Additional Substituents Research Articles

Synthesis of Allahabadolactone A

A synthesis of allahabadolactone A is described employing diastereoselective Diels-Alder and selenocyclization reactions, starting from (R)-citronellal and propylene oxide. The Diels-Alder substrate is built up in an efficient manner by rhodium-catalyzed alkyne hydroboration and palladium-catalyzed coupling reactions of E-1,2-dichloroethene. It is observed that the Diels-Alder reaction only displays high diastereoselectivity when the diene bears an additional alkene substituent but not an alkyne substituent.

Induction of Single-Handed Helicity of Polyacetylenes Using Mechanically Chiral Rotaxanes as Chiral Sources.

Effective induction of preferred-handed helicity of polyacetylenes by pendant mechanically chiral rotaxanes is discussed. Polyacetylenes possessing optically active mechanically chiral rotaxanes in the side chains were synthesized by the polymerization of the corresponding enantiopure [2]rotaxane-type ethynyl monomers prepared by the chiral-phase HPLC separations. The CD Cotton effects revealed that the polyacetylenes took preferred-handed helical conformations depending on the rotaxane chirality. The preferred-handed helix was not disturbed by an additional chiral substituent on the rotaxane side chain. These results demonstrate the significance and utility of mechanically chiral rotaxanes for the effective construction of asymmetric fields.

Induction of Single‐Handed Helicity of Polyacetylenes Using Mechanically Chiral Rotaxanes as Chiral Sources

AbstractEffective induction of preferred‐handed helicity of polyacetylenes by pendant mechanically chiral rotaxanes is discussed. Polyacetylenes possessing optically active mechanically chiral rotaxanes in the side chains were synthesized by the polymerization of the corresponding enantiopure [2]rotaxane‐type ethynyl monomers prepared by the chiral‐phase HPLC separations. The CD Cotton effects revealed that the polyacetylenes took preferred‐handed helical conformations depending on the rotaxane chirality. The preferred‐handed helix was not disturbed by an additional chiral substituent on the rotaxane side chain. These results demonstrate the significance and utility of mechanically chiral rotaxanes for the effective construction of asymmetric fields.

Base-modified GDP-mannose derivatives and their substrate activity towards a yeast mannosyltransferase

We have previously developed a new class of inhibitors and chemical probes for glycosyltransferases through base-modification of the sugar-nucleotide donor. The key feature of these donor analogues is the presence of an additional substituent at the nucleobase. To date, the application of this general concept has been limited to UDP-sugars and UDP-sugar-dependent glycosyltransferases. Herein, we report for the first time the application of our approach to a GDP-mannose-dependent mannosyltransferase. We have prepared four GDP-mannose derivatives with an additional substituent at either position 6 or 8 of the nucleobase. These donor analogues were recognised as donor substrates by the mannosyltransferase Kre2p from yeast, albeit with significantly lower turnover rates than the natural donor GDP-mannose. The presence of the additional substituent also redirected enzyme activity from glycosyl transfer to donor hydrolysis. Taken together, our results suggest that modification of the donor nucleobase is, in principle, a viable strategy for probe and inhibitor development against GDP-mannose-dependent GTs.

Pyrrolo[2,3-d]pyrimidine (7-deazapurine) as a privileged scaffold in design of antitumor and antiviral nucleosides.

7‐Deazapurine (pyrrolo[2,3‐d]pyrimidine) nucleosides are important analogues of biogenic purine nucleosides with diverse biological activities. Replacement of the N7 atom with a carbon atom makes the five‐membered ring more electron rich and brings a possibility of attaching additional substituents at the C7 position. This often leads to derivatives with increased base‐pairing in DNA or RNA or better binding to enzymes. Several types of 7‐deazapurine nucleosides with potent cytostatic or cytotoxic effects have been identified. The most promising are 7‐hetaryl‐7‐deazaadenosines, which are activated in cancer cells by phosphorylation and get incorporated both to RNA (causing inhibition of proteosynthesis) and to DNA (causing DNA damage). Mechanism of action of other types of cytostatic nucleosides, 6‐hetaryl‐7‐deazapurine and thieno‐fused deazapurine ribonucleosides, is not yet known. Many 7‐deazaadenosine derivatives are potent inhibitors of adenosine kinases. Many types of sugar‐modified derivatives of 7‐deazapurine nucleosides are also strong antivirals. Most important are 2′‐C‐methylribo‐ or 2′‐C‐methyl‐2′‐fluororibonucleosides with anti‐HCV activities (several compounds underwent clinical trials). Some underexplored areas of potential interest are also outlined.

