Benzylidene Group Research Articles

Synthesis of lacto- N-neotetraose and lacto- N-tetraose using the dimethylmaleoyl group as amino protective group

The disaccharide donor O-[2,3,4,6-tetra- O-acetyl-β- d-galactopyranosyl)-(1→4)-3,6-di- O-benzyl-2-deoxy-2-dimethylmaleimido-α,β- d-glucopyranosyl] trichloroacetimidate ( 7) was prepared by reacting O-(2,3,4,6-tetra- O-acetyl-α- d-galactopyranosyl) trichloroacetimidate with tert-butyldimethylsilyl 3,6-di- O-benzyl-2-deoxy-2-dimethylmaleoylamido-glucopyranoside to give the corresponding disaccharide 5. Deprotection of the anomeric center and then reaction with trichloroacetonitrile afforded 7. Reaction of 7 with 3′- O-unprotected benzyl (2,4,6-tri- O-benzyl-β- d-galactopyranosyl)-(1→4)-2,3,6-tri- O-benzyl-β- d-glucopyranoside ( 8) as acceptor afforded the desired tetrasaccharide benzyl (2,3,4,6-tetra- O-acetyl-β- d-galactopyranosyl)-(1→4)-(3,6-di- O-benzyl-2-deoxy-2-dimethylmaleimido-β- d-glucopyranosyl)-(1→3)-(2,4,6-tri- O-benzyl-β- d-galactopyranosyl)-(1→4)-2,3,6-tri- O-benzyl-β- d-glucopyranoside. Replacement of the N-dimethylmaleoyl group by the acetyl group, O-debenzylation and finally O-deacetylation gave lacto- N-neotetraose. Similarly, reaction of O-[(2,3,4,6-tetra- O-acetyl-β- d-galactopyranosyl)-(1→3)-4,6- O-benzylidene-2-deoxy-2-dimethylmaleimido-α,β- d-glycopyranosyl] trichloroacetimidate as donor with 8 as acceptor afforded the desired tetrasaccharide benzyl (2,3,4,6-tetra- O-acetyl-β- d-galactopyranosyl)-(1→3)-(4,6-benzylidene-2-deoxy-2-dimethylmaleimido-β- d-glucopyranosyl)-(1→3)-(2,4,6-tri- O-benzyl-β- d-galactopyranosyl)-(1→4)-2,3,6-tri- O-benzyl-β- d-glucopyranoside. Removal of the benzylidene group, replacement of the N-dimethylmaleoyl group by the acetyl group and then O-acetylation afforded tetrasaccharide intermediate 15, which carries only O-benzyl and O-acetyl protective groups. O-Debenzylation and O-deacetylation gave lacto- N-tetraose ( 1). Additionally, known tert-butyldimethylsilyl (2,3,4,6-tetra- O-acetyl-β- d-galactopyranosyl)-(1→3)-4,6- O-benzylidene-2-deoxy-2-dimethylmaleimido-β- d-glucopyranoside was transformed into O-[2,3,4,6-tetra- O-acetyl-β- d-galactopyranosyl)-(1→3)-4,6-di- O-acetyl-2-deoxy-2-dimethylmaleimido-α,β- d-glucopyranosyl] trichloroacetimidate as glycosyl donor, to afford with 8 as acceptor the corresponding tetrasaccharide 22, which is transformed into 15, thus giving an alternative approach to 1.

Phosphorylation of Conjugated Enamines

Introduction of benzylidene group at α-position of enamines derived from cyclic ketones substantially increases strength of C-P bond thus permitting further syntheses without splitting of the C-P bond. A wide set of phosphorylated derivatives of type (I) were prepared and their properties were studied. Combination of an enamine moiety with other nucleophilic centers such as C or N in a molecule allows to carry out cyclisation giving five- and six-membered phosphorus-containing heterocycles of types (II, III).

