[Oligonucleotides with peptide internucleotide linkage. A novel class of modified oligonucleotides].

Oligonucleotide analogues with replacement of one or more internucleotide phosphodiester linkages with glycine, L- and D-alanine residues have been synthesized (C3'-NH-C(O)-CH(X)-NH-C(O)-C4', X = H, (S)-CH3 and (R)-CH3). The stability of the duplexes formed by the modified oligonucleotides and their wild-type complements have been studied. Incorporation of glycine and L-alanine residues have been shown to substantially decrease the stability the modified duplexes in comparison with that of the wild-type ones (DeltaT(m) approximately -2 degrees C per modification), while the analogs with D-alanine-containing linkages appeared to form duplexes with increased stability (DeltaT(m), approximately +0.2 degrees C per modification).

[Synthesis of 5'-deoxy-5'-ethoxycarbonylmethyl nucleosides, the precursors of oligonucleotides with the amide internucleoside bond C3'-NH-C(O)-CH2-C5'].

A method for the synthesis of 5'-deoxy-5'-ethoxycarbonylmethyl nucleosides has been developed. 3-O-Benzyloxymethyl-1,2-O-isopropylidene-alpha-D-allofuranose was oxidized by sodium periodate to form a 5-aldo derivative, which was converted by the reaction with triethylphosphonoacetate in the presence of sodium hydride into a 5-deoxy-5-ethoxycarbonylmethylene derivative. The hydration of the unsaturated compound gave 5-deoxy-5-ethoxycarbonylmethyl-l,2-O-isopropylidene-alpha-D-ribofuranose. After the benzylation of 3-hydroxyl, the removal of the isopropylidene group by heating with acetic acid, and the subsequent acetylation, l,2-di-O-acetyl-3-O-benzyl-5-deoxy-5-ethoxycarbonylmethyl-D-ribofuranose was obtained, which reacted with persilylated nucleic acid bases to form 5'-deoxy-5'-ethoxycarbonylmethyl nucleosides.

[Oligonucleotide analogues containing internucleotide C3'-CH2-C(O)-NH-C5' bonds].

A dinucleoside bearing an amide internucleotide C3'-CH2-C(O)-NH-C5' bond was synthesized by the interaction of 3'-deoxy-3'-carboxylmethylribothymidine-2',3'-lactone obtained by hydrolysis of 2'-O-acetyl-5'-O-benzoyl-3'-deoxy-3'-ethoxycarboxylmethylribothymidine with 5'-deoxy-5'-amino-3'-O-(tert-butyldimethylsilyl)thymidine. After standard manipulations with protective groups, the dinucleoside was converted into 3'-O-(2-cyanoethyl-N,N'-diisopropylphosphoroamidite), which was used for the synthesis of modified oligonucleotides on an automatic synthesizer. Duplex melting curves formed by modified and complementary natural oligonucleotides were measured and the melting temperatures and thermodynamic parameters of duplex formation were calculated. The introduction of one modified bond into oligonucleotides caused only an insignificant decrease in the duplex melting temperatures compared with the nonmodified ones.

[Synthesis of 3'-deoxy-3'-carboxymethylnucleosides, precursors of oligonucleotides with an amide internucleoside bond].

An improved method for the synthesis of 3-deoxy-3-carboxymethylnucleosides was suggested. Oxidation of 5-O-benzoyl-l,2-O-isopropylidene-alpha-D-xylofuranose resulted in the 3-keto derivative, which was treated with triethylphosphonoacetate in the presence of sodium hydride to obtain the 3-deoxy-3-ethoxycarbonylmethylene derivative. Hydrogenation of the unsaturated compound proceeded strictly stereospecifically and gave the product with the ribo configuration. Acetolysis of the resulting compound with AcOH-Ac2O-CH3SO3H led to 1,2-di-O-acetyl-5-O-benzoyl-3-deoxy-3-ethoxycarbonylmethyl-D-ribofuranose, whose interaction with persilylated nucleic bases gave 3-deoxy-3-ethoxycarbonylmethylnucleosides in a total yield of 42-49% from the starting compound.

[Oligonucleotide analogues containing the internucleotide linker C3'-NH-CO-CH2-N(CH3)-C5'].

Oligonucleotide analogues were synthesized whose internucleoside linker contains an amide bond and a methylamino group (C3'-NH-CO-CH2-N(CH3)-C5'). Melting curves for duplexes formed by modified oligonucleotides and natural oligonucleotides complementary to them were measured, and the melting temperatures and thermodynamic parameters of duplex formation were calculated. The introduction of one modified dinucleoside linker into the oligonucleotide only slightly decreases the melting temperatures of these duplexes compared with unmodified ones. The CD spectra of modified duplexes were studied, and their spatial structures are discussed.

[Oligonucleotide analogues bearing an acyclonucleoside linked by an internucleotide amide bond].

