Anil K. Saikia

Synthesis of cetyltrimethylammonium tribromide (CTMATB) and its application in the selective oxidation of sulfides to sulfoxides

Abstract The bright yellow crystalline cetyltrimethylammonium tribromide (CTMATB) reagent has been synthesized from the reaction of CTMAB and KBr with H 2 MoO 4 ·H 2 O, H 2 O 2 and H 2 SO 4 in the molar ratio 1:2:0.01:4:0.93. CTMATB selectively oxidizes a variety of dialkyl and alkyl aryl sulfides to the corresponding sulfoxides in high yields under mild conditions.

Stereoselective One-Pot, Three-Component Synthesis of 4-Aryltetrahydropyran via Prins-Friedel-Crafts Reaction

A diastereoselective one-pot, three-component Prins-Friedel-Crafts reaction was developed for the synthesis of 4-aryltetrahydropyran derivatives from the reaction of carbonyl compounds with homoallylic alcohol in the presence of arene promoted by boron trifluoride etherate.

Stereoselective One-Pot, Three-Component Synthesis of 4-Amidotetrahydropyran

The reaction of aldehyde with allylsilane in acetonitrile mediated by boron trifluoride etherate generated 4-aminotetrahydropyrans in good yields. The product is highly stereoselective.

Stereoselective Synthesis of Amido and Phenyl Azabicyclic Derivatives via a Tandem Aza Prins-Ritter/Friedel–Crafts Type Reaction of Endocyclic N-Acyliminium Ions

A simple protocol is described for the synthesis of amido and phenyl hexahydroindolizin-3(2H)-one, hexahydro-1H-quinolizin-4(6H)-one, and 1,3,4,10b-tetrahydropyrido[2,1-a]isoindol-6(2H)-one derivatives via endo-trig (aza-Prins type) cyclization followed by an intermolecular Ritter/Friedel-Crafts reaction of cyclic N-acyliminium ions, which are derived from the boron trifluoride etherate treatment of regioselectively reduced N-homoallyl imides. The reactions are highly diastereoselective with excellent yields.

Molecular mechanism underlying antileishmanial effect of oxabicyclo[3.3.1]nonanones: Inhibition of key redox enzymes of the pathogen

We report oxabicyclo[3.3.1]nonanones as inhibitors of key redox enzymes, trypanothione synthetase (TryS), and trypanothione reductase (TryR) of Leishmania. Further, detailed cellular effects of 4-(4,4,8-Trimethyl-7-oxo-3-oxabicyclo[3.3.1]non-2-yl)-benzoic acid methyl ester, a oxabicyclo[3.3.1]nonanones, on the parasite were investigated. As these compounds inhibit key redox enzymes (TryR amd TryS), treatment of these compounds resulted in increased reactive oxygen species (ROS), mitochondrial membrane damage, activation of caspase like proteases, and DNA damage that finally leads to apoptosis. Although the compound has modest IC50 value against parasite (4.9±0.4 μM), they identify a novel chemical space to design and develop drugs based on these compounds against the Leishmania parasite. This is first report of oxabicyclo[3.3.1]nonanones as antileishmanial.

Unveiling the mode of action of antibacterial labdane diterpenes from Alpinia nigra (Gaertn.) B. L. Burtt seeds.

The labdane diterpene, (E)-labda-8(17), 12-diene-15, 16-dial (compound A) and its epoxide analogue, (E)-8β, 17-Epoxylabd-12-ene-15, 16-dial (compound B) were isolated from the seeds of Alpinia nigra for the first time. The antibacterial activities of both compounds were evaluated against three Gram-positive and four Gram-negative bacteria, and flow cytometric analysis revealed that these compounds caused significant damage to the bacterial cell membranes. Further, field emission scanning electron microscope imaging and cell leakage analysis confirmed that the labdane diterpenes were responsible for bacterial cell membrane damage and disintegration. Our findings provide new insight into the broad-spectrum effects of two natural labdane diterpenes that may be useful in the future development of herbal antibiotic products.

A novel synthesis of oxabicyclo[3.3.1]nonanone via (3,5)-oxonium-ene reaction.

Oxabicyclo[3.3.1]nonanone can conveniently be prepared by the reaction of trans-p-menth-6-ene-2,8-diol and aldehyde or epoxide mediated by boron trifluoride etherate in good yields. The reaction proceeds via (3,5)-oxonium-ene-type reaction.

Palladium(ii) chloride catalyzed selective acetylation of alcohols with vinyl acetateElectronic supplementary information (ESI) available: 1H, 13C NMR and IR spectral data of 4b, 1H NMR, elemental analysis and IR spectral data of 5b; 1H and IR spectral data of 1b, 2b, 3b, 6b, 7b, 8b, 9b, 11b and 13b. See http://www.rsc.org/suppdata/cc/b4/b401218f/

PdCl(2) can catalyze the acetylation of primary and secondary alcohols with vinyl acetate. The reaction is selective and mild with high yields. Tertiary alcohols, phenols and amines are unaffected under these reaction conditions.

Diastereoselective Synthesis of Substituted Tetrahydrothiopyrans via (3,5)-Thionium–Ene Cyclization Reaction

Tetrahydrothiopyrans have been efficiently synthesized in good yields with excellent diastereoselectivity from aldehydes and substituted 5-methylhex-4-ene-1-thiol via (3,5)-thionium-ene cyclization reaction mediated by boron trifluoride etherate.

Synthesis of oxabicyclo[3.3.1]nonenes and substituted tetrahydropyrans via (3,5)-oxonium-ene reaction

An efficient methodology for the synthesis of oxabicyclo[3.3.1]nonenes and substituted tetrahydropyrans has been developed in moderate yields from the reaction of geraniol with aldehydes and epoxides promoted by boron trifluoride etherate.