The Synthesis of Four Dideoxygenated Analogues of β-Maltosyl-(1→4)-Trehalose

Four derivatives of β-maltosyl-(1→4)-trehalose were prepared, each with two deoxy functions in one of the constitutive disaccharide building blocks. 2,3-Di-O-acetyl-4,6-dideoxy-4,6-diiodo-α-D-galactopyranosyl- (1→4) −1,2,3,6-tetra-O-acetyl-D-glucopyranose (3) was employed as a precursor for the 4‴,6‴-dideoxygenated tetrasaccharide 9: coupling of 3 with 2,3,6-tri-O-benzyl-α-D-glucopyranosyl 2,3,6-tri-O-benzylidene-α-D-glucopyranoside (4) furnished the tetrasaccharide 5 which was deiodinated and deprotected to yield the target tetrasaccharide 9. Secondly, the dideoxygenated maltose derivative 3-deoxy-4,6-O-isopropylidene-2-O-pivaloyl-β-D-glucopyranosyl- (1→4) −1,6-anhydro-3-deoxy-2-O-pivaloyl-β-D-glucopyranose (10) was ring-opened to the anomeric acetate 11. A [2+2] block synthesis with 4 in TMS triflate mediated glycosylation gave a tetrasaccharide which was deprotected to the 3″,3‴-dideoxygenated analogue of β-maltosyl-(1→4)-trehalose. For the third tetrasaccharide, 2,3,2″,3′-tetra-O-benzyl-α,α-trehalose was iodinated at the primary positions and deiodinated in the presence of palladium-on-carbon, then this acceptor was selectively glycosylated with hepta-O-acetyl-maltosyl bromide (20). Removal of protective groups furnished the maltosyl trehalose tetrasaccharide deoxygenated at positions C-6 and C-6′. to prepare a 3,3′-dideoxygenated trehalose, the free hydroxyl groups of 2-O-benzyl-4,6-O-(R)-benzylidene-α-D-glucopyranosyl 2-O-benzyl-4,6-O-(R)-benzylidene-α-D-glucopyranoside (25) were reduced by Barton-McCombie deoxygenation. One of the benzylidene groups was opened reductively with sodium cyanoborohydride. The resulting free hydroxyl group at the 4′-position was glycosylated in a Koenigs-Knorr reaction with 20 to yield the 3,3′-dideoxygenated tetrasaccharide 32, the fourth target oligosaccharide, after deprotection.

Thermal and Rheological Properties of Physical Gels Formed from Benzylidene-d-sorbitol Derivatives

Abstract The thermal and rheological properties of gels formed from 2,4-(mono)-O-benzylidene-d-sorbitol (MBS), 1,3 : 2,4-di-O-benzylidene-d-sorbitol (DBS), and 1,3 : 2,4 : 5,6-tri-O-benzylidene-d-sorbitol (TBS) in ethylene glycol (EG) and from DBS in glycerol (GL) were investigated. In all the gels studied, the values of the enthalpy of melting for the gel obtained from the Eldridge–Ferry plot agreed well with those obtained from the peak area of the DSC curves. This agreement has not been demonstrated clearly for biopolymeric systems thus far but can now be successfully shown by first using small molecule systems. In conclusion, the transitions of the gel formation and gel melting proceed via a second order or higher order process. The experimental results show that the ease by which formation and stabilization of gels takes place for the sorbitol derivatives in EG is in the following order: DBS > TBS > MBS. Accordingly, the main reason for the stabilization of sorbitol gels in alcoholic solvents is concluded to be not simply due to hydrogen bonding or hydrophobic interactions among benzylidene groups but rather it is due to a delicate balance of chemical structure that facilitates the formation of crystals. In particular, the symmetric structure of a DBS molecule, which has a rigid and chiral ten-member ring symmetrically connected with two benzylidene groups in equatorial positions, is considered to be the most crucial reason to form most stable gels studied in this work.

Condensed heterocyclic compounds: synthesis and antiinflammatory activity of novel thiazolo[3,2-alpha] pyrimidines.

In this study, thirty six new 2-benzylidene-7-methyl-3-oxo-5- phenyl-2,3-dihydro-5H-thiazolo[3,2-alpha]pyrimidine-6-carboxylic acid methyl esters were synthesized and characterized by spectral, crystallographic, and elemental analysis. The antiinflammatory activity of the compounds was tested by the carrageenan hind paw edema test. It was found that compound 6a having a 2-meth-oxyphenyl group at position 5 and a benzylidene group at position 2 was the most potent compound in this series. All the compounds that were tested for ulcer activity gave positive results.

