A new naphthalene derivative, isotorachrysone [1], was isolated from t
he stem bark of Rhamnus nakaharai along with several known compounds.
The antiplatelet effects of isotorachrysone [1], isotorachrysone perac
etate [2], 6-methoxysorigenin [3], quercetin 3-O-methyl ether [4], and
quercetin 3-O-methyl ether peracetate [5] were studied using washed r
abbit platelets. Of the compounds rested, 1, 2, 4, and 5 showed potent
antiplatelet effects on arachidonic acid (AA-) and collagen-induced p
latelet aggregation. Compound 5 also showed potent antiplatelet, effec
ts on platelet-activating factor-(PAF-) induced platelet aggregation.
Isotorachrysone [1] and its peracetate [2] were also studied for antip
latelet activity in human platelet-rich plasma (PRP) and both showed p
otent inhibition of the secondary aggregation induced by epinephrine.
The antiplatelet effects of 1 and 2 are due partially co an inhibitory
effect on thromboxane formation.