH, 4-OH, and 6-OH groups for the receptor 1-â-Man complex.
The geometry is based on the PM3 calculations where Zn of receptor
1 is replaced by Al and the ethyl groups are by hydrogen. In the figure,
hydrogens are omitted for clarity except for the OH protons. C1 and
O5 of the ligand are also omitted.
Comparison of Induced Circular Dichroism in Porphyrin
Soret Band by Carbohydrates with That by Amino Acid
Esters. We have reported that chiral amino acid esters induced
characteristic biphasic CD in the Soret band of porphyrin
receptor upon ditopic binding.17 L-Amino acid esters consis-
tently induced biphasic CD in the Soret band with positive
Cotton effects at higher energy and negative Cotton effects at
lower energy. We also pointed out the importance of the
carbonyl chromophore in the induced CD.18 The relative
orientation of the carbonyl group to porphyrin was suggested
to determine the ICD pattern. In contrast to amino acid esters,
carbohydrates have five chiral carbons; thus, diverse patterns
of ICD are expected. We found that the patterns of the ICD
again sensitively reflect receptor-ligand binding modes. The
magnitudes of Cotton effects for carbohydrate complexes were
comparable or weaker than those for amino acid ester com-
plexes: the values of |∆ꢀ| of the ICD for the complexes between
receptors 1-5 and carbohydrates were 0-26 cm-1 M-1, while
those for the complexes between trans isomer of 3, [trans-5,
15-bis(2-hydroxy-1-naphthyl)porphyrinato]zinc, and amino acid
fixation of the ligand in a similar fashion (4-HO‚‚‚Zn and
3-OH‚‚‚N) would determine the ICD patterns.
It is noteworthy that R-Man and â-Man induced biphasic CD
in 1, while R-Glc and â-Glc induced very weak CD at 15 °C,
although both carbohydrates were bound strongly to 1. Thus,
the stereochemistry at the C2 position had significant influence
on the induced CD pattern and intensity. The 1H NMR studies
revealed that the 2-OH group of Man and Glc was not involved
in the direct hydrogen bonding with receptors 1 and 2. We
can ascribe the different ICD between Man and Glc to the
following two mechanisms: (1) the coupling of the local wave
function of the 2-OH group with that of porphyrin causes the
different ICD and (2) the 2-OH group indirectly affects the
binding mode to lead to the different ICD. One important
observation for the mechanism of induced CD is that the
receptor 1-R-Glc complex showed only weak Cotton effects
at 15 °C but distinct biphasic Cotton effects at -60 °C (Figure
3b). This ICD pattern was similar to that of the 1-Man
complex. Considering the similar 1H NMR CIS patterns
between the 1-Man complex and the 1-Glc complex, one can
ascribe the weak ICD for the receptor 1-R-Glc complex at room
temperature to the thermal fluctuations. In contrast, the ICD
of the 1-Man complex was less sensitive to temperature (Figure
3a), possibly owing to the stronger 3-OH‚‚‚N hydrogen bond.
If the hydrogen-bonding-network in the receptor 1-Man
complex, as schematically depicted in Figure 7, is assumed, then
the orientation of the O-H bond and the C-O bond would be
fixed relative to the porphyrin. Any deviation of the orientation
of the transition dipole moments from the 5-15 axis and the
10-20 axis would contribute to the CD, and their sum would
lead to the observed ICD if each contribution does not cancel
each other. Figure 9 displays the geometry of the 1-Man
complex according to the molecular orbital calculations, in
which one can see that the directions of these bonds are deviated
from the axis. Although prediction of the bond directions is
beyond the precision of the calculations, the figure suggests that
the complex becomes optically active in terms of the directions
of these bonds, provided that the ligand is fixed on the porphyrin
plane.
esters were 10-65 cm-1 M-1
.
Mechanism of Induced CD. The distinct biphasic CD
induced in receptor 3 by Glc is contrasting with the weak CD
signal induced in receptor 1 by the same ligand. When the small
binding constant for receptor 3-Glc complexes is considered,
this observation evidently indicates that the ICD reflects the
interaction modes such as relative orientations of the ligand to
the receptor and the number of stable receptor-ligand configu-
rations and not the binding affinity.
As shown in Table 6, the ICD patterns of complexes with
receptor 2 were similar to those of the corresponding complexes
with receptor 1, although the magnitudes were reduced, showing
that combination of zinc and only one quinolyl nitrogen was
able to induce the observed ICD pattern, and the second quinolyl
nitrogen in 1 had only secondary effects on the ICD. This is
in accordance with the 1H NMR CIS patterns, which also
indicated that both 1 and 2 bind Glc and Man in a similar fashion
via the 4-HO‚‚‚Zn coordination and the 3-OH‚‚‚N hydrogen
bonding. Among the zinc porphyrin-amino acid ester com-
plexes, only ditopic binding (Zn‚‚‚NH2 and OH‚‚‚OdC) lead
to distinct biphasic ICD. The fact that both 1 and 2 showed
similar ICD patterns for Man and Glc indicates that ditopic
These results evidently demonstrate that ICD is the powerful
tool to probe the binding modes in the porphyrin-carbohydrate
complexes such as ligand orientation and its fluctuation in the
complex. It would be more powerful in investigation of
(17) Mizutani, T.; Ema, T.; Yoshida, T.; Kuroda, Y.; Ogoshi, H. Inorg.
Chem. 1993, 32, 2072.
(18) Mizutani, T.; Ema, T.; Yoshida, T.; Renne, T.; Ogoshi, H. Inorg.
Chem. 1994, 33, 3558.

8998 J. Am. Chem. Soc., Vol. 119, No. 38, 1997
Mizutani et al.
polysaccharide recognition, where its 1H NMR spectra are much
more complicated and less useful for probing receptor-ligand
structures.
complex to form hydrogen-bonding-network among the receptor,
the ligand, and the additive.
