PyransCyclization: Changing an open-chain hydrocarbon to a closed ring. (McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)Pyran Copolymer: Copolymer of divinyl ether and maleic anhydride that acts as an immunostimulant with antineoplastic and anti-infective properties. It is used in combination with other antineoplastic agents.Acronine: A pyrano-acridone alkaloid found in RUTACEAE plants.Polymers: Compounds formed by the joining of smaller, usually repeating, units linked by covalent bonds. These compounds often form large macromolecules (e.g., BIOPOLYMERS; PLASTICS).Lip DiseasesHexobarbital: A barbiturate that is effective as a hypnotic and sedative.Poly A-U: A double-stranded polyribonucleotide comprising polyadenylic and polyuridylic acids.Bryostatins: A group of 20-member macrolactones in which there are three remotely substituted pyran rings that are linked by a methylene bridge and an E-disubstituted alkene, and have geminal dimethyls at C8 and C18 carbons. Some interact with PROTEIN KINASE C.Leukemia, Experimental: Leukemia induced experimentally in animals by exposure to leukemogenic agents, such as VIRUSES; RADIATION; or by TRANSPLANTATION of leukemic tissues.Spiro Compounds: A group of compounds consisting in part of two rings sharing one atom (usually a carbon) in common.Stereoisomerism: The phenomenon whereby compounds whose molecules have the same number and kind of atoms and the same atomic arrangement, but differ in their spatial relationships. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)PolynucleotidesAlkenes: Unsaturated hydrocarbons of the type Cn-H2n, indicated by the suffix -ene. (Grant & Hackh's Chemical Dictionary, 5th ed, p408)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.