Preparation of pyridine-stretched 2’-deoxyhypoxanthosine phosphoramidite

Pyridine-stretched 2!-deoxyhypoxanthosine (strH) phosphoramidite was prepared in eight steps from Hoffer’s sugar (2!-deoxy-3,5-di-O-(p-toluoyl)-α-D-erythro-pentofuranosyl chloride). Improved synthesis of the Hoffer sugar was achieved without need for distillation or chromatographic separation of intermediates, or use of gaseous HCl. Conditions were optimised to provide a key nitrile intermediate for the preparation of strH whereby the cesium salt of 4(5)-nitroimidazole was glycosylated using Hoffer’s sugar. The nitrile intermediate was also used to prepare pyridine-stretched 2!-deoxyadenosine (strA) and pyridine-stretched 2!-deoxy-diaminopurine (strD). Preliminary studies indicate that strH forms a stronger, size-expanded base pair with adenine compared with the Watson-Crick thymine-adenine base pair.