Phenylboronic acid esters of the common 2-deoxy-aldoses

Article abstract of DOI:10.1016/j.carres.2011.05.031

Phenylboronic acid esters are formed by the three common 2-deoxy aldoses: 2-deoxy-D-erythro-pentose ('2-deoxy-D-ribose'), 2-deoxy-D-lyxo-hexose ('2-deoxy-D-galactose'), and 2-deoxy-D-arabino-hexose ('2- deoxy-D-glucose'). The major species that was formed

Full text of DOI:10.1016/j.carres.2011.05.031

Carbohydrate Research 346 (2011) 1752–1759
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Phenylboronic acid esters of the common 2-deoxy-aldoses
⇑
David Heß, Peter Klüfers
Ludwig-Maximilians-Universität, Department Chemie, Butenandtstraße 5-13, 81377 München, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 April 2011
Received in revised form 24 May 2011
Accepted 27 May 2011
Available online 21 July 2011
Phenylboronic acid esters are formed by the three common 2-deoxy aldoses: 2-deoxy-
D
-erythro-pentose
-arabino-hexose (‘2-
-glucose’). The major species that was formed from equimolar quantities of boronic acid and
(‘2-deoxy-
deoxy-
D-ribose’), 2-deoxy-D-lyxo-hexose (‘2-deoxy-D-galactose’), and 2-deoxy-D
D
the aldose, was the 3,4-monoester of the pentopyranose in a skew-boat conformation, and the 4,6-mono-
ester in the case of the two hexopyranoses. A double molar quantity of boronic acid led, for both 2-deoxy-
hexoses, to the diester of the open-chain aldehydo isomer as the major product: the 3,5:4,6-diester for
the lyxo-configured deoxy-hexose, and the 3,4:5,6-diester of the arabino-configured isomer. Minor prod-
ucts of all reactions were identified by a combined NMR/DFT methodology.
Keywords:
Deoxy-glycoses
Phenylboronic acid esters
Aldehydo isomers
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
2-Deoxy-aldoses may be different. Due to the lack of the elec-
tron-withdrawing 2-hydroxy function, the anomeric hydroxy
The coordination chemistry of the glycoses (‘reducing sugars’,
aldoses and ketoses) is governed by the unusual adaptability of
their chelating O-atom pattern to a (semi)metal’s pattern of li-
gand-binding sites. In contrast to a usual ligand that is able to
match its ligating donor sites to the metal centre by adapting only
its conformation, a glycose’s variability is unique because its con-
figuration is adaptable as well. Due to the coexistence of the vari-
ous isomers (pyranose, furanose, open-chain forms) in a glycose’s
solution equilibrium, a dynamic ligand library is thus provided to
a central metal. In addition, common conformational matching is
available for the more flexible isomers such as the furanose ano-
mers. Stable chelates require a deprotonation of the coordinating
hydroxy functions. Depending on the metal’s Lewis acidity, the
more acidic anomeric hydroxy function is either a preferred bind-
ing site (weak-to-moderate Lewis acidity), or it is avoided if a cen-
tral metal’s Lewis acidity is so high that it prefers bonding to the
strongly basic alkoxide functions stemming from the weakly acidic
alcoholic hydroxy group.
The phenylborylene moiety provides a small semimetal centre
of intermediate-to-strong acidity. Accordingly, aldoses form equi-
librium mixtures of phenylboronic acid esters that may include
the glycose’s anomeric centre but do not necessarily do so. Exam-
ples include the parent aldoses of the 2-deoxy-aldoses of this work.
On the one hand, ribose forms a 2,4-chelate with its pyranose form
and thus excludes the anomeric hydroxy function. On the other
hand, glucose was transformed into a 1,2:3,5-diborylated furanose
diester, thus including the anomeric hydroxy group.1,2
group is no longer significantly more acidic than the alcoholic
OH functions. A metal probe that has weak-to-moderate Lewis-
acidic such as palladium(II) thus loses its usual preference for che-
lates that include the 1-OH function and, instead, shows a mixture
of chelates that is governed by rules other than the order of
acidities.3
In this work, we will be reporting on the esters formed by phen-
ylboronic acid and the three common 2-deoxy-aldoses derived
from the 2-epimeric couples ribose/arabinose, galactose/gulose,
and glucose/mannose, namely 2-deoxy-D-erythro-pentose (ery-
dPen), 2-deoxy- -lyxo-hexose (lyx-dHex), and 2-deoxy-
D
D-arabino-
hexose (ara-dHex), respectively. The analytical strategy chosen
accounts for the fact that the phenylborylene residue is able to force
a glycose into unstable conformations such as pyranose boats. The
NMR-spectroscopic analysis, based, as in related work, on 2D tech-
niques and the use of Karplus relationships to identify the isomer in
question, thus did not reach the same degree of confidence as in the
palladium-based work. The reason was that the last step of the lat-
ter can use the so-called ‘coordination-induced shift’ (CIS) to iden-
tify heteroatom binding in a five-membered chelate ring by a
typical downfield shift of the respective 13C NMR signals. A prere-
quisite of the CIS determination is the availability of the chemical
shifts of the free, non-derivatised glycose isomer as the reference
state. The method thus is not applicable if the spectra of the refer-
ence molecules are unknown due to either a too small amount of
the respective glycose isomer or the glycose’s transformation to
an unstable conformation in the chelate. In the compounds of this
work, both obstacles had to be surmounted, as well as the pro-
nounced tendency of the boron centre to form six-membered che-
late rings which give rise to a less characteristic CIS pattern.
⇑
Corresponding author.
E-mail address: kluef@cup.uni-muenchen.de (P. Klüfers).
0008-6215/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2011.05.031

D. Heß, P. Klüfers / Carbohydrate Research 346 (2011) 1752–1759
1753
As a substitute for the lacking CIS-based arguments, we chose a
C5
C4
computer-chemical approach. The Karplus-relationship-based pro-
cedure thus was either followed by or just replaced by a first-prin-
ciples calculation of the molecules that appeared to be possible
alternatives, and their calculated 13C NMR shift pattern was com-
pared with the experimental spectrum to identify the correct
molecular structure.2 The method was validated for 2-deoxy-gly-
coses by the investigation of a methyl aldopyranoside of each
O5
C2
C6
O1
O4
B1
C1
C3
O3
2-deoxy-aldose of this work, namely Me-b-ery-dPenp, Me-
a-lyx-
C7
dHexp, and Me- -ara-dHexp (following IUPAC usage, in this work
a
‘p’ denotes a pyranose, ‘f’ a furanose). The three glycosides are well-
suited for a calibration procedure since they are configurationally
fixed, have restricted chelating properties because of the lack of a
1-OH function, and afforded crystal-structure analysis of their
borylene derivatives.
C8...
