Photohuperzine A—A new photoisomer of huperzine A: Structure elucidation, formation kinetics and activity assessment

A new photoisomer of the promising “anti-Alzheimer” drug candidate (±) huperzine A is described. The new substance was formed via a photoisomerization reaction and was found to be 1-amino-13-ethylidene-11-methyl-6-aza-tetracyclo-[7.3.1.02.7.04.7]-trideca-2,10-diene-5-one using NMR analysis. The kinetics of its formation was studied and proven to be of first-order. The described photoisomer showed a significant loss in activity, being more than 100 times less active than (−) huperzine A itself. The new substance was named photohuperzine A, referring to its photopyridone substructure.