Synthesis and sweet taste of optically active (–)-haematoxylin and of some (±)-haematoxylin derivatives
In order to explain the sweet taste of the natural polyphenolic compound (+)-haematoxylin 1, four (±)-haematoxylin derivatives 4–7 and the enantiomer (–)-haematoxylin have been synthesized and tasted. Unlike haematoxylin, the derivatives 4–7 have a restricted number of different possibilities of binding to the sweet taste receptor according to the Shallenberger–Acree–Kier model. This allowed the study of the most likely orientation of these compounds in the active site of receptor. The results are supported by the comparison of the molecular structures with the receptor models of Temussi–Goodman and Tinti–Nofre. The synthesis of the (–)-enantiomer of haematoxylin also allows for discussion of the relationship between configuration and sweet taste in these compounds.