Figure 1. ORTEP representation of the molecular structure of BPh(Me-b-ery-
dPenp3,4HÀ2) in crystals of 1b (40% probability ellipsoids). Distances (Å) and
angles (°): B1–O3 1.366(2), B1–O4 1.368(2), O3–B1–O4 113.6(2); O1–C1–C2–C3
151.4(2), O3–C3–C4–O4: 9.2(2)°. Puckering Å parameters of the pyranose ring O5–
2. Results and discussion
2.1. 2-Deoxy-pyranosides
C1–. . .: Q = 0.704(2) Å, h = 95.5(2)°,
conformation between 2SO and 2,5B. The flat chelate ring (Q = 0.089(2) Å,
= 268(1)°) is slightly 4T3-twisted.17
u = 141.1(2)°, which resembles a skew-boat
u
The only product of the reaction of equimolar quantities of
phenylboronic acid and methyl 2-deoxy-b-D-erythro-pentopyrano-
are compiled in the Section 4 (1H NMR spectra) and in Table 1
(
The methyl 2-deoxy-D-hexopyranosides, both the lyxo- and the
arabino-configured isomer, reacted with an equimolar amount of
phenylboronic acid under 4,6-esterification. The crystal-structure
side (Me-b-ery-dPenp) showed some of the mentioned features. A
Karplus-relationship-based analysis resulted in a skew-boat con-
formation of the product which went along with an almost
eclipsed conformation of the former 3,4-diol function. The confor-
mation was indicative of the esterification of the 3,4-diol function.
In agreement with the formation of a five-membered chelate ring,
the significant downfield shifts of the 13C3 and 13C4 NMR signals
were expected (Table 1). However, the conformational change
was also observable by the large upfield shifts of the remaining
pyranose-atom signals. In a DFT approach, the 13C NMR shift pat-
tern was reproduced with a mean deviation of 1.1 ppm, and a
maximum deviation of 2.4 ppm for the anomeric carbon. Crystal-
structure analysis showed the conformation of the pyranose ring
more precisely. In crystals of BPh(Me-b-ery-dPenp3,4HÀ2) (1b),
the chelate ring, which is annellated to the pyranose skew boat,
is almost flat in terms of O3–C3–C4–O4 torsion (Fig. 1).
13C NMR spectra).
analyses of BPh(Me-
a
-lyxo-dHexp4,6H
)
À2
(2) (Fig. 2) and
BPh(Me- -arabino-dHexp4,6HÀ2) (3) (Fig. 3) showed molecules
a
whose pyranose part resides in the stable 4C1 chair whereas a
half-chair conformation resulted for the chelate rings. The observa-
tion that six-membered chelate rings give rise to a CIS pattern dif-
ferent from that of their five-membered counterparts (weakly
downfield–strongly upfield–weakly downfield for the three
carbons of the six-membered cycle versus strongly downfield–
strongly downfield for the vicinal diol’s carbons of a five-mem-
bered chelate), is obvious from Table 1. At the same time, the shifts
related to the carbon atoms in the vicinity to the chelate were min-
or in agreement with a smaller alteration of the conformation in
the borylated and the reference state. The match of DFT-calculated
The investigation on the b-anomer was completed by spectro-
scopic/DFT work on the respective
a glycoside (1a). The results
Table 1
Experimental (dexp) and calculated (dcalcd
boronic-acid esters of the 2-deoxy-pyranosides 1–3 in DMSO-d6
)
13C NMR chemical shifts (ppm) of the
C1
97.8
95.4
2.4
100.4
À2.6
96.4
94.7
1.7
98.6
À2.2
98.6
97.8
0.8
C2
C3
C4
C5
C6
OMe
1a
1b
2
dexp
dcalcd
dexp À dcalcd
dref
dexp À dref
dexp
dcalcd
dexp À dcalcd
dref
dexp À dref
dexp
dcalcd
dexp À dcalcd
dref
dexp À dref
33.3
32.7
0.6
35.0
À1.7
30.4
31.1
À0.7
34.1
À3.7
32.1
33.4
À1.3
32.7
À0.6
71.8
70.8
1.0
67.1
4.7
72.6
72.4
0.2
66.6
6.0
61.6
61.7
À0.1
65.1
À3.5
61.0
60.9
0.1
63.2
À2.2
64.4
64.7
À0.3
71.3
À6.9
54.8
52.4
2.4
55.3
À0.5
54.5
53.2
1.3
54.5
0.0
C9...
O4
C8
C2
O6
C6
B1
72.0
72.9
À0.9
64.3
7.7
74.5
75.1
À0.6
67.3
7.2
C4
C5
O5
63.6
65.8
À2.2
64.8
À1.2
69.8
70.1
À0.3
67.4
2.4
64.9
65.2
À0.3
61.1
3.8
54.4
53.4
À1.0
53.9
0.5
O3
C3
C1
O1
98.0
0.6
C7
3
dexp
dcalcd
dexp À dcalcd
dref
dexp À dref
98.5
98.0
0.5
97.7
0.8
38.1
37.7
0.4
37.9
0.2
66.2
67.1
À0.9
68.1
À1.9
77.0
77.2
À0.2
71.7
5.3
64.6
64.0
0.6
73.1
À8.5
63.8
64.3
À0.5
61.1
2.7
54.3
53.4
0.9
53.8
0.5
Figure 2. ORTEP representation of the molecular structure of BPh(Me-a-lyxo-
dHexp4,6HÀ2) in crystals of 2 (40% probability ellipsoids). Distances (Å) and angles
(°): B1–O4 1.369(3), B1–O6 1.362(3), O4–B1–O6 122.9 (3). Puckering parameters:
pyranose ring O5–C1–. . .: Q = 0.550(3), h = 0.0(3), which resembles a 4C1 confor-
dref denotes chemical shifts of the free glycosides in the same solvent. dexp À dref is
mation; chelate ring B1–O4–. . .: Q = 0.451(3) Å, h = 52.3(4)°,
u = 172.1(4), rather
close to a C5E envelope.
the coordination-induced shift (CIS).

1754
D. Heß, P. Klüfers / Carbohydrate Research 346 (2011) 1752–1759
acid and 2-deoxy-D-erythro-pentose. A DMSO solution of the free
O6
C6
glycose showed the four cyclic isomers, namely anomeric couples
of both two pyranoses and two furanoses. Three esters were de-
tected after the workup of equimolar batches of phenylboronic
acid and the deoxyaldose. The major species 4b closely resembled
the 3,4-ester of the respective methyl pyranoside in terms of its
crystal structure and its NMR properties (Scheme 1, Fig. 4, Table
2). The crystallised major species was the b-anomer. The least
abundant species 4a of the three detected was the corresponding
C8
B1
O4
C4
O5
C1
C5
C9...
C7
C2
C3
O3
O1
a
-isomer. In agreement with DFT calculations, its conformation
was assigned to a B2,5 boat (Scheme 1). The species of intermediate
quantity 4c was assigned to the 1,3-chelate of the 4C1-
-pyranose
Figure 3. ORTEP representation of the molecular structure of BPh(Me-
dHexp4,6HÀ2) in crystals of 3 (40% probability ellipsoids). Distances (Å) and angles
(°): B1–O4 1.363(4), B1–O6 1.372(4), O4–B1–O6 122.7(3). Puckering parameters:
a
-arabino-
a
chair in terms of the DFT calculation which was supported by the
detection of an H(O4) proton in the 1H NMR spectrum (Table 2).
