Synthesis and characterization of organomodified Na-MMT using cation and anion surfactants

The Sodium Montmorillonite (Na-MMT) is not susceptible to polymer due to its organophilic character and low basal spacing. The primary objective of this study was to improve Na-MMT platelets separation by organically modifying it with cation and anion exchanges using Cetyl trimethyl ammonium bromide (CTAB) and Sodium dodecyl sulfate (SDS) respectively. Basal spacing, presence of functional groups, Zetapotential with particle size analysis and thermal stability of the Organomodified Na-MMT (OMMT) were characterized using XRD, FTIR, zeta-potential analyzer and TGA respectively. The basal spacing of CTAB modified OMMTincreased to 19.5 ? from 11.0 ? which corresponds to the basal spacing of Na-MMT. The SDS modified OMMT did not show any increase in the basal spacing. FTIR spectra of CTAB modified Na-MMT illustrated the attachment of CTAB functional groups to Na-MMT, while the same was absent in the case of SDS modified Na-MMT. The zeta-potential of Na-MMT shifted from −24.88 mV to 15.66 mV in the case of CTAB modified Na-MMT and 12.49 mV for SDS modified Na-MMT, indicating a greater surface potential of the modified nanoclay. The TGA showed greater weight loss for CTAB modified Na-MMT than that for Na-MMT, indicating the effective Na⁺ ion exchange with alkyl amines.     

Allylation of p-ketoaldehydes and functionalized imines by diallyltin dibromide: Formation of skipped and conjugated dienes

Diallyltin dibromide reacts with β-keto-aldehydes possessing no aromatic side groups and with (hydroxy) aryl imines to afford the expected homoallyl alcohols or amines respectively. With β-ketoaldehydes having aromatic side groups, skipped or conjugated dienes are obtained depending on whether or not an aqueous work up procedure is used.     

A flexible enantioselective synthesis of (+)-centrolobine and 5-epi-diospongin-A using asymmetric transfer hydrogenation/tandem Grubbs cross-metathesis/oxy-Michael reaction as key steps

An efficient enantioselective synthesis of (+)-centrolobine and 5-epi-diospongin-A was achieved by the use of asymmetric transfer hydrogenation (ATH)/tandem Grubbs cross-metathesis/oxy-Michael reaction. Furthermore, this strategy allows for diastereodivergent access to every representative member of the family.     

Synthesis and Antimicrobial Evaluation of Novel N-Substituted β-Hydroxy Benzimidazole Sulfone Fluoroquinolones by Selective Oxidation Using Ticl4-H2O2

Abstract

The synthesis of N-substituted β-hydroxy benzimidazole sulfones containing 8-methoxy fluoroquinolone has been described and they were evaluated for antimicrobial activities. The compounds of N-substituted β-hydroxy benzimidazole sulfides (4a–e) and N-substituted β-hydroxy benzimidazole sulfones (5a–e) at C-7 of fluoroquinoline exhibited superior activity in vitro. 8-Methoxy fluoroquinolone carboxylic acid (1), reaction with piperizine in acetonitrile in presence of triethylamine under reflux gives 7-piperazinyl-8-methoxyfluoroquinolone (2). The latter is reacted with epichlorohydrine in presence of NaOH in acetone yielded N-substituted epoxide (3), which on treatment with 5-substituted-2-mercaptobenzimidazoles gives N-substituted β-hydroxy benzimidazole sulfides (4). Further, 4 on treatment with TiCl₄-H₂O₂ and in DCM yielded the corresponding N-substituted β-hydroxy benzimidazole sulfone (5).     

A concise enantioselective total synthesis of (+)-epi-muricatacin,using asymmetric hydrogenation/intramolecular iodoetherification as key steps

A concise enantioselective total synthesis of (+)-epi-muricatacin, a potent cytotoxic agent, is described. A key feature of this protocol is a catalytic asymmetric hydrogenation and a chiral auxiliary mediated intramolecular iodoetherification to ensure a high degree of distereo- and enantiocontrol.     

First stereoselective total synthesis of stagonolide G

First stereoselective total synthesis of nonenolide stagonolide G involving a convergent strategy is described. The key reactions include Keck allylation and Grubbs ring closing metathesis reaction.     

Development and validation of a reversed-phase HPLC method for monitoring of synthetic reactions during the manufacture of a key intermediate of an anti-hypertensive drug

A reversed-phase high-performance liquid-chromatographic method for monitoring of reactions involved in process development of a key intermediate of antihypertensive drugs, e.g, doxazosin mesylate, prazosin, alfuzosin, terazosin, etc., has been developed and validated. The HPLC profiles of impurities of 4-amino-2-chloro-6,7-dimethoxyquinazoline were used as fingerprints to follow the synthetic procedures in the manufacturing unit. The separation was accomplished on an Inertsil ODS-3 column with isocratic elution using acetonitrile-ammonium acetate (10 mM; pH 4.0; 50:50 v/v) as mobile phase and a photodiode array detector set at 240 nm at ambient temperature. The method was validated with respect to accuracy, precision, linearity, and limits of detection and quantification. The method could detect the impurities at a level of 0.01 to 0.20 microg/mL and it was found to be suitable not only for monitoring of reactions but also for quality assurance of 4-amino-2-chloro-6,7-dimethoxyquinazoline.     

A carbohydrate approach for the synthesis of tetrahydropyran containing C16-C29 fragment of sorangicin A

A carbohydrate derived synthesis of C16-C29 fragment of sorangicin A is described utilizing regioselective epoxide opening, segment-coupled Prins cyclization reaction and cross metathesis as the key steps.     

Chemistry of selected cyclic P(III) compounds possessing a P-Cl bond

The compounds [CH₂(6-t-Bu-4-Me-C₆H₂O)₂]PCl (1), (OCH₂CMe₂CH₂O)-PCl (2), and [ClPN(t-Bu)]₂ (3) have been utilized as precursors in the synthesis of (i) new pentacoordinate phosphorus compounds [e.g. CH₂(6-t-Bu-4-Me-C₆H₂O)₂ P(NRR′)(O₂C₆C1₄), CH₂(6-t-Bu-4-Me-C₆H₂O)₂PX[OC(O-i-Pr)N=N(C(O)O-i-Pr)],(ii) cyclic phosphates and their complexes [e.g. imidazolium⁺CH₂(6-t-Bu-4-Me-C₆H₂O)₂PO₂ ^-.MeOH], (iii) new cycloaddition products [e.g. CH₂(6-t-Bu-4-Me-C₆H₂O)₂PC(CO₂Me)C(CO₂Me)C(O)N, (iv) macrocyclic compounds [e.g. [(t-BuN)P]₂[-OCH₂CMe₂CH₂O-]_h2] and (v) phosphonates [e.g. (OCH₂CMe₂CH₂O)P (O)CH₂C(CN)=CHC₅H₄FeC₅H₅]. The synthetic and structural aspects of these new products are discussed.     

A sector finite element for dynamic analysis of thick plates

A 24 degree of freedom sector finite element is developed for the static and dynamic analysis of thick circular plates. The element formulation is based on Reissner's thick plate theory. The convergence characteristic of the elements is first studied in a static example of an unsymmetrically loaded annular plate. The obvious advantageous effect of including the twist derivatives of deflection as degrees of freedom is shown. The elements are then used to analyze the natural frequencies of an annular plate with various ratios of inner to outer radius. The results are in good agreement with an alternative solution in which thick plate theory is used. The versatility of this finite element is finally demonstrated by performing free vibration analysis of an example of clamped sector plates with various thicknesses and different sectorial angles.