Mechanically axially chiral catenanes and noncanonical chiral rotaxanes

Author(s):  
John Maynard ◽  
Peter Gallagher ◽  
David Lozano ◽  
Patrick Butler ◽  
Steve Goldup

Chirality, the property of objects that are distinct from their own mirror image, is important in many scientific areas but particularly chemistry, where the appearance of molecular chirality because of rigid arrangements of atoms in space famously influences a molecule’s biological properties. Less generally appreciated is that two molecular rings with chemically distinct faces combined like links in a chain results in a chiral structure even when the rings are achiral. To date, no enantiopure examples of such mechanically axially chiral catenanes has been reported. We re-examined the symmetry properties of the mechanically axially chiral motif and identified a straightforward route to such molecules from simple building blocks. We also identify that common representations of axially chiral catenanes obscure that a previously overlooked stereogenic unit arises when a ring is threaded onto a dumbbell-shaped molecule to generate a rotaxane. These insights allowed us to demonstrate the first stereoselective syntheses of an axially chiral catenane and a noncanonical axially chiral rotaxane motif. With methods to access these structures in hand, the process of exploring their properties and applications can now begin.

2021 ◽  
Author(s):  
John Maynard ◽  
Peter Gallagher ◽  
David Lozano ◽  
Patrick Butler ◽  
Steve Goldup

Chirality, the property of objects that are distinct from their own mirror image, is important in many scientific areas but particularly chemistry, where the appearance of molecular chirality because of rigid arrangements of atoms in space famously influences a molecule’s biological properties. Less generally appreciated is that two molecular rings with chemically distinct faces combined like links in a chain results in a chiral structure even when the rings are achiral. To date, no enantiopure examples of such mechanically axially chiral catenanes has been reported. We re-examined the symmetry properties of the mechanically axially chiral motif and identified a straightforward route to such molecules from simple building blocks. We also identify that common representations of axially chiral catenanes obscure that a previously overlooked stereogenic unit arises when a ring is threaded onto a dumbbell-shaped molecule to generate a rotaxane. These insights allowed us to demonstrate the first stereoselective syntheses of an axially chiral catenane and a noncanonical axially chiral rotaxane motif. With methods to access these structures in hand, the process of exploring their properties and applications can now begin.


2021 ◽  
Author(s):  
John Maynard ◽  
Peter Gallagher ◽  
David Lozano ◽  
Patrick Butler ◽  
Steve Goldup

Chirality, the property of objects that are distinct from their own mirror image, is important in many scientific areas but particularly chemistry, where the appearance of molecular chirality because of rigid arrangements of atoms in space famously influences a molecule’s biological properties. Less generally appreciated is that two molecular rings with chemically distinct faces combined like links in a chain results in a chiral structure even when the rings are achiral. To date, no enantiopure examples of such mechanically axially chiral catenanes has been reported. We re-examined the symmetry properties of the mechanically axially chiral motif and identified a straightforward route to such molecules from simple building blocks. We also identify that common representations of axially chiral catenanes obscure that a previously overlooked stereogenic unit arises when a ring is threaded onto a dumbbell-shaped molecule to generate a rotaxane. These insights allowed us to demonstrate the first stereoselective syntheses of an axially chiral catenane and a noncanonical axially chiral rotaxane motif. With methods to access these structures in hand, the process of exploring their properties and applications can now begin.


2022 ◽  
Author(s):  
Stephen Goldup ◽  
John Maynard ◽  
Peter Gallagher ◽  
David Lozano ◽  
Patrick Butler

Abstract The term chiral was introduced by Lord Kelvin over a century ago to describe objects that are distinct from their own mirror image. Chirality is relevant in many scientific areas, but particularly chemistry because different mirror image forms of a molecule famously have different biological properties. Chirality typically arises in molecules due to a rigidly chiral arrangement of covalently bonded atoms. Less generally appreciated is that molecular chirality can arise when molecules are threaded through one another to create a mechanical bond. For example, when two molecular rings with chemically distinct faces are joined like links in a chain the resulting structure is chiral even when the rings themselves are not. We re-examined the symmetry properties of such mechanically axially chiral catenanes and in doing so identified a straightforward route to these molecules from simple building blocks. This also led to the discovery of a previously overlooked mechanical stereogenic unit that can arise when such a ring encircles a dumbbell-shaped axle to generate a rotaxane. These insights allowed us to produce the first highly enantioenriched axially chiral catenane and the same approach gave access to a molecule containing the newly identified noncanonical axially chiral rotaxane motif. With methods to access these structures in hand, the process of exploring their properties and applications can now begin.


