The Thread &amp; Cut Method: Syntheses of Molecular Knot Precursors

Fenlon, Edward E.; Ito, Brandon R.

doi:10.1002/ejoc.200800387

Cited by 19 publications

(15 citation statements)

References 39 publications

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“…Although other syntheses of trefoil knots have been reported [15][16][17][18][19][20][21][22] (as have composites of trefoil knots 23 and other molecular topologies such as catenanes [24][25][26][27][28] and Borromean links 29 ), higher-order molecular knots remain elusive. Here, we report on the synthesis of a molecular pentafoil knot that combines the use of metal helicates to create crossover points 30 , anion template assembly to form a cyclic array of the correct size [31][32][33] , and the joining of the metal complexes by reversible imine bond formation 34-37 aided by the gauche effect 38 to make the continuous 160-atom-long covalent backbone of the most complex non-DNA molecular knot prepared to date.…”

mentioning

confidence: 99%

A synthetic molecular pentafoil knot

Ayme

Beves

Leigh³

et al. 2011

Nature Chem

390

243

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Knots are being discovered with increasing frequency in both biological and synthetic macromolecules and have been fundamental topological targets for chemical synthesis for the past two decades. Here, we report on the synthesis of the most complex non-DNA molecular knot prepared to date: the self-assembly of five bis-aldehyde and five bis-amine building blocks about five metal cations and one chloride anion to form a 160-atom-loop molecular pentafoil knot (five crossing points). The structure and topology of the knot is established by NMR spectroscopy, mass spectrometry and X-ray crystallography, revealing a symmetrical closed-loop double helicate with the chloride anion held at the centre of the pentafoil knot by ten CH ... Cl -hydrogen bonds. The one-pot self-assembly reaction features an exceptional number of different design elements-some well precedented and others less well known within the context of directing the formation of (supra)molecular species. We anticipate that the strategies and tactics used here can be applied to the rational synthesis of other higher-order interlocked molecular architectures.K nots are important structural features in DNA 1 , are found in some proteins [2][3][4][5] and are thought to play a significant role in the physical properties of both natural and synthetic polymers 6,7 . Although billions of prime knots are known to mathematics 8 , to date the only ones to have succumbed to chemical synthesis using building blocks other than DNA are the topologically trivial unknot (that is, a simple closed loop without any crossing points) and the next simplest knot (featuring three crossing points), the trefoil knot 9,10 . A pentafoil knot-also known as a cinquefoil knot or Solomon's seal knot (the 5 1 knot in Alexander-Briggs notation 11 )-is a torus knot 12 with five crossing points, is inherently chiral, and is the fourth prime knot (following the unknot, trefoil knot and figure-of-eight knot) in terms of number of crossing points and complexity 8,11,12 .Sauvage reported the first molecular knot synthesis 13 , using a linear metal helicate 14 to generate the three crossing points required for a trefoil knot. Although other syntheses of trefoil knots have been reported [15][16][17][18][19][20][21][22] (as have composites of trefoil knots 23 and other molecular topologies such as catenanes [24][25][26][27][28] and Borromean links 29 ), higher-order molecular knots remain elusive. Here, we report on the synthesis of a molecular pentafoil knot that combines the use of metal helicates to create crossover points 30 , anion template assembly to form a cyclic array of the correct size [31][32][33] , and the joining of the metal complexes by reversible imine bond formation 34-37 aided by the gauche effect 38 to make the continuous 160-atom-long covalent backbone of the most complex non-DNA molecular knot prepared to date.So far, attempts to make molecular knots with more than three crossing points by extending the linear helicate strategy of Sauvage to ligands with more coordination sites...

