Stereocontrolled Synthesis of C1−C17 Fragment of Narasin via a Free Radical-Based Approach

Brazeau, Jean-Francois; Guilbault, Audrey-Anne; Kochuparampil, Jummey; Mochirian, Philippe; Guindon, Yvan

doi:10.1021/ol902414u

Cited by 22 publications

(10 citation statements)

References 24 publications

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“…The inseparable mixture of 14 a , b was then treated with N ‐bromosaccharin (NBSac)14 to provide a mixture of C2 tertiary bromides 11 a ; 11 b with high 3,7‐ cis selectivity. Alternatively, acetals 15 a , b were treated with tetrasubstituted enoxysilanes 16 and SnCl 4 4e to afford C2 tertiary bromides 12 a ; 12 b with excellent 3,7‐ trans stereocontrol.…”

Section: Resultsmentioning

confidence: 99%

Diastereoselective Hydrogen‐Transfer Reactions: An Experimental and DFT Study

Godin¹,

Prévost²,

Gorelsky³

et al. 2013

Chemistry A European J

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Radical reductions of halogenated precursors bearing a heterocycle exo (α) to the carbon-centered radical proceed with enhanced anti-selectivity, a phenomenon that we termed "exocyclic effect". New experimental data and DFT calculations at the BHandHLYP/TZVP level demonstrate that the origin of the exocyclic effect is linked to the strain energy required for a radical intermediate to reach its reactive conformation at the transition state (ΔE(≠)(strain)). Furthermore, radical reductions of constrained THP systems indicate that high 2,3-anti inductions are reached only when the radical chain occupies an equatorial orientation. Hydride deliveries to different acyclic substrates and calculations also suggest that the higher anti-selectivities obtained with borinate intermediates are not related to the formation of a complex mimicking an exocycle. From a broader standpoint, this study reveals important conformational factors for reactions taking place at a center vicinal to a heterocycle or an α-alkoxy group.

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Section: Resultsmentioning

confidence: 99%

Diastereoselective Hydrogen‐Transfer Reactions: An Experimental and DFT Study

Godin¹,

Prévost²,

Gorelsky³

et al. 2013

Chemistry A European J

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“…The formation of 13 as the major diastereomer is expected as a combination of Felkin-control and the cyclic 6-membered transition state in the crotylation step. 30 Using BF 3 •OEt 2 , 13 was then exposed to ((1-methoxyvinyl)oxy)trimethylsilane 32 at low temperature which provided methyl ester 14 as a single diastereomer (confirmed by X-ray diffraction) in excellent yield. Finally, ozonolysis of 14 followed by reductive work-up generated aldehyde 7 ( Fig.…”

Section: Resultsmentioning

confidence: 99%

Expanding the antibacterial selectivity of polyether ionophore antibiotics through diversity-focused semisynthesis

et al. 2020

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Polyether ionophores are complex natural products capable of transporting cations across biological membranes. Many polyether ionophores possess potent antimicrobial activity and a few selected compounds have ability to target aggressive cancer cells. Nevertheless, ionophore function is believed to be associated with idiosyncratic cellu-lar toxicity and, consequently, human clinical development has not been pursued. Here, we demonstrate that structurally novel polyether ionophores can be efficiently constructed by recycling components of highly abundant polyethers to afford analogues with enhanced anti-bacterial selectivity compared to a panel of natural polyether ionophores. We used classic degradation reactions of the natural polyethers lasalocid and monensin and combined the resulting fragments with building blocks provided by total synthesis, including halogen-functionalized tetronic acids as cation-binding groups. Our results suggest that structural optimization of polyether ionophores is possible and that this area represents a potential opportunity for future methodological innovation.

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“…We have tried to extract the strategic disconnections toward the carbon skeletons and key methods involved in the construction of the structural subunits, rather than comprehensively detailing every synthetic step from all the different approaches. A compilation of synthetic studies on other carboxyl polyether ionophore natural products completed in the time period from 2001 to 2018 is given in Table S1 (Supporting Information) with key transformations highlighted …”

Section: Recent Progress In the Synthesis Of Polyether Ionophores: Zimentioning

confidence: 99%

Chemical Syntheses and Chemical Biology of Carboxyl Polyether Ionophores: Recent Highlights

2019

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Stereocontrolled Synthesis of C1−C17 Fragment of Narasin via a Free Radical-Based Approach

Abstract: An efficient synthesis of the C1-C17 western unit of narasin was achieved from (S)-Roche ester. Highlights in our synthesis include the successful exploitation of three stereoselective sequences of Lewis acid mediated reaction followed by free-radical-based hydrogen transfer.

Cited by 22 publications

References 24 publications

Diastereoselective Hydrogen‐Transfer Reactions: An Experimental and DFT Study

Diastereoselective Hydrogen‐Transfer Reactions: An Experimental and DFT Study

Expanding the antibacterial selectivity of polyether ionophore antibiotics through diversity-focused semisynthesis

Chemical Syntheses and Chemical Biology of Carboxyl Polyether Ionophores: Recent Highlights

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