Interaction of Valdecoxib with β-cyclodextrin: Experimental and Molecular Modeling Studies

This study aimed to investigate the effect of β-cyclodextrin on aqueous solubility and dissolution rate of valdecoxib and also to get an insight of molecular interactions involved in formation of valdecoxib‐β-cyclodextrin inclusion complex. Phase solubility analysis indicated complex with possible stoichiometry of 1:1 and a stability constant of 234.01 M⁻¹. Thermodynamic studies in water indicated exothermic nature of inclusion complexation.␣Valdecoxib‐β-cyclodextrin complexes (1:1 M) were prepared by kneading method, solution method and␣freeze–drying method. The complex was characterized by differential scanning calorimetry (DSC), powder X-ray diffractometry (P-XRD), Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance␣(¹H-NMR) spectroscopy. Molecular modeling was used to help establish the mode of interaction of β-cyclodextrin with valdecoxib. ¹H-NMR analysis suggested that the unsubstituted phenyl ring of valdecoxib display favorable interaction with the hydrophobic cavity of β-cyclodextrin, which was confirmed by molecular dynamic simulations. An inclusion complex model has been established for explaining the observed enhancement of solubility of valdecoxib in water by β-cyclodextrin. Dissolution studies in water showed that the valdecoxib in freeze-dried complex dissolved much faster than the uncomplexed drug and physical mixture. This improvement in dissolution rate is attributed to the increased solubility and wettability due to encapsulation along with decreased crystallanity caused by complex formation, which is evident by DSC and P-XRD studies.     

Accelerated microdroplet synthesis of benzimidazoles by nucleophilic addition to protonated carboxylic acids

We report a metal-free novel route for the accelerated synthesis of benzimidazole and its derivatives in the ambient atmosphere. The synthetic procedure involves 1,2-aromatic diamines and alkyl or aryl carboxylic acids reacting in electrostatically charged microdroplets generated using a nano-electrospray (nESI) ion source. The reactions are accelerated by orders of magnitude in comparison to the bulk. No other acid, base or catalyst is used. Online analysis of the microdroplet accelerated reaction products is performed by mass spectrometry. We provide evidence for an acid catalyzed reaction mechanism based on identification of the intermediate arylamides. Their dehydration to give benzimidazoles occurs in a subsequent thermally enhanced step. It is suggested that the extraordinary acidity at the droplet surface allows the carboxylic acid to function as a C-centered electrophile. Comparisons of this methodology with data from thin film and bulk synthesis lead to the proposal of three key steps in the reaction: (i) formation of an unusual reagent (protonated carboxylic acid) because of the extraordinary conditions at the droplet interface, (ii) accelerated bimolecular reaction because of limited solvation at the interface and (iii) thermally assisted elimination of water. Eleven examples are shown as evidence of the scope of this chemistry. The accelerated synthesis has been scaled-up to establish the substituent-dependence and to isolate products for NMR characterization.

We report a metal-free novel route for the accelerated synthesis of benzimidazole and its derivatives in the ambient atmosphere.     

Microwave-assisted ketone-ketone rearrangement: an improved synthesis of 3-(4-alkoxyphenyl)-3- methylbutan-2-ones

[reaction: see text] A novel procedure for the preparation of 3-(4-alkoxyphenyl)-3-methylbutan-2-one in excellent yield is described via polymer-supported AlCl3-catalyzed rearrangement of 1-(4-ethoxyphenyl)-2,2-dimehtylpropan-1-one, followed by O-alkylation under microwave irradiation condition.     

A convenient synthesis of Fe(CO)2(η-S2CNMe2)2 and Fe(η-S2CNMe2)2 from the monodentate dithiocarbamato derivative, [(η-C5H5)(CO)3W(η-SCSNMe2)] and Fe2(CO)9

A high yield synthesis of the carbonyl dithiocarbamato derivative Fe(CO)₂(η²-S₂CNMe₂)₂ and Fe(η²-S₂CNMe₂)₂ by photolysis with visible light of solutions containing Fe₂(CO)₉ or Fe₃(CO)₁₂ and [(η⁵-C₅H₅)(CO)₃W(η¹-SCSNMe₂)] is reported.     

Total synthesis of microcarpalide

[reaction: see text] An efficient, convergent approach for the total synthesis of microcarpalide (1) is described. The synthetic strategy features the Sharpless asymmetric dihydroxylation, regioselective epoxide opening with various nucleophiles such as a lithium acetylide and cuprates derived from the vinyl stannane and the vinyl iodide for the construction of a C7-C8 trans-double bond and Yamaguchi macrolactonization as the key steps.     

