Construction of oligonucleotide arrays on a glass surface using a heterobifunctional reagent, N-(2-trifluoroethanesulfonatoethyl)-N-(methyl)-triethoxysilylpropyl-3-amine (NTMTA)

A rapid method for construction of oligonucleotide arrays on a glass surface, using a novel heterobifunctional reagent, N-(2-trifluoroethanesulfonatoethyl)-N-(methyl)-triethoxysilylpropyl-3-amine (NTMTA), has been described. The heterobifunctional reagent, NTMTA, carries two different thermoreactive groups. The triethoxysilyl group on one end is specific towards silanol functions on the virgin glass surface, while the trifluoroethanesulfonyl (tresyl) group on the other end of the reagent reacts specifically with aminoalkyl- or mercaptoalkyl- functionalized oligonucleotides. Immobilization of oligonucleotides on a glass surface has been realized via two routes. In the first one (A), 5′- aminoalkyl- or mercaptoalkyl-functionalized oligonucleotides were allowed to react with NTMTA to form a oligonucleotide-triethoxysilyl conjugate which, in a subsequent reaction with unmodified (virgin) glass microslide, results in surface-bound oligonucleotides. In the second route (B), the NTMTA reagent reacts first with a glass microslide whereby it generates trifluoroethanesulfonate ester functions on it, which in a subsequent step react with 5′-aminoalkyl or mercaptoalkyl oligonucleotides to generate support-bound oligonucleotides. Subsequently, the oligonucleotide arrays prepared by both routes were analyzed by hybridization experiments with complementary oligonucleotides. The constructed microarrays were successfully used in single and multiple nucleotide mismatch detection by hybridizing these with fluorescein-labeled complementary oligonucleotides. Further more, the proposed method was compared with the existing methods with respect to immobilization efficiency of oligonucleotides.     

Introduction of 5'-terminal functional groups into synthetic oligonucleotides for selective immobilization

Oligodeoxyribonucleotides terminating in a 5'-primary amine group are synthesized using solid-phase supported phosphoramidite chemistry. The 5'-terminal amine group in the deprotected oligomers is further derivatized with either succinic anhydride to give 5'-carboxylic acid or with dithiobis(succinimidylpropionate) followed by treatment with dithioerythritol to produce 5'-thiol-terminated oligonucleotides. The 5'-thiol-terminated oligonucleotides are selectively immobilized on solid supports containing either p-chloromercuribenzoate or 2,2'-dithiobis(5-nitropyridine) activated thiol groups.     

Determination of oligonucleotide molecular masses by MS-MALDI

MALDI mass spectrometry (MS) of 14- to 42-mer homogeneous oligonucleotides and their mixtures was carried out using a Vision 2000 instrument (Thermo BioAnalysis, Finnigan, United States). Conditions for the determination of oligonucleotide molecular masses were optimized by applying various matrices and operation modes. The most reproducible results with minimal uncontrolled decomposition of the oligonucleotides including their apurinization during the MALDI MS registration were obtained using 2,4,6-trihydroxyacetophenone as a matrix instead of 3-hydroxypicolinic acid, usually employed in the mass spectrometry of oligonucleotides. Our approach allows the determination of molecular masses of oligonucleotides obtained by chemical synthesis and the evaluation of their component composition and purity. It was applied to the mass spectrometric analysis of oligonucleotides containing a 3'-(methyl-C-phosphonate) group or a modified 1,N6-ethenodeoxyadenosine unit.     

Preparation of DNA-duplexes, containing internucleotide thiophosphate groups in various positions of the recognition site for the EcoRII restriction endonuclease

Twenty-four 12-mer DNA duplexes, each containing a chiral phosphorothioate group successively replacing one of the internucleotide phosphate groups either in the EcoRII recognition site (5'CCA/TGG) or near to it, were obtained for studying the interaction of the restriction endonuclease EcoRII with internucleotide DNA phosphates. Twelve of the 12-mer oligonucleotides were synthesized as Rp and Sp diastereomeric mixtures. Six of them were separated by reversed-phase HPLC using various buffers. Homogeneous diastereomers of the other oligonucleotides were obtained by enzymatic ligation of the Rp and Sp diastereomers of 5- to 7-mer oligonucleotides preliminarily separated by HPLC with the corresponding short oligonucleotides on a complementary DNA template. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2003, vol. 29, no. 6; see also http://www.maik.ru.     

Preparation of rabbit antibodies to 4,4'-dimethoxytriphenylmethyl, the protective group in oligonucleotide synthesis.

