Solid-phase synthesis of bis-2-imidazolidinethiones from resin-bound tripeptides

Synthesis of Diazacyclic and Triazacyclic Small-Molecule Libraries Using Vicinal Chiral Diamines Generated from Modified Short Peptides and Their Application for Drug Discovery

Small-molecule probes are powerful tools for studying biological systems and can serve as lead compounds for developing new therapeutics. Especially, nitrogen heterocycles are of considerable importance in the pharmaceutical field. These compounds are found in numerous bioactive structures. Their synthesis often requires several steps or the use of functionalized starting materials. This review describes the use of vicinal diamines generated from modified short peptides to access substituted diaza- and triazacyclic compounds. Small-molecule diaza- and triazacyclic compounds with different substitution patterns and embedded in various molecular frameworks constitute important structure classes in the search for bioactivity. The compounds are designed to follow known drug likeness rules, including "Lipinski's Rule of Five". The screening of diazacyclic and traizacyclic libraries has shown the utility of these classes of compounds for the de novo identification of highly active compounds, including antimalarials, antimicrobial compounds, antifibrotic compounds, potent analgesics, and antitumor agents. Examples of the synthesis of diazacyclic and triazacyclic small-molecule libraries from vicinal chiral polyamines generated from modified short peptides and their application for the identification of highly active compounds are described.

Bis-Cyclic Guanidine Heterocyclic Peptidomimetics as Opioid Ligands with Mixed μ-, κ- and δ-Opioid Receptor Interactions: A Potential Approach to Novel Analgesics

The design and development of analgesics with mixed-opioid receptor interactions has been reported to decrease side effects, minimizing respiratory depression and reinforcing properties to generate safer analgesic therapeutics. We synthesized bis-cyclic guanidine heterocyclic peptidomimetics from reduced tripeptides. In vitro screening with radioligand competition binding assays demonstrated variable affinity for the mu-opioid receptor (MOR), delta-opioid receptor (DOR), and kappa-opioid receptor (KOR) across the series, with compound 1968-22 displaying good affinity for all three receptors. Central intracerebroventricular (i.c.v.) administration of 1968-22 produced dose-dependent, opioid receptor-mediated antinociception in the mouse 55 °C warm-water tail-withdrawal assay, and 1968-22 also produced significant antinociception up to 80 min after oral administration (10 mg/kg, p.o.). Compound 1968-22 was detected in the brain 5 min after intravenous administration and was shown to be stable in the blood for at least 30 min. Central administration of 1968-22 did not produce significant respiratory depression, locomotor effects or conditioned place preference or aversion. The data suggest these bis-cyclic guanidine heterocyclic peptidomimetics with multifunctional opioid receptor activity may hold potential as new analgesics with fewer liabilities of use.

1,5-Disubstituted Acylated 2-Amino-4,5-dihydroimidazoles as a New Class of Retinoic Acid Receptor-Related Orphan Receptor (ROR) Inhibitors

A growing body of evidence suggests a pathogenic role for pro-inflammatory T helper 17 cells (Th17) in several autoimmune diseases, including multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease, type I diabetes, and psoriasis-diseases for which no curative treatment is currently available. The nuclear retinoic acid receptor-related orphan receptors alpha and gamma (RORα/γ), in particular the truncated isoform RORγt that is specifically expressed in the thymus, play a critical role in the activation of a pro-inflammatory Th17 response, and RORγ inverse agonists have shown promise as negative regulators of Th17 for the treatment of autoimmune diseases. Our study underscores the screening of a large combinatorial library of 1,5-disubstituted acylated 2-amino-4,5-dihydroimidazoles using a demonstrated synthetic and screening approach and the utility of the positional scanning libraries strategy for the rapid identification of a novel class of ROR inhibitors. We identified compound 1295-273 with the highest activity against RORγ (3.3 µM IC₅₀) in this series, and almost a two-fold selectivity towards this receptor isoform, with 5.3 and 5.8 µM IC₅₀ against RORα and RORβ cells, respectively.

