Taxamycins: a new enediyne family with synthetic and biological potential

Lu, Yee-Fung; Harwig, Curtis; Fallis, Alex G.

doi:10.1139/v95-279

Cited by 18 publications

(5 citation statements)

References 27 publications

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“…Conversion of the latter compound to ketone 12 (deprotection/oxidation) proceeded smoothly as previously reported (two steps, 92% overall yield) . The subsequent coupling of 12 with enediyne fragment 13 , however, was significantly improved by using LiHMDS in the presence of LaCl 3 ·2LiCl, affording, after in situ acetylation, the desired enediyne 14 in 90% overall yield (compared with 69% yield under the originally employed conditions) . Removal of the MEM group from 14 followed by Swern oxidation of the resulting secondary alcohol and concomitant oxidation of the isoxazoline to the isoxazole moiety furnished keto–isoxazole 15 (85% overall yield for the two steps).…”

supporting

confidence: 58%

Total Synthesis of Shishijimicin A

Nicolaou

et al. 2015

J. Am. Chem. Soc.

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supporting

confidence: 58%

Total Synthesis of Shishijimicin A

Nicolaou

et al. 2015

J. Am. Chem. Soc.

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“…93 Some years before, (Z)-1-trimethylsilyl-6-tbutyldiphenylsilylhex-3-en-1,5-diyne (149) was obtained in 64% yield by sequential Pd(PPh 3 ) 4 /CuI-catalyzed alkynylation of 1 with t-butyldiphenylsilylacetylene and trimethylsilylacetylene in Et 2 O at 21°C in the presence of n-BuNH 2 (Scheme 56). 95,96 Scheme 56. Synthesis of 3-en-1,5-diyne 149.…”

Section: Excellent Site Selectivity Was Unexpectedly Observed Bymentioning

confidence: 99%

“…95,96 Compounds 149 and 150 were then used as building blocks in the preparation of enediyne 151 (Figure 8), [95][96][97] a substance that mimics the enediyne antibiotics, esperamicin and calicheamicin. Moreover, compound 152 (Figure 8), which was obtained in high yield by desilylation of 150 with K 2 CO 3 in a mixture of MeOH and benzene at room temperature, 96 was employed as a building block in the synthesis of the bicyclo[7.3.1]trideca-4,9-dien-2,6-diyne 153 98 and racemic calicheamicinone (154) (Figure 8). 99 Compound 153 is a calicheamicin-taxoid mimic that possesses the Taxotere side chain and an enediyne core.…”

Section: Excellent Site Selectivity Was Unexpectedly Observed Bymentioning

confidence: 99%

Development and applications of highly selective palladium-catalyzed monocoupling reactions of (cyclo)alkenes and 1,3-alkadienes bearing two or three electrophilic sites and bis(enol triflates) with terminal alkynes

et al. 2013

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The motivation for writing this review with 558 references, which covers the literature up to the end of September 2012, is to fill a part of this gap by illustrating highly selective Pd/Cu-catalyzed and Cu-free Pd-catalyzed monoalkynylation reactions of (cyclo)alkenes and 1,3-butadienes bearing two or three identical or different electrophilic sites and bis(enol triflates) with terminal alkynes. However, Pd-catalyzed selective monocoupling reactions of 1-alkynes with (hetero)aryl halides or pseudohalides with two identical or different electrophilic sites will not be covered. Moreover, Pd-catalyzed monocoupling reactions of 1-alkynes with non-conjugated diene systems bearing an electrophilic site on each carbon–carbon double bond have also been considered to be beyond the scope of this review.\ud \ud In addition to describing and commenting on the aforementioned monoalkynylation reactions of (cyclo)alkenes and 1,3-dienes with two or three identical or different electrophilic sites and bis(enol triflates), emphasis has been placed on the use of Pd-catalyzed monoalkynylations of (cyclo)alkenes and 1,3-butadienes bearing two or three identical or different electrophilic sites and bis(enol triflates) as key steps of the syntheses of core structures and models of enediyne antitumor antibiotics, pharmacologically active compounds, and bioactive naturally occurring compounds including insect sex pheromone components, and fungal and plant metabolites. Moreover, the review has been focused on the formation of disubstituted acetylenic derivatives by one-pot site-selective Pd-catalyzed consecutive alkynylation reactions of di(pseudo)halogenated olefinic substrates with two different terminal alkynes. Where appropriate, the reasons for the observed stereo-, site-, and/or chemoselectivities of the reported Sonogashira-type monoalkynylation reactions have been mentioned and discussed