Antibodies were raised in 2 rabbits by immunization with carrier proteins covalently bound to deoxyguanosine bearing a 4,4'-dimethoxytriphenylmethyl group protecting the 5'-hydroxy terminus of deoxyribose. After several injections with such complexes, immune sera were tested with an immuno-enzymatic method using as antigens several compounds containing the hapten, as well as synthetic oligonucleotides bearing, or not, this protective group at the 5' terminus. One of the two antisera appeared to recognize the dimethoxytrityl group bound to carrier molecules, and thus might find a useful application for the detection, quantitation, and control of oligonucleotides obtained by automatic synthesis.     

Biotinyl and phosphotyrosinyl phosphoramidite derivatives useful in the incorporation of multiple reporter groups on synthetic oligonucleotides.

Non-nucleosidic phosphoramidite linker units suitable for use on commercial DNA synthesis machines have been designed for the direct incorporation of biotin and a new reporter group, phosphotyrosine, at multiple sites on synthetic oligonucleotides. The units are based on a 3-carbon glyceryl backbone where the reporter group is attached to the 2-O-position through a 3-aminopropyl spacer. 17-mer oligonucleotides were synthesized carrying at the 5'-end 1, 2, 4 or 8 biotinyl units or 1, 2, 4 or 8 phosphotyrosinyl units respectively and used for the detection of DNA on nitrocellulose filters by hybridization. Subsequent incubation of the filters with a monoclonal antibody to the reporter group followed by secondary detection using enhanced chemiluminescence (ECL) resulted in amplification of signal strengths as the number of reporter groups was increased. The results were quantitated by use of a charge couple device (CCD) camera. Spacing of biotin moieties by thymidyl residues resulted in further improvements in signal strengths, whereas similar spacing of phosphotyrosinyl units did not.     

一种基于关键路径法的DNA计算用寡核苷酸序列设计算法

在原有的生物大分子序列比对算法的基础上,结合图论中的关健路径法,提出了一种新的计算两寡核苷酸序列间最大配对程度的算法。采用此算法结合生成并测试的方法,能够寻找给定长度的一组适用于DNA计算的寡核苷酸序列。同时采用DNA芯片杂交方法验证了用该算法设计的一组序列的杂交特异性。     

Quantitative Parametrs of Cooperative Interactions of the Oligodeoxyribonucleotides on the Complementary Template

Abstract

The cooperative interactions of oligonucleotides on the complementary template were studied using the quantitative analysis of the template alkylation with the oligonucleotides bearing covalently attached 4-[N-(2-chloroethyl)-N-methylamino]benzyl group at 5′-end. The influence of the mismatched nucleotides and the stabilizing N-(2-hydroxyethyl)phenazinium group at the 5′- and 3′-ends of the oligonucleotides on the parameters of cooperativity was evaluated.     

Trityl mass-tags for encoding in combinatorial oligonucleotide synthesis.

Combinatorial libraries of oligonucleotides on beads were synthesised by a split-and-mix strategy using 5'-DMTr- or 5'-Fmoc- nucleoside phosphoramidites. Trityl moieties with different masses were used to encode for the bases coupled at each step in the synthesis of oligonucleotides selected by hybridisation from the libraries. Tags orthogonal to the nucleotides added were produced by coupling amines of different MW to an activated carboxyl group(s) on the trityl moiety. Tags can be released from the support by laser irradiation and measured directly by TOF without matrix. Alternatively, they may be released by an acidic treatment and then analysed by (MA)LDI-TOF.     

Preparation of oligodeoxynucleotide 5'-triphosphates using solid support approach

We report a synthetic procedure for conversion of oligonucleotides to their 5'-triphosphate derivatives with moderate yield. The oligonucleotides were synthesized on solid support using standard phosphoramidite protocols. The DMT protection group was removed and the 5'-OH was phosphitylated using 2-chloro-4H-1,3,2-benzodioxaphosphorin-4-one followed by reaction with tributyammonium pyrophosphate and iodine oxidation. After subsequent removal from support and complete deprotection, the products were isolated by anion-exchange HPLC chromatography. Structures of several 5'-triphosphate derivatives have been proven by phosphorus NMR, Mass-spectrometry and by HPLC comparison with authentic samples.     

