Pueraria mirifica (Leguminosae) has been used in folk medicine as "kwao keur" for rejuvenating purpose in Thailand and Burma. We present the total synthesis of kwakhurin (3), a characterictic isoflavone component of P. mirifica, as an index of quality standard for commercial "kwao keur." Furthermore, we examine the convenient HPLC analysis for P. mirifica and commercial supplements. 1) Total Synthesis of Kwakhurin (3) Route A. Via deoxybenzoin: Doxybenzoin derivative 14 was prepared by Friedel-Crafts acylation of resorsin 8 and phenylacetic acid 13 after protection of the phenolic function with a triisopropyl group. Construction of isolfavone skeleton followed by chemical modifications afforded kwakhurin triisopropyl ether 25; however deprotection of the isopropyl groups in 25 was failed. Route B. Convergent synthesis: Isoflavone skeleton 36, which was protected with MEM groups, was constructed by Suzuki-Miyaura coupling of 3-bromochromone 31 (AC-ring) and aryl boronic acid 35 (B-ring) in the presence of TBAB as an additive. No improvement was observed in microwave-assisted coupling reaction. After chemical modifications Claisen rearrangement of 1,1-dimethylallyl ether 42 in PhNEt_2 gave 6'-prenylisoflavone 39 in high yield. Successive methylation and deprotection of 39 yielded a target kwakhurin (3) in good yield. The total yield was 12% from 32. 2) Convenient HPLC Analysis for P. mirifica Independently, analysis of miroestrol (1), one of active principles of P. mirifica, by HPLC was examined under several conditions.
