C.-M. Lian et al. / Chinese Chemical Letters 25 (2014) 134–136
135
(m, 7H, C3-H), 5.30–5.10 (m, 6H, C12ꢀ7-H), 5.04–4.90, 4.90–4.67
(m, 7H, C5-H), 4.40–4.10, 4.07–3.97 (m, 14H, C6-H, C6-H0), 4.13–
3.90 (m, 7H, C2-H), 4.15–3.87 (m, 7H, C4-H), 3.04–2.87, 1.24 (m,
26H, –CH2–), 2.10–1.94 (m, 66H, Ac-CH3), 0.87–0.84 (t, J = 7 Hz, 3H,
OAc
OAc
OAc
O
O
O
O
H2
C
AcO
AcO
O
N
H
CH3
AcO
AcO
OAc
OAc
13
OAc
O
O
5
R-CH3); 13C NMR (100 MHz, DMSO-d6):
d 170.07–169.18 (–CO–),
153.62 (–CONH–), 95.56 (C12ꢀ7), 91.00 (C11), 74.02 (C4), 70.90,
69.43 (C3), 69.89, 68.02 (C5), 69.43, 68.68 (C2), 62.80, 61.00 (C6),
40.12, 31.28–22.09 (–CH2–), 20.53–20.26 (Ac-CH3), 13.93 (R-CH3);
MALDI-FTMS (m/z): calcd. for [M+Na]+: 2338.8, found: 2338.8,
calcd. for [M+K]+: 2354.8, found: 2354.8.
1
Fig. 1. Chemical structure of sept-D-glucopyranose tetradecyl carbamate 1.
2,3,4,6-Tetra-O-acetyl-
acetyl-
-glucopyranosyl]5-(1 ! 4)-1,2,3, 6-tetra-O-acetyl-
glucopyranosyl (4): Yield 12%; white solid; 1H NMR (500 MHz,
DMSO-d6):
6.10 (s, 1H, C11-H), 5.40–5.36, 5.30–5.18 (m, 7H, C3-
a
-D
-glucopyranosyl-[(1 ! 4)-2,3,6-tri-O-
a-D
a, b- -
D
3. Results and discussion
d
H), 5.28–5.15 (m, 6H, C12-7-H), 5.02–4.70 (m, 7H, C5-H), 4.15–4.10,
4.03–3.93 (m, 7H, C2-H), 4.37–4.10, 4.03–3.96 (m, 14H, C6-H, C6-
H0), 4.10–4.05, 4.00–3.90 (m, 7H, C4-H), 2.19–1.95 (m, 69H, –CH3);
Chemical shift changes of the oligosaccharides 3, 4, 5, 1 could be
observed clearly in the HSQC NMR spectra (Fig. S1, in Supporting
information). For per-acetylated
b-cyclodextrin 3, the seven
13C NMR (125 MHz, DMSO-d6):
d 170.02–169.06 (–CO–), 95.84,
acetylated monosaccharide units have exactly identical structures
whose chemical shifts in the same glucose ring are all the same in
1H NMR and 13C NMR. Since the two protons in C6 (C6-H, C6-H0) are
not chemically equivalent, their chemical shifts are 4.42–4.39 and
4.26–4.22, respectively (Fig. S1a). When the cyclic structure of
compound 3 was transformed into an open chain oligo-glucose
structure (maltoheptaose 4), the chemical environment of the
seven acetylated monosaccharide units changed accordingly: The
original identical proton and 13C chemical shifts turned into
chemical shift clusters around the original positions. The largest
deviation of proton and 13C chemical shift were generated in C11-H
and C11, which moved from 5.06 and 96.57 to 6.10 and 88.12
respectively. These signals were far from the proton and 13C
chemical shifts of C12ꢀ7-H and C12ꢀ7, which were at 5.28–5.15 and
95.84, 95.53 ppm, respectively (Fig. S1b). The possible reason for
proton chemical shift alterations was the change of the shielding
effect of the carbonyl group on the C11 anomeric hydroxy group.
The C11-H was in the deshielding zone of the carbonyl group and
when the acetyl group on the C11 anomeric hydroxyl was
selectively removed (compound 5), the chemical shift of C11-H
was moved upfield from 6.10 to 5.13–5.08 ppm (Fig. S1c). When
the C11 anomeric hydroxyl was converted into a carbamate, the
95.53 (C12ꢀ7), 88.12 (C11), 74.00, 73.66 (C4), 71.15, 70.90, 68.86
(C3), 69.86, 68.86, 68.76 (C2), 69.40, 69.17, 67.72 (C5), 62.75, 62.39,
61.33 (C6), 20.98–20.21 (–CH3); MALDI-FTMS (m/z): calcd. for
[M+Na]+: 2141.6, found: 2141.6, calcd. for [M+K]+: 2157.6, found:
2157.5.
2,3,4,6-Tetra-O-acetyl-
acetyl-
-glucopyranosyl]5-(1 ! 4)-2,3,6-tri-O-acetyl-
copyranose (5): Yield 37%; white solid; 1H NMR (400 MHz,
DMSO-d6): 5.45–5.35, 5.30–5.15 (m, 7H, C3-H), 5.25–5.10 (m,
a
-D
-glucopyranosyl-[(1 ! 4)-2,3,6-tri-O-
a-D
a, b-D
-glu-
d
6H, C12ꢀ7-H), 5.13–5.08 (m, 1H, C11-H), 5.05–4.55 (m, 7H, C5-H),
4.38–4.10, 4.12, 4.00 (m, 14H, C6-H, C6-H0), 4.12–3.90 (m, 7H, C2-
H), 4.00–3.82 (m, 7H, C4-H), 2.08–1.91 (m, 66H, –CH3); 13C NMR
(100 MHz, DMSO-d6):
d
170.10–169.14 (–CO–), 95.54 (C12ꢀ7),
88.00 (C11), 74.21, 74.03 (C4), 71.35, 70.87, 68.65 (C3), 71.30,
69.82, 69.41, 68.00 (C5), 68.88, 68.00 (C2), 62.77, 61.35 (C6),
20.57–20.25 (–CH3); MALDI-FTMS (m/z): calcd. for [M+Na]+:
2099.6, found: 2099.6, calcd. for [M+K]+: 2115.6, found: 2115.6.
2,3,4,6-Tetra-O-acetyl-
acetyl-
-glucopyranosyl]5-(1 ! 4)-2,3,6-tri-O-acetyl-
copyranose tetradecyl carbamate (1): Yield 85%; white solid; 1H
NMR (400 MHz, DMSO-d6):
5.79–5.77 (m, 1H, C11-H), 5.48–5.13
a
-D
-glucopyranosyl-[(1 ! 4)-2,3,6-tri-O-
a-D
a, b-D
-glu-
d
Scheme 1. Synthesis of sept-D-glucopyranose tetradecyl carbamate 1. Reagents and conditions: (a) Ac2O, pyridine, 50 8C, 10 h, 83%; (b) 70% aq. HClO4, Ac2O, 0 8C, 20 h, then
23 8C, 2 h, 12%; (c) EDA, acetic acid, dry THF, 30 8C, 39 h, 70% and (d) tetradecyl isocyanate, TEA, toluene, 80 8C, 6 h, 85%.