Spectroscopic and theoretical studies of some N-methoxy-N-methyl-2-[(4′-substituted) phenylsulfonyl]propanamides

Structure-Property Relationship Study of N-(Hydroxy)Peptides for the Design of Self-Assembled Parallel β-Sheets

The design of novel and functional biomimetic foldamers remains a major challenge in creating mimics of native protein structures. Herein, we report the stabilization of a remarkably short β-sheet by incorporating N-(hydroxy)glycine (Hyg) residues into the backbone of peptides. These peptide-peptoid hybrids form unique parallel β-sheet structures by self-assembly upon hydrogenation. Our spectroscopic and crystallographic data suggest that the local conformational perturbations induced by N-(hydroxy)amides are outweighed by a network of strong interstrand hydrogen bonds.

Spectroscopic and theoretical studies of some 4′-substituted-phenyl 2-(ethanesulfonyl)acetates. Structure of 4′-nitrophenyl 2-(ethanesulfonyl)acetate

An analysis of carbonyl bands in the infrared spectra of some 2-ethylsulfonyl 4′-substituted phenylacetates bearing substituents NO2 (1), H (2) and OMe (3), supported by B3LYP/6-31G(d,p) and SM5.42R at PM3 level calculations, along with natural bond orbital analysis (NBO) and X-ray diffraction (for 1) was performed. Theoretical data indicated the existence of two stable gauche conformations (g 1 and g 2). The g 1 conformer is the most stable, least polar and has the lowest νCO frequency. The more intense, lower frequency carbonyl doublet component found in CCl4 solution is assigned to the g 1 conformer. As the solvent dielectric constant increases (going from CCl4 to MeCN) the higher frequency νCO doublet increases in intensity. This behaviour is reproduced by the solvation free energy calculations, supporting the conformer assignments. NBO calculations indicate that the most important orbital interaction is LPO9 → π*C7=O8 for both conformers, which corresponds to [C=O ↔ C+–O-] conjugation. This stabilises the g 1 conformer to a greater extent and is responsible for the lower νCO frequency. The sum of the selected NBO delocalisation energies for 1–3 indicates that the g 1 conformer is more stable. It is concluded that the calculated greater stability of the g 1 conformer is due to a balance of attractive electrostatic and orbital interactions along with relevant hydrogen bonds. The X-ray crystal structure analysis of 1 shows the presence of two crystallographic independent but almost superimposable molecules each which adopt a cis geometry. The molecules are consolidated into the three-dimensional crystal packing by C–H…O interactions as well as by nitro- N–O…π(phenyl) contacts.

Oligo(N-alkoxy glycines): trans substantiating peptoid conformations

Peptoid oligomers possess many desirable attributes bioactive peptidomimetic agents, including their ease of synthesis, chemical diversity, and capability for molecular recognition. Ongoing efforts to develop functional peptoids will necessitate improved capability for control of peptoid structure, particularly of the backbone amide conformation. We introduce alkoxyamines as a new reagent for solid phase peptoid synthesis. Herein, we describe the synthesis of N-alkoxy peptoids, and present NMR data indicating that the oligomers adopt a single stable conformation featuring trans amide bonds. These findings, combined with results from computational modeling, suggest that N-alkoxy peptoid oligomers have a strong propensity to adopt a polyproline II type secondary structure.

Synthesis, spectral and conformational studies of some N-arylsulfonyl-t(3)-isopropyl-r(2),c(6)-diarylpiperidin-4-ones

A series of N-arylsulfonyl-t(3)-isopropyl-r(2),c(6)-diarylpiperidin-4-ones 1-8 were synthesized and characterized unambiguously by (1)H, (13)C NMR, 2D-COSY and HSQC NMR spectroscopy. The conformational preferences of 1-8 have been discussed on the basis of the coupling constants, and they suggest normal chair conformation with equatorial orientations of all the substituents in 1-8. The preferred conformation of aryl sulfonyl group at nitrogen and isopropyl group at C-3 was determined theoretically using density functional calculations.