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,2-dihydroxy-6,7,8,6’-tetramethxyflavone, isolated or synthesized, showed a strong cytotoxic activity(ED_(50)=1.5_(ug)/m1 against L_(1210) cell, T/C=166% against ascites form of S-180, inhibition of solid form S-_(180)=38%). Other active flavones which have shown less activity than the natural product are as follows(ED_(50) against L1210 in parenthesis)... wogonin2(15,000_(ug)/ml), baicalein 3 (15,000_(ug)/ml), 5,8-dihydroxy-6,7-dimethoxyflavone 5 (7.5_(ug)/ml), 5.2’, 6’-trihydroxy-6,7,8-trimethoxyflavone 12 (4.5_(ug)/ml), 5-hydroxy-6,7,8-trimethoxy-2’-benzyloxyflavone 22 (15.4_(ug)/ml). It could not be argued that there is any strucure activity-relationship for flavones tested. However, a fixed conformation between rings B and C of the flavones seems to be required for the cytotoxicity. Geranylation of baicalein have improved both cytotoxic and antitumour activities (ED_(50) and T/C of baicalein=15.00_(ug)/ml and 126%, those of geranylbaicalein=2.3_(ug)/ml and 1448%). Geranylation of Skullcapflavone II series did not improve the activity. Inhibition of the activity of the membrane bound ATPase is one of the cytotoxic mechanisms of 5,2’-dihydroxy-6,7,8,6’-tetramethoxyflavone, 1, so that it has to do with the transport system of the nutrients into the cell. This inhibition could be correlated to the UV-absorption of the skullcapflavone II series.
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