Fig. 3. Nomenclature for spacer-linked etomidate esters. All etomidate esters contain the etomidate backbone with the chiral carbon in the (R )-entantiomeric form. This chiral center is not modified by our syntheses and thus remains in the R  configuration for all of our ester-linked etomidate esters, and is not specifically referenced in our nomenclature system. Etomidate analogs have a two-carbon spacer between the etomidate backbone and the labile ester moiety (shown), whereas metomidate analogs have a one-carbon spacer. An aliphatic group may be located either immediately adjacent to the labile ester moiety (on the α carbon) or one carbon away from that ester (on the β carbon). The enantiomeric configuration of the aliphatic group is defined as either R  or S .