V. Subramanian

Computational design of high triplet energy host materials for phosphorescent blue emitters

A series of host molecules for blue electrophosphorescence have been designed using density functional theory by incorporating electron donors (carbazole (cbz) and diphenylamine (tph)) and electron acceptors (benzimidazole (bzi) and diphenylphosphine oxide (pho)) into the p-bis(triphenylsilyl)benzene (UGH2) moiety. Results obtained from the electronic structure calculations show that the triplet energy (ET), HOMO and LUMO energy levels and HOMO–LUMO gap (Eg) of the designed hosts can be modulated through different linking topologies. Among the designed host molecules benzimidazole with an N-linkage exhibits a higher triplet energy, when compared to the same host with a C-linkage. Asymmetric substitution on an inert host (UGH2) more effectively tunes the charge injection barrier from neighboring layers, HOMO and LUMO energies and Eg than symmetric substitution. The electron injection barrier is substantially diminished when electron transporting units are substituted in the para-position of the core unit compared to the same in the meta-position. Among the newly designed host molecules mcbz–pN–bzi, pcbz–pN–bzi, and ptph–pN–bzi are found to be good host materials for blue emitting phOLEDs.

A Highly Selective Chemosensor for Cyanide Derived from a Formyl-Functionalized Phosphorescent Iridium(III) Complex

A new phosphorescent iridium(III) complex, bis[2,6-difluorophenyl-4-formylpyridinato-N,C4]iridium(III) (picolinate) (IrC), was synthesized, fully characterized by various spectroscopic techniques, and utilized for the detection of CN(-) on the basis of the widely known hypothesis of the formation of cyanohydrins. The solid-state structure of the developed IrC was authenticated by single-crystal X-ray diffraction. Notably, the iridium(III) complex exhibits intense red phosphorescence in the solid state at 298 K (ΦPL = 0.16) and faint emission in acetonitrile solution (ΦPL = 0.02). The cyanide anion binding properties with IrC in pure and aqueous acetonitrile solutions were systematically investigated using two different channels: i.e., by means of UV-vis absorption and photoluminescence. The addition of 2.0 equiv of cyanide to a solution of the iridium(III) complex in acetonitrile (c = 20 μM) visibly changes the color from orange to yellow. On the other hand, the PL intensity of IrC at 480 nm was dramatically enhanced ∼5.36 × 10(2)-fold within 100 s along with a strong signature of a blue shift of the emission by ∼155 nm with a detection limit of 2.16 × 10(-8) M. The cyanohydrin formation mechanism is further supported by results of a (1)H NMR titration of IrC with CN(-). As an integral part of this work, phosphorescent test strips have been constructed by impregnating Whatman filter paper with IrC for the trace detection of CN(-) in the contact mode, exhibiting a detection limit at the nanogram level (∼265 ng/mL). Finally, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed to understand the electronic structure and the corresponding transitions involved in the designed phosphorescent iridium(III) complex probe and its cyanide adduct.

Bader’s Theory of Atoms in Molecules (AIM) and its Applications to Chemical Bonding

AbstractIn this perspective article, the basic theory and applications of the “Quantum Theory of Atoms in Molecules” have been presented with examples from different categories of weak and hydrogen bonded molecular systems.n Graphical AbstractIn this perspective article, the basic theory and applications of the “Quantum Theory of Atoms in Molecules” have been presented with examples from different categories of weak and hydrogen bonded molecular systems.

Photophysical and electroluminescence properties of bis(2′,6′-difluoro-2,3′-bipyridinato-N,C4′)iridium(picolinate) complexes: effect of electron-withdrawing and electron-donating group substituents at the 4′ position of the pyridyl moiety of the cyclometalated ligand

