Sodium Bismuthate
3067
baccatin 4 is very well suited for a systematic structure–activity relationship
[
9,10]
study for the development of new Taxol and Taxotere analogues.
structure of 4 was confirmed by a direct comparison with respect to
reported compound (Mp and NMR).
The
[
10]
In conclusion, we have shown an operationally simple and readily
available oxidation of primary allylic alcohols and naturally occurring
baccatin to keto compounds. A representative procedure is given here:
Sodium bismuthate (8 mmol) was added to the baccatin (2 mmol) in
aqueous acetic acid (4 mL, 50% v/v) and acetone (2 mL). The mixture was
heated to reflux. At the end of reaction [indicated by TLC (30 min)] the
mixture was filtered through a pad of Celite and diluted with water (10 mL).
The mixture was extracted with methylene chloride (3 Â 20 mL). The
combined organic layer was washed with sodium bicarbonate solution
(
3 Â 10 mL, 10%) and brine (10 mL), dried over anhydrous sodium sulfate,
and concentrated under reduced pressure. The resultant crude product was
purified by column chromatography over silica gel using ethyl acetate–
hexanes to afford 13-keto-baccatin. Mp 210–2128C; IR (CHCl ): 3550
3
(
OH), 1725 (C 55 O), 1680 (conj C 55 O); NMR (CDCl ): 1.72 (s), 4.15 (d),
.35 (d, J ¼ 8), 7.58 (m), 8.10 (dd, J ¼ 2, 8), 2.22 (s), 2.33 (s).
3
4
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2
3
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4
5
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(
(
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(
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1
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1