HO O
O
THP O
O
THPO
68 69
THP = tetrahydropyrranyl
Selectride
OH
70
CH 3 C 6 H 4 SO 2 Cl
N
N NH
N
NH 2
N
N
N
NH 2
THPO
N
OTHP
71
72
73
H 3 O+ N C^6 H^5 COCl
N
N
NHCOC 6 H 5
OTHP
N
N
N
NHCOC 6 H 5
OH
74
P
O
CH 3 C 6 H 5 SO (^3) OOiiPrPr
P
O
OOiPriPr
NaH
N
N
N
NHCOC 6 H 5
O
O 3 SC 6 H 4 CH 3
THPO
P
O
OOHH
N
N
N
NH 2
O
75
77 78
76
NN
N N
Replacement of one of the carbon atoms in the sugar moiety by oxygen,
in effect converting that ring to an acetal, leads to yet another false sub-
strate for viral reverse transcriptase. Glycosilation of the silylated purine
( 79 ) with chiral dioxolane ( 80 ), prepared in several steps from anhydro-
mannose, in the presence of ammonium nitrate affords the coupling
product as a mixture of anomers. The mixture of products is then separated
on a chromatographic column. The desired diastereomer ( 81 ) is the reacted
N
N N
N
Cl
F
Si(CH 3 ) 3
- O
tBuPh 3 SiO O OCOCH 3
79
80
N
N N
N
Cl
F
O
tBuPh 3 SiO O
tBuPh 3 SiO
81
NH 3
N
N N
N
NH 2
H 2 N
O
O
83
Bu 4 F
N
N N
N
Cl
NH 2
O
tBuPh 3 SiO O
82
N
N N
N
NH 2
H 2 N
O
HO O
84
NH 3
198 BICYCLIC FUSED HETEROCYCLES