Synthesis, absolute configuration, and molecular modeling study of etoxadrol, a potent phencyclidine-like agonist.

Etoxadrol (2a), one of the eight possible optical isomers of 2-ethyl-2-phenyl-4-(2-piperidyl)-1,3-dioxolane, was synthesized from (S,S)-1-(2-piperidyl)-1,2-ethanediol, which was obtained from cleavage of dexoxadrol (1a, (S,S)-2,2-diphenyl-4-(2-piperidyl)-1,3-dioxolane). The absolute configuration of etoxadrol hydrochloride, a phencyclidine-like compound biologically, was determined to be 2S, 4S, and 6S at its three chiral centers by single-crystal X-ray analysis. Epietoxadrol (2b), epimeric with etoxadrol at the C-2 center, was also obtained from the synthesis. This much less potent enantiomer has the 2R,4S,6S configuration. The affinity of etoxadrol to the phencyclidine binding site was found to be comparable to that of phencyclidine itself and was 35 times more potent than its epimer, epietoxadrol. Three diastereomeric mixtures were prepared that had low affinity for the phencyclidine site. In studies of the discriminative stimulus properties of these compounds, it was found that only etoxadrol substituted for the phencyclidine stimulus. With use of computer-assisted molecular modeling techniques, a hypothetical phencyclidine binding site model has been developed that, unlike our former hypothesis based on Dreiding models, correctly predicts the higher affinity of etoxadrol and the lesser affinity of epietoxadrol for the phencyclidine site.

Synthesis and pharmacologic properties of 6-succinylcodeine.

In our search for a ligand to be used for affinity chromatography in the separation of putative, codeine-specific receptors, we have synthesized a pharmacologically active codeine derivative, 6-succinylcodeine (Ib). The structure of the compound has been confirmed. It is markedly less toxic than the parent compound, codeine (Ia), and has significantly weaker antitussive properties in the cat. On the other hand, its antinociceptive properties in the mouse and effects on guinea pig ileum are comparable to those of codeine. An interesting pharmacological property of Ib is its hypotensive effect in both cats and rhesus monkeys. The compound has been successfully coupled to an aminoalkyl agarose matrix. When coupled to the matrix, the drug loses its capacity to cause contraction of the guinea pig ileum but this property is restored upon alkaline hydrolysis of the coupled beads. Whether the diminished antitussive properties, as compared to the parent compound, or the loss of capacity to inhibit guinea pig ileum contractility when coupled to agarose would limit its usefulness for affinity chromatography of codeine-specific receptors is being investigated.