Conclusions. The binding affinities of a series of receptors
determined by UV-vis titration experiments indicated that, for
diastereoselective recognition of carbohydrates, the binding
pocket of receptor 1 consisting of Lewis base/Lewis acid/Lewis
base was found to be effective. The comparison of the affinity
Induced CD Probing Binding Modes. The following
examples display that the receptor-ligand interaction modes
are deduced from their ICD spectra: (1) The ICD patterns of
R-Man and 2-O-Me-R-Man were similar for 4, while they were
different for 1 and 3. Particularly, the signs of the CD induced
in receptor 3 by R-Man were reversed of that induced by 2-O-
Me-R-Man. Therefore, one can expect that the binding mode
of the 3-R-Man complex is different from that of the 3-2-O-
Me-R-Man complex. (2) It is interesting to note the differences
in ICD between R- and â-anomers: the patterns of CD induced
by the R-anomers in 1-3 were similar to those induced by the
corresponding â-anomers, while those induced by R-anomers
in 4 were different from those induced by the corresponding
â-anomers. Particularly, the opposite sign of the Cotton effects
of 4-R-Gal to that of 4-â-Gal indicates that R-Gal and â-Gal
were bound to 4 in a different fashion. Therefore, the
stereochemistry at C1 did not affect the ICD of 1-3, while it
affected the ICD of 4. Although the binding constants by 4 of
R-anomers were similar to those of â-anomers, the binding mode
was different, possibly due to the longer distance between the
zinc atom and the OH group in 4.
Effects of Polar Additives on the Binding. In the binding
pocket of lectins, water often participates in the hydrogen-
bonding-network to stabilize the sugar-receptor complex. The
role of a water molecule in the hydrophobic environment in
thermodynamics of the interaction is thus an interesting
problem.19 In our model systems, polar additives showed
different effects on the complex formation depending on whether
receptors have basic recognition sites (1) or acidic recognition
sites (3 and 4). Only inhibition of binding was observed for
receptor 1, while promoting effects of binding by water,
alcohols, phenols, and ethers were observed for receptor 3 and
receptor 4. The ICD signals of 3-â-Glc complex grew with
increasing tert-butyl alcohol concentrations, indicating that tert-
butyl alcohol did interact with the complex to stabilize it.20
To elucidate the effects of the steric factors and acidity of
the OH group of the additives on the binding constants, the
free energy changes in binding (-∆G°) in the presence of water,
methyl alcohol, tert-butyl alcohol, phenol, p-nitrophenol, p-
methoxyphenol, and p-dimethoxybenzene were compared (Fig-
ures 4-6). Both of methyl alcohol and tert-butyl alcohol
showed the promoting effects on the binding, suggesting that
steric demand was not severe. The stronger effects of p-
methoxyphenol than those of p-nitrophenol and phenol indicate
that acidity of the OH group is not the major factor for the
present effects. Distinct effects of p-methoxyphenol and
p-dimethoxybenzene strongly suggest that the ether group assists
the binding. Here again, acid/base combination seems to play
important roles. The assistance by the methoxy group of the
additives implies that, for the host with three Lewis acidic sites,
the Lewis basic methoxy group accepts hydrogen from the
1
for a series of receptors and ligands, and the H NMR and
circular dichroism study revealed that receptor 1 with this
binding pocket recognized the trans,trans-1,2-dihydroxy-3-
(hydroxymethyl) moiety of carbohydrate through the zinc site
and two quinolyl sites. Receptor 2, in which only one quinolyl
nitrogen and zinc can interact with ligands, the 1,2-trans-
dihydroxy moiety was preferentially recognized. The patterns
of induced CD parallel those of the CIS in the 1H NMR spectra,
suggesting that ICD was a facile probe to elucidate the binding
mode. Variable temperature CD study demonstrated that Glc
was fluctuating in receptor 1 at 15 °C, while Man was
comparatively fixed in the binding pocket of 1 even at 15 °C.
Low affinity of 1 for 2-O-Me-R-Man, R-Gal, and â-Gal suggests
that the neighboring alkoxy group has considerable inhibitory
effects on the binding. Addition of alcohols and ethers simply
suppressed the binding by 1, while it assisted the binding by 3
and 4. In the complex between acidic receptors (3 and 4) and
the ligands, Lewis basic ethers would assist the formation of
hydrogen-bonding-networks. The intramolecular and intermo-
lecular hydrogen-bonding-networks formed in the binding
pocket markedly affected the selectivity of binding, and their
control is the key to the design of receptor for carbohydrates.
Experimental Section
Instrumentation. 1H and 13C NMR spectra were recorded using a
JEOL A-500 spectrometer in chloroform-d and DMSO-d6, respectively.
1H NMR chemical shifts in CDCl3 were referenced to CHCl3 (7.24
ppm), and 13C NMR chemical shifts in DMSO-d6 were reported relative
to DMSO (39.5 ppm). UV-vis spectra were recorded on a Hewlett-
Packard 8452 diode array spectrometer equipped with a thermostated
cell compartment. Circular dichroism spectra were recorded on either
a JASCO J-600 or a JASCO J-720 spectropolarimeter. A cryostat
(Oxford, DN1704) was used for CD spectral measurements at low
temperatures. Mass spectra were obtained using a JEOL JMS SX-
102A mass spectrometer.
Materials. Ether and THF were distilled from sodium benzophenone
ketyl radical. Pyridine, DMF, toluene, DMSO, and CH2Cl2 were
distilled from CaH2. Benzoyl chloride was distilled from CaCl2. Acetyl
chloride was distilled from P2O5. Methanol and ethanol were dried by
refluxing with and distilling from magnesium. Octanol was distilled
from sodium. Cyclohexene was distilled just before use. Acetic acid
was dried by refluxing with acetic anhydride in the presence of 0.2%
of 2-naphthalenesulfonic acid as a catalyst and was then fractionally
distilled. Acetic anhydride was refluxed with and distilled from
magnesium. cis- and trans-(2-Hydroxymethyl)cyclohexanol were
prepared according to the reported procedure.21 Materials for spec-
troscopic studies were obtained as follows. CHCl3 containing amylenes
as a stabilizer was purchased from Aldrich (A.C.S. HPLC grade, 99.9%,
stabilized with amylenes) and was used as received. HPLC-grade water
and spectrophotometric-grade methyl alcohol were used as received.
tert-Butyl alcohol was dried by refluxing with and distilling from
sodium. p-Nitrophenol, phenol, p-methoxyphenol, and p-dimethoxy-
benzene were completely dried under reduced pressure just before use,
and their purity was checked by elemental analysis to avoid the
influence by water contamination. Unless otherwise noted, other
materials were obtained from commercial sources and used without
further purification.
