Study of the base discrimination ability of DNA and 2'-O-methylated RNA oligomers containing 2-thiouracil bases towards complementary RNA or DNA strands and their application to single base mismatch detection

Precise detection of target DNA and RNA sequences using chemically modified oligonucleotides is of crucial importance in gene analysis and gene silence. The hybridisation and base discrimination abilities of oligonucleotides containing 2'-O-methyl-2-thiouridine (s(2)Um) in homo- and hetero-duplexes composed of DNA and RNA strands have been studied in detail. When s(2)Um was incorporated into RNA or DNA strands, the hybridisation and base discrimination abilities of the modified RNA or DNA oligomers towards the complementary RNA strands were superior to those of the corresponding unmodified oligomers. On the other hand, their base discrimination abilities towards complementary DNA strands were almost the same as those of the unmodified ones. The base discrimination abilities of 2-thiouracil base-containing oligonucleotide probes on slide glass plates were also studied. These modified probes exhibited efficient detection of mismatched base pairing.

A pyrimidopyrimidoindole nucleoside (dC PPI): photophysical properties and thermal stability of the modified DNA duplexes

A new fluorescent deoxycytidine analog, 10-(2-deoxy-beta -D-ribofuranosyl)-pyrimido[4',5' :4,5]-pyrimido[1,6-a]indole-6,9(7H)-dione (dC(PPI)) was synthesized. Its fluorescent properties were studied in detail. It was found that this fluorescent nucleoside dC(PPI) could be used as a fluorescent label for DNA probes with minimal disturbance of their overall structure.

Efficient synthesis of functionalized oligodeoxyribonucleotides with base-labile groups using a new silyl linker

In this study, we developed new 3'-terminal deoxyribonucleoside-loading reagents 1 with a new silyl-type linker. These reagents could increase the efficiency of introduction of 3'-terminal deoxyribonucleoside components into polymer supports to a level of 17-29micromol/g. The efficiency was higher than that of previous T-loading reagents because reagents 1 contain a 4-aminobutyryl residue as a spacer. Moreover, we could synthesize not only unmodified DNA oligomers but also a base-labile modified DNA oligomer using resins 9a-d in the activated phosphite method without base protection.

'Protected DNA Probes' capable of strong hybridization without removal of base protecting groups

We propose a new strategy called the ‘Protected DNA Probes (PDP) method’ in which appropriately protected bases selectively bind to the complementary bases without the removal of their base protecting groups. Previously, we reported that 4-N-acetylcytosine oligonucleotides (ac⁴C) exhibited a higher hybridization affinity for ssDNA than the unmodified oligonucleotides. For the PDP strategy, we created a modified adenine base and synthesized an N-acylated deoxyadenosine mimic having 6-N-acetyl-8-aza-7-deazaadenine (ac⁶az⁸c⁷A). It was found that PDP containing ac⁴C and ac⁶az⁸c⁷A exhibited higher affinity for the complementary ssDNA than the corresponding unmodified DNA probes and showed similar base recognition ability. Moreover, it should be noted that this PDP strategy could guarantee highly efficient synthesis of DNA probes on controlled pore glass (CPG) with high purity and thereby could eliminate the time-consuming procedures for isolating DNA probes. This strategy could also avoid undesired base-mediated elimination of DNA probes from CPG under basic conditions such as concentrated ammonia solution prescribed for removal of base protecting groups in the previous standard approach. Here, several successful applications of this strategy to single nucleotide polymorphism detection are also described in detail using PDPs immobilized on glass plates and those prepared on CPG plates, suggesting its potential usefulness.

Synthesis and properties of DNA oligomers containing 2'-deoxynucleoside N-oxide derivatives

Cytosine and adenine N-oxide derivatives have long been known as products resulting from the oxidative damage of DNA by peroxides such as hydrogen peroxide. Although the synthesis and properties of 2'-deoxynucleoside N-oxide derivatives have been well described, little has been reported about the chemical and biochemical behavior of initially formed DNA oligomers containing these N-oxide bases. In this study, we established a convenient method for the solid-phase synthesis of oligodeoxynucleotides incorporating 2'-deoxycytidine N-oxide (dC O) or 2'-deoxyadenosine N-oxide (dA O) by using the postsynthetic oxidation of N-protected DNA oligomers except for the target dC or dA site with m-CPBA in MeOH in a highly selective manner. In this strategy, the benzoyl, phthaloyl, and (4-isopropylphenoxy)acetyl groups proved to serve as base protecting groups to avoid oxidation of adenine, cytosine, and guanine, respectively, at the unmodified sites.

