Amination of 2-hydroxy- and 2,3-dihydroxynaphthazarins. Synthesis of echinamines A and B, metabolites produced by the sand dollar Scaphechinus mirabilis

Abstract

2-Hydroxynaphthazarins reacted with aqueous ammonia at the C¹=O carbonyl group, following the addition-elimination pattern with formation of 8-aminojuglone derivatives. Reactions of 2,3-dihydroxynaphthazarins with the same reagent involved the C²=O carbonyl group of the corresponding 1,2-naphthoquinoid tautomer to produce 2-aminonaphthazarin derivatives. 7-Ethyl-2,3,6-trihydroxynaphthazarin (echinochrome) reacted with aqueous ammonia to give 3(2)-amino-7-ethyl-2(3),6-dihydroxynaphthazarins (echinamines A and B) that are metabolites recently isolated from the sand dollar Scaphechinus mirabilis.