(19) (a) Miller, D. M., III.; Olson, J. S.; Pflugrath, J. W.; Quiochio, F.
A. J. Biol. Chem. 1980, 255, 2465. (b) Miller, D. M., III.; Olson, J. S.;
Pflugrath, J. W.; Quiochio, F. A. J. Biol. Chem. 1983, 258, 13665. (c)
Bourne, Y.; Rouge, P.; Cambillau, C. J. Biol. Chem. 1990, 265, 18161.
(20) To examine how ligand aggregation affects the dependence of K
on additive concentration, we compared the behaviors of 1 and 3. Even
though the binding constants were determined in the same concentration
range of â-Gal, the binding constant between 3 and â-Gal increased while
that between 1 and â-Gal simply decreased with increasing tert-butyl alcohol
concentration, suggesting that the effects of tert-butyl alcohol cannot be
ascribed to the dissolution of aggregate of â-Gal. The increased CD band
by the addition of tert-butyl alcohol to the 3-â-Glc complex also indicates
that the effects of additives were due to the interaction between the additive
and the complex.
Receptors and Carbohydrates. [cis-5,15-Bis(2-hydroxy-1-naph-
thyl)-2,3,7,8,12,13,17,18-octaethylporphyrinato]zinc(II) (3) and [trans-
(21) Gaunitz, S.; Schwarz, H.; Bohlmann, F. Tetrahedron 1975, 31, 185.
(22) Aoyama, Y.; Kamohara, T.; Yamagishi, A.; Toi, H.; Ogoshi, H.
Tetrahedron Lett. 1987, 28, 2143.

Molecular Recognition of Carbohydrates
J. Am. Chem. Soc., Vol. 119, No. 38, 1997 8999
5,15-bis(2,7-dihydroxy-1-naphthyl)-2,3,7,8,12,13,17,18-octaethylpor-
as an eluent and further purified by recrystallization from CHCl3/hexane.
Pure 2 was dried in vacuo at room temperature for over 50 h: UV-
vis (CHCl3 containing amylenes) λmax (log ꢀ) 417 nm (5.45), 543 nm
phyrinato]zinc(II) (4) were prepared according to the published
1
1
procedure.23 Assignments of H NMR signals were done by H-1H
COSY or H-1H PDQF experiments.
(4.18), 579 nm (3.93); H NMR (500 MHz, CDCl3) δ 10.10 (s, 2H),
1
1
8.57 (dd, J ) 4.0, 1.8 Hz, 2H), 8.55 (dd, J ) 6.7, 1.5 Hz, 2H), 8.44
(dd, J ) 8.2, 1.8 Hz, 2H), 8.29 (dd, J ) 8.2, 1.5 Hz, 2H), 7.88 (dd, J
) 8.2, 6.7 Hz, 2H), 7.38 (dd, J ) 8.6, 4.0 Hz, 2H), 3.89 (q, J ) 7.6
Hz, 8H), 2.48-2.41 (m, 4H), 2.32-2.25 (m, 4H), 1.76 (t, J ) 7.6 Hz,
12H), 0.71 (t, J ) 7.6 Hz, 12H); HRMS calcd for C54H54N6Zn m/z
850.3702, found 850.3717.
Octyl â-D-Glucopyranoside. Spectroscopic data (Dojindo labora-
tories, used as received): 1H NMR (500 MHz, 1.7 mM in CDCl3 at 25
°C) δ 4.29 (d, J ) 7.6 Hz, 1H, 1-H), 3.93-3.78 (m, 2H), 3.88 (dt, J
) 9.5, 6.7 Hz, 1H, CH3-(CH2)6-CH2O-), 3.61-3.48 (m, 2H), 3.51 (dt,
J ) 9.5, 7.0 Hz, 1H, CH3-(CH2)6-CH2O-), 3.41-3.32 (m, 2H), 2.62
(d, J ) 2.1 Hz, 1H, 3-OH), 2.50 (d, J ) 2.8 Hz, 1H, 4-OH), 2.37 (d,
J ) 2.1 Hz, 1H, 2-OH), 1.96 (t, J ) 7.0 Hz, 1H, 6-OH), 1.61 (m, 2H,
CH3-(CH2)5CH2-CH2O-), 1.26 (m, 10H, CH3-(CH2)5CH2-CH2O-), 0.86
(t, J ) 7.0 Hz, 3H, CH3-(CH2)6-CH2O-).
Synthesis of [cis- and trans-5,15-Bis(8-quinolyl)-2,3,7,8,12,13,17,
18-octaethylporphyrinato]zinc(II). It was synthesized according to
the reported procedure.22
8-Formylquinoline. 8-Methylquinoline (1.46 g, 10 mmol) and
selenium dioxide (1.3 g, 12 mmol) were mixed, and the suspension
was stirred for 2 h at 160 °C. After the suspension was cooled to
room temperature, the reaction mixture was poured to saturated aqueous
NaHCO3 and extracted with dichloromethane. The organic layer was
dried over K2CO3 and evaporated. The residue was recrystallized from
ethanol to obtain 8-formylquinoline (367 mg, 23%): 1H NMR (500
MHz, CDCl3) δ 11.46 (d, J ) 0.9 Hz, 1H), 9.07 (dd, J ) 4.3, 1.5 Hz,
1H), 8.35 (dd, J ) 7.3, 1.5 Hz, 1H), 8.26 (dd, J ) 8.3, 1.5 Hz, 1H),
8.11 (dd, J ) 8.3, 1.5 Hz, 1H), 7.70 (dd, J ) 7.3, 7.3 Hz, 1H), 7.53
(dd, J ) 8.6, 4.3 Hz, 1H).
cis- and trans-5,15-Bis(8-quinolyl)-2,3,7,8,12,13,17,18-octaeth-
ylporphyrin. To a solution of 3,3′,4,4′-tetraethyl-2,2′-dipyrrylmethene
hydrobromide (326 mg, 0.967 mmol)23 in ethanol (10 mL) was added
under N2 a solution of NaBH4 (39.7 mg, 1.65 mmol) in ethanol (3
mL) until the reaction mixture turned from dark brown to pale brown.
