Reactions of 1-halocycloheptenes with potassium t-Butoxide and with sodium pyrrolidide

Reactions of 1-halocycloheptenes with KO-t-Bu in DMSO and THF were studied. The principal products obtained could be accounted for on the basis of two competing dehydrohalogenation mechanisms. These are: dehydrohalogenation across the C₁-C₂ bond to give cycloheptyne; and dehydrohalogenation across the C₁-C₇ bond to give 1,2-cycloheptadiene. One or both of these intermediates react with KO-t-Bu to give 1-t-butoxycycloheptene in poor yield. The principal product from the three 1-halocycloheptenes in both solvents is tricyclo[7.5.0.0²8]tetradeca-2,14-diene (4), the dimer of 1,2-cycloheptadiene. Also formed are 5, the 2(8), 14-diene isomer of 4, presumably by cycloaddition of 1,2-cycloheptadiene and cycloheptyne, and 6, the 2,13-diene isomer of 4, by rearrangement of 4 effected by KO-t-Bu.Also studied were rections of 1 chloro- and 1-iodocycloheptene with sodium pyrrolidide (Na- NC₄H₈) in THF. These reactions give 1-(1-pyrrolidino)cycloheptene in fair yield together with smaller amounts of the 14-carbon hydrocarbons. Reactions of 1-chlorocycloheptene-1-¹⁴C and 4-chloro- and 4-iodobicyclo[5.1.0]oct-3-ene leading to (1-pyrrolidino)cycloheptenes were found to occur via both the corresponding cycloheptyne and 1,2-cycloheptadiene.     

Area per surfactant molecule values of gemini surfactants at the liquid-hydrophobic solid interface

Areas per surfactant molecule at the liquid/hydrophobic solid (A(LS)) and the liquid/air (A(LA)) interface as a function of the spacer length are reported for cationic gemini surfactants having (CH2)n spacer s. A(LA) increases with increasing spacer length up to 6-8 CH2 groups in the spacer and then levels off. A(LS) values indicate a more closely packed arrangement of the surfactant molecules than that at the liquid/air interface. Comparison of A(LA) and A(LS) values indicates that the surfactant molecules at the liquid/hydrophobic solid interface are almost three times as closely packed as those at the liquid/air interface. A comparison of the experimental values of the area per surfactant molecule at both interfaces was made with those calculated from dimensions of the surfactant molecule in vacuo.     

Cycloartenol to Buxus alkaloids

Cycloartenol, a pentacyclic triterpene alcohol, has emerged as an obligatory intermediate in the biosynthesis of sterols in higher plants and algae. Cycloartenol has also been implicated in the biosynthesis of steroidal alkaloids. TheBuxus alkaloids, which have a pregnane-type framework, are considered to arise from cycloartenol by catabolic processes with nitrogen incorporation at an appropriate stage, although no biosynthetic studies appear to have been carried out. Thus, cycloartenol is an important substrate in nature for elaborating a rather large group of secondary metabolites. In an effort to mimic some of these processes in the laboratory, we have carried out transformations of cycloartenol intoBuxus alkaloids. New routes for side-chain degradation of cycloartenol and cyclolaudenol have been developed. A novel method for functionalization at C-16 has been worked out and a new strategy for regioselective oxygenation of 4-methyl has been exploited. Synthesis of buxandonine, cycloprotobuxine-F, cycloprotobuxine-A, cyclobuxophyllinine-M and 31-norcyclolaudenone have been achieved.     

Synthesis and Characterization of Mn-Doped ZnO Nanocrystals

We report the synthesis and characterization of several sizes of Mn-doped ZnO nanocrystals, both in the free-standing and the capped particle forms. The sizes of these nanocrystals could be controlled by capping them with polyvinylpyrollidone under different synthesis conditions and were estimated by X-ray diffraction and transmission electron microscopy. The absorption properties of PVP-capped Mn-doped ZnO exhibit an interesting variation of the band gap with the concentration of Mn. Fluorescence emission, electron paramagnetic resonance, and X-ray absorption spectroscopy provide evidence for the presence of Mn in the interior as well as on the surface of the nanocrystals.     

The anomeric effect in 2-arylseleno-1,3-dithianes

The anomeric effect in a series of 2-(4-substituted-phenylseleno)-1,3-dithianes (substituents, R = NO₂, CF₃, H, OMe, NMe₂) decreases in the sequence NO₂>CF₃>H>OMe>NMe₂, providing systematic experimental evidence for the role of stabilizing orbital interactions.     

