Basic Aglycone Structures of Anthracyclines

Hans Brockmann, a pioneer of research on antibiotics, pubhshed the isolation and structure elucidation of the first anthracyclines. According to his definition [1], anthracychnes are red to orange natural or synthetic dyes with a skeleton of 7,8,9,10-tetrahydro-tetracene-5,12-quinone and mono- to tetrasaccharide moieties attached, usually to ring D of the aglycone. In this review, the numbering system proposed by Brockmann (see structure 1) will be used. 

As the benzylic hydroxy group in position 7 is removed easily, and further hydroxylation and/or oxidation in other positions can occiu, at least 15 D-ring modifications (5-19) can be distinguished (Fig. 1), which gave rise to nearly 500 natmal anthracyclines isolated to date. However, as the nitrogen-free sugar residues are split off easily already under weakly acidic conditions during the isolation process, not aU of them may be truly natoal. 

The absolute configuration in ring D was investigated as early as 1961 [11-13], mainly by comparison of their circular dichroism (CD) curves Most anthracychnones known at that time were (7S,9K,10H)-configured a few (e.g. Q -isorhodomycinone, 7-epi-41c) had the 7R configuration. Later, other stereoisomers were also isolated. 

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