1998 ◽  
Vol 63 (2) ◽  
pp. 211-221 ◽  
Author(s):  
Miloš Tichý ◽  
Luděk Ridvan ◽  
Miloš Buděšínský ◽  
Jiří Závada ◽  
Jaroslav Podlaha ◽  
...  

The axially chiral bis(α-amino acid)s cis-2 and trans-2 as possible building blocks for polymeric structures of novel type of helicity were prepared. Their configuration has been determined by NMR spectroscopy and, in the case of the trans-isomer, confirmed by single-crystal X-ray diffraction. Analogous pair of stereoisomeric diacids cis-3 and trans-3, devoid of the amino groups, was also prepared and their configuration assigned. The observed differences in the NMR spectra of cis- and trans-isomers of 2 and 3 are discussed from the viewpoint of their different symmetry properties.


2007 ◽  
Vol 62 (10) ◽  
pp. 1235-1245 ◽  
Author(s):  
Simone Schnabel ◽  
Caroline Röhr

Stoichiometric hydrates of Li3VO4, the hexahydrate and two polymorphs of the octahydrate, were prepared by evaporation of alkaline aqueous solutions 1 molar in LiOH and 0.5 molar in the metavanadate LiVO3 at r. t. with or without the addition of Lithium sulfide, i. e. at different pH values. Their crystal structures have been determined and refined using single crystal X-ray data; all lithium and hydrogen atom positions were localised and refined without contraints. All three title compounds crystallise in non-centrosymmetric space groups. The water molecules belong to the tetrahedral coordination spheres of the Li cations, i. e. they are embedded as water of coordination exclusively. The tetrahedral orthovanadate(V) anions VO3−4 and the LiO4 tetrahedra are connected via common O corners to form building units which are further held together by strong, nearly linear hydrogen bonds. The hexahydrate Li3VO4 ・ 6H2O (space group R3, a = 962.9(2), c = 869.2(2) pm, Z = 3, R1 = 0.0260) contains isolated orthovanadate(V) anions VO3−4 surrounded by a 3D network of cornersharing Li(H2O)4 tetrahedra forming rings of three, seven and eight units. The water molecules are ‘isolated’ in the sense that no hydrogen bonds are formed between water molecules. The octahydrate is dimorphous: The triclinic polymorph of Li3VO4 ・ 8H2O (space group P1, a = 592.6(2), b = 651.3(2), c = 730.2(4) pm, α = 89.09(2), β = 89.43(2), γ = 88.968(12)°, Z = 1, R1 = 0.0325) contains two types of chains of tetrahedra: One consists of corner-sharing Li(H2O)4 tetrahedra only, the second one is formed by alternating LiO4 and VO4 tetrahedra, also sharing oxygen corners. Only one water molecule is ‘isolated’, the other seven form a branched fragment of a chain with hydrogen bonds between them. In the monoclinic form of Li3VO4・8H2O (space group Pc, a = 732.6(1), b = 653.7(1), c = 1292.9(3) pm, β = 112.21(1)°, Z = 2, R1 = 0.0289) a fragment of a chain of three LiO4 tetrahedra, two of which share a common edge, and one VO4 tetrahedron represent the formular unit. These building blocks are connected via hydrogen bonds formed by three ‘isolated’ water molecules and a chain fragment of five connected water molecules.


1996 ◽  
Vol 61 (2) ◽  
pp. 288-297 ◽  
Author(s):  
Vladimír Pouzar ◽  
Ivan Černý

New approach to the preparation of steroids with connecting bridge, based on an O-carboxymethyloxime (CMO) structure, and with terminal hydroxy group, is presented. 17-CMO derivatives of 3β-acetoxy- and 3β-methoxymethoxyandrost-5-en-17-one were condensed with α,ω-amino alcohols to give derivatives with a chain of seven to nine atoms. After THP-protection, these compounds were converted to 3-keto-4-ene derivatives. An alternative synthesis consisted in transformation of 17-CMO derivatives with bonded amino acids by reduction of the terminal carboxyl. The resulting compounds were designed as building blocks for the preparation of bis-haptens for sandwich immunoassays.


2013 ◽  
Vol 85 (8) ◽  
pp. 1683-1692 ◽  
Author(s):  
Valeria Corne ◽  
María Celeste Botta ◽  
Enrique D. V. Giordano ◽  
Germán F. Giri ◽  
David F. Llompart ◽  
...  