After 1.5 h of stirring at room temperature, the solvent was evaporated,
and ether (20 mL) was added to the residue. The precipitate was filtered
off, and the filtrate was evaporated to yield 3,3′,4,4′-tetraethyl-2,2′-
dipyrrylmethane (246 mg, 0.954 mmol). 3,3′,4,4′-Tetraethyl-2,2′-
dipyrrylmethane (246 mg, 0.954 mmol) and 8-formylquinoline (157
mg, 1.00 mmol) were dissolved in methanol (11.5 mL, degassed by
N2 bubbling for 1 h), and a solution of p-toluenesulfonic acid
monohydrate (59 mg, 0.31 mmol) in methanol (4 mL, degassed) was
added dropwise. The reaction mixture was then stirred for 20 h in the
dark. After the solvent was evaporated, the residue was dissolved in
THF (27.6 mL), followed by the addition of a solution of chloranil
(345 mg, 1.4 mmol) in THF (2.8 mL). The solution was stirred for
1.2 h. After the solvent was evaporated, the residue was purified by
silica gel column chromatography (CHCl3/acetone ) 25:1) to separate
the trans and cis isomers. The cis isomer was recrystallized from
CHCl3/hexane: UV-vis (CHCl3 containing amylenes) λmax (log ꢀ) 416
nm (5.26), 512 nm (4.16), 546 nm (3.63), 579 nm (3.79), 631 nm (3.08);
1H NMR (500 MHz, CDCl3) δ 10.10 (s, 2H), 8.72 (dd, J ) 3.7, 1.6
Hz, 2H), 8.47 (dd, J ) 8.6, 1.8 Hz, 2H), 8.34 (dd, J ) 6.4, 0.9 Hz,
2H), 8.28 (dd, J ) 8.5, 1.2 Hz, 2H), 7.84 (dd, J ) 8.3, 7.1 Hz, 2H),
7.46 (dd, J ) 8.5, 4.0 Hz, 2H), 3.96-3.87 (m, 8H), 2.57-2.50 (m,
4H), 2.43-2.35 (m, 4H), 1.79 (t, J ) 7.7 Hz, 12H), 0.76 (t, J ) 7.3
Hz, 12H), -1.68 (br, 2H); HRMS calcd for C54H56N6 m/z 788.4566,
found 788.4597.
[cis- and trans-5,15-Bis(8-quinolyl)-2,3,7,8,12,13,17,18-octaeth-
ylporphyrinato]zinc(II). To the free base porphyrin (11.1 mg, 14.4
µmol) dissolved in CHCl3 (20 mL) was added methanol saturated with
zinc acetate (1.5 mL), and the solution was refluxed for 30 min. The
reaction mixture was poured to water, and the resultant mixture was
extracted with CHCl3. The organic layer was washed with water, dried
over Na2SO4, and evaporated.
[cis-5,15-Bis(8-quinolyl)-2,3,7,8,12,13,17,18-octaethylporphyrina-
to]zinc(II) (1). The cis isomer was separated via silica gel column
chromatography using 17% EtOAc in CHCl3 as an eluent and further
purified by recrystallization from CHCl3/hexane. Pure 1 was dried in
vacuo at room temperature for over 50 h: UV-vis (CHCl3 containing
amylenes) λmax (log ꢀ) 417 nm (5.43), 543 nm (4.23), 579 nm (3.97);
1H NMR (500 MHz, CDCl3) 10.11 (s, 2H), 8.59 (dd, J ) 4.9, 1.5 Hz,
2H), 8.46 (m, 4H), 8.29 (dd, J ) 8.2, 1.5 Hz, 2H), 7.85 (dd, J ) 7.0,
8.2 Hz, 2H), 7.41 (dd, J ) 8.5, 4.0 Hz, 2H), 3.95-3.83 (m, 8H), 2.51-
2.44 (m, 4H), 2.29-2.22 (m, 4H), 1.79 (t, J ) 7.6 Hz, 12H), 0.73 (t,
J ) 7.3 Hz, 12H); HRMS calcd for C54H54N6Zn m/z 850.3702, found
850.3710.
Octyl r-D-Glucopyranoside. Spectroscopic data (Sigma, used as
received): 1H NMR (500 MHz, 1.9 mM in CDCl3 at 25 °C) δ 4.85 (d,
J ) 4.0 Hz, 1H, 1-H), 3.87-3.78 (m, 2H), 3.74-3.62 (m, 2H), 3.71
(dt, J ) 9.5, 6.5 Hz, 1H, CH3-(CH2)6-CH2O-), 3.57-3.53 (m, 1H),
3.48-3.40 (m, 1H), 3.43 (dt, J ) 9.0, 7.0 Hz, 1H, CH3-(CH2)6-CH2O-
), 2.55 (d, J ) 2.1 Hz, 1H, 3-OH), 2.47 (d, J ) 2.8 Hz, 1H, 4-OH),
1.97 (d, J ) 10.7 Hz, 1H, 2-OH), 1.89 (dd, J ) 7.0, 5.5 Hz, 1H, 6-OH),
1.58 (m, 2H, CH3-(CH2)5CH2-CH2O-), 1.26 (m, 10H, CH3-(CH2)5CH2-
CH2O-), 0.87 (t, J ) 7.0 Hz, 3H, CH3-(CH2)6-CH2O-).