Automated parallel synthesis of 5′-triphosphate oligonucleotides and preparation of chemically modified 5′-triphosphate small interfering RNA

A fully automated chemical method for the parallel and high-throughput solid-phase synthesis of 5′-triphosphate and 5′-diphosphate oligonucleotides is described. The desired full-length oligonucleotides were first constructed using standard automated DNA/RNA solid-phase synthesis procedures. Then, on the same column and instrument, efficient implementation of an uninterrupted sequential cycle afforded the corresponding unmodified or chemically modified 5′-triphosphates and 5′-diphosphates. The method was readily translated into a scalable and high-throughput synthesis protocol compatible with the current DNA/RNA synthesizers yielding a large variety of unique 5′-polyphosphorylated oligonucleotides. Using this approach, we accomplished the synthesis of chemically modified 5′-triphosphate oligonucleotides that were annealed to form small-interfering RNAs (ppp-siRNAs), a potentially interesting class of novel RNAi therapeutic tools. The attachment of the 5′-triphosphate group to the passenger strand of a siRNA construct did not induce a significant improvement in the in vitro RNAi-mediated gene silencing activity nor a strong specific in vitro RIG-I activation. The reported method will enable the screening of many chemically modified ppp-siRNAs, resulting in a novel bi-functional RNAi therapeutic platform.     

Highly parallel oligonucleotide purification and functionalization using reversible chemistry

We have developed a cost-effective, highly parallel method for purification and functionalization of 5'-labeled oligonucleotides. The approach is based on 5'-hexa-His phase tag purification, followed by exchange of the hexa-His tag for a functional group using reversible reaction chemistry. These methods are suitable for large-scale (micromole to millimole) production of oligonucleotides and are amenable to highly parallel processing of many oligonucleotides individually or in high complexity pools. Examples of the preparation of 5'-biotin, 95-mer, oligonucleotide pools of >40K complexity at micromole scale are shown. These pools are prepared in up to ~16% yield and 90-99% purity. Approaches for using this method in other applications are also discussed.     

Oligonucleotides containing 2'-O-[2-(2,3-dihydroxypropyl)amino-2-oxoethyl]uridine as suitable precursors of 2'-aldehyde oligonucleotides for chemoselective ligation

2'-O-[2-(2,3-Diacetoxypropyl)amino-2-oxoethyl]uridine 3'-phosphoramidite was prepared and used in solid-phase synthesis to obtain oligonucleotides containing a 1,2-diol group, which may then be converted into a 2'-aldehyde group. The oligonucleotides were conjugated efficiently to various molecules by chemoselective ligation that involves an addition-elimination reaction between the 2'-aldehyde group and a suitable nucleophile, such as a hydrazine, a O-alkylhydroxylamine or an 1,2-aminothiol. The method was applied successfully to the conjugation of peptides to oligonucleotides at the 2'-position.     

Carboranyl oligonucleotides: 4. synthesis and physicochemical studies of oligonucleotides containing 2'-O-(o-carboran-1-yl)methyl group

Boronated oligonucleotides are potential candidates for antisense oligonucleotide technology (AOT), boron neutron capture therapy (BNCT), and as tools in molecular biology. A method was developed for the solid phase synthesis of oligonucleotides containing 2'-O-(o-carboran-1-yl-methyl) (2'-CBM) group. Synthesis was performed using a standard beta-cyanoethyl cycle and automated DNA synthesizer. Manual steps were performed for the insertion of a modified monomer bearing the 2'-CBM group. Several tetradecanucleotides complementary to DNA-HCMV, and bearing 2'-CBM modification near the 3'-end or 5'-end or in the middle of the oligonucleotide chain were synthesized. The resulting oligomers were characterized by polyacrylamide gel electrophoresis (PAGE), reverse phase high-performance liquid chromatography (RP-HPLC), matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and ultraviolet spectroscopy (UV), circular dichroism (CD), and melting temperature (Tm) measurements. Tm of duplexes formed between 2'-CBM-modified tetradecanucleotides and complementary DNA and RNA template were compared with those formed by the unmodified oligonucleotide and complementary sequence. The stability of 2'-CBM oligonucleotides in the presence of phosphodiesterase I from Crotalus atrox venom and in human serum was studied. Oligonucleotides bearing the 2'-CBM group are characterized by increased resistance to enzymatic digestion, increased lipophilicity, and the ability to form stable duplexes with complementary templates.     

Parallel thermodynamic analysis of duplexes on oligodeoxyribonucleotide microchips.

A microchip method has been developed for massive and parallel thermodynamic analyses of DNA duplexes. Fluorescently labeled oligonucleotides were hybridized with oligonucleotides immobilized in the 100 x 100 x 20 mum gel pads of the microchips. The equilibrium melting curves for all microchip duplexes were measured in real time in parallel for all microchip duplexes. Thermodynamic data for perfect and mismatched duplexes that were obtained using the microchip method directly correlated with data obtained in solution. Fluorescent labels or longer linkers between the gel and the oligonucleotides appeared to have no significant effect on duplex stability. Extending the immobilized oligonucleotides with a four-base mixture from the 3'-end or one or two universal bases (5-nitroindole) from the 3'- and/or 5'-end increased the stabilities of their duplexes. These extensions were applied to increase the stabilities of the duplexes formed with short oligonucleotides in microchips, to significantly lessen the differences in melting curves of the AT- and GC-rich duplexes, and to improve discrimination of perfect duplexes from those containing poorly recognized terminal mismatches. This study explored a way to increase the efficiency of sequencing by hybridization on oligonucleotide microchips.     

