Experimental and theoretical study of the mechanism and rate constants of the sequential 5-exo-trig spirocyclization involving vinyl, aryl and N-alkoxyaminyl radicals

In this research the sequential generation and cyclization of N-alkoxyaminyl radicals to produce 1-azaspiro[4.4]nonane, a prominent scaffold in organic and medicinal chemistry, was studied. Competition experiments in benzene at 80 °C with brominated oxime ethers using Bu₃SnH as chain transfer and AIBN as the initiator generated vinyl or aryl radicals which were captured by oxime ethers, allowing approximate 5-exo-trig cyclization constants at 4.6 × 10⁸ s^-1 and 9.9 × 10⁸ s^-1 respectively to be established. Similar results were obtained by kinetic studies using the transition state theory (TST) from ab initio calculations with density functional theory (DFT) using the M06-2X, B3LYP, mPW1PW91 and TPSSh functionals in combination with the 6-311+G(d, p) basis set. Additionally, it was found that the 5-exo-trig cyclization of the N-alkoxyaminyl radical onto CC double bonds is a reversible process whose constants were determined to be in the range of 6.2 × 10⁰ s^-1 and 3.5 × 10⁶ s^-1 at 80 °C, depending on the nature of the substituents. The calculation of the radical stabilization energy (RSE) shows that the N-alkoxyaminyl radical is a very stable species and its reactivity in the addition on alkenes is governed by its nucleophilic character and the stability of the carbon-centered radical formed after cyclization. The reduction constant of the N-alkoxyaminyl radical with Bu₃SnH in the gas phase at 80 °C was also estimated to be 3.4 × 10⁰ M^-1 s^-1 through computational calculations. This information facilitates the rational planning of cascades and other methodologies applied to the construction of carbocyclic and aza-heterocyclic compounds.

Structural and functional computational analysis of nicotine analogs as potential neuroprotective compounds in Parkinson disease

As the mechanism of interaction between nicotinic receptors with nicotine analogs is not yet fully understood, information at molecular level obtained from computational calculations is needed. In this sense, this work is a computational study of eight nicotine analogs, all with pyrrolidine ring modifications over a nicotine-based backbone optimized with B3LYP-D3/aug-cc-pVDZ. A molecular characterization was performed focusing on geometrical parameters such as pseudo-rotation angles, atomic charges, HOMO and LUMO orbitals, reactivity indexes and intermolecular interactions. Three analogs, A2 (3-(1,3-dimethyl-4,5-dihydro-1h-pirazole-5-yl) pyridine), A3 (3-(3-methyl-4,5-dihydro-1H-pyrazol-5-yl)-pyridine) and A8 (5-methyl-3-(pyridine-3-yl)-4,5-dihydroisoxazole), were filtered suggesting putative neuroprotective activity taking into account different reactivity values, such as their lowest hardness: 2.37 eV (A8), 2.43 eV (A2) and 2.56 eV (A3), compared to the highest hardness value found: 2.71 eV for A5 (3-((2S,4R)-4-(fluoromethyl)-1-methylpyrrolidine-2-il) pyridine), similar to the value of nicotine (2.70 eV). Additionally, molecular docking of all 8 nicotine analogs with the α 7 nicotinic acetylcholine receptor (α 7 nAChR) was performed. High values of interaction between the receptor and the three nicotine analogs were obtained: A3 (-7.1 kcal/mol), A2 (-6.9 kcal/mol) and A8 (-6.8 kcal/mol); whereas the affinity energy of nicotine was -6.4 kcal/mol. Leu116 and Trp145 are key residues in the binding site of α 7 nAChR interacting with nicotine analogs. Therefore, based upon these results, possible application of these nicotine analogs as neuroprotective compounds and potential implication at the design of novel Parkinson's treatments is evidenced.

Crystal structure, spectroscopic characterization and Hirshfeld surface analysis of aqua-dichlorido-{N-[(pyridin-2-yl)methyl-idene]aniline}copper(II) monohydrate

The reaction of N-phenyl-1-(pyridin-2-yl)methanimine with copper chloride dihydrate produced the title neutral complex, [CuCl2(C12H10N2)(H2O)]·H2O. The CuII ion is five-coordinated in a distorted square-pyramidal geometry, in which the two N atoms of the bidentate Schiff base, as well as one chloro and a water mol-ecule, form the irregular base of the pyramidal structure. Meanwhile, the apical chloride ligand inter-acts through a strong hydrogen bond with a water mol-ecule of crystallization. In the crystal, mol-ecules are arranged in pairs, forming a stacking of symmetrical cyclic dimers that inter-act in turn through strong hydrogen bonds between the chloride ligands and both the coordinated and the crystallization water mol-ecules. The mol-ecular and electronic structures of the complex were also studied in detail using EPR (continuous and pulsed), FT-IR and Raman spectroscopy, as well as magnetization measurements. Likewise, Hirshfeld surface analysis was used to investigate the inter-molecular inter-actions in the crystal packing.

