Recent advances in the synthesis of cyclic 5'-nornucleoside phosphonate analogues.

Nucleoside phosphonates are isosteric, isopolar, and isoelectronic with phosphates. Nucleoside phosphonates can undergo enzymatic phosphorylation for conversion into the corresponding diphosphoryl phosphonates, which are naturally occurring nucleoside triphosphate analogues. The biological activity, which is mostly antiviral and antitumor but sometimes is as specific enzyme inhibitor, is briefly presented to help discover compounds with increased activity over natural nucleosides to provide structure-activity data. This review focuses on the synthesis of three types of cyclic 5'-nucleoside phosphonate analogues: (1) furanose 5'-nornucleoside phosphonates, (2) carbocyclic 5'-nornucleoside phosphonates, and (3) apiose 5'-nornucleoside phosphonates.