5 research outputs found
Funeral at Dawn
2-Alkenyltriflylanilides react with
allenes upon treatment with
catalytic amounts of Pd(OAc)<sub>2</sub> and Cu(II) to give highly
valuable 2,3-dihydro-1<i>H</i>-benzo[<i>b</i>]azepines,
in good yields, and with very high regio- and diastereoselectivities.
Density functional theory (DFT) calculations suggest that the C–H
activation of the alkenylanilide involves a classical concerted metalation–deprotonation
(CMD) mechanism
Effect of Organochloride Guest Molecules on the Stability of Homo/Hetero Self-Assembled α,γ-Cyclic Peptide Structures: A Computational Study Toward the Control of Nanotube Length
We present here a molecular dynamics study on peptide nanotubes
composed of <i>cis-</i>3-aminocyclohexanecarboxylic acid-(γ-Ach)
or <i>cis-</i>3-aminocyclopentanecarboxylic acid (γ-Acp)-based
α,γ-cyclohexapeptides and also on those formed by heterodimeric
pairs from a combination of the two aforementioned peptides (γ-Ach/Acp),
which is the first time that a self-assembling cyclic peptide nanotube
composed of heteromeric units is investigated. The main advantage
of these types of nanotube is that they have a partially hydrophobic
inner cavity, a property that makes them very exciting alternatives
to classical nanotubes. In an effort to analyze the fine details of
these ensembles, we investigated the dynamical behavior of model dimeric
structures that mimic the fundamental repeating structural motif of
longer nanotubes. Despite the structural analogy of the β-sheet
interaction, our results suggest that extrapolation of the information
obtained from those “capped” dimers to nanotube properties
has some limitations because several significant differences have
been found between the two systems. This finding is not only relevant
for α,γ-cyclic peptide nanotubes but also shows that special
care should also be taken when considering other related peptide nanotubes
in which N-methylated dimers are used to obtain information about
the stability and formation of the nanotubes. The structural and dynamical
behavior of dimers and nanotubes in nonpolar (chloroform) and polar
protic solvents (water) has been analyzed using state-of-the-art theoretical
methods. A marked destabilizing effect on the structure was observed
in aqueous solution for all systems studied, suggesting that most
of the water molecules that compete for the hydrogen bonds are those
that occupy the internal cavity. We show that the introduction of
organochloride molecules within the dimers and nanotubes is stabilized
in water, and this property opens the door to a large number of possible
future applications that are an important challenge in the field of
molecular self-assembly, such as in drug delivery processes to control
nanotube length by means of appropriate guests. A precise control
of the nanotube length can be envisaged from the MD simulations of
the encapsulation of 1,2-bis[2-(2,2,2-trichloroethoxy)ethoxy]ethane
inside its inner cavity, opening a very interesting possibility in
this area
Palladium-Catalyzed Conjugate Addition of Terminal Alkynes to Enones
A practical protocol for the hydroalkynylation of enones using Pd catalysis is reported. The reaction proceeds efficiently with a variety of alkynes as well as with several cyclic and acyclic enones, providing synthetically relevant β-alkynyl ketones in good to excellent yields
Palladium(II)-Catalyzed Annulation between <i>ortho</i>-Alkenylphenols and Allenes. Key Role of the Metal Geometry in Determining the Reaction Outcome
2-Alkenylphenols
react with allenes, upon treatment with catalytic
amounts of Pd(II) and Cu(II), to give benzoxepine products in high
yields and with very good regio- and diastereoselectivities. This
contrasts with the results obtained with Rh catalysts, which provided
chromene-like products through a pathway involving a β-hydrogen
elimination step. Computational studies suggest that the square planar
geometry of the palladium is critical to favor the reductive elimination
process required for the formation of the oxepine products
<i>cis</i>-Platinum Complex Encapsulated in Self-Assembling Cyclic Peptide Dimers
A new cyclic peptide
dimer that encapsulates cisplatin complexes
in its internal cavity is described. The resulting complex showed
cytotoxic activity at A2780 ovarian cancer cell lines independent
of acquired platinum resistance