Oxy-4-aminopyrimidine

Thymine is 5-methyl-2,4-dioxypyrimidine. Cytosine is 2-oxy-4-aminopyrimidine. Uracil is 2,4-dioxypyrimidine. 

The bases found in RNA (ribonucleic acid) are the purine heterocyclics adenine (6-aminopurine) and guanine (2-amino-6-oxypurine) and their complementary pyrimidine bases uracil (2,4-dioxypyrimidine) and cytosine (2-oxy-4-aminopyrimidine), respectively (Section 1, Appendix). In RNA double-stranded duplexes adenine (A) base-pairs with uracil (U) via two hydrogen bonds (A=U) and guanine base-pairs with cytosine (C) via 3 hydrogen bonds (G=C). Adenine forms the nucleoside adenosine by an N-glycosidic link with the... 

Cytosine (2-oxy-4-aminopyrimidine) Cytidine Deoxycytidine Cytidine monophosphate (CMP) Deoxycytidine monophosphate (dCMP)... 

Fig. 3-29 Thymine (5-methyi-2,4-dioxypyrimidine), cytosine (2-oxy-4-aminopyrimidine), and uracii (2,4-dioxypyrimidine).

Three different substituted pyrimidines are found in the nucleic acids, namely cytosine (2-oxy-4-aminopyrimidine) which is present in both DNA and RNA, uracil (2,4-dioxypyrimidine) which is present in RNA but not in DNA and thymine (5-methyluracil) which is present in DNA but not in RNA. They all exhibit keto-enol tautomerism. 

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