Chemical simulation of polycyclic diterpenoid biosynthesis using mercury(II) triflate/N,N-dimethylaniline complex: mechanistic aspects of a biomimetic olefin cyclization

Nishizawa, Masatoyo; Takenaka, Hideyuki; Hayashi, Yûji

doi:10.1021/jo00356a008

Cited by 88 publications

(27 citation statements)

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“…Aplysin-20 (546) and isoaplysin-20 (557) were the first members of this group to be isolated from the sea hare Aplysia kurodai in 1971 by Yamamura and Hirata [485,486] and in 1977 by Yamamura and Terada [496], respectively. The initially proposed structures were revised after the total syntheses of the natural products [488,[497][498][499]. The rearranged labdane 558 was obtained from Laurencia perforata, along with the pimarane derivatives 567 and 568 [495].…”

Section: Labdanes Pimaranes and Related Diterpenesmentioning

confidence: 99%

The Laurencia Paradox: An Endless Source of Chemodiversity

Harizani

Iοannou

Roussis

2016

Progress in the Chemistry of Organic Natural Products

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Nature, the most prolific source of biological and chemical diversity, has provided mankind with treatments for health problems since ancient times and continues to be the most promising reservoir of bioactive chemicals for the development of modern drugs. In addition to the terrestrial organisms that still remain a promising source of new bioactive metabolites, the marine environment, covering approximately 70% of the Earth's surface and containing a largely unexplored biodiversity, offers an enormous resource for the discovery of novel compounds. According to the MarinLit database, more than 27,000 metabolites from marine macro- and microorganisms have been isolated to date providing material and key structures for the development of new products in the pharmaceutical, food, cosmeceutical, chemical, and agrochemical sectors. Algae, which thrive in the euphotic zone, were among the first marine organisms that were investigated as sources of food, nutritional supplements, soil fertilizers, and bioactive metabolites.Red algae of the genus Laurencia are accepted unanimously as one of the richest sources of new secondary metabolites. Their cosmopolitan distribution, along with the chemical variation influenced to a significant degree by environmental and genetic factors, have resulted in an endless parade of metabolites, often featuring multiple halogenation sites.The present contribution, covering the literature until August 2015, offers a comprehensive view of the chemical wealth and the taxonomic problems currently impeding chemical and biological investigations of the genus Laurencia. Since mollusks feeding on Laurencia are, in many cases, bioaccumulating, and utilize algal metabolites as chemical weaponry against natural enemies, metabolites of postulated dietary origin of sea hares that feed on Laurencia species are also included in the present review. Altogether, 1047 secondary metabolites, often featuring new carbocyclic skeletons, have been included.The chapter addresses: (1) the "Laurencia complex", the botanical description and the growth and population dynamics of the genus, as well as its chemical diversity and ecological relations; (2) the secondary metabolites, which are organized according to their chemical structures and are classified into sesquiterpenes, diterpenes, triterpenes, acetogenins, indoles, aromatic compounds, steroids, and miscellaneous compounds, as well as their sources of isolation which are depicted in tabulated form, and (3) the biological activity organized according to the biological target and the ecological functions of Laurencia metabolites.

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Section: Labdanes Pimaranes and Related Diterpenesmentioning

confidence: 99%

The Laurencia Paradox: An Endless Source of Chemodiversity

Harizani

Iοannou

Roussis

2016

Progress in the Chemistry of Organic Natural Products

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“…Unlike direct Brønsted acid [4] and Hg II [15] activation/ polycyclization, Pd II prefers to coordinate and activate the least substituted alkene, [16] ensuring activation at the terminus. As shown in Scheme 1, the isolable C 6 F 5 CN adduct [17] efficiently (1 h, RT, CH 2 Cl 2 ) converted 3 to a new metalcontaining product devoid of alkene resonances ( 1 H NMR spectroscopy) as a 93:7 mixture of isomers according to 31 P NMR spectroscopy.…”

mentioning

confidence: 99%

Pd^II‐ and Pt^II‐Mediated Polycyclization Reactions of 1,5‐ and 1,6‐Dienes: Evidence in Support of Carbocation Intermediates

