Proofreading of a mutagenic nucleotide, N4-aminodeoxycytidylic acid, by Escherichia coli DNA polymerase I

The Hydrazine Moiety in the Synthesis of Modified Nucleosides and Nucleotides

Synthetic nucleoside mimics are re-emerging as crucial contenders for antiviral and anticancer medications. While, Ribavirin stands out for its unique antiviral properties, predominantly associated with its distinctive triazole heterocycle as a nucleobase, the exploration of alternative nitrogen-based aromatic heterocycles hold great promises for the discovery of novel bioactive nucleoside mimics. Although nucleoside derivatives synthesized from hydrazine-ribose units have been in development for many decades, they have been little evaluated biologically and even less for their antiviral properties. With the aim of taking a closer look at these under-explored derivatives and investigating their synthetic pathways, this review provides an overview of the molecular design, the chemical synthesis, and the biological activity, when available, of these nucleoside analogues. Overall, the entire body of work already done motivates further exploration of these analogues and encourages us of formulating structurally novel nucleoside drug candidates featuring innovative mode of action.

The synthesis and properties of oligodeoxyribonucleotides containing N6-methoxyadenine

Oligodeoxyribonucleotides containing N6-methoxyadenine (M) have been synthesized. The order of stability of duplexes consisting of synthesized oligodeoxyribonucleotides, 5'd(CCTGGTAXCAGGTCC)3'-5'd(GGACCTGNTACCAGG)3' (X = M, A, G. N = A, G, T, C), was M: A (Tm = 52 degrees C) greater than M: T (50 degrees C) greater than M: G (48 degrees C) greater than M: C (46 degrees C) observed by thermal denaturation in a buffer of 0.01 M Na cacodylate, and 0.1 M NaCl at pH 7.0. The Tms are within a range of 6 degrees of difference, which is smaller than those of Tms of the duplexes containing A:N pairs (11 degrees) and G:N pairs (11 degrees). DNA replication study on a template-primer system, 5'd(32p-CAGCTTTCGC)3' 3'd(GTCGAAAGCGMAGTCG)5', showed that TTP and dCTP were incorporated into DNA strands at a site opposite to M by Klenow DNA polymerase, but dATP and dGTP were not.

Ab initio molecular orbital study of the mispairing ability of a nucleotide base analogue, N4-aminocytosine

The intrinsic properties of N4-aminocytosine, a base analogue of cytosine, are analyzed by an ab initio molecular orbital method. Relative stabilities of four possible isomeric structures of N4-aminocytosine are shown. The more stable isomer has the smaller dipole moment, so the relative stabilities of the isomers in solutions are subject to solvent polarity. The mutagenicity of this base analogue must arise because it can behave like either cytosine or thymine. It can form a guanine-cytosine-like base pair more easily than cytosine, and an adenine-thymine-like base pair less easily than thymine.

Induction of mutation in mouse FM3A cells by N4-aminocytidine-mediated replicational errors

To explore the potential use of a nucleoside analog, N4-aminocytidine, in studies of cellular biology, the mechanism of mutation induced by this compound in mouse FM3A cells in culture was studied. On treatment of cells in suspension with N4-aminocytidine, the mutation to ouabain resistance was induced. The major DNA-replicating enzyme in mammalian cells, DNA polymerase alpha, was used to investigate whether the possible cellular metabolite of N4-aminocytidine, N4-aminodeoxycytidine 5'-triphosphate (dCamTP), can be incorporated into the DNA during replication. Using [3H]dCamTP in an in vitro DNA-synthesizing system, we were able to show that this nucleotide analog can be incorporated into newly formed DNA and that it can serve as a substitute for either dCTP or dTTP. dCamTP in the absence of dCTP maintained the activated calf thymus DNA-directed polymerization of deoxynucleoside triphosphates as efficiently as in its presence. Even in the presence of dCTP, dCamTP was incorporated into the polynucleotide. When dCamTP was used as a single substrate in the poly(dA)-oligo(dT)-directed polymerase reaction, it was incorporated into the polynucleotide fraction. The extent of incorporation was 4% of that of dTTP incorporation when dTTP was used as a single substrate. Even in the presence of dTTP, dCamTP incorporation was observed. A copolymer containing N4-aminocytosine residues was shown to incorporate guanine residues opposite the N4-aminocytosines. However, we were unable to observe adenine incorporation opposite N4-aminocytosine in templates. These cell-free experiments show that an AT-to-GC transition can take place in the presence of dCamTP during DNA synthesis, strongly suggesting that the mutation induced in the FM3A cells by N4-aminocytidine is due to replicational errors.

Induction of mutation in mouse FM3A cells by N4-aminocytidine-mediated replicational errors

To explore the potential use of a nucleoside analog, N4-aminocytidine, in studies of cellular biology, the mechanism of mutation induced by this compound in mouse FM3A cells in culture was studied. On treatment of cells in suspension with N4-aminocytidine, the mutation to ouabain resistance was induced. The major DNA-replicating enzyme in mammalian cells, DNA polymerase alpha, was used to investigate whether the possible cellular metabolite of N4-aminocytidine, N4-aminodeoxycytidine 5'-triphosphate (dCamTP), can be incorporated into the DNA during replication. Using [3H]dCamTP in an in vitro DNA-synthesizing system, we were able to show that this nucleotide analog can be incorporated into newly formed DNA and that it can serve as a substitute for either dCTP or dTTP. dCamTP in the absence of dCTP maintained the activated calf thymus DNA-directed polymerization of deoxynucleoside triphosphates as efficiently as in its presence. Even in the presence of dCTP, dCamTP was incorporated into the polynucleotide. When dCamTP was used as a single substrate in the poly(dA)-oligo(dT)-directed polymerase reaction, it was incorporated into the polynucleotide fraction. The extent of incorporation was 4% of that of dTTP incorporation when dTTP was used as a single substrate. Even in the presence of dTTP, dCamTP incorporation was observed. A copolymer containing N4-aminocytosine residues was shown to incorporate guanine residues opposite the N4-aminocytosines. However, we were unable to observe adenine incorporation opposite N4-aminocytosine in templates. These cell-free experiments show that an AT-to-GC transition can take place in the presence of dCamTP during DNA synthesis, strongly suggesting that the mutation induced in the FM3A cells by N4-aminocytidine is due to replicational errors.