Synthesis and chiroptical properties of (naphthyl)ethylidene ketals of carbohydrates in solution and solid state

Article abstract of DOI:10.1016/j.tet.2007.12.011

1,3-Dioxolane- and dioxane-type (1- and 2-naphthyl)ethylidene ketals of p-methoxyphenyl α-l-rhamnopyranoside and β-d-glucopyranoside were prepared and their stereochemistry studied by solution and solid-state circular dichroism, X-ray diffraction, and cou

Full text of DOI:10.1016/j.tet.2007.12.011

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 1676e1688
www.elsevier.com/locate/tet
Synthesis and chiroptical properties of (naphthyl)ethylidene ketals
of carbohydrates in solution and solid state
a
Gabor Kerti , Tibor Kurtan , Aniko Borbas , Zoltan B. Szabo , Andras Liptak ,
a,
b
b
b
*
´
´
´
´
´
Laszlo Szilagyi , Zita Illyes-Tunde , Attila Benyei , Sandor Antus
´
a,b,
´
´
, Masayuki Watanabe ,
a
a
c
d
*
´
´
´
´
´
´
¨
Ettore Castiglioni d, Gennaro Pescitelli e, Piero Salvadori e
a Department of Organic Chemistry, University of Debrecen, PO Box 20, H-4010 Debrecen, Hungary
b Research Group for Carbohydrates of the Hungarian Academy of Sciences, University of Debrecen, PO Box 55, H-4010 Debrecen, Hungary
c Institute of Physical Chemistry, University of Debrecen, PO Box 7, H-4010 Debrecen, Hungary
d JASCO Corporation, Hachioji-shi, Tokyo 192-85387, Japan
e Universita` di Pisa, Dipartimento di Chimica e Chimica Industriale, via Risorgimento 35, 56126 Pisa, Italy
Received 20 September 2007; received in revised form 21 November 2007; accepted 6 December 2007
Available online 8 December 2007
´
Dedicated to Professor Csaba Szantay on the occasion of his 80th birthday
Abstract
1,3-Dioxolane- and dioxane-type (1- and 2-naphthyl)ethylidene ketals of p-methoxyphenyl a-L-rhamnopyranoside and b-D-glucopyranoside
were prepared and their stereochemistry studied by solution and solid-state circular dichroism, X-ray diffraction, and coupled-oscillator CD cal-
culations on the solid-state and MMFF-calculated geometries. Intermolecular exciton-coupled interactions between the nearby aromatic chro-
mophores in the solid state and different conformers in solution and solid state could be identified as the main reason for the difference between
solution and solid-state CDs.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Solid-state CD; Intra- and intermolecular exciton-coupled interactions; 1- and 2-Naphthyl chromophores
1. Introduction
(LiAlH4eAlCl3) yielded 4-ONAP ethers whereas reagents
such as NaCNBH3 or BH3eMe3NeAlCl3 gave 6-ONAP de-
rivatives with excellent regioselectivity. It has also been shown
for (2-naphthyl)methylene acetals of glycosides that both the
stereochemistry and the direction of the hydrogenolytic cleav-
age could be safely detected by CD based on the 1Bb transition
of the 2-naphthyl chromophore when another aromatic protec-
tive group like benzyl or p-methoxyphenyl was present in the
molecule.6 As a continuation of our work on the chiroptical
properties of aromatic chromophores and aromatic ketal pro-
tective groups,6e9 we report herein the synthesis and stereo-
chemical study of 1,3-dioxane- and dioxolane-type (1- or
2-naphthyl)ethylidene ketals of glycosides by using X-ray
analysis, solution and solid-state CD measurements, and cou-
pled-oscillator CD calculations.
The protecting group strategy is an essential component in
the design and synthesis of oligosaccharides.1,2 One of us has
already shown3 that ketals prepared from acetophenone dime-
thylacetal and different b-D-gluco-, b-L-arabino- and a-L-
rhamnopyranoside derivatives are very useful building blocks
for the synthesis of oligosaccharides, since their reductive
ring-cleavage by LiAlH4eAlCl3 took place in a stereoselective
manner. Recently, it has also been recognized4,5 that dioxane-
type (2-naphthyl)methylene acetals of glycosides show the
same property; reaction of their 4,6-O-acetals with AlH3
* Corresponding authors. Fax: þ36 52 453836.
´
E-mail address: kurtant@tigris.klte.hu (T. Kurtan).
0040-4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.12.011

G. Kerti et al. / Tetrahedron 64 (2008) 1676e1688
1677
2. Results and discussion
In contrast, the naphthalene 1La bands of both (10S)- and (10R)-
3 were negative regardless of the different absolute configura-
tion of their ketal carbon.
For the preparation of 1,3-dioxolane-type naphthylethyl-
idene ketals, p-methoxyphenyl a-L-rhamnopyranoside (1)
was selected as starting material. Its reaction with 2-(1,1-dime-
thoxyethyl)naphthalene (6) resulted in the formation of two
isomeric (2-naphthyl)ethylidene ketals (10R)-2 and (10S)-2 in
the presence of (þ)-10-camphorsulfonic acid, while the reac-
tion with 1-(1,1-dimethoxyethyl)naphthalene (7) in the pres-
ence of p-toluenesulfonic acid (PTS) provided only a single
product (10R)-4 with high yield (89%). The ketals were
characterized as the acetates [(10R)-3, (10S)-3, and (10R)-5],
which also allowed the separation of (10R)-3 from (10S)-3
(Scheme 1).
(10R)-5, obtained as a single product in the reaction with
1-(1,1-dimethoxyethyl)naphthalene (7), showed a compara-
tively weak positive CD couplet [225 nm (3.2), 220 nm
(ꢀ11.6)] around 225 nm, opposite in sign to that of (10R)-3.
This corroborates previous results showing that the electric
transition moment of the 1Bb transition of the 1-naphthyl chro-
mophore is perpendicular to that of the 2-naphthyl chromo-
phore in analogous derivatives, which results in opposite CD
couplets due to exciton coupling.13 In addition, the naphtha-
lene 1La band of (10R)-5 also had negative CE, as was observed
for both (10S)- and (10R)-3.
On the basis of our earlier results,6 CD spectroscopy
seemed a convenient tool for the configurational assignment
of the newly formed stereogenic center of the dioxolane
ring. For this purpose, the chiroptical properties of analogous
dioxolane-type (2-naphthyl)methylene glycoside acetals 8 and
9 were studied first (Fig. 1), the absolute configurations of
which had been unambiguously determined earlier.10 In the
absence of a second aromatic chromophore, both (10S)-8 and
(10R)-8 methyl glycosides gave positive CE above 220 nm
with significantly different intensities [(10R)-8: 224 nm
(19.4), (10S)-8: 223 nm (2.4)]. In the presence of a glycosidic
In order to confirm unambiguously the configurational
assignments of the ketal carbon and reveal the preferred con-
formation of the naphthyl groups in the solid state, single crys-
tals of (10R)-3 and (10R)-5 were studied by X-ray diffraction.
The X-ray structures of (10R)-3 and (10R)-5 (Fig. 2) confirmed
the (10R) configuration of the acetal carbon and showed that
both 1-naphthyl and 2-naphthyl rings adopt near perpendicu-
lar conformation with respect to the methyl group, namely,
0
0
00
00
0
0
00
00
the torsional angles uC-2 ,C-1 ,C-2 ,C-1 and uC-2 ,C-1 ,C-1 ,C-2
were 74.1ꢁ and 104.7ꢁ, respectively. The negative and positive
projection angles q between the long axes of the naphthyl and
phenyl rings in (10R)-3 and (10R)-5 (q3¼ꢀ77.0ꢁ, q5¼þ55.3ꢁ,
looking through the centers) were in accordance with the mea-
sured negative and positive CD couplets, respectively, as
prescribed by the exciton-coupled CD (ECCD) theory.11
According to the hypothesis that CD spectra of bis-chromo-
phoric compounds 3 and (10R)-5 are dominated, at least in
a certain wavelength range, by the exciton coupling between
the two strong chromophores, it should be possible to repro-
duce them by means of coupled-oscillator calculations. We
employed DeVoe’s method,14 a classical all-order treatment
widely used for configurational and conformational investi-
gations of organic molecules.15 Parameters for DeVoe cal-
culations were extracted from chromophore spectra in
acetonitrile (naphthalene and 1,4-dimethoxybenzene, DMB),
1
p-methoxyphenyl (PMP) group, the Bb band around 225 nm
was split to a bisignate CD band in (10R)-9 [229 nm (ꢀ8.9),
221 nm (13.8)], while (10S)-9 gave a positive exciton11,12 cou-
1
plet due to interaction of the naphthalene Bb transition with
the aryl 1La and 1B transitions [226 nm (38.2), 216 nm
(ꢀ1.9), 194 nm (ꢀ15.2)] as shown in Figure 1a and Table 1.
The solution CD spectrum of (10S)-3, the (2-naphthyl)ethyl-
idene analogue of (10S)-9, showed a similar positive exciton
couplet as (10S)-9 (Fig. 1b) suggesting the same stereochemi-
stry. (10R)-3 gave a near mirror image spectrum below 240 nm,
which confirmed that the absolute configuration of the ketal
carbon, reflecting into the exciton coupling between naphtha-
lene 1Bb and 1La/1B transitions of the p-methoxyphenyl group,
determines the CD curve below 240 nm in (10S)- and (10R)-3.
4'''
OMe
OMe
OMe
OMe
1'''
O
O
O
O
i
ii
O
O
O
AcO
+
HO
AcO
O
HO
O
O
O
1'
2'
O
O
O
HO
2"
OH
1
OMe
CH3
CH3
CH3
1"
iii
O
(1'R)-2 and (1'S)-2
MeO OMe
(1'R)-3
MeO
MeO
(1'S)-3
O
RO
O
O
CH3
(1'R)-4: R = H
(1'R)-5: R = Ac
iv
7
6
Scheme 1. (i) 2-(1,1-Dimethoxyethyl)naphthalene (6)/(þ)-10-camphorsulfonic acid/dry MeCN. (ii) Ac2O/dry pyr., crystallization. (iii) 1-(1,1-dimethoxyethyl)-
naphthalene (7)/PTS, dry MeCN. (iv) Ac2O/dry pyr.