Condensed Heterocyclic Compounds: Synthesis and Antiinflammatory Activity of Novel Thiazolo[3,2-a]pyrimidines

In this study, thirty six new 2-benzylidene-7-methyl-3-oxo-5-phenyl-2,3-dihydro-5H-thiazolo[3,2-a]pyrimidine-6-carboxylic acid methyl esters were synthesized and characterized by spectral, crystallographic, and elemental analysis. The antiinflammatory activity of the compounds was tested by the carrageenan hind paw edema test. It was found that compound 6a having a 2-methoxyphenyl group at position 5 and a benzylidene group at position 2 was the most potent compound in this series. All the compounds that were tested for ulcer activity gave positive results.

N-Benzyl-3-benzylideneisoindolin-1-one

The title compound, C22H17NO, is formed by the palladium-catalyzed reaction between N-benzyl-o-iodo­benzamide and phenylacetylene. The molecules contain three planar parts, namely the isoindolinone moiety (A) and the phenyl rings of the benzyl and benzylidene groups (B and C), and display the Z configuration. Rings B and C are inclined by 14.9 (1)° with respect to each other and are approximately orthogonal to the isoindolinone moiety A; the dihedral angles A/B and A/C are 98.23 (4) and 111.08 (3)°, respectively.

Synthesis and characterization of photo-crosslinkable poly(benzylidene phosphoramide ester)s

Polyphosphoramide esters containing a photo-sensitive bisbenzylidene group in the main chain were synthesized from 2,7-bis(4-hydroxy-3-methoxybenzylidene) cycloheptanone with various N-arylphosphoramidic dichlorides by interfacial polycondensation using a phase transfer catalyst. The structure of the polymers was confirmed by infra-red and 1H, 13C and 31P nuclear magnetic resonance spectroscopy. The molecular weights were determined by gel permeation chromatography, and the thermal stabilities were evaluated by thermogravimetric analysis and differential scanning calorimetry. The photo-crosslinking property of these polymers was studied by ultraviolet spectroscopy. The crosslinking proceeds via 2π + 2π cycloaddition reaction of the benzylidene group. The substitution on the pendant phenyl group has no significant effect on the rate of crosslinking.

The Synthesis of the 3′- and 3′′′-Monodeoxygenated Derivatives of β-Maltosyl-(1→4)-Trehalose

Two derivatives of β-maltosyl-(1→4)-trehalose monodeoxygenated at C-3′ or C-3′′′ have been synthesized in [2+2] block syntheses. Starting from 4,6;4′,6′-di-O-benzylidene-trehalose (3) the 3′-hydroxyl group was singled out by selective pivaloylation and reduced by a Barton-McCombie reaction. The benzylidene group in the vicinity of the deoxy function could be reductively opened to supply a suitable monodeoxygenated glycosyl acceptor (8). Standard glycosylation with hepta-O-acetylmaltosyl bromide and deprotection led to 3′-deoxymaltosyl-(1→4)-trehalose 13. For the synthesis of a 3′-deoxygenated derivative of maltose we used 1,6-anhydromaltose as starting material. From the tributyltin hydride reduction of the 3,3′-bis-thiocarbonylimidazole derivative 18, the 3′-monodeoxygenated derivative 20 was obtained in low yield. After opening of the 1,6-anhydro ring, the maltosyl derivative was activated as trichloroacetimidate 24. Glycosylation followed by standard deprotection furnished the 3′′′-deoxymaltosyl-(1→4)-trehalose 28.

Synthesis of methyl α-glycosides of some higher oligosaccharide fragments of the O-antigen of Vibrio cholerae O1, serotype Inaba and Ogawa

The title oligosaccharides, the tri-through the hexasaccharide in the Inaba series and the penta- and the hexasaccharide in the Ogawa series, have been synthesized using 1-thioglycosides of precursors to 3- O-benzyl-perosamine (4-amino-4,6-dideoxy- d-mannose) as building blocks and N-iodosuccinimide/silver triflate as a promoter. The azido groups in the assembled oligosaccharides were reduced to amino groups, which were then acylated using 2,4-O- benzylidene-3-deoxy- l -glycero- tetronic acid as the derivatizing reagent. Catalytic hydrogenolysis, simultaneously of the benzyl and benzylidene groups, gave the desired products that were characterized by 1H and 13C NMR spectroscopy.

