KINETICS FOR THE ACID-CATALYZED HYDROLYSIS OF O-BRIDGED, S-BRIDGED AND N-BRIDGED 5',8-CYCLONUCLEOSIDES RELATED TO ADENOSINE

Kinetics of the acid-catalysed hydrolysis of O-5',8-cycloadenosine, S- 5',8-cyclo-5'-thioadenosine and N-5',8-cyclo-5'-amino-5'-deoxyadenosin e have been studied. the S- and N-bridged cyclonucleosides are hydroly sed exclusively by the rupture of the N-glycosidic bond, white the O-b ridged compound undergoes concurrent cleavage of the N-glycosidic and 5',8-cyclo linkages, the proportion of the former reaction being marke dly increased with increasing temperature. The conformations of the sa me cyclonucleosides have been elucidated by molecular modelling (SYBYL ) and H-1 NMR spectroscopy. The effect of the sugar ring puckering on the hydrolytic stability is discussed.