Evidences of complex formation between DABA-based nucleo-gamma-peptides with alternate configuration backbone

In the present work, we report the synthesis and the characterization of dab PNA hexamers with diaminobutyric acid backbone of D- or/and L-configuration. In particular, the four nucleo-amino acids we synthesized, D- and L-diaminobutyryl adenines and D- and L-diaminobutyryl thymines, were used in various combinations to assemble the following oligomers: H-G-(t( L-dab))(6)-K-NH(2), H-G-(t( D-dab))(6)-K-NH(2), H-G-(a( L-dab))(6)-K-NH(2), H-G-(t( L-dab)-t( D-dab))(3)-K-NH(2), H-G-(a( L-dab)-a( D-dab))(3)-K-NH(2), H-G-(a( L-dab)-t( D-dab))(3)-K-NH(2). By using CD and UV spectroscopies, we investigated the ability of complementary dab PNA strands to bind to each other. We found that binding occurs only between oligomers with backbone of alternate configuration [(t( L-dab)-t( D-dab))(3)/(a( L-dab)-a( D-dab))(3) and (a( L-dab)-t( D-dab))(3)/(a( L-dab)-t( D-dab))(3)] and implies cooperative hydrogen bonds and base stacking. Furthermore, interesting properties relative to the self-complementary oligomer (a( L-dab)-t( D-dab))(3) forming palindromic complexes emerged from preliminary dynamic light-scattering experiments that suggested the formation of multimeric aggregates. These results, together with the high serum stability of the DABA-based oligomers, as shown by HPLC analysis, encourage us to further study dab PNAs as new self-recognizing bio-inspired polymers, to develop new nanomaterials in biotechnological and biomedical applications.