Nucleic acid related compounds. 114. Synthesis of 2,6-(disubstituted)purine 2′,3′-dideoxynucleosides and selected cytotoxic, anti-hepatitis b, and adenosine deaminase substrate activities

Synthesis and cytotoxicity of 9-(2-deoxy-2-alkyldithio-β-D-arabinofuranosyl)purine nucleosides which are stable precursors to potential mechanistic probes of ribonucleotide reductases

A series of 2[prime or minute]-thionucleosides, as potential inhibitors of ribonucleotide reductases, has been synthesized. Treatment of the 3[prime or minute],5[prime or minute]-O-TPDS-2[prime or minute]-O-(trifluoromethanesulfonyl)adenosine with potassium thioacetate gave the arabino epimer of 2[prime or minute]-S-acetyl-2[prime or minute]-thioadenosine which was deacetylated to give 9-(3,5-O-TPDS-2-thio-[small beta]-d-arabinofuranosyl)adenine in high yield. Treatment of the latter with diethyl azodicarboxylate-C(3)H(7)SH-THF gave 2[prime or minute]-propyl disulfide which was desilylated to give 9-(2-deoxy-2-propyldithio-[small beta]-d-arabinofuranosyl)adenine. Subsequent tosylation (O5[prime or minute]) and displacement of the tosylate with pyrophosphate afforded the 5[prime or minute]-O-diphosphate in a stable form as propyl mixed-disulfide, which upon treatment with dithiothreitol releases 9-(2-thio-[small beta]-d-arabinofuranosyl)adenine 5[prime or minute]-diphosphate. The arabino 2[prime or minute]-mercapto group might interact with the crucial thiyl radical at cysteine 439 leading to the inhibition of ribonucleotide reductases via formation of a Cys439-2[prime or minute]-mercapto disulfide bridge. The 2,6-diamino-, 2-amino-6-chloro- and 2-amino-6-methoxypurine ribosides were also converted to the corresponding 2[prime or minute]-deoxy-2[prime or minute]-propyldithio-[small beta]-d-arabinofuranosyl nucleosides, which might serve as convenient precursors to the arabino epimer of 2[prime or minute]-thioguanosine. Analogously, 2[prime or minute]-deoxy-2[prime or minute]-propyldithioadenosine was prepared from 9-([small beta]-d-arabinofuranosyl)adenine. The nucleoside disulfides show modest cytotoxicity in a panel of human tumor cell lines.

Half-life of the duck hepatitis B virus covalently closed circular DNA pool in vivo following inhibition of viral replication

Covalently closed circular DNA (cccDNA) is a crucial intermediate in the replication of hepadnaviruses. We inhibited the replication of duck hepatitis B virus in congenitally infected ducks with a combination of lamivudine and a dideoxyguanosine prodrug. Inhibition of viral replication should prevent renewal of the cccDNA pool, and its decay was measured in liver biopsy samples collected over a 5-month period. In three ducks, the cccDNA pools declined exponentially, with half-lives ranging from 35 to 57 days. In two others, the pools declined exponentially for about 70 days but then stabilized at about 6 copies/diploid genome. The selection of drug-resistant virus mutants is an unlikely explanation for this unexpected stabilization of cccDNA levels. Liver sections stained for the cell division marker PCNA showed that animals in which cccDNA loss was continuous had significantly greater numbers of PCNA-positive nuclei than did those animals in which cccDNA levels had plateaued.