Scheme 3 Reaction conditions: (a) tosyl chloride, pyridine, 83% (14), quant. (19); (b) 2, K2CO3, DMF, 100 1C, 16 h, 74% (15), 65% (20); (c) 4,
Cu/CuSO4ꢀH2O, t-BuOH/THF/H2O (1 : 1 : 1), 70 1C, 48 h, 81% (16), 79% (21); (d) NaOMe, MeOH, rt, overnight, 91% (17), quant. (22).
Table 1 Photochromic properties of azobenzene glycoconjugates
Notes and references
E : Za GS
E : Za PSS
t1/2 (h)
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Azobenzene glycoconjugate
6
Man-azo
99 : 1
98 : 2
99 : 1
99 : 1
99 : 1
—
—
14
21.3
15.5
16
8
Man-azo-Man
Man-azo-Man
Man-(azo)2-Man
(Man-azo)3
3 : 97
1 : 99
33 : 67b
63 : 37b
12
17
22
a
E : Z ratios were determined by 1H-NMR spectroscopy (10 mg in
b
0.5–0.6 mL). Averaged over all branches. GS: ground state; PSS:
photostationary state; t1/2: half life, determined by UV-VIS spectro-
scopy (cf. ESI).
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Finn and K. B. Sharpless, Angew. Chem., Int. Ed., 2001, 40, 2004–2021.
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Fig. 2 Two resonance structures of 6 explaining fast Z - E relaxation.
The detailed kinetics of photoisomerisation of azobenzene
clusters 17 and 22 will be determined in due course.
In conclusion, mono- and oligovalent azobenzene glyco-
conjugates with exciting photochromic properties have been made
available employing click chemistry. Photoisomerisation of the
di- and trivalent azobenzene clusters 17 and 22 is influenced by
intramolecular effects leading to a mixture of isoforms. Multi-
valent glycoazobenzenes will be further investigated in advanced
NMR studies and utilised for fabrication of photoswitchable
multivalent glycoassemblies (arrays) for biological testing.
This work was supported by the DFG (Deutsche Forschungs-
gemeinschaft, SFB 677).
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c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 7519–7521 7521