The calculation resulted in a mean difference of 0.8 ppm which
reliably substantiated the assignment made. The CIS values for 4c
pyranose ring O5–C1–. . .: Q = 0.567(3), h = 9.9(3),
slightly distorted 4C1 conformation; chelate ring B1–O4–. . .: Q = 0.465(3) Å,
h = 129.0(4)°, = 349.1(4), resembling a distorted EC5 envelope.
u = 269(2), which resembles a
u
(Table 2) nicely illustrate the point made above. Since the free
a-
and experimental shifts was 1.0 (mean) and 2.1 (maximum) for 2,
and 0.9 (mean) and 1.1 (maximum) for 3. In the following sections,
we will interpret a corresponding match of experimental and cal-
culated shifts as indicative of a reliable structure assignment.
pyranose prefers the 1C4 chair, its chemical shifts are not applicable
to evaluate a true CIS.4 Accordingly, the tabulated dexp À dref values
contain an increment from both boron binding (the CIS) and the
conformational change, and thus did not permit a straightforward
interpretation. As an intermediate result it might be stated that by
offering two alcoholic and one hemiacetal hydroxy function, the
major species was the ester of a cis-vicinal alcoholic diol function
2.2. 2-Deoxy-glycoses
2.2.1. 2-Deoxy-D-erythro-pentose
With the methodological background presented in the preced-
ing section we attempted to analyse the esters of phenylboronic
instead of the apparently strain-free
a-pyranose 1,3-chelate that
includes the anomeric hydroxy function.
5
4
5
2
O
HO
OH
O
3
1
4
1
4
2
3
3
1
OH
O
2
O
O
O
O
O
5
O
PhB
BPh
4c
BPh
BPh
4b
4a
BPh
O
1
CHO
O
2
O
3
4
5
O
O
O
4
O
1
6
PhB
O
6
3
5
2
4
2
O
BPh
5
H
1
HO
O
O
6
3
O
OH
PhB
α: 5a, β: 5b
5c
5d
OHC1
O
3
BPh
O
BPh
BPh
6
O
2
O
PhB
4
6
5
O
4
5
O
5
O
5
O
O
O
6
1
HO
HO
PhB
1
O
2
3
O
O
O
OH
1
4
4
OH
6
3
3
2
2
PhB
O
α: 6a, β: 6b
α: 6c, β: 6d
6e
6f
6
6
6
5
5
OMe
O
OMe
HO
O
PhB
4
5
O
PhB
O
O
HO
O
O
1
1
1
4
4
MeO
2
3
3
3
2
2
OH
O
O
OH
O
O
BPh
BPh
α: 7a, β: 7b
7c
7d
Scheme 1. Phenylboronic acid mono- and diesters.

D. Heß, P. Klüfers / Carbohydrate Research 346 (2011) 1752–1759
1755
Table 2 (continued)
O1
C5
C1
0.7
C2
C3
C4
5.2
C5
C6
2.4
OMe
O5
C2
C4
dexp À dref
dexp
0.1 À2.3
À8.9
C1
6cc
96.4
96.0
43.7
43.9
71.5
73.4
75.2
76.1
À0.9
77.5
79.6
2.1
71.3
72.4
À1.1
62.6
64.6
À2.0
O4
B1
dcalcd
C3
dexp À dcalcd
dexp
dcalcd
dexp À dcalcd
dexp
dcalcd
dexp À dcalcd
dexp
dcalcd
dexp À dcalcd
dexp
dcalcd
dexp À dcalcd
dref
dexp À dref
dexp
dcalcd
dexp À dcalcd
dref
dexp À dref
dexp
dcalcd
dexp À dcalcd
dexp
dcalcd
dexp À dcalcd
0.4 À0.2 À1.9
96.8
97.0
0.2
6dc
6ec,d
6fc,d
7a
42.2
42.5
0.3
70.1
71.6
1.5
72.0b
73.5
1.5
64.6
O3
C6
197.5
197.9
À0.4 À3.2 À2.1
97.1
95.8
1.3 À0.4 À0.1
93.2
93.1
0.1
49.5
52.7
75.6
77.7
83.5
83.6
À0.1
87.7
87.5
0.2
78.6
79.4
À0.8
75.0
74.1
0.9
68.3
69.5
À1.2
68.9
68.5
0.4
C7...
38.7
39.1
71.4
71.5
Figure 4. ORTEP representation of the molecular structure of BPh(b-ery-
dPenp3,4HÀ2 in crystals of 4b (50% probability ellipsoids). Distances (Å) and
angles (°): B1–O3 1.365(3), B1–O4 1.373(3), O3–B1–O4 113.7(2); torsion angles:
O1–C1–C2–C3 148.4(2), O3–C3–C4–O4: 14.5(2)°. Puckering parameters of the
71.6
74.7
3.1
81.5
80.7
0.8
75.6
73.5
2.1
69.8
5.8
63.8
63.6
0.2
72.1
À8.3
67.2
67.1
0.2
76.7
À9.5
64.1 60.2
64.5 59.4
À0.4
61.1 59.9
3.0 0.3
)
0.8
ap
92.3
72.0
83.5
pyranose ring O5–C1–. . .: Q = 0.715(2) Å, h = 94.5(2)°,
u = 145.1(2), which resem-
0.9 À0.4 À2.0
97.6
96.7
0.9
96.9
0.7
bles a 2SO skew conformation, distorted towards a 2,5B boat. The chelate ring
7b
74.3
76.4
2.1
74.5
0.5 À2.4
82.1
81.4
0.7
84.4
81.6
2.8
75.0
73.3
1.7
69.6
4.7
63.7 60.2
64.2 59.5
0.5
61.1 59.9
2.6
(Q = 0.141(2) Å,
u
= 269(1)°) is 4T3-twisted.17
0.7
bp
86.8
Table 2
0.3
Experimental (dexp) and calculated (dcalcd
boronic-acid esters of the 2-deoxy-glycoses 4–7 in DMSO-d6
)
13C NMR chemical shifts (ppm) of the
7cc
105.1
104.4
0.8
83.0
82.0
1.0
78.6
79.4
0.8
67.7
69.7
2.0
63.4
66.3 55.0
2.9
C1
91.4
89.9
1.5
93.7
À2.3 À0.3
88.8
88.7
0.1
91.3
À2.5 À4.5
88.4
88.1
C2
C3
C4
C5
C6
OMe
7dc
105.3
104.8
0.5
82.3
82.1
0.2
83.6
83.6
0.0
80.3
80.0
0.3
74.4
76.6
2.1
66.9 57.3
65.8 54.8
1.2
4a
dexp
dcalcd
dexp À dcalcd
dref
dexp À dref
dexp
dcalcd
dexp À dcalcd
dref
dexp À dref
dexp
dcalcd
dexp À dcalcd
dref
dexp À dref
dexp
dcalcd
dexp À dcalcd
dref
dexp À dref
dexp
dcalcd
dexp À dcalcd
dref
dexp À dref
dexp
dcalcd
dexp À dcalcd
dexp
dcalcd
dexp À dcalcd
dref
dexp À dref
dexp
dcalcd
dexp À dcalcd
dref
dexp À dref
dexp
36.5
35.8
72.8b
72.6
72.4b
72.1
0.7
62.4
60.0
2.4
2.6
0.7 À0.2
ap
36.8
67.6
5.2
66.6
5.8
65.2
À2.8
60.7
60.7
0.0
63.1
À2.4
59.5
59.9
À0.4
65.2
À5.7
7dc,d dexp
106.0
105.6
0.4
83.6
82.7
0.9 À0.2
84.5
84.7
81.4
80.4
1.0
74.4
77.3
À2.9
68.6 57.6
66.3 55.3
2.3
dcalcd
dexp À dcalcd
2.3
4b
32.1
31.5
72.4
73.1
74.3
75.1
À0.8
67.4
6.9
If available, dref denotes chemical shifts of the respective free glycose in the same
solvent. dexp À dref is the coordination-induced shift (CIS). For 5c, the wrong con-
figuration (the 3,4;5,6-diester) resulted in the dexp À dcalcd row À4.0, 0.1, À6.4,
À10.2, À11.9, À2.2. For 6e, the wrong configuration (the 3,5;4,6-diester) resulted in
the dexp À dcalcd row À4.3, 2.7, 3.4, 13.0, 15.0, 3.3.
