These data support the potential of developing sd-rxRNAs as a therapeutic for ocular disease.

No abstract

High-resolution NMR spectroscopy has been used to establish the conformational consequences of the introduction of a single 3[prime or minute]-S-phosphorothiolate link in the DNA strand of a DNA : RNA hybrid. These systems are of interest as potential antisense therapeutic agents. Previous studies on similarly modified dinucleotides have shown that the conformation of the sugar to which the sulfur is attached shifts to the north (C(3[prime or minute])-endo/C(2[prime or minute])-exo). Comparisons made between NOESY cross-peak intensities, and coupling constants from PE-COSY spectra, for both non-modified and modified duplexes confirm that this conformational shift is also present in the double helical oligonucleotide system. In addition it is noted that in both the dinucleotides and the modified duplex, the conformation of the sugar ring 3[prime or minute] to the site of modification is also shifted to the north. That this pattern is observed in the small monomeric system as well as the larger double helix is suggestive of some pre-ordering of the sequences. The conclusion is supported by consideration of the (1)H chemical shifts of the heterocyclic bases near the site of the modification. The enhanced stability that these conformational changes should bring was confirmed by UV thermal melting studies. Subsequently a series of singly and doubly 3[prime or minute]-S-phosphorothiolate-modified duplexes were investigated by UV. The results are indicative of an additive effect of the modification with thermodynamic benefit being derived from alternate spacing of two modified linkers.

No abstract

Synthesis and Nucleic-Acid-Binding Properties of Sulfamide-and 3'-N-Sulfamate-Modified DNA. -An improved synthesis of sulfamide dinucleosides and a new access to 3'-N-sulfamate-modified dinucleosides is presented, involving the use of hitherto little utilized 4-nitrophenyl chlorosulfate to introduce the sulfamate groups. The influence of sulfamide and sulfamate linker on the dinucleotide conformation is studied. Furthermore, the novel dinucleotides are incorporated into a DNA oligomer and the effects on stability and on the affinity of the oligomer for complementary DNA and RNA strains is tested. It is shown that 3'-N-sulfamate nulceosides are worthy of further development for applications as antisense or antigene therapeutic agents. -(FETTES, KEVIN J.; HOWARD, NIGEL; HICKMAN, DAVID T.; ADAH, STEVEN; PLAYER, MARK R.; TORRENCE, PAUL F.; MICKLEFIELD, JASON; J. Chem. Soc., Perkin Trans. 1 (2002) 4, 485-495; Dep. Chem., Univ. Manchester Inst. Sci. Technol., Manchester M60 1QD, UK; EN)

A range of a-alkoxyphosphonates, including novel a-methoxyallyl phosphonates have been prepared from acetals. The latter have been used to provide an efficient and convenient synthesis of conjugated methoxy dienes, in which E-geometry predominates in the newly formed double bond but the geometry of the original ally1 system is preserved.

For the first time a fully automated procedure has been developed for the incorporation of a 3'-S-phosphorothiolate linkage into DNA, using phosphorothioamidite monomers. Coupling yields with either of the activators 5-ethylthiotetrazole or 4,5-dicyanoimidazole were in the range of 80-90%. Coupling yields were equally good when performed on either a 0.2 or 1 mumole reaction column, thus facilitating large scale synthesis.

Contrary to a previous report, the sulfurisation of phosphorus(III) derivatives by 3-amino-1,2,4-dithiazole-5-thione (xanthane hydride) does not yield carbon disulfide and cyanamide as the additional reaction products. The reaction of xanthane hydride with triphenyl phosphine or trimethyl phosphite yields triphenyl phosphine sulfide or trimethyl thiophosphate, respectively, and thiocarbamoyl isothiocyanate which has been trapped with nucleophiles. The reaction pathway involves initial nucleophilic attack of the phosphorus at sulfur next to the thiocarbonyl group of xanthane hydride followed by decomposition of the phosphonium intermediate formed to products. The Hammett rho-values for the sulfurisation of substituted triphenyl phosphines and triphenyl phosphites in acetonitrile are approximately -1.0. The entropies of activation are very negative (-114+/-15 J mol-1 K-1) with little dependence on solvent which is consistent with a bimolecular association step leading to the transition state. The negative values of DeltaS(not equal) and rho values indicate that the rate limiting step of the sulfurisation reaction is formation of the phosphonium ion intermediate which has an early transition state with little covalent bond formation. The site of nucleophilic attack has been also confirmed using computational calculations.