To preorganize PNA for duplex formation, a new cyclic pyrrolidinone PNA analog has been designed. In this analog the aminoethyl-glycine backbone and the methylene-carbonyl linker are connected, introducing two chiral centers compared to PNA. The four stereoisomers of the adenine analog were synthesized, and the hybridization properties of PNA decamers contg. one analog were measured against complementary DNA, RNA, and PNA strands. The (3S,5R) isomer was shown to have the highest affinity toward RNA, and to recognize RNA and PNA better than DNA. The (3S,5R ) isomer was used to prep. a fully modified decamer which bound to rU10 with only a small decrease in Tm (DTm/mod = 1 DegC) relative to aminoethyl-glycine PNA. [on SciFinder (R)]