Heterocyclic CompoundsAza CompoundsHeterocyclic Compounds, Bridged-RingPalladiumNitrogen CompoundsAntimitotic AgentsCyclizationHeterocyclic Compounds, 2-RingMolecular StructureHeterocyclic Compounds with 4 or More RingsHeterocyclic Compounds, 3-RingMagnetic Resonance SpectroscopyHeterocyclic Compounds, 1-RingAzathioprineAzacitidineSulfur CompoundsVolatile Organic CompoundsStructure-Activity RelationshipSpiro CompoundsSpectrometry, Mass, Fast Atom BombardmentPlant ExtractsDrug Evaluation, PreclinicalSmall Molecule LibrariesModels, MolecularStereoisomerismPhenolsSulfhydryl Compounds