2‐Bromo‐6‐(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)pyridine,a new unexpected bifunctional building block for combinatorial chemistry

The first reported structure of a pyridin‐2‐ylboron derivative, viz. the title compound, C₁₁H₁₅BBrNO₂, (I), is compared with its regioisomer 2‐bromo‐5‐(4,4,5,5‐tetra­methyl‐1,3,2‐dioxa­borolan‐2‐yl)­pyridine, (II) [Sopková‐de Oliveira Santos, Lancelot, Bouillon & Rault (2003). Acta Cryst. C59, o111o113 ]. Structural differences are observed, firstly in the orientation of the dioxaborolane ring with respect to the pyridine ring and secondly in the bond angles of the BO₂ group. These differences do not explain the experimentally observed differences in chemical reactivity between (I) and (II) but do confirm the relatively lower stability of (I). However, ab initio calculations of the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), based on the known crystal structures of the two compounds, show different distributions, which correspond to the differences observed during chemical reactions.     

A directing group switch in copper-catalyzed electrophilic C–H amination/migratory annulation cascade: divergent access to benzimidazolone/benzimidazole

We present here a copper-catalyzed electrophilic ortho C–H amination of protected naphthylamines with N-(benzoyloxy)amines, cyclization with the pendant amide, and carbon to nitrogen 1,2-directing group migration cascade to access N,N-disubstituted 2-benzimidazolinones. Remarkably, this highly atom-economic tandem reaction proceeds through a C–H and C–C bond cleavage and three new C–N bond formations in a single operation. Intriguingly, the reaction cascade was altered by the subtle tuning of the directing group from picolinamide to thiopicolinamide furnishing 2-heteroaryl-imidazoles via the extrusion of hydrogen sulfide. This strategy provided a series of benzimidazolones and benzimidazoles in moderate to high yields with low catalyst loading (66 substrates with yields up to 99%). From the control experiments, it was observed that after the C–H amination an incipient tetrahedral oxyanion or thiolate intermediate is formed via an intramolecular attack of the primary amine to the amide/thioamide carbonyl. It undergoes either a 1,2-pyridyl shift with the retention of the carbonyl moiety or H₂S elimination for scaffold diversification. Remarkably, inspite of a positive influence of copper in the reaction outcome, from our preliminary investigations, the benzimidazolone product was obtained in good to moderate yields in two steps under metal-free conditions. The N-pyridyl moiety of the benzimidazolone was removed for further manipulation of the free NH group.

A novel directing group switch strategy is explored in a copper-catalyzed divergent synthesis of benzimidazolone via electrophilic C–H amination/cyclization/1,2-C → N directing group migration cascade and benzimidazole through the extrusion of H₂S.     

Targeting Mechanisms of the DNA Damage Response (DDR) and DNA Repair by Natural Compounds to Improve cAT-Triggered Tumor Cell Death

Recently, we identified secalonic acid F (SA), 5-epi-nakijiquinone Q (NQ) and 5-epi-ilimaquinone (IQ) as natural compounds (NC) affecting mechanisms of the DNA damage response (DDR). Here, we further characterized their effects on DDR, DNA repair and cytotoxicity if used in mono- and co-treatment with conventional anticancer therapeutics (cAT) (cisplatin (Cis), doxorubicin (Doxo)) in vitro. All three NC influence the phosphorylation level of selected DDR-related factors (i.e., pCHK1, pKAP1, pP53, pRPA32) in mono- and/or co-treatment. Both SA and NQ attenuate the Cis- and Doxo-induced G2/M-phase arrest and effectively stimulate caspase-mediated apoptosis. Notably, SA impacts DNA repair as reflected by enhanced steady-state levels of Cis-(1,2-GpG)-DNA adducts and Doxo-induced DNA double-strand breaks (DSB). Moreover, SA decreased the mRNA and protein expression of the homologous recombination (HR)-related DSB repair factors RAD51 and BRCA1. Both SA and NQ promote Cis- and Doxo-induced cytotoxicity in an additive to synergistic manner (CI ≤ 1.0). Summarizing, we conclude that SA promotes cAT-driven caspase-dependent cell death by interfering with DSB repair and DDR-related checkpoint control mechanisms. Hence, SA is considered as the most promising lead compound to evaluate its therapeutic window in forthcoming pre-clinical in vivo studies.     

