Über die absolute Konfiguration der Cantharsäure und des Palasonins

The absolute configurations of (+)-cantharic acid, a chiral derivative of the achiral insect defensive substance cantharidin (1), and of palasonin, a lower homologue of 1 occurring in the plant Butea frondosa, were shown to be represented by formulas 2 and 3, respectively (scheme 1). These results were obtained by application of the Horeau method (table 1) on the (+)-cantharic acid derivatives (+)-5, (−)-7, and (−) 11 (scheme 2), and the palasonin derivatives (+)-29 and (+)-30 (scheme 4), as well as by comparison of the chiroptical properties (tables 2 and 3) of a number of derivatives, prepared from either cantharic acid or palasonin. – Attempts to incorporate various radioactively labelled precursors into palasonin (3), using young and adult plants, have been so far unsuccessful.