dihydrotetrabenazine dihydrotetrabenazine dihydrotetrabenazine or dtbz is an organic compound with the chemical formula c19h29no3. it is a close analog of tetrabenazine. dtbz and its derivatives, when labeled with positron emitting isotopes such as carbon-11 and fluorine-18, are used as pet radioligands for examining vmat2. dihydrotetrabenazine identifiers cas number 3466-75-9 3d model (jsmol) interactive image chemspider 110379 y pubchem cid 123836 comptox dashboard (epa) dtxsid90956148 inchi inchi=1s/c19h29no3/c1-12(2)7-14-11-20-6-5-13-8-18(22-3)19(23-4)9-15(13)16(20)10-17(14)21/h8-9,12,14,16-17,21h,5-7,10-11h2,1-4h3key: weqlwgndnrarge-uhfffaoysa-n smiles coc1=c(oc)c=c(c(cc(o)c(cc(c)c)c2)n2cc3)c3=c1 properties chemical formula c19h29no3 molar mass 319.445 g·mol−1 except where otherwise noted, data are given for materials in their standard state (at 25 °c , 100 kpa). infobox references use in positron emission tomography carbon-11 labeled (+)dtbz(right) and fluorine-18 labeled fluoropropylated (+)dtbz(left) dtbz as a pet radioligand with affinity for vmat2 was developed in the mid 1990s by david e. kuhl and colleagues at the university of michigan. there are two enantiomers of alpha-dihydrotetrabenazine, and the dextrorotary(or (+) isomer) has a high affinity of about 1 nanomolar ki whereas the levorotary (or (-) isomer) has approximately 1000 fold lower affinity with a ki of about 2 micromolar. vmat2 is a membrane bound protein and a biomarker for parkinson's disease. binding of dtbz to vmat2 in individuals with parkinson's disease is significantly reduced. moreover, the vmat2 density as determined by dtbz has been shown to be well, inversely correlated with the severity of parkinson's disease. avid radiopharmaceuticals has sponsored clinical trials of av-133 (or fluoropropyl-(+)-dtbz) to identify subjects with dopaminergic degeneration.