Double-stranded polydeoxyribonucleotides containing 6-thiodeoxyguanosine and 6-thiodeoxyinosine. Poly(d(A-C)-d(T-s 6 G)),poly(d(A-s 6 G)-d(T-C)) and poly(d(A-C)-d(T-s 6 I))

Synthesis of oligonucleotides containing 2'-deoxy-6-thioguanosine at a predetermined site

A new approach has been devised for the synthesis of oligonucleotides containing 2'-deoxy-6-thioguanosine [d(s6G)]. The synthesis of oligonucleotides containing d(s6G) requires special protection and deprotection strategies to prevent the thione functionality from undergoing oxidation and hydrolysis. Previous attempted syntheses have neglected to address this problem. By using the cyanoethyl protecting group for the thione and phenoxyacetyl for the exocyclic amino group, it was possible to deprotect oligonucleotides with a mixture of sodium hydroxide and sodium hydrogen sulfide without any significant conversion of d(s6G) to deoxyguanosine. Application of this strategy will allow investigation of the structural as well as biological activity of d(s6G)-containing oligonucleotides.

Combined enzymatic and chemical approaches to the synthesis of unique polyribonucleotides

The enzymatic polymerization by polynucleotide phosphorylase of 6-chloro-9-(beta-D-ribofuranosyl)purine 5'-diphosphate to poly(6-chloropurinylic acid) and its conversion to poly(6-thioninosinic acid) is described. The sulfur isostere of poly(I) was found not to form a complex with poly(C), but to form a self-association complex with a Tm around 295 degrees K. The sedimentation velocities, pKa and Tm values of the polymer have been examined under various conditions. A two (or more) stranded helical array is suggested as the most probable structure. Thermal loss of the thione chromophore was noted for poly- (S6I), S6IMP and S6I; the degradation product from S6I was shown to be inosine.