Monatshefte f€ ur Chemie 136, 1629–1639 (2005) DOI 10.1007/s00706-005-0350-7 An Efficient Route to Emodic Amine and Analogous O-Methyl Protected Derivatives Starting from Emodin Bernd Lackner, Klaus Bretterbauer, and Heinz Falk  Institute of Organic Chemistry, Johannes Kepler University Linz, 4040 Linz, Austria Received May 20, 2005; accepted May 25, 2005 Published online August 10, 2005 # Springer-Verlag 2005 Summary. Emodic amine could be synthesized in a five-step approach in excellent overall yield by following a modified Curtius rearrangement strategy, starting from the naturally occurring emodin. This unique emodin derived 6-amino substituted polyhydroxylated anthraquinone may serve as a promising synthon for a new class of amino functionalized photodynamically active hypericin deriv- atives. In addition, the partially O-methyl protected 6-amino- and 6-carboxy-anthraquinones could be synthesized in high yields via selective O-methyl ether cleavage from the corresponding tri-O-methyl derivatives. Keywords. Anthraquinones; Curtius rearrangement; Emodic amine; Selective O-methyl ether cleav- age; Microwave assisted synthesis. Introduction The polyhydroxylated anthraquinone emodin (1, 1,3,8-trihydroxy-6-methyl-9,10- anthraquinone) is a wide-spread natural product occurring in fungi, lichens, and a variety of plants (e.g. rhubarb, aloe) which exhibits tumor cell-growth inhibition [1], antibiotic [2], anti-viral [3], and cytostatic [4] activity. There is a continued interest in the syntheses of new anthraquinone derivatives, either as promising bio- logically active compounds or as valuable synthons for the preparation of photo- dynamically active hypericin derivatives, which is one of the main interests in our research group [5]. Polyhydroxylated anthraquinones bearing amino groups appear to be found rather seldom in nature. Thus, to the best of our knowledge 5-amino- physcion (2, 5-amino-1,8-dihydroxy-3-methoxy-6-methyl-9,10-anthraquinone [6]) isolated by Steglich et al. [7] from the fungal species Dermocybe canaria consti- tutes the only natural representative of an amino substituted emodin derivative (see Fig. 1). Further examples for amino substituted anthraquinones are the powerful  Corresponding author. E-mail: heinz.falk@jku.at