The tripler-forming ability of oligonucleotide analogues containing conformationally locked C-nucleosides, 5-(2-O,4-C-methylene- beta-D-ribofuranosyl)oxazole or its 2-phenyl congener, towards a purine sequence of duplex DNA with a single C.G base pair interruption is studied. (C) 1999 Elsevier Science Ltd. All rights reserved.