The present application provides novel compounds and methods for preparing and using these compounds. In one embodiment, the compounds are of the structure of formula (I), wherein R1-R4 are defined herein. In a further embodiment, these compounds are useful in method for regulating one or both of the P2X3 or P2X2/3 receptors. In another embodiment, these compounds are useful for treating pain in patients by administering one or more of the compounds to a patient. In another embodiment, these compounds are useful for treating respiratory dysfunction in patients by administering one or more of the compounds to a patient.