期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 21, 期 44, 页码 15769-15784出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201502389
关键词
alkenes; cyclization; enzyme catalysis; polycycles; terpenoids
资金
- Japan Society for the Promotion of Science [25450150, 18380001]
- Grants-in-Aid for Scientific Research [25450150] Funding Source: KAKEN
Oxidosqualene cyclases catalyze the transformation of oxidosqualene (1) into numerous cyclic triterpenes. Enzymatic reactions of 24-noroxidosqualene (8) and 30-noroxidosqualene (9) with Euphorbia tirucalli -amyrin synthase were conducted to examine the role of the branched methyl groups of compound 1 in the -amyrin biosynthesis. Substrate 8 almost exclusively afforded 30-nor--amyrin (>95.5%), which was produced through a normal cyclization pathway, along with minor products (<4.5%). However, a lack of the Me-30 group (analogue 9) resulted in significantly high production of premature cyclization products, including 6/6/6/5-fused tetracyclic and 6/6/6/6/5-fused pentacyclic skeletons (64.6%). In addition, the fully cyclized product (35.4%) having the 6/6/6/6/6-fused pentacycle was produced; however, the normally cyclized product, 29-nor--amyrin was present in only 18.6% of these products. The conversion yield of substrate 8 possessing a Z-Me group at the terminus was approximately twofold greater than that of compound 9 with an E-Me group. Thus, the Me-30 group is essential for the correct folding of a chair-chair-chair-boat-boat conformation of compound 1 for the production of the -amyrin scaffold, whereas the Me-24 group exerts little influence on the normal polycyclization cascade. Here, we show that the Me-30 group plays critical roles in constructing the ordered architecture of a chair-chair-chair-boat-boat structure, in facilitating the ring-expansion reactions, and in performing the final deprotonation reaction at the correct position.
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