Gallium Complexation, Stability, and Bioconjugation of 1,4,7-Triazacyclononane Derived Chelators with Azaheterocyclic Arms.

We have recently introduced a 1,4,7-triazacyclononane (TACN) based chelating system with additional five-membered azaheterocyclic substituents for complexation of radioactive Cu2+ ions. In this work, we investigated the complexation properties of these novel chelators with Ga3+. In labeling experiments, we could show that the penta- and hexadentate imidazole derivatives NODIA-Me 4 and NOTI-Me 1 can be labeled with 68Ga in specific activities up to ∼30 MBq nmol-1, while the corresponding thiazole derivative NOTThia 2 did not label satisfactorily under identical conditions. NMR studies on the Ga complexes of 1 and the model compound NODIA-Me-NH-Me 5 revealed formation of rigid 1:1 chelates with a slow macrocyclic interconversion and inert Ga-N bonds to the methylimidazole residues on the NMR time scale. The TACN-derived bifunctional chelator NODIA-Me was furthermore conjugated to a prostate-specific membrane antigen (PSMA) targeting moiety to give the corresponding bioconjugate NODIA-Me-PSMA 7. Serum stability and ligand challenge experiments of 68Ga-7 confirmed formation of a stable complex for up to 4 h. The remaining coordination site of five-coordinate Ga complexes was found to be occupied by monodentate ligands including hydroxide and chloride anions depending on the conditions. According to density functional theory calculations, coordination of monodentate ligands as well as of the amide group for the bioconjugated ligand are energetically plausible. Finally, the labeled bioconjugate 68Ga-7 exhibited rapid renal clearance in biodistribution studies performed by small animal PET imaging with no indication of transchelation/demetalation in vivo. Altogether, our results provide strong evidence for a stable Ga complexation of our novel TACN-based chelators bearing imidazole arms. Despite the formation of two complexes incorporating different monodentate ligands in vitro, the imidazole type ligands show promise as chelating agents for the future development of gallium based radiopharmaceuticals.

3,5-Bis(3-dimethylaminomethyl-4-hydroxybenzylidene)-4-piperidone and related compounds induce glutathione oxidation and mitochondria-mediated cell death in HCT-116 colon cancer cells

This study aims at investigating the cytotoxicity and some of the modes of action of 3,5-bis(3-dimethylamino-4-hydroxybenzylidene)-4-piperidone trihydrochloride 3 and two related compounds 2 (which lacks the dimethylaminomethyl groups) and 4 (which has an additional dimethylaminoethyl substituent in both aryl rings) in order to ascertain the contribution of dimethylaminoethyl substituent to bioactivity. The bioactivities of 2–4 were compared with curcumin 5. Both 2 and 3 displayed submicromolar GI50 values towards HCT-116 cells and were significantly more potent than 4, 5 and 5-fluorouracil (5-FU). All of the compounds displayed greater toxicity towards HCT-116 cells than human CRL-1790 non-malignant colon cells. In HCT-116 cells, the compounds 2, 3 and 5 increased the ratio of oxidised to reduced glutathione and destabilized the mitochondrial membrane potential. Both 2 and 5 produced an increase in mitochondrial superoxide and a burst in intracellular reactive oxygen species in HCT 116 cells. In addition, 2 and 4 stimulated respiration in rat liver mitochondria while 2 and 5 induced mitochondrial swelling. The results suggest that 2 and 5 cause oxidation or cross-linking of the thiols which control the mitochondrial permeability transition.

