Meet 1,3-dimethylurea. Its structure is tiny: CH3NH-CO-NHCH3 But notice the two methyl groups. One sits on each nitrogen. Those methyl groups can act like molecular instructions.
In classical heterocyclic synthesis, 1,3-dimethylurea can be converted into ring structures such as 1,3-dimethyl-6-aminouracil and used in routes toward methylxanthines including caffeine and theophylline. The methyl groups were already in position before the complex ring system was built.
Global Chemical Database