1-(2'-DEOXY-BETA-D-XYLOFURANOSYL)THYMINE BUILDING-BLOCKS FOR SOLID-PHASE SYNTHESIS AND PROPERTIES OF OLIGO(2'-DEOXYXYLONUCLEOTIDES)

1-(2'-Deoxy-beta-D-threo-pentofuranosyl)thymine (= 1-(2'-deoxy-beta-D-xylofuranosyl)thymine; xT(d); 2) was converted into its phosphonate 3b as well as its 2-cyanoethyl phosphoramidite 3c. Both compounds were used for solid-phase synthesis of d[(xT)12-T] (5), representing the first DNA fragment build up from 3'-5'-linked 2'-deoxy-beta-D-xylonucleosides. Moreover, xT(d) was introduced into the innermost part of the self-complementary dodecamer d(G-T-A-G-A-A-xT-xT-C-T-A-C)2 (9). The CD spectrum of d[(xT)12-T] (5) exhibits reversed Cotton effects compared to d(T12) (6; see Fig. 1), implying a left-handed single strand. With d(A12) (7) it could be hybridized to form a propably left-handed double strand d(A12).d[(xT)12-T] (7.5) which was confirmed by melting experiments in combination with temperature-dependent CD spectroscopy. While 5 was hydrolyzed by snake-venom phosphodiesterase, it was resistant towards calf-spleen phosphodiesterase. The modified, self-complementary duplex 9 was hydrolyzed completely by snake-venom phosphodiesterase, at a twelvefold slower rate compared to unmodified 8; calf-spleen phosphodiesterase hydrolyzed 9 only partially.