Optimization of a privileged structure leading to potent and selective human melanocortin subtype-4 receptor ligands

Regioselective One-Pot Synthesis, Biological Activity and Molecular Docking Studies of Novel Conjugates N-(p-Aryltriazolyl)-1,5-benzodiazepin-2-ones as Potent Antibacterial and Antifungal Agents

Novel 1,2,3-triazolo-linked-1,5-benzodiazepinones were designed and synthesized via a Cu(I)-catalyzed 1,3-dipolar alkyne-azide coupling reaction (CuAAC). The chemical structures of these compounds were confirmed by 1H NMR, 13C NMR, HMBC, HRMS, and elemental analysis. The compounds were screened for their in vitro antibacterial and antifungal activities. Several compounds exhibited good to moderate activities compared to those of established standard drugs. Furthermore, the binding interactions of these active analogs were confirmed through molecular docking.

Alpha-melanocyte stimulating hormone: production and degradation

Proopiomelanocortin (POMC) is a polypeptide hormone precursor that is expressed in the brain and in peripheral tissues such as in the pituitary gland, immune system, and skin. In the brain, POMC is processed to form several peptides including alpha-melanocyte stimulating hormone (α-MSH). alpha-MSH is expressed in the hypothalamic arcuate nucleus and in the nucleus tractus solitarius of the brainstem where it has a crucial role in the regulation of metabolic functions. Specifically, α-MSH is an anorexigenic peptide. Its production and maturation processes have been shown to be regulated according to the metabolic condition of the organism. This review summarizes our current knowledge on α-MSH processing including its maturation and degradation processes and pharmacological aspects of its manipulation.

Discovery of a spiroindane based compound as a potent, selective, orally bioavailable melanocortin subtype-4 receptor agonist

We report the design, synthesis and properties of spiroindane based compound 1, a potent, selective, orally bioavailable, non-peptide melanocortin subtype-4 receptor agonist. Compound 1 shows excellent erectogenic activity in the rodent models.

Targeting melanocortin receptors: an approach to treat weight disorders and sexual dysfunction

The melanocortin system has multifaceted roles in the control of body weight homeostasis, sexual behaviour and autonomic functions, and so targeting this pathway has immense promise for drug discovery across multiple therapeutic areas. In this Review, we first outline the physiological roles of the melanocortin system, then discuss the potential of targeting melanocortin receptors by using MC3 and MC4 agonists for treating weight disorders and sexual dysfunction, and MC4 antagonists to treat anorectic and cachectic conditions. Given the complexity of the melanocortin system, we also highlight the challenges and opportunities for future drug discovery in this area.

Privileged Structures in GPCRs

Certain kinds of ligand substructures recur frequently in pharmacologically successful synthetic compounds. For this reason they are called privileged structures. In seeking an explanation for this phenomenon, it is observed that the privileged structure represents a generic substructure that matches commonly recurring conserved structural motifs in the target proteins, which may otherwise be quite diverse in sequence and function. Using sequence-handling tools, it is possible to identify which other receptors may respond to the ligand, as dictated on the one hand by the nature of the privileged substructure itself or by the rest of the ligand in which a more specific message resides. It is suggested that privileged structures interact with the partially exposed receptor machinery responsible for the switch between the active and inactive states. Depending on how they have been designed to interact, one can predispose these substructures to favour either one state or the other; thus privileged structures can be used to create either agonists or antagonists. In terms of the mechanism of recognition, the region that the privileged structures bind to are rich in aromatic residues, which explains the prevalence of aromatic groups and atoms such as sulphur or halogens in many of the ligands. Finally, the approach described here can be used to design drugs for orphan receptors whose function has not yet been established experimentally.

Proteochemometric modeling reveals the interaction site for Trp9 modified α-MSH peptides in melanocortin receptors

