Synthesis and crystal structures of some 8,5'-carbamoyloxy-bridged purine nucleosides

The X-ray analysis of 8,5'-(N-carbamoyloxy)-2-dimethylamino- methylene-9-(2',3'-0-isopropylidene-beta-D-ribofuranosyl)guanine (2a) has disclosed that some bond angles are significantly larger or smaller than the corresponding angles of normal ribonucleosides. Abnormally longer or shorter bond lengths have also been found. The base-sugar torsion angle of 2a has proved to reside between the C1'-C2' and C1'-C3' lines, and quite near the latter line. Some new 8,5'-carbamoyloxy bridged adenosines were also synthesized as 2',3'-protected forms.