Synthesis and Evaluation of a Class of Compounds Inhibiting the Growth of Stromal Antigen 2 (STAG2)-Mutant Ewing Sarcoma Cells

STAG2 (SA2) is a critical component of the cohesin complex that regulates gene expression and the separation of sister chromatids in cells. Mutations in STAG2 have been identified in over thirty different types of cancers including non-small cell lung, bladder and Ewing sarcoma. Selectively inhibiting cancer cells lacking of STAG2 is an attractive approach for the cancer therapy. Here we report that a small molecule, StagX1, identified through a high-throughput screening, inhibits the growth of Ewing sarcoma cells possessing mutant STAG2 . A new synthetic route to the StagX1 scaffold and new versions of the molecule along with their activity in a cell viability assay are reported.

Diastereoselective Rhodium Catalyzed [4 + 2] Cycloisomerization of Allenes

A diastereoselective [4 + 2] cycloisomerization of asymmetric allenyl dienes is reported. The asymmetric dienyl allenes are synthesized using the method reported by Ma. These substrates readily undergo diastereoselective intramolecular rhodium catalyzed [4 + 2] cycloisomerization analogous to thermal intramolecular Diels-Alder reactions. Overall, 29 examples are presented with tethers possessing nitrogen, oxygen, and carbon. Diastereoselectivities range from 99:1 to 90:10 in most examples.

Screening of Focused Compound Library Targeting Liver X Receptors in Pancreatic Cancer Identified Ligands with Inverse Agonist and Degrader Activity

Pancreatic ductal adenocarcinoma (PDAC) is the predominant form of pancreatic cancer. PDACs harbor oncogenic mutations in the KRAS gene, and ongoing efforts to directly target its mutant protein product to inhibit tumor growth are a priority not only in pancreatic cancer but in other malignancies such as lung and colorectal cancers where KRAS is also commonly mutated. An alternative strategy to directly targeting KRAS is to identify and target druggable receptors involved in dysregulated cancer hallmarks downstream of KRAS dysregulation. Liver X receptors (LXRs) are members of the nuclear receptor family of ligand-modulated transcription factors and are involved in the regulation of genes which function in key cancer-related processes, including cholesterol transport, lipid and glucose metabolism, and inflammatory and immune responses. Modulation of LXRs via small molecule ligands has emerged as a promising approach for directly targeting tumor cells or the stromal and immune cells within the tumor microenvironment. We have previously shown that only one of the two LXR subtypes (LXRβ) is expressed in pancreatic cancer cells, and targeting LXR with available synthetic ligands blocked the proliferation of PDAC cells and tumor formation. In a screen of a focused library of drug-like small molecules predicted to dock in the ligand-binding pocket of LXRβ, we identified two novel LXR ligands with more potent antitumor activity than current LXR agonists used in our published studies. Characterization of the two lead compounds (GAC0001E5 and GAC0003A4) indicates that they function as LXR inverse agonists which inhibit their transcriptional activity. Prolonged treatments with novel ligands further revealed their function as LXR "degraders" which significantly reduced LXR protein levels in all three PDAC cell lines tested. These findings support the utility of these novel inhibitors in basic research on ligand design, allosteric mechanisms, and LXR functions and their potential application as treatments for advanced pancreatic cancer and other recalcitrant malignancies.

Correction: Diastereoselective synthesis of 1,3-disubstituted isoindolines and sultams via bronsted acid catalysis

Correction for 'Diastereoselective synthesis of 1,3-disubstituted isoindolines and sultams via bronsted acid catalysis' by Ye Tao et al., Chem. Commun., 2018, 54, 11292-11295.

