Novel Synthesis of the Ortho Ester Derivative of 4,5-Epoxymorphinan

Unexpected Rearrangement Reactions of the 14-Aminonaltrexone Skeleton

The reaction of 14-aminonaltrexone with acetic anhydride was found to produce a range of different novel compounds between the free compound and its hydrochloride. The hydrochloride produced a compound with an acetylacetone moiety, whereas the free form produced a compound with a pyranopyridine moiety. Efforts to isolate reaction intermediates and density functional theory calculations have elucidated those formation mechanisms with both bearing the novel morphinan-type skeleton. Furthermore, a derivative with the acetylacetone moiety showed binding to opioid receptors.

Favorskii-Type Rearrangement of the 4,5-Epoxymorphinan Skeleton

The aldol condensation of naltrexone with various aryl aldehydes gives the corresponding 7-benzylidenenaltrexone derivatives in high yields. However, novel C-ring-contracted morphinan compounds were produced when 2-pyridinecarboxaldehyde or its related analogues were used as a coupling partner. The key structural feature was the existence of the tetrahydrofuran ring (4,5-epoxy ring, E-ring) of the morphinan skeleton. The time-resolved in situ IR spectroscopy of the reaction system indicated the short-lived absorption of the distorted cyclopropanone intermediate.

Novel synthesis of a 1,3,5-trioxazatriquinane skeleton using a nitrogen clamp

An alpha-hydroxyaldehyde derived from naltrexone was converted to an oxazoline dimer with ammonium chloride and sodium acetate in MeOH under reflux. The resulting dimer was treated with dl-camphorsulfonic acid in CHCl(3) to give the trimer. The method for trimer synthesis was also applied to general alpha-hydroxyaldehydes to afford trimers in good yield.