Electrochemically Mediated Oxidative Transformations of Substituted 4-Methoxystilbenes: Effect of Ortho-Substituted Nucleophilic Groups.

A systematic study was undertaken to determine the influence of ortho'-substituted nucleophilic groups (OH, NH2, or NHR) on the reactivity of anodically generated 4-methoxy- and 3,4-dimethoxystilbene cation radicals. The results showed that when ortho-substituted nucleophilic groups such as OH and NHR are present in the other ring, both direct and crossover intramolecular cation-nucleophile reactions occur to give bisbenzofurans/bisindoles or fused bisbenzopyrans/bisquinolines, respectively. Where an additional 3-methoxy substituent is present, bridged oxocine/azocine products are formed in addition to the bisbenzopyrans/bisquinolines and bisbenzofurans/bisindoles. Mechanistic rationalization of the observed behavior is presented based on a generalized pathway involving fast cation radical dimerization following electron transfer, followed by direct and crossover trapping of the benzylic cations by the ortho-substituted oxygen and nitrogen nucleophilic groups. In the instances where an additional 3-methoxy group is present, the bridged oxocine/azocine products are also formed as a result of competing aromatic substitution (Friedel-Crafts reaction). The results have shed further light and provided additional clarification on the reactivity of anodically generated stilbene cation radicals.

Enantioselective Organocatalytic Synthesis of a Secoyohimbane-Inspired Compound Collection with Neuritogenic Activity.

Natural products provide evolutionary validated core structures to inspire the synthesis of new compound collections endowed with neurite growth-promoting activity. Rhynchophylline is the major component of Uncaria species, and has been used to treat neurological diseases in Chinese traditional medicine. Based on the structure of this spirocyclic secoyohimbane alkaloid, we developed a highly enantioselective and efficient organocatalyzed synthesis method to provide a tetracyclic secoyohimbane scaffold incorporating a quaternary and three tertiary stereogenic centers, in a one-pot multistep reaction sequence. A compound collection of derived secoyohimbanes was synthesized and expanded by decorating the periphery of the basic scaffold with additional substituents to increase the diversity. Evaluation of the different subcollections of secoyohimbanes for modulation of neurite outgrowth in the SH-SY5Y human cell line led to the discovery of new compounds that promote neurite outgrowth.

3′-(4-Chlorophenyl)-4′-phenyl-3H,4′H-spiro[benzo[b]thiophene-2,5′-isoxazol]-3-one

The molecule of the title compound, C22H14ClNO2S, is built up from an isoxazole ring linked to a benzothiophene ring system with additional phenyl and 4-chlorophenyl substituents. The benzothiophene system is virtually planar with the largest deviation from the mean plane being 0.041 (2) Å, while the isoxazole ring adopts an envelope conformation. The plane of the benzothiophene ring system is almost perpendicular to those of the phenyl and the 4-chlorophenyl rings, with dihedral angles of 64.76 (10) and 82.81 (10)°, respectively, between them. The phenyl ring is inclined by 85.76 (12)° to the plane of the 4-chlorophenyl ring, which in turn lies close to the plane of the isoxazole ring. In the crystal, molecules are linked by weak C—H...O hydrogen bonds and offset π–π interactions between the aromatic rings of adjacent benzothiophene ring systems. These combine to form a three-dimensional network structure.

