scholarly journals Diastereoselective addition of alkenylchromium(III) reagents to Garner’s aldehyde: Nozaki-Hiyama-Kishi coupling approach to sphingosines and ceramides

2014 ◽  
Vol 79 (6) ◽  
pp. 627-636 ◽  
Author(s):  
Zorana Ferjancic ◽  
Radomir Matovic ◽  
Filip Bihelovic
Keyword(s):  
Hydrophobic Interactions ◽  
Easy Access ◽  
Allylic Alcohols ◽  
Protecting Group ◽  
Carbon Chains ◽  
Diastereoselective Addition ◽  
Coupling Approach

The intermolecular Nozaki-Hiyama-Kishi coupling between alkenylchromium(III) reagents, derived from either (E)-2-bromostyrene or (E)-1-iodopentadec-1-ene, and conformationally rigid Garner's aldehyde resulted in stereoselective formation of Felkin-type allylic alcohols in good yields, thus providing an easy access to sphingosines. In addition, when the protecting group in Garner's aldehyde was changed (from Boc to N-octanoyl), a reversal of stereoselectivity was observed in the reaction with (E)-pentadec-1-enylchromium(III), probably as a result of hydrophobic interactions between long carbon chains of the reaction partners.

scholarly journals Structural basis for the broad substrate specificity of two acyl-CoA dehydrogenases FadE5 from mycobacteria

2020 ◽  
Vol 117 (28) ◽  
pp. 16324-16332
Author(s):  
Xiaobo Chen ◽  
Jiayue Chen ◽  
Bing Yan ◽  
Wei Zhang ◽  
Luke W. Guddat ◽  
...  
Keyword(s):  
Substrate Specificity ◽  
Mycobacterium Smegmatis ◽  
Hydrophobic Interactions ◽  
Carbon Chain ◽  
Structural Basis ◽  
Broad Substrate Specificity ◽  
Carbon Chains ◽  
Binding Cavity ◽  
Π Stacking Interaction ◽  
Acyl Coa Dehydrogenases

FadE, an acyl-CoA dehydrogenase, introduces unsaturation to carbon chains in lipid metabolism pathways. Here, we report that FadE5 fromMycobacterium tuberculosis(MtbFadE5) andMycobacterium smegmatis(MsFadE5) play roles in drug resistance and exhibit broad specificity for linear acyl-CoA substrates but have a preference for those with long carbon chains. Here, the structures ofMsFadE5 andMtbFadE5, in the presence and absence of substrates, have been determined. These reveal the molecular basis for the broad substrate specificity of these enzymes. FadE5 interacts with the CoA region of the substrate through a large number of hydrogen bonds and an unusual π–π stacking interaction, allowing these enzymes to accept both short- and long-chain substrates. Residues in the substrate binding cavity reorient their side chains to accommodate substrates of various lengths. Longer carbon-chain substrates make more numerous hydrophobic interactions with the enzyme compared with the shorter-chain substrates, resulting in a preference for this type of substrate.

scholarly journals A new class of organogelators based on triphenylmethyl derivatives of primary alcohols: hydrophobic interactions alone can mediate gelation

2017 ◽  
Vol 13 ◽  
pp. 138-149 ◽  
Author(s):  
Wangkhem P Singh ◽  
Rajkumar S Singh
Keyword(s):  
Hydrophobic Interactions ◽  
Water Soluble ◽  
Protecting Group ◽  
Primary Alcohols ◽  
Alkyl Chains ◽  
New Class ◽  
Group A ◽  
Gelation Concentration ◽  
Xrd Techniques ◽  
Derivatives Of

In the present work, we have explored the use of the triphenylmethyl group, a commonly used protecting group for primary alcohols as a gelling structural component in the design of molecular gelators. We synthesized a small library of triphenylmethyl derivatives of simple primary alcohols and studied their gelation properties in different solvents. Gelation efficiency for some of the derivatives was moderate to excellent with a minimum gelation concentration ranging between 0.5–4.0% w/v and a gel–sol transition temperature range of 31–75 °C. 1,8-Bis(trityloxy)octane, the ditrityl derivative of 1,8-octanediol was the most efficient organogelator. Detailed characterizations of the gel were carried out using scanning electron microscopy, FTIR spectroscopy, rheology and powder XRD techniques. This gel also showed a good absorption profile for a water soluble dye. Given the non-polar nature of this molecule, gel formation is likely to be mediated by hydrophobic interactions between the triphenylmethyl moieties and alkyl chains. Possible self-assembled packing arrangements in the gel state for 1,8-bis(trityloxy)octane and (hexadecyloxymethanetriyl)tribenzene are presented. Results from this study strongly indicate that triphenylmethyl group is a promising gelling structural unit which may be further exploited in the design of small molecule based gelators.

scholarly journals Molecular Dynamics of graphene bilayer: in water armchair AB 9x4y turbostratic.