Synthesis of 1-Azaspiro[4.4]nonane Derivatives Enabled by Domino Radical Bicyclization Involving Formation and Capture of Alkoxyaminyl Radicals

The application of a domino radical bicyclization for the synthesis of compounds containing the 1-azaspiro[4.4]nonane skeleton in 11-67% yields as a mixture of diastereomers is described (trans configuration preference). This process involved formation and capture of alkoxyaminyl radicals. For this purpose, O-benzyl oxime ethers with a brominated or iodinated aromatic ring or a terminal alkynyl group and an alkenyl moiety were employed as starting materials. The bicyclization was initiated by 2,2'-azobisisobutyronitrile or triethylborane and promoted by Bu₃SnH. The best results were obtained with O-benzyl oxime ethers containing an alkenyl moiety tethered to electron withdrawing groups or aryl substituents, whereas oxime radical precursor attached to methyl-substituted olefin precluded the capture of alkoxyaminyl radical, giving rise mainly to monocyclized product.

Standardized Extract from Caesalpinia spinosa is Cytotoxic Over Cancer Stem Cells and Enhance Anticancer Activity of Doxorubicin

Cancer stem cells (CSC) are the primary cell type responsible for metastasis and relapse. ABC-transporters are integral membrane proteins involved in the translocation of substrates across membranes protecting CSC from chemotherapeutic agents. A plant extract derived from C. spinosa (P2Et) previously investigated for its antitumor activity has been shown to reduce lung and spleen metastasis in mice that have been transplanted with breast cancer cells, suggesting that P2Et has a significant activity against cancer stem cells (CSC). P2Et extract was thoroughly characterized by HPLC/MS. The cytotoxicity of P2Et extract was evaluated using a MTT assay in human and murine cell lines with different profiles of resistance, by Pgp overexpression or by enrichment in cancer stem cells. The synergistic effect of P2Et with doxorubicin was evaluated in vitro in several cell lines and in vivo in mice transplanted with TS/A cells, a highly resistant cell line and enriched in CD44[Formula: see text]CD24[Formula: see text]CSC. The chromatographic fingerprint of P2Et extract revealed 13 gallotannins. We also found that P2Et extract was cytotoxic to cells regardless of their resistant phenotype. Similarly, complementary activities were observed as drug efflux reversion and antioxidant activity. Short-treatment with P2Et extract, revealed a synergistic effect with doxorubicin in resistant cell lines. In vivo the P2Et increases mice survival in a TS/A breast cancer model associated with augmentation of calreticulin expression. Our results suggest that P2Et treatment could be used as adjuvant along with conventional chemotherapy to treat tumors with a MDR phenotype or with high frequency of CSC.

Standardized Extract from Caesalpinia spinosa is Cytotoxic Over Cancer Stem Cells and Enhance Anticancer Activity of Doxorubicin

Cancer stem cells (CSC) are the primary cell type responsible for metastasis and relapse. ABC-transporters are integral membrane proteins involved in the translocation of substrates across membranes protecting CSC from chemotherapeutic agents. A plant extract derived from C. spinosa (P2Et) previously investigated for its antitumor activity has been shown to reduce lung and spleen metastasis in mice that have been transplanted with breast cancer cells, suggesting that P2Et has a significant activity against cancer stem cells (CSC). P2Et extract was thoroughly characterized by HPLC/MS. The cytotoxicity of P2Et extract was evaluated using a MTT assay in human and murine cell lines with different profiles of resistance, by Pgp overexpression or by enrichment in cancer stem cells. The synergistic effect of P2Et with doxorubicin was evaluated in vitro in several cell lines and in vivo in mice transplanted with TS/A cells, a highly resistant cell line and enriched in CD44[Formula: see text]CD24[Formula: see text]CSC. The chromatographic fingerprint of P2Et extract revealed 13 gallotannins. We also found that P2Et extract was cytotoxic to cells regardless of their resistant phenotype. Similarly, complementary activities were observed as drug efflux reversion and antioxidant activity. Short-treatment with P2Et extract, revealed a synergistic effect with doxorubicin in resistant cell lines. In vivo the P2Et increases mice survival in a TS/A breast cancer model associated with augmentation of calreticulin expression. Our results suggest that P2Et treatment could be used as adjuvant along with conventional chemotherapy to treat tumors with a MDR phenotype or with high frequency of CSC.

1-Benzyl-piperidin-4-one O-(2-bromo-benz-yl)oxime

In the title mol-ecule, C(19)H(21)BrN(2)O, the piperidone ring adopts a chair conformation with a total puckering amplitude Q(T) of 0.554 (2) Å. The dihedral angle between the benzene rings is 64.10 (7)°. There are no significant inter-molecular inter-actions.