Pyrazine Chemistry. V. Synthesis of Methylanhydropicroroccellin and Dimethylpicroroccellin

Abstract

The structure of the lichen diketopiperazine, picroroccellin, has been studied by the synthesis of several of its degradation products. The three possible formulations of methylanhydropicroroccellin (3), (4) and (5) were synthesized and from the physical and chemical properties, the former two compounds were shown to be dissimilar from the naturally derived material. Furthermore, the reactivity of the 3- methoxypiperazine-2,5-dione (5) entirely paralleled that reported for picroroccellin and was consistent with the oxygen functions being located at the 3- and 6-positions of the piperazine-2,5-dione ring. Dimethylpicroroccellin (23) was synthesized, so establishing the trans- stereochemistry of this compound. The properties of (23) were identical with those recorded for the naturally derived material. Hence we conclude that picroroccellin should be reformulated as (2).