Synthetic Studies on Sialoglycoconjugates 91: Total Synthesis of Gangliosides GD1C and GT1A

A first total synthesis of gangliosides GD1c and GT1a containing Neu5Acα(2→8) Neu5Acα(2→3)Gal residue in their non-reducing terminal is described. Condensation of methyl O-[methyl 5-acetamido-8-O-(5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylono-11,9-lactone) -4,7- di-O-acetyl-3,5-dideoxy-D-glycero-α-D-galcto-2-nonulopyranosyranosylanate]-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-D-gala-ctopyranoside (1) with 2-(trimethylsilyl)ethyl O-(2-acetamido-4,6-O-benzylidene-2-deoxy-β-D-galactopyranosyl)- (1→4) -O -(2,3,6-tri-O-benzyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (2) or 2-(trimethylsilyl)ethyl O-(2-acetamido-6-O-benzyl-2-deoxy-β-D-galactopyranosyl)-(1→4)-(9-[methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→3)]-O-(2,6-di-O-benzyl-β-D-galactopyranosyl) - (1→4) - 2,3,6-tri-O-benzyl-β-D-glucopyranoside (3) in the presence of dimethyl(methylthio)sulfonium triflate (DMTST) gave the corresponding hexa-and heptasaccharide derivatives 4 and 5, respectively. These oligosaccharides were converted into the α-trichloroacetimidates 10 and 11 via reductive removal of the benzyl groups and/or benzylidene group, O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group and treatment with trichloroacetonitrile, which, on coupling with 2-azidosphingosine derivatives 12 or 13, gave the β-glycosides 14 and 15, respectively. Finally, 14 and 15 were transformed, via selective reduction of the azido group, coupling with octadecanoic acid and removal of all protecting groups, into the title gangliosides GD1c 18 and GT1a 19.

Synthesis of the monosaccharide units of the O-specific polysaccharide of Shigella sonnei

The monosaccharide components of the O-specific polysaccharide 1 of the lipopolysaccharide of the enteropathogenic bacterium Shigella sonnei were synthesized as their methyl glycosides 2 and 3 in their natural anomeric form. The key intermediate to the diaminotrideoxygalactose derivative 2 was ethyl 3-O-acetyl-2-deoxy-2-phthalimido-1-thio-β-d-glucopyranoside (9) that was converted to its ditosylate 10. Regioselective deoxygenation at C-6 followed by nucleophilic displacement of the secondary tosyloxy group by azide afforded the 4-azido thioglycoside 13. Methyl trifluoromethanesulfonate-assisted methanolysis of 13 gave the O-glycoside 14. Replacement of the phthalimido by an acetamido group followed by catalytic reduction of the azido group led to the diamino-trideoxygalactose derivative 2. The precursor to the l-altruronic acid derivative 3 was methyl α-l-glucopyranoside (19) that was routinely converted to the benzylidene-protected 2,3-anhydro-allopyranoside 22. Regioselective opening of the epoxide ring by NaN3 afforded the 2-azido derivative 23 that was benzylated at HO-3. Hydrolytic removal of the benzylidene group followed by TEMPO oxidation of C-6 and subsequent esterification with MeI gave the key l-azido-altruronic acid intermediate 29 that was transformed to the acetamidoaltruronic acid derivative 3. High resolution NMR data of the altruronic acid derivatives indicate that the conformation of their pyranose ring is crucially dependent on the substitution pattern: the 2-azido altruronic acid derivatives prefer the 4C1 conformation whereas the 2-acetamido congeners exist preferentially in the 1C4 conformation.

A simple approach to the synthesis of muramic acid and isomuramic acid: 1H and 13C NMR characterisation

A simple and efficient synthesis of 2-amino-3- O-[( R)-1-carboxyethyl]-2-deoxy- d-glucose (muramic acid, 6) and its stereoisomer 2-amino-3- O-[( S)-1-carboxyethyl]-2-deoxy- d-glucose (isomuramic acid, 7) from methyl 2-acetamido-4,6- O-benzylidene-2-deoxy-α- d-glucopyranoside ( 1) is described. Condensation of the O-3 oxyanion of 1 with an excess of methyl ( R,S)-2-bromopropionate, followed by alkaline hydrolysis of the crude product and subsequent acidification, afforded crystalline methyl 2-acetamido-4,6- O-benzylidene-3- O-[( R,S)-1-carboxyethyl]-2-deoxy-α- d-glucopyranoside ( 2), in 72% yield, as a mixture of diastereomers. Esterification of 2 with an excess of diazomethane afforded quantitatively the corresponding mixture of epimeric esters, which were very easily separated by column chromatography on silica gel, giving pure ( R) and ( S) epimeric esters. Removal of the benzylidene and acetyl groups by acid hydrolysis gave, respectively, muramic acid ( 6), in 95% yield and isomuramic acid ( 7), in 93% yield. 1H and 13C NMR data are given. © 1997 Elsevier Science Ltd.