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confidence: 99%

A synthetic molecular pentafoil knot

Ayme

Beves

Leigh³

et al. 2011

Nature Chem

390

243

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“…The crude products were purified by column chromatography on silica gel to obtain 12-tridecen-1-ol (41, 109 mg, 93% yield) [60] as colorless oil. and quinoline (91 mg, 0.71 mmol, 1.2 eq.)…”

Section: Synthesis Of 12-tridecen-1-ol (41)mentioning

confidence: 99%

“…The reaction was quenched by replacement of the reaction atmosphere with nitrogen, and the catalyst was removed by filtration using Celite, and the organic solvent was removed by evaporation in vacuo to obtain crude colorless oil. The crude products were purified by column chromatography on silica gel to obtain 12-tridecen-1-ol (41, 109 mg, 93% yield) [60] as colorless oil.…”

Section: Synthesis Of 12-tridecen-1-ol (41)mentioning

confidence: 99%

Total Synthesis and Structural Elucidation of Two Unusual Non‐Methylene‐Interrupted Fatty Acids in Ovaries of the Limpet Cellana toreuma

Shimada

Sugawara

Korenaga

et al. 2017

Lipids

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In our previous study, unusual odd-numbered dienoic acids with a terminal olefin were found as minor components in ovaries of the Japanese limpet Cellana toreuma, and the synthetic interests have been focused onto their structural confirmation and the inspection into their potential biological activity. Here, we describe an efficient and stereoselective total synthesis of two new unusual dienoic acids, 19:2∆7,18 and 21:2∆7,20, through a common pathway involving the strategic combination of alkyne-zipper reaction and Lindlar hydrogenation for the construction of their unique carbon chains. In our synthetic study, 2-propyn-1-ol was at first subjected to alkylation and alkyne-zipper reaction to form the two fragments, and the subsequent carbon chain elongation was achieved by the usual coupling reaction to obtain the C-19 and C-21 products bearing an internal acetylenic group. Then, the internal acetylenic group of these products was subjected to Lindlar hydrogenation to form a Z-alkenyl moiety, and the subsequent deprotection of the products was carried out under an acidic condition without isomerization of the internal Z-alkenyl group. Total synthesis of target fatty acids, 19:2∆7,18 and 21:2∆7,20, was finally accomplished by two-step oxidation of the resulting alcohols into carboxylic acids in a highly chemoselective manner, and the structures of these unusual natural fatty acids were finally elucidated by identifying the GC-MS spectra of the methyl esters of authentic and synthetic fatty acids.

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“…Preliminary experimental work from our group suggests that trefoil knots with backbones containing 63‐ or 72‐atoms are feasible (vide infra). Systematic investigation of the lower limits of knot size should be possible with TLC (thread, link, and cut) knots68 due to a modular design with the ability to adjust the size of the knots produced simply by varying the length of linker 1, linker 2, or the tail (Figure 3). The knot‐tying (linking) step is a ring‐closing olefin metathesis77 (RCM) under high dilution during which threading of the tails through the macrocycles can occur.…”

Section: What Are the Lower Size Limits For Molecular Knots?mentioning

confidence: 99%

“…When productive threading occurs from the same face of the macrocycles (e.g., both top‐down) the trefoil knot results after the cutting step. However, with longer tails threading of the two tails can occur from opposite faces leading to the figure eight knot 68…”

Section: What Are the Lower Size Limits For Molecular Knots?mentioning

confidence: 99%

Open Problems in Chemical Topology

Fenlon

2008

Eur J Org Chem

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The historical origins of chemical topology are highlighted and seven open problems in the discipline are defined. The current state of experimental work towards their solutions is reviewed. Open problems discussed include size and tightness limits on molecular knots, synthesis of knots more complex than the trefoil, measurement of the enantiomerization barrier of a topological rubber glove, and syntheses of a polyethylene trefoil knot, a stable open knot with stoppers, and a molecular Whitehead link.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

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The Thread & Cut Method: Syntheses of Molecular Knot Precursors

Cited by 19 publications

References 39 publications

A synthetic molecular pentafoil knot

A synthetic molecular pentafoil knot

Total Synthesis and Structural Elucidation of Two Unusual Non‐Methylene‐Interrupted Fatty Acids in Ovaries of the Limpet Cellana toreuma

Open Problems in Chemical Topology

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