Oligonucleotide analogues bearing an acyclocytidine linked to thymidine by an amide (3'-O-CH2-CO-N-5') bond were synthesized. Melting curves of duplexes formed by modified oligonucleotides and complementary natural oligomers were obtained and thermodynamic parameters of their formation were measured. Replacement of dCpT by a modified dinucleotide only moderately decreased the melting temperature of these modified duplexes in comparison with unmodified duplexes containing complementary natural bases. CD spectra of modified duplexes were studied, and the duplex spatial structures are discussed. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2008, vol. 34, no. 2; see also http://www.maik.ru.

[Oligodeoxynucleotides containing substituted 4-nitroindoles: synthesis and study of their DNA duplexes].

The synthesis of oligonucleotides containing 1-(2-deoxy-beta-D-ribofuranosyl)-2-methyl-4-nitroindole and 1-(2-deoxy-beta-D-ribofuranosyl)-2-phenyl-4-nitroindole is described. The synthesized modified oligonucleotides were used for studying the stability of intermolecular DNA duplexes with one unnatural strand and for evaluation of discriminating potential of 2-methyl- and 2-phenyl-4-nitroindoles toward nucleic bases. For comparison, an unmodified oligonucleotide and oligonucleotides bearing 5-nitroindole were used. It was shown that 2-methyl-4-nitroindole was only insignificantly inferior in stability to 5-nitroindole and characterized by a similar discriminating potential. 2-Phenyl-4-nitroindole provided a more pronounced duplex destabilization, the discrimination toward natural bases being decreased. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2008, vol. 34, no. 2; see also http:// www.maik.ru.

[Theoretical study of the structure of adenosine deaminase complexes with adenosine analogues: I. Aza-, deaza- and isomeric azadeazaanalogues of adenosine].

The conformational models of the active site of adenosine deaminase (ADA) and its complexes in the basic state with adenosine and 13 isosteric analogues of the aza, deaza, and azadeaza series were constructed. The optimization of the conformational energy of the active site and the nucleoside bound with it in the complex was achieved in the force field of the whole enzyme (the 1ADD structure was used) within the molecular mechanics model using the AMBER 99 potentials. The stable conformational states of each of the complexes, as well as the optimal conformation of the ADA in the absence of ligand, were determined. It was proved that the conformational state that is close to the structure of the ADA complex with 1-deazaadenosine (1ADD) known from the X-ray study corresponds to one of the local minima of the potential surface. Another, a significantly deeper minimum was determined; it differs from the first minimum by the mutual orientation of side chains of amino acid residues. A similar conformational state is optimal for the ADA active site in the absence of the bound ligand. A qualitative correlation exists between the values of potential energies of the complexes in this conformation and the enzymatic activity of ADA toward the corresponding nucleosides. The dynamics of conformational conversions of the active site after the binding of substrate or its analogues, as well as the possibility of the estimation of the inhibitory properties of nucleosides on the basis of calculations, are discussed.

[Binding of unnatural alpha,beta-oligocytidylates with DNA duplexes]. / Issledovanie sviazyvaniia neprirodnykh alpha,beta-oligotsitidilatov s dupleksami DNK.

Binding of short fluorescently labeled AT-containing DNA duplexes with modified oligocytidylates is studied. The latter are modified to contain unnatural alpha-anomers along with natural beta-nucleotides; the nucleotide composition is selected according to putative pattern of unconventional triplex formation between duplex and oligomer bases. Nondenaturing gel electrophoresis is used to study complexation of fluorescent duplexes with cytidyl oligomers and oligocytidylate self-association at low temperatures. A DNA duplex of random AT composition is shown to bind with an excess of the corresponding oligocytidylate in 0.1 M Tris-HCl in the presence of Mg2+. Binding is observed at neutral pH values, while more basic pH (8.0) prevents complexation of the AT duplex and oligocytidylate. Contrary to oligonucleotides of irregular composition, a regular dA30:dT30 duplex does not bind with the dC strand. It is also shown that alternating self-complementary duplex d(AT)16 and oligocytidylate d(CbetaCalpha)15 do not form complexes, and poly-dC self-associates are formed instead. The effect of 2'-O-methylation of the third strand on complex formation and self-association is also analyzed. The results suggest that a modified oligocytidylate binds with a random-composition duplex, albeit with lower efficiency.

[Theoretical study of antagonists and inhibitors of mammalian adenosine deaminase. II. Isomeric aza-deazaanalogues of adenosine]. / Teoreticheskoe issledovanie antagonistov i ingibitorov adenozindezaminazy mlekopitaiushchikh. II. Isomernye aza-dezazaanalogi adenozina.

Isomeric aza-deazaanalogues of adenosine and their N1-protonated forms (except for that of 8-aza-1-deazaadenosine) were studied by computer modeling to find a relationship between their molecular structures and the properties as substrates for the mammalian adenosine deaminase. The atomic charge distribution and maps of the electrostatic potential around their van der Waals molecular surface were calculated using the ab initio STO-3G method. The conformational studies were carried out by the MM+ method of molecular mechanics. The previously proposed mechanism of the substrate acceptance in the active site of mammalian adenosine deaminase was refined, and the potential substrate properties were predicted for two previously unstudied adenosine analogues, 5-aza-9-deazaadenosine and 8-aza-3-deazaadenosine.

