A two-directional strategy for the diversity-oriented synthesis of macrocyclic scaffolds.

Macrocyclic compounds represent a structural class with exceptional potential for biological activity; however, they have historically been underrepresented in screening collections and synthetic libraries. In this article we report the development of a highly step-efficient strategy for the diversity-oriented synthesis of complex macrocyclic architectures, using a modular approach based on the two-directional synthesis of bifunctional linear precursors and their subsequent combination in a two-directional macrocyclisation process. In this proof of principle study, the synthesis of 14 such compounds was achieved.

Total synthesis of (-)-histrionicotoxin 285A and (-)-perhydrohistrionicotoxin.

Starting from commercially available ( S)-glycidol, and via a common intermediate, the total synthesis of (-)-histrionicotoxin 285A and (-)-perhydrohistrionicotoxin has been achieved. Key to this synthesis was the efficient construction of a six-membered, chiral, cyclic nitrone.

Investigation of conjugate addition/intramolecular nitrone dipolar cycloadditions and their use in the synthesis of dendrobatid alkaloid precursors.

The sequential intramolecular conjugate addition of the oxime 13 followed by intramolecular dipolar cycloaddition of the intermediate nitrone 14 affords a mixture of the isoxazolidines 15, 16 and 17. The tricyclic 6,5,5-adduct 15 is believed to be the product of kinetic control and can be equilibrated with the epimeric tricyclic 6,5,5-isoxazolidine 17 through a beta-elimination/conjugate addition process. Conditions have been developed for the two-step conversion of the ketone 12 under thermodynamic control into the racemic tricyclic 6,6,5-adduct 16 which is the core precursor of all the known histrionicotoxin alkaloids.