1678
G. Kerti et al. / Tetrahedron 64 (2008) 1676e1688
40
30
20
10
0
(a)
(b)
1Bb
45
(1'S)-9
(1'S)-3
(1'R)-5
30
15
(1'S)-8
(1'R)-8
0
×10
1La
-15
-10
-20
-30
-45
(1'R)-9
(1'R)-3
240
180
200
220
260
280
300
320
180
200
220
wavelength (nm)
240
260
wavelentgh(nm)
60
40
(c)
OR3
O
(1'S)-3
×3
20
AcO
O
O
0
R1
R2
-20
-40
-60
-80
-100
(1'S)-8: R1 = 2-naphthyl, R2 = H, R3 = Me
(1'R)-8: R1 = H , R2 = 2-naphthyl, R3 = Me
(1'S)-9: R1 = 2-naphthyl, R2 = H, R3= PMP
(1'R)-9: R1 = H , R2 = 2-naphthyl, R3 = PMP
(1'R)-3
×10
(1'R)-5
200
220
240
wavelength (nm)
260
280
300
Figure 1. (a) Solution CD spectra of (10R)- and (10S)-8, (10R)- and (10S)-9. (b) CD spectra of (10R)- and (10S)-3 and (10R)-5 in acetonitrile. (c) Solid-state CD of
(10R)- and (10S)-3 and (10R)-5 measured as KCl pellet.
supported by ZINDO calculations (see Section 4.3). DeVoe-
calculated CD spectra using the solid-state geometries of
(10R)-3 and (10R)-5 are reported in Figure 3. The high-energy
region is determined by the coupling between strong dipole-
(10R)-3 and (10R)-5, resulting in four relevant (in terms of
exciton coupling) minima for each compound. They differed
0
0
00
00
0
0
00
00
in the torsional angles uC-2 ,C-1 ,C-2 ,C-1 and uC-2 ,C-1 ,C-1 ,C-2
(either zþ90ꢁ or ꢀ90ꢁ) for the naphthyleketal linkage,
1
1
1
ꢁ
ꢁ
000
allowed transitions (naphthyl Bb with phenyl La and B),
and the calculated CD for (10R)-3 is in good agreement with
the experimental spectrum; the result for (10R)-5 is less satis-
factory, although the positive couplet is reproduced. On the
and uH-1,C-1,O-1,C-1 (either zþ40 or ꢀ40 ) for the DMBe
C1 linkage; in all ꢁcases, the DMB moiety was planar
000
000
(uC-1,O-1,C-1 ,C-2 z0 ). Although the overall conformational
ensembles for (10R)-3 and (10R)-5 are of course quite complex,
we thought that the four minima would well represent average
situations of conformational sets each characterized by a pecu-
liar exciton coupling. Thus, the CDs for the four geometries
and their weighted average (relative to MMFF energies)
were calculated with DeVoe’s method (Fig. 4). For (10R)-3,
among the four low-energy conformers considered, the lowest
energy one (conf. 1, 50% population at 298 K) resembled the
X-ray structure. Both the calculated CD of the lowest energy
conformer and the weighted average reproduced well the mea-
sured CD below 240 nm, but the opposite sign was calculated
for the measured negative CE around 280 nm. For (10R)-5,
among the four conformers, the second lowest energy one
(conf. 2, population 30%) was similar to the X-ray structure
and since it had much more intense CD than the lowest energy
conformer, it dominated the CD. However, the contribution
from other conformers reduces the overall intensity, bringing
it closer to the experimental CD.
1
contrary, the sign for naphthyl La CD band is wrongly pre-
dicted, indicating that it depends on other mechanisms of op-
tical activity than the coupled-dipole, which cannot be taken
into account by the present calculations. One of the advantages
of DeVoe-type calculations is that the information of dominant
exciton couplings is very easily extracted.15 For (10R)-3, the
CD in the 190e230 nm region is dominated by the couplings
1
between naphthyl Bb transition with all high-energy phenyl
1
transitions 1La (dominant), 1Ba, and Bb. For (10R)-5, the
1
dominant coupling terms are those between naphthyl Bb and
1
phenyl Ba,b transitions.
The good agreement between DeVoe calculation results
using the X-ray geometry of (10R)-3 and the measured solution
CD suggested that the solid-state structure was also prevalent
in solution and brought the largest contribution to the CD. In
order to confirm this hypothesis further and to extend it to
(10R)-5, a conformational search with MMFF was run on

G. Kerti et al. / Tetrahedron 64 (2008) 1676e1688
1679
Table 1
Solution and solid-state CD data of the studied compounds
15
Compound l [nm] (D3) for solution and l [nm] (f)a
for solid-state CD measurements
(1'R)-5
10
5
(10R)-3
(10S)-3
(10R)-5
MeCN: 285sh (ꢀ0.9), 282sh (ꢀ1.1), 275 (ꢀ1.4), 271sh (ꢀ1.3),
266sh (ꢀ1.1), 225 (ꢀ38.7), 218 (3.1), 208 (ꢀ2.9), 195 (14.1).
KCl: 285sh (ꢀ1.4), 280 (ꢀ1.5), 228 (ꢀ3.7), 218 (1.0),
210 (ꢀ2.0), 194 (1.8).
0
MeCN: 283 (ꢀ1.1), 279sh (ꢀ1.0), 271sh (ꢀ0.62), 232sh (10.8),
225 (51.5), 216 (ꢀ12.5), 195 (ꢀ22.7).
-5
(1'R)-3
KCl: 286 (ꢀ0.7), 281sh (ꢀ0.6), 229 (19.1), 212 (ꢀ5.0),
196 (ꢀ10.2).
MeCN: 288sh (ꢀ0.7), 285sh (ꢀ0.8), 278 (ꢀ1.3), 268sh (ꢀ1.0),
225 (3.2), 220 (ꢀ11.6).
-10
200
220
240
260
280
300
320
KCl: 292 (4.0), 282sh (3.5), 260sh (ꢀ8.0), 233 (ꢀ107.2),
226sh (27.6), 216 (62.3), 195 (ꢀ14.75).
wavelength (nm)
(10R)-8
(10S)-8
Hexane: 284 (ꢀ0.4), 273 (ꢀ0.6), 224 (19.4), 218sh (9.4),
214sh (4.7), 188 (2.5).
Figure 3. DeVoe calculations of (10R)-3 and (10R)-5 using the X-ray geometries
as input.
Hexane: 225sh (2.2), 223 (2.4), 221sh (2.0), 217sh (1.6),
209sh (ꢀ0.8), 199 (ꢀ1.7).
(10R)-9
(10S)-9
(10R)-11
MeCN: 229 (ꢀ8.9), 221 (ꢀ13.8), 195 (2.9), 182 (ꢀ2.3).
MeCN: 226 (38.2), 216 (ꢀ1.9), 210 (ꢀ1.2), 194 (ꢀ15.2).
MeCN: 283 (ꢀ4.4), 274sh (ꢀ3.1), 233sh (5.8), 225 (33.3),
218 (ꢀ15.3), 216 (ꢀ15.0), 211sh (ꢀ7.8), 194 (ꢀ11.3).
KCl: 289sh (1.2),b 277 (2.5),b 268sh (2.1),b 228 (14.6),
225sh (9.5), 215 (ꢀ5.4), 191 (ꢀ2.9).
(10R)-5 were measured with the KCl pellet technique, to be
correlated with the solid-state X-ray structures and the solu-
tion CDs. Since the results of DeVoe-type calculations using
MMFF or X-ray geometries proved that the X-ray structures
of (10R)-3 and (10R)-5 were also dominant and/or determined
the CD properties in solution, solid-state CDs were expected
to be similar to the solution ones if intermolecular coupling
interactions do not have a significant contribution.23 In accor-
dance, the solid-state CDs of (10R)- and (10S)-3 were almost
identical with the solution ones supporting the view of a prev-
alent intramolecular origin of the solid-state CD (Fig. 1c and
Table 1). In contrast, in the solid-state CD of (10R)-5, all of
the CEs were reversed compared to its solution spectrum; their
magnitudes were markedly increased and a strong negative cou-
(10S)-12a
MeCN: 293 (1.3), 283sh (0.9), 272sh (0.1), 223 (ꢀ39.6), 213sh
(ꢀ9.1), 209sh (ꢀ5.0), 201sh (ꢀ3.8), 196sh (12.5), 193 (14.7).
KCl: 296 (1.2), 284sh (0.3), 278sh (ꢀ0.4), 263sh (ꢀ0.9),
227 (ꢀ13.1), 201 (ꢀ2.3), 192 (3.8).
a
Values of ellipticity [f (mdeg)] are not corrected for the concentrations.
Measured at higher concentration than the high-energy transition.
b
The comparison of the measured solid-state CD with the
one computed for the solid-state X-ray geometry has recently
allowed the determination of the absolute configuration or the
conformation of several natural16e21 and synthetic22 com-
pounds. We intended to apply this methodology to (naphthyl)-
ethylidene ketals as well whose X-ray structures have been
determined. Thus the solid-state CDs of (10R)-3, (10S)-3, and
1
1
plet appeared in the naphthyl Bb/phenyl La region [233 nm
(ꢀ107.2), 216 nm (62.3)]. Based on CD and MMFF calcula-
tions, the observed solid-state CD of (10R)-5 could not be
due to conformational differences between the solution and
Figure 2. ORTEP structures of (a) (10R)-3, (b) (10R)-5, (c) (10R)-11, and (d) (10S)-12a.

