"Front Matter". In: Organosilanes in Radical Chemistry - Index of

64 Reducing Agents
N
N
N
S
N
O
S
H
O
H
Me
(TMS) 3 SiH
AIBN, 80 �C
H
100%
H
Me
(4.34)
In the case of nucleosides, deoxygenation represents an important procedure,
when occurring on the hydroxyl group in the position 2 0 . In fact, this is the
simplest method to convert ribonucleosides to deoxyribonucleosides (Reaction
4.35) which provide the units to be incorporated in DNA oligomers [59]. Also
many new potent anti-HIV and antiviral drugs, recently introduced in therapy,
have the 2 0 - or 3 0 -deoxy as well as 2 0 ,3 0 -dideoxy nucleoside skeleton. The
formation of thiocarbonyl derivatives of the alcoholic function on the sugar
moiety and its subsequent radical reduction give the easiest access to these
substrates, avoiding any other side reactions. 2 0 -Deoxyapio-b-d-furanosyl nucleosides
were prepared from the corresponding thiocarbonate derivatives (Reaction
4.36), and tested against HIV, Herpes simplex and other viruses [72].
Analogously, in Reaction (4.37) the removal of 2 0 -hydroxyl group has been
accomplished via the phenoxythiocarbonyl derivative under normal conditions
to produce the protected spironucleoside in good yield [73]. Pharmaceutically
important 2 0 - and/or 3 0 -deoxynucleosides were described in a patent and the key
step for the synthesis was achieved by treating the new and economically more
convenient (cyanoethylthio)-thiocarbonyl derivatives of nucleosides, instead of
classical xanthates, with (TMS) 3SiH in very mild conditions (Reaction 4.38)
[74]. In the field of nucleoside mimics, b-2 0 -deoxypseudouridine [75] and b-2 0 -
deoxyzebularine [76] were prepared by radical-based deoxygenation from the
corresponding b-pseudouridine and b-zebularine using (TMS) 3SiH as reducing
agent.
RO
O
N
N
RO O NHPh
S
NH 2
N
N
N
NH2 N
(TMS) 3SiH RO
O
N N
AIBN, 80 �C (4.35)
R,R = −Si(i-Pr) 2OSi(i-Pr) 2−
RO
97%