Herein, we have synthesized a series of 2′,6′-difluoro-2,3′-bipyridine cyclometalating ligands by substituting electron-withdrawing (–CHO, –CF3, and –CN) and electron-donating (–OMe and –NMe2) groups at the 4′ position of the pyridyl moiety and utilized them for the construction of five new iridium(III) complexes (Ir1–Ir5) in the presence of picolinate as an ancillary ligand. The photophysical properties of the developed iridium(III) compounds were investigated with a view to understand the substituent effects. The strong electron-withdrawing (–CN) group containing the iridium(III) compound (Ir3) exhibits highly efficient genuine green phosphorescence (λmax = 508 nm) at room temperature in solution and in thin film, with an excellent quantum efficiency (ΦPL) of 0.90 and 0.98, respectively. On the other hand, the –CF3 group substituted iridium(III) compound (Ir2) displays a sky-blue emission (λmax = 468 nm) with a promising quantum efficiency (ΦPL = 0.88 and 0.84 in solution and in thin film, respectively). The –CHO substituted iridium(III) complex (Ir1) showed greenish-yellow emission (λmax = 542 nm). Most importantly, the strong electron-donating –NMe2 substituted iridium(III) complex (Ir5) gives a structureless and a broad emission profile in the wavelength region 450 to 700 nm (λmax = 520 nm) with a poor quantum efficiency. An intense blue phosphorescence with impressive quantum efficiency, especially in thin-film noted in the case of the –OMe substituted iridium(III) complex (Ir4). Comprehensive density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches have been performed on the ground and excited states of the synthesized iridium(III) complexes, in order to obtain information about the absorption and emission processes and to gain deeper insights into the photophysical properties. The combinations of a smaller ΔES1–T1 and higher contribution of 3MLCT in the emission process result in the higher quantum yields and lifetime values for complexes Ir1–Ir3. Multi-layered Phosphorescent Organic Light Emitting Diodes (PhOLEDs) were designed using the phosphorescent dopants Ir2, Ir3 and Ir4 and their elecroluminescence properties were evaluated. Compound Ir4 at a doping level of 5 wt% shows the best performance with an external quantum efficiency of 4.7%, in the nonoptimized device, and a power efficiency of 5.8 lm W−1, together with a true-blue chromacity CIEx,y = 0.15, 0.17 recorded at the maximum brightness of 33180 cd m−2.

Theoretical design of core modified (oxa and thia) porphyrin based organic dyes with bridging thiophene linkers

Density functional theory calculations at the B3LYP/6-31G* level of theory are employed to assess the suitability of core modified porphyrin analogs as organic dyes for solar cell application. The composite photosensitizer consists of a core modified (mono/di oxa and thia substituted) porphyrin as donor bridged at the β-position to the acceptor (cyanoacrylic acid group) by a thiophene unit. The vertical excitation energy of the modeled dyes is calculated using the time-dependent density functional theory (TD-DFT) approach. The designed sensitizers are screened based on their electronic properties, such as HOMO–LUMO gap, position of HOMO–LUMO energy levels with respect to the conduction band of TiO2 and redox potential of the electrolyte, UV-vis absorption spectra etc. The free energy of injection was also evaluated based on the redox properties of the dyes in their ground and excited states. Apart from investigating the electronic structure of the dyes, we have also carried out theoretical calculations to model the interaction of the dye with the surface of the semiconductor by considering a (TiO2)16 nanocluster.

Splicing modulators act at the branch point adenosine binding pocket defined by the PHF5A–SF3b complex

Pladienolide, herboxidiene and spliceostatin have been identified as splicing modulators that target SF3B1 in the SF3b subcomplex. Here we report that PHF5A, another component of this subcomplex, is also targeted by these compounds. Mutations in PHF5A-Y36, SF3B1-K1071, SF3B1-R1074 and SF3B1-V1078 confer resistance to these modulators, suggesting a common interaction site. RNA-seq analysis reveals that PHF5A-Y36C has minimal effect on basal splicing but inhibits the global action of splicing modulators. Moreover, PHF5A-Y36C alters splicing modulator-induced intron-retention/exon-skipping profile, which correlates with the differential GC content between adjacent introns and exons. We determine the crystal structure of human PHF5A demonstrating that Y36 is located on a highly conserved surface. Analysis of the cryo-EM spliceosome Bact complex shows that the resistance mutations cluster in a pocket surrounding the branch point adenosine, suggesting a competitive mode of action. Collectively, we propose that PHF5A–SF3B1 forms a central node for binding to these splicing modulators.

Evasion of immunosurveillance by genomic alterations of PPARγ/RXRα in bladder cancer

Muscle-invasive bladder cancer (MIBC) is an aggressive disease with limited therapeutic options. Although immunotherapies are approved for MIBC, the majority of patients fail to respond, suggesting existence of complementary immune evasion mechanisms. Here, we report that the PPARγ/RXRα pathway constitutes a tumor-intrinsic mechanism underlying immune evasion in MIBC. Recurrent mutations in RXRα at serine 427 (S427F/Y), through conformational activation of the PPARγ/RXRα heterodimer, and focal amplification/overexpression of PPARγ converge to modulate PPARγ/RXRα-dependent transcription programs. Immune cell-infiltration is controlled by activated PPARγ/RXRα that inhibits expression/secretion of inflammatory cytokines. Clinical data sets and an in vivo tumor model indicate that PPARγHigh/RXRαS427F/Y impairs CD8+ T-cell infiltration and confers partial resistance to immunotherapies. Knockdown of PPARγ or RXRα and pharmacological inhibition of PPARγ significantly increase cytokine expression suggesting therapeutic approaches to reviving immunosurveillance and sensitivity to immunotherapies. Our study reveals a class of tumor cell-intrinsic “immuno-oncogenes” that modulate the immune microenvironment of cancer.Muscle-invasive bladder cancer (MIBC) is a potentially lethal disease. Here the authors characterize diverse genetic alterations in MIBC that convergently lead to constitutive activation of PPARgamma/RXRalpha and result in immunosurveillance escape by inhibiting CD8+ T-cell recruitment.

