Access to <sup>18</sup>
F-labelled isoxazoles by ruthenium-promoted 1,3-dipolar cycloaddition of 4-[<sup>18</sup>
F]fluoro-<i>N</i>
-hydroxybenzimidoyl chloride with alkynes
作者:Silvia Roscales、Torsten Kniess
DOI:10.1002/jlcr.3708
日期:2019.6.30
4-[18F]Fluoro-N-hydroxybenzimidoyl chloride (18FBIC), an 18F-labelled aromatic nitrile oxide, was developed as building block for Ru-promoted 1,3-dipolar cycloaddition with alkynes. 18FBIC is obtained in a one-pot synthesis in up to 84% radiochemical yield (RCY) starting from [18F]fluoride with 4-[18F]fluorobenzaldehyde (18FBA) and 4-[18F]fluorobenzaldehyde oxime (18FBAO) as intermediates, by reaction of 18FBAO with N-chlorosuccinimide (NCS). 18FBIC was found to be a suitable and stable synthon to give access to 18F-labelled 3,4-diarylsubstituted isoxazoles by [Cp*RuCl(cod)]-catalysed 1,3-dipolar cycloaddition with various alkynes. So the radiosynthesis of a fluorine-18–labelled COX-2 inhibitor [18F]1b, a close derivative of valdecoxib, was performed with 18FBIC and 1-ethynyl-4-(methylsulfonyl)benzene, providing [18F]1b in up to 40% RCY after purification in 85 minutes. The application of 18FBIC as a building block in the synthesis of 18F-labelled heterocycles will generally extend the portfolio of available PET radiotracers.
4-[18F]氟-N-羟基苯并咪唑氯化物(18FBIC)是一种18F标记的芳香氰氧化物,作为铑促进的1,3双极环加成反应与炔烃的构建单元。18FBIC通过从[18F]氟化物出发,利用4-[18F]氟苯甲醛(18FBA)和4-[18F]氟苯甲腙(18FBAO)作为中间体,在一锅合成中获得,放射化学产率(RCY)高达84%。该反应是通过将18FBAO与N-氯琥珀酰亚胺(NCS)反应得到的。研究发现,18FBIC是一个合适且稳定的合成单元,可以通过[Cp*RuCl(cod)]催化的1,3双极环加成反应与多种炔烃反应,合成18F标记的3,4-二芳基取代异恶唑。因此,利用18FBIC和1-乙炔基-4-(甲基磺酰)苯进行了氟-18标记的COX-2抑制剂[18F]1b的放射合成,作为与瓦尔德考昔(valdecoxib)相近的衍生物,经过85分钟的纯化后,得到[18F]1b,RCY最高可达40%。将18FBIC作为18F标记杂环合成的构建单元,通常将扩展可用的正电子发射断层扫描(PET)放射示踪剂的种类。