Bifacial nucleoside as a surrogate for both T and A in duplex DNA

A new functional bifacial nucleoside derived from 7-aminopyrimido[4,5-d]pyrimidine-2,4(1H,3H)-dione, a Janus-type nucleobase, has been synthesized and incorporated into DNA oligonucleotides. The nucleobase, having self-complementary H-bonding faces, mimics both T and A and engages in the corresponding Watson-Crick-like base pairs, forming stable duplexes.