Stability and pharmacokinetics of separase inhibitor-Sepin-1 in Sprague-Dawley rats

Separase, a sister chromatid cohesion-resolving enzyme, is an oncogene and overexpressed in many human cancers. Sepin-1 (2,2-dimethyl-5-nitro-2H-benzimidazole-1,3-dioxide) is a potent separase inhibitor that impedes cancer cell growth, cell migration, and wound healing, suggesting that Sepin-1 possesses a great potential to target separase-overexpressing tumors. As a part of the IND-enabling studies to bring Sepin-1 to clinic, herein we report the results from a 28-day repeat-dose pharmacokinetic study of Sepin-1 in rats. Sepin-1 was intravenously administered to Sprague-Dawley rats once daily for 28 days at three different (5, 10, and 20 mg/kg) doses. Blood samples were collected after administration of doses on days 1 and 28. Sepin-1 is unstable and isomerizes in basic solutions, but it is stable in acidic buffer such as citrate-buffered saline (pH 4.0). UHPLC-MS analysis indicated Sepin-1 was rapidly metabolized in vivo. One of the major metabolites was an amine adduct of 2,2-dimethyl-5-nitro-2H-benzimidazole (named Sepin-1.55). The concentration of Sepin-1.55 in blood samples was Sepin-1 dose-dependent and used for pharmacokinetic analysis of Sepin-1. T_max was approximately 5-15 min. The data suggest that no Sepin-1 accumulation occurred from daily repeat dosing and similar exposures on the first and final day of dosing. Data also suggest a gender difference, namely that female rats have more exposure and slower clearance than male rats. The data support that Sepin-1 is a potential drug candidate that can be further developed to treat Separase-overexpressing human tumors.

In Vivo and In Vitro Analyses of Novel Peptidomimetic Disruptors for the Serotonin 5-HT2C Receptor Interaction With Phosphatase and Tensin Homolog

Hypofunction of the serotonin (5-HT) 5-HT_2C receptor (5-HT_2CR) has been implicated in a variety of disorders including substance use disorders. As such, approaches to enhance 5-HT_2CR signaling display therapeutic potential. In the present study, we show that disruption of the 5-HT_2CR interaction with the protein phosphatase and tensin homolog (PTEN) via peptidomimetics enhances 5-HT_2CR-mediating signaling in vitro and potentiates selective 5-HT_2CR agonists in behavioral rodent models. Overall, the present study provides further evidence that 5-HT_2CR activity can be modulated through an allosteric protein-protein interaction. This work provides the groundwork for the continued exploration of protein-protein interactions that can allosterically modulate this critical receptor and other important G protein-coupled receptors (GPCRs) for new therapeutic development through mechanisms that may display clinical utility.

Biophysical validation of serotonin 5-HT2A and 5-HT2C receptor interaction

The serotonin (5-HT) 5-HT_2A receptor (5-HT_2AR) and 5-HT_2C receptor (5-HT_2CR) in the central nervous system are implicated in a range of normal behaviors (e.g., appetite, sleep) and physiological functions (e.g., endocrine secretion) while dysfunctional 5-HT_2AR and/or 5-HT_2CR are implicated in neuropsychiatric disorders (e.g., addiction, obesity, schizophrenia). Preclinical studies suggest that the 5-HT_2AR and 5-HT_2CR may act in concert to regulate the neural bases for behavior. Here, we utilize three distinct biophysical and immunocytochemistry-based approaches to identify and study this receptor complex in cultured cells. Employing a split luciferase complementation assay (LCA), we demonstrated that formation of the 5-HT_2AR:5-HT_2CR complex exists within 50 nm, increases proportionally to the 5-HT_2CR:5-HT_2AR protein expression ratio, and is specific to the receptor interaction and not due to random complementation of the luciferase fragments. Using a proximity ligation assay (PLA), we found that cells stably expressing both the 5-HT_2AR and 5-HT_2CR exhibit 5-HT_2AR:5-HT_2CR heteroreceptor complexes within 40 nm of each other. Lastly, bioluminescence resonance energy transfer (BRET) analyses indicates the formation of a specific and saturable 5-HT_2AR:5-HT_2CR interaction, suggesting that the 5-HT_2AR and 5-HT_2CR form a close interaction within 10 nm of each other in intact live cells. The bioengineered receptors generated for the LCA and the BRET exhibit 5-HT-mediated intracellular calcium signaling as seen for the native receptors. Taken together, this study validates a very close 5-HT_2AR:5-HT_2CR interaction in cultured cells.

