Five isoliquiritigenin analogues,
including a new methylene-bridged
bischalcone (1), were isolated from Spatholobus
suberectus. Cytotoxicity screening of these isolates and
several synthetic derivatives indicated that the introduction, removal,
position modification, or glycosylation of hydroxy groups in isoliquiritigenin
did not improve the resultant cytotoxicity against the MCF-7 and MDA-MB-231
human breast cancer cell lines. In addition, cyclization of OH-2′
chalcones or reduction of the α,β-unsaturated carbonyl
double bond decreased such cytotoxicity substantially. However, methylation
of hydroxy groups resulted in a marked increase in such cytotoxic
activity. Among these active isoliquiritigenin analogues, 3′,4′,5′,4″-tetramethoxychalcone
(3h) was obtained as a compound with promising cytotoxic
activity.