Octyl â-D-Galactopyranoside. This compound was synthesized by
the literature procedure.24 Obtained crude product was purified via
silica gel column chromatography (EtOAc/MeOH ) 6:1). Further
purification was done by recrystallizing from EtOH/hexane. The
crystals were completely dried at 60 °C under reduced pressure for
100 h: 1H NMR (500 MHz, 2.5 mM in CDCl3 at 25 °C) δ 4.24 (d, J
) 7.3 Hz, 1H, 1-H), 4.01-3.95 (m, 2H), 3.93-3.85 (m, 2H), 3.66-
3.58 (m, 2H), 3.55-3.48 (m, 2H), 2.78 (d, J ) 2.4 Hz, 1H, 4-OH),
2.61 (d, J ) 4.6 Hz, 1H, 3-OH), 2.38 (d, J ) 1.8 Hz, 1H, 2-OH), 2.09
(dd, J ) 7.9, 4.9 Hz, 1H, 6-OH), 1.62 (m, 2H, CH3-(CH2)5CH2-CH2O-
), 1.27 (m, 10H, CH3-(CH2)5CH2-CH2O-), 0.86 (t, J ) 7.3 Hz, 3H,
CH3-(CH2)6-CH2O-); 13C NMR (125.65 MHz, DMSO-d6) δ 103.47 (1-
C), 75.09, 73.51, 70.56, 68.47, 68.13, 60.40, 31.29, 29.37, 28.91, 28.73,
25.57, 22.11, 13.95. Anal. Calcd for C14H28O6: C, 57.51; H, 9.65.
Found: C, 57.30; H, 9.88.
Octyl r-D-Galactopyranoside. This compound was obtained as a
complex mixture by the literature procedure.26 The crude product was
then passed through a Dowex 1 × 2 (OH form, Dow Chemical Co.)
chromatographic column (EtOH/MeOH ) 1:1) to give the pure
R-anomer, which was completely dried at 60 °C under reduced pressure
for 100 h: 1H NMR (500 MHz, 2.3 mM in CDCl3 at 25 °C) δ 4.94 (d,
J ) 3.7 Hz, 1H, 1-H), 4.08 (m, 1H, 4-H), 3.98-3.94 (m, 1H, 5-H),
3.87-3.69 (m, 4H), 3.71 (dt, J ) 9.8, 6.7 Hz, 1H, CH3-(CH2)6-CH2O-
), 3.44 (dt, J ) 9.5, 6.7 Hz, 1H, CH3-(CH2)6-CH2O-), 2.80 (d, J ) 0.6
Hz, 1H, 4-OH), 2.53 (d, J ) 3.7 Hz, 1H, 3-OH), 2.20 (dd, J ) 7.9, 4.6
Hz, 1H, 6-OH), 1.88 (d, J ) 10.4 Hz, 1H, 2-OH), 1.59 (m, 2H, CH3-
(CH2)5CH2-CH2O-), 1.27 (m, 10H, CH3-(CH2)5CH2-CH2O-), 0.86 (t, J
) 7.3 Hz, 3H, CH3-(CH2)6-CH2O-); 13C NMR (125.65 MHz, DMSO-
d6) δ 98.84 (1-C), 71.14, 69.58, 68.84, 68.37, 66.88, 60.57, 31.25, 29.11,
28.84, 28.68, 25.71, 22.07, 13.94. Anal. Calcd for C14H28O6: C, 57.51;
H, 9.65. Found: C, 57.21; H, 9.48.
Octyl â-D-Mannopyranoside. This compound was synthesized by
the literature procedure.25 The obtained product was further purified
by a Dowex 1 × 2 (OH form, Dow Chemical Co.) chromatographic
column (EtOH/MeOH ) 2:1). The product was completely dried at
60 °C under reduced pressure for 100 h: 1H NMR (500 MHz, 0.6 mM
in CDCl3 at 25 °C) δ 4.52 (d, J ) 1.2 Hz, 1H, 1-H), 3.99 (m, 1H),
3.95-3.87 (m, 2H), 3.85-3.80 (m, 1H), 3.76-3.72 (m, 1H), 3.55-
3.47 (m, 2H), 3.30-3.26 (m, 1H), 2.47 (d, J ) 9.5 Hz, 1H, 3-OH),
[trans-5,15-Bis(8-quinolyl)-2,3,7,8,12,13,17,18-octaethylporphy-
rinato]zinc(II) (2). The trans isomer was separated by passing through
triethylamine pretreated silica gel column using 5% EtOAc in CHCl3
(24) Matsumura, S.; Imai, K.; Yoshikawa, S.; Kawada, K.; Uchibori, T.
J. Am. Oil Chem. Soc. 1990, 67, 996.
(25) Kaur, K. J.; Hindsgaul, O. Glycoconjugate J. 1991, 8, 90.
(26) Konradsson, P.; Roberts, C.; Fraser-Reid, B. Recl. TraV. Chim. Pays-
Bas 1991, 110, 23.
(23) Mizutani, T.; Murakami, T.; Kurahashi, T.; Ogoshi, H. J. Org. Chem.
1996, 61, 539.

9000 J. Am. Chem. Soc., Vol. 119, No. 38, 1997
Mizutani et al.
2.42 (d, J ) 2.8 Hz, 1H, 4-OH), 2.36 (d, J ) 2.4 Hz, 1H, 2-OH), 2.04
(t, J ) 6.7 Hz, 1H, 6-OH), 1.60 (m, 2H, CH3-(CH2)5CH2-CH2O-), 1.26
(m, 10H, CH3-(CH2)5CH2-CH2O-), 0.86 (t, J ) 7.0 Hz, 3H, CH3-(CH2)6-
CH2O-); 13C NMR (125.65 MHz, DMSO-d6) δ 100.22 (1-C), 77.49,
73.71, 70.56, 68.36, 67.17, 61.37, 31.23, 29.18, 28.86, 28.68, 25.58,
22.06, 13.94; Anal. Calcd for C14H28O6: C, 57.51; H, 9.65. Found:
C, 57.24; H, 9.81.