The Metabolism of Separase Inhibitor Sepin-1 in Human, Mouse, and Rat Liver Microsomes

Separase, a known oncogene, is widely overexpressed in numerous human tumors of breast, bone, brain, blood, and prostate. Separase is an emerging target for cancer therapy, and separase enzymatic inhibitors such as sepin-1 are currently being developed to treat separase-overexpressed tumors. Drug metabolism plays a critical role in the efficacy and safety of drug development, as well as possible drug–drug interactions. In this study, we investigated the in vitro metabolism of sepin-1 in human, mouse, and rat liver microsomes (RLM) using metabolomic approaches. In human liver microsomes (HLM), we identified seven metabolites including one cysteine–sepin-1 adduct and one glutathione–sepin-1 adduct. All the sepin-1 metabolites in HLM were also found in both mouse and RLM. Using recombinant CYP450 isoenzymes, we demonstrated that multiple enzymes contributed to the metabolism of sepin-1, including CYP2D6 and CYP3A4 as the major metabolizing enzymes. Inhibitory effects of sepin-1 on seven major CYP450s were also evaluated using the corresponding substrates recommended by the US Food and Drug Administration. Our studies indicated that sepin-1 moderately inhibits CYP1A2, CYP2C19, and CYP3A4 with IC₅₀ < 10 μM but weakly inhibits CYP2B6, CYP2C8/9, and CYP2D6 with IC₅₀ > 10 μM. This information can be used to optimize the structures of sepin-1 for more suitable pharmacological properties and to predict the possible sepin-1 interactions with other chemotherapeutic drugs.

Novel Bivalent 5-HT2A Receptor Antagonists Exhibit High Affinity and Potency in Vitro and Efficacy in Vivo

The 5-HT_2A receptor (5-HT_2AR) plays an important role in various neuropsychiatric disorders, including substance use disorder and schizophrenia. Homodimerization of this receptor has been suggested, but tools that allow direct assessment of the relevance of the 5-HT_2AR:5-HT_2AR homodimer in these disorders are necessary. We chemically modified the selective 5-HT_2AR antagonist M100907 to synthesize a series of homobivalent ligands connected by ethylene glycol linkers of varying lengths that may be useful tools for probing 5-HT_2AR:5-HT_2AR homodimer function. We tested these molecules for 5-HT_2AR antagonist activity in a cell line stably expressing the functional 5-HT_2AR and quantified a downstream signaling target, activation (phosphorylation) of extracellular regulated kinases 1/2 (ERK_1/2), in comparison to in vivo efficacy of altering spontaneous or cocaine-evoked locomotor activity in rats. All of the synthetic compounds inhibited 5-HT-mediated phosphorylation of ERK_1/2 in the cellular signaling assay; the potency of the bivalent ligands varied as a function of linker length, with the intermediate linker lengths being the most potent. The K_i values for the binding of bivalent ligands to 5-HT_2AR were only slightly lower than the values for the parent (+)-M100907 compound, but significant selectivity for 5-HT_2AR over 5-HT_2BR or 5-HT_2CR binding was retained. In addition, the 11-atom-linked bivalent 5-HT_2AR antagonist (2 mg/kg, intraperitoneally) demonstrated efficacy on par with that of (+)-M100907 in inhibiting cocaine-evoked hyperactivity. As we develop further strategies for ligand-evoked receptor assembly and analyses of diverse signaling and functional roles, these novel homobivalent 5-HT_2AR antagonist ligands will serve as useful in vitro and in vivo probes of 5-HT_2AR structure and function.