H3B-6527 Is a Potent and Selective Inhibitor of FGFR4 in FGF19-Driven Hepatocellular Carcinoma

Activation of the fibroblast growth factor receptor FGFR4 by FGF19 drives hepatocellular carcinoma (HCC), a disease with few, if any, effective treatment options. While a number of pan-FGFR inhibitors are being clinically evaluated, their application to FGF19-driven HCC may be limited by dose-limiting toxicities mediated by FGFR1-3 receptors. To evade the potential limitations of pan-FGFR inhibitors, we generated H3B-6527, a highly selective covalent FGFR4 inhibitor, through structure-guided drug design. Studies in a panel of 40 HCC cell lines and 30 HCC PDX models showed that FGF19 expression is a predictive biomarker for H3B-6527 response. Moreover, coadministration of the CDK4/6 inhibitor palbociclib in combination with H3B-6527 could effectively trigger tumor regression in a xenograft model of HCC. Overall, our results offer preclinical proof of concept for H3B-6527 as a candidate therapeutic agent for HCC cases that exhibit increased expression of FGF19. Cancer Res; 77(24); 6999-7013. ©2017 AACR.

Abstract DDT01-04: Discovery and development of H3B-6545: A novel, oral, selective estrogen receptor covalent antagonist (SERCA) for the treatment of breast cancer

Mutations in the estrogen receptor (ER) are detected in up to 30% of patients that initially respond but subsequently relaps to anti-endocrine therapies. ERα mutations, likely through constitutively activating ERα, can functionally confer resistance to existing classes of endocrine therapies. Current endocrine therapies are only partially effective in the ERα mutant setting and a significant proportion of endocrine-therapy resistant breast cancer metastases continue to remain dependent on ERα signaling for growth/survival indicating a critical need to develop the next generation of ERα antagonists that can overcome ERα wild-type and mutant activity. Here we describe a novel series of compounds with a unique mode of inhibition that potently target both wild-type and mutant ERα. These compounds are Selective Estrogen Receptor Covalent Antagonists (SERCAs) that inactivate the estrogen receptor by targeting a cysteine that is not present in other nuclear hormone receptors, leading to a unique biological and activity profile differentiated from Selective Estrogen Receptor Modulators (SERMs) and Selective Estrogen Receptor Degraders (SERDs). Using structure-based drug design approaches we have identified a first-in-class clinical candidate, H3B-6545. H3B-6545 is a highly selective small molecule that potently antagonizes wild-type and mutant ERα in biochemical and cell based assays. In vitro comparisons with standard of care and other experimental agents confirm increased cell potency of H3B-6545 under continuous as well as washout treatment conditions. In vivo, once daily oral dosing of H3B-6545 shows potent activity and superior efficacy to fulvestrant in the MCF-7 xenograft model with maximal antitumor activity at doses >10x below the maximum tolerated dose in mice. In addition, H3B-6545 shows superior antitumor activity to tamoxifen and fulvestrant in patient derived xenograft models of estrogen receptor positive breast cancer including models carrying ERα mutations In non-clinical safety studies in rat and monkeys, H3B-6545 is well tolerated across a broad dose range and at exposures that significantly exceed those required for efficacy in mouse xenograft models. In summary, H3B-6545 is a first-in-class, orally available and potent selective estrogen receptor covalent antagonist with a compelling preclinical efficacy and safety profile that is being developed for the treatment of breast cancer. Citation Format: Peter G. Smith, Xiaoling Puyang, Craig Furman, Guo Zhu Zheng, Deepti Banka, Michael Thomas, Vanitha Subramanian, Sean Irwin, Nicholas Larsen, Benjamin Caleb, Craig Karr, Jeremy Wu, Morgan O’Shea, Joyce Yang, Allison Davis, Amy Kim, Nathalie Rioux, Victoria Rimkunas, Huilan Yao, Crystal MacKenzie, Pavan Kumar, Sherri Smith, Sean Eckley, Andrew Hart, George Lai, Christopher Rowbottom, Peter Fekkes, Silvia Buonamici, Dominic Reynolds, Lihua Yu, Tarek Sahmoud, Markus Warmuth, Lorna Mitchell, Ping Zhu, Manav Korpal. Discovery and development of H3B-6545: A novel, oral, selective estrogen receptor covalent antagonist (SERCA) for the treatment of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr DDT01-04. doi:10.1158/1538-7445.AM2017-DDT01-04