 The RT enzyme can undergo change due to mutations that can disturb NNRTI binding.The first two classes of compounds that were identified as NNRTIs were the 1-(2-2-hydroxyethoxymethyl)-6-(phenylthio)thymine (HEPT) and tetrahydroimidazo[4,5,1-jkj][1,4]benzodiazepin-2(1H)-one and -thione (TIBO) compounds.The discovery of the TIBO compounds led to the definition of the NNRTI class in the late 1980s when they were unexpectedly found to inhibit RT.