Synthesis and activity of functionalizable derivatives of the serotonin (5-HT) 5-HT2A receptor (5-HT2AR) antagonist M100907

The approach of tethering together two known receptor ligands, to be used as molecular probes for the study of G protein-coupled receptor (GPCR) systems, has proven to be a valuable approach. Selective ligands that possess functionality that can be used to link to other ligands, are useful in the development of novel antagonists and agonists. Such molecules can also be attached to reporter molecules, such as fluorophores, for the study of GPCR dimerization and its role in signaling. The highly selective serotonin (5-HT) 5-HT_2A receptor (5-HT_2AR) antagonist M100907 (volinanserin) is of clinical interest in the treatment of neurological and mental health disorders. Here, we synthesized the most active (+)-M100907 enantiomer as well as a series of derivatives that possessed either an alkyne or an azide. The triazole resulting from the dipolar cycloaddition of these groups did not interfere with the ability of the bivalent ligand to act as an antagonist. Thus, we have synthesized a number of compounds which will prove useful in elucidating the role of the 5-HT_2AR in the central nervous system.

Diastereoselective synthesis of 1,3-disubstituted isoindolines and sultams via bronsted acid catalysis

Isoindolines and sultams formed under mild conditions.

Synthesis and Structure-Activity Relationships of Tool Compounds Based on WAY163909, a 5-HT2C Receptor Agonist

The development of probe molecules that can be used to investigate G protein-coupled receptor (GPCR) pharmacology, trafficking, and relationship with other GPCRs is an important and growing area of research. Here, we report the synthesis of analogues of the known selective serotonin (5-HT) 5-HT_2C receptor (5-HT_2CR) agonist WAY163909 which were designed to allow for the attachment of a second ligand, signaling or reporter molecules, as well as immobilization agents to the parent molecule with the maintenance of agonist activity. This goal was accomplished by the synthesis of novel molecules in which sites a-d were modified and resulting compounds were analyzed pharmacologically in vitro.

Spontaneous Deciduosarcoma in a Domestic Rabbit (Oryctolagus cuniculus)

Deciduosarcoma is a rare, hormonally dependent neoplasm with features of malignancy, previously reported only in rabbits enrolled in chronic toxicology studies involving estrogens with or without progestins. An exploratory laparotomy was performed on a 6-year-old pet Dutch dwarf rabbit following palpation of a 6-cm-diameter abdominal mass. Grossly, the mass was fleshy and nodular, adhered to but not appearing to originate from the small intestine, with a smaller mass of similar appearance involving the uterus, and an effaced mesenteric lymph node. Histologically, the mass was characterized by spindloid cells and large epithelioid cells with abundant pale eosinophilic vacuolated cytoplasm and an infiltrative pattern of growth. Giant cells with large, bizarre, hyperchromatic nuclei were common. Cells were positive by immunohistochemistry for vimentin and progesterone and estrogen receptors and negative for pancytokeratin (AE1/AE3), cytokeratin 18, desmin, alpha-smooth muscle actin (SMA), and CD10. Based on histologic and immunohistochemical findings, a diagnosis of deciduosarcoma was made.

[4+2+2] Cycloaddition catalyzed by a new cationic rhodium-bisphosphine monooxide complex

A rhodium-BozPHOS based complex is reported. This complex is competent in catalyzing the [4+2+2] cycloisomerization of cyclooctatrienes in moderate to good yields. The X-ray crystal structure of this complex is reported, along with formation of both bicyclic and tricyclic cyclooctatrienes.

Synthesis of a 2(1H)-pyridone library via rhodium-catalyzed formation of isomunchones

Through the use of the dipolar cycloaddition of isomunchones with olefins the 2(1H)-pyridone ring system has been synthesized. (1) The use of different cyclization partners followed by diversification of the initial scaffold has provided libraries of 4-hydroxy-2(1H)-pyridones. There are no examples of this ring system in either PubChem or the MLSMR.

