1. We synthesized 10 chroman derivatives (CD-1 to CD-10) derived from khellactone, including praeruptorin A and praeruptorin B and examined the effects of these compounds on rabbit platelet aggregation.
2. These compounds exhibited an inhibitory effect on platelet-activating factor (PAF)-induced platelet aggregation and their effects were more potent on PAF-induced platelet aggregation than on adenosine triphosphate (ADP)-, arachidonate (AA)- or collagen-induced platelet aggregation. In particular, (±)-cis-5-methoxy-6-methoxycarbonyl-2,2-dimethyl-3,4, -ditiglyloxychroman (CD-6), (±)-cis-5-methoxy-6-(2-methoxycarbonylethenyl)-2,2-dimethyl-3,4-ditiglyloxychroman (CD-8), (±)-cis-3,4-diacetoxy-5-methoxy-2,2-dimethyl-6-propylchroman (CD-9) and (±)-cis-5-methoxy-2,2-dimethyl-6-propyl-3,4-ditiglyloxy-chroman (CD-10) showed a moderate inhibition of PAF-induced platelet aggregation.
3. From these findings, it is suggested that compounds with potent PAF antagonist activities have the following features: (i) a tiglyloxy moiety is required at the 3 and 4 positions; and (ii) the methoxy moiety is also required at the 5 position of chroman skeleton in khellactone.