Natural products chemistry. Part 124. Revised structure and synthesis of a new acridone alkaloid, hallacridone from Ruta graveolens tissue cultures

Abstract

The synthesis of 6-hydroxy-2,1 2-dimethyl-3H-pyrano[2,3-c]acridine-3,7(12H)-dione (1) by two different routes revealed the previously proposed structure of hallacridone, to be incorrect. Careful examination of the spectral characteristics, of an authentic sample of hallacridone, led us to suggest a revised structure, 2-acetyl-5-hydroxy-11 -methylfuro[2,3-c]acridin-6(11H)-one (2), which we unambiguously confirmed by total synthesis. The biosynthetic significance of hallacridone (2) is discussed.