Ezequiel Q. Morales

Correlation between Conformational Equilibria of Free Host and Guest Binding Affinity in Non-preorganized Receptors

Positive cooperativity between host conformational equilibria and guest binding has been widely reported in protein receptors. However, reported examples of this kind of cooperativity in synthetic hosts are scarce and largely serendipitous, among other things because it is hard to envision systems which display this kind of cooperativity. In order to shed some light on the correlation between conformational equilibria of free host and guest binding, selected structural modifications have been performed over a family of nonpreorganized hosts in order to induce conformational changes and to analyze their effect on the binding affinity. The conformational effect was evaluated by a theoretical conformational search and correlated with the ability of the receptors. All data suggest that those receptors that display the best association constants are able to sample folded conformations analogous to the conformational requirements for the binding of the guests. On the contrary, for those receptors where folded conformers are scarce, then the association constant and enantioselectivity clearly drop.

Circular dichroic studies of 2-amino-2-deoxy-galactopyranosides - conformations of the 2-(N-acetyl-p-bromobenzamido) group

Abstract The CD spectra of methyl 2-amino-2-deoxy-D-galactopyranoside mono- N -acylates (acetyl or p -bromobenzoyl) resemble those of the corresponding O -acylates and can be accounted for by the additivity rule. However, the CD of pyranosides containing the N -acetyl- p -bromobenzamido imide group (NAcBz) are far more complex than those of mono- N -acylates and their O -counterparts, and furthermore, the solvent- and temperature-dependent changes differ for the α- and β-anomers. These differences can be accounted for by the different conformations of the 2-NAcBz group.

Stereochemical studies of cyclonoyl systems

Abstract The kinetically controlled electrophilic additions to (Z,Z)-1-hydroxy-cyclonona-2,6-diene and to (Z)-threo-1-hydroxy-2,3-epoxy-6-cyclononene are studied. The stereoselectivity of these reactios can be explained by the conformational preferences of the cyclononyl systems, which are revealed by the CD exciton chirality methodology and molecular mechanics calculations. An absolute configurational study is also included.

Structural elucidation and absolute configuration of novel β-agarofuran (epoxyeudesmene) sesquiterpenes from Maytenus magellanica(Celastraceae)

Six dihydro-β-agarofuran [5,11-epoxy-5β,10α-eudesm-4(14)-ene] sesquiterpenes with a novel substitution pattern were isolated from Maytenus magellanica and their structures were elucidated by means of 1H and 13C NMR spectroscopic studies, including 1H–13C heteronuclear correlation (HETCOR), long range correlation spectra with inverse detection (HMBC) and NOE experiments. Their absolute configurations were determined by application of the CD exciton chirality method while hydrolysis and preparation of derivatives provided additional information. One of the sesquiterpenes exhibited significant antifeedant activity against Spodoptera littoralis.

Conformationally controlled transannular reaction of a 12-membered macrocyclic trienol

Abstract Iodine-induced transannular ring enlargements of several epoxide derivatives of the cyclotrienol (Z,E,Z)-1-hydroxy-cyclododeca-2,5,9-triene ( 1 ) are presented. The diastereoselection exhibited by both the inter- and intramolecular reactions studied, appears to be associated with the conformational preferences of the macrocycle since simple molecular mechanics calculations allowed semiquantitative predictions in the product distributions. An absolute configurational study based on CD exciton chirality methodology is also included.

Water-Induced Programmable Synthesis of Water Pores

Abstract A time-sequential approach to study the hydration thermodynamics of designed organic compacts should prove useful in other cases where cavities are occupied by multiple water molecules, i. e. natural cell water channels as aquaporins.