Synthesis of oligonucleotides terminally modified by bulky and negatively charged substituents and their hybridization with RNA targets

2'-O-methyl RNAs having phosphorylated cyclohexane groups at the 5' and 3'-terminal bases were synthesized and their hybridization properties toward RNA targets were studied. It was proved that the duplex of the modified 2'-O-methyl RNAs and the target RNA longer than the 2'-O-methyl RNA was less stable than that with the short target. In addition, it was also clarified that the selectivity toward the short target was improved by the introduction of the phosphate group in comparison with that without the phosphate group.

Binding of MutS protein to oligonucleotides containing a methylated or an ethylated guanine residue, and correlation with mutation frequency

The MutS-based mismatch repair (MMR) system has been conserved from prokaryotes to humans, and plays important roles in maintaining the high fidelity of genomic DNA. MutS protein recognizes several different types of modified base pairs, including methylated guanine-containing base pairs. Here, we looked at the relationship between recognition and the effects of methylating versus ethylating agents on mutagenesis, using a MutS-deficient strain of E. coli. We find that while methylating agents induce mutations more effectively in a MutS-deficient strain than in wild-type, this genetic background does not affect mutagenicity by ethylating agents. Thus, the role of E. coli MMR with methylation-induced mutagenesis appears to be greater than ethylation-induced mutagenesis. To further understand this difference an early step of repair was examined with these alkylating agents. A comparison of binding affinities of MutS with O⁶-alkylated guanine base paired with thymine, which could lead to transition mutations, versus cytosine which could not, was tested. Moreover, we compared binding of MutS to oligoduplexes containing different base pairs; namely, O⁶-MeG:T, O⁶-MeG:C, O⁶-EtG:T, O⁶-EtG:C, G:T and G:C. Dissociation constants (K_d), which reflect the strength of binding, followed the order G:T- > O⁶-MeG:T- > O⁶-EtG:T- = O⁶-EtG:C- ≥ O⁶-MeG:C- > G:C. These results suggest that a thymine base paired with O⁶-methyl guanine is specifically recognized by MutS and therefore should be removed more efficiently than a thymine opposite O⁶-ethylated guanine. Taken together, the data suggest that in E. coli, the MMR system plays a more significant role in repair of methylation-induced lesions than those caused by ethylation.

Synthesis and properties of oligonucleotides with iodo-substituted aromatic aglycons: investigation of possible halogen bonding base pairs

Ab initio calculations of halogen bond energies of artificial base pairs constructed between iodinated aromatic nucleobase mimics and nitrogen-containing acceptor molecules such as pyridine and imidazole suggest that modified base pairs are converted to optimized planar base pairs with weak Delta E values of -0.19 to -3.93 kcal/mol. To evaluate the contribution of halogen bonding toward duplex stabilization of such modified nucleobase mimics introduced into artificial base pairs, we synthesized three C-nucleoside analogues 1-3 with several iodinated aromatic rings and an imidazole nucleoside derivative 4 and incorporated them into oligodeoxynucleotides. Hybridization studies of modified oligodeoxynucleotides incorporating iodoaromatic bases showed their unique universal base-like ability; however, no indication of halogen bond formation was observed. A more sophisticated design is required for the development of new base pairs stabilized by halogen bonding.

Synthesis and properties of oligodeoxynucleotides containing 5-carboxy-2'-deoxycytidines

5-Carboxy-2'-deoxycytidine (dC(COO-)) was synthesized as an anion-carrier to seek a new possibility of modified oligodeoxynucleotides capable of stabilization of duplexes and triplexes. The base pairing properties of this compound were evaluated by use of ab initio calculations. These calculations suggest that the Hoogsteen-type base pair of dC(COO-)-G is less stable than that of the canonical C+-G pair and the Watson-Crick-type base pair of dC(COO-)-G is slightly more stable than the natural G-C base pair. The modified cytosine base showed a basicity similar to that of cytosine (pKa 4.2). It turned out that oligodeoxynucleotides 13mer and 14mer incorporating dC(COO-) could form duplexes with the complementary DNA oligomer, which were more stable than the unmodified duplex. In contrast, it formed a relatively unstable triplex with the target ds DNA.