Tandem versus single C-C bond forming reaction under palladium-copper catalysis: regioselective synthesis of α-pyrones fused with thiophene

We herein report a highly convenient protocol for rapid construction of α-pyrone fused with thiophene. This includes one-pot and regioselective synthesis of 4,5-disubstituted and 5-substituted thieno[2,3-c]pyran-7-ones, 6,7-disubstituted and 6-substituted thieno[3,2-c]pyran-4-ones. The synthesis of thieno[2,3-c]pyran-7-ones involves palladium mediated cross coupling of 3-iodothiophene-2-carboxylic acid with terminal alkynes in a simple synthetic operation. The coupling-cyclization reaction was initially studied in the presence of Pd(PPh₃)₂Cl₂ and CuI in a variety of solvents. 5-Substituted 4-alkynylthieno[2,3-c]pyran-7-ones were isolated in good yields when the reaction was performed in DMF. Similarly, 6-substituted 7-alkynylthieno[3,2-c]pyran-4-ones were synthesized via palladium-catalyzed cross coupling of 2-bromothiophene-3-carboxylic acid with terminal alkynes. A tandem C-C bond forming reaction in the presence of palladium catalyst rationalizes the formation of coupled product in this apparently three-component reaction. The cyclization step of this coupling-cyclization-coupling process occurs in a regioselective fashion to furnish products containing six-membered ring only. This sequential C-C bond forming reaction however, can be restricted to the formation of single C-C bond by using 10% Pd/C-Et₃N-CuI-PPh₃ as catalyst system in the cross coupling reaction. 5-Substituted thieno[2,3-c]pyran-7-ones were obtained in good yields when the coupling reaction was performed under this condition. Some of the compounds synthesized were tested in vitro for their anticancer activities.     

Chemistry of ayurvedic crude drugs—V : Guggulu (resin from commiphora mukul)—5 some new steroidal components and,stereochemistry of guggulsterol-I at C-20 and C-22

20α-hydroxy-4-pregnen-3-one (5), 20β-hydroxy-4-pregnen-3-one (6), 16β-hydroxy-4,17(20)Z-pregnadien-3-one (4) and 16α-hydroxy-4-prenen-3-one (10) have been isolated as new steroidal components of the gum-resin from Commiphora mukul. A simple procedure for the synthesis of 4 is described. Chirality at C-20, C-22 in guggulsterol-I (3) has been clarified.     

Detection of an α-Muonium-substituted methyl radical

Mössbauer spectroscopic and magnetic measurements have been made on a novel magnetic protein produced by the controlled reconstitution of ferritin. The data indicate that the predominant mineral form in the iron-containing cores is maghemite (-Fe₂O₃) rather than magnetite (Fe₃O₄).     

Imidazopyridazine Acetylcholinesterase Inhibitors Display Potent Anti-Proliferative Effects in the Human Neuroblastoma Cell-Line,IMR-32

Imidazo[1,2-b]pyridazine compounds are a new class of promising lead molecules to which we have incorporated polar nitro and amino moieties to increase the scope of their biological activity. Two of these substituted 3-nitro-6-amino-imidazo[1,2-b]pyridazine compounds (5c and 5h) showed potent acetylcholinesterase (AChE) inhibitory activity (IC₅₀ 40–50 nM), which we have previously reported. In this study, we wanted to test the biological efficacy of these compounds. Cytotoxicity assays showed that compound 5h mediated greater cell death with over 43% of cells dead at 100 μM and activation of caspase 3-mediated apoptosis. On the other hand, compound 5c mediated a dose-dependent decrease in cell proliferation. Both compounds showed cell cycle arrest in the G₀/G₁ phase and reduced cellular ATP levels leading to activation of adenosine monophosphate-activated protein kinase (AMPK) and enhanced mitochondrial oxidative stress. It has to be noted that all these effects were observed at doses beyond 10 μM, 200-fold above the IC₅₀ for AChE inhibition. Both compounds also inhibited bacterial lipopolysaccharide-mediated cyclooxygenase-2 and nitric oxide release in primary rat microglial cells. These results suggested that the substituted imidazo (1,2-b) pyridazine compounds, which have potent AChE inhibitory activity, were also capable of antiproliferative, anti-migratory, and anti-inflammatory effects at higher doses.     

Selected Class of Enamides Bearing Nitro Functionality as Dual-Acting with Highly Selective Monoamine Oxidase-B and BACE1 Inhibitors

A small series of nitro group-bearing enamides was designed, synthesized (NEA1–NEA5), and evaluated for their inhibitory profiles of monoamine oxidases (MAOs) and β-site amyloid precursor protein cleaving enzyme 1 (β-secretase, BACE1). Compounds NEA3 and NEA1 exhibited a more potent MAO-B inhibition (IC₅₀ value = 0.0092 and 0.016 µM, respectively) than the standards (IC₅₀ value = 0.11 and 0.14 µM, respectively, for lazabemide and pargyline). Moreover, NEA3 and NEA1 showed greater selectivity index (SI) values toward MAO-B over MAO-A (SI of >1652.2 and >2500.0, respectively). The inhibition and kinetics studies suggested that NEA3 and NEA1 are reversible and competitive inhibitors with K_i values of 0.013 ± 0.005 and 0.0049 ± 0.0002 µM, respectively, for MAO-B. In addition, both NEA3 and NEA1 showed efficient BACE1 inhibitions with IC₅₀ values of 8.02 ± 0.13 and 8.21 ± 0.03 µM better than the standard quercetin value (13.40 ± 0.04 µM). The parallel artificial membrane permeability assay (PAMPA) method demonstrated that all the synthesized derivatives can cross the blood–brain barrier (BBB) successfully. Docking analyses were performed by employing an induced-fit docking approach in the GLIDE module of Schrodinger, and the results were in agreement with their in vitro inhibitory activities. The present study resulted in the discovery of potent dual inhibitors toward MAO-B and BACE1, and these lead compounds can be fruitfully explored for the generation of newer, clinically active agents for the treatment of neurodegenerative disorders.