Carbohydrate-based dendrimers - Carbohydrate Chemistry: Chemical and Biological Approaches - page 264

33

31 32

Scheme 8 Photoaddition of a per-2,6-diallyl- b -cyclodextrin.

34

36

35 37

Scheme 9 Example of reductive amination of a saccharide.

per-2,6-diallyl-b-cyclodextrin 31 with b-D-thioglucose 32. 36 With 42
equivalents of the latter in methanol, the irradiation of the 14 allyl
functions was successful and gave 33 with 70% yield. This model could
be exploited with different thiol reagents more proper to build a den-
drimer (Scheme 8).
The second one is the synthesis of a lactoside glycodendron where the
photoaddition is combined with a reductive amination. 37 This latter
occurs between an amine and an aldehyde to form an imine that is
reduced into the corresponding open chain amine. This reaction has
the great advantage to not require extensive use of protecting groups
(Scheme 9).
In this example, the same starting trisaccharide 38, which has
been developed by Turnbull et al. was used for both reactions. 38 For
the photoaddition, the alkene groups were introduced to 38 by
allylation under acidic conditions to give 39. Then, this compound was
irradiated in the presence of hepta-O-acetyl-1-thio-b-lactose 40 and was
easily deprotected to give the compound 41 in very good yields (73%)
(Scheme 10).