0.6 À0.7
bp
36.6
65.1
7.3
4c
32.3
33.5
68.4
69.5
65.9
67.8
À1.9
66.6
À0.7
70.2
70.1
0.1
b
May be interchanged.
c
0.3 À1.2 À1.1
No CIS values due to missing assignment of the free glycose.
d
ap
93.7
36.8
67.6
0.8
In toluene-d8.
e
À5.3 À4.5
Is not observed in the experiment.
Chemical shifts of the free glycose in DMSO-d6.
f
5a
91.4
92.2
À0.8
90.9
33.3
31.2
63.5
65.2
63.9
64.2
À0.3
70.6
À6.7
65.2
65.4
0.2
61.5
4.2
2.1 À1.7
ap
33.9 64.6
67.6
2.6
2.2.2. 2-Deoxy-D-lyxo-hexose
Esters free of strain and, at the same time, without hemiacetal
contribution, were found in equimolar batches of boronic acid
0.5 À0.6 À1.1
93.8
93.4
0.4
5b
36.1
33.3
67.4
69.0
69.0
69.1
À0.1
66.5
2.5
67.8
67.8
0.0
75.3
À7.5
65.0
65.2
À0.3
60.9
4.1
and 2-deoxy-
reaction mixture contained two products, a slightly larger quantity
of BPh( -lyx-dHexp4,6H-2) (5a) and the respective b-anomer 5b.
D-lyxo-hexose (lyx-dHex). A DMSO solution of the
2.8 À1.6
bp
94.0
36.8 68.2
À0.2 À0.7 À0.8
197.4
197.2
0.2 À2.1
97.5
96.1
1.4
97.4
0.1 À4.8
91.5
92.5
1.0
a
5cc,d
47.6
49.7
69.9
69.4
0.5
68.9
66.9
2.0
64.1
63.6
0.5
65.2
65.3
À0.1
Crystallisation succeeded from dichloromethane. Structure
analysis revealed the b-anomer, 5b, BPh(b-lyx-dHexp4,6H-2)
(Fig. 5).
5dd,f
38.4
37.4
1.0
73.9
72.3
1.6
70.1
3.8
88.1
90.7
À2.6
83.4
4.7
76.2
77.2
À1.0
70.5
5.7
67.5
67.1
0.4
63.0
4.5
Reaction of a double molar amount of phenylboronic acid with
lyx-dHex resulted in the formation of a major (5c) and two minor
species in terms of NMR spectroscopy in toluene solution (5d,
5e). Compound 5d was identified as the 1,3:5,6-diester of the
b-furanose—supported by the lack of a H(O1) proton’s 1H NMR sig-
nal. No suggestion has been made as to the identity of 5e. The ma-
jor diester was completely unexpected. Compound 5c, as the only
species, exhibited a 13C NMR signal typical for a free aldehyde
(Table 2). The diester was formed through the four alcoholic hydro-
xy functions. A Karplus-relationship-based analysis favoured the
3,5:4,6-diester (two internested six-membered chelate rings) in-
stead of the 3,4:5,6-isomer with two five-membered chelate rings
bf
43.2
6a
65.9
68.0
À3.1
67.8
À1.9
77.6
77.2
0.4
72.2
5.4
64.4
64.4
0.0
64.1
64.6
0.5
39.8
ap
90.6
0.9
39.1
72.5
À8.1
61.3
2.8
6b
94.2
93.4
0.8
41.5
41.5
68.6
70.5
76.9
76.3
0.6
68.0
67.5
0.5
63.8
64.3
0.5
dcalcd
dexp À dcalcd
dref
0.0 À1.9
bp
93.5
41.4 70.9
71.7
76.9
61.4

1756
D. Heß, P. Klüfers / Carbohydrate Research 346 (2011) 1752–1759
C15...
C14
O6
C8...
C7
O6
C6
B1
B2
O5
C6
C5
O4
C4
O4
C5
O5
O1
C1
C4
O1
B1
C8
O3
C7
O3
C3
C2
O2
C2
C1
C3
Figure 5. ORTEP representationof themolecular structureof BPh(b-lyx-dHexp4,6H-2
)
in crystals of 5b (50% probability ellipsoids). Distances (Å) and angles (°): B1–O4
1.346(6), B1–O6 1.384(6), O4–B1–O6 123.6 (4). Puckering parameters: pyranose
ring O5–C1–. . .: Q = 0.566(2) Å, h = 2.6(2)°, which resembles a 4C1 conformation;
C9...
chelate ring B1–O4–. . .: Q = 0.480(2) Å, h = 56.9(2)°,
u
= 176.1(3), close to a C5E
envelope.
Figure 7. Structure of (7d). ORTEP representation of the molecular structure of
(BPh)2(3-O-Me- -Glcf1,2;5,6HÀ4) in crystals of 7d (40% probability ellipsoids).
(Scheme 1). This experimental result was supported by DFT analy-
sis. A reliable assignment was possible for the 3,5:4,6-diester only,
which, moreover, revealed itself to be the stable configuration by
12 kJ molÀ1 on the chosen level of theory. Still, it should be noted
at this point that under the same experimental conditions, the gly-
a-D
Distances (Å) and angles (°): B1–O1 1.373(3), B1–O2 1.376(3), B2–O5 1.365(2), B2–
O6 1.356(2), O1–B1–O2 112.5(2), O5–B2–O6 113.5(2); diol torsion angles: O1–C1–
C2–O2 À4.6(2), O5–C5–C6–O6 À0.1(2)°. Puckering parameters of the furanose ring
O4–C1–. . .: Q = 0.341(2),
u = 316.6(3), which resembles a conformation between
3T4 and E4. The chelate rings are almost unpuckered.
cose’s nor-2-methylene derivatives
D-lyxose and D-xylose do not
form an open-chain aldehyde diester.
