CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

For the actual synthesis, (Scheme IV.3.1), 83d was chosen as a starting material.
The free hydroxyl group was converted to the corresponding benzoate derivative 145 in
90% yield, by treating with BzCN in the presence of Et 3 N. Compound 145 was
characterized from the disappearance of a sharp band at ~3400 cm -1 in its IR spectrum, and
presence of multiplets at δ 5.66-5.71 (1H) in the 1 H NMR spectrum (Fig. IV.3.1).
Compound 145 was subjected to hydroboration-oxidation 165 of its terminal olefin moiety to
furnish the alcohol 146 in 90% yield. Its IR band at 3466 cm -1 and additional signal at ~δ
3-4 in place of olefinic multiplets in the 1 H NMR spectrum (Fig. IV.3.2) were consistent
with its structure. The hydroxyl group of 146 was oxidized with PCC 115 to give the
aldehyde 147 (IR peak at 1720 cm -1
and 1 H NMR resonance at δ 9.75 ppm).
Debenzoylation of 147 under alkaline conditions directly produced the furanose 148
possessing a protected hydroxymethyl at the 3-C position. Its IR spectrum showed
characteristic hydroxyl band in place of the CHO band. The 1 H NMR spectra of 148 are
shown in Fig. IV.3.3. The hydroxyl group of compound 148 was acetylated to produce the
acetate derivative 149. The appearance of a 1 H NMR singlet at δ 1.96 and 2.04 (2s, 3H)
confirmed the acetate group. Finally, Vorbruggen coupling 163a
of 149 with silylated
thymine furnished the 3'-C branched nucleoside 150.
164