Total Synthesis of 4-Farnesyl-2-Nitropyrrole Natural Products


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  • 4-ファルネシル-2-ニトロピロール天然物の全合成


<p>Heronapyrroles A–C (1–3) are secondary metabolites produced by a marine-derived Streptomyces sp. (CMB-M0423) isolated from beach sand off Heron Island, Australia, by Capon and co-workers in 2010 (Figure 1).1Heronapyrroles A–C exhibit activity against the Gram-positive bacteria Staphylococcus aureus ATCC 9144 (IC500.6–1.1 mM) and Bacillus subtilis ATCC 6633 (IC501.1–6.5 mM), while they display no cytotoxicity toward mammalian cell lines and are inactive against the Gram-negative bacteria. The rare structures as naturally occurring members, 4-farnesylated-2-nitropyrroles which have ever been limited to cytotoxic nitropyrrolins A–E (4–8) reported by Fenical and co-workers (Figure 2),2 were revealed on the basis of spectroscopic analysis. The absolute configurations at C7 and C15 in heronapyrrole A (1) were determined to be 7S and 15R by the modified Mosher method.3 The same 7S and 15R absolute configurations for heronapyrroles B (2) and C (3) were inferred on biogenetic grounds.</p><p>The unique structures and incomplete stereostructures combined with the promising and selective biological activity prompted synthetic chemists to synthesize the heronapyrroles. In 2012 Schmidt and Stark reported the total synthesis of (–)-heronapyrrole C, an antipode of natural (+)-heronapyrrole C, and proposed the relative and absolute stereochemistry of the natural product.4Recently, the total synthesis of (+)-heronapyrrole C (11) was reported by Brimble and co-workers, and they confirmed the correct stereochemical assignment of natural (+)-heronapyrrole C as shown in 11 (Scheme 1).5 Considering the plausible biogenetic relationship between heronapyrroles A–C proposed by Capon and co-workers in Scheme 1,1 the research results by Stark and Brimble might raise a new problem regarding the stereochemistry originlly assigned for heronapyrroles A and B. Thus, we decided to carry out the synthesis of heronapyrroles A and B and solve the stereochemical problem. In this symposium, we report the total synthesis and complete stereochemical assignment of natural (+)-heronapyrroles A (9) and B (10) (Schemes 2 and 3).11</p><p>We also report the total synthesis of nitropyrrolins A (4), B (5), and D (7) (Scheme 4) and (+)-heronayrrole C (11).12</p>



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