Octyl r-D-Mannopyranoside. This compound was obtained as a
complex mixture by the literature procedure.26 The crude product was
then passed through a Dowex 1 × 2 (OH form, Dow Chemical Co.)
chromatographic column (EtOH/MeOH ) 2:1) to give the pure
R-anomer, which was completely dried at 60 °C under reduced pressure
for 100 h: 1H NMR (500 MHz, 0.3 mM in CDCl3 at 25 °C) δ 4.82 (d,
J ) 1.5 Hz, 1H, 1-H), 3.93 (m, 1H), 3.89-3.77 (m, 4H), 3.68-3.61
(m, 1H), 3.66 (dt, J ) 9.5, 6.7 Hz, 1H, CH3-(CH2)6-CH2O-), 3.39 (dt,
J ) 9.5, 6.4 Hz, 1H, CH3-(CH2)6-CH2O-), 2.37 (d, J ) 5.5 Hz, 1H,
3-OH), 2.34 (d, J ) 3.1 Hz, 1H, 4-OH), 2.19 (d, J ) 4.6 Hz, 1H,
2-OH), 1.99 (t, J ) 6.7 Hz, 1H, 6-OH), 1.55 (m, 2H, CH3-(CH2)5CH2-
CH2O-), 1.25 (m, 10H, CH3-(CH2)5CH2-CH2O-), 0.87 (t, J ) 7.3 Hz,
3H, CH3-(CH2)6-CH2O-); 13C NMR (125.65 MHz, DMSO-d6) δ 99.70
(1-C), 73.91, 71.00, 70.39, 66.97, 66.17, 61.26, 31.23, 28.97, 28.77,
28.66, 25.73, 22.05, 13.93. Anal. Calcd for C14H28O6: C, 57.51; H,
9.65. Found: C, 57.27; H, 9.82.
Matsumura et al.,24 in which 1.2 equiv of silver trifluoromethane-
sulfonate was used instead of silver carbonate and 3.2 equiv of
tetramethylurea was added together with octanol and silver trifluo-
romethanesulfonate to minimize orthoester formation. Purification was
done by silica gel column chromatography (hexane/EtOAc ) 2:1). The
yield was 43%: 1H NMR (500 MHz, CDCl3) δ 5.28 (m, 1H), 5.04 (m,
1H), 4.84 (s, 1H), 4.27 (m, 1H), 4.12-3.88 (m, 3H), 3.65 (m, 1H),
3.44 (m, 1H), 2.09-2.00 (m, 12H), 1.55 (m, 2H), 1.24 (m, 10H), 0.87
(t, J ) 7.0 Hz, 3H).
Octyl r-D-Mannopyranoside. Deacetylation was carried out by
the reported procedure.25 Less than 1% of â-anomer was detected by
1H NMR. The product was passed through a silica gel column (EtOAc/
MeOH ) 9:1) and was used for the next reaction. The yield was
92%: 1H NMR (500 MHz, 0.3 mM in CDCl3 at 25 °C) δ 4.82 (d, J )
1.5 Hz, 1H, 1-H), 3.93 (m, 1H), 3.89-3.77 (m, 4H), 3.68-3.61 (m,
1H), 3.66 (dt, J ) 9.5, 6.7 Hz, 1H, CH3-(CH2)6-CH2O-), 3.39 (dt, J )
9.5, 6.4 Hz, 1H, CH3-(CH2)6-CH2O-), 2.37 (d, J ) 5.5 Hz, 1H, 3-OH),
2.34 (d, J ) 3.1 Hz, 1H, 4-OH), 2.19 (d, J ) 4.6 Hz, 1H, 2-OH), 1.99
(t, J ) 6.7 Hz, 1H, 6-OH), 1.55 (m, 2H, CH3-(CH2)5CH2-CH2O-), 1.25
(m, 10H, CH3-(CH2)5CH2-CH2O-), 0.87 (t, J ) 7.3 Hz, 3H, CH3-(CH2)6-
CH2O-); 13C NMR (125.65 MHz, DMSO-d6) δ 99.70 (1-C), 73.92,
71.00, 70.40, 66.97, 66.17, 61.26, 31.24, 28.98, 28.78, 28.68, 25.75,
22.07, 13.94.
Octyl 4,6-O-Benzylidene-r-D-mannopyranoside. Benzylidenation
was effected by PhCH(OMe)2HBF4‚OEt2.28 The temperature was kept
at -40 °C during the reaction and gradually increased to room
temperature. The crude product was purified by silica gel column
chromatography (hexane/EtOAc ) 8:5) and further purified by recrys-
tallization from hexane/EtOAc. The yield was 67%: 1H NMR (500
MHz, CDCl3) δ 7.49-7.47 (m, 2H), 7.38-7.34 (m, 3H), 5.56 (s, 1H),
4.85 (d, J ) 1.2 Hz, 1H, 1-H), 4.26 (m, 1H), 4.10-4.03 (m, 2H), 3.91
(m, 1H), 3.84-3.79 (m, 2H), 3.68 (dt, J ) 9.8, 6.7 Hz, 1H), 3.41 (dt,
J ) 9.5, 6.7 Hz, 1H), 2.54 (d, J ) 2.1 Hz, 1H, OH), 2.53 (d, J ) 3.4
Hz, 1H, OH), 1.59-1.51 (m, 2H), 1.27 (m, 10H), 0.87 (t, J ) 7.0 Hz,
3H).
Octyl 4,6-O-Benzylidene-3-O-benzyl-r-D-mannopyranoside. The
procedure reported by Boger et al.29 was used for selective benzylation
of the equatorial 3-OH group of octyl 4,6-O-benzylidene-R-D-man-
nopyranoside. The crude product was purified by silica gel column
chromatography (hexane/EtOAc ) 4:1). The yield was 81%: 1H NMR
(500 MHz, CDCl3) δ 7.50-7.47 (m, 2H), 7.37-7.27 (m, 8H), 5.60 (s,
1H, benzylidene-H), 4.85 (d, J ) 11.9 Hz, 1H, benzyl-H), 4.84 (d, J
) 1.5 Hz, 1H, 1-H), 4.71 (d, J ) 11.9 Hz, 1H, benzyl-H), 4.25 (m,
1H), 4.08 (m, 1H), 4.04 (m, 1H, 2-H), 3.92 (dd, J ) 9.5, 3.0 Hz, 1H,
3-H), 3.85-3.81 (m, 2H), 3.67 (dt, J ) 9.5, 7.0 Hz, 1H, CH3-(CH2)6-
CH2O-), 3.38 (dt, J ) 9.5, 7.0 Hz, 1H, CH3-(CH2)6-CH2O-), 2.63 (d,
J ) 1.5 Hz, 1-H, 2-OH), 1.55 (m, 2H, CH3-(CH2)5CH2-CH2O-), 1.26
(m, 10H, CH3-(CH2)5CH2-CH2O-), 0.87 (t, J ) 7.5 Hz, 3H, CH3-(CH2)6-
CH2O-).