2.2.3. 2-Deoxy-
The most complicated mono-esterification pattern of this work
was provided by 2-deoxy- -arabino-hexose (ara-dHex). No less
D
-arabino-hexose
Skipping the dangling formylmethyl functions in the two diesters
transforms the 2-deoxy-
metrical threitol diester (BPh)2(
same procedure transforms the 2-deoxy-
D
-lyxo-hexose derivative into the C2-sym-
-ThreHÀ4) (Thre = threitol). The
-arabino-hexose diester
D
D
than four monoesters were identified: the expected anomeric cou-
ple of the 4,6-borylene derivative of the pyranose (6a and 6b), but
also the 3,5-ester of the furanose anomers (6c and 6d). All assign-
ments were confirmed by DFT calculations (Table 2). In 2:1 batches
of boronic acid and the glycose, the same notable result was ob-
tained as for the lyxo-configured isomer. Besides minor quantities
of an obvious b-furanose diester 6f (Table 2) which resembles the
phenylboronic acid diester of glucose, the major species 6e exhib-
ited an aldehyde signal in the 13C NMR spectra (Fig. 6).1 Experi-
mental and computer-chemical assignment (Table 2) here
revealed the 3,4:5,6-diester with two adjacent five-membered che-
late rings instead of the motif of internested six-membered rings
(Scheme 1). In agreement with this result, the non-observed
3,5:4,6-diester is 8 kJ molÀ1 unstable with respect to the stable
isomer.
D
to the Ci-symmetrical erythritol diester (BPh)2(ErytHÀ4) (Eryt =
erythritol). Both diesters have been structurally resolved.5 In fact,
their configuration resembles the partial structures found in 5c
and 6f. Moreover, the energy difference of the stable (the double-
six-membered-ring motif) and the less stable bonding pattern is
the same as found in this work. However, the preference for the cen-
trosymmetrical double-five-ring motif is more pronounced for 6f
than for the parent structures.
2.2.4. 3-O-Methyl-
As a final check on the DFT-assisted species assignment, 3-O-
methyl-
-glucose was included in this investigation.6 The glucose
D-glucose
D
derivative has along with the deoxy-glycoses the reduction of the
number of hydroxy functions by one in common. As a result of
the reactions with phenylboronic acid in molar ratios of 1:1 and
2:1, the preference of alcoholic hydroxy functions as the first
The differing results for the constitution of the two open-chain
diesters are rationalised by focusing on the diester moiety itself.
a2
a6
a5
a4
a3
f5
f6
f4
f2
f1
a1
f3
200
190
100
90
80
70
60
50
40
Figure 6. 13C NMR spectrum of the reaction mixture of two moles of phenylboronic acid and 1 mol of 2-deoxy-
D-arabino-hexose.

D. Heß, P. Klüfers / Carbohydrate Research 346 (2011) 1752–1759
1757
choice for esterification appears to be a loose rule of thumb. Thus,
not only the expected anomeric couple of pyranose 4,6-esters (7a
and 7b) was observed, but also, in minor quantities, the 1,2-fura-
nose ester 7c. The identification of this latter compound was an-
other example which demonstrates the benefit of the chosen
methodology. CIS values are not available since no furanose iso-
mers have been detected by means of standard NMR spectroscopy
400 MHz, 13C: 101 MHz) or a Joel Eclipse 500 (1H: 500.16 MHz,
13C: 125.77 MHz) NMR spectrometer. The signals of the deuterated
solvents (13C, DMSO-d6: 39.52 ppm, toluene-d8: 20.40 ppm) and
the residual protons therein (1H, DMSO-d6: 2.50 ppm, toluene-d8:
2.09 ppm) were used as an internal secondary reference for the
chemical shift.11 If possible, the 1H and 13C signals were assigned
by means of DEPT135, HMQC and COSY experiments. Mass spectra
were recorded on a Joel JMS-700 spectrometer in DEI+ mode.
Crystals suitable for X-ray crystallography were selected by
means of a polarisation microscope, mounted on a tip of a glass fi-
bre, and subjected to XRD on either a Nonius Kappa CCD or a Stoe
IPDS diffractometer, both operating with graphite-monochromat-
in solutions of 3-O-methyl-D-glucose. Hence, the required dref val-
ues are not available. In a DFT approach, however, the mean 1.4-
ppm deviation of observed and calculated shift was in the expected
range for a correct assignment. With a higher boronic-acid supply,
the furanose 1,2:5,6-diester 7d was the major species. Crystallisa-
tion of the latter species succeeded. Figure 7 shows the molecular
structure exhibiting the typical flat chelate rings.
ed MoK
a radiation (k = 0.71073 Å). The structures were solved by
direct methods (SHELXS, SIR97) and refined by full-matrix least-
squares calculations on F2 (SHELXL-97).12,13 Hydrogen atoms were
included in idealised positions, riding on their parent atoms. Aniso-
tropic displacement parameters were refined for all non-hydrogen
atoms. Crystallographic details are summarised in Table 3. All com-
pounds, except 5bÁCH2Cl2, were weak anomalous scatterers. Except
for 5bÁCH2Cl2, Friedel opposites were thus merged and the absolute
structures were assigned according to the known stereochemist-
ries of the respective starting materials.14 A Flack parameter is thus
given for 5b only in Table 3. The refined structures were analysed
with PLATON and visualised with ORTEP.15,16 CCDC 818915
(5bÁ0.5CH2Cl2), 818916 (4b), 818917 (7d), 818918 (2), 818919
(3), and 818920 (1b) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
the Cambridge Crystallographic Data Center via www.ccdc.cam.a-
c.uk/data_request/cif.
Reaction of boronic acid with methyl glycopyranosides: Phenyl-
boronic acid (1 mmol) and the respective glycopyranoside
(1 mmol) were mixed with 20 mL of dioxane and refluxed in a
Dean–Stark apparatus until a distillate of approximately 15 mL
was collected. The remaining solvent was removed under reduced
pressure. The colourless crude products were obtained in quantita-
tive yield. Crystals were grown upon slow evaporation of solutions
from dichloromethane. For NMR analysis, phenylboronic acid
(1 mmol) and the respective glycopyranoside (1 mmol) were dis-
solved in 1 mL of DMSO-d6 and stirred for 2 h at room temperature
prior to measurement.
The reaction of boronic acid with glycoses: to a solution of the
respective glycose (1 mmol) in water (1 mL) a solution of phenyl-
boronic acid (1 or 2 mmol) in methanol (1 mL) was added. The
reaction mixture was stirred for 2 h at room temperature and then
evaporated to dryness under reduced pressure. The colourless
crude products were obtained in quantitative yield and were ana-
lysed by mass spectrometry and NMR spectroscopy, using either
DMSO-d6 or toluene-d8. Crystals were obtained upon slow evapo-
ration of solutions from acetone or dichloromethane.
