3-adenylcyclobutane-1,1-dimethanol were synthesized by direct introduction of the heterocycles (Scheme 1). The mono-O-substituted methoxytrityl derivatives were separately converted to octameric phosphodiesters on an aminomethyl-polystyrene carrier by the phosphotriester method. These oligomers of carba-nucleosides were prepared in order to study their annealing behaviour towards ribo- and deoxyribo-nucleic