Octyl 4,6-O-Benzylidene-3-O-benzyl-2-O-methyl-r-D-mannopy-
ranoside. The procedure for methylation of benzyl 3,4,6-tri-O-benzyl-
â-L-glucopyranoside30 was found to be effective for methylation of octyl
4,6-O-benzylidene-3-O-benzyl-R-D-mannopyranoside. The crude prod-
uct was purified by silica gel column chromatography (hexane/EtOAc
) 4:1). The yield was 89%: 1H NMR (500 MHz, CDCl3) δ 7.45-
7.42 (m, 2H), 7.32-7.19 (m, 8H), 5.55 (s, 1H), 4.82 (d, J ) 12.2 Hz,
1H), 4.76 (d, J ) 1.2 Hz, 1H), 4.65 (d, J ) 12.2 Hz, 1H), 4.17 (dd, J
) 10.1, 4.3 Hz, 1H), 4.08 (dd, J ) 9.8, 9.8 Hz, 1H), 3.89 (dd, J )
10.1, 3.4 Hz, 1H), 3.79 (dd, J ) 10.1, 10.1 Hz, 1H), 3.71 (dt, J ) 4.6,
9.5 Hz, 1H), 3.59 (dt, J ) 9.5, 7.0 Hz, 1H), 3.52 (dd, J ) 3.1, 1.5 Hz,
1H), 3.49 (s, 3H), 3.32 (dt, J ) 9.8, 6.7 Hz, 1H), 1.50 (m, 2H), 1.22
(m, 10H), 0.82 (t, J ) 7.0 Hz, 3H).
Octyl 6-O-Benzoyl-â-D-glucopyranoside. To a solution of octyl
â-D-glucopyranoside (155 mg, 0.52 mmol) and pyridine (3.7 mL) in
dichloromethane (3.0 mL) was added benzoyl chloride (144 mg, 1.03
mmol) in dichloromethane (6.0 mL) dropwise over 6 h at -40 °C.
After the reaction mixture was allowed to warm to room temperature
over 12 h, excess benzoyl chloride was decomposed by the addition of
MeOH. The solvent was evaporated, and the residue was purified by
column chromatography on silica gel (ether/acetone ) 4:1) to obtain
octyl 6-O-benzoyl-â-D-glucopyranoside (43.9 mg, 0.11 mmol, 22%):
1H NMR (500 MHz, CDCl3) δ 8.07-7.43 (m, 5H, benzoyl-H), 4.75
(dd, J ) 12.2, 4.6 Hz, 1H, 6-H), 4.53 (dd, J ) 12.2, 2.2 Hz, 1H, 6-H),
4.30 (d, J ) 7.7 Hz, 1H, 1-H), 3.89 (dt, J ) 9.4, 7.7 Hz, 1H, CH3-
(CH2)6-CH2O-), 3.61 (t, J ) 9.1 Hz, 1H, 3-H), 3.57 (m, 1H, 5-H), 3.52
(dt, J ) 9.6, 7.0 Hz, 1H, CH3-(CH2)6-CH2O-), 3.48 (m, 1H, 4-H), 3.38
(dd, J ) 9.5, 8.0 Hz, 1H, 2-H), 3.14 (s, 1H, 4-OH), 2.81 (s, 1H, 3-OH),
2.46 (s, 1H, 2-OH), 1.64-1.59 (m, 2H, CH3-(CH2)5CH2-CH2O-), 1.28-
1.24 (m, 10H, CH3-(CH2)5CH2-CH2O-), 0.87 (t, J ) 5.5 Hz, 3H, CH3-
(CH2)6-CH2O-); HRMS calcd for C21H33O7 m/z 397.2226, found
397.2237.
Octyl 6-O-Acetyl-â-D-glucopyranoside. To a solution of octyl â-D-
glucopyranoside (152 mg, 0.51 mmol) and pyridine (3.7 mL) in
dichloromethane (3.0 mL) was added acetyl chloride (80 mg, 1.0 mmol)
in dichloromethane (6.0 mL) dropwise over 6 h at -40 °C. After the
reaction mixture was allowed to warm to room temperature over 12 h,
excess acetyl chloride was decomposed by the addition of MeOH. The
solvent was evaporated. The residue was purified by column chro-
matography on silica gel (ether/acetone ) 4:1) to obtain octyl 6-O-
acetyl-â-D-glucopyranoside (52.6 mg, 0.16 mmol, 31%): 1H NMR (500
MHz, CDCl3) δ 4.55-4.51 (dd, J ) 12.5, 4.7 Hz, 1H, 6-H), 4.27 (d,
J ) 7.8 Hz, 1H, 1-H), 4.25 (dd, J ) 12.5, 2.5 Hz, 1H, 6-H), 3.90 (dt,
J ) 24.7, 19.4 Hz, 1H, CH3-(CH2)6-CH2O-), 3.58 (m, 1H, 3-H), 3.50
(dt, J ) 24.7, 19.4 Hz, 1H, CH3-(CH2)6-CH2O-), 3.44 (m, 1H, 5-H),
3.39 (m, 2H, 2-H and 4-H), 3.02 (s, 1H, 4-OH), 2.78 (s, 1H, 3-OH),
2.43 (s, 1H, 2-OH), 2.21 (s, 3H, CH3CO2-), 1.65-1.57 (m, 2H, CH3-
(CH2)5CH2-CH2O-), 1.37-1.21 (m, 10H, CH3-(CH2)5CH2-CH2O-), 0.87
(t, J ) 5.4 Hz, 3H, CH3-(CH2)6-CH2O-); HRMS calcd for C16H31O7
m/z 335.2056, found 335.2063.