The interactions of alpha-MSH peptides with melanocortin receptors (MCRs) were located by proteochemometric modeling. Nine alpha-MSH peptide analogues were constructed by exchanging the Trp9 residue in the alpha-MSH core with the natural or artificial amino acids Arg, Asp, Cys, Gly, Leu, Nal, d-Nal, Pro, or d-Trp. The nine peptides created, and alpha-MSH itself, were evaluated for their interactions with the 4 wild-type MC(1,3-5)Rs and 15 multichimeric MCRs, each of the latter being constructed from three sequence segments, each taken from a different wild-type MC(1,3-5)R. The segments of the chimeric MCRs were selected according to the principles of statistical molecular design and were arranged so as to divide the receptors into five parts. By this approach, a set of 19 maximally diverse MC receptor proteins was obtained for which the interaction activity with the 10 peptides were measured by radioligand binding thus creating data for 190 ligand-protein pairs, which were subsequently analyzed by use of proteochemometric modeling. In proteochemometrics, the structural or physicochemical properties of both interaction partners, which represent the complementarity of the interacting entities, are used to create multivariate mathematical descriptions. (Here, physicochemical property descriptors of the receptors' and peptides' amino acids were used). A valid, highly predictive (Q2 = 0.74) and easily interpretable model was then obtained. The model was further validated by its ability to correctly predicting the affinity of alpha-MSH for new point and cassette-mutated MC4/MC1Rs, and it was then used to identify the receptor residues that are important for affording the high affinity and selectivity of alpha-MSH for the MC1R. It was revealed that these residues are located in several quite distant parts of the receptors' transmembrane cavity and must therefore cause their influence at various stages of the dynamic ligand-binding process, such as by affecting the conformation of the ligand at the vicinity of the receptor and taking part in the path of the ligand's entry into its binding pocket. Our study can be used as a template how to create high resolution proteochemometric models when there are a limited number of natural proteins and ligands available.

Novel piperazines: Potent melanocortin-4 receptor antagonists with anxiolytic-like activity

In the present study, we found that a novel piperazine compound, 11a, showed a moderate affinity (IC(50)=333nM) for the MC4 receptor. We developed the new type of piperazine compounds and found that mono-piperazine 11b exhibited a high-affinity (IC(50)=40.3nM) for the MC4 receptor. We also found that a series of biphenyl analogues exhibited a high-affinity for the receptor, and in particular, compound 11j exhibited the highest affinity for the MC4 receptor with an IC(50) value of 14.5nM. Furthermore, some of these compounds, when administered orally, significantly reversed the stress-induced anxiety-like behavior in rats. In this paper, we report the synthesis, structure-activity relationships, and oral activity of the novel mono-piperazines as MC4 receptor antagonists.

Synthesis of Diphenylmethyl Analogues and Their Affinity for the Melanocortin-4 Receptor and the Serotonin Transporter

While examining antagonists of the melanocortin-4 receptor (MC4 receptor), we found that compound 12b, containing a diphenylmethyl moiety, had a relatively high affinity for the MC4 receptor. When diphenylmethyl analogues were further examined, compounds 12c and 18 were also found to exhibit a high affinity for the MC4 receptor (IC(50)=46.7 nM and 33.2 nM, respectively). Furthermore, compound 12c was also found to show a high affinity for the serotonin transporter (IC(50)=10.7 nM). Here, we describe the synthesis and biological evaluation of various diphenylmethyl analogues in relation to their actions on the MC4 receptor and the serotonin transporter.

The MC4 receptor and control of appetite

Mutations in the human melanocortin (MC)4 receptor have been associated with obesity, which underscores the relevance of this receptor as a drug target to treat obesity. Infusion of MC4R agonists decreases food intake, whereas inhibition of MC receptor activity by infusion of an MC receptor antagonist or with the inverse agonist AgRP results in increased food intake. This review addresses the role of the MC system in different aspects of feeding behaviour. MC4R activity affects meal size and meal choice, but not meal frequency, and the type of diet affects the efficacy of MC4R agonists to reduce food intake. The central sites involved in the different aspects of feeding behaviour that are affected by MC4R signalling are being unravelled. The paraventricular nucleus plays an important role in food intake per se, whereas MC signalling in the lateral hypothalamus is associated with the response to a high fat diet. MC4R signalling in the brainstem has been shown to affect meal size. Further genetic, behavioural and brain-region specific studies need to clarify how the MC4R agonists affect feeding behaviour in order to determine which obese individuals would benefit most from treatment with these drugs. Application of MCR agonists in humans has already revealed side effects, such as penile erections, which may complicate introduction of these drugs in the treatment of obesity.

Privileged structure based ligands for melanocortin-4 receptors—Aliphatic piperazine derivatives

Aliphatic carbocyclic replacement of the benzyl group of compound 1 yielded compounds with high affinity for the melanocortin-4 receptor (MC4R). Compounds with a cyclohexyl group showed a consistent high affinity, while different polar groups with less basicity were good replacements for the original diethyl amines. Substitution of the polar group found in these privileged structures with an aliphatic moiety produced compounds with high affinity for MC4R.