Details of the computational procedure applied have been doc-
umented in a previous work.2 The structures were optimised in the
gas phase at the B3LYP/6-31+G(2d,p) level of theory with very tight
convergence criteria. NMR shielding constants were calculated
separately for 1a–b, 2, 3, 4a–c, 5a–b, 6a–d, 7a–c in DMSO and
5c–d, 6e–f, 7d in toluene from the optimised structures at the
PBE1PBE/6-311++G(2d,p) level of theory. The polarisable contin-
uum model (PCM) was applied to account for solvation.
3. Conclusion
Phenylboronic acid diol esters are characterised by the stereo-
electronic requirements of the planar boron centre. In agreement
with its sp2 hybridisation, the O–B–O angle was expected to be
about 120° (in phenylboronic acid dimethylester, without the influ-
ence of a chelate ring, the O–B–O angle was calculated as 127.7° on
the same level of theory used for the diol esters). As a consequence,
six-membered chelate rings adopt a half-chair conformation. Five-
membered chelate rings are flat, the diol torsion angle O–C–C–O
being typically in the range of 5–15°. These restrictions exclude
the vicinal diol functions of a pyranose chair, both cis- and trans-
configured, and lead to some strain in five-membered chelate rings.
Taking 2-deoxy-
thus seem possible: the 1,3-ester of both the
D
-erythro-pentose as an example, several esters
-furanose and the
4C1-
a-pyranose, and the 3,4-esters of the a- and the b-pyranose in
a
a conformation close to either a B2,5- or 2,5B-boat. Of these candi-
dates, the 3,4-ester of the 2,5B-b-pyranose provides the major spe-
cies, its B2,5
contribute minor species. The remaining three species, the cis-1,3-
furanose chelate and the 3,4-esters of both the 2,5B-
and the B2,5
-a a-pyranose-1,3-ester
-anomer and the 4C1-
a
-
b-pyranose conformer, were unobserved. In fact, these isomers
were calculated as unstable on the B3LYP/6-31+G(2d,p) level of the-
ory (see the Supplementary data). This rule holds for the cis-1,3-
furanose as long as it is needed for the formation of a second chelate.
The tendency to accept a less stable binding site to enable dies-
ter formation provided the reason for the most unexpected result
of this work. Even the open-chain aldehydo isomer contributes a
bis-chelator to the ligand library of the two investigated 2-
deoxy-hexoses. Notably, for the two investigated 2-deoxy-hexoses,
the aldehydo diester was not observed as a minor species but was
the major isomer in the respective batches of 2:1 molar ratio of
boronic acid and the deoxy-hexose. It should be noted that this re-
sult is obviously not transferable to the aldopentoses despite the
same number of four alcoholic hydroxy functions in both glycose
classes.2
4. Experimental section
4.1. Methods and materials
Phenylboronic acid (Aldrich), 2-deoxy-
deoxy- -ribose’, ABCR), 2-deoxy- -lyxo-hexose (‘2-deoxy-
ose’, Glycon), 2-deoxy- -arabino-hexose (‘2-deoxy- -glucose’,
ABCR) were used in reagent-grade quality as supplied. Methyl 2-
deoxy-b- -ribopyranoside, methyl 2-deoxy- -galactopyranoside
and methyl 2-deoxy- -glucopyranoside were synthesised as pre-
D-erythro-pentose (‘2-
D
D
D
-galact-
D
D
4.2. 1H NMR spectra of the individual species
D
a
-D
Compound 1a: DMSO-d6, 400 MHz, 20.3 °C: d = 1.65–1.72 (m,
2
3
a
-D
1H, H2a, J2a,2b 14.3 Hz), 2.27 (ddd, 1H, H2b, J2b,3 6.1 Hz), 3.24 (s,
7–10
2
viously described.
3H, OMe), 3.83 (dd, 1H, H5a, J5a,5b 12.5 Hz), 3.89 (dd, 1H, H5b),
4.56–4.61 (sp, 2H, H1 and H4, J1,2a 7.2 Hz, J1,2b 4.1 Hz, J4,5a
4.5 Hz, J4,5b 5.4 Hz), 4.70–4.75 (m, 1H, H3).
3
3
3
NMR spectra were recorded at room temperature on a Joel
Eclipse 270 (1H: 270 MHz, 13C: 67.9 MHz), Joel Eclipse 400 (1H:
3

1758
D. Heß, P. Klüfers / Carbohydrate Research 346 (2011) 1752–1759
Table 3
Crystallographic data
a
1b
2
3
4b
5bÁ0.5CH2Cl2
7d
CCDC number
818920
818918
C13H17BO5
264.082
Colourless
0.24 Â 0.10 Â 0.07
200(2)
818919
C13H17BO5
264.082
Colourless
0.31 Â 0.038 Â 0.024
200(2)
818916
C11H13BO4
220.030
Colourless
0.39 Â 0.27 Â 0.21
200(2)
818915
818917
C19H20B2O6
365.980
Colourless
0.44 Â 0.30 Â 0.08
173(2)
Empirical formula
C12H15BO4
C12.50H16BClO5
292.522
Colourless
0.29 Â 0.26 Â 0.22
200(2)
M (g molÀ1
Colour
)
234.06
Colourless
0.13 Â 0.09 Â 0.06
200(2)
Size (mm3)
T (K)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Orthorhombic
P212121
5.12140(10)
10.9441(3)
21.2409(5)
90
1190.53(5)
4
1.30586(5)
0.095
Monoclinic
P21
Monoclinic
P21
Monoclinic
P21
Tetragonal
P41212
11.123(2)
11.123
22.6950(6)
90
2807.8(6)
8
orthorhombic
P212121
7.2528(6)
9.6512(11)
27.185(2)
90
1902.9(3)
4
1.2775(2)
0.092
10.3230(4)
5.0832(2)
12.5937(6)
98.230(2)
654.03(5)
2
11.8169(10)
4.6576(3)
12.2481(10)
95.030(4)
671.52(9)
2
6.2861(3)
4.9563(3)
17.4836(11)
95.831(4)
541.90(5)
2
b (°)
V (Å3)
Z
q
l
(g cmÀ3
(mmÀ1
)
)
1.3410(1)
0.101
1.3061(2)
0.098
1.3485(1)
0.100
1.3840(3)
0.285
Absorption correction
Reflections measured
Rint
None
8816
0.0279
None
4516
0.0348
None
4478
0.0457
None
4203
0.0440
Multi-scan
21,610
0.0439
Multi-scan
14,220
0.0354
Mean
r(I)/I
0.0201
0.0253
0.0384
0.0369
0.0441
0.0366
h range
3.43–27.48
1605
1462
3.58–25.39
1333
1248
3.46–25.02
1351
1131
3.26–27.64
1398
1118
4.19–26.35
2851
2132
4.28–26.28
2217
1677
Reflections in refinement
Observed reflections
Parameters
155
174
174
146
179
245
Restraints
0
1
1
1
0
0
x, y (weighting scheme)
0.0521, 0.1414
0.0349
0.0942
0.0589, 0.1429
0.0405
0.1097
0.0658, 0.0084
0.0406
0.1092
0.0524, 0.0468
0.0388
0.0989
0.0500, 0
0.0364
0.0875
0.0341, 0
0.0289
0.0596
R(Fobs
)
Rw(F2)
S
1.108
1.143
1.088
1.057
0.952
0.903
Shift/errormax
0.001
À0.139, 0.122
0.001
À0.198, 0.180
0.001
À0.183, 0.140
0.001
À0.176, 0.151
0.001
À0.325, 0.212
0.001
À0.115, 0.128
Residual densities (e Å3)
a
Flack parameter: À0.03(10).
