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step of this total synthesis, the O-1-protected D -glucopyranose 1 is
selectively acetalized with benzaldehyde at positions O-4 and O-6. The
resulting acetal 2 is then esterified with 3,4- O -diphenylketal-protected
gallic acid 8 and subsequently desilylated with n -Bu 4 NF. The resulting
diester 3 is then subjected to a fully diastereoselective biaryl coupling
using Pb(OAc) 4 .
HO
O
Ph
O
PhCHO, ZnCl 2, 90%
O
HO
HO O
R
HO
R
HO
HO
1. 8, DCC, DMAP
2. n -Bu 4 NF, 88%
1 : R = OBn( o -NO 2 )
2 : R = OBn( o -NO 2 )
O
O
Ph
Ph
O
O
O
O
O
O
R
R
O
O
O
O
Pb(OAc) 4
O
O
O
O
46%
O
H, CPh 2
O
O
HO
O
O
O
HO
O
H, CPh 2
Ph
Ph
O
4 : R = OBn( o -NO 2 )
Ph
Ph
3 : R = OBn( o -NO 2 )
1. BnCl, K 2 CO 3
2. h ν
3. 7 , Et 3 N, 52%
O
Ph
O
HO
O
O
O
OR
O
HO
O
OG
O
O
HO
O
O
O
O
HO
O
O
1. 80% AcOH, reflux
Bn, CPh 2
HO
O
2. Pd/C, H 2, 17%
O
HO
OH
O
HO
5 : R = TBG
Bn, CPh 2
6 : sanguiin H-5
O
Cl
COOH
OBn
OH
OBn
OH
BnO
OBn
TBSO
OBn
OH
O
OBn
O
O
O
Ph
8
7
tribenzylgalloyl (TBG)
galloyl (G)
Ph
Fig. 5.2 Total synthesis of sanguiin H-5 ( 6 ).
 
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