Asymmetric synthesis of shikonin and alkannin
XU Yan;CUI Jia-hua;WANG Ru-bing;LI Shao-shun;School of Pharmacy,Shanghai Jiao Tong University;
Objective To invent a convient route for total synthesis of shikonin and alkannin in excellent enantiomeric excess and high yield. Methods The key intermediate( R) or( S)-4-methyL-1-( 1,4,5,8-tetramethoxynaphthalen-2-yl) pent-3-en-1-ol( 4) was synthesized from 1,4,5,8-tetramethoxy-2-naphthaldehyde via Reformatsky reaction,Dess-Martin oxidization and asymmetric hydrogenation by chiral chlorodiisopinocampheylborane( DIP-Cl). After compound 4 was in hand,shikonin and alkanin can be obtained respectively by three chemical redections,including acetylation-oxidation,reduction-acetylation and oxidation-hydrolysis.Results and Conclusions Structures of the target compounds and other intermediates are confirmed by1H-NMR. The total yield reaches 41. 6% with excellent enantiomeric excesses( 96% e. e. for shikonin and95% e. e. for alkannin).