SYNTHESIS OF C-3 COUPLED BIFLAVONOIDS AND C-3 COUPLED BIFLAVONOID ANALOGUES

摘要

The invention relates to methods for the preparation of an optically inactive and optically active compounds which are selected from the group consisting of C-3 coupled biflavonoids and C-3 coupled biflavonoid analogues from a starting material or intermediate which are respectively selected from the group consisting of optically inactive or optically active flavan-3-ols and optically active flavan-3-ones, the method comprising the steps of (a) providing an optically inactive or active compound having a fIavan-3-ol structure or a compound which is a flavan-3-one, (b) if a compound having a flavan-3-ol structure with a hydroxy group on the C-3 carbon is selected as starting material, converting the hydroxy group on the C-3 carbon of the compound having the flavan-3-ol structure to an oxo group to form a flavan-3-one of that compound, (c) providing a compound having a nucleophilic aromatic moiety, which compound is selected from the group of compounds having a nucleophilic aromatic moiety and which have flavonoid base structures and compounds having a nucleophilic aromatic moiety and which do not have a flavonoid base structure, (d) contacting the flavan-3-one provided by step (a) or obtained by step (b) with the compound containing the nucleophilic aromatic moiety in the presence of a Lewis acid; (e) forming a first intermediate compound wherein the oxo group on the C-3 carbon is converted to a hydroxy group by virtue of nucleophilic addition when the compound containing the nucleophilic aromatic moiety is contacted to the C-3 carbon of the flavan-3-one, (f) subjecting the first intermediate compound to dehydration so as to introduce a double bond between the C-3 carbon and C-4 carbon of the intermediate compound with the concomitant removal of the hydroxy group from the C-3 carbon to form an optically active flavene compound which is substituted by the nucleophilic aromatic moiety on the C-3 carbon, (g) optionally subjecting the resultant flavene compound to hydroboration-oxidation hydration thereby removing said double bond between the C-3 carbon and the C-4 carbon with the concomitant introduction of a hydroxy group at the C-4 carbon to form a second intermediate compound, (h) further optionally oxidizing the second intermediate compound of step (g) thereby converting the hydroxy group at the said C-4 carbon to an oxo group, thereby forming a biflavonoid or biflavonoid analogue which is substituted by the selected nucleophilic aromatic moiety on the C-3 carbon, (ι) further optionally, and alternatively to step (h), subjecting the resultant flavene compound of step (f) to OsC₄ dihydroxylation thereby removing said double bond between the C-3 carbon and C-4 carbon with the concomitant introduction of a hydroxy group at the C-4 carbon and a hydroxy group at the C-3 carbon to form a third intermediate compound, and (j) subjecting the third intermediate compound to dehydration whereby the hydroxy group at the C-3 carbon is removed and a double bond is introduced between the C-3 carbon and C-4 carbon thereby forming an enol product and allowing such enol product to rearrange spontaneously to form a biflavonoid or biflavonoid analogue having an oxo group at its C-4 carbon and which is substituted by the selected nucleophilic aromatic moiety on its C-3 carbon.