Double‐stranded ladderphanes with C2‐symmetric planar chiral ferrocene linkers

ABSTRACTEight ladderphanes with C2‐symmetric planar chiral ferrocene linkers are synthesized by ring opening metathesis polymerization of bisnorbornene monomers using Grubbs‐I catalyst. The aminobenzoate in both monomers and polymers shows absorption maximum around 320 nm. Both monomers and polymers are Circular dichroism (CD) active. Little enhancements of CD profiles around 320 nm are observed for ladderphanes having chiral chloro‐ or phenyl‐substituted ferrocene linkers. However, ladderphanes with a phenyl substituent on the cyclopendienyl ring exhibits enhancement of CD curves aound 240–300 nm. The congested phenyl moieties in adjacent linkers in this polymer might be well oriented such that interactions between these aromatic substituents on different monomeric units might provoke the enhancement of the CD curves in this region. When the methyl‐substituted cyclopendienyl ligand is used for chiral ferrocene linkers, the ladderphanes exhibit two‐fold enhancement of CD spectrum around 320 nm. This enhancement is further increased when the cyclopentadienyl ligand contains an additional phenyl substituent, owing to exciton coupling between aminobenzoate moieties in adjacent monomeric units. Moreover, the intensity of the CD curves in the region of 240–300 nm is significantly increased. These results suggest that the later polymer may adopt a posible helical structure. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2999–3010

Synthesis of conformationally restricted 1,3-dioxanes to analyze the bioactive conformation of 1,3-dioxane-based σ1 and PCP receptor antagonists

The receptor binding profile of 2-phenyl-4-(aminoethyl)-1,3-dioxanes is dependent on the additional substituent in 2-position, the substituents at the amino moiety and the stereochemistry. Herein, conformationally restricted 1,3-dioxanes bearing an axially oriented phenyl moiety in 2-position were prepared and pharmacologically evaluated. Two subsequent intramolecular transacetalization reactions represent the key steps in the synthesis of the tricyclic system. The resulting alcohol 17 was transformed into amines 20–23 with axially (a-series) or equatorially oriented aminoethyl moiety (b-series). The primary amines 20a and 20b did not interact with the PCP binding site of the NMDA receptor, which is explained by the additional methylene moiety between the acetalic center and the phenyl moiety, the missing substituent at the acetalic position and/or a non-optimal three-dimensional arrangement of the pharmacophoric elements. The benzylamine 21b with an equatorially oriented aminoethyl moiety shows high σ1 affinity (Ki=5.9nM). Compared with the conformationally flexible 1,3-dioxane 5, the σ1 affinity of 21b is 3-fold and the σ1/σ2 selectivity is 5-fold increased.

Pyridylpyrazole N^N ligands combined with sulfonyl-functionalised cyclometalating ligands for blue-emitting iridium(iii) complexes and solution-processable PhOLEDs.

A series of blue iridium(iii) complexes (12-15) comprising sulfonyl-functionalised phenylpyridyl cyclometalating ligands and pyridylpyrazole N^N ligands are reported, with an X-ray crystal structure obtained for 12. The complexes are highly emissive with photoluminescence quantum yields of 0.52-0.70 in dichloromethane solutions: two of the complexes (12 and 14) show emissions at λ 457 nm which is considerably blue-shifted compared to the archetypal blue emitter FIrpic (λmax 468 nm). The short excited state lifetimes (1.8-3.3 μs) and spectral profiles are consistent with phosphorescence from a mixture of ligand-centred and MLCT excited states. Density functional (DFT) and time dependent DFT (TD-DFT) calculations are in agreement with the electrochemical properties and the blue phosphorescence of the complexes. The additional mesityl substituent on the pyridylpyrazole ligand of 12 and 13 enhances the solubility of the complexes facilitating thin film formation by solution processing. Phosphorescent organic light-emitting diodes (PhOLEDs) have been fabricated using 12 or 13 in a solution-processed single-emitting layer using either poly(vinylcarbazole) (PVK) or 1,3-bis(N-carbazolyl)benzene (mCP) as host. The most blue-shifted electroluminescence (λ 460 nm, CIEx,y 0.15, 0.21) is obtained for an OLED containing complex 12 and mCP, with a brightness of 5400 cd m-2 at 10 V which is high for PhOLEDs with similar blue CIE coordinates using a solution-processed emitter layer.

Anodic Oxidation of 18 Halogenated and/or Methylated Derivatives of CB11H12.