[Theoretical study of antagonists and inhibitors of mammalian adenosine deaminase. I. Adenosine and its aza- and deaza-analogs]. / Teoreticheskoe issledovanie antagonistov i ingibitorov adenozindezaminazy mlekopitaiushchikh. I. Adenozin i ego aza- i dezazaanalogi.

Aza- and deazaanalogues of adenosine, including their 1-protonated forms (except for that of 1-deazaadenosine), were studied by computer computation to find a relationship between their molecular structures and substrate properties for the mammalian adenosine deaminase. The atomic charge distribution and maps of the electrostatic potential around their van der Waals molecular surface were calculated for these compounds using the ab initio STO-3G method. The conformational studies were carried out by the MM+ method of molecular mechanics. The mechanism that determines the substrate selectivity of mammalian adenosine deaminase is discussed. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2002, vol. 28, no. 4; see also http://www.maik.ru.

[Enhancing the stability of oligonucleotide duplexes. The effect of adding 1-(2'-deoxy-beta-d-ribofuranosyl)-5-nitroindole]. / Povyshenie stabil'nosti dupleksov oligonukleotidov. Effekt prisoedineniia 1-(2'-dezoksi-beta-d-ribofuranozil)-5-nitroindola.

We studied the properties of DNA duplexes containing 5-nitroindole (N) in one of the chains. We synthesized 8-membered oligos with N at the 5' or at the 3' end: 5'-d(NXGACCGTC)-3' or 5'-d(GACCGTCXN)-3', where X is one of the four natural bases, making all four kinds of oligos with and without N. We also prepared 11-membered oligos complementary to the above octanucleotides: 5'-d(TGACGGTCYZT)-3' and 5'-d(TZYGACGGTCT)-3', where Y and Z are A, G, C, or T. The stability of duplexes obtained with these oligos was assessed by melting, and the thermodynamic parameters delta H, delta S, and Tm were calculated. Comparison of the melting curves for modified and nonmodified duplexes demonstrated that the presence of N at the 5' end of one chain raises the Tm by 6.6 degrees C on average; if N is at the 3' end of the same chain, the Tm increases by about 3 degrees C.

[The hierarchy of complexes and compact structures of trivaline with nucleic acids. III. Complexes of trivaline with trinucleotides forms a rod-like structure with length of about 1000 A in solution]. / Ob ierarkhii kompleksov i kompaktnykh struktur trivalina s nukleinovymi kislotami. III. Kompleksy trivalina s trinukleotidami obrazuiut v rastvore palochkoobraznye struktury dlinoi 1000 A]

We demonstrated the ability of trivaline in the course of interaction with certain trinucleotides in solution to form extended fibre-like structures with lengths of up to several thousand angstroms. Such structures were observed for complexes of trivaline with both deoxyribo- and ribonucleotides with homopurine, homopyrimidine, or random sequences, with or without terminal 5'-phosphate. A model of organization of such structures is proposed. It is based on tetramer complex of trivaline with short nucleotides, two structural units of which, consisting of trivaline tetramer and two trinucleotides, form the octamer complex. It has three perpendicular axes of symmetry of the second order. The spatial location of bases in this structure is additionally fixed by nucleopeptide interactions. The latter create favourable conditions for arranging hydrogen bonds between trinucleotides belonging to different tetramer complexes and stacking interactions between the bases of each nucleotide. Octamer complexes are able to form regular aggregates in the form of a "stack", consisting of dozens of elementary units. These aggregates can be electron microscopically visualized as extended fibre-like structures.

[Reconstruction of a sequenced sequence using results of stacked hybridization with an oligonucleotide matrix]. / Rekonstruktsiia sekvenirumoi posledovatel'nosti po rezultatam gibridizatsii vstyk s oligonukleotidnoi matritsei.

The efficiency of additional rounds of continuous stacking hybridization in DNA sequence reconstruction by hybridization with oligonucleotide matrix (SHOM) is considered. At first, DNA is hybridized with a matrix of oligonucleotides of the length L. The overlapping of the tuples which have formed perfect duplexes with the DNA, on the one hand, has enabled us to reconstruct unambiguously a part of the sequence, and on the other hand, suggested a modified scheme for reconstructing the remaining part. Then the additional hybridizations should be carried out in the presence of shorter oligonucleotides of the length l, that are able to form perfect duplexes of the length L + l in continuous hybridization closely to matrix tuples. In this case the stability of a duplex consisting of l-tuples and long DNA is enhanced due to stacking interaction. The information obtained about the succession of L + l sites considerably increases the efficiency of reconstruction, which can eventually reach the efficiency of a matrix consisting of (L + l)-tuples. We propose here an algorithm for compiling such a set of l-tuples to be added that the number of additional hybridizations can be appreciably diminished. For an octanucleotide matrix and different sets of pentanucleotides to be used for continuous stacking hybridization, the length of unambiguously sequenced DNA undergoes a rise from 200 to some thousands bp.