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More recently, a glycopeptide mimetic has been synthesized using this
methodology by the same author.
20
The anomeric position of an acety-
lated glucuronic acid unit was substituted by an azido group for future
branching. A commercial aminotriester 24 was coupled at the 6-position
ring of 23 in order to increase three times the number of carboxyl acid.
To form an anomeric N-acyl glycosylamine, the unsubstituted glyco-
sylamine is usually used
21-23
but this form is quite labile and prone to
potential anomerization and dimerization. Here the azide function was
directly converted into its corresponding glycosyl amide without previous
reduction to an amine. A modified Staudinger reaction was used with
trimethylphosphine in the presence of different amino acids derivatives,
for instance 26 activated with HOBt to give 27 (Scheme 5).
23
26
27
25
24
Scheme 5 Synthesis of a glycopeptidodendron's monomer - a: DIC, HOBt, DCM, 12h,
53%; b: 26, DIC, HOBt, PMe
3
, THF, 0
1
C-rt, 12h, 68%.
27
28
30
29
Scheme 6 Synthesis of two glycopeptidodendron with different generations (0 and 1) -
a: i. TFA, C
2
H
4
Cl
2
, 3h, 79%, ii. 28, HATU, DIPEA, DMF, 6h, 50%.
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