A novel type of structurally simple nonpeptide inhibitors for alpha-chymotrypsin. Induced-fit binding of methyl 2-allyl-3-benzenepropanoate to the S2 subsite pocket

CH-π hydrogen bonds in biological macromolecules

This is a sequel to the previous Perspective "The CH-π hydrogen bond in chemistry. Conformation, supramolecules, optical resolution and interactions involving carbohydrates", which featured in a PCCP themed issue on "Weak Hydrogen Bonds - Strong Effects?": Phys. Chem. Chem. Phys., 2011, 13, 13873-13900. Evidence that weak hydrogen bonds play an enormously important role in chemistry and biochemistry has now accumulated to an extent that the rigid classical concept of hydrogen bonds formulated by Pauling needs to be seriously revised and extended. The concept of a more generalized hydrogen bond definition is indispensable for understanding the folding mechanisms of proteins. The CH-π hydrogen bond, a weak molecular force occurring between a soft acid CH and a soft base π-electron system, among all is one of the most important and plays a functional role in defining the conformation and stability of 3D structures as well as in many molecular recognition events. This concept is also valuable in structure-based drug design efforts. Despite their frequent occurrence in organic molecules and bio-molecules, the importance of CH-π hydrogen bonds is still largely unknown to many chemists and biochemists. Here we present a review that deals with the evidence, nature, characteristics and consequences of the CH-π hydrogen bond in biological macromolecules (proteins, nucleic acids, lipids and polysaccharides). It is hoped that the present Perspective will show the importance of CH-π hydrogen bonds and stimulate interest in the interactions of biological macromolecules, one of the most fascinating fields in bioorganic chemistry. Implication of this concept is enormous and valuable in the scientific community.

EXPLORING THE ROLE OF C–H … π INTERACTIONS ON THE STRUCTURAL STABILITY OF ANTIMICROBIAL PEPTIDES

A computational analysis on the C – H … π interactions in a group of 53 antimicrobial peptides was investigated. A total of 162 C – H … π interactions were observed. Side-chain to side-chain C – H … π interactions are the predominant type of interactions in antimicrobial peptides data set. There was an average of one significant C – H … π interaction for every 7 residues in the antimicrobial peptides investigated. Long-range C – H … π interactions are the predominant type of interactions. The secondary structure preference, solvent accessibility and stabilization centers of these of C – H … π interacting residues were estimated. It is likely that the C – H … π interactions contribute significantly to the overall stability of antimicrobial peptides. These interactions were observed after a molecular dynamics study on these set of antimicrobial peptides using CHARMM force field.

Application of a Recyclable Pseudoephedrine Resin in Asymmetric Alkylations on Solid Phase

A pseudoephedrine resin has been successfully employed in asymmetric alkylations on solid phase. Immobilized pseudoephedrine amides are conveniently prepared by the one-step attachment of pseudoephedrine to Merrifield resin through the hydroxyl group and subsequent acylation on nitrogen. Deprotonation and alkylation of the resin-bound amides proceeds smoothly. Ketones and alcohols are cleaved from the resin in high enantiomeric excess and moderate to good overall yield. The parallel, asymmetric solid-phase synthesis of a small library of chiral ketones and alcohols has been carried out to illustrate the utility of the approach. Finally, the pseudoephedrine resin can be conveniently recycled and utilized with no significant loss in the yield or enantiomeric excess of the products.

CH/pi interaction in the conformation of peptides. A database study

A study was carried out, with use of the Cambridge Structural Database, to examine the role of the CH/pi interaction in the conformation of peptides. A number of short intramolecular CH/pi distances have been shown in the crystal structure of peptides bearing at least an aromatic residue in the sequence. The molecular structure in the crystal was inspected individually to know whether the conformation is merely a consequence of the so-called packing forces, or the CH/pi interaction plays a role. It has been demonstrated that the CH/pi interaction constitutes one of the key factors in controlling the conformation of peptides.