Research is proposed in four diverse but related areas. One long range goal is a better understanding of the role of cyclic nucleotides (cAMP in particular and also cGMP) in cell proliferation and maligant transformation through a detailed knowledge of their interactions with key enzymes, protein kinase (PK-1 and PK-2) and various phosphodiesterases. NMR studies of the phosphate ring conformation and phosphorus covalency in model enzyme-cyclic nucleotide systems and of cAMP-PK adducts themselves will be pursued. The influence of stereoelectronic effects on chair-twist equilibria of the phosphate ring will be assessed by 1 H NMR. New synthetic investigations of neutral cyclic nucleotide derivatives are aimed at: 1) prodrug delivery of known or potential antivirals and antitumor agents, with a focus on previously targeted thymidylate synthase in thymidine kinase-deficient drug- resistant HSV-1 mutants; and, 2) potential cAMP or cGMP antagonist/agonist molecules for study in Dictyostelium discoideum/cAMP receptor protein systems and with cGMP-activated phosphodiesterases. Biological activities will be determined collaboratively. Certain P (III)-containing cyclic nucleotides will serve as precursors to models with valuable biological properties or useful in dinucleotide synthesis. A thorough knowledge of the conformational properties of the 1,3,1- oxazaphosphorinane ring system of the clinically valuable antitumor agent cyclophosphamide will be pursued as a partial basis for understanding its activity and the design of improved drugs. Specifically, NMR and X-ray crystallographic studies should yield knowledge of the influence of stereoelectronic effects in determining conformation. Detailed knowledge of the scope and mechanism of the formation of azetidines from certain 1,3,2-oxazaphosphorinanes will be sought. The eventual target is biologically active azetidinones. 17 O NMR studies will be aimed at the non-degradative correlation of 17 0 spectral parameters with phosphorus configuration in biologically important P-chiral nucleoside-derived phosphate triesters, phosphonates, and phosphoramidates. A new phosphite to phosphonate photo-Arbuzov rearrangement will be applied to the synthesis of novel antivirals based on acyclic nucleosides and 2',3'-dideoxy- and 2',3'-didehydro-2, 3' -dideoxy ribonucleosides. The focus is on antivirals active against a broad spectrum of viruses including HIV.