Compound 1b: DMSO-d6, 400 MHz, 21.0 °C: d = 1.76 (ddd, 1H,
4.22–4.25 (m, 1H, H6b), 4.67–4.71 (m, 1H, H1), 4.95 (d, 1H, O3-
H), 6.63 (dd, 1H, O1-H).
2
3
3
H2a, J2a,2b 15.4 Hz, J2a,3 3.3 Hz), 2.32 (ddd, 1H, H2b, J2b,3
2
3.6 Hz), 3.49 (s, 3H, OMe), 3.62 (d, 1H, H5a, J5a,5b 13.2 Hz), 3.80
Compound 5c: Toluene-d8, 400 MHz, 22 °C: d = 1.74 (ddd, 1H,
3
3
2
3
3
(dd, 1H, H5b), 4.64 (dd, 1H, H4, J4,5a <1 Hz, J4,5b 1.9 Hz), 4.71
(dd, 1H, H1, 3J1,2a 7.7 Hz, 3J1,2b 5.5 Hz), 4.82 (dt, 1H, H3, 3J3,4 8.3 Hz).
Compound 2: DMSO-d6, 400 MHz, 20.3 °C: d = 1.57–1.68 (m, 1H,
H2a), 1.70–1.80 (m, 1H, H2b), 3.25 (s, 3H, OMe), 3.87–3.94 (m, 1H,
H2a, J2a,2b 16.6 Hz, J2a,3 5.6 Hz), 2.01 (ddd, 1H, H2b, J2b,3
3
3
8.6 Hz), 3.42 (t, 1H, H4, J4,5 2.2 Hz), 3.46–3.48 (m, 1H, H5, J5,6a
2.2 Hz, J5,6b 2.8 Hz), 3.57 (dd, 1H, H6a, J6a,6b 12.1 Hz), 4.03 (dd,
1H, H6b), 4.50–4.54 (m, 1H, H3, J3,4 2.2 Hz), 9.31–9.32 (m, 1H,
H1, J1,2a 1.7 Hz, J1,2b 1.9 Hz).
3
2
3
3
2
3
3
H3), 4.02 (dd, 1H, H6a, J6a,5 1.1 Hz, J6a,6b 12.1 Hz), 4.23 (dd, 1H,
3
H6b, J6b,5 1.9 Hz), 4.76–4.80 (m, 1H, H1), 4.92 (d, 1H, O3-H).
Compound 5d: Toluene-d8, 400 MHz, 22 °C: d = 1.63 (dd, 1H,
2
3
3
Compound 3: DMSO-d6, 400 MHz, 20.6 °C: d = 1.63 (ddd, 1H,
H2a, J2a,2b 12.3 Hz, J2a,3 <1 Hz), 2.12–2.16 (m, 1H, H2b, J2b,3
2
3
3
3
H2a, J2a,2b 13.3 Hz, J2a,3 11.3 Hz), 2.01 (dd, 1H, H2b, J2b,3
2.8 Hz), 3.69 (d, 1H, H4, J4,5 1.9 Hz), 3.73–3.79 (m, 1H, H6a),
4.00–4.04 (sp, 1H, H6b), 4.34 (d, 1H, H3, J3,4 <1 Hz), 5.28 (d, 1H,
H1, J1,2a <1 Hz, J1,2b 3.0 Hz).
3
5.1 Hz), 3.26 (s, 3H, OMe), 3.62–3.68 (sp, 1H, H3), 3.68–3.73 (sp,
3
3
3
1H, H5, J5,6b 5.0 Hz), 3.71–3.79 (sp, 1H, H3), 3.93 (t, 1H, H6a,
3
2J6a,6b 9.9 Hz), 4.14 (dd, 1H, H6b), 4.81 (d, 1H, H1, J1,2a 3.5 Hz,
Compound 6a: DMSO-d6, 400 MHz, 21 °C: d = 1.56–1.63 (m, 1H,
H2a), 1.89–1.95 (sp, 1H, H2b), 5.22–5.23 (m, 1H, H1), 6.51 (d, 1H,
O1-H).
Compound 6b: DMSO-d6, 400 MHz, 21 °C: d = 1.41–1.50 (m, 1H,
H2a), 2.03–2.08 (m, 1H, H2b), 4.83–4.87 (m, 1H, H1), 6.87 (d, 1H,
O1-H).
Compound 6c: DMSO-d6, 400 MHz, 21 °C: d = 1.93–2.04 (m, 1H,
H2a, 2J2a,2b 14.3 Hz), 2.32 (dd, 1H, H2b), 3.59–3.65 (m, 2H, H6a+b),
4.19–4.21 (m, 1H, H5), 4.27 (d, 1H, H4), 4.71 (dd, 1H, H3), 5.44–
5.48 (m, 1H, H1), 6.35 (d, 1H, O1-H).
Compound 6d: DMSO-d6, 400 MHz, 21 °C: d = 1.89–1.95 (sp, 1H,
H2a), 2.22–2.29 (m, 1H, H2b), 5.37–5.39 (m, 1H, H1), 6.18 (d, 1H,
O1-H).
3J1,2b <1 Hz), 5.3 (d, 1H, O3-H).
Compound 4a: No 1H NMR signals detected.
Compound 4b: DMSO-d6, 400 MHz, 25 °C: d = 1.73 (ddd, 1H,
2
3
3
H2a, J2a,2b 15.1 Hz, J2a,3 3.3 Hz), 2.26 (ddd, 1H, H2b, J2b,3
2
3.9 Hz), 3.57 (d, 1H, H5a, J5a,5b 13.1 Hz), 3.90 (dd, 1H, H5b), 4.62
(dd, 1H, H4, J4,5a <1 Hz, J4,5b 1.9 Hz), 4.79–4.83 (m, 1H, H3, J3,4
8.1 Hz), 5.02–5.07 (m, 1H, H1, J1,2a 8.0 Hz, J1,2b 5.2 Hz), 6.31 (d,
1H, O1H).
3
3
3
3
3
Compound 4c: DMSO-d6, 400 MHz, 25 °C: d = 1.99–2.11 (m, 2H,
H2a+b), 3.23–3.28 (m, 1H, H5a), 3.68–3.75 (m, 1H, H5b), 3.73–3.79
(m, 1H, H4), 4.41–4.49 (m, 1H, H3), 5.2 (d, 1H, O4H), 5.42 (br, 1H,
H1).
