Enantiocontrolled Synthesis of Calabar Bean and Aphanophine Alkaloids

The high and diverse biological activity of most alkaloids besides their few side effects has oriented the synthetic researches to develop new procedures for production of such natural products. For instance the African Calabar bean alkaloids, (-)-physovenine and (-)- physostigmine are widely used medicinally as cholinergic and miotics. It is useful in the treatment of glaucoma and myasthenia gravis and as antidote for organophosphate poisoning. Physostigmine can sufficiently improve the memory of the Alzheimer s patients. In addition (-)-aphanorphine alkaloid, possesses narcotic analgesic and anesthetic activity. Such alkaloids occur in nature in one enantiomeric form, i.e. (-)-physostigmine, (-)- physovenine and (-)-aphanorphine which are the only forms having biological activity. Thus, the enantiocontrolled synthesis is a critical process in obtaining of the biologically active physostigmine, physovenine and aphanorphine. Dioxabicyclooctane derivative can be used as chiral building block having levoglucosenone chromophore and different protective groups in both enantiomeric pure forms in order to synthesis the desired alkaloids.