Anodic oxidation of [CB11H12]- and 18 of its halogenated and/or methylated derivatives was examined. Reversible oxidation was found for four of the anions in liquid SO2 and for four more in 1,1,1,3,3,3-hexafluoroisopropyl alcohol. The oxidation occurred at ∼1 V (for [CB11Me12]-) up to more than 4 V (for [1-H-(2-6)-F5-(7-12)-(CF3)6-CB11]-) relative to ferrocene/ferricinium. The anodic peak potentials are reproduced by a set of additive position-sensitive substituent increments.

Local-Excitation versus Charge-Transfer Characters in the Triplet State: Theoretical Insight into the Singlet–Triplet Energy Differences of Carbazolyl-Phthalonitrile-Based Thermally Activated Delayed Fluorescence Materials

The singlet–triplet energy differences, ΔEST, of a series of carbazolyl-phthalonitrile (CzPN) derivatives were calculated at the levels of density functional theory (DFT) and time-dependent (TD) DFT using the gap-tuned, range-separated ωB97X functional. The studied CzPN derivatives include 4-(9H-carbazol-9-yl)phthalonitrile (CzPN), 4,5-di(9H-carbazol-9-yl)phthalonitrile (2CzPN), 3,4,5-tris(9H-carbazol-9-yl)phthalonitrile (3CzPN), and 3,4,5,6-tetra(9H-carbazol-9-yl)phthalonitrile (4CzPN). As additional Cz substituents are introduced, both the HOMO–LUMO energy gap, ΔEH–L, and ΔEST continuously decrease. Both natural transition orbital analysis and a quantitative assessment of the local-excitation (LE) and charge-transfer (CT) contributions to the excited states consistently demonstrate that the S1 states of all of the CzPN derivatives have a predominantly CT nature. In contrast, in the T1 state, the LE feature is dominant, but the CT character increases with the number of Cz groups. The decomposition of exc...

Reaction Chemistry to Characterize the Molecular Initiating Event in Skin Sensitization: A Journey to Be Continued.

The publication by the OECD of the adverse outcome pathway (AOP) for skin sensitization has accelerated the development and validation of mechanistic tests and testing strategies to assess the potential of new molecules to trigger skin allergies. The molecular initiating event (MIE) in the AOP is reaction with skin peptides/proteins. It is followed by a number of cellular events. Currently, only one in chemico test to characterize the MIE was proposed to and underwent adoption by the OECD, while two cell-based assays have completed the process. A multitude of further cellular assays is currently in the validation pipeline, but no further reactivity test has gone through full standardization. Here, we review data on in chemico methods, identify gaps, and discuss how these methods can be improved to better characterize the MIE and to become even more informative. We focus on the importance of kinetics, the information gained from studying adduct formation, and the difficulties posed by side reactions such as peptide oxidation. We then highlight mechanistic insights from reaction chemistry: the relative contribution of different target nucleophiles, the migration of amino acid modifications, and the potential of peptide-cross-linking. We illustrate in a case study how kinetic in chemico methods might have been used to better predict the risk of three preservatives, which have led to serious epidemics of contact dermatitis. In a case study on Michael acceptors, we show the impact of additional substituents around the electrophilic olefin moiety on reactivity, and we highlight the shortcomings which current in silico methods to predict reaction chemistry still have, illustrating the need for experimental in chemico data to improve such models. Finally, based on the information reviewed and the presented case studies, a strong argument is made to continue the journey of developing nonredundant, informative in chemico methods, and not to solely focus on new cell-based methods to further populate the AOP for skin sensitization.