Small Molecule Compounds Identified from Mixture-Based Library Inhibit Binding between Plasmodium falciparum Infected Erythrocytes and Endothelial Receptor ICAM-1

Specific adhesion of P. falciparum parasite-infected erythrocytes (IE) in deep vascular beds can result in severe complications, such as cerebral malaria, placental malaria, respiratory distress, and severe anemia. Cerebral malaria and severe malaria syndromes were associated previously with sequestration of IE to a microvasculature receptor ICAM-1. The screening of Torrey Pines Scaffold Ranking library, which consists of more than 30 million compounds designed around 75 molecular scaffolds, identified small molecules that inhibit cytoadhesion of ICAM-1-binding IE to surface-immobilized receptor at IC₅₀ range down to ~350 nM. With their low cytotoxicity toward erythrocytes and human endothelial cells, these molecules might be suitable for development into potentially effective adjunct anti-adhesion drugs to treat cerebral and/or severe malaria syndromes. Our two-step high-throughput screening approach is specifically designed to work with compound mixtures to make screening and deconvolution to single active compounds fast and efficient.

Increased diversity of libraries from libraries: chemoinformatic analysis of bis-diazacyclic libraries

Combinatorial libraries continue to play a key role in drug discovery. To increase structural diversity, several experimental methods have been developed. However, limited efforts have been performed so far to quantify the diversity of the broadly used diversity-oriented synthetic libraries. Herein, we report a comprehensive characterization of 15 bis-diazacyclic combinatorial libraries obtained through libraries from libraries, which is a diversity-oriented synthetic approach. Using MACCS keys, radial and different pharmacophoric fingerprints as well as six molecular properties, it was demonstrated the increased structural and property diversity of the libraries from libraries over the individual libraries. Comparison of the libraries to existing drugs, NCI diversity, and the Molecular Libraries Small Molecule Repository revealed the structural uniqueness of the combinatorial libraries (mean similarity <0.5 for any fingerprint representation). In particular, bis-cyclic thiourea libraries were the most structurally dissimilar to drugs retaining drug-like character in property space. This study represents the first comprehensive quantification of the diversity of libraries from libraries providing a solid quantitative approach to compare and contrast the diversity of diversity-oriented synthetic libraries with existing drugs or any other compound collection.

Synthesis of Symmetric Bis(imidazole-4,5-dicarboxamides) Substituted with Amino Acids

A series of symmetric bis(imidazole-4,5-dicarboxamides) (bis-I45DCs) were prepared with amino acid esters and a variety of linker groups. The critical pyrazine intermediates, substituted with amino acid esters, were synthesized by stoichiometric control of the amino acid ester, even though primary alkanamines, in comparison, generally offer less selectivity for this reaction. Diamines are added to subsequently react with and open the remaining acyl imidazole bonds in the pyrazine intermediates and thereby yield the bis-I45DCs.

Combinatorial chemistry: libraries from libraries, the art of the diversity-oriented transformation of resin-bound peptides and chiral polyamides to low molecular weight acyclic and heterocyclic compounds

Combinatorial chemistry has deeply impacted the drug discovery process by accelerating the synthesis and screening of large numbers of compounds having therapeutic and/or diagnostic potential. These techniques offer unique enhancement in the potential identification of new and/or therapeutic candidates. Our efforts over the past 10 years in the design and diversity-oriented synthesis of low molecular weight acyclic and heterocyclic combinatorial libraries derived from amino acids, peptides, and/or peptidomimetics are described. Employing a "toolbox" of various chemical transformations, including alkylation, oxidation, reduction, acylation, and the use of a variety of multifunctional reagents, the "libraries from libraries" concept has enabled the continued development of an ever-expanding, structurally varied series of organic chemical libraries.

Nickel-catalyzed highly regio- and chemoselective cocyclotrimerization of propiolates with allenes: a novel route to polysubstituted benzene derivatives

The Ni(dppe)Br(2)/Zn system effectively catalyzes the cocyclotrimerization of propiolates with allenes. The reaction is highly regio- and chemoselective to afford polysubstituted benzene derivatives in good to excellent yields. [reaction: see text]