Synthesis of polyurethane from cashew nut shell liquid (CNSL), a renewable resource

A novel thermoplastic polyurethane was prepared from cardanol, a renewable resource and a waste of the cashew industry. Cardanol was recovered from cashew nut shell liquid (CNSL) by double vacuum distillation. It was characterized by CHN analysis and IR, ¹H-NMR, and ¹³C-NMR spectroscopy techniques. Cardanol is a meta-substituted long chain phenol. The long aliphatic chain unit substituent was found to be a monoene. The monomer, 4-[(4-hydroxy-2-pentadecenylphenyl)diazenyl]phenol was prepared from cardanol. It was a dihydroxy compound as characterized by CHN analyzer, UV, and ¹H-NMR spectroscopy. The polyurethane was synthesized from this dihydroxy compound by the treatment with 4,4′-diphenylmethane diisocyanate (MDI) in dimethylformamide (DMF) solvent at 80–90°C under nitrogen atmosphere. The polymer was characterized by ¹H-NMR, FTIR, and UV spectroscopy. The elemental analysis was done for determining the percentage content of C, H, and N, and the intrinsic viscosity [η] of polymer showed 1.85 dL/gm. Thermogravimetric investigations (TGA) of the cardanol, the dihydroxy compound, and the polyurethane were performed to study their decomposition. The semicrystalline nature of the PU was confirmed by differential scanning calorimetry (DSC) and dynamic mechanical thermal analyzer (DMTA). The wide-angle X-ray diffraction (WAXS) study of PU shew a broad amorphous halo indicative of absence of crystallinity in the polymer, which has been explained as due to strong hydrogen bonding in the hard phase. PU may possibly be useful as a telecommunication and as a nonlinear optical material. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36 : 391–400, 1998     

Nonobtuse tetrahedral partitions

We show how to generate refinements of tetrahedral partitions, where no obtuse angles appear. Such partitions play an important role in deriving discrete maximum principles and maximum norm error estimates for the finite element method. © 2000 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 16: 327–334, 2000     

Energetics,Conformation, and Recognition of DNA Duplexes Modified by Monodentate RuII Complexes Containing Terphenyl Arenes

We studied the thermodynamic properties, conformation, and recognition of DNA duplexes site‐specifically modified by monofunctional adducts of Ru^II complexes of the type [Ru^II(η⁶‐arene)(Cl)(en)]⁺, in which arene=para‐, meta‐, or ortho‐terphenyl (complexes 1 , 2 , and 3 , respectively) and en=1,2‐diaminoethane. It has been shown (J. Med. Chem. 2008 , 51, 5310) that 1 exhibits promising cytotoxic effects in human tumor cells, whereas 2 and 3 are much less cytotoxic; concomitantly with the high cytotoxicity of 1 , its DNA binding mode involves combined intercalative and monofunctional (coordination) binding modes, whereas less cytotoxic compounds 2 and 3 bind to DNA only through a monofunctional coordination to DNA bases. An analysis of conformational distortions induced in DNA by adducts of 1 and 2 revealed more extensive and stronger distortion and concomitantly greater thermodynamic destabilization of DNA by the adducts of nonintercalating 2 . Moreover, affinity of replication protein A to the DNA duplex containing adduct of 1 was pronouncedly lower than to the adduct of 2 . On the other hand, another damaged‐DNA‐binding protein, xeroderma pigmentosum protein A, did not recognize the DNA adduct of 1 or 2 . Importantly, the adducts of 1 induced a considerably lower level of repair synthesis than the adducts of 2 , which suggests enhanced persistence of the adducts of the more potent and intercalating 1 in comparison with the adducts of the less potent and nonintercalating 2 . Also interestingly, the adducts of 1 inhibited DNA polymerization more efficiently than the adducts of 2 , and they could also be bypassed by DNA polymerases with greater difficulty. Results of the present work along with those previously published support the view that monodentate Ru^II arene complexes belong to a class of anticancer agents for which structure–pharmacological relationships might be correlated with their DNA‐binding modes.     

Synthesis of iboga alkaloids by Pd-catalyzed heteroannulation of 2-iodoaniline with an internal alkyne as the key step

A convenient synthetic route to the iboga-scaffolds is described. Important steps include a Pd-catalyzed regiospecific indole formation between internal alkyne-substituted isoquinuclidine and 2-iodoaniline. The final cyclization was done using Trost’s Pd(II)-Ag(I) mixed-metal-mediated cyclization method originally developed for the synthesis of ibogamine. Both exo- (iboga) and endo-isomers (epi-iboga) at C-19 substitution with -CO₂Me have been reported.