Synthesis of branched oligonucleotides with three different sequences using an oxidatively removable tritylthio group

We synthesized a three-way branched oligodeoxynucleotide (ODN) 30-mer using a new branch unit with acid-labile DMTr and oxidatively cleavable TrS groups as orthogonal protecting groups. The branched ODN was successfully synthesized using 5-[3,5-bis(trifluoromethyl)phenyl]-1H-tetrazole and (2R,8aS)-(+)-(camphorylsulfonyl)oxaziridine as the activator of phosphoramidite units and the oxidizing reagent, respectively. We also found that the TrS group was orthogonal to the Lev, TBDMS, and Fmoc groups. These results indicate the possibility of the synthesis of more complex four- and five-way branched ODNs by the combined use of DMTr, TrS, Lev, TBDMS, and Fmoc groups.

An effective method for the in situ synthesis of DNA-CPG conjugates using chemical ligation technology as tools for SNP analysis

In this paper, we report a new method for the SNP analysis by using a chemical ligation (CL) technique on CPG plates with high coupling efficiency. This method showed markedly high match/mismatch discrimination ability. Particularly, replacement of thymidine with 2-thiothymidine in DNA probes used in the CL technology resulted in significant improvement of the base discrimination ability of the thymine base in this system.

Synthesis of deoxycytidine derivatives and their use for the selective photo crosslinking with 5-methylcytosine

New photoactivatable nucleosides, 4-N-[3-(trifluoromethyl)diazirinyl]benzoyldeoxycytidine derivatives and these corresponding phosphoramidite derivatives were synthesized for the use as photo crosslinking probes. The carbene species was generated by UV irradiation so that it could react with the benzylic C-H of toluene to give a cross-linking product. The diazirine modified DNA 12mer was successfully synthesized by our N-unprotected phosphoramidite method. We studied its hybridization and photo crosslinking abilities. When a 5-methyl deoxycytidine containing complementary DNA oligomer was irradiated in the presence of the DNA 12 mer, crosslinking products were observed.

Synthesis and properties of artificial base pairs by use of halogen bonds

Artificial base pairs by use of halogen bonding were designed and their interaction energies were estimated by ab initio calculations. The optimized structures of the artificial base pairs were almost consistent with those of the canonical base pairs, and the interaction energies were ca. 5-11 kcal/mol. To investigate the thermal stability of the base pairs containing halogen bonds in oligodeoxynucleotide duplexes, deoxynucleoside 3'-phosphoramidite building blocks as halogen bonding acceptors and donors were synthesized and used for incorporation into oligodeoxynucleotides. UV-melting experiments suggest that these halogen bonding base pairs have low stability compared with the A-T base pair. Furthermore, the effect of the halogen bonding on stabilization of duplexes was studied in detail by comparison with the hybridization ability of oligodeoxynucleotides containing a modified base having a iodo group with that of the complementary DNA strands lacking the donor site.

Synthesis and properties of DNA oligomers containing 2'-deoxycytidine-N-oxide

The main product obtained by oxidation of 2'-deoxycytidine with hydrogen peroxide is 2'-deoxycytidine N-oxide. Although its chemical synthesis and properties of 2'-deoxycytidine N-oxide have been well established, little has been reported about the chemical and biochemical behavior of DNA oligomers containing this modified deoxynucleoside. In this study, we synthesized DNA oligomers containing 2'-deoxycytidine N-oxide by use of a post-synthetic oxidative method. It should be noted that this modified base could be incorporated in oligodeoxynucleotides at appropriate positions by this strategy. The ability of the base pair formation was significantly low because of the blocking of the canonical hydrogen bonding site.

cis-Tetrahydrofuran-3,4-diol structure as a key skeleton of new protecting groups removable by self-cyclization under oxidative conditions

