A Potent and Selective Quinoxalinone-Based STK33 Inhibitor Does Not Show Synthetic Lethality in KRAS-Dependent Cells.

The KRAS oncogene is found in up to 30% of all human tumors. In 2009, RNAi experiments revealed that lowering mRNA levels of a transcript encoding the serine/threonine kinase STK33 was selectively toxic to KRAS-dependent cancer cell lines, suggesting that small-molecule inhibitors of STK33 might selectively target KRAS-dependent cancers. To test this hypothesis, we initiated a high-throughput screen using compounds in the Molecular Libraries Small Molecule Repository (MLSMR). Several hits were identified, and one of these, a quinoxalinone derivative, was optimized. Extensive SAR studies were performed and led to the chemical probe ML281 that showed low nanomolar inhibition of purified recombinant STK33 and a distinct selectivity profile as compared to other STK33 inhibitors that were reported in the course of these studies. Even at the highest concentration tested (10 µM), ML281 had no effect on the viability of KRAS-dependent cancer cells. These results are consistent with other recent reports using small-molecule STK33 inhibitors. Small molecules having different chemical structures and kinase-selectivity profiles are needed to fully understand the role of STK33 in KRAS-dependent cancers. In this regard, ML281 is a valuable addition to small-molecule probes of STK33.

Synthesis and profiling of a diverse collection of azetidine-based scaffolds for the development of CNS-focused lead-like libraries.

The synthesis and diversification of a densely functionalized azetidine ring system to gain access to a wide variety of fused, bridged, and spirocyclic ring systems is described. The in vitro physicochemical and pharmacokinetic properties of representative library members are measured in order to evaluate the use of these scaffolds for the generation of lead-like molecules to be used in targeting the central nervous system. The solid-phase synthesis of a 1976-membered library of spirocyclic azetidines is also described.

Build/couple/pair strategy for the synthesis of stereochemically diverse macrolactams via head-to-tail cyclization.

A build/couple/pair (B/C/P) strategy was employed to generate a library of 7936 stereochemically diverse 12-membered macrolactams. All 8 stereoisomers of a common linear amine precursor were elaborated to form the corresponding 8 stereoisomers of two regioisomeric macrocyclic scaffolds via head-to-tail cyclization. Subsequently, these 16 scaffolds were further diversified via capping of two amine functionalities on SynPhase Lanterns. Reagents used for solid-phase diversification were selected using a sparse matrix design strategy with the aim of maximizing coverage of chemical space while adhering to a preset range of physicochemical properties.

Carbon-carbon bond-forming reactions of α-thioaryl carbonyl compounds for the synthesis of complex heterocyclic molecules.

Strategies for the formation of carbon-carbon bonds from the α-thioaryl carbonyl products of substituted lactams are described. Although direct functionalization is possible, a two step process of oxidation and magnesium-sulfoxide exchange has proven optimal. The oxidation step results in the formation of two diastereomers that exhibit markedly different levels of stability toward elimination, which is rationalized on the basis of quantum mechanical calculations and X-ray crystallography. Treatment of the sulfoxide with i-PrMgCl results in the formation of a magnesium enolate that will undergo an intramolecular Michael addition reaction to form two new stereogenic centers. The relationship between the substitution patterns of the sulfoxide substrate and the efficiency of the magnesium exchange reaction are also described.

Synthesis of a stereochemically diverse library of medium-sized lactams and sultams via S(N)Ar cycloetherification.

We have implemented an aldol-based "build/couple/pair" (B/C/P) strategy for the synthesis of stereochemically diverse 8-membered lactam and sultam scaffolds via S(N)Ar cycloetherification. Each scaffold contains two handles, an amine and aryl bromide, for solid-phase diversification via N-capping and Pd-mediated cross coupling. A sparse matrix design strategy that achieves the dual objective of controlling physicochemical properties and selecting diverse library members was implemented. The production of two 8000-membered libraries is discussed including a full analysis of library purity and property distribution. Library diversity was evaluated in comparison to the Molecular Library Small Molecule Repository (MLSMR) through the use of a multifusion similarity (MFS) map and principal component analysis (PCA).

An aldol-based build/couple/pair strategy for the synthesis of medium- and large-sized rings: discovery of macrocyclic histone deacetylase inhibitors.

