P-stereocontrolled synthesis of oligo(nucleoside N3′→O5′ phosphoramidothioate)s – opportunities and limitations

摘要

3′- N -(2-Thio-1,3,2-oxathiaphospholane) derivatives of 5′- O -DMT-3′-amino-2′,3′-dideoxy-ribonucleosides ( _(N) OTP-N), that bear a 4,4-unsubstituted, 4,4-dimethyl, or 4,4-pentamethylene substituted oxathiaphospholane ring, were synthesized. Within these three series, _(N) OTP-N differed by canonical nucleobases ( i.e. , Ade ~(Bz) , Cyt ~(Bz) , Gua ~(iBu) , or Thy). The monomers were chromatographically separated into P-diastereomers, which were further used to prepare N _(NPS) N′ dinucleotides ( 3 ), as well as short P-stereodefined oligo(deoxyribonucleoside N3′→O5′ phosphoramidothioate)s (NPS-) and chimeric NPS/PO- and NPS/PS-oligomers. The condensation reaction for _(N) OTP-N monomers was found to be 5–6 times slower than the analogous OTP derivatives. When the 5′-end nucleoside of a growing oligomer adopts a C3′- endo conformation, a conformational ‘clash’ with the incoming _(N) OTP-N monomer takes place, which is a main factor decreasing the repetitive yield of chain elongation. Although both isomers of N _(NPS) N′ were digested by the HINT1 phosphoramidase enzyme, the isomers hydrolyzed at a faster rate were tentatively assigned the R _(P) absolute configuration. This assignment is supported by X-ray analysis of the protected dinucleotide ~(DMT) dG ~(iBu) _(NPSMe) T _(OAc) , which is P-stereoequivalent to the hydrolyzed faster P-diastereomer of dG _(NPS) T.