The preparation of a new class of backbone-modified PNA\ud mimetic incorporating thymine is described. Target dipeptoid\ud monomer 21 was synthesised from an N-[2-(thymin-1-yl)ethyl]\ud glycinate ester and a properly protected iminodiacetic\ud acid. The distinctive structural motif in the backbone is a\ud carboxy group, inserted to impart water solubility to the\ud oligomer. Two achiral oligopeptoid sequences (8-mer and 12-\ud mer), characterised by the shift of the amide carbonyl group\ud away from the nucleobase, were efficiently assembled according\ud to solid-phase synthesis protocols. Thermal denatur-ation studies showed that the two homopyrimidine oligopeptoids\ud do not effectively hybridise with complementary sequences\ud of DNA and RNA or fully synthetic (2,4-diamino)-\ud triazin-6-yl-tagged peptoid 22. A possible reason could reside\ud in the concurrent unfavourable influence of the anionic\ud N-(carboxymethyl) moieties and the flexible nucleobase/\ud backbone ethylene linker