- NMR-based molecular ruler for determining the depth of intercalants within the lipid bilayer. Part I. Discovering the guidelines
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The development of "molecular rulers" would allow one to quantitatively locate intercalants within the liposomal bilayer. To this end, we have attempted to correlate the 13C NMR chemical shift of a polarizable "reporter" carbon (e.g., carbonyl) of the intercalant-with the ET(30) polarity it experiences, and with its Angstrom distance from the interface. This requires families of molecules with the same two "reporter carbons" separated by a fixed distance, residing at various depths/polarities within the bilayer. The families studied included 4,4-dialkylcyclohexa-2,5-dienones 1, benzenediacetic esters 15, benzenedipropionic esters 17, 4-alkoxybenzaldehydes 19 and methyl 4-alkoxybenzoates 22. These compounds possessed the following characteristics: (1) a planar backbone; (2) polar/hydrophilic "head" groups; (3) modular hydrophobic tails; (4) large changes in the 13C NMR chemical shift (Δδ) of the reporter atoms with solvent polarity. These studies revealed a fifth requirement, namely: (5) the reporter carbons must not be strongly conjugated, lest it reflect the charge build-up at another site within the conjugated system.
- Cohen, Yael,Bodner, Efrat,Richman, Michal,Afri, Michal,Frimer, Aryeh A.
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p. 98 - 113
(2009/12/31)
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- Neighboring Group Participation in Lewis Acid-Promoted and Annulations. The Stereocontrolled Synthesis of Tricyclic Ethers
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A variety of 1,4- and 1,5-keto aldehydes derived from cycloalkanes are coupled with the bis(trimethylsilyl) enol ether of methyl acetoacetate in the presence of either TMSOTf or TrSbCl6 to generate tricyclic ethers.The reactions proceed with excellent regiochemical control by a mechanism involving neighboring group participation.This mechanism involves initial formation of a bicyclic oxocarbenium ion intermediate from the keto aldehyde substrates.The geometries of selected bicyclic intermediates have been optimized using the AM1 method allowing successful prediction of the stereochemical outcomes in the cyclization in most cases.Epimerization of α-chiral keto aldehyde substrates does not appear to occur in these Lewis acid-promoted annulation reactions.
- Molander, Gary A.,Cameron, Kimberly O.
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p. 5931 - 5943
(2007/10/02)
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- 1,5-DICARBONYL COMPOUNDS A GENERAL PREPARATION METHOD
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In this report, a general method for the preparation of 1,5-dicarbonyl compounds and six membered ring annelation is described.This method involves the reaction of hemiacetal vinylogs 1 with enol ethers 2 or 3 in the presence of a Lewis acid.This reaction was successfully applied to the enol ethers of α and α,α'-hindered ketones such as 2,2,6-trimethyl cyclohexanone. α-Cyperone and 6-epi-α-cyperone were obtained using this process.
- Duhamel, P.,Hennequin, L.,Poirier, J. M.,Tavel, G.,Vottero, C.
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p. 4777 - 4786
(2007/10/02)
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- Geminal Acylation-Alkylation at a Carbonyl Carbon via Regiospecifically Generated Metalloenamines
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A useful procedure for effecting geminal disubstitution at the carbonyl carbon atom of aldehydes and ketones has been developed in which the sequence of reactions results in the replacement of the two carbon-oxygen bonds of the carbonyl function with an acyl group and an alkyl or hydroxyalkyl group.Of particular importance is the facile application of these procedures to the efficient construction of quaternary carbon atoms that bear alkyl appendages containing differentiated functionality.This novel methodology features the initial conversion of carbonyl compounds 1 into the substituted 2-azadienes 10 or 11 by Wittig-Horner reaction.Subsequent reaction of these 2-azadienes produced in situ with n-butyllithium results in the formation of the metalloenamines 12 and 13 (R4 = n-Bu) which undergo reactions with a wide variety of electrophiles to give, after hydrolysis of the intermediate imines, the α-substituted aldehydes 14 or the α-substituted ketones 15 in good of excellent overall yields.New procedures for the annelation of cyclopentenones such as 22 and cyclohexenones 26 at the carbonyl carbon of ketones are described as is an important variant of a directed aldol reaction, 1 --> 28.Although a number of individual manipulations are necessary to effect the geminal disubstitution of a carbonyl functional group, it is generally feasible to execute the entire sequence of reactions in single flask, thereby rendering this methodology very convenient to implement in practice.
- Martin, Stephen F.,Phillips, Gerald W.,Puckette, Thomas A.,Colapret, John A.
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p. 5866 - 5872
(2007/10/02)
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