4449-39-2

The coupling reaction of activated nucleobases, such as the sodium salts of N-benzoyladenine and 6-chloropurine and 2,4-bis-O-trimethylsilylthymine, with 1-α-chloro-2-deoxy-3,5-di-O-p-toluoylribofuranose (1) in a mixture of acetonitrile and tetrahydrofuran leads to the stereospecific formation of α-anomeric 2'-deoxynucleosides with satisfactory yields.The ratio of the distribution between the resulted α- and β-stereoisomers was about 3:1 in each case.The method is simple and applicable to the preparation of both purine and pyrimidine α-2'-deoxynucleosides.

The synthesis and labeling of 99mTc-N3-{N′-[2- sulfanyl-ethylamino)acetyl]-2-aminoethyl-sulfanyl-1-hexanamide}thymidine ( 99mTc-NHT) were studied. In the presence of sodium glucoheptonate (GH) and ethylene diamine tetraace

This paper deals with kinetic studies of TMSOTf-mediated C1′ epimerization of β-thymidine to α-thymidine. The effect of neighboring group participation by various 5′-hydroxy protecting groups, such as toluoyl, Et2CHC(O), Et2NC(O), and Et2NC(S), on the β→α conversion is described in detail. The time dependence of the ratio of the α and β anomers in the C1′ epimerization was estimated by 1H NMR. The α/β equilibrium constants K and the rate constants kα and kβ were calculated on the basis of the experimental data. As the result, it was concluded that, in acetonitrile, the α/β equilibrium constants K are thermodynamically affected by steric hindrance from the 5′-hydroxy protecting group. On the other hand, the rate constants kα and kβ are mainly influenced by the stability of the oxonium ion intermediate. In particular, formation of an intramolecularly cyclized iminium ion intermediate from the oxonium ion intermediate, due to the neighboring group participation by the diethylthiocarbamoyl group, tended to decrease the overall reaction rate. Finally, the α/β C1′ epimerization could be carried out with a high α anomer selectivity of 89% through the use of the Et2CHC(O) group. Thus, 5′-O-pixyl-α-thymidine could be synthesized from β-thymidine as a key intermediate for the synthesis of α-DNA in a considerably improved overall yield of 40%.

The synthesis of O-silyl- and O-acyl-protected furanose glycals from free thymidine was investigated. The method of glycal formation reported by Pedersen et al. was successfully expanded to include 5-ester (toluoyl) protected glycals as well as various combinations of 5'-ester and 3- and 5- tert-butyldimethylsilyl and tert-butyldiphenylsilyl protection. Gram quantities of furanoid glycals can be prepared in a few days in two-four steps in overall yields ranging from 17 to 80%.

α-Thyimdine (4) was synthesized from thyimdine (1) in 3 steps in 36% overall yield without using chromatography and with the possibility of increasing the yield to 85% by reusing the remaining α,β-mixture. 1-(2-Deoxy-3,5-di-O-p-toluoyl-α-D-erythro-pentofu

Stereoselectivities in the coupling rection between 1-O-methyl-3,5-di-O-p-toluoyl-2-deoxyribofuranoside and suitably protected purine and pyrimidine derivatives have been examined in acetonitrile with varying equivalents of SnCl4.The best result in α-nucleoside formation was obtained when the coupling reaction was carried out in the presence of ten equivalents of SnCl4.

α-2'-Deoxyoctathymydilic acid phosphorothioate analog bearing 3'-monophosphate was conveniently synthesized via phosphoramidite method using a riboadenosine attached Teflon-based solid support.The obtained oligomer exhibited enhanced stability toward the digestion by common nucleases.

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