Convenient Routes for the Preparation of Barium Permanganate and other Permanganate Salts

Two convenient methods were developed to transform KMnO₄ into barium permanganate and other permanganate salts via BaMnO₄ or Mn₂O₇ intermediates. Pure BaMnO₄ was prepared by the reaction of KMnO₄ with KI in the presence of BaCl₂ and NaOH. Hydrothermal reaction of barium manganate with excess carbon dioxide for 1.5 h at 100 °C led to barium‐permanganate with almost quantitative yield. Mn₂O₇ was prepared by means of the reaction of KMnO₄ and sulfuric acid monohydrate in a two‐phase (CCl₄‐H₂SO₄.H₂O) system. In the presence of excess barium carbonate and catalytic amount of water barium permanganate could be obtained with a moderate yield. Similarly, other permanganate salts (Zn, Cd, Cu, Mg, Ca, Ni, Al, Fe, Ce, rare earth metals) were prepared by substituting the BaCO₃ for the appropriate metal oxides, hydroxides or carbonates.     

Synthesis of porphyrinyl-nucleosides

Several porphyrinyl-nucleosides were prepared in the reaction of the OH group of one, two or four meso-p-hydroxyphenyl substituents of porphyrin with 5′-O-tosylates of 2′,3′-O-isopropylidene-adenosine or -uridine, or 5′-O-tosylthymidine; the remaining porphyrin meso-substituents were p-tolyl, p-hydroxyphenyl or 4-pyridyl. The following porphyrinyl-nucleosides were obtained with 8–17% yield: meso-di(p-tolyl)di(p-phenylene-5′-O-2′,3′-O-isopropylidene-adenosine) (or -uridine)porphyrins 1,2 , the respective meso-tetranucleosideporphyrins 3,4 -meso-mono(p-phenylene-5′-O-thymidine)porphyrins 5–7 , meso-di(p-tolyl)di(p-phenylene-5′-O-thymidine)porphyrins 8,9 and the meso-di(p-hydroxyphenyl)di(p-phenylene-5′-O-thymidine)porphyrins 10. Other compounds prepared belonged to the series: meso(4-pyridyl)_4?n(p-phenylene-5′-O-2′,3′-O-isopropylideneuridine)_nporphyrin, n = 1, 2 or 4, 11–13. N-Methylation gave the water soluble iodide salts: (N-methyl-4-pyridinium)4_4?n(p-phenylene-5′-O-2′,3′-isopropylideneuridine)_nporphyrins, n = 1, 2 or 4, 14–16. The ms fab showed in most cases stepwise detachment of the CH₂(5′)-nucleoside fragments. The porphyrins meso disubstituted by thymidine represent a convenient substrate for the build-up of both nucleoside units into the oligo/polynucleotide chains.     

Synthesis and characterisation of the methylene-inserted mixed-chalcogenide compounds Fe2(CO)6(μ-SeCH2Te) and Fe2(CO)6(μ-SCH2Te)

The methylene-bridged, mixed-chalogen compounds Fe₂(CO)₆(μ-SeCH₂Te) (1) and Fe₂(CO)₆(μ-SCH₂Te) (3) have been synthesised from the room temperature reaction of diazomethane with Fe₂(CO)₆(μ-SeTe) and Fe₂(CO)₆(μ-STe), respectively. Compounds 1 and 3 have been characterised by IR, ¹H, ¹³C, ⁷⁷Se and ¹²⁵Te NMR spectroscopy. The structure of 1 has been elucidated by X-ray crystallography. The crystalsare monoclinic,space group P2₁/n, A = 6.695(2), B = 13.993(5), C = 14.007(4)Å, β = 103.03(2)°, V = 1278(7) ų, Z = 4, D_c = 2.599 g cm⁻³ and R = 0.030 (R_w = 0.047).     

An efficient one-pot synthesis of pyrrolines and tetrahydropyridines from their chloro-precursors via in situ aza-Wittig reaction

A simple and efficient method for synthesizing pyrrolines and tetrahydropyridines via an intramolecular aza-Wittig reaction has been achieved by microwave irradiation of the corresponding chloro-alkane derivatives in the presence of tertiary phosphite and sodium azide. The in situ formation of the alkyl azides makes this a facile and safe method for aza-Wittig reactions.