Synergism between a serotonin 5-HT2A receptor (5-HT2AR) antagonist and 5-HT2CR agonist suggests new pharmacotherapeutics for cocaine addiction

Relapse to cocaine dependence, even after extended abstinence, involves a number of liability factors including impulsivity (predisposition toward rapid, unplanned reactions to stimuli without regard to negative consequences) and cue reactivity (sensitivity to cues associated with cocaine-taking which can promote cocaine-seeking). These factors have been mechanistically linked to serotonin (5-hydroxytryptamine, 5-HT) signaling through the 5-HT(2A) receptor (5-HT(2A)R) and 5-HT(2C)R; either a selective 5-HT(2A)R antagonist or a 5-HT(2C)R agonist suppresses impulsivity and cocaine-seeking in preclinical models. We conducted proof-of-concept analyses to evaluate whether a combination of 5-HT(2A)R antagonist plus 5-HT(2C)R agonist would have synergistic effects over these liability factors for relapse as measured in a 1-choice serial reaction time task and cocaine self-administration/reinstatement assay. Combined administration of a dose of the selective 5-HT(2A)R antagonist M100907 plus the 5-HT(2C)R agonist WAY163909, each ineffective alone, synergistically suppressed cocaine-induced hyperactivity, inherent and cocaine-evoked impulsive action, as well as cue- and cocaine-primed reinstatement of cocaine-seeking behavior. The identification of synergism between a 5-HT(2A)R antagonist plus a 5-HT(2C)R agonist to attenuate these factors important in relapse indicates the promise of a bifunctional ligand as an anti-addiction pharmacotherapeutic, setting the stage to develop new ligands with improved efficacy, potency, selectivity, and in vivo profiles over the individual molecules.

Structure-based redesign of an edema toxin inhibitor

Edema factor (EF) toxin of Bacillus anthracis (NIAID category A), and several other toxins from NIAID category B Biodefense target bacteria are adenylyl cyclases or adenylyl cyclase agonists that catalyze the conversion of ATP to 3',5'-cyclic adenosine monophosphate (cAMP). We previously identified compound 1 (3-[(9-oxo-9H-fluorene-1-carbonyl)-amino]-benzoic acid), that inhibits EF activity in cultured mammalian cells, and reduces diarrhea caused by enterotoxigenic Escherichia coli (ETEC) at an oral dosage of 15μg/mouse. Here, molecular docking was used to predict improvements in potency and solubility of new derivatives of compound 1 in inhibiting edema toxin (ET)-catalyzed stimulation of cyclic AMP production in murine monocyte-macrophage cells (RAW 264.7). Structure-activity relationship (SAR) analysis of the bioassay results for 22 compounds indicated positions important for activity. Several derivatives demonstrated superior pharmacological properties compared to our initial lead compound, and are promising candidates to treat anthrax infections and diarrheal diseases induced by toxin-producing bacteria.

Synthesis and evaluation of dimeric derivatives of 5-HT(2A) receptor (5-HT(2A)R) antagonist M-100907

It is now well accepted that at least some serotonin receptors exist in dimeric and oligmeric forms. The linking of receptor ligands has been shown to have potential in the development of selective agonists and antagonists for traditionally refractive receptors. Here we report the development of a dimeric version of the known 5-HT(2A)R antagonist, M-100907. Derivatives of M-100907 were synthesized to determine an appropriate site for the linker connection. Then, homodimers with polyether linkers of different lengths were functionally tested in a bioassay to determine the optimal linker length. Attachment at the catechol of M-100907 with linkers between 12 and 18 atoms in length proved to be optimal.

Design, synthesis, and diversification of 3,5-substituted enone library

This paper describes the synthesis of a 300 member library of 3,5-substituted enones. The synthesis starts with 6 different bromoenones that are accessed from the corresponding 1,3 diones. These bromides are then diversified by Suzuki coupling with a variety of aromatic and vinyl boronic acids. Additionally a small series of triazoles was synthesized by a Sonogashira coupling reaction dipolar cycloaddition sequence. The library was analyzed by principal component analysis to examine its diversity.

Pd-NHC catalyzed cyclopentannulation of diazabicyclic alkenes with ortho-aryl halides

Pd-NHC catalyzed cyclopentannulation of diazabicyclic alkenes with ortho- functionalized aryl halides is described. In all the reactions, a single diastereomer of the cyclopentannulated product is observed, and this reaction is very efficient under microwave irradiation.

