Pyrimidines are heterocyclic six-membered nitrogen-containing carbon ring structures with uracil cytosine and thymine being the basal structures of ribose-containing nucleosides (uridine cytidine and thymidine respectively) or deoxyribose-containing deoxynucleosides and their corresponding ribonucleotides or deoxyribonucleotides.

Reference standards.

Microgrewiapine A is a selective cytotoxic agent for colon cancer cells over normal colon cells and to exhibit nicotinic receptor antagonistic activity for both the hα3β4 and hα4β2 receptor subtypes.