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“…Even triple bonds can be present in direct proximity of the aldehyde group [6] or in conjugation with other double bonds [10] (Scheme 3). Even triple bonds can be present in direct proximity of the aldehyde group [6] or in conjugation with other double bonds [10] (Scheme 3).…”

Section: Scheme 2 Oxidation Of Hetero Aromatic Aldehydesmentioning

confidence: 99%

Sodium Chlorite-Hydrogen Peroxide — A Mild and Selective Reagent for the Oxidation of Aldehydes to Carboxylic Acids

Raach¹,

Reiser²

2000

J. prakt. Chem.

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605The oxidation of aldehydes to carboxylic acids is in principle easy to achieve. A number of reagents are known for this transformation [1], nevertheless, only few selective methods that reliably work with all types of aldehydes and also tolerate a broad range of other functional groups are available. Sodium chlorite had been discovered [2] to be effective for the conversion of aldehydes to carboxylic acids under mild conditions (equation 1), but side reactions could not always be avoided. RCHO + HClO 2 → RCOOH + HOCl(1) Problems arise due to the formation of hypochlorite, which is a more powerful oxidation reagent than chlorite and moreover, is able to oxidize the latter to chlorine dioxide. Consequently, to circumvent the complications described scavengers for hypochlorite were tested such as 2-methyl-2-butene [3], resorcinol [4] or sulfamic acids [5]. All these additives, although effective, display certain disadvantages. Eventually, hydrogen peroxide was introduced as trapping reagent by Dalcanale and Montanari [6], which subsequently had been adopted for many oxidations of aldehydes with sodium chlorite.A distinct advantage of the combination of hydrogen peroxide-sodium chlorite is the exclusive formation of inorganic by-products in the course of the oxidation. From an operational point of view the formation of oxygen, as depicted in equation 2, is a good indication for the progress of the reaction. Best reaction conditions have been achieved in aqueous acetonitrile buffered with NaH 2 PO 4 at pH 4.3, while with very sensitive substrates up to 5 equivalents of hydrogen peroxide at pH 2 are employed in order to accelerate the reduction of HOCl. Reactions are carried out at room temp. or even at 0 °C.Following these procedures, aliphatic, α,β-unsaturated and aromatic aldehydes can be converted to carboxylic acids with very few limitations. Moreover, this protocol has been proved so versatile that it had become also the method of choice as the final transformation for the two step conversion of alcohols to carboxylic acids which is initiated by the selective formation of aldehydes by periodinane [7], MnO 2 [8] or Swern-oxidation [9].Carboxylic acids are readily obtained from the corresponding aromatic and hetero aromatic aldehydes (Scheme 1 and 2). Electron rich substrates can be troublesome, giving rise to side products formed by chlorination or oxidation of the aromatic ring. The substitution of H 2 O 2 by DMSO as trapping reagent has been demonstrated to be a viable alternative to circumvent such problems. Oxidation of an electron donor has also to be considered as a possible obstacle. Unprotected aromatic amines and pyrrols are not tolerated as substrates resulting in no defined products, while thioethers are oxidized to sulfoxides and sulfones [6]. Ar H O Ar OH O R Me MeS S Me O S O O Me Ar = + R = H (93 %) R = OMe (86 %) R = OH (7 %) R = NH 2 (tars) R = NHCOMe (98 %) OH MeO (91 %) (chlorinated compounds only) 75 % 25 % Scheme 2 Oxidation of hetero aromatic aldehydes α,β-Unsaturated aldehydes can also be...

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Taxamycins: a new enediyne family with synthetic and biological potential

Cited by 18 publications

References 27 publications

Total Synthesis of Shishijimicin A

Total Synthesis of Shishijimicin A

Development and applications of highly selective palladium-catalyzed monocoupling reactions of (cyclo)alkenes and 1,3-alkadienes bearing two or three electrophilic sites and bis(enol triflates) with terminal alkynes

Sodium Chlorite-Hydrogen Peroxide — A Mild and Selective Reagent for the Oxidation of Aldehydes to Carboxylic Acids

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