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-[7.3.1.0(2.7).0(4.7)]-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.