摘要：

Ionomycin is a narrow-spectrum ionophore antibiotic isolated from Streptomyces conglobatus. X-ray crystallographic analysis of its calcium complex (1; see Scheme 1) revealed a carboxylic acid group and an unusual β-diketone moiety which, in combination, are responsible for its avidity for divalent cations. Ionomycin has little value as an antibiotic but it is widely used as a tool in cell biology for the investigation of processes requiring calcium mobilization. The three total syntheses reported to date exemplify the utility of chiral enolate chemistry (Evans et al.), the chiron approach (Hanessian et al.), and asymmetric ring-opening of symmetrical 8-oxabicyclo[3.2.1]oct-6-enes (Lautens et al.) for the construction of polypropionate chains. In addition, numerous fragment syntheses have also been reported. Herein, we describe a synthesis of ionomycin and its calcium complex (1) from four key fragments 2-5 (Scheme 1). Our synthesis features: 1) the use of a stereoselective gold(III)-catalyzed cycloisomerization of an a-hydroxyallene to create a dihydrofuran ring, and 2) the use of a rhodium-catalyzed rearrangement of an α-diazo-β-hydroxyketone to generate the β-diketone moiety.

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