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Regioselective acetylation of 7‐deacetylforskolin with 11 C‐acetyl chloride
Author(s) -
Sasaki Toru,
Furukata Kohsuke,
Ishii Shinichi,
Iimori Takamasa,
Ikegami Shiro,
Nozaki Tadashi,
Senda Michio
Publication year - 1996
Publication title -
journal of labelled compounds and radiopharmaceuticals
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.432
H-Index - 47
eISSN - 1099-1344
pISSN - 0362-4803
DOI - 10.1002/(sici)1099-1344(199604)38:4<337::aid-jlcr845>3.0.co;2-z
Subject(s) - chemistry , dichloromethane , toluene , pyridine , acetyl chloride , triethylamine , yield (engineering) , chloride , medicinal chemistry , organic chemistry , solvent , acetylation , forskolin , selectivity , catalysis , biochemistry , materials science , receptor , metallurgy , gene
Reaction conditions were studied to control the acetylating position on 7‐deacetylforskolin using [ 11 C]acetyl chloride. In a preliminary study using non‐labeled acetyl chloride, pyridine, lutidine, triethylamine, N, N‐diisopropylethylamine, dimethylaminopyridine (DMAP) and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) were tested as the base in the acetylation. Pyridine was effective in selective acetylation to yield forskolin in any solvent, and DBU was effective for 1‐acetyl‐7‐deacetylforskolin. Among toluene, dichloromethane and dichloroethane, toluene was the most suitable as the solvent for the selective acetylation of the 7‐OH group to give forskolin with any base. In the selectivity of acetylation with [ 11 C]acetyl chloride, more [ 11 C]forskolin was obtained than [ 11 C]1‐acetyl‐7‐deacetylforskolin (70:30) in the presence of pyridine in toluene. [ 11 C]1‐Acetyl‐7‐deacetylforskolin was preferentially synthesized with DBU in dichloromethane, and the ratio of [ 11 C]1‐acetyl‐7‐deacetylforskolin to [ 11 C]forskolin was 98:2. For the yield of the [ 11 C]acetylated product, DBU in dichloromethane was also suitable to obtain [ 11 C]1‐acetyl‐7‐deacetylforskolin. However, that of pyridine in toluene did not confer any advantages upon the yield of [ 11 C]forskolin compared with DMAP in toluene.