One-pot synthesis of unsymmetrical N-heterocyclic carbene ligands from N-(2-iodoethyl)arylamine salts

An approach that provides symmetrical, unsymmetrical, and asymmetric N-heterocyclic carbene (NHC) ligands is reported. Reaction of iodoethanol with aniline provides N-(2-iodoethyl)arylamine salts that are then converted to the corresponding iodide. Reaction with aliphatic or aromatic amines followed by triethyl orthoformate was used to provide 26 different NHC ligands.

Novel pyridopyrimidine derivatives as inhibitors of stable toxin a (STa) induced cGMP synthesis

A series of pyridopyrimidine derivatives were synthesized and evaluated for their ability to inhibit cyclic nucleotide synthesis in the presence of stable toxin a of Escherichia coli. The structure activity relationships around the basic core structure were examined and examples with better activity and potentially better pharmacological properties are presented.

Chemical genetic screening of KRAS-based synthetic lethal inhibitors for pancreatic cancer

Pancreatic cancer is one of the deadliest diseases largely due to difficulty in early diagnosis and the lack of effective treatments. KRAS is mutated in more than 90% of pancreatic cancer patients, and oncogenic KRAS contributes to pancreatic cancer tumorigenesis and progression. In this report, using an oncogenic KRASV12-based pancreatic cancer cell model, we developed a chemical genetic screen to identify small chemical inhibitors that selectively target pancreatic cancer cells with gain-of-function KRAS mutation. After screening ~3,200 compounds, we identified one compound that showed selective synthetic lethality against the KRASV12 transformed human pancreatic ductal epithelial cell over its isogenic parental cell line. These selective KRASV12-synthetic lethal compounds may serve as leads for subsequent development of clinically-effective treatments for pancreatic cancer.

Preparation of a library of unsymmetrical ureas based on 8-azabicyclo[3.2.1]octane scaffold

This paper reports the preparation of a library of unsymmetrical ureas based on 8-azabicyclo[3.2.1]octane scaffold. The reported synthetic route uses nortropane-8-carbonyl chlorides as key intermediates that, when treated with a slight excess of amine, give the corresponding ureas in high yield (129 examples).

Synthesis and screening of small molecule inhibitors of anthrax edema factor

The synthesis and development of a novel class of molecules that inhibit anthrax edema factor, an adenylyl cyclase, is reported. These molecules are derived from the initial discovery that histidine and imidazole adducts of the prostaglandin PGE(2) reduce the net secretory response of cholera toxin-challenged mice and act directly on the action of anthrax edema factor, a calmodulin-dependent adenylyl cyclase. The simple enones examined in this letter were prepared by palladium-catalyzed Suzuki reaction.

Substrate specificity and screening of the integral membrane protease Pla

This paper reports a study to find small peptide substrates for the important virulence factor of Yersinia pestis, plasminogen activator, Pla. The method used to find small substrates for this protease is reported along with studies examining the ability of these peptides to inhibit activity of the enzyme. Through the use of parallel synthesis and positional scanning, small tripeptides were identified that are viable substrates for the protease.

Synthesis and screening of 3-substituted thioxanthen-9-one-10,10-dioxides

This manuscript describes methods appropriate for the parallel synthesis of libraries based on the tricyclic thioxanthen-9-one-10,10-dioxide scaffold. The novel compounds were synthesized from previously reported 3-chlorothioxanthen-9-one-10,10-dioxide and commercially available 3-carboxylic acid thioxanthen-9-one-10,10-dioxide. The library members were screened for activity in a fluorescence polarization assay for inhibitors of BRCT domains of breast cancer gene 1 and in cell-based secreted alkaline phosphatase reported replicon system for activity against hepatitis C virus.

Rhodium-Catalyzed Synthesis of Eight-Membered Rings

Experiments to develop a rhodium catalyst for the [4 + 2 + 2] cycloisomerization of dienynes with a second alkyne are described. The generality of the reaction is probed in terms of dienyne structure and alkyne structure. A catalyst system that provides cyclooctatrienes in greater than 70% yield is reported. Several experiments to determine the nature of the catalyst are described.

