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

摘要

2-Nitroimidazole was silylated using hexaethyldisilazane and then reacted with 1-O-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 tert-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-O-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)_2 necessary for other methods. The Vorbrüggen conditions enable a shorter route to azomycin nucleoside analogues than the previous coupling procedures.