Scientists in Japan have succeeded in synthesizing artificial nucleotides and incorporating them into a DNA strand. You can view the paper online. You’ll notice, however, that the nucleotides were created by removing the imidazole ring from adenine and guanine, and by methylating cytosine and thymine. None of the changes affected the hydrogen donor-acceptor pairs on the molecules. It would have been a lot more interesting had the hydrogen bonding character of the double helix been changed. It is a first step, though.