Compound 5a: DMSO-d6, 500 MHz, 20 °C: d = 1.59–1.62 (m, 1H,
Compound 6e: Toluene-d8, 400 MHz, 21 °C: d = 2.05 (ddd, 1H,
2
2
3
3
H2a, J2a,2b 12.0 Hz), 1.71–1.75 (m, 1H, H2b), 3.96 (dd, 1H, H6a,
H2a, J2a,2b 17.1 Hz, J2a,3 5.4 Hz), 2.15 (ddd, 1H, H2b, J2a,3
7.4 Hz), 3.61–3.65 (m, 1H, H4), 3.98–4.02 (sp, 2H, H5 and H6a),
4.09–4.14 (m, 1H, H6b), 4.52–4.57 (m, 1H, H3), 9.24–9.26 (m, 1H,
3
2J6a,6b 12.0 Hz), 3.98–4.04 (sp, 1H, H3), 4.17 (br, 1H, H5, J5,6a
1.1 Hz), 4.22–4.25 (m, 1H, H6b), 4.25 (sp, 1H, H4), 4.85 (d, 1H,
O3-H), 5.21 (br, 1H, H1), 6.33 (dd, 1H, O1-H).
3
3
H1, J1,2a 1.3 Hz, J1,2b 1.7 Hz).
Compound 5b: DMSO-d6, 500 MHz, 20 °C: d = 1.52–1.59 (m, 1H,
Compound 6f: Toluene-d8, 400 MHz, 21 °C: d = 1.31 (dt, 1H,
2
2
3
H2a, J2a,2b 12.0 Hz), 1.74–1.77 (sp, 1H, H2b), 3.71–3.76 (m, 1H,
H2a, J2a,2b 12.4 Hz), 1.58 (dd, 1H, H2b, J2b,3 1.4 Hz), 3.35 (dd,
2
3
2
H3), 4.02 (d, 1H, H6a, J6a,6b 11.8 Hz), 4.14–4.15 (m, 1H, H4),
1H, H4, J4,5 8.9 Hz), 3.92–3.98 (m, 1H, H6a, J6a,6b 9.3 Hz), 4.14–

D. Heß, P. Klüfers / Carbohydrate Research 346 (2011) 1752–1759
1759
3
4.18 (dd, 1H, H6b), 4.35–4.37 (m, 1H, H3, J3,4 1.9 Hz), 4.44–4.50
280.1118, exp.: [M]+ peak not found. Compound 7d: calcd for
19H20B2O6 [M]+: 366.1446, found: 366.1454.
3
3
3
(m, 1H, H5, J5,6a 8.0 Hz, J5,6b 6.1 Hz), 5.22 (d, 1H, H1, J1,2a
C
3
3.0 Hz, J1,2b <1 Hz).
Compound 7a: DMSO-d6, 400 MHz, 25 °C: d = 3.38 Hz (sp, 1H,
H2), 3.66 (s, 3H, OCH3), 5.02 (sp, 1H, H1), 6.79 (d, 1H, O1-H).
Compound 7b: DMSO-d6, 400 MHz, 25 °C: d = 3.12–3.15 (m, 1H,
H2), 3.66 (s, 3H, OCH3), 4.52–4.56 (m, 1H, H1), 5.36 (d, 1H, O2-H),
6.99 (d, 1H, O1-H).
Acknowledgements
We are indebted to Patrick Nimax, B.Sc., and Jessica Steinbacher,
B.Sc., for their contribution in their practical courses.
Compound 7c: No 1H NMR signals detected.
Supplementary data
Compound 7d: DMSO-d6, 400 MHz, 25 °C: d = 3.43 (s, 3H,
3
2
OCH3), 3.98 (d, 1H, H3, J3,4 3.4 Hz), 4.27–4.31 (m, 2H, H6, J6a,6b
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.carres.2011.05.031.
3
3
9.2 Hz), 4.33 (dd, 1H, H4, J4,5 6.8 Hz), 4.88 (ddd, 1H, H5, J5,6a
8.0 Hz, J5,6a 4.3 Hz), 5.03 (d, 1H, H2, J2,3 <1 Hz), 6.28 (d, 1H, H1,
3
3
3J1,2 4.3 Hz).
References
Toluene-d8, 400 MHz, 25 °C: d = 3.06 (s, 3H, OCH3), 3.61 (d, 1H,
3
3
1. Draffin, S. P.; Duggan, P. J.; Fallon, G. D.; Tyndall, E. M. Acta Crystallogr., Sect. E:
Struct. Rep. Online 2005, E61, o1733–o1735.
H3, J3,4 3.3 Hz), 4.00 (dd, 1H, H4, J4,5 6.5 Hz), 4.13 (dd, 1H, H6a,
2J6a,6b 9.3 Hz), 4.26 (dd, 1H, H6b), 4.30 (d, 1H, H2, J2,3 <1 Hz),
3
2. Reichvilser, M. M.; Heinzl, C.; Klüfers, P. Carbohydr. Res. 2010, 345, 498–502.
3. Schwarz, T.; Heß, D.; Klüfers, P. Dalton Trans. 2010, 39, 5544–5555.
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7. Crotti, P.; Di Bussolo, V.; Favero, L.; Macchia, F.; Pineschi, M. Tetrahedron:
Asymmetry 1996, 7, 779–786.
3
3
4.57–4.63 (m, 1H, H5, J5,6a 8.3 Hz, J5,6b 7.2 Hz), 5.82 (d, 1H, H1,
3J1,2 4.4 Hz).
4.3. High-resolution DEI mass spectra
Compound 1a: calcd for C12H15BO4 [M]+: 234.1063, found:
234.1058. Compound 1b: calcd for C12H15BO4 [M]+: 234.1063,
found: 234.1068. Compound 2: calcd for
8. Deriaz, R. E.; Overend, W. G.; Stacey, M.; Wiggins, L. F. J. Chem. Soc. 1949, 2836–
2841.
9. Hughes, I. W.; Overend, W. G.; Stacey, M. J. Chem. Soc. 1949, 2846–2849.
10. Overend, W. G.; Shafizadeh, F.; Stacey, M. J. Chem. Soc. 1950, 671–677.
11. Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997, 62, 7512–7515.
12. Sheldrick, G. Acta Crystallogr., Sect. A 2008, 64, 112–122.
13. Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo, C.;
Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl. Crystallogr.
1999, 32, 115–119.
14. Flack, H. D.; Bernardinelli, G. J. Appl. Crystallogr. 2000, 33, 1143–1148.
15. Spek, A. J. Appl. Crystallogr. 2003, 36, 7–13.
16. Farrugia, L. J. Appl. Crystallogr. 1997, 30, 565.
C
13H17BO5 [M]+:
264.1169, found: 264.1190. Compound 3: calcd for C13H17BO5
[M]+: 264.1169, found: 264.1175. Compound 4: calcd for
C
11H13BO4 [M]+: 220.0907, found: 220.0917. Compounds 5a–b:
calcd for C12H15BO5 [M]+: 250.1013, found: 250.1017. Compounds
5c–d: calcd for C18H18B2O5 [M]+: 336.1340, found: 336.1372. Com-
pounds 6a–d: calcd for
C
12H15BO5 [M]+: 250.1013, found:
250.0995. Compounds 6e–f: calcd for C18H18B2O5 [M]+: 336.1340,
found: 336.1365. Compounds 7a–c: calcd for C13H17BO6 [M]+:
17. IUPAC Pure Appl. Chem. 1981, 53, 1901–1905.