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NO
2
NO
2
OAll
OAll
F
F
HO
OMs
O
OH
VOF
3
-mediated
AB-ring formation
S
N
Ar-mediated
C-
O
-D-ring formation
Cl
OH
OH
HO
Cl
O
Cl
O
O
H
N
H
N
H
N
H
N
H
N
O
H
N
NHTfa
H
NH
2
NH
2
O
O
H
H
H
H
H
H
H
H
MeHN
OBn
O
O
O
NH
NH
H
H
O
O
MeO
OMe
OH
OBn
MeHN
OMe
MeHN
OH
OBn
HO
BnO
NO
2
F
OH
O
OAll
H
N
NO
2
CH
3
Boc
HO
NH
O
OH
F
H
O
N
H
condensation to the
heptapeptide precursor
O
Cl
O
HO
S
N
Ar-mediated D-
O
-E-ring
formation and deprotection steps
HO
O
O
NHDdm
H
N
H
N
H
N
N
H
NH
CH
3
O
H
H
H
H
O
O
NHBoc
H
N
H
O
O
H
NHDdm
HO
2
C
OBn
OBn
BnO
Scheme 2-7. Synthetic strategy of ring closure reactions according to Evans et al.
83
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