CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

directly afforded the furanose, which was acetylated to produce the acetate derivative 24.
Finally, coupling of 24 with silylated thymine gave the 3'-C branched nucleoside 25.
8d
O
O
i-iii iv, v
O
CHO
O
vi
OAc
O
OR 1
R 2
23
R 1 = Bz, R 2 = CH 2 OTBDPS
R 2
24
R 2 = CH 2 OTBDPS
O
O
H 3 C
NH
O N
O
O
R 2
25
i) BzCl, pyridine, 0 o C; ii) Me 2 S-BH 3 , hexane, H 2 O 2 -NaOH; iii) PCC, CH 2 Cl 2 ; iv) K 2 CO 3 , MeOH; v) Ac 2 O, pyridine;
vi) Thymine, HMDS, (NH4) 2 SO 4 , TMSOTf, CH 2 Cl 2 .
Scheme 9
The synthesis of 27 (Scheme 10) was accomplished starting from syn-12a, which
on tosylation, acid-catalyzed deketalization and subsequent reaction with NaN 3 gave the
azidodiol 26. Regio-selective monotosyalation of its primary hydroxyl function and base
treatment of the resultant tosylate furnished the target azido epoxide 27.
12a
i - iii
HO
OH
N 3
Ph
i, iv
O
N 3
26 27
i) p-TsCl, pyridine, 0 o C; ii) NaN 3 , DMF, ; iii) Aqueous CF 3 CO 2 H, CH 2 Cl 2 , 0 o C; iv) K 2 CO 3 , MeOH, 25 o C.
Ph
Scheme 10
For the synthesis of 32 (Scheme 11), 7d was silylated, subjected to boranemediated
hydroxylation at the olefin moiety, and subsequently benzoylated to afford 28.
This was further deketalised in acidic condition to afford diol 29. NaIO 4 cleavage of 29,
Wittig olefination of the resulting aldehyde, and catalytic hydrogenation yielded 30.
Alkaline hydrolysis of the benzoate 30 and PCC oxidation of the product alcohol yielded
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