Nature of photochemically induced transannular hydrogen abstractions of taxinines

Kobayashi, Takuo; Kurono, Masayasu; Sato, Hideo; Nakanishi, K.

doi:10.1021/ja00763a057

Cited by 34 publications

(9 citation statements)

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“…Similar reactions with α,β-unsaturated carbonyl compounds involving hydrogen abstraction and radical combination have been previously reported, often without considering them in a broader context of organic synthesis [79,80,[101][102][103][104][105][106][107][108][109][110][111][112][113]. Acetone is frequently used as a sensitizer in photochemical reactions of α,β-unsaturated lactones.…”

Section: Intramolecular Radical Addition With Electronically Excited mentioning

confidence: 62%

Photochemically induced radical reactions with furanones

Oelgemöller

Hoffmann

2015

Pure and Applied Chemistry

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Radicals are easily generated via hydrogen transfer form secondary alcohols or tertiary amines using photochemical sensitization with ketones. They can subsequently add to the electron deficient double bond of furanones. The addition of the alcohols is particularly efficient. Therefore, this reaction was used to characterize and to compare the efficiency of different photochemical continuous flow microreactors. A range of micro-structured reactors were tested and their performances evaluated. The enclosed microchip enabled high space-time-yields but its microscopic dimensions limited its productivity. In contrast, the open microcapillary model showed a greater potential for scale-up and reactor optimization. A 10-microcapillary reactor was therefore constructed and utilized for typical R&D applications. Compared to the corresponding batch processes, the microreactor systems gave faster conversions, improved product qualities and higher yields. Similar reactions have also been carried out with electronically excited furanones and other α,β-unsaturated ketones. In this case, hydrogen is transferred directly to the excited olefin. This reaction part may occur either in one step, i.e., electron and proton are transferred simultaneously, or it may occur in two steps, i.e., the electron is transferred first and the proton follows. In the first case, a C-C bond is formed in the α position of the α,β-unsaturated carbonyl compound and in the second case this bond is formed in the β position. For the first reaction, the influence of stereochemical elements of the substrate on the regioselectivity of the hydrogen abstraction on the side chain has been studied.

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Section: Intramolecular Radical Addition With Electronically Excited mentioning

confidence: 62%

Photochemically induced radical reactions with furanones

Oelgemöller

Hoffmann

2015

Pure and Applied Chemistry

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“…2). The absolute stereochemistry of 3 was established by the following photochemical reaction 18 ; irradiation of taxinine (37), of which absolute stereochemitry has been determined by X-ray analysis, 19 in dioxane with an Hg-lamp gave rise to compounds 3 and 22-Z-form of 3 (Fig. 3).…”

Section: B 2(3!20)-abeo-taxanes (6/10/6-membered Ring Systems)mentioning

confidence: 99%

“…A concerted s s 2 þ p s 2 route was proposed for the photochemical reaction. 18 Taxuspine H (8) was elucidated as a 5-decinnamoyl-5-(3-N,N-dimethylamino-3-phenylpropanoyl)taxuspine C by NMR data and photochemical reaction from taxine II (41) into 8.…”

Section: B 2(3!20)-abeo-taxanes (6/10/6-membered Ring Systems)mentioning

confidence: 99%

“…The biosynthesis of taxane skeleton (6/8/6-membered ring system) has recently been suggested to involve cyclization of geranylgeranyl diphosphate to taxa-4(5),11-diene by Croteau et al, 25 while the pathway of the 3,11-cyclotaxanes (6/5/5/6-membered ring system) has been proposed to be derived from taxanes by concerted s s 2 þ p s 2 route. 18 The 11(15!1)-abeotaxanes (5/7/6-membered ring system) may be biogenetically generated through a WagnerMeerwein rearrangement of ring A in a 6/8/6-membered ring system. 26 On the other hand, the -verticillene.…”

Section: Taxanes (6/8/6-membered Ring System)mentioning

confidence: 99%

“…It was interesting that compounds 16, 18, 19, 22, 49, 63, 72, and 73 without an oxetane ring and an N-acylphenylisoserine moiety exhibited such cytotoxicity. These cytotoxic compounds 16,18,19,22,49,63,72, and 73 possessed an acetoxy group at C-2, while the other functional groups were different from one another. A combination of the acetoxy group at C-2 and the other functional groups such as an oxetane ring may be important for cytotoxicity against KB cells, as many researchers have pointed out that no northern part (positions 7, 9, and 10) but the southern part (positions 1, 2, 4, and 5) of taxoids is intimately associated with its cytotoxicity.…”

Section: F Cytotoxicity Studiesmentioning

confidence: 99%

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Bioactive taxoids from the Japanese yew Taxus cuspidata

Kobayashi

Shigemori

2002

Medicinal Research Reviews

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A series of new taxoids, named taxuspines A-H and J-Z (1-25) and taxezopidines A-H and J-L (26-36), have been isolated together with 37 known taxoids (37-73) including paclitaxel (53) from the Japanese yew, Taxus cuspidata Sieb. et Zucc. (Taxaceae). These new taxoids possess various skeletons containing 5/7/6, 6/10/6, 6/5/5/6, 6/8/6, or 6/12-membered ring systems. Among the new taxoids, some non-taxol-type compounds remarkably reduced CaCl(2)-induced depolymerization of microtubules, or increased cellular accumulation of vincristine in multidrug-resistant tumor cells as potent as verapamil. On the other hand, chemical derivatization of taxinine (37), one of major taxoids obtained from this yew, led to the discovery of unusual reactions of taxinine derivatives. Here we describe our recent results on the isolation, structure elucidation, and bioactivity of these new and known taxoids and the formation of unexpected products of the unusual reactions of taxinine.

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