Koh¹,

Gagné²

2004

Angew Chem Int Ed

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Biomimetic polyolefin cascade reactions [1,2] represent some of the most challenging problems in reaction design, and their products are ubiquitous in the natural world.[3] Since the Brønsted-Lewis acids (BLAs) of Yamamoto et al. are the only known synthetic catalysts for asymmetric catalytic initiation of cation-olefin cyclizations, [4,5] [7] and Toyota, Ihara et al. [8] demonstrated that nucleophilic enols lead to carbocyclic products by b-hydride elimination [9] or protonation. [10] Although substituent effects [11] and stereochemical studies [6c] support a cationic and cyclic intermediate, respectively, the exact nature of this intermediate is unclear, and direct evidence for this cation is lacking.[12] We therefore initiated a plan that first gathered evidence supporting the intermediacy of the carbocyclic cation, while also determining whether it could function as a point for initiating new metal-mediated reactivity. The key to our pursuit was a recent report by Vitagliano et al. of a dicationic Pt complex of a pyridyl bisphosphane pincer ligand [Pt(PNP)](BF 4 ) 2 (PNP = 2,6-bis(diphenylphosphanylmethyl)pyridine) that catalyzes the dimerization of ethylene and 2-methyl-2-butene. [13,14] Intermolecular nucleophilic addition of 2-methyl-2-butene to coordinated ethylene was proposed, with turnover by a sequence of 1,2-hydride shifts. Most importantly, b-hydride elimination did not occur, since no open cis coordination sites were available, and this suggests that this complex might be capable of initiating cation formation while preserving the stereochemistry of the MÀC bond.Our first approach to trapping the putative cation utilized the Pd analogue of the Vitagliano complex 1 and dienylphenol 3. Unlike direct Brønsted acid [4] and Hg II [15] activation/ polycyclization, Pd II prefers to coordinate and activate the least substituted alkene, [16] ensuring activation at the terminus. As shown in Scheme 1, the isolable C 6 F 5 CN adduct [17] efficiently (1 h, RT, CH 2 Cl 2 ) converted 3 to a new metalcontaining product devoid of alkene resonances ( 1 H NMR spectroscopy) as a 93:7 mixture of isomers according to 31 P NMR spectroscopy. This compound is stable up to 100 8C, though demetalation with NaBH 4 at room temperature rapidly [14b] yielded tricycle 4 in 90 % yield (two steps) and d.r. > 99:1. [18] Since a single diastereomer was observable in the crude demetalation product, we surmised that the isomer mixture for the Pd alkyl complex must result from epimers at the metal-containing stereocenter, a situation suggestive of competing chair-chair and boat-chair transition states, [19] each with a degree of concertedness in the CÀC/CÀO bondforming event, that is, a free carbocation is not likely formed [cf. Eq. (1)]. [1,20] Pincer complex [Pt(PPP)](BF 4 ) 2 (2, PPP = bis(2-diphenylphosphanylethyl)phenylphosphane), [21] derived from commercially available triphos, provided the intermediate alkyl complex with a slightly higher diastereoselectivity (96:4), and 4 in similarly high yield (87 %) and selectivity (> 99:1...

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“…(1) those belonging to the α-chamigrene series possessing a trisubstituted double bond between C-7 and C-8 (1-26); (2) those belonging to the β-chamigrene series not designated (246) 5,7-cycloeudesmane (446) aristolane (450)(451)(452)(453)(454)(455)(456)(457)(458)(459)(460)(461)(462)(463) triquinane (490)(491)(492) cedrane (494) 3,6-cyclo-precapnellane (493) aromadendrane (496)(497)(498) africanane (495) calenzanane (500)(501) cyclococane (499) not designated (502) rhodolaurane (508)(509)(510)(511) omphalane (503)(504) not designated (512) gomerane (505)(506)(507) 6,8-cycloeudesmane (447) cyclolaurane (225)(226)(227)(228)(229)(230)…”

Section: Chamigranes and Related Sesquiterpenesmentioning

confidence: 99%

“…Another Japanese L. nipponica population afforded spirolaurenone (487) [78,199,454,455], which also features a spiro[4.5]decane system. Laurencia obtusa from Cayo Coco, Cuba, afforded bromocyclococanol (499), possessing the tricyclic skeleton cyclococane, postulated to be biosynthetically related to the bisabolanes [461]. Laurenones A (488) and B (489), isolated from a different L. nipponica population from Japan, were considered as biogenetic transformation products of 487 [457].…”

Section: Miscellaneous Sesquiterpenesmentioning

confidence: 99%