Possible nucleobases

Question

Just for fun I was playing around with other possible ways to put together purine nucleobases by changing where the double bonds go on the pyrimidine ring and where amino groups, carbonyls and hydrogens were placed in the 1, 2, 3, & 6 positions. All without adding any other functional groups, like methyl or hydroxyl groups and without changing the imidazole ring. I was able to come up with 13 different configurations. Searching on the internet I was able to find many of the molecules and by extension I think I’ve been able to put names to all but one. Can you confirm the names I’ve used, let me know if I’ve missed any, and help me with the identity of the 13th one? I came up with the following: Adenine, 2,6-diaminopurine, Iso Guanine, 𝛽-Iso Guanine, Xanthine, Guanine, 𝛽-Guanine, Hypoxanthine, 𝛽-Hypoxanthine, Iso Hypoxanthine, 𝛽-Iso Hypoxanthine, Iso Adenine. The 13th molecule I haven't found a name for is a purine with only hydrogen bound to the 2 and 6 positions and 3 double bonds in the pyrimidine ring. Looking for stuff like this on the internet I was struck by how little information I could find. Can you point me to any related resources or literature? Thanks, Andy

Answer 1

To answer your last question, the ring is just called purine. I assume you are interested, ultimately, in how such bases may be put into DNA or RNA. There has been a great deal of such research over the last three decades. The general name for such research is studies in nonstandard DNA bases or noncanonical DNA bases. There now exist organisms that contain such nonstandard DNA base pairs as part of their genome. Peter G. Schultz is one chemist who has done a lot of work in this area. For many years it was known that even the AT GC type of pairing Watson and Crick came up with was not the only possible one. Look up Hoogsteen base pairs for another way for purines and pyrimidines to fit together in a double helix. Changing bases is not the only way to make new structures. Replacing the sugar-phosphate backbone with peptide bonds (as seen in proteins) with purine and pyrimidine bases hanging off the chain gives peptide nucleic acids (PNAs). These can bond to themselves or give mixed duplexes with regular DNA strands.

If you are more interested in the rings themselves, that branch of organic chemistry is called heterocyclic chemistry. It is very important because most of the small molecule drugs used in human medicine contain heterocyclic rings.