DFT and structural studies of 2-oxo-1,2,3,4-tetrahydropyridines

Quantum chemical calculations based on density functional theory (DFT) and X-ray crystal structure analysis of some ethyl 4-aryl-6-methyl-2-oxo-1,2,3,4-tetrahydropyridine-5-carboxylates (THPYs) were applied in order to elucidate the effect of variations of the additional substituent on the C4-aryl ring on the molecular geometry, conformation and packing of molecules in the crystalline lattice. Due to the presence of the C4 stereocenter, these compounds exist as a racemic mixture in the crystal structure. Intermolecular interactions between the potential hydrogen donor (NH) and hydrogen acceptor (2-CO) of the heterocycle in the enantiomeric pair forming a sheet like dimeric structure, which provides especial stability to the crystal packing. The existence of the short intramolecular interactions (CH⋯π) and (CH⋯O) are a key feature which imparts also additional stability to the molecular conformation in the solid state. Most computational data including conformation of the heterocycle, the values of the bond lengths and angles are well in agreement with the experimental data. Ring flip calculations for 4-phenyl substituent explain the extreme torsional strain caused by the eclipsing of the carbon-hydrogen bonds in 3-CH2 moiety with the neighboring C4Caryl and C4H bonds and also the changes of some characteristic bond lengths and angles. These calculations indicate the more favored pseudo-axial orientation of the phenyl group over the pseudo-equatorial orientation.

Discovery of 2-((R)-4-(2-Fluoro-4-(methylsulfonyl)phenyl)-2-methylpiperazin-1-yl)-N-((1R,2s,3S,5S,7S)-5-hydroxyadamantan-2-yl)pyrimidine-4-carboxamide (SKI2852): A Highly Potent, Selective, and Orally Bioavailable Inhibitor of 11β-Hydroxysteroid Dehydrogenase Type 1 (11β-HSD1).

A series of picolinamide- and pyrimidine-4-carboxamide-based inhibitors of 11β-hydroxysteroid dehydrogenase type 1 was synthesized and evaluated to optimize the lead compound 9. The combination of the replacement of a pyridine ring of 9 with a pyrimidine ring and the introduction of an additional fluorine substituent at the 2-position of the phenyl ring resulted in the discovery of a potent, selective, and orally bioavailable inhibitor, 18a (SKI2852), which demonstrated no CYP and PXR liabilities, excellent PK profiles across species, and highly potent and sustainable PD activity. Repeated oral administration of 18a significantly reduced blood glucose and HbA1c levels and improved the lipid profiles in ob/ob mice. Moreover, the HbA1c-lowering effect of metformin was synergistically enhanced in combination with 18a.

Synthesis of morphan derivatives with additional substituents in 8-position

Abstract The morphan system (2-azabicyclo[3.3.1]nonane) as a substructure of morphine is of major interest in medicinal chemistry. Herein, the synthesis of morphan derivatives with additional substituents at the propano bridge is reported. In order to avoid the isolation of the smelly and volatile nitrile 6 and the very polar primary amine 9, an efficient one-pot, three-step sequential transformation of the mesylate 5 into amides 10 was developed. The key step of the synthesis was the stereoselective intramolecular opening of the epoxides 11a–d leading to the exo-configured 8-hydroxymorphans 12a–d. The configuration of the exo-configured hydroxymorphan 12d bearing the κ- and σ-pharmacophoric 3,4-dichlorophenylacetyl moiety was inverted by oxidation and stereoselective reduction. An X-ray crystal structure analysis of the benzamide 12c confirmed the relative configuration of the hydroxymorphans 12a–d and 14d.

ChemInform Abstract: The 4.4′‐Benzidine Rearrangement of 4‐Alkyl Substituted Hydrazobenzenes.

Abstract When treated with dilute inorganic acids N , N ′-diarylhydrazines (hydrazobenzenes) with an alkyl substituent in the 4-position undergo [5,5]-sigmatropic rearrangement reactions to furnish 4-(4′-aminophenyl)-4-alkylcyclohexa-2,5-dienimines ( ipso -benzidines) in moderate to excellent yields. Steric bulk of the 4-alkyl substituent in the starting material decreases the yield of the respective ipso -benzidine. Additional electron-donating alkyl substituents in the ortho - and/or meta -positions on both rings generally promote the reaction and consequently increase the yield of the 4.4′-benzidine rearrangement product. Described herein are our findings regarding the scope and limits of this unusual benzidine rearrangement.