1680
G. Kerti et al. / Tetrahedron 64 (2008) 1676e1688
(a)
(b) 30
10
0
Conf. 1 (abs. min.)
Conf. 2 (+0.48 kcal/mol)
Conf. 3 (+1.78)
Conf. 1 (abs. min.)
Conf. 2 (+0.05 kcal/mol)
20
Conf. 3 (+1.81)
Conf. 4 (+1.86)
Conf. 4 (+2.34)
Weighted average
10
0
Weighted average
-10
-20
-30
-10
200
220
240 260
wavelength (nm)
280
300
320
200
220
240 260
wavelength (nm)
280
300
320
Figure 4. DeVoe calculations of (10R)-3 (a) and (10R)-5 (b) using MMFF geometries.
solid-state geometries, and it could not be of only intramolec-
ular origin. In order to shed light on this solid-state CD, the
relative arrangement of the aromatic naphthyl and DMB chro-
mophores from different molecules were checked in the crys-
tal lattice from the X-ray analysis of (10R)-5 (Fig. 5). The
X-ray data clearly showed that the naphthyl groups of different
(10R)-5 molecules are not stacked and neighboring naphthyl
groups are tilted relative to one another. With this orientation
an intermolecular coupling is feasible between neighboring
naphthyl and anisole chromophores. The sign and intensity
of the ECCD interaction between two chromophores can be
estimated on the basis of the projection angle q (looked
through the centers) and the center-to-center distance r
(Fig. 2).11,12 A positive acute projection angle q is associated
with a positive couplet; the maximum ECCD intensity is ob-
served for qzꢂ70ꢁ, while qz0ꢁ and 180ꢁ lead to negligible
ECCD. In addition, the exciton coupling strength varies with
the inverse third power of distance, rꢀ3. Within a threshold
two DMB groups. Some of the intermolecular naphthylenaph-
thyl distances are even shorter than the intramolecular separa-
˚
tion of l0i0nked naphthyl and DMB moieties, which is 7.0 A for
0
˚
the C-1 eC-1 distance, and 9.4 A for the center-to-center
distance. The naphthyl group denoted with letter A in Figure 5,
taken as a probe, has two nearby naphthyls (B and C) with
˚
center-to-center distances rAB and rAC¼7.0 A, plus a third
˚
naphthyl (D) at rAD¼9.4 A. The relative alignment of naph-
thyls BeD with A allows for a strong exciton interaction of
their long-axis polarized transitions. The projection angles
between the long axes of naphthyls A and B/C are qA,B and
qA,C¼ꢀ37.8ꢁ, both associated with negative ECCD. The
same is true for the A/D coupling, having qA,D¼ꢀ66.0ꢁ. The
dimethoxybenzene moiety E is the closest interacting chromo-
˚
phore to naphthyl A, with a distance rAE¼5.4 A and a projec-
tion angle qA,E¼þ45.0ꢁ between the long axes, which should
lead to a moderate positive ECCD. A second DMB (F) lies at
distance rAF¼7.3 A with projection angle qA,F¼ꢀ45.0ꢁ.
˚
˚
center-to-center distance of 10 A, each naphthyl in the crystal
To support the expectations for intermolecular couplings in
the lattice, DeVoe calculations were performed to ascertain the
coupling interactions of the naphthyl and DMB moieties of the
probe molecule with the respective surrounding chromo-
phores. Three interacting naphthyls (B, C, D) and two DMB’s
(E and F) were taken into account for the probe naphthyl (A),
and four naphthyls and one DMB (not indicated) for the probe
DMB (A0). The DeVoe-calculated CD (Fig. 6) consists of
a strong negative ECCD for the naphthyl-centered system
and small positive one for the DMB-centered one around
220 nm. Provided that these interactions are additive,12 the
CDs of the two systems can be added to produce a strong
negative couplet for the overall interchromophoric interaction
sensed by each (10R)-5 molecule in the lattice. It must, however,
be stressed that DeVoe calculations on compounds containing
multiple naphthalene units tend to overestimate degenerate
naphthylenaphthyl coupling terms in comparison with non-
degenerate couplings between naphthyls and other chromo-
phores;15a therefore, the intensity of the negative couplet in
Figure 6 is probably exaggerated.
lattice of (10R)-5 is surrounded by three other naphthyls and
D
A'
F
A
B
C
E
r
Figure 5. Orientation of the neighboring molecules of (10R)-5 in the solid state
emphasizing the intermolecular exciton-coupled interactions of the aromatic
chromophores, and definition of the projection angle for two long-axis
polarized naphthyl transitions.
This result confirms that, rather than the intramolecular
naphthyleDMB coupling, it is the intermolecular naphthyle
naphthyl interaction that dominates the solid-state CD of

G. Kerti et al. / Tetrahedron 64 (2008) 1676e1688
1681
250
200
150
100
50
intramolecular Np/DMB
(A/A') coupling
0
-50
-100
-150
intermolecular
Figure 7. Orientation of the neighboring molecules of (10R)-3 in the solid-state.
The naphthyl and DMB moieties of two aligned molecules are stacked closely
and the stacking pairs of the same kind are also arranged on the top of one
another.
couplings of DMB (A')
intermolecular
couplings of Np (A)
180
200
220 240 260
wavelength (nm)
280
Figure 6. DeVoe calculations of the couplings between the probe naphthyl
(Np) and DMB chromophores (A and A0 in Fig. 5) with the closest, strong
interacting chromophores in (10R)-5 crystals. For Np A, three Np’s and two
DMB’s were included; for DMB A0, four Np’s and one DMB were included.
To compare with the intramolecular coupling between A and A0 (also shown),
spectra are scaled to the number of coupling chromophores (five for both A
and A0).
as starting material (Scheme 2), since the products (10R)-11
and 12 could be compared with the analogous (2-naphthyl)-
methylene acetal 13 published earlier (Fig. 8).6
OH
HO
HO
O
O
OH
OMe
R2
10
(10R)-5. In solution, the regular arrangement of the chromo-
phores is disrupted and hence only the intramolecular naph-
thyleDMB interaction is measured. The present correlation
of the solid-state and solution CD, X-ray analysis, and CD
calculation of (10R)-5 provides a rare example demonstrating
the presence of intermolecular ECCD interactions in the
solid-state, and allowing the difference between the solution
and solid-state CD to be interpreted.
2'
1'
R1
iii,iv
i,ii
2"
1"
O
O
O
AcO
O
O
O
O
O
AcO
OAc
OAc
OMe
OMe
(1'S)-12a: R1= 1-naphthyl, R2= CH3
(1'R)-11
(1'R)-12b: R1= CH3 R2= 1-naphthyl
Scheme 2. (i) 6, (þ)-10-CSA, dry DMF. (ii) Ac2O/dry pyr. (iii) 7, PTS, dry
DMF. (iv) Ac2O/dry pyr.
The X-ray analysis of (10R)-3 also explains the similarity of
its solution and solid-state CD spectra (Fig. 7). In the single
crystal, every two proximal molecules of (10R)-3 are closely
stacked in a head-to-head and tail-to-tail fashion, namely two
naphthyls are stacked somewhat displaced and two anisoles
are stacked aligned. Due to such an orientation, no ECCD is
possible between the stacking chromophores, since the projec-
tion angles of their long-axis transitions are 0ꢁ or 180ꢁ. Distinct
stacking pairs of the same chromophore are arranged parallel
on top of one another somewhat rotated, but the projection
angles are again close to 0ꢁ or 180ꢁ. Since the intramolecular
interactions remain the strongest in the single crystal, the
solid-state CD is quite similar to the solution one. DeVoe cal-
culations on lattice structure of (10R)-3 confirmed that the cou-
plings between stacked naphthyls are null, while those between
the probe naphthyl and surrounding non-stacked naphthyls
give a positive couplet [231 (þ19.5), 211 (ꢀ21.2)]. Its intensity
(scaled to four couplings) is one order of magnitude smaller
than that calculated for (10R)-5 lattice. The comparison with
the computed naphthyleDMB intramolecular coupling in
(10R)-3 (Fig. 3) is biased in favor of the naphthylenaphthyl
couplings, as discussed above. However, the overall result is
in full accordance with the view that intermolecular exciton
couplings in the crystals play a decisive role in the solid-state
CD of (10R)-5 but not in that of (10R)-3.
The reaction of 10 with 6 in the presence of (þ)-10-
camphorsulfonic acid provided the (2-naphthyl)ethylidene
ketal (10R)-11 in moderate yield. The CD spectrum of (10R)-
11 could be compared with that of its deacetylated (2-naph-
thyl)methylene ketal analogue 13 in which the equatorial
arrangement of the 2-naphthyl group had been unambiguously
determined (Fig. 8).6 Since both (10R)-11 and 13 gave a posi-
tive CE at 225 nm and a negative one at 194 nm due to the
interaction of naphthyl Bb and phenyl B transitions, their
CD data suggested that the naphthyl group of (10R)-11 was
also oriented equatorially, which was also confirmed by its
X-ray analysis (Fig. 1d).
1
1
The X-ray data also revealed that the 2-naphthyl group has
an equatorial parallel conformation with the torsional angle
ꢁ
0
0
00
00
uC-2 ,C-1 ,C-2 ,C-1 ¼ꢀ7.3 . An MMFF conformational analysis
of (10R)-11 revealed instead that all the calculated low-energy
conformers have a perpendicular orientation of the naphthyl
ꢁ
0
0
00
00
ring with respect to methyl group (uC-2 ,C-1 ,C-2 ,C-1 zꢂ90 ).
By means of torsional energy scans, the parallel orientation
was estimated to have a much higher energy than the perpen-
dicular one, by 2.20 kcal/mol (MMFF) or 1.40 kcal/mol (semi-
empirical AM1). The unfavorable parallel orientation of the
naphthyl group may have been induced during the crystalliza-
tion to produce a closely stacked head-to-head/tail-to-tail
pair in the single crystal, similar to that of (10R)-3. Similar
to (10R)-3, no ECCD is possible within each stacking pair,
For the preparation of 1,3-dioxane-type naphthylethylidene
ketals, p-methoxyphenyl b-D-glucopyranoside 10 was selected