An aldol-based build/couple/pair (B/C/P) strategy was applied to generate a collection of stereochemically and skeletally diverse small molecules. In the build phase, a series of asymmetric syn- and anti-aldol reactions were performed to produce four stereoisomers of a Boc-protected γ-amino acid. In addition, both stereoisomers of O-PMB-protected alaninol were generated to provide a chiral amine coupling partner. In the couple step, eight stereoisomeric amides were synthesized by coupling the chiral acid and amine building blocks. The amides were subsequently reduced to generate the corresponding secondary amines. In the pair phase, three different reactions were employed to enable intramolecular ring-forming processes: nucleophilic aromatic substitution (S(N)Ar), Huisgen [3+2] cycloaddition, and ring-closing metathesis (RCM). Despite some stereochemical dependencies, the ring-forming reactions were optimized to proceed with good to excellent yields, providing a variety of skeletons ranging in size from 8- to 14-membered rings. Scaffolds resulting from the RCM pairing reaction were diversified on the solid phase to yield a 14 400-membered library of macrolactams. Screening of this library led to the discovery of a novel class of histone deacetylase inhibitors, which display mixed enzyme inhibition, and led to increased levels of acetylation in a primary mouse neuron culture. The development of stereo-structure/activity relationships was made possible by screening all 16 stereoisomers of the macrolactams produced through the aldol-based B/C/P strategy.

Hypericum in infection: Identification of anti-viral and anti-inflammatory constituents.

The Iowa Center for Research on Botanical Dietary Supplements seeks to optimize Echinacea, Hypericum, and Prunella botanical supplements for human-health benefit, emphasizing antiviral, anti-inflammatory and anti-pain activities. This mini-review reports on ongoing studies on Hypericum. The Center uses the genetically diverse, well-documented Hypericum populations collected and maintained at the USDA-ARS North Central Regional Plant Introduction Station (NCRPIS), and the strength of research in synthetic chemistry at Iowa State University to tap natural diversity, to help discover key constituents and interactions among constituents that impact bioactivity and toxicity. The NCRPIS has acquired more than 180 distinct populations of Hypericum, with a focus on Hypericum perforatum L. (Hypericaceae), representing about 13% of currently recognized taxa. Center chemists have developed novel synthetic pathways for key flavones, acyl phloroglucinols, hyperolactones and a tetralin that have been found in Hypericum, and these compounds are used as standards and for bioactivity studies. Both light-dependent and light-independent anti-viral activities have been identified by using bioactivity-guided fractionation of H. perforatum and a HIV-1 infection test system. Our Center has focused on light-independent activity, potentially due to novel chemicals, and polar fractions are undergoing further fractionation. Anti-inflammatory activity has been found to be light-independent, and fractionation of a flavonoid-rich extract revealed four compounds (amentoflavone, chlorogenic acid, pseudohypericin and quercetin) that interacted in the light to inhibit lipopolysaccharide-induced prostaglandin E(2) activity. The Center continues to explore novel populations of H. perforatum and related species to identify constituents and interactions of constituents that contribute to potential health benefits related to infection.

Accessing skeletal diversity using catalyst control: formation of n and n + 1 macrocyclic triazole rings.

A regioselective intramolecular Huisgen cycloaddition was performed on various azido alkyne substrates giving rise to macrocyclic triazole rings. Using catalyst control, a common intermediate has been converted to two structurally unique macrocycles with either a 1,5- or a 1,4-triazole resulting in an n or n + 1 ring size. This is the first example of an intramolecular ruthenium-catalyzed Huisgen cycloaddition.

Diastereoselective synthesis of gamma-lactams by a one-pot, four-component reaction.

A new one-pot, four-component reaction (4CR) between amines, maleic anhydrides, aldehydes, and thiols has been discovered to form tetra- and pentasubstituted gamma-lactams with high diastereoselectivity. Each component is independently variable and employed in equivalent stoichiometry, producing only water as a byproduct.

Phytochemical medicinal agents. A quinone-based route to pterocarpins.

The synthesis of 6,9 di-demethoxy kushecarpin A has been achieved by the coupling of a benzofuran anion with a quinone monoketal followed by a regioselective cyclization and a stereoselective hydrogenation reaction.

A direct synthesis of hyperolactone C.

Hyperolactone C is prepared from furan 4. The key transformation is a tandem Claisen rearrangement/lactonization.