A variety of carbonate-type acyl groups having a cis-tetrahydrofuran-3,4-diol (1,4-anhydroerythritol) backbone structure and a TrS or MMTrS group have been examined as new "protected" protecting groups of the 5'-hydroxyl group of nucleosides. These acyl groups were designed in a manner where they could be deprotected by I(2)-promoted removal of the TrS or MMTrS group followed by self-cyclization involving an intramolecular attack of the once-generated neighboring hydroxyl group on the acyl carbon. It turned out that these acyl groups could be introduced into the 5'-hydroxyl group of a 3'-O-protected thymidine derivative by use of the corresponding acyl imidazolides or 4-nitrophenyl esters as well as by reaction with carbonyldiimidazole or 4-nitrophenyl chloroformate. Among the acyl groups tested, it was found that the CTFOC group could be easily introduced into the 5'-hydroxyl group of 3'-masked deoxyribonucleoside derivatives and rapidly removed under mild conditions using iodine.

Synthesis and base recognition ability of oligoribonucleotides incorporating 2'-O-methyl-3-deazaguanosine

2'-O-methyl-oligoribonucleotides incorporating a 3-deazaguanine (3DG) were synthesized. Melting temperature (Tm value) analysis indicates the stability and base discriminating ability of the 2'-O-methyl-RNA/RNA duplex.

Development of new N-unprotected phosphoramidite building blocks having a silyl-type linker

New silyl-type linkers 2 and 3 were developed for the synthesis of oligonucleotides having base-labile functional groups in the phosphoramidite method without base protection. These linkers could be introduced into polymer supports in high yields and easily cleaved under neutral conditions. Particularly, the use of the N-unprotected phosphoramidite building block 3 having a silyl-type linker enabled us to synthesize oligodeoxynucleotides without protecting groups for the amino groups of 3'-terminal deoxyribonucleosides.

Fluorescent pyrimidopyrimidoindole nucleosides: control of photophysical characterizations by substituent effects

10-(2-Deoxy-beta-D-ribofuranosyl)pyrimido[4',5':4,5]pyrimido[1,6-a]indole-6,9(7H)-dione (dCPPI) and its derivatives were synthesized via the Suzuki-Miyaura coupling reaction of 5-iododeoxycytidine with 5-substituted N-Boc-indole-2-borates and characterized by UV-vis and fluorescence spectroscopy. The new fluorescent nucleosides showed rather large Stokes shifts (116-139 nm) in an aqueous buffer. The fluorescent intensities were dependent on the nature of the substituents on the indole rings. The electron-withdrawing groups increased the fluorescent intensity while the electron-donating groups having lone pairs decreased it. Among the substituted dCPPI derivatives tested, the trimethylammonium derivative of dCPPI was found to emit the brightest fluorescent light. The solvatochromism of dCPPI and its derivatives was also studied. Some of the dCPPI derivatives showed interesting solvent-dependent fluorescence enhancement and could be useful as new fluorescent structural probes for nucleic acids. The Lippert-Mataga analyses of the Stokes shift were also carried out to obtain estimated values of the dipole moment of the excited states of some of the derivatives.

Recognition of target chain-length by use of oligonucleotides having bulky substituents at the terminal bases

We synthesized 2'-O-methyl RNAs having bulky substituents at the 5' and 3'-terminal bases and examined their hybridization properties. The hybridization of the modified RNAs to the targets RNA was studied varying the chain length of the targets. As the result, it was proved that the duplex of the modified 2'-O-methyl RNAs and the long targets were destabilized in comparison with that of the modified 2'-O-methyl RNAs and the short targets. We hope that these oligonucleotides which could recognize the target chain-length would be the simple and convenient tool for the detection of small RNAs such as the microRNAs.

