Preparation of α-galactooligoglycosides by cell walls from Cryptococcus laurentii using a novel α-galactosyl donor

The cell walls of an acapsular strain of the yeast Cryptococcus laurentii catalyze the regioselective formation of α-galactooligosaccharides through self-condensation of 4-nitrophenyl α-d-galactopyranoside and of a novel activated α-galactosyl donor 2,2,2-trifluoroethyl α-d-galactopyranoside. The latter substance can be easily prepared by several methods and is highly soluble in water and therefore can be used in higher initial concentrations suppressing secondary product hydrolysis. The preparative reaction catalyzed by cell walls provided 17.4% and 2% of corresponding 2,2,2-trifluoroethyl galactobioside and galactotrioside, respectively, while the reaction with 4-nitrophenyl α-d-galactopyranoside provided the corresponding 4-nitrophenyl galactobioside and galactotrioside in 6.6 and 2.5% yields, respectively. The reactions proceeded with strict α-(1 → 6)-regioselectivity.     

The molecular basis of pharmacological chaperoning in human α-galactosidase

Fabry disease patients show a deficiency in the activity of the lysosomal enzyme α-galactosidase (α-GAL or α-Gal A). One proposed treatment for Fabry disease is pharmacological chaperone therapy, where a small molecule stabilizes the α-GAL protein, leading to increased enzymatic activity. Using enzyme kinetics, tryptophan fluorescence, circular dichroism, and proteolysis assays, we show that the pharmacological chaperones 1-deoxygalactonojirimycin (DGJ) and galactose stabilize the human α-GAL glycoprotein. Crystal structures of complexes of α-GAL and chaperones explain the molecular basis for the higher potency of DGJ over galactose. Using site-directed mutagenesis, we show the higher potency of DGJ results from an ionic interaction with D170. We propose that protonation of D170 in acidic conditions leads to weaker binding of DGJ. The results establish a biochemical basis for pharmacological chaperone therapy applicable to other protein misfolding diseases.     

Intramolecular Induction of Asymmetric Darzen's Condensation of Aldehydes with Chiral α-Chloroacetates

Inconvergentwithourinterestintheasymmetricsynthesisofnaturalproducts,intramolecularinductionofasymmetricDarzen'scondensationlofaldehydeswithQchloroacetatesofchiralalcoholswasstudies,asshowninScheme1.Scheme1.R*OH CICH,COCI~CICH,COOR*i(-)-menthol(450%)3( )-Jsomenthoi(i56%)5(-)-8-phenylmenthoi(74%)2( )-neomenthol(147%)4( )-f6nchol(478%)6(-)-8-11-naphthylmenthoi(99%)I-henumbersintileparenthesisilldicatedthece%oftilecorrcspondillgmethy13-pllcn}lgl}'cidatcobtainedh\'trallscstcrltiationBenza…     

Enantioselective Hydrogenation of α,β-Unsaturated Cyclic Ketones by Double Asymmetric Induction Preparation of (R)-Muscone

(R)-Muscone[(R)-6]isanodoriferouscomPoundisolatedfromthemalemuskdeer.BecauseofthenatUralsupplyisseverelylbotofanumberofSyntheticmethodshaveaPPearedintheliteratUre['].However,eachofthepublishedenahoselechveopthehcprocessessuffersfromoneormoreofthefollowingflollgandcomplicatedprocess,lowcheforcalandophcalvields,andscarcityofstartingmaterials[2].Inl98o,TrostetaldeveloPedashortprocesstoopthesize(dl)-musconeingoodcheforca1yteld,andthestartinmaterialiseasil3'a.ailablef3];Ouradriistoobtain(R)-mu…     

Spirophosphoranes D′ α-Cetoacides. Structure Cristalline. Induction Asymetrique

Des couples d'énantiomères diastéréoisomères de spirophosphoranes ont été préparés en faisant réagir le trichlorophosphane sur l'acide céto-2-glutarique. Par cristallisation sélective, un couple a été isolé dont la structure a été déterminée par diffraction des rayons X. Les sels de triéthylammonium de thiolo et sélénospirophosphoranes ont été obtenus en faisant réagir le soufre ou (et) le sélénium sur les spirophosphoranes préparés à partir des acides phénylpyruvique et céto-2-glutarique. Tous ces résultats ont été rationalisés par des calculs semi-empiriques.     

Synthesis of New α-Heterocyclic α-Aminophosphonates

α-heterocyclic α-aminophosphonates were obtained in good yields by N-of several nitrogen heterocycles with α-azido-α-aminophosphonate 1. ¹ Elachqar, A., El Hallaoui, A., Roumestant, M. L. and Viallefont, Ph. 1994. Synthetic Comm, 24: 1279 [CSA][Taylor & Francis Online], [Web of Science ®] , [Google Scholar]     

New general synthesis of α-alkoxyketones via α'-alkylation, α-alkylation and α,α'-dialkylation of α-alkoxyketimines

α-Methoxy- and α-ethoxyketones, as important intermediates in organic synthesis and flavor compounds in food chemistry, were synthesized by deprotonation of N-(1-alkoxy-2-propylidene)isopropylamine, prepared by condensation of the corresponding α-alkoxyacetone with isopropylamine, and subsequent reaction of the corresponding 1-azaallylic anions with alkyl halides to afford α'-alkylated, α-alkylated and α,α'-dialkylated ketimines. Hydrolysis of the imino function led to the desired substituted α-alkoxyketones. The ratio of α-, α'-, and α,α'-(di)alkylated compounds depended on the amount of base used and on the nature of the alkylating reagent.     