Modern organic chemistry requires easily obtainable chiral building blocks that show high chemical versatility for their application in the synthesis of enantiopure compounds. Biomass has been demonstrated to be a widely available raw material that represents the only abundant source of renewable organic carbon. Through the pyrolitic conversion of cellulose or cellulose-containing materials it is possible to produce levoglucosenone, a highly functionalized chiral structure. This compound has been innovatively used as a template for the synthesis of key intermediates of biologically active products and for the preparation of chiral auxiliaries, catalysts, and organocatalysts for their application in asymmetric synthesis.


Author(s):  
Anna de Kluijver ◽  
Klaas G.J. Nierop ◽  
Teresa M. Morganti ◽  
Martijn C. Bart ◽  
Beate M. Slaby ◽  
...  

AbstractSponges produce distinct fatty acids (FAs) that (potentially) can be used as chemotaxonomic and ecological biomarkers to study endosymbiont-host interactions and the functional ecology of sponges. Here, we present FA profiles of five common habitat-building deep-sea sponges (class Demospongiae, order Tetractinellida), which are classified as high microbial abundance (HMA) species. Geodia hentscheli, G. parva, G. atlantica, G. barretti, and Stelletta rhaphidiophora were collected from boreal and Arctic sponge grounds in the North-Atlantic Ocean. Bacterial FAs dominated in all five species and particularly isomeric mixtures of mid-chain branched FAs (MBFAs, 8- and 9-Me-C16:0 and 10 and 11-Me-C18:0) were found in high abundance (together ≥ 20% of total FAs) aside more common bacterial markers. In addition, the sponges produced long-chain linear, mid- and a(i)-branched unsaturated FAs (LCFAs) with a chain length of 24‒28 C atoms and had predominantly the typical Δ5,9 unsaturation, although also Δ9,19 and (yet undescribed) Δ11,21 unsaturations were identified. G. parva and S. rhaphidiophora each produced distinct LCFAs, while G. atlantica, G. barretti, and G. hentscheli produced similar LCFAs, but in different ratios. The different bacterial precursors varied in carbon isotopic composition (δ13C), with MBFAs being more enriched compared to other bacterial (linear and a(i)-branched) FAs. We propose biosynthetic pathways for different LCFAs from their bacterial precursors, that are consistent with small isotopic differences found in LCFAs. Indeed, FA profiles of deep-sea sponges can serve as chemotaxonomic markers and support the conception that sponges acquire building blocks from their endosymbiotic bacteria.


1988 ◽  
Vol 8 (7) ◽  
pp. 2753-2762
Author(s):  
M Bywater ◽  
F Rorsman ◽  
E Bongcam-Rudloff ◽  
G Mark ◽  
A Hammacher ◽  
...  

The autocrine effects of platelet-derived growth factor (PDGF) A- and B-chain homodimers (PDGF-AA and PDGF-BB) on rat-1 cells and human fibroblasts have been investigated by using human PDGF A- and B-chain cDNA clones expressed in a retroviral vector. Infection with replication-defective virus carrying the B-chain cDNA resulted in a phenotypical transformation resembling that induced by simian sarcoma virus. The resulting cells were focus forming in monolayer cultures, grew to high saturation densities, and formed large colonies in soft agar. The PDGF A-chain transfectants showed no transformed morphology and lacked focus-forming activity but grew to high saturation density in monolayer culture and formed small colonies in soft agar. A similar but weaker effect was obtained with an A-chain cDNA variant containing a 69-base-pair insertion in the 3' end of the protein-coding domain. A- and B-chain transfectants released PDGF receptor-competing activity into the medium, but only the medium conditioned by the B-chain transfectants possessed potent mitogenic activity on human fibroblasts. Both types of transfectants had downregulated levels of PDGF receptors; however, the B-chain transfectants were downregulated to significantly lower levels. Metabolic labeling and immunoprecipitations with PDGF antiserum showed that the PDGF B-chain protein was processed to a 24-kilodalton cell-associated and a 30-kilodalton secreted dimeric protein. The A-chain protein was rapidly secreted as a 31-kilodalton dimeric protein. The present study shows a marked difference in the autocrine effects of PDGF-AA and -BB expressed under the control of a retroviral promoter and suggests that different biological properties may be assigned to these two PDGF isoforms.


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