Abstract
The hemisynthesis of the naturally occurring bioactive flavonoid glycoside icariin (1) has been accomplished in eleven steps with 7% overall yield from kaempferol. The 4′-OH methylation of kaempferol, the 8-prenylation of 3-O-methoxymethyl-4′-O-methyl-5-O-prenyl-7-O-benzylkaempferol (8) via para-Claisen–Cope rearrangement catalyzed by Eu(fod)3 in the presence of NaHCO3, and the glycosylation of icaritin (3) are the key steps.
Highlights
The plants of the Genus Epimedium, known as “Yin-YangHuo”, were used in traditional Chinese medicine and are believed to invigorate the kidney and enhance the “Yang”
Icariin exerts a variety of important bioactivities, reports concerning its synthesis are very scarce
We focus on developing an efficient procedure for the selective prenylation of flavonols for facile access to icariin (1)
Summary
The plants of the Genus Epimedium, known as “Yin-YangHuo”, were used in traditional Chinese medicine and are believed to invigorate the kidney and enhance the “Yang”. One Chinese patent reported a 15-step total synthesis of icariin from benzyl alcohol with 0.6% overall yield [15]. The 11-step synthesis of icaritin, starting from 2,4,6-trihydroxyacetophenone via microwave-assisted Claisen rearrangement reaction as the key step, was succeeded with an overall yield of 23% [16].
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