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AcO
OH
O
HO
O
a, b
AcO
O
HO
AcNH
OH
A
C
HN
OAc
5
N
3
A
C
O
O
N
N
N
FmocHN
CO
2
H
A
C
O
O
AcNH
c
OH
OAc
FmocHN
O
(a)
1
OAc
OAc
AcO
AcO
O
a, b
O
AcO
AcO
AcHN
N
3
OAc
O
6
N
3
OAc
AcO
O
FmocHN
CO
2
H
AcO
NN
N
AcHN
O
c
OH
FmocHN
(b)
2
O
SCHEME 10.4
(a) Synthesis of pyranose building block
1
[30a]. Reaction conditions: a)
NaH, propargyl bromide, dry DMF, RT, 2.5 hours; b) NEt
3
/Ac
2
O, DMAP, RT, overnight;
c) 5 mol% Cu(OAc)
2
, 15 mol% Na ascorbate, 1:1 H
2
O/
t
BuOH, MW 80
◦
C,
5 minutes.
(b) Synthesis of hexose building block
2
[30b]. Reaction conditions: a) propargyl alcohol,
BF
3
·
<
Et
2
O, CH
2
Cl
2
,35
◦
C, 7 hours; b) Zn, AcOH then Ac
2
O/pyridine; c) 5 mol% Cu(OAc)
2
,
15 mol% Na ascorbate, 1:1 H
2
O/
t
BuOH, MW 80
◦
C,
<
5 minutes.
corroborated by other reports [32]. We have also observed a sequence-dependent
elimination of the azide during repetitive Fmoc deprotection cycles under microwave
conditions (data not shown). Other reports also suggest that the azide moiety is not
compatible with Boc chemistry, specifically the HF cleavage [33]. Our subsequent
investigations have therefore made use of propargylglycine (Pra) for SPPS, as the
alkyne functionality is fully stable under both Fmoc and Boc chemistry reaction
conditions.
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