Interglycosidic acetals. Part 3. Synthesis and structure determination of cyclic monobenzylidene acetals of cyclodextrin derivatives bridging between two contiguous ?-glucopyranosyl residues

Transacetalation of fully 6- O -pivaloylated α-, β-, and γ-cyclodextrins with benzaldehyde dimethylacetal in the presence of (+)-10-camphorsulfonic acid gave monobenzylidene acetals ( 4, 5, 6 ) in moderately good yields. Benzylation of the β-cyclodextrin derivative 5 followed by acid-catalyzed hydrolysis of the benzylidene group and acetylation afforded a di- O -acetyl-non-adeca- O -benzyl derivative 9 . NMR spectroscopic analysis of 9 , including two-dimensional HOHAHA and 1 H 13 C correlation experiments revealed that the benzylidene group bridged the O-2 and O-3 positions of contiguous d -glucopyranosyl residues. Reductive ring-opening of the benzylidene acetal with lithium aluminum hydride/aluminum chloride afforded predominantly a 2 1 - O -unprotected derivative 10 in good yield.

Interglycosidic acetals. Part 3. Synthesis and structure determination of cyclic monobenzylidene acetals of cyclodextrin derivatives bridging between two contiguous d-glucopyranosyl residues

Transacetalation of fully 6- O-pivaloylated α-, β-, and γ-cyclodextrins with benzaldehyde dimethylacetal in the presence of (+)-10-camphorsulfonic acid gave monobenzylidene acetals ( 4, 5, 6) in moderately good yields. Benzylation of the β-cyclodextrin derivative 5 followed by acid-catalyzed hydrolysis of the benzylidene group and acetylation afforded a di- O-acetyl-non-adeca- O-benzyl derivative 9. NMR spectroscopic analysis of 9, including two-dimensional HOHAHA and 1H 13C correlation experiments revealed that the benzylidene group bridged the O-2 and O-3 positions of contiguous d-glucopyranosyl residues. Reductive ring-opening of the benzylidene acetal with lithium aluminum hydride/aluminum chloride afforded predominantly a 2 1- O-unprotected derivative 10 in good yield.

Enantioselective Michael reaction of ketone lithium enolates using a chiral amine ligand

The enantioselective Michael reaction of ketone lithium enolates using a chiral amine ligand ( 1) was studied. Michael adducts ( 4) of up to 94% ee were obtained by the reaction between methyl ketones ( 2) and Michael acceptors ( 3) having a benzylidene group.

Synthetic Studies on Sialoglycoconjugates 85: Synthesis of Sialyl Lewis X Ganglioside Analogs Containing a Variety of Anionic Substituents in Place of Sialic Acid

Abstract Three sialyl-Lex ganglioside analogs containing carboxymethyl, sulfate, and phosphate groups in place of the sialic acid moiety, have been synthesized. Glycosylation of 2-(trimethylsilyl)ethyl O-(2,3,4-tri-O-benzyl-α-L-fucopyranosyl)-(1→3)-O-(2-acetamido-6-O-benzyl-2-deoxy-β-d-glucopyranosyl) - (1→3) - 2, 4, 6-tri-O-benzyl-β-d-galactopyranoside (10) with methyl 2,4,6-tri-O-benzoyl-3-O-(methoxycarbonyl)methyl-1-thio-β-d-galactopyranoside (6) or methyl 2-O-benzoyl-4,6-O-benzylidene-3-O-levulinoyl-1-thio-β-d-galactopyranoside (9) using dimethyl-(methylthio)sulfonium triflate (DMTST) as a promoter, afforded the corresponding tetrasaccharide derivatives 11 and 19. Compounds 11 and 19 were converted into the α-trichloroacetimidates 14 and 23, via reductive removal of the benzyl and benzylidene groups, O-acetylation, removal of the 2-(trimethylsilyl)ethyl group, and treatment with trichloroacetonitrile, which, on coupling with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (15) or 2-(tetradecyl)hexadecan-1-ol (24), gave the lipophilic derivatives 16 and 25. Compound 16 was transformed, via selective reduction of the azido group, condensation with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester group, into the title compound 18 in good yield. Compound 25 was treated with hydrazine acetate to give compound 26, which in turn was transformed, via sulfation or phosphorylation, and O-deacylation, into the target compounds 28 and 31.

