Synthesis of 19-trideuterated ent-testosterone and the GABA_A receptor potentiators ent-androsterone and ent-etiocholanolone

19-Trideuteromethyl enantiomers of androgens namely ent-testosterone, ent-androsterone and ent-etiocholanolone were prepared by total synthesis. The isotope labeling at the C-19 angular methyl group was achieved by using deuterated methyl iodide (99.5% d3) for introduction of C-19 before closure of the steroid A-ring. This method yields 19,19,19-trideuterated steroids without increasing the number of steps involved in the total synthesis of ent-androgens. Analysis by mass spectrometry (MS) showed no loss of deuterium during incorporation of C-19 into ent-testosterone. The availability of the compounds will enable these ent-androgens to be distinguished by MS from their natural enantiomers in future pharmacokinetic and metabolic studies.