Synthesis and Fluorescent Properties of Bi- and Tricyclic 4-N-Carbamoyldeoxycytidine Derivatives

New bi- and tricyclic deoxycytidine derivatives (dChpd, dCmpp, dCtpp, dCppp) were synthesized as analogues of a fluorescent nucleoside, dChpp, previously reported. The carbamoyl group of dChpd and the 5-position of the cytosine ring are bridged via an ethylene linker so that the modified group forms a nonplanar structure with the cytosine ring. The fluorescent study of dChpd indicated that the coplanar structure between the carbamoyl group and the cytosine ring is of importance. N-Methylation of the carbamoyl group (dCmpp) weakened the intensity of the fluorescence of dChpp, and the derivative (dCtpp), which had a thiocarbamoyl group, lost its fluorescent property. Moreover, addition of a pyrrolo-ring (dCppp) to dChpp enhanced the intensity of fluorescence, and an emission light was observed with a marked Stokes shift of 120 nm.

Synthesis and biological properties of new phosmidosine analogs having an N-acylsulfamate linkage

A new phosmidosine analog 10, in which the proline and 8-oxoadenosine moieties were linked by an N-acyl sulfamate linkage, was successfully synthesized by the sulfamoylation of an 8-oxoadenosine derivative 5 followed by coupling with an L-proline derivative 8. An L-alanine-substituted derivative 13 and its derivative 14 without the alanyl residue were also synthesized. The morphological reversion activity of these synthetic compounds in v-src(ts) NRK cells and their antitumor activity in L1210 and KB cells were studied. As the result, neither L-proline- nor L-alanine-substituted phosmidosine analogs 10 and 13 showed any antitumor activity. Contrary to these results, the derivative 14 lacking the amino acid residue showed potent antitumor activities against cancer cells.

Synthesis of fluorescent cyclic cytosine nucleosides and their fluorescent properties upon incorporation into oligonucleotides

We report here the synthesis and spectroscopic characterization of a new fluorescent pyrimidopyrimidoindole nucleoside derivative (dC(PPI)) modified at the cytosine base. The photophysical properties of dC(PPI) were examined by fluorescent spectroscopy and quantum chemical calculations. It was found that dC(PPI)-labeled oligonucleotides gave almost the same thermal stability as that of the corresponding unmodified sequences. In addition, the quantum yield of dC(PPI) in the double-stranded state was significantly higher than that in the single-stranded state.

DNA synthesis without base protection using the phosphoramidite approach

In the strategy of DNA synthesis without base protection, a recent O-selective phosphorylation procedure known as the "activated phosphite method" is used to generate reactive phosphite intermediates from N-unprotected phosphoramidite building blocks. This new strategy proved to be advantageous over previous strategies because the cleavage of the N-P(III) bond, which can be formed by the significant phosphitylation of the nucleobase amino groups, can be omitted. The activated phosphite method provides an attractive route to high-throughput synthesis of DNA and the synthesis of alkali-labile modified DNAs such as oligonucleotides containing DNA lesions. This unit presents two convenient methods for the synthesis of N-unprotected deoxynucleoside 3'-phosphoramidite units and detailed procedures for automated synthesis of oligodeoxyribonucleotides from these phosphoramidite units.

Synthesis of 2'-O-methyl-RNAs incorporating a 3-deazaguanine, and UV melting and computational studies on its hybridization properties

2′-O-Methyl-RNAs incorporating 3-deazaguanine (c³G) were synthesized by use of N,N-diphenylcarbamoyl and N,N-dimethylaminomethylene as its base protecting groups to suppress sheared-type 5′-GA-3′/5′-GA-3′ tandem mismatched base pairing which requires the N³ atom. These modified RNAs hybridized more weakly with the complementary and single mismatch-containing RNAs than the unmodified RNAs. The T_m experiments were performed to clarify the effects of replacement of the fifth G with c³G on stabilization of 2′-O-methyl-(5′-CGGCGAGGAG-3′)/5′-CUCCGAGCCG-3′ and 2′-O-methyl-(5′-CGGGGACGAG-3′)/5′-CUCGGACCCG-3′duplexes, which form sheared-type and face-to-face type 5′-GA-3′/5′-GA-3′ tandem mismatched base pairs, respectively. Consequently, this replacement led to more pronounced destabilization of the former duplex that needs the N³ atom for the sheared-type base pair than the latter that does not need it for the face-to-face type base pair. A similar tendency was observed for 2′-O-methyl-RNA/DNA duplexes. These results suggest that the N³ atom of G plays an important role in stabilization of the canonical G/C base pair as well as the base discrimination and its loss suppressed formation of the undesired sheared-type mismatched base pair. Computational studies based on ab initio calculations suggest that the weaker hydrogen bonding ability and larger dipole moment of c³G can be the origin of the lower T_m.