Immobilization of β-galactosidase on Polystyrene Microspheres Attached L-Alanine

This study investigated the properties of immobilized β-galactosidase on polymeric beads having Schiff base. Polystyrene microspheres attached L-Alanine (FMPS-Ala) was synthesized from (4-formyl-3-methoxyphenoxymethyl)polystyrene (FMPS) and L-alanine by condensation. A coordinasyon polymer involving Ni²⁺(FMPS-Ala-Ni) was produced with the template method and characterized. β-galactosidase was immobilized onto the (FMPS), (FMPS-Ala) and (FMPS-Ala-Ni) complexes via covalent bonds. The Km/Vmax values were calculated as 0.343 mM/0.0259 mM min^?1for free β-galactosidase and 0.104 mM/0.0126 mM min^?1, 0.0617 mM/0.0417 mM min^?1and 0.210 mM/0.0287 mM min^?1for β-galactosidase immobilized to the (FMPS), (FMPS-Ala) and (FMPS-Ala-Ni) supports, respectively. The storage stability of (FMPS-Ala-Ni) was determined to be higher than that of the (FMPS) and (FMPS-Ala) polymers.     

Convenient synthesis of α-diarylmethylphosphonates by HOTf catalyzed Friedel-Crafts arylation of α-aryl α-hydroxyphosphonates

We report a convenient catalytic Friedel-Crafts arylation of α-aryl α-hydroxyphosphonates with various (hetero)aromatic compounds. HOTf (trifluoromethanesulfonic acid) is identified to be the best Brønsted acid catalyst, and the desired α-diarylmethylphosphonates were obtained in up to 41–95% yield.     

Addition of some α-halogeno ethers to α-thiooxides of alkenes

Summary Products of the addition of allyl chloromethyl ether, -chloroethyl methyl ether, -acetoxyethyl chloromethyl ether, cyclohexyl chloromethyl ether, and -chloroethyl ethyl ether to the thiooxides of ethylene and propylene have been prepared.     

Preparation of α-Halovinyl Sulfides by Eliminative Deoxygenation of α-Halosulfoxides

Abstract

Vinyl sulfides are useful synthetic intermediates¹ which have received increasing attention recently both as masked carbonyl moieties² and in carbon-carbon bond forming reactions.³ With regard to the latter, vinyl sulfide derivatives which are substituted in the α-position with halogen, tin, selenium, etc., are particularly useful due to the ready formation of anions upon treatment with a variety of organometallic reagents.^{3 d ? 1} We report here that synthetically useful halovinyl sulfides can be produced in high yield by the eliminative deoxygenation of the corresponding α-halosulfoxides induced by electrophilic silicon reagents.     

Carbonylation of α-Haloketones

The catalytic carbonylation reactions of -haloketones in the presence of palladium compounds were studied. Chloroketones were selectively converted into -ketoesters, whereas bromoacetophenone was partially reduced to acetophenone. The reaction rate at atmospheric pressure was much lower than that at an elevated pressure. A reaction mechanism was proposed.     

Synthesis of α-alkylthioacroleins

Monomeric -alkylthioacroleins were obtained by the reaction of alkylthioacetaldehydes with formaldehyde and diethylamine hydrochloride. The structures of the -alkylthioacroleins were confirmed by NMR spectroscopy and mass spectrometry as well as by chemical transformations of these compounds.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 188–190, January, 1996.     

Synthesis of α-Telluroketones

α-Telluroketones were prepared by reacting 4-methoxyphenyltellurium trichloride either with ketones or silyl enol ethers of ketones. The products upon pirolysis furnish α-chloro ketones.     

Study of the enantioselectivity of the CAL-B-catalysed transesterification of α-substituted α-propylmethanols and α-substituted benzyl alcohols

A study of the enantioselectivity exhibited by the lipase B from Candida antarctica in the transesterification of different α-substituted α-propylmethanols with vinyl acetate is shown. The best results are obtained when the large-sized (L) substituent of the alcohol is either a phenyl group or more especially a cyclohexyl group, although the reaction rates are lower than when linear or slightly branched groups are present. It is also found that ramification at the β-position of the L substituent has a deleterious effect on both lipase activity and enantioselectivity. Moreover, some α-substituted benzyl alcohols bearing medium-sized (M) substituents larger than an ethyl and smaller than a propyl group are resolved by means of this methodology with moderate-good enantioselectivities (E=46–57) and similar reaction rates.     

Rearrangement of α-Phenylselenenylketones

1,3-rearrangements of phenylselenenylketones which lack steric bulk at the α-carbon can be conveniently achieved by taking advantage of the greater reactivity of sodium enolates relative to their lithium counterparts.     

Synthesis of α-oxazolinylalkanamides

The synthesis of α-oxazolinylalkanamides 2, based on the reaction of α-chloroalkyloxazolines 1 with hexacarbonyltungsten [W(CO)₆] and lithium amides, has been developed. A plausible mechanism involving the ketene 5 as the intermediate is also proposed.