2020 ◽  
Author(s):  
Keli Cristina Barbosa dos Reis ◽  
Anderson Barbosa Lima ◽  
Roberto Ribeiro Faria ◽  
Lourival Rodrigues de Souza ◽  
Victor de Sousa Batista ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Aqueous Solution ◽  
Hydrophobic Interactions ◽  
Aromatic Rings ◽  
Graphene Bilayer ◽  
Rotational Angle ◽  
Carbon Chains ◽  
Molecular Behavior ◽  
Carboxylic Groups ◽  
Conformational Freedom

Graphene forms armchair or zigzag bilayers with AA or AB lined sheets, which differ its properties. This work present a Molecular dynamics study of a graphene bilayer model developed to understand the way of its interactions in aqueous solution, including SDS and LAS surfactants. Structures of 9x and 4y aromatic rings shows a turbostratic stacking with 3,33Å between the sheets. This structure as stable in water and attract the surfactants with sp3 carbon chains, with hydrophobic interactions and carboxylic groups at the edges. It exhibits stable behavior from room temperature to 368K, with a rotational angle of 20Å between the leaves, demonstrating a turbostratic alignment. The adhered surfactants are aligned horizontally, following the movement of the bilayer. They present altered conformational freedom, with the polar portion out of the plane, near to the edges. The reproducibility of experimental intermolecular interactions with hydrophobic portions of the surfactants was also obtained, maintaining a trajectory with turbostratic angulation between the leaves. The predicted molecular behavior of graphene bilayer in aqueous solution contributes to the planning of graphene-based materials.

The Morken Synthesis of (+)-Discodermolide

2017 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Clinical Trials ◽  
Primary Alcohol ◽  
Selective Reduction ◽  
Practical Approach ◽  
Silyl Ether ◽  
Protecting Group ◽  
Lead Structure ◽  
Anticancer Properties ◽  
Stereogenic Centers ◽  
Diastereoselective Addition

The anticancer properties of discodermolide 3 were exciting enough that Novartis undertook a commercial-scale total synthesis. While initial clinical trials were not suc­cessful, it is still a very promising lead structure. James P. Morken of Boston College developed (Angew. Chem. Int. Ed. 2014, 53, 9632) a practical approach, based on the Still–Gennari coupling of the phosphonate 1 with the aldehyde 2. The preparation both of 1 and of 2 showed to advantage the diene borylations that have been developed by the Morken group over the past several years. The alde­hyde 5 was prepared by enantioselective hydroformation of the protected acrolein 4. Borylation of pentadiene 6 followed by diastereoselective addition to 5 set, after oxi­dation, the three new stereogenic centers of 7. Ir-catalyzed hydroboration led to the primary alcohol, that was carried through aldehyde deprotection and oxidation to the ester 8. Oxidation of the alcohol to the acid 9 followed by activation with 10 and cou­pling with the anion 11 then completed the synthesis of 1. The preparation of the key Z-trisubstituted alkene chiron 16 again began with enantioselective hydroformylation of the allyl silyl ether 12 to 13. The addition of 14 proceeded with high diastereoselectivity. Nickel-catalyzed borylation of 15 was also highly diastereoselective, leading to an intermediate that was oxidized to the primary alcohol, then carried on the iodide 16. Pt-catalyzed enantioselective borylation of 6 followed by the addition of chloro­methyl lithium led, after oxidation, to the diol 17. Exposure of the derived bis tosyl­ate to potassium t-butoxide led to facile elimination of the homoallylic tosylate. The remaining tosyl protecting group was then removed reductively to give 18. The Roush reductive aldol protocol using the enolate derived from 19 was applied to the derived aldehyde, leading to 20, that was carried on to 21. Under carefully defined conditions, the E-enolate of 21 coupled efficiently with the allylic iodide 17 to give 2. Still–Gennari coupling with 1 to give 22 followed by selective reduction, deprotection, and lactonization then completed the synthesis of (+)-discodermolide 3.

Oxidative thiocyanation of allylic alcohols: an easy access to allylic thiocyanate within K2S2O8 and NH4SCN

2022 ◽  
Author(s):  
Keyuan Zhang ◽  
Tianbing Liang ◽  
Yulong Wang ◽  
Chonglong He ◽  
Mingyou Hu ◽  
...  
Keyword(s):  
Practical Method ◽  
Allylic Alcohol ◽  
Easy Access ◽  
Allylic Alcohols ◽  
Leaving Group

A practical method for the synthesis of allylic thioacyanate from allylic alcohol was disclosed employing K2S2O8 as the oxidant and NH4SCN as the thiocyanate source. Without introducing a leaving group...

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