Mohamed Takhi

Acylation of alcohols with acetic anhydride catalyzed by TaCl5: Some implications in kinetic resolution

Abstract TaCl 5 and TaCl 5 -Silica gel have been effectively used as Lewis acid catalysts for acetylation of alcohols. Also TaCl 5 -Chiral ligands have been used for kinetic resolution of 2° alcohols albeit in low ees.

TaCl5-silicagel and TaCl5 as new Lewis acid systems for selective tetrahydropyranylation of alcohols and thioacetalisation, trimerisation and aldolisation of aldehydes.

Abstract TaCl5 adsorbed on silicagel has been utilized for the first time as Lewis acid catalyst for protection of aldehydes and alcohols as thiocetals and THP ethers respectively. Similarly TaCl5 has been exploited as an useful Lewis acid for chemoselective trimerisation and/or aldolisation of aldehydes. Very active Lewis acid catalyst system comprising of TaCl5-silicagel has been utilized for thioacetalisation of aldehydes and tetrahydropyranylation of alcohols. Similarly TaCl5 alone was exploited as good Lewis acid for selective trimerisation and/or aldolisation of aldehyde which is solvent dependent.

SOLVENT FREE N-ALKYL AND N-ARYLIMIDES PREPARATION FROM ANHYDRIDES CATALYZED BY TACL5-SILICA GEL

Abstract The first Lewis acid catalyzed and solvent free procedure for the preparation of imides from the corresponding anhydrides is described involving TaCl 5 -silica gel as Lewis acid under microwave irradiation.

AN EXPEDITIOUS APPROACH FOR THE SYNTHESIS OF OPTICALLY ACTIVE ALLYL ALCOHOLS

Aldehyde tosylhydrazones having an adjacent O-isopropylidene group undergo a condensation-fragmentation process in the presence of alkyl magnesium and alkyllithium reagents to yield chiral allyl alcohols.

Phenolics from needles of himalayan Taxus baccata

Chemical investigation on the needles of the Himalayan yew, Taxus baccata, has resulted in the isolation of several phenolic compounds including 3-demethyl-(−)-secoisolariciresinol, a new lignan, and taxuside, a new phenolic glucoside. The structures of the new compounds were derived from their spectral data and chemical transformations.

Trichloroacetimidate as a Leaving Group in the Ferrier Rearrangement: Highly Stereoselective Synthesis of Pseudogalactal Glycosides

The Ferrier rearrangement of a galactal derivative 2 bearing the trichloroacetimidate functionality as a leaving group at the C-3 position was performed in the presence of trimethylsilyl triflate as catalyst; the corresponding pseudogalactal glycosides were obtained in excellent yield and stereoselectivity with a wide range of acceptors.

Stereochemistry of 4-aryl-2-butanols from himalayan Taxus baccata

Abstract 4-(4′-Hydroxyphenyl)-2 R -butanol, 4-(3′,4′-dihydroxyphenyl)-2 R -butanol and 4-(3′-methoxy-4′-hydroxy- phenyl)-2 R -butanol have been isolated from the needles of Himalayan Taxus baccata . These two compounds have not previously been reported in stereospecific forms. Their stereochemistry has been determined by enzymatic reduction of their corresponding 2-butanones.

A lignan from needles of Himalayan Taxus baccata

Abstract A new lignan, 4- O -methyl-3′- O -demethyl-(-)-secoisolariciresinol, has been isolated from the needles of Himalayan yew, Taxus baccata . The structure of the compound was established from its spectral data and chemical reactions.

Discovery of azetidine based ene-amides as potent bacterial enoyl ACP reductase (FabI) inhibitors

A novel and potent series of ene-amides featuring azetidines has been developed as FabI inhibitors active against drug resistant Gram-positive pathogens particularly staphylococcal organisms. Most of the compounds from the series possessed excellent biochemical inhibition of Staphylococcus aureus FabI enzyme and whole cell activity against clinically relevant MRSA, MSSA and MRSE organisms which are responsible for significant morbidity and mortality in community as well as hospital settings. The binding mode of one of the leads, AEA16, in Escherichia coli FabI enzyme was determined unambiguously using X-ray crystallography. The lead compounds displayed good metabolic stability in mice liver microsomes and pharmacokinetic profile in mice. The in vivo efficacy of lead AEA16 has been demonstrated in a lethal murine systemic infection model.

STEREOSELECTIVE SYNTHESIS OF PSEUDOGLYCAL C-GLYCOSIDES VIA TRICHLOROACETIMIDATE ACTIVATION OF GLYCALSa

A variety of functionalized pseudoglycal C-glycosides (C-pseudoglycals or C-hex-2-enopyranosides) have been obtained in excellent yield and stereoselectivity from the trimethylsilyl triflate (Me 3SiOTf) catalyzed reaction of trichloroacetimidate derivative 2 with silylated nucleophiles such as allyl and propargyl silanes and silyl enol ethers. a Dedicated to Prof. Joachim Thiem on the occasion of his 60th birthday.