π-Cation Interactions in Molecular Recognition: Perspectives on Pharmaceuticals and Pesticides

The π-cation interaction that differs from the cation-π interaction is a valuable concept in molecular design of pharmaceuticals and pesticides. In this Perspective we present an up-to-date review (from 1995 to 2017) on bioactive molecules involving π-cation interactions with the recognition site, and categorize into systems of inhibitor-enzyme, ligand-receptor, ligand-transporter, and hapten-antibody. The concept of π-cation interactions offers use of π systems in a small molecule to enhance the binding affinity, specificity, selectivity, lipophilicity, bioavailability, and metabolic stability, which are physiochemical features desired for drugs and pesticides.

Liver cirrhosis reversion is improved in hamsters with a neurointermediate pituitary lobectomy

Regulating mechanisms of fibrosis is an important goal in the treatment of fibrosis and liver cirrhosis. The role of arginine vasopressin (AVP) in promoting fibrosis in several organs has been well documented. However, the result of an AVP deficiency during liver fibrosis has not been reported. We herein study the effects of an AVP deficiency, which was induced by neurointermediate pituitary lobectomy (NIL), on liver cirrhosis and liver cirrhosis reversion. Hamsters were intact (control) or underwent CCl₄-induced cirrhosis, the latter animals divided into four groups: Cirrhotic, NIL-cirrhotic, Cirrhotic-reversion (R) and NIL-cirrhotic-R. Liver function, liver histopathology (including the fibrosis area and collagen types) and liver expression of MMP-13 and TIMP-2 were assessed. Results show that the AVP deficiency decreased the levels of alkaline phosphatase in serum and the expression of type I collagen and TIMP-2, and increased type III collagen deposition, MMP-13 expression and the size of regeneration nodules in NIL-cirrhotic and NIL-cirrhotic-R animals. A significantly greater recovery was found in the NIL-cirrhotic-R than the Cirrhotic-R group. We conclude that an AVP deficiency participates importantly in hamster liver regeneration by: 1) prompting the fibroblasts to produce type III collagen deposit, 2) influencing the activity of AP from bile duct cells, and 3) inhibiting TIMP-2 expression while favoring the fibrolytic activity of MMP-13.

Application of Docking Methodologies in QSAR-Based Studies

The computational strategies permeate all aspects of drug discovery such as virtual screening techniques. Virtual screening can be classified into ligand based and structure based methods. The ligand based method such as Quantitative Structure Activity Relationship (QSAR) is used when a set of active ligand compounds is recognized and slight or no structural information is available for the receptors. In structure based drug design, the most widespread method is molecular docking. It is widely accepted that drug activity is obtained through the molecular binding of one ligand to receptor. In their binding conformations, the molecules exhibit geometric and chemical complementarity, both of which are essential for successful drug activity. The molecular docking approach can be used to model the interaction between a small drug molecule and a protein, which allow us to characterize the performance of small molecules in the binding site of target proteins as well as to clarify fundamental biochemical processes.

The Synthesis of 5-Amino-dihydrobenzo[b]oxepines and 5-Amino-dihydrobenzo[b]azepines via Ichikawa Rearrangement and Ring-Closing Metathesis

The combination of Ichikawa's rearrangement and a ring-closing metathesis reaction of allyl carbamates is presented as a method for the preparation of 5-amino-substituted 2,5-dihydro-benzo[b]oxepines, 2,5-dihydro-benzo[b]azepines, and 2,5-dihydro-benzo[b]thiepins. It was demonstrated that the use of nonracemic allyl carbamates enables the synthesis of enantioenriched benzo-fused seven-membered heterocycles. Finally, it was shown that further functionalization of the obtained structures allows access to pharmacologically active 5-amino-substituted 2,3,4,5-tetrahydro-1-benzo[b]oxepine scaffolds.

Deciphering the GPER/GPR30-agonist and antagonists interactions using molecular modeling studies, molecular dynamics, and docking simulations

The G-protein coupled estrogen receptor 1 GPER/GPR30 is a transmembrane seven-helix (7TM) receptor involved in the growth and proliferation of breast cancer. Due to the absence of a crystal structure of GPER/GPR30, in this work, molecular modeling studies have been carried out to build a three-dimensional structure, which was subsequently refined by molecular dynamics (MD) simulations (up to 120 ns). Furthermore, we explored GPER/GPR30's molecular recognition properties by using reported agonist ligands (G1, estradiol (E2), tamoxifen, and fulvestrant) and the antagonist ligands (G15 and G36) in subsequent docking studies. Our results identified the E2 binding site on GPER/GPR30, as well as other receptor cavities for accepting large volume ligands, through GPER/GPR30 π-π, hydrophobic, and hydrogen bond interactions. Snapshots of the MD trajectory at 14 and 70 ns showed almost identical binding motifs for G1 and G15. It was also observed that C107 interacts with the acetyl oxygen of G1 (at 14 ns) and that at 70 ns the residue E275 interacts with the acetyl group and with the oxygen from the other agonist whereas the isopropyl group of G36 is oriented toward Met141, suggesting that both C107 and E275 could be involved in the protein activation. This contribution suggest that GPER1 has great structural changes which explain its great capacity to accept diverse ligands, and also, the same ligand could be recognized in different binding pose according to GPER structural conformations.