Development of building blocks for the synthesis of N-heterocyclic carbene ligands

[reaction: see text] The synthesis of a series of NHC building blocks that can then be incorporated into more complicated structures by palladium catalysis is reported. This approach is used for the synthesis of three amino acids containing NHC side chains. The ability to use the amino acids in solid-phase peptide synthesis to make NHC-containing peptides is also demonstrated. Additionally, the NHC side chain can be deprotected and coordinated to a catalytically active transition metal. Finally, it is illustrated that the building blocks participate in Suzuki coupling to provide access to substituted NHC ligands.

Synthesis of phosphine containing amino acids: utilization of peptide synthesis in ligand design

Combinatorial chemistry has recently burst on the scene as a valuable tool for the discovery of new drug candidates. The ability to synthesize hundreds of compounds for screening is a useful complement to rational drug design. There are many similarities between the design of new therapeutic agents and the development of new asymmetric ligands, the most important of which is the limitation of a rational design strategy. For this reason a program was begun that would allow the use of combinatorial technology in the development of new ligands for transition metal catalyzed asymmetric reactions. Because of the large number of catalytic reactions they are involved in the system was based around phosphine ligands. This paper reports the synthesis of phosphine derivatives of alanine, proline, and the aromatic amino acids tyrosine and hydroxyphenylglycine. Examples of the use of these amino acids in the synthesis of peptides possessing helical and beta-turn secondary structures are presented. Metal complexes of these peptide-based ligands are used in hydrogenation and alkylation reactions.

Catalysis with Phosphine-Containing Amino Acids in Various “Turn” Motifs

We have been actively involved in the development of parallel approaches for the discovery of phosphine ligands. Our approach has been based on the incorporation of phosphine-containing amino acids into peptide sequences that are designed to have stable secondary structures. We have examined helical and turn secondary structures and have reported that alkylation of cyclopentenyl acetate with dimethylmalonate can be catalyzed in high enantiomeric excess (ee) with a beta-turn-based ligand. The importance of the peptide secondary structure was demonstrated through the synthesis of a series of peptide ligands where the nature of the turn-forming residues was probed. Additionally, other turn-forming units and a variety of different phosphine-containing amino acids have been examined for their ability to control the selectivity of the allylation reaction. This paper reports the results obtained through the examination of different turn motifs as well as different phosphine substitutions on the "best" turn sequence, Pps-Pro-d-Xxx-Pps.

High asymmetric induction with beta-turn-derived palladium phosphine complexes

[reaction: see text] Work toward the development of a bisphosphine ligand system for the palladium-catalyzed addition to cyclic allyl acetates is reported. A parallel approach using phosphine-containing amino acids in conjunction with natural amino acids was used to develop a selective ligand system. The ligand system was examined while attached to the polymer support as well as in solution. Selectivites with the difficult substrate 3-acetoxycyclopentene of up to 95% ee are reported.

Parallel approach to selective catalysts for palladium-catalyzed desymmetrization of 2,4-cyclopentenediol

[reaction: see text] Work toward the development of a bis-phosphine ligand system for the palladium-catalyzed desymmetrization of meso-diols is reported. A parallel approach using phosphine-containing amino acids and a "representational search" was taken to find a polymer-supported catalyst system. The selectivities reported are comparable to many other polymer-bound asymmetric catalysts.

Rhodium catalyzed [4 + 2 + 2] cycloaddition and alkyne insertion: a new route to eight-membered rings

A novel variation of the rhodium catalyzed [4 + 2] reaction is reported. A catalyst system that forms an eight-membered ring product from the incorporation of an alkyne into a dienyne is discussed. The products are formed with high diastereoselectivity and in good yield. The highest yields are obtained with alkynes that possess either an oxygen or nitrogen in the propargyl position. Examples are presented where the tether between the alkyne and the diene contains three or four atoms.