1682
G. Kerti et al. / Tetrahedron 64 (2008) 1676e1688
(a)
40
30
(1'R)-11
20
H
10
13
O
O
O
0
O
HO
OH
-10
-20
-30
-40
OMe
13
(1'S)-12a
180
190
200
210
wavelength (nm)
220
230
240
250
(b)
35
30
25
20
15
10
5
(1'R)-11 (MeCN)
(1'R)-11 (KCl)
× 3
0
-5
-10
-15
-20
(1'S)-12a
200
220
240 260
wavelength (nm)
280
300
320
Figure 8. (a) CD spectra of compounds (10R)-11, (10S)-12a, and 13 in acetonitrile. (b) CD spectra of (10R)-11 and (10S)-12a in KCl and solution CD of (10R)-11.
and only very weak ones are possible between distinct pairs,
since the projection angles of the long-axis polarized naphthyl
transitions were close to 0ꢁ or 180ꢁ. It is also noteworthy that
in contrast to (10R)-3, the planes of the distinct stacking pairs
of the same chromophores are arranged alternately orthogonal
on top of one another. Thus the solid-state CD should be
mainly of intramolecular origin and derive from a different
conformer than that predominant in solution. In addition to
the different orientation of the naphthyl ring, the solid-state
000
polarized phenyl transitions is less effective due to the dif-
ferent conformation as discussed above. DeVoe calculations
on the X-ray structure (Fig. 9) show that the less intense naph-
thyl 1Ba transition (short-axis polarized) brings about the
stronger contribution to the moderate positive couplet as
found in the corresponding experimental CD.
The reaction of 10 with 7 in the presence of PTS afforded
a mixture of the axial and equatorial 1-naphthyl ketals, which
structure of (10R)-11 shows a second torsion uC-1 ,O-1,C-1,H-1
¼
10
5
27ꢁ, far from the MMFF geometries where it is zꢂ60ꢁ. In
practice, the overall arrangement between the exciton-
coupled naphthyl and DMB chromophores differs a lot between
solid-state and lowest energy MMFF-computed structures of
(10R)-11. In agreement with these findings, in the solid-state
CD of (10R)-11 (Fig. 8b), the naphthyl 1La band showed a posi-
tive CE at 277 nm compared to the negative solution one
[283 nm (ꢀ4.4)]. Minor differences are also seen in the shape
and cross-over points of the positive CD couplet around
220 nm: in fact, the two couplets are of different origin. The
strong positive CD couplet in solution is due to the coupling
0
-5
-10
-15
(1'R)-11
(1'S)-12a
1
1
between naphthyl Bb and phenyl La/1Ba transitions, as de-
200
220
240
wavelength (nm)
260
280
300
320
duced from DeVoe calculations on the four low-energy
MMFF-calculated conformers, differing in the torsions
ꢁ
uC-2 ,C-1 ,C-2 ,C-1 zꢂ90 and uC-1 ,O-1,C-1,H-1zꢂ60ꢁ (Fig. 10a).
Figure 9. DeVoe calculations of (10R)-11 and (10S)-12a using the X-ray geo-
metries as input.
0
0
00
00
000
1
In the solid-state, the coupling of naphthyl Bb with long-axis

G. Kerti et al. / Tetrahedron 64 (2008) 1676e1688
1683
(a)
(b)
20
10
0
10
0
Conf. 1 (abs. min.)
Conf. 2 (+0.01 kcal/mol)
Conf. 3 (+0.97)
Conf. 4 (+0.98)
Weighted average
Conf. 1 (abs. min.)
Conf. 2 (+0.62 kcal/mol)
Conf. 3 (+1.02)
Conf. 4 (+1.64)
Weighted average
-10
-20
-10
-20
200
220
240
wavelength (nm)
260
280
300
320
200
220
240
260
wavelength (nm)
280
300
320
Figure 10. DeVoe calculations of (10R)-11 (a) and (10S)-12a (b) using MMFF geometries.
could be separated after acetylation as (10S)-12a and (10R)-
12b, respectively (Scheme 2). Due to steric crowding,
(10R)-12b was quite unstable and it was slowly decomposing
in solution and partially rearranging to the thermodynamically
more stable axial ketal (10S)-12a. Thus the stereochemical
study was focused on (10S)-12a, the single crystals of which
could be produced in hexane/ethyl acetate 10:1 for X-ray anal-
ysis (Fig. 2d). The X-ray data showed that its 1-naphthyl group
observed exciton-coupled interactions and to determine the
conformers in solution and in the solid state. For (10R)-3 and
(10S)-12a, nearly identical solution and solid-state CDs were
measured, which implies that the conformations found in their
X-ray structures are also prevalent in solution. This hypothesis
was further confirmed by DeVoe CD calculations on their
X-ray and MMFF-calculated geometries, which reproduced
the solid-state and solution CDs, respectively. The study of
their X-ray clusters also showed that no significant intermolec-
ular ECCD can be expected between the stacking molecules or
the stacking pairs. In contrast, the solution and solid-state CDs
of (10R)-5 were very different and the CD calculations proved
that this difference cannot be derived from different conforma-
tions in solution and solid state, but instead is due to intermo-
lecular ECCDs between neighboring aromatic chromophores
in the solid state. In the crystal lattice of (10R)-5, intermolec-
ular exciton couplings are responsible for intense ECCD that
may override the intramolecular one. A DeVoe calculation
of a solid-state cluster extracted from the X-ray data repro-
duced the large negative exciton couplet of (10R)-5. This ex-
ample emphasizes that the intermolecular ECCD of strong
aromatic chromophores have to be considered as a possible
reason for differences between solid-state and solution CDs.
Moreover, it also provides a rare example of recognition of
intermolecular ECCD interactions in the solid state. (10R)-11
has different conformations in solution and solid state but
0
0
00
00
has an axial orientation with torsional angle uC-2 ,C-1 ,C-1 ,C-2
¼
102.4ꢁ, which implies a near perpendicular conformation of
the naphthyl with respect to the methyl group. A similar
conformer was also found as the most stable one by a MMFF
conformational search. As in the other cases above, three
other low-energy MMFF conformers were also taken in to
ꢁ
0
0
00
00
account, differing in the torsions uC-2 ,C-1 ,C-1 ,C-2 zꢂ90 and
uC-1 ,O-1,C-1,H-1zꢂ60ꢁ. The DeVoe-calculated CDs of the
000
individual conformers and their averaged spectrum (Fig. 10b)
reproduced the strong negative CD couplet (Table 1 and Fig. 8)
1
that derives from the coupling between the naphthyl Bb and
1
phenyl Ba,b transitions. On the contrary, the positive CD
1
sign of naphthyl La transition [293 (1.3), 283sh (0.9), 272sh
(0.1)] was not predicted by the DeVoe method, probably due
to its non-excitonic origin. The solid-state CD spectrum of
(10S)-12a was quite similar to the solution one; a negative CD
1
couplet below 240 nm and a positive naphthyl La band were
measured (Table 1 and Fig. 8). A DeVoe calculation on the
X-ray geometry (Fig. 9) reproduced again the experimental
1
except for the naphthyl La band, the solution and solid-state
1
solid-state CD except for the sign of naphthyl La band. The
CD spectra had only subtle differences, both having a positive
ECCD below 240 nm. However, the CD calculations con-
firmed that the positive exciton couplets in solution and solid
state derived from different mechanisms, i.e., the coupling of
different naphthyl electric transition moments with the long-
axis polarized phenyl transitions.
similarity of the solution and solid-state CDs, as well as the
CD calculation results, demonstrate that the solid-state CD of
(10S)-12a is mainly determined by the same intramolecular
effects that are prevalent in solution. This is further supported
by the structural similarity between the solid-state geometry
and the lowest energy MMFF conformer.
4. Experimental
3. Conclusion
4.1. General
Solution and solid-state circular dichroism, X-ray diffrac-
tion, and DeVoe-type CD calculations on the solid-state geo-
metry and on the calculated MMFF conformers of (10R)-3,
(10R)-5, (10R)-11, and (10S)-12a allowed us to interpret the
Melting points were determined on a Kofler hot-stage appa-
ratus and are uncorrected. The NMR spectra were recorded on
Bruker-AMX 500 (1H: 500 MHz; 13C: 125 MHz), Bruker WP

