Stereochemistry and Biological Activities of Constituents from Cynanchum Taiwanianum

The stereochemistry of new acetophenones, cyanadione B-D !(2 -4), isolated from Cynanchum taiwanianum, elucidated by computer modelling calculation and NOESY spectrum. It establishes the absolute configurations of cynandiones B-D ( 2-4) as 7R; 7 " S, 7S; 7 " S and 7R, 7 " R, respectively. Cynandione B (2) strongly inhibited the release of beta- glucuronidase and lysozyme in formyl-methionyl-leucyl- phenylalamine (fMLP )-stimulated rat neutrophils in a concentration-dependent manner with IC50 values of 1.5 +/- 0 .2 and 1.6 +/- 0.2 mu M, respectively. 2,5- Dihydroxyacetophenone (6) strongly inhibited the aggregation of washed rabbit platelets induced by arachidonic acid in a concentration-dependent manner with an IC50 value of about 4.8 mu M. In human citrated platelet- rich plasma, 2,5- dihydroxyacetophenone (6) inhibited the secondary phase, but not the primary phase, of aggregation induced by adrenaline and ADP. These results suggest that the antiplatelet effect of 2,5- dihydroxyacetophenone (6) is due to inhibition of the formation of thromboxane A(2). (C) 1998 Elsevier Science B.V