Some Metabolic Properties of Nucleotides of 1-beta-d-arabino-furanosylcytosine.

have been prepared and studied for possible incorporation into polynucleotides. Arab inosylcytosine mono-, di-, and triphosphates were synthesized by both chemical and enzymatic methods. Labeled and unlabeled arabinosylcytosine nucleotides were tested for their capacity to serve as substrates for purified polynucleotide phosphorylase, deoxyribonucleic acid-dependent ribonucleic acid polymerase, deoxyribonucleic acid polymerase, and the enzyme which incorporates adenosine monophosphate and cytidine monophosphate into amino acid acceptor ribonucleic acid. The inhibitory effects of these nucleotides were also determined on these enzymes. Arabinosyl cytosine diphosphate was found to be completely inert as a substrate for polynucleotide phosphorylase, although it strongly inhibited the polymerization of adenosine di phosphate and cytidine diphosphate into polyadenylate and polycytidylate, respectively. In mixtures having 15 moles of arabinosylcytosine diphosphate to 85 moles of adenosine diphosphate or cytidine diphosphate, polymerization of the diphos phate substrates catalyzed by polynucleotide phosphorylase was inhibited by more than 95 per cent. No incorporation of tritium-labeled arabinosylcytosine nucleotides was detected in the ribonucleic acid or deoxyribonucleic acid synthesized in the pres ence of the labeled compounds. Thus, tritiated arabinosylcytosine triphosphate was found to be less than 1 per cent as effective a substrate as cytidine triphosphate for ribonucleic acid polymerase, deoxycytidine triphosphate for deoxyribonucleic acid polymerase, and cytidine triphosphate for the enzyme incorporating adenosine monophosphate and cytidine monophosphate into amino acid acceptor ribonucleic acid. No marked inhibition of these enzymes was produced by arabinosylcytosine triphos phate in amounts equal to the cytidine triphosphate or deoxycytidine triphosphate present. The absence of incorporation of arabinosylcytosine into polynucleotides tends to eliminate some significant potential toxicities in the development of chemo therapy with this compound.