L-alpha-lyxopyranosyl (4 '-> 3 ') oligonucleotides: A base-pairing system containing a shortened backbone

[GRAPHICS] The L-alpha-lyxopyranosyl (4'-->3') oligonucleotide system shows cooperativ e base-pairing in spite of containing only five instead of the usual six co valent bonds per repetitive backbone unit. In contrast, corresponding D-bet a-ribofuranosyl (4'-->3') oligonucleotides do not show adenine-thymine pair ing under comparable conditions. The difference in pairing behavior relates to the conformation of the two systems' vicinal 3',4'-phosphodiester subst ituents, which is diaxial in the lyxopyranosyl system and 3'-axial-4'-equat orial in the ribopyranosyl system.