1684
G. Kerti et al. / Tetrahedron 64 (2008) 1676e1688
200 SY (1H: 200 MHz, 13C: 50 MHz), and Bruker Aspect
3000 (1H: 360 MHz) spectrometers using TMS as internal
standard. Chemical shifts were reported in parts per million.
Optical rotation were determined with a PerkineElmer 241
polarimeter. CD spectra were recorded on a J-810 spectropo-
larimeter. The CD spectra were measured in millidegrees
and normalized into D3max [l molꢀ1 cmꢀ1]/l [nm] units. For
solid-state CD protocol, see Refs. 16e22. IR spectra were
recorded on an PerkineElmer 16 PC FTIR spectrometer and
absorption bands presented in cmꢀ1. Precoated silica gel plates
(Kieselgel 60 F254, 0.25 mm, Merck) were used for analytical
and preparative TLC. High resolution FAB mass spectra were
measured on a JEOL JMS-DX303 HF mass spectrometer
using a glycerol matrix and Xe ionizing gas and ESI-TOF
MS measurements were performed on a MicroTOF-Q instru-
ment (Bruker Daltonik GmbH, Bremen, Germany).
percentage of observed reflections and high but acceptable R
factors of around 9%. However, bond length and bond angle
data are reasonable and the overall error can be attributed to
the generally low quality of the crystals (Table 2). Full crystal-
lographic data (excluding structure factors) of (10R)-3, (10R)-5,
11, and (10S)-12a have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication
no. CCDC 660892e660895. Copies of the data can be ob-
tained free of charge on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: þ44 1223 336 033;
e-mail: deposit@ccdc.cam.ac.uk).
4.2.1. (10R)-p-Methoxyphenyl 6-deoxy-2,3-O-(1-naphthy)-
ethylidene-a-L-rhamnopyranoside [(10R)-2] and (10S)-
p-methoxyphenyl 6-deoxy-2,3-O-(1-naphthy)ethylidene-
a-L-rhamnopyranoside [(10S)-2]
To a suspension of 1 (201.6 mg, 0.75 mmol) in CH3CN
(5 ml), 1-(1,1-dimethoxyethyl)naphthalene (6) (915 mg,
4.24 mmol) and a catalytic amount of (þ)-10-camphorsulfonic
acid (98.3 mg, 0.393 mmol) were added, and the mixture was
stirred at room temperature for 2.5 h. Dichloromethane
(10 ml) was added to the mixture and washed with saturated
aqueous solution of Na2CO3 and brine. The combined organic
layer was dried on Na2SO4, filtered, and concentrated to give
a foam (264 mg, 84%). For the spectroscopic characterization,
100 mg were purified by preparative TLC (hexane/ethyl
acetate¼4:1), which afforded 90% (10R)-2 and 10% (10S)-2
as isolated yields.
4.2. X-ray crystallography
Data were collected at 293(1) K, Enraf Nonius MACH3
˚
diffractometer, Mo Ka radiation l¼0.71073 A, u motion.
Raw data were evaluated using the XCAD424 or the PROFIT25
software, the structure was solved using direct methods
by SIR-9226 and refined on F2 using SHELX-9727 program.
Refinement was performed anisotropically for non-hydrogen
atoms. Hydrogen atoms were placed into geometric position.
Publication material was prepared with the WINGX-97
suite.28 The ORTEP29 and PLATON programs30 were used
for crystallographic calculations. Except for (10R)-5, the crys-
tals were rather weakly diffracting ones, resulting in low
1
(10R)-2: H NMR (200 MHz, CDCl3) d 7.98e7.39 (m, 7H,
H-naphthyl), 6.97e6.75 (m, 4H, H-phenyl), 5.70 (s, 1H, H-1),
Table 2
Crystallographic data of (10R)-3, (10R)-5, (10R)-11, and (10S)-12a
Ref. No.
(10R)-3
(10R)-5
(10R)-11
(10S)-12a
Empirical formula
Formula weight
Crystal system
Space group
C27H28O7
464.49
C27H28O7
464.49
C29H30O9
522.53
C29H30O9
522.53
Orthorhombic
P212121 (no. 19)
6.1398(10)
7.684(2)
Orthorhombic
P212121 (no. 19)
12.0219(10)
12.492(2)
15.6533(10)
90
Monoclinic
P21 (no. 4)
5.6715(10)
8.4110(10)
27.6179(10)
91.90(1)
Monoclinic
P21 (no. 4)
13.812(4)
6.413(7)
˚
a (A)
˚
b (A)
˚
c (A)
50.5601(10)
90
15.666(6)
97.43(3)
b (ꢁ)
3
V (A )
˚
2385.4(7)
4
2350.8(4)
4
1316.7(3)
2
1376.0(16)
2
Z
Dimensions of crystal (mm)
Crystal color
and habit
0.36/0.25/0.2
Colorless block
0.36/0.25/0.2
Colorless block
0.35/0.2/0.15
Colorless prism
0.56/0.03/0.02
Colorless needle
Dcalcd (g cmꢀ3
)
1.293
0.09
25.3
1.312
0.10
26.0
1.318
0.10
25.5
811
1.261
0.09
25.3
m (Mo Ka)/mmꢀ1
qmax (ꢁ)
No. observed
2099
1456
1048
reflections [I>2.00s(I)]
No. independent reflections
No. variables
2945
307
2585
307
2192
343
2954
343
Residuals: R1(F)/wR2(F2)a
Goodness of fit
Max./Min. peak
0.090/0.243
1.29
0.056/0.219
0.86
0.094/0.216
0.90
0.086/0.239
1.36
0.35/ꢀ0.34
0.25/ꢀ0.23
0.24/ꢀ0.25
0.35/ꢀ0.32
in final difference
ꢀ3
˚
map/e A
P
P
P
P
2
2 1=2
a
R1ðFÞ ¼ ðjF0j ꢀ jFcjÞ= ðjF0jÞ; wR2ðF2Þ ¼ ½ wðjF02j ꢀ jFc2jÞ = wðjF02jÞ ꢃ
.