Convenient synthesis of N-unprotected deoxynucleoside 3'-phosphoramidite building blocks by selective deacylation of N-acylated species and their facile conversion to other N-functionalized derivatives

[reaction: see text] A new route to N-unprotected deoxynucleoside 3'-phosphoramidite building blocks by use of highly selective N-deacylation of commercially available N-acylated deoxynucleoside 3'-phosphoramidites is described. These compounds could be readily converted to other types of N-protected species by facile N-acylations with acylating reagents.

A general method for the synthesis of 2'-O-cyanoethylated oligoribonucleotides having promising hybridization affinity for DNA and RNA and enhanced nuclease resistance

[reaction: see text] An effective method for the synthesis of 2'-O-cyanoethylated oligoribonucleotides as a new class of 2'-O-modified RNAs was developed. The reaction of appropriately protected ribonucleoside derivatives with acrylonitrile in t-BuOH in the presence of Cs2CO3 gave 2'-O-cyanoethylated ribonucleoside derivatives in excellent yields, which were converted by a successive selective deprotection/protection strategy to 2'-O-cyanoethylated 5'-O-dimethoxytritylribonucleoside 3'-phosphoramidite derivatives in high yields. Fully 2'-O-cyanoethylated oligoribonucleotides, (Uce)12 and (GceAceCceUce)3, were successfully synthesized in the phosphoramidite approach by use of the phosphoramidite building blocks. It was also found that oligoribonucleotides having a 2'-O-cyanoethylated ribonucleoside (Uce, Cce, Ace, or Gce) could be obtained by the selective removal of the TBDMS group from fully protected oligoribonucleotide intermediates without loss of the cyanoethyl group by use of NEt3 x 3HF as a desilylating reagent. The detailed T(m) experiments revealed that oligoribonucleotides containing 2'-O-cyanoethylated ribonucleosides have higher hybridization affinity for both DNA and RNA than the corresponding unmodified and 2'-O-methylated oligoribonucleotides. In addition, introduction of a cyanoethyl group into the 2'-position of RNA resulted in significant increase of nuclease resistance toward snake venom and bovine spleen phosphodiesterases compared with that of the methyl group.

Triplex forming ability of oligonucleotides containing 2'-O-methyl-2-thiouridine or 2-thiothymidine

The triplex forming ability of oligonucleotides containing 2'-O-methyl-2-thiouridine (s2Um) and 2-thiothymidine (s2T) was studied. The UV melting experiments revealed that triplex forming oligonucleotides (TFOs) containing both s2Um or s2T stabilized significantly parallel triplexes. The main reason for stabilization of triplexes was due to the stacking effect of the 2-thiocarbonyl group. Moreover, it turned out that these modified TFOs had a high selectivity in recognition of a matched Hoogsteen base from a mismatched one.

Synthesis and Properties of a New Fluorescent Bicyclic 4-N-Carbamoyldeoxycytidine Derivative

[reaction: see text] A bicyclic 4-N-carbamoyldeoxycytidine derivative (1, dC(hpp)) geometrically locked was synthesized as a new fluorescent nucleobase. The hybridization properties of oligodeoxynucleotides containing dC(hpp) were investigated by use of T(m) analysis. It was found that dC(hpp) forms stable base pairs not only with the complementary guanine base, but also with the adenine base. Interestingly, the fluorescence of dC(hpp) was suppressed only when a dC(hpp)-dG base pair was formed.

A new protecting group for the 5'-hydroxyl group having O-S single bond oxidatively cleavable under mild conditions

We developed a new protecting group, ie., cis-[4-[[(4-methoxytrityl)sulfenyl]oxy]tetrahydrofuran-3-yl]oxycarbonyl (MTFOC), which could be removed under neutral conditions involving the oxidative removal of the MMTrS group followed by the self-cyclization of the resulting intermediate. The introduction of the protecting group into the 5-hydroxyl group of a thymidine derivative and its deprotection were studied.