Synthetic Studies on Sialoglycoconjugates 81: Synthesis of Positional Isomers of Sialyl Lewis X Epitope Containing 1-Deoxy-dGlucose in Place ofN-Acetylglucosamine, and Their Inhibitory Activity to Selectin-Mediated Adhesion

Abstract Three sialyl-Lex epitope analogs, which carry fucose and α-sialyl-(2→3)-galactose residues at O-2 and O-3, O-3 and O-2, and O-4 and O-6 positions of 1-deoxy-D-glucose backbone, respectively, have been synthesized. Glycosylation of 1,5-anhydro-4,6-O-benzylidene-D-glucitol (1) or 1,5-anhydro-6-O-benzoyl-2,3-di-O-benzyl-d-glucitol (4) prepared from 1,5-anhydro-d-glucitol, with methyl 2,3,4-tri-O-benzyl-1-thio-β-L-fucopyranoside (5) using dimethyl(methylthio)sulfonium triflate (DMTST) as a promoter, afforded the corresponding fucosyl 1,5-anhydro-d-glucitol derivatives 7, 8 and 9. Glycosylation of 7, 8 or 10 derived from 9, with methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d-glyceroα-d-galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-d-galactopyranoside (11) in the presence of DMTST gave the expected tetrasaccharide derivatives 12, 16 and 20. Hydrolysis of the benzylidene group in 12 and 16 gave compounds 13 and 17. Finally 13, 17 and 20 were transformed, by reduct...

O-Benzylidene Derivatives of D-Arabinose Diethyl and Dipropyl Dithioacetal

Benzylidenation of D-arabinose diethyl and dipropyl dithioacetals with α,α-dimethoxytoluene in the presence of p-toluenesulfonic acid has been studied in detail. Under kinetic control the two terminal dioxolan -type 4,5-O-(R)- and 4,5-O-(S)-benzylidene diastereomers are formed first which are in equilibrium with each other In the thermodynamic phase of the reaction the corresponding dioxan -type 3,5-O-(R)- benzylidene isomer is formed too, but all three monobenzylidene isomers are gradually converted into the four possible dioxolan -type 2,3 : 4,5-di-O benzylidene diastereomers . The dioxan -type 2,4:3,5-di-O-benzylidene isomer was present only in trace amounts. When benzaldehyde was used as reagent in the presence of hydrochloric acid or zinc chloride only the 2,3: 4,5-di-O-benzylidene diastereomers were formed. Partial hydrolysis of the dibenzylidene derivatives yielded the corresponding 2,3-O-benzylidene diastereomers. Structures, including the chirality of the benzylidene groups, were determined by n.m.r. spectroscopy. A mechanism suggested for the reaction was partially supported by equilibration studies.

The 2-(2-Chloroacetoxyethyl)benzoyl Group - Stable to Hydrogenolysis and Cleavable beside other Acyl Groups

The 2-(2-chloroacetoxyethyl)benzoyl (CAEB) group is prepared from isochromane in 4 steps and used as a temporary protecting group for carbohydrates. The CAEB group functions as a neighboring active, 1,2- trans -directing blocking group for glycosyl donors. It does not show transesterification to less reactive nucleophiles and is stable toward hydrogenolysis. CAEB can be cleaved off with thiourea and without effecting other acyl groups. It is suited for orthogonal protection strategies in combination with acetyl, benzoyl, benzyl and benzylidene groups in saccharide synthesis. The 2-(2-chloroacetoxyethyl)benzoyl (CAEB) group is used as a hydrogenolytically stable protecting group for carbohydrates. It behaves as a 1,2- trans -directing temporary blocking of position 2 in glycosyl donors and can be cleaved without affecting other acyl