Preparation of Nucleosides Derived from 2-Nitroimidazole and d-Arabinose, d-Ribose, and d-Galactose by the Vorbrüggen Method and Their Conversion to Potential Precursors for Tracers To Image Hypoxia

2015-12-16T20:13:09Z (GMT) by Anna Schweifer Friedrich Hammerschmidt
2-Nitroimidazole was silylated using hexaethyldisilazane and then reacted with 1-<i>O</i>-acetyl derivatives of d-arabinose, d-ribose, and d-galactose in acetonitrile at mild temperatures (−20 °C to rt), catalyzed by triethylsilyl triflate (Vorbrüggen conditions). The α-anomer was formed in the former case and the β-anomers in the latter two cases (highly) selectively. When d-arabinose and d-ribose were silylated with <i>tert</i>-butyldiphenylsilyl chloride in pyridine at the hydroxyl groups at C-5 and acetylated at the other ones in a one-pot reaction, mixtures of anomeric 1-<i>O</i>-acetyl derivatives were obtained. These were coupled by the Vorbrüggen method and then deblocked at C-5 and tosylated to give precursors for tracers to image hypoxia in four steps without using Hg(CN)<sub>2</sub> necessary for other methods. The Vorbrüggen conditions enable a shorter route to azomycin nucleoside analogues than the previous coupling procedures.