4,5-bis(ethoxycarbonyl)-[1,3]dioxolan-2-yl as a new orthoester-type protecting group for the 2'-hydroxyl function in the chemical synthesis of RNA

We wish to report 4,5-bis(ethoxycarbonyl)-[1,3]dioxolan-2-yl as a new protecting for the 2'-hydroxyl function. Our cyclic orthoester-type group is compatible with the DMTr strategy for oligonucleotide synthesis. This group was introduced to the 2'-hydroxyl group of appropriately protected nucleoside derivatives in good yields under mild acidic conditions. Post-synthetic conversion of the moiety of this protecting group with an amine resulted in formation of a new amide moiety that is more stable to acid deprotection in aqueous solution, but it can still be easily removed by treatment with acids in organic solvents. In this article, we also describe the stability of not only the original and modified protecting groups but also internucleotidic phosphate linkages of protected RNA intermediates under deprotection conditions.

Use of Ferrocene Scaffolds as Pendant Groups in Hairpin-Type Pyrrole-Imidazole Polyamide Molecules Showing Sequence-Selective Binding to DNA Duplexes

[reaction: see text] The synthesis and properties of new conjugate molecules, Fc-PIA, composed of ferrocene (Fc) and pyrrole-imidazole polyamides (PIA) are reported. As a PIA sequence, we chose Im-Py-Im/Py-Im-Py considering its future application to the SNPs detection of genes having a GCG/CGC sequence. Two types of Fc-containing linkers, i.e., ferrocene-1,1'-dicarboxamide and ferrocenecarboxamide, were designed, and several Fc-PIPA molecules having these linkers were synthesized. Titration studies by use of circular dichroism revealed that the carboxamide-type Fc-PIA could bind to the target DNA with an association constant of 10(7) M(-1). In contrast, ferrocene dicarboxamide-type compounds have slightly weaker affinity for the target DNA. However, the affinity could be recovered by replacing one of the pyrrole residues with beta-alanine. We carried out the CV measurement and observed quasi-irreversible oxidation of the ferrocene moieties in the Fc-PIA compounds. These properties of Fc-PIA indicate the potential usefulness of these molecules in electrochemical detection of genes.

Chemically Stabilized Phenylboranylidene Groups Having a Dimethoxytrityl Group as a Colorimetrically Detectable Protecting Group Designed forcis-1,2-Diol Functions of Ribonucleosides in the Solid-Phase Synthesis of m22,2G5‘ppT

To not only improve the inherently poor stability of the phenylboranylidene group as a protecting group of the 2',3'-cis-diol function of ribonucleosides but also introduce a colorimetrically detectable function into its mother structure, various 2-[(dialkylamino)methyl]phenylboronic acid derivatives having a [(4,4'-dimethoxytrityl)oxy]methyl group were synthesized. The reaction of uridine with these substituted phenylboronic acid derivatives gave the corresponding 2',3'-O-phenylboranylideneuridine derivatives. The stability of these phenylboranylidene groups was examined. As a result, it was shown that the steric hindrance around the amino group greatly influenced the stability of the 2-substituted phenylboranylidene groups. The 2-aminomethyl-5-[[(4,4'-dimethoxytrityl)oxy]methyl]phenylboranylidene group was the most stable. Its 2-dimethylamino counterpart, the 2-[(dimethylamino)methyl]-5-[[(4,4'-dimethoxytrityl)oxy]methyl]phenylboranylidene group, was the second most stable. When the most and second stable protecting groups were applied to the synthesis of m(2)(2,2)G(5)(')ppT on controlled pore glass, the second stable protecting group showed the best result. The use of this DMTr-containing protecting group enabled us to estimate colorimetrically the amount of the m(2)(2,2)G residue that was incorporated into the reactive site of the pT-loaded CPG resin.