Separation of modified 2'-deoxyoligonucleotides using ion-pairing reversed-phase HPLC

A group of 18-mers of the same base sequence, but with differing alkyl modifications is used to investigate effects of these modifications on retention of oligonucleotides using ion-pairing reversed-phase liquid chromatography (IP-RPLC). It is shown that IP-RPLC is able to distinguish between oligonucleotides differing only by a single alkyl group. The identity of the nucleobase and position and length of the alkyl adduct affect retention of the oligonucleotide. These separation phenomena result from changes in charge and hydrophobicity upon alkylation. As demonstrated in this paper; chromatographic selectivity, unique to IP-RPLC, greatly facilitates the purification process of modified oligonucleotides.     

Synthesis of oligonucleotide 2'-conjugates via amide bond formation in solution

An efficient method for synthesis of 2'-O-carboxymethyl oligonucleotides is described. Fully deprotected oligonucleotides containing a carboxymethyl group at the 2'-position of sugar residue were obtained by a two-step procedure by periodate cleavage of an oligonucleotide containing 1,2-diol group followed by oxidation of the 2'-aldehyde resulted with sodium chlorite. 2'-O-Carboxymethyl oligonucleotides prepared were efficiently coupled in aqueous solution in the presence of a water-soluble carbodiimide to a number of amino acid derivatives or short peptides to afford novel 2'-conjugates of high purity in good yield. The method is thus shown to be suitable in principle for preparation of oligonucleotide-peptide conjugates containing an amide linkage between the 2'-carboxy group of a modified oligonucleotide and the amino terminus of a peptide.     

Biosensor detection of triplex formation by modified oligonucleotides

Due to the instability of DNA oligonucleotides in biological solutions, antisense or antigene therapies aimed at modulation of specific gene expression will most likely require the use of oligonucleotides with modified backbones. Here, we examine the use of a surface plasmon resonance biosensor (BIAcore) to compare triplex-directed binding of modified oligonucleotides targeted to a region of the murine c-myc promoter. We describe optimization of experimental conditions to minimize nonspecific interactions between the oligonucleotides and the sensor chip surface, and the limitations imposed by certain backbones and sequence types. The abilities of pyrimidine oligonucleotides with various modified backbones to form specific triple helices with an immobilized hairpin duplex were readily determined using the biosensor. Modification of the third-strand oligonucleotide with RNA or 2(')-O-methyl RNA was found to enhance triplex formation, whereas phosphorothioate or phosphotriester substitutions abrogated it. A comparison of these results to DNase I footprinting experiments using the same oligonucleotides showed complete agreement between the two sets of data.     

PREPARATION OF OLIGODEOXYNUCLEOTIDE 5′-TRIPHOSPHATES USING SOLID SUPPORT APPROACH

We report a synthetic procedure for conversion of oligonucleotides to their 5′-triphosphate derivatives with moderate yield. The oligonucleotides were synthesized on solid support using standard phosphoramidite protocols. The DMT protection group was removed and the 5′-OH was phosphitylated using 2-chloro-4H-1,3,2-benzodioxaphosphorin-4-one followed by reaction with tributyammonium pyrophosphate and iodine oxidation. After subsequent removal from support and complete deprotection, the products were isolated by anion-exchange HPLC chromatography. Structures of several 5′-triphosphate derivatives have been proven by phosphorus NMR, Mass-spectrometry and by HPLC comparison with authentic samples.     

Microarray fabrication with covalent attachment of DNA using bubble jet technology

We have developed a method for fabricating DNA microarrays that uses a Bubble Jet ink jet device to eject 5'-terminal-thiolated oligonucleotides to a glass surface. The oligonucleotides are covalently attached to the glass surface by heterobifunctional crosslinkers that react with the amino group on the substrate and a thiol group on the oligonucleotide probe. Using this method, we fabricated DNA microarrays that carried 64 groups of 18-mer oligonucleotides encoding all possible three-base mutations in the mutational "hot spot" of the p53 tumor-suppressor gene. These were screened with a fluorescently labeled synthetic 18-mer oligonucleotide derived from the p53 gene, or segments of the p53 gene that had been PCR amplified from genomic DNA of two cell lines of human oral squamous cell carcinoma (SCC). This allowed us to discriminate between matched hybrids and 1 bp-mismatched hybrids.