Isoquinolines: A group of compounds with the heterocyclic ring structure of benzo(c)pyridine. The ring structure is characteristic of the group of opium alkaloids such as papaverine. (From Stedman, 25th ed)Sulfur Oxides: Inorganic oxides of sulfur.Thalictrum: A plant genus of the family RANUNCULACEAE. Members contain isoquinoline alkaloids and triterpene glycosides.Cyclization: Changing an open-chain hydrocarbon to a closed ring. (McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)Molecular Structure: The location of the atoms, groups or ions relative to one another in a molecule, as well as the number, type and location of covalent bonds.