Addendum to the ESCOP Monograph on Harpagophytum Procumbens** (Letter to the Editor) (Letter to the Editor‪)‬

Constituents New co-active constituents have been identified (Boje, 2002; Munkombwe, 2003). The constituent 6-acetylacetoside allows the two Harpagophytum species to be distinguished (being present in the procumbens and absent in the zeyheri species). It has an I[C.sub.50] of 47 [micro]g/ml in the in vitro human neutrophil elastase assay, which also shows inhibitory activity of caffeic acid (I[C.sub.50] 86 [micro]g/ml) and the ethyl acetate fraction extracted from the tubers (I[C.sub.50] 95 [micro]g/ml)--though the aqueous fraction showed no activity (Boje, 2002) and the activity of other identifiable constituents (8-feruloylharpagide and 6-O-acetylacetoside) was weak. The ratio of 8-para-coumaroyl-harpagide to the sum of harpagoside and 8-para-coumaroyl-harpagide is another distinguishing feature between the raw materials derived from the two species (Eich et al., 1998): it is below 10 in procumbens and above 31 in zeyheri (Feistel and Gaedtke, 2000; Schneider et al., 2001), and an intermediate percentage is found in products derived from mixtures of the raw materials.