G. Kerti et al. / Tetrahedron 64 (2008) 1676e1688
1685
4.48 (d, 1H, J¼5.3 Hz, H-2), 4.34 (dd, 1H, J¼7.6, 5.3 Hz,
H-3), 3.70 (s, 3H, OMe), 3.70e3.60 (m, 1H, H-5), 3.06 (dd,
1H, J¼9.8, 7.6 Hz, H-4), 1.94 (s, 1H, OH), 1.66 (s, 3H, acetal
Me), 0.95 (d, 3H, J¼6.2 Hz, C-5 Me); 13C NMR (50 MHz,
CDCl3, 25 ꢁC) d 155.0 (C-q phenyl), 150.2 (C-q phenyl),
141.6 (C-q naphthyl), 132.9 (2ꢄC-q naphthyl), 128.4e123.2
(7ꢄC-t naphthyl), 117.8 (2ꢄC-t phenyl), 114.6 (2ꢄC-t
phenyl), 109.8 (C acetal), 96.2 (C-1), 79.2e72.7 (C-2 to C-4),
66.4 (C-5), 55.6 (OMe), 28.9 (Me), 17.1 (C-6). Calcd for
[MþNa]þ 445.162, found mass for C27H28O7 [MþNa]þ
445.162.
1H NMR (500 MHz, CDCl3) d 7.97e7.48 (m, 7H, H-naph-
thyl), 6.94 (dd, 2H, J¼9.3, <1 Hz, H-arom.), 6.80 (dd, 2H,
J¼9.3, <1 Hz, H-arom.), 5.70 (s, 1H, H-1), 5.09 (dd, 1H,
J¼9.9, 7.5 Hz, H-4), 4.42 (dd, 1H, J¼7.5, 5.5 Hz, H-3), 4.09
(d, 1H, J¼6 Hz, H-2), 3.93 (m, 1H, H-5), 3.75 (s, 3H,
OMe), 2.18 (s, 3H, OAc), 1.89 (s, 3H, acetal Me), 1.12 (d,
3H, J¼6.4 Hz, C-5 Me); 13C NMR (125 MHz, CDCl3,
25 ꢁC) d 170.2 (C acetyl), 155.0 (C-q phenyl), 150.2 (C-q phe-
nyl), 140.9 (C-q naphthyl), 133.0e132.8 (C-q naphthyl),
128.3e123.4 (7ꢄC-t naphthyl), 117.5 (2ꢄC-t phenyl), 114.6
(2ꢄC-t phenyl), 110.0 (C acetal), 96.0 (C-1), 76.0 (C-2,
C-3), 74.9 (C-4), 64.9 (C-5), 55.6 (OMe), 28.9 (Me), 21.1
(acetyl), 17.1 (C-6). Calcd for [MþNa]þ 487.173, found
mass for C27H28O7 [MþNa]þ 487.175.
1
(10S)-2: [a]D þ18.9 (c 0.1, CHCl3), H NMR (200 MHz,
CDCl3) d 7.99e7.47 (m, 7H, H-naphthyl), 6.97e6.78 (m,
4H, H-phenyl), 5.68 (s, 1H, H-1), 4.32 (t, 1H, J¼6.4 Hz),
4.07 (d, 1H, J¼6.4 Hz, H-2), 3.90e3.60 (m, 2H), 3.76 (s,
3H, OMe), 1.85 (s, 3H, acetal Me), 1.70 (s, 1H, OH), 1.31
(d, 3H, J¼6.2 Hz, C-5 Me); 13C NMR (125 MHz, CDCl3,
25 ꢁC) d 154.9 (C-q phenyl), 150.1 (C-q phenyl), 140.8 (C-q
naphthyl), 133.0 (C-q naphthyl), 132.8 (C-q naphthyl), 130.9e
123.3 (7ꢄC-t naphthyl), 117.5 (2ꢄC-t phenyl), 114.5 (2ꢄC-t
phenyl), 109.8 (C acetal), 96.1 (C-1), 78.4e75.2 (C-2 to C-4),
66.6 (C-5), 55.6 (OMe), 29.2 (Me), 17.5 (C-6). Calcd for
[MþNa]þ 445.162, found mass for C27H28O7 [MþNa]þ
445.163.
4.2.3. (10R)-p-Methoxyphenyl 6-deoxy-2,3-O-(1-naphthyl)-
ethylidene-a-L-rhamnopyranoside [(10R)-4]
To a suspension of 1 (300 mg, 1.11 mmol) in CH3CN
(10 ml), 1-(1,1-dimethoxyethyl)naphthalene (7) (480 mg,
2.22 mmol) and a catalytic amount of p-toluenesulfonic acid
(10 mg, 0.053 mmol) were added and the mixture was stirred
at room temperature for 5 h. Then the mixture was neutralized
with triethylamine and evaporated in vacuum. The residue
was purified by column chromatography (hexane/ethyl
acetate¼9:1) to give a foam (419 mg, 89%). [a]D ꢀ74.9
1
4.2.2. (10R)-p-Methoxyphenyl 4-O-acetyl-6-deoxy-2,3-O-
(2-naphthyl)ethylidene-a-L-rhamnopyranoside [(10R)-3]
and (10S)-p-methoxyphenyl 4-O-acetyl-6-deoxy-2,3-O-
(c 0.9, CHCl3); H NMR (200 MHz, CDCl3) d 8.57 (d, 1H,
J¼9.3 Hz, H-naphthyl), 7.92e7.42 (m, 6H, H-naphthyl),
7.05e6.82 (m, 4H, H-phenyl), 5.78 (s, 1H, H-1), 4.60 (d,
1H, J¼5.3 Hz, H-2), 4.46 (dd, 1H, J¼7.6, 5.3 Hz, H-3),
3.78 (s, 3H, OMe), 3.77e3.71 (m, 1H, H-5), 3.12 (dd, 1H,
J¼9.8, 7.6 Hz, H-4), 1.88 (s, 1H, OH), 1.87 (s, 3H, acetal
Me), 1.01 (d, 3H, J¼6.2 Hz, C-5 Me); 13C NMR (125 MHz,
CDCl3, 25 ꢁC) d 155.0 (C-q phenyl), 150.3 (C-q phenyl),
140.2 (C-q naphthyl), 134.4 (C-q naphthyl), 129.8 (C-q
naphthyl), 129.0e122.6 (C-t naphthyl), 117.8 (C-t phenyl),
114.6 (C-t phenyl), 110.5 (C acetal), 96.3 (C-1), 79.1e66.3
(C-2 to C-5), 55.6 (OMe), 29.0 (Me), 16.9 (C-6). Calcd for
[MþNa]þ 445.162, found mass for C27H28O7 [MþNa]þ
445.163.
(2-naphthyl)ethylidene-a-L-rhamnopyranoside [(10S)-3]
The 9:1 mixture of (10R)-2 and (10S)-2 (158 mg,
0.374 mmol) was treated with pyridine (1.5 ml) and acetic
anhydride (1.5 ml) for 12 h at room temperature. Then the
solution was slowly quenched with aqueous 10% HCl and
extracted with ethyl acetate (3ꢄ10 ml). The organic layer
was washed with saturated aqueous solution of NaHCO3
(3ꢄ) and brine, dried (MgSO4), filtered, and concentrated in
vacuum to give a yellow oil (221 mg, 85%). The (10R)-3 iso-
mer was crystallized from hexane (mp: 111e112 ꢁC), and
the residue was purified further by preparative TLC (hexane/
ethyl acetate¼3:1) to give (10S)-3, mp: 131e133 ꢁC.
(10R)-3: [a]D ꢀ91.9 (c 0.8, CHCl3); IR nmax (KBr) 2932,
1742, 1592, 1508, 1376, 1284, 1230, 1138, 1038, 826,
4.2.4. (10R)-p-Methoxyphenyl 4-O-acetyl-6-deoxy-2,3-O-
(1-naphthyl)ethylidene-a-L-rhamnopyranoside [(10R)-5]
(10R)-4 (88 mg, 0.208 mmol) was treated with pyridine
(0.5 ml) and acetic anhydride (0.5 ml) for 12 h at room tem-
perature. Then the solution was slowly quenched with aqueous
10% HCl and extracted with ethyl acetate (3ꢄ10 ml). The
organic layer was washed with saturated aqueous solution of
NaHCO3 (3ꢄ) and brine, dried (MgSO4), filtered, and concen-
trated in vacuum to give a foam (94 mg, 93%), which was
crystallized from hexane. Mp: 144e145 ꢁC; [a]D ꢀ82.2 (c
0.9, CHCl3); IR nmax (KBr) 2932, 1744, 1508, 1370, 1288,
748 cmꢀ1 1H NMR (500 MHz, CDCl3) d 8.05e7.46 (m,
;
7H, H-naphthyl), 6.84 (dd, 2H, J¼8.8, <1 Hz, H-arom.),
6.82 (dd, 2H, J¼8.8, <1 Hz, H-arom.), 5.73 (s, 1H, H-1),
4.64 (m, 2H, H-2þH-3), 4.59 (m, 1H, H-4), 3.84 (m, 1H,
H-5), 3.56 (s, 3H, OMe), 2.08 (s, 3H, OAc), 1.73 (s, 3H, acetal
Me), 0.93 (d, 3H, J¼6.2 Hz, C-5 Me); 13C NMR (125 MHz,
CDCl3, 25 ꢁC) d 169.3 (C acetyl), 155.1 (C-q phenyl), 150.2
(C-q phenyl), 140.3 (C-q naphthyl), 133.1 (C-q naphthyl),
132.9 (C-q naphthyl), 128.6e123.4 (7ꢄC-t naphthyl), 117.7
(2ꢄC-t phenyl), 114.7 (2ꢄC-t phenyl), 110.4 (C acetal),
96.1 (C-1), 76.6e73.5 (C-2 to C-4), 64.8 (C-5), 55.6 (OMe),
28.6 (Me), 20.9 (acetyl), 16.9 (C-6). Calcd for [MþNa]þ
487.173, found mass for C27H28O7 [MþNa]þ 487.174.
1228, 1128, 1102, 1038, 826, 780 cmꢀ1
;
1H NMR
(500 MHz, CDCl3) d 8.51e7.47 (m, 7H, H-naphthyl), 7.02
(dd, 2H, J¼9.2, <1 Hz, H-arom.), 6.84 (dd, 2H, J¼9.2,
<1 Hz, H-arom.), 4.66e4.64 (m, 2H, H-2þH-3), 4.62 (m,
1H, H-4), 3.85 (m, 1H, H-5), 3.78 (s, 3H, OMe), 2.04 (s,
3H, OAc), 1.89 (s, 3H, acetal Me), 0.93 (d, 3H, J¼6.2 Hz,
(10S)-3: [a]D ꢀ25.8 (c 1.0, CHCl3); IR nmax (KBr) 2934,
1740, 1570, 1508, 1378, 1224, 1138, 1106, 1040, 768 cmꢀ1
;

