Medicinal Chemistry - Volume 10, Issue 1, 2014

Opioid peptides have the potential to be pharmaceutical agents for the treatment of pain because they modulate nociceptive pathways at supraspinal, spinal and peripheral levels. Unfortunately, peptides are generally hydrophilic compounds and therefore unable to cross the blood-brain barrier (BBB) by passive diffusion to reach the central nervous system (CNS) in an amount sufficient to activate appropriate receptors. Endomorphins (EMs) belong to the class of endogenous opioids eliciting the strongest analgesic effect, but only after direct administration to the CNS. Extensive research is in progress to better understand the relationships between EM structure and bioavailability. This article deals with the recent investigations that allow the design of stable and neuroactive EM analogs with enhanced brain passage and uptake.

In a previous study we found that fluorescence-marked vancomycin – a glycopeptide antibiotic – is taken up into human tumor cells. To expand on these investigations we now used the lipoglycodepsipeptide antibiotic ramoplanin. Compared to vancomycin it is not only a bigger molecule, but it also has two potential binding sites for coupling to the imaging agents. Three different ramoplanin imaging conjugates were synthesized, two used for fluorescence imaging and one for magnetic resonance imaging. The two fluorescent dyes used in confocal laser scanning microscopy (CLSM) and fluorescence activated cell sorting (FACS) were fluorescein isothiocyanate (FITC) and rhodamine isothiocyanate (RITC). The third was the magnetic resonance imaging (MRI) contrast agent gadolinium-1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid (GdDOTA). The uptake of ramoplanin conjugates, their specificity for different cell lines and the accessibility of the conjugates by imaging methods were evaluated on 8 human cell lines (two benign, six malignant) by CLSM, FACS and MRI experiments. Cytotoxicity of the ramoplanin conjugates was determined in the FACS experiments with the propidium iodide and Annexin-V-Fluos indicating any disruption in the cell membranes. Cytoplasmic uptake of the ramoplanin conjugates was observed in confocal laser scanning images and was measured using FACS and MRI experiments. Compared to the vancomycin conjugates the ramoplanin conjugates showed much weaker and slower uptake. Additionally, uptake of the ramoplanin conjugates led to strong membrane disruption and cell death.

Four series of 1,3-diaza-2-functionalized-adamantan-6-one derivatives, bearing at the 2 position SO, SO2, POCl and PO2H functional groups, were synthesized via a key quadruple Mannich reaction, followed by transformation of an aminal functionality into the final 2-thia- and 2-phospha compounds. The compounds were tested for cytotoxic activity against the mouse B16-F10 melanoma cell line. Malignant melanoma is notorious for its high resistance to chemotherapy, and new anti-melanoma drugs are urgently needed. The 2-thia compounds exhibited poor proliferation inhibition activity, but the 2-phospha derivatives showed significant activity, with IC50 values of 10-60 μM. The compounds induced cell death by G2/M cell cycle arrest, which led to apoptosis, as determined by Annexin V-FITC/PI staining, mitochondrial membrane potential changes assessed by the JC-1 reagent, caspases 3 and 7 activation, and morphological changes.

A series of novel non-peptide boronic acid derivatives were designed and synthesized via rational drug design principles. All target compounds were screened for the proteasome inhibitory activities in vitro. Selected compounds (6a and 7j) were evaluated for their cytotoxic activities in vitro. Among these tested compounds, two (6a, 7j) displayed better proteasome inhibitory activities than that of the lead compound PI-083, and compound 6a was the most potent one with IC50 value of 161.90±29.46 nM. However, both of the two compounds (6a, 7j) exhibited weak cytotoxic activities, the discrepancy may lie in the compensatory pathways of the ubiquitin-proteasome pathway that promote tumor cell survival.

In our previous study, a protein engineering approach, accounting for the effects of single point mutations of the binding site residues on the stability of 22 thiazolo[4,5-d]pyrimidines in complex with the intracellular kinase domain of EGFR (PDB ID: 1XKK), was established in a systematic manner to be an efficient strategy for the identification of anti-EGFR-related-cancer drug candidates. The inhibitory activities of two lignad molecules, 4-(7-(3-chloro-4-morpholinophenylamino)thiazolo[4,5-d]pyrimidin-2-ylamino)benzenesulfonamide and 4-(7-(4-morpholinophenylamino) thiazolo[4,5-d]pyrimidin-2-ylamino)benzenesulfonamide, exhibited some sort of uniqueness. Regardless of a slight mutual structural difference between these two ligands in only a peripheral Cl atom, their inhibitory activities against EGFR appeared to be associated with two quite opposite structural bases respectively. Herein, the fundamental rationalization of the remarkable standpoint is elaborated using both molecular docking and molecular dynamics simulations. Consequently, a number of implications of vital importance for the successful structure-based design of prospective drugs against EGFR-related cancers are discussed.

