Abstract:

The total syntheses for 5,7-dihydroxy-3-isopentenylflavone(1a, yield 80.6%) and 5-hydroxy-3-isopentenylflavone(1b, yield 84.9%) were performed through selective protection of phenolic hydroxyl groups, acylation, Bake-Venkataraman rearrangement, prenylation, cyclization and demethylation, which started from 2,4,6-trihydroxyacetophenone and 2,6-dihydroxyacetophenone, respectively. The structures of all the compounds were characterized by ¹H NMR and ¹³C NMR, and the biological activities of the target compounds(1a and 1b)were predicted by the density functional theory(DFT) calculations. The results showed that the isopentenyl substituent at C3 could remarkably improve the biological activities of the flavonoids, and it was requirement for various biological activities of the flavonoids. In addition, the biological activities were 5,7-dihydroxy-3-isopentenylflavone(1a)>5-hydroxy-3-isopentenylflavone(1b). The reason might lie in the fact that the 7-OH of the flavonoids could enhance the biological activities. The synthetic routes in the present work might reveal potential applicability in the total syntheses of other 3-alkylfavones natural compounds and the biological activities of the target compounds could lay a good foundation on studying the structure-activity relationship of 3-alkylfavones.

Key words: 5,7-Dihydroxy-3-isopentenylflavone, 5-Hydroxy-3-isopentenylflavone, Total synthesis