Determination of Absolute Configuration of Natural Products by X-ray Diffraction: A Novel Approach of Incorporating Heavy-Atom-C
Pp. 99-106 (8)
Suchada Chantrapromma, Hoong-Kun Fun, Surat Laphookhieo, Saroj Cheenpracha and Chatchanok Karalai
In this study, the method of determining the absolute configurations of 14b-hydroxy-3β-O-(L-thevetosyl)-5β-card-20(22)-enolide (I) which was isolated from the air-dried fruits of Cerbera odollam and 3α-feruloyl-taraxerol (II) which was isolated from the air-dried fruits of Bruguiera cylindrica will be presented. The novel method  of incorporating heavy-atom-containing solvent molecules into the single crystal structure of the compounds and refinement of the Flack parameter  was used to find the absolute configurations of these natural products. Compounds (I) has a cardenolide skeleton whereas compound (II) has a taraxerol skeleton. The present X-ray study shows the absolute L-form of (I) and the absolute α-form of (II). We have clearly demonstrated for the first time a novel approach which is an extremely useful and easy method to determine the absolute stereochemistry of natural products by X-ray diffraction. The importance of determining the absolute stereochemistry of natural products is emphasised in this work.
Department of Chemistry, Faculty of Science, Prince of Songkla University, Hat-Yai, Songkhla 90112, Thailand.