biotin An organic heterobicyclic compound that consists of 2-oxohexahydro-1H-thieno[3,4-d]imidazole having a valeric acid substituent attached to the tetrahydrothiophene ring. The parent of the class of biotins. An organic heterobicyclic compound that consists of 2-oxohexahydro-1<em>H</em>-thieno[3,4-<em>d</em>]imidazole having a valeric acid substituent attached to the tetrahydrothiophene ring. The parent of the class of biotins. vitamin B7 biotins