In an effort to develop safe and efficacious compounds for the treatment of metabolic disorders, new compounds based on a combination of clofibric acid, the active metabolite of clofibrate, and trans-stilbene, chalcone, and other lipophilic groups were synthesized. They were evaluated for PPARα transactivation activity; all branched derivatives showed an increase of the transcriptional activity of receptor compared to the linear ones. Noteworthy, stilbene and benzophenone branched derivatives activated the PPARα better than clofibric acid.

As a part of a research project pertaining to the synthesis of novel candidates as nonsedating, nonclassic H1 histaminergic (H1) blockers with low toxicity profiles, some new 5-substituted aminomethylenepyrimidine-2,4,6-triones were designed based on the H1 histaminic receptor pharmacophore model. The interactions between the designed compounds and the H1 receptor were studied using molecular docking on the homology model of H1 receptor. The designed compounds were synthesized and biologically evaluated for H1-blocking activity; using isolated segments of guinea pig ileum. Compounds 15,18,19 and 21 exhibited comparable activities to acrivastine (22) as reference nonsedating drug. The C log P of designed compounds revealed lower values in reference to acrivastine (22) which might indicate decreased tendency for crossing the blood brain barrier.

Helicobacter pylori pathogenic action involves the colonization of the gastrointestinal tract and a large production of reactive oxygen species (ROS) by the neutrophils attracted to the site of infection. The aim of this study was to evaluate caffeic acid and its alkyl esters as inhibitors of the release of ROS by Helicobacter pylori activated neutrophils and their bactericidal effect. The increased hydrophobicity caused by esterification had direct consequence in their efficiency as bactericidal agents against H. pylori and inhibitors of the production of ROS by neutrophils. The minimum inhibitory concentration (MIC) decreased from higher than 1000 μg/mL (caffeic acid) to 250 μg/mL to butyl and heptyl caffeate. The release of total ROS, superoxide anion and hypochlorous acid by activated neutrophils was also significantly decreased and the esters were more efficient than the acid precursor. In conclusion, the alkyl esters of caffeic acid have two properties that are complementary for the treatment of H. pylori infections: bactericidal activity and inhibitory effect upon generation of ROS by neutrophils. Hence, we propose that these easily synthesized and non-expensive substances should be applied to in vivo experimental models of H. pylori induced gastric infections.

A series of novel Ligustrazinyl amides was designed, synthesized and evaluated for their protective effect on the injured vascular endothelial cells. The preliminary results demonstrated that some compounds possessed more potent activities than that of Ligustrazine in stimulating replication of the injured human umbilical vascular endothelial cells (HUVECs) that is damaged by hydrogen peroxide. Among the active compounds, compounds 8i, 8t and 8u exhibited the highest potency with low EC50 values of 0.037, 0.070 and 0.055 mM, respectively. Structure-activity relationships were briefly discussed.

Since Alzheimer disease (AD) is a multifactorial disease, recent therapeutical approaches concentrate on the development of a multitargeting drug. Various protein kinases are known to be involved in the progression of AD. A first series of 3-ethoxycarbonyl-1-aza-9-oxafluorenes has been synthesized and biologically evaluated as AD-relevant protein kinase inhibitors. A concentration-dependent inhibition of important AD-relevant kinases has been characterized after the selectivity of kinase inhibition had been demonstrated. Structure-activity relationships of protein kinase inhibition are discussed and first multitargeting inhibitors have been identified.

The sigma (σ) receptor system consists of at least two major receptor subtypes: σ1 and σ2. Several potential therapeutic applications would benefit from structural knowledge of the σ2 receptor but gaining this knowledge has been hampered by the difficulties associated with its isolation and, thus, characterization. Here, a ligand based approach has been adopted using the program PHASE® and a group of 41 potent and structurally diverse σ2 ligands to develop several pharmacophore models for different families of σ2 ligands. These pharmacophores were analyzed to identify the different binding modes to the receptor and were combined together to construct a comprehensive pharmacophore that was used to develop a structural model for the σ2 binding pocket. A total of six binding modes were identified and could be classified as neutral or charged modes. The results presented here also indicate the significance of hydrophobic interactions to σ2 binding and the requirement of hydrogen bonding interactions to increase the affinity for this receptor subtype. This work adds breadth to our knowledge of this receptor’s binding site, and should contribute significantly to the development of novel selective σ2 ligands.