Synthesis of a biotin-conjugate of phosmidosine O-ethyl ester as a G1 arrest antitumor drug

This paper deals with the synthesis of a stable biotin-phosmidosine conjugate molecule 3 that is required for isolation of biomolecules that bind to phosmidosine (1). It was found that introduction of a biotin residue into the 6-N position of phosmidosine could be carried out by reaction of an N7-Boc-7,8-dihydro-8-oxoadenosine derivative 13 with phenyl chloroformate followed by displacement with a diamine derivative 6 along with the simultaneous removal of the Boc group and one of the two phenoxycarbonyl groups and the successive condensation with an N-tritylated biotin derivative 5. The condensation of an N-prolylphosphorodiamidite derivative 4 with an appropriately protected 7,8-dihydro-8-oxoadenosine derivative 17 having the biotin residue gave the coupling product 18, which was deprotected to give the biotin-phosmidosine (O-ethyl ester) conjugate 3.

(+)-3-[2-(Benzo[b]thiophen-2-yl)-2-oxoethyl]-1-azabicyclo[2.2.2]octane as potent agonists for the alpha7 nicotinic acetylcholine receptor

A series of 3-substituted 1-azabicyclo[2.2.2]octanes was discovered as the alpha7 nicotinic acetylcholine (alpha7) receptor agonists. It was found that (+)-3-[2-(benzo[b]thiophen-2-yl)-2-oxoethyl]-1-azabicyclo[2.2.2]octane (+)-15b has potent agonistic activity for the alpha7 receptor.

SNPs analysis by use of oligonucleotides containing 2'-O-methyl-2-thiouridines

In this study, we report an improved method for the synthesis of oligonucleotides containing 2-thiouridine (s2U) derivatives. The hybridization affinity and base pair recognition ability of oligonucleotides having 2-thiouracil moieties with both the complementary RNAs and DNAs were also studied in detail. These results indicate that oligonucleotides containing s2U derivatives could be used as powerful tools for chip-based SNPs detection.

SNPs analysis by use of protected oligonucleotide probes

Loss of large amounts of DNA probe occurred at the deprotection step of the in situ synthesis of DNA microarrays for analysis of SNPs or gene expression. In this study, we developed "Protected Oligonucleotide Probes" that can avoid elimination of probe DNAs and allow their highly efficient synthesis. The protected oligonucleotide probes containing dC(ac) and d[oxoA(ac)] instead of dC and dA proved to have similar affinity for ssDNA having the complementary sequence and base recognition ability compared with the corresponding unmodified DNA probes.

Synthesis and hybridization properties of 2'-O-methyl-RNA incorporating 3-deazaguanine derivatives

3-Deazaguanine (3DG) and its 2-N-acylated derivatives were incorporated into 2'-O-methyl-RNAs, and the hybridization and base discrimination properties were clarified by measuring UV-melting profiles. The 2'-O-methyl-RNA incorporating a 3DG hybridized less strongly in comparison to that without 3-deaza modification to both fully-matched and singly mismatched target strands. The T(m) decrease was the largest in the case of the fully matched duplex so that the base discrimination ability was decreased. Interestingly, the acetylation of the amino group of 3DG could compensate the T(m) decrease of the fully matched duplex by 3DG. Moreover, it was also proved that the base pair of 2-N-acetyl-3-deazaguanine and uracil was much weaker than the G-U pair. These results indicate the possibility of the development of guanine analogs that can recognize cytosine more precisely than guanine by use of the 2-N-acyl-3-deazaguanine skeleton.

Synthesis of 2'- or 3'-O-heteroaryl substituted nucleic acid derivatives and their biological properties

The successful preparation of 3'-O-heteroaryl substituted thymidine derivatives were developed by the reaction of 5'-O-(tert-butyldimethylsilyl)thymidine with heteroaromatic halides in the presence of sodium hydride. In a similar manner, 2' or 3'-O-heteroaryl substituted uridine derivatives were obtained by the use of 5'-O-(tert-butyldimethylsilyl)uridine. All the arylations proceeded selectively at the site of the hydroxyl group and reactions of heteroaromatic halides with the nucleobase residues were not observed. Desilylation of the nucleic acid derivatives synthesized afforded 2'- or 3'-O-heteroaryl substituted thymidine or uridine derivatives in good yields. The anti-BVDV assay of the synthesized 2'- or 3'-O-heteroarylsubstituted thymidine and uridine derivatives were studied.