1686
G. Kerti et al. / Tetrahedron 64 (2008) 1676e1688
C-5 Me); 13C NMR (125 MHz, CDCl3, 25 ꢁC) d 169.1 (C ace-
tyl), 155.0 (C-q phenyl), 150.2 (C-q phenyl), 139.0 (C-q naph-
thyl), 134.3 (C-q naphthyl), 129.9 (C-q naphthyl), 129.1e
123.2 (7ꢄC-t naphthyl), 117.7 (2ꢄC-t phenyl), 114.6 (2ꢄC-t
phenyl), 110.9 (C acetal), 96.1 (C-1), 76.2e75.8 (C-2, C-3),
73.2 (C-4), 64.9 (C-5), 55.6 (OMe), 28.6 (Me), 20.7 (C acetyl),
16.8 (C-6). Calcd for [MþNa]þ 487.173, found mass for
C27H28O7 [MþNa]þ 487.175.
128.33, 127.74, 126.55, 126.31, 125.90, 123.52, 117.76,
114.69, 103.39 (C acetal), 96.28 (C-1), 77.27, 75.73, 71.50,
64.54 (C-2 to C-5), 55.65 (OMe), 21.00 (C acetyl), 17.10
(C-6). Calcd for [MþNa]þ 473.157, found mass for
C26H26O7 [MþNa]þ 473.158.
Yield for the (10R) acetal: 0.226 g (13%); [a]D ꢀ17.2 (c 0.2,
CHCl3); mp: 125e128 ꢁC (EtOAcehexane); 1H NMR
(200 MHz, CDCl3) d 8.07 (1H, s, H-arom.), 7.98e7.82 (3H,
m, H-arom.), 7.71 (1H, dd, H-arom.), 7.55e7.45 (2H, m,
H-arom.), 7.03 (2H, d, J¼9.1 Hz, H-arom.), 6.84 (2H, d,
J¼9.1 Hz, H-arom.), 6.13 (1H, s, H-acetal), 5.76 (1H, s,
H-1), 5.10 (1H, dd, J¼6.8, 10.0 Hz), 4.62e4.48 (2H, m),
4.08e3.92 (1H, m), 3.77 (3H, s, OMe), 2.13 (3H, s, OAc),
1.16 (d, 3H, J¼6.6 Hz, C-5 Me); 13C NMR (200 MHz
CDCl3) d 169.88 (C acetyl), 155.13, 150.09, 135.50, 134.05,
133.75, 133.00, 128.47, 128.30, 127.71, 126.90, 126.58,
126.20, 125.90, 123.99, 123.53, 117.74, 114.69, 104.96 (C
acetal), 96.06 (C-1), 78.10, 75.68, 74.84, 64.92 (C-2 to C-5),
55.62 (OMe), 21.00 (C acetyl), 17.12 (C-6). Calcd for
[MþNa]þ 473.157, found mass for C26H26O7 [MþNa]þ
473.159.
4.2.5. (10S)-p-Methoxyphenyl 2,3-O-(2-naphthyl)methylene-
a-L-rhamnopyranoside and (10R)-p-methoxyphenyl 2,3-O-
(2-naphthyl)methylene-a-L-rhamnopyranoside
[deacetylated derivatives of (10S)-9 and (10R)-9]
To a solution of p-methoxyphenyl a-L-rhamnopyranoside
(1) (4.045 g, 15 mmol) in DMF (10 ml), 2-(dimethoxyme-
thyl)naphthalene (4.7 ml, 23 mmol, 1.55 equiv) and p-toluene-
sulfonic acid (220 mg) were added and the mixture was stirred
for 90 h at room temperature, when the conversion reached
90% (TLC: hexane/ethyl acetate¼7:3). The solution was
diluted with dichloromethane (DCM) (200 ml) and was
extracted once with aq NaHCO3 (50 ml) and with water
(3ꢄ30 ml). The united aqueous phases were extracted once
more with DCM, and the united organic layers were dried
over MgSO4, filtered and evaporated in vacuum. The syrupy
residue was purified by column chromatography using hex-
ane/ethyl acetate¼8:2þ5% triethylamine (TEA) as the eluent.
Yield of 4.768 g (78%) was directly used for the next step.
4.2.7. (10R)-p-Methoxyphenyl 2,3-di-O-acetyl-4,6-O-
(2-naphthyl)ethylidene-b-D-glucopyranoside [(10R)-11]
To a suspension of 10 (175 mg, 0.62 mmol) in DMF (5 ml),
2-(1,1-dimethoxyethyl)naphthalene (6) (710 mg, 3.29 mmol)
and a catalytic amount of (þ)-10-camphorsulfonic acid
(87 mg, 0.348 mmol) were added and the mixture was stirred
at room temperature for 3 h. The mixture was neutralized with
triethylamine and evaporated in vacuum. Then diethyl ether
was added to the mixture and washed with brine (3ꢄ). The or-
ganic layer was dried (MgSO4), filtered, and concentrated in
vacuum. The residue was purified by column chromatography
(hexane/ethyl acetate¼1:1) to give a foam (93 mg, 35%),
which was treated with pyridine (1 ml) and acetic anhydride
(1 ml) for 12 h at room temperature. Then the solution was
slowly quenched with aqueous 10% HCl and extracted with
ethyl acetate (3ꢄ10 ml). The organic layer was washed with
saturated aqueous solution of NaHCO3 (3ꢄ) and brine, dried
(MgSO4), filtered, and concentrated in vacuum to give
a foam (101 mg, 91%), which was crystallized from cyclohex-
ane (mp: 159e161 ꢁC). [a]D þ7.1 (c 0.4, CHCl3); IR nmax
(KBr) 2956, 2898, 1748, 1508, 1372, 1220, 1128, 1074,
4.2.6. (10S)-p-Methoxyphenyl 4-O-acetyl-2,3-O-
(2-naphthyl)methylene-a-L-rhamnopyranoside [(10S)-9]
and (10R)-p-methoxyphenyl 4-O-acetyl-2,3-O-(2-naphthyl)-
methylene-a-L-rhamnopyranoside [(10R)-9]
p-Methoxyphenyl 2,3-O-(2-naphthyl)methylene-a-L-rham-
nopyranoside [(10S) and (10R)] (1.606 g, 3.9 mmol) was dis-
solved in pyridine (4 ml) and acetic anhydride (3 ml) was
added and the solution was stirred at room temperature for
3 h (TLC: hexane/ethyl acetate¼7:3). The mixture was poured
onto ice-water and was extracted with DCM (100 ml). The
organic solution was washed twice with sulfuric acid solution
(0.05 M), once with water and twice with aq NaHCO3 solu-
tion. The organic layer was dried over MgSO4, filtered, and
evaporated and the residue was purified by column chromato-
graphy using hexane/ethyl acetate¼8:2þ5% TEA as the elu-
ent. The complete separation of (10S) (Rf: 0.53) and (10R)
(Rf: 0.44) acetals could not be achieved. The homogeneous
fractions were collected and used for spectroscopic character-
ization, the non-homogeneous fractions weighed 1.060 g.
Yield for the (10S) acetal: 0.279 g (16%); [a]D ꢀ19.7 (c 0.1,
CHCl3); mp: 181e182 ꢁC (EtOH); 1H NMR (200 MHz,
CDCl3) d 8.00e7.80 (4H, m, H-arom.), 7.60e7.44 (3H,
m, H-arom.), 7.01 (2H, d, J¼9.1 Hz, H-arom.), 6.84 (2H,
d, J¼9.1 Hz, H-arom.), 6.42 (1H, s, H-acetal), 5.71 (1H, s,
H-1), 5.14 (1H, dd, J¼7.8 and 10.2 Hz), 4.72 (1H, dd,
J¼5.1 and 7.8 Hz), 4.44 (1H, d, J¼5.1 Hz), 4.09e3.91
(1H, m), 3.78 (3H, s, OMe), 2.18 (3H, s, OAc), 1.21 (d, 3H,
J¼6.2 Hz, C-5 Me); 13C NMR (200 MHz, CDCl3) d 170.23
(C acetyl), 155.16, 150.17, 135.50, 133.83, 132.91, 128.49,
1
1034, 830, 754 cmꢀ1; H NMR (500 MHz, CDCl3) d 7.97e
7.47 (m, 7H, H-naphthyl), 6.93 (dd, 2H, J¼9.1, <1 Hz, H-
arom.), 6.81 (dd, 2H, J¼9.1, <1 Hz, H-arom.), 5.38 (t, 1H,
J¼9.4 Hz, H-3), 5.28 (t, 1H, J¼7.9 Hz, H-2), 5.01 (d, 1H,
J¼7.9 Hz, H-1), 4.12 (m, 2H, H-6), 4.04 (t, 1H, J¼9.4 Hz,
H-4), 3.76 (s, 3H, OMe), 3.57 (m, 1H, H-5), 2.16 (s, 3H,
OAc), 2.09 (s, 3H, OAc), 1.80 (s, 3H, acetal Me); 13C NMR
(125 MHz, CDCl3, 25 ꢁC) d 170.2 (C acetyl), 169.6 (C acetyl),
155.8 (C-q phenyl), 150.9 (C-q phenyl), 140.6 (C-q naphthyl),
133.1 (C-q naphthyl), 132.9 (C-q naphthyl), 128.5e123.1
(7ꢄC-t naphthyl), 118.6 (2ꢄC-t phenyl), 114.6 (2ꢄC-t phe-
nyl), 100.9 (C-1), 100.5 (C acetal), 72.3 (C-2, C-3), 70.9
(C-4), 67.8 (C-5), 62.5 (C-6), 55.6 (OMe), 22.6 (Me), 20.9

