n. 1. A single-ringed, crystalline organic base, C4H4N2, that is the parent compound of a large group of biologically important compounds. 2. Any of a group of substituted derivatives of pyrimidine, including the nitrogen bases uracil, cytosine, and thymine, which are components of nucleic acids. Barbiturates and certain other drugs are also pyrimidines. [Alteration of PYRIDINE.] |
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