Enantioselective conjugate additions of arylboronic acids to β-substituted cyclic enones have been previously reported from our laboratories. Air- and moisture-tolerant conditions were achieved with a catalyst derived in situ from palladium(II) trifluoroacetate and the chiral ligand (S)-t-BuPyOx. We now report a combined experimental and computational investigation on the mechanism, the nature ...

The conformational analysis of peptides containing a single a,a-di-n-propylglycine (Dpg) residue incorporated into valine-rich sequences has been undertaken in order to delineate the possible role of sequence effects in stabilizing fully extended (C5) or local helical conformations at this residue. The three peptides Boc–Val–Dpg–Val–OMe (3), Boc–Val–Val–Dpg–Val–OMe (4), Boc–Val–Val–Dpg–Val–Val–...

The isomerization of phosphodiester functionality of nucleic acids from 3',5'- to a less common 2',5'-linkage influences the complex interplay of stereoelectronic effects that drive pseudorotational equilibrium of sugar rings and thus affect the conformational propensities for compact or more extended structures. The present study highlights the subtle balance of non-covalent forces at play in ...

The determination of the energetics of the temperature-dependent two-state N $ S pseudorotational equilibrium through 3JHH analysis in 36 nucleos(t)ides and 3 abasic sugars has allowed us for the first time to quantify the strength of various nucleobase-dependent anomeric and gauche effects, and how their interplay finally steers the sugar conformation. The plots of the pDdependent thermodynami...

The 20 standard amino acids together with 64 tri-nucleotide codons selected in the genetic code constitute a paradigm of complexity in Nature. Atomic rationals for the choice of nucleobases by Nature have recently received much attention. For the importance of stereoelectronic effect in noncovalent intermolecular interaction and biomolecular recognition, the nitrogen atoms of sp hybrid in nucle...

A regioselective fluorocyclisation of β,γ-unsaturated oximes through I(I)/I(III) catalysis is disclosed to generate 5-fluoromethylated isoxazolines. The transformation leverages p-iodotoluene as an inexpensive catalyst, Selectfluor® the terminal oxidant and amine⋅HF complex (1 : 7.5) both fluoride Brønsted acid source. λ3-iodane p-TolIF2, which generated in situ, engages pendant alkene substrat...

Density functional theory calculations demonstrate that the reversal of regiochemical outcome of the addition for substituted methyl propiolates in the rhodium-catalyzed [(2 + 2) + 2] carbocyclization with PPh3 and (S)-xyl-binap as ligands is both electronically and sterically controlled. For example, the ester functionality polarizes the alkyne π* orbital to favor overlap of the methyl-substit...

High-level ab initio molecular orbital calculations are used to study the magnitude and origin of the penultimate unit effect in atom transfer radical polymerization (ATRP) of dimers involving the comonomers methyl acrylate (MA), methyl methacrylate (MMA), and propylene (P). The penultimate unit effects depend on the nature of the terminal unit and the halogen and can be significant, with the M...

Non-natural peptide analogs have significant potential for the development of new materials and pharmacologically active ligands. One such architecture, the β-peptoids (N-alkyl-β-alanines), has found use in a variety of biologically active compounds but has been sparsely studied with respect to folding propensity. Thus, we here report an investigation of the effect of structural variations on t...