Pyranoacridones acronycine

Acronycine was first synthesized in 1967-68 by Beck et al. who published simultaneously three interrelated syntheses of that alkaloid (13, 14). Around ten other total syntheses have been reported up till now (15-26). Most of the synthetic strategies developped are sufficiently versatile to permit access to acronycine structural analogues as far as substitution on the A ring is concerned. Syntheses of analogues modified at B, C and D rings have been comparatively less explored. Most of them rely on chemical modifications performed on a preformed pyranoacridone skeleton, at the latest steps of the synthesis. 

The synthesis of natural pyranoacridone alkaloids and analogues has received more attention than that of their flirano counterparts, due to the interesting antitumor properties exhibited by acronycine and some of its derivatives. Two main strategies have been developed for the synthesis of pyrano[2,3-c]acridin-7-one and pyrano[3,2-A]acridin-7-one alkaloids. 

In addition, oxidation reactions performed on pyranoacridones led to several alkaloids modified on the C and D rings, and to acronycine analogues with improved antitumor activity. 

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