Synthesis of Octyl 2-O-Methyl-r-D-mannopyranoside. Mannose
Pentaacetate. Mannose pentaacetate was prepared from mannose and
anhydrous sodium acetate in acetic anhydride by the reported proce-
dure.27 The obtained product was a mixture of R- and â-anomers and
a small amount of straight-chain mannose peracetate. Since separation
was quite difficult, this mixture was subjected to the next reaction after
passing through a silica gel column (hexane/EtOAc ) 1:1).
Octyl 2-O-Methyl-r-D-mannopyranoside. Removal of both the
benzyl group and the benzylidene group was done by catalytic transfer
hydrogenation reported by Hanessian et al.31 The crude product was
purified first by silica gel column chromatography (EtOAc/MeOH )
(28) Albert, R.; Dax, K.; Pleschko, R.; Stutz, A. E. Carbohydr. Res. 1985,
137, 282.
(29) Boger, D. L.; Honda, T. J. Am. Chem. Soc. 1994, 116, 5647.
(30) Boger, D. L.; Teramoto, S.; Zhou, J. J. Am. Chem. Soc. 1995, 117,
7344.
Octyl 2,3,4,6-Tetra-O-acetyl-r-D-mannopyranoside. This pyra-
noside was obtained stereoselectively by a modified procedure of S.
(27) Rosevear, P.; VanAken, T.; Baxter, J.; Ferguson-Miller, S. Bio-
chemistry 1980, 19, 4108.
(31) Hanessian, S.; Liak, T. J.; Vanasse, B. Synthesis 1981, 396.

Molecular Recognition of Carbohydrates
J. Am. Chem. Soc., Vol. 119, No. 38, 1997 9001
9:1) and then by passing through a Dowex 1 × 2 (OH form, Dow
Chemical Co.) chromatographic column using methanol as an eluent.
The pure product was obtained in a 98% yield as hygroscopic liquid:
1H NMR (500 MHz, CDCl3) δ 4.89 (d, J ) 1.2 Hz, 1H, 1-H), 3.87-
3.74 (m, 3H), 3.67 (dt, J ) 9.8, 6.7 Hz, 1H, CH3-(CH2)6-CH2O-), 3.65
(m, 1H, 4-H), 3.58 (m, 1H, 5-H), 3.46 (s, 3H, CH3O-), 3.45 (dd, J )
1.5 Hz, 1H, 2-H), 3.38 (dt, J ) 9.5, 6.4 Hz, 1H, CH3-(CH2)6-CH2O-),
2.45 (d, J ) 2.7 Hz, 1H, 4-OH), 2.29 (d, J ) 10.4 Hz, 1H, 3-OH),
2.02 (dd, J ) 7.0, 5.8 Hz, 1H, 6-OH), 1.56 (m, 2H, CH3-(CH2)5CH2-
CH2O-), 1.26 (m, 10H, CH3-(CH2)5CH2-CH2O-), 0.87 (t, J ) 7.3 Hz,
3H, CH3-(CH2)6-CH2O-); 13C NMR (125.65 MHz, DMSO-d6) δ 96.51
(1-C), 80.57, 73.96, 70.88, 67.24, 66.35, 61.15, 58.55, 31.24, 29.00,
28.78, 28.67, 25.74, 22.08, 13.94. Anal. Calcd for C15H30O6‚1/4H2O:
C, 57.95; H, 9.89. Found: C, 58.03; H, 9.82.
carbohydrate addition being taken into account during analysis.
Assuming 1:1 complexation, the binding constants were evaluated by
a least-squares parameter estimation based on the damping Gauss-
Newton method. Calculated curves were well fitted to absorbance
changes.
It was reported that glycopyranosides aggregate when dissolved in
organic solvent at a high concentration.8 The UV-vis titration
experiments of 1 and 2 were performed in the low-concentration range
of the ligands, where no aggregation occurs. For the binding of Man
by receptors 3 and 4, at the highest concentration of Man, aggregation
occurred. However the standard deviations of binding constants of
these receptor-ligand complexes were 6-10%, comparable to those
for other complexes, showing that the errors owing to the ligand
aggregation were negligibly small.
1H NMR Study of Binding. CDCl3 was completely deacidified
by passing through alumina (basic, activity super 1, ICN) just before
use. To 0.3-0.8 mM of carbohydrate in CDCl3 was added a stock
solution of 1 or 2 in CDCl3 at 25 °C, and the complexation-induced
shifts of signals for carbohydrates were recorded. The concentration
of 1 or 2 was kept considerably low ([H-G]/[G]total < 20%) to avoid
signal broadening. The CIS values were determined by extrapolating
the chemical shift to 100% complex, based on the concentrations of
the complex calculated from K determined by UV-vis titration.
UV-Vis Titrations and CD Spectral Measurements. Binding
constants were determined by UV-vis titrations. To avoid the influence
by the ethanol added as a stabilizer to chloroform, amylene-containing
chloroform was used throughout the study. The water concentration
1
was estimated to be about 0.002% from H NMR. The atropisomer-
ization from the cis isomer (1) to the trans isomer (2) in a CDCl3
solution occurred slowly: 5% of 1 was isomerized to 2 at room
temperature for 100 h although no isomerization was observed in the
solid state. Therefore, the receptor solution was prepared just before
use. Cis to trans isomerization in receptors 3 and 4 was too slow to
observe.
The details of the determination of the binding constant are as
follows. To ca. 5 × 10-6 M of 1-5 in CHCl3 was added a stock
solution of carbohydrate ligands in CHCl3 at 15 °C. The changes in
absorbance at around 424 nm in the Soret band were monitored at eight
different concentrations of carbohydrate, with volume change due to
Acknowledgment. We thank T. Kobatake for his kind help
in the mass spectroscopy measurements. This work was sup-
ported by a Grant-in Aid for Scientific Research from the
Ministry of Education, Science, Sports, and Culture, Japan.
JA9713183