The synthetic potentialities of cerium(III) chloride are demonstrated by the synthesis of a nine-membered ring heterocycle component of Griseoviridin (3) in optically active form. The key step involves the stereospecific formation of the alpha-carbalkoxy alkenyl sulfide moiety using a combination system of cerium(III) chloride heptahydrate and sodium iodide.
Approaches toward the Total Synthesis of the Nine-Membered Thio-Lactone Core of Griseoviridin
作者:Xavier Moreau、Jean-Marc Campagne
DOI:10.1021/jo034195f
日期:2003.6.1
toward the synthesis of the macrocyclic thiolactone core of griseoviridin have been studied. Intramolecular palladium-catalyzed thiol coupling and esterification (carboxylate activation) have led to the formation of unexpectedrearranged products. An intermolecular palladium-catalyzed thiol/vinyl iodide coupling followed by an esterification (alcohol activation) ultimately led to the nine-membered
The enzyme-mediated enantioselective hydrolysis of poly(ethylene glycol) (PEG)-supported carbonates is disclosed. The water-soluble carbonates were prepared by immobilization of a racemic secondary alcohol (4-benzyloxy-2-butanol) onto low-molecular weight (av MW 550 and 750) monometboxy PEG through a carbonate linker. For the screening of the hydrolytic enzymes, the substrate was enantioselectively hydrolyzed by commercially available lipase from porcine pancreas (PPL; Type II, Sigma) to afford the optically active compounds. In this system, the separation of the remaining (S)-substrate and the resulting (R)-alcohol was achieved by an extraction process without a laborious column chromatography. The (S)-carbonate was easily hydrolyzed with K2CO3 to afford the corresponding (S)-alcohol. Other MPEG-supported substrates were also hydrolyzed to afford the corresponding optically active alcohols. (c) 2006 Elsevier Ltd. All rights reserved.
Studies directed toward the total synthesis of streptogramin antibiotics. Enantiospecific approach to the nine-membered macrocycle of griseoviridin