G. Kerti et al. / Tetrahedron 64 (2008) 1676e1688
1687
(C acetyl), 20.7 (C acetyl). Calcd for [MþNa]þ 545.178,
found mass for C29H30O9 [MþNa]þ 545.180.
Table 3
Spectral parameters for 1,4-dimethoxybenzene (DMB) and naphthalene used
in DeVoe calculations
Band Calculateda
Experimentalb
Pol. lmax Dn
(nm) (kK) (kK) (D2)
4.2.8. (10S)-p-Methoxyphenyl 2,3-di-O-acetyl-4,6-O-
(1-naphthyl)ethylidene-b-D-glucopyranoside [(10S)-12a]
and (10R)-p-methoxyphenyl 2,3-di-O-acetyl-4,6-O-
lmax
f
n
D
(nm)
1Lb
1La
1Bb
1Ba
1Lb
1La
1Bb
1Ba
289.0 0.06
256.2 0.19
208.4 0.67
207.2 0.83
315.3 0.004
296.5 0.15
235.3 1.65
225.9 0.57
L
S
L
S
L
S
L
S
288 34.7 2.6
224 44.7 3.6
2.3
7.0
(1-naphthyl)ethylidene-b-D-glucopyranoside [(10R)-12b]
To a suspension of 10 (286 mg, 1 mmol) in DMF (5 ml),
1-(1,1-dimethoxyethyl)naphthalene (7) (276 mg, 1.3 mmol)
and a catalytic amount of p-toluenesulfonic acid (19 mg,
0.1 mmol) were added and the mixture was stirred at room
temperature for 40 h. The mixture was neutralized with TEA
and evaporated in vacuum. Then diethyl ether was added to
the mixture and washed with water (3ꢄ). The organic layer
was dried (MgSO4), filtered, and concentrated in vacuum.
The residue was purified by column chromatography (hex-
ane/ethyl acetate¼1:1) to give a foam (102 mg, 23%), which
was treated with pyridine (0.5 ml) and acetic anhydride
(0.5 ml) for 12 h at room temperature. Then the solution was
slowly quenched with aqueous 10% HCl and extracted with
ethyl acetate (3ꢄ10 ml). The organic layer was washed with
saturated aqueous solution of NaHCO3 (3ꢄ) and brine, dried
(MgSO4), filtered, and concentrated in vacuum to give
a foam (94.5 mg, 84%), which was crystallized from hexane/
ethyl acetate¼10:1 to give (10S)-12a (mp: 154e156 ꢁC).
[a]D ꢀ78.3 (c 0.1, CHCl3); IR nmax (KBr) 3048, 2954, 1750,
S
L
193 51.5c 2.5c 10.0c
51.8c 2.5c 12.0c
H3CO
OCH3
312 32.0 nc
276 36.2 4.0
220 45.4 2.0e 45.0e
47.6e 2.0e 12.0e
ncd
5.4
S
L
a
ZINDO/S calculations on B3LYP/6e31G(d) optimized structures (DMB in
C2h symmetry); f, oscillator strength; Pol.: polarization direction as indicated
in the diagrams (L, long axis; S, short axis).
b
From UV spectra in acetonitrile, concentrations 1.16 mM (DMB) and
1.39 mM (naphthalene), 0.01 cm cell. Legend: n, transition frequency in kK
(103 cmꢀ1); Dn, half-height bandwidth in kK; D, dipole strength in square
Debye (1 D2¼10ꢀ36 cgs). These values were used in DeVoe calculations.
c
Values calculated with two-Gaussians fit of the absorption band, assuming
a frequency separation of 0.3 kK as found by ZINDO.
d
Not considered in the calculations.
Band 1Ba appearing as a short-wavelength shoulder on the most intense
e
one.32 Parameters calculated assuming a frequency separation of 1.7 kK as
found by ZINDO.
4.3. Computational section
1508, 1374, 1246, 1222, 1176, 1106, 1084, 1036, 760 cmꢀ1
;
1H NMR (500 MHz, CDCl3) d 7.90e7.44 (m, 7H, H-naph-
thyl), 6.85 (dd, 2H, J¼8.8, <1 Hz, H-arom.), 6.68 (dd, 2H,
J¼8.8, <1 Hz, H-arom.), 5.37 (t, 1H, J¼8.1 Hz, H-3), 5.01e
4.96 (m, 2H, H-1þH-2), 4.12 (m, 1H, H-6a), 3.79 (m, 1H,
H-6b), 3.76 (s, 3H, OMe), 3.68 (m, 1H, H-5), 3.67 (m, 1H,
H-4), 2.18 (s, 3H, OAc), 2.04 (s, 3H, OAc), 1.78 (s, 3H, acetal
DeVoe calculations were run with a Fortran program writ-
ten by Hug,31 using MMFF-optimized geometries or solid-
state structures as input. Spectral parameters for transition
dipoles (reported in Table 3) were extracted from UV spectra
of 1,4-dimethoxybenzene (DMB) and naphthalene in aceto-
nitrile, supported by ZINDO calculations on DFT-optimized
structures. Dipoles were placed in the center or respective
chromophores. For DeVoe calculations of cell clusters, the
DMB or naphthalene chromophore in a central molecule was
allowed to couple with all chromophores belonging to distinct
13
Me); C NMR (125 MHz, CDCl3, 25 ꢁC) d 170.3 (C acetyl),
169.4 (C acetyl), 155.8 (C-q phenyl), 150.9 (C-q phenyl),
134.9 (C-q naphthyl), 134.3 (C-q naphthyl), 130.7 (C-q naph-
thyl), 129.8e125.1 (7ꢄC-t naphthyl), 118.8 (2ꢄC-t phenyl),
114.5 (2ꢄC-t phenyl), 103.4 (acetal), 100.7 (C-1), 72.4e
72.0 (C-2 to C-4), 67.0 (C-5), 63.1 (C-6), 55.6 (OMe), 30.2
(Me), 21.0 (C acetyl), 20.6 (C acetyl). Calcd for [MþNa]þ
545.178, found mass for C29H30O9 [MþNa]þ 545.180.
For the spectroscopic identification of (10R)-12b, 50 mg of
the foam were purified by preparative TLC (hexane/ethyl
˚
molecules at distances <10 A (center-to-center).
MMFF conformational searches and AM1 calculations were
runusingSpartan’06, Wavefunction, Inc, IrvineCA, withdefault
parameters and convergence criteria. ZINDO and DFT calcula-
tions were run using Gaussian’03 W, Revision D.01, Gaussian,
Inc., Pittsburgh PA. DFT geometry optimizations were executed
with B3LYP/6-31G(d) method, using an input C2h-symmetric
structure forDMB and D2h-symmetricstructure for naphthalene.
1
acetate¼2:1). H NMR (200 MHz, CDCl3) d 8.44e8.39 (m,
1H, H-naphthyl), 7.87e7.79 (m, 3H, H-naphthyl), 7.48e7.41
(m, 3H, H-naphthyl), 6.93e6.77 (m, 4H, H-phenyl), 5.39
(t, 1H, J¼9.2 Hz), 5.29 (t, 1H, J¼9.2 Hz), 4.20 (t, 1H,
J¼9.2 Hz), 4.10e4.03 (m, 2H), 3.76 (s, 3H, OMe), 3.64e
3.55 (m, 1H), 2.19 (s, 3H, OAc), 2.09 (s, 3H, OAc), 1.93
(s, 3H, acetal Me); 13C NMR (50 MHz, CDCl3, 25 ꢁC) d 170.1
(C acetyl), 169.6 (C acetyl), 155.8 (C-q phenyl), 150.9 (C-q phe-
nyl), 138.4 (C-q naphthyl), 134.4 (C-q naphthyl), 129.9 (C-q
naphthyl), 129.4e124.1 (7ꢄC-t naphthyl), 118.6 (2ꢄC-t phe-
nyl), 114.6 (2ꢄC-t phenyl), 101.3 (acetal), 100.9 (C-1), 72.3e
67.8 (C-2 to C-5), 62.5 (C-6), 55.6 (OMe), 23.4 (Me), 20.8 (C
acetyl), 20.7 (C acetyl). Calcd for [MþNa]þ 545.178, found
mass for C29H30O9 [MþNa]þ 545.179.
Acknowledgements
S.A. and T.K. thank the Hungarian Scientific Research
Fund (OTKA) and National Office for Research and Techno-
logy (NKTH) for financial support (T-049436, NI-61336 and
K-68429).
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