Studies On The Total Synthesis Of Natural Prenylated Flavonoids

This thesis aims at the studies on the total synthesis of3,5-diprenylated flavonoids,which consists of mainly the following parts:Part1:The first chapter briefly review the structure, biologicalactivity, physico-chemical property and synthesis of flavonoid.Part2:Total synthesis of abyssinone-VI-4-O-methyl ether and abyssinone-IV-4’-O-methyl etherTwo new prenylated flavonoids, abyssinone-VI-4-O-methyl ether and abyssinone-IV-4’-O-methyl ether isolated from the root bark of Erythrina mildbraedii communis has been first synthesized in five steps through hydroxyl protection, C-prenylation, aldol condensation, cyclization and deprotection starting from cheap2,4-dihydroxyacetophenone and4-hydroxybenzaldehyde. All structures of new compounds were confirmed by IR,1H NMR and MS.Part3:Total synthesis of Abyssinone-V-4’-O-methyl etherAbyssinone-V-4’-O-methyl ether was isolated from the stem bark of Erythrina burtti. It is a3,5-diprenylated flavanone synthesized in five steps through hydroxyl protection, C-prenylation, aldol condensation, cyclization and deprotection starting from cheap2,4,6-trihydroxyacetophenone and4-hydroxybenzaldehyde. All structures of new compounds were confirmed by IR,1H NMR and MS.Part4:Total synthesis of Sigmoidin ESigmoidin E was a new prenylated flavones isolated from the Cameroonian medicinal plants of the genus Etytbrina sigmoidea, its different places with the previous three compounds was that one of prenyl has a cyclization reaction with4-hydroxyl into a benzo pyran ring. It has been first synthesized in six steps through hydroxyl protection, C-prenylation, aldol condensation, cyclization and deprotection starting from cheap2,4,6-trihydroxyacetophenone and4-hydroxybenzaldehyde. All structures of new compounds were confirmed by IR,1H NMR and MS. Some of the key compounds has also been confirmed by HRMS and13C NMR.The key intermediate of the four compounds was the synthesis of4-hydroxy-3,5-di-(3-methylbut-2-enyl)benzaldehyde that features regioselective prenylation of4-hydroxybenzaldehyde. The reaction of prenylation on4-hydroxybenzaldehyde has been reported and gave a mixture of prenylated compounds according to Robert M. Moriarty’s report. It is worthy to note that4-hydroxy-3,5-di-(3-methylbut-2-enyl)-benzaldehyde could not be separated from the mixture by direct silica gel column chromatography because of having the same polarity with an another product. It was get by a two-step sequence:(1) the mixture was separated from the reaction residue by Si gel column chromatography eluting with petroleum ether-EtOAc (10:1);(2) pure product6was obtained by crystallizing with petroleum ether at O8C for24h as a white solid.