text: As aromatic compounds have been exhausted to a large extent as building blocks for life science products, N-heterocyclic structures prevail nowadays. They are found in many natural products, such as chlorophyll, hemoglobin, and the vitamins biotin, folic acid, niacin (PP), pyridoxine (vitamin B), riboflavin (vitamin B), and thiamine (vitamin B). In synthetic life science products, N-heterocyclic moieties are widely used in both pharmaceuticals and agrochemicals. 
  Thus, β-lactams are structural elements of penicillin and cephalosporin antibiotics, imidazoles are found both in modern herbicides, e.g. Arsenal (imazapyr) and pharmaceuticals, e.g. the antiulcerants Tagamet (cimetidine. see above) and Nexium (omeprazole), the antimycotics Daktarin (miconazole), Fungarest (ketoconazole) and Travogen (isoconazole). Tetrazoles and tetrazolidines are pivotal parts of the "sartan" class of hypertensives, e.g. Candesartan cilexetil (candesartan), Avapro (irbesartan), Cozaar (losartan) and Diovan (valsartan).
  A vast array of pharmaceuticals and agrochemicals are based on pyrimidines, such as Vitamin B1 (thiamine), the sulfonamide antibiotics, e.g. Madribon (sulfadimethoxime) and –half a century later– the sulfonyl urea herbicides, e.g. Eagle (amidosulfuron) and Londax (bensulfuron-methyl). Benzodiazepine derivatives are the pivotal structural elements of breakthrough CNS Drugs, such as Librium (chlordiazepoxide) and Valium (diazepam). Pyridine derivatives are found in both well-known Diquat and Chlorpyrifos herbicides, and in modern nicotinoid insecticides, such as Imidacloprid.
  Even modern pigments, such as diphenylpyrazolopyrazoles, quinacridones, and engineering plastics, such as polybenzimidazoles, polyimides, and triazine resins, exhibit an N-heterocyclic structure.