13062-00-5Relevant articles and documents
Stereoselective synthesis of exocyclic alkenes by Cu-catalyzed allylmagnesiation, Pd-catalyzed alkylation, and Ru-catalyzed ring-closing metathesis: Highly stereoselective synthesis of (Z)- and (E)-γ-bisabolenes
Anastasia, Luigi,Dumond, Yves R.,Negishi, Ei-Ichi
, p. 3039 - 3043 (2001)
Highly efficient stereoselective syntheses of both (Z)- and (E)-γ-bisabolenes (1) were achieved by ring closing metathesis of stereodefined tetrasubstituted alkenes. Both (Z)- and (E)-tetrasubstituted alkene precursors were obtained by Cu-catalyzed stereoselective addition of allylmagnesium bromide to propargyl alcohols, followed by Pd-catalyzed cross coupling of alkylzinc derivatives. This represents the first application of ring-closing metathesis to the stereoselective synthesis of exocyclic alkenes.
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Wolinsky,L.E. et al.
, p. 697 - 699 (1976)
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Structure of epi-isozizaene synthase from streptomyces coelicolor A3(2), a platform for new terpenoid cyclization templates
Aaron, Julie A.,Lin, Xin,Cane, David E.,Christianson, David W.
experimental part, p. 1787 - 1797 (2011/02/22)
The X-ray crystal structure of recombinant epi-isozizaene synthase (EIZS), a sesquiterpene cyclase from Streptomyces coelicolor A3(2), has been determined at 1.60 A resolution. Specifically, the structure of wild-type EIZS is that of its closed conformation in complex with three Mg2+ ions, inorganic pyrophosphate (PPi), and the benzyltriethylammonium cation (BTAC). Additionally, the structure of D99N EIZS has been determined in an open, ligand-free conformation at 1.90 A resolution. Comparison of these two structures provides the first view of conformational changes required for substrate binding and catalysis in a bacterial terpenoid cyclase. Moreover, the binding interactions of BTAC may mimic those of a carbocation intermediate in catalysis. Accordingly, the aromatic rings of F95, F96, and F198 appear to be well-oriented to stabilize carbocation intermediates in the cyclization cascade through cation π interactions. Mutagenesis of aromatic residues in the enzyme active site results in the production of alternative sesquiterpene product arrays due to altered modes of stabilization of carbocation intermediates as well as altered templates for the cyclization of farnesyl diphosphate. Accordingly, the 1.64 A resolution crystal structure of F198A EIZS in a complex with three Mg2+ ions, PPi, and BTAC reveals an alternative binding orientation of BTAC; alternative binding orientations of a carbocation intermediate could lead to the formation of alternative products. Finally, the crystal structure of wild-type EIZS in a complex with four Hg 2+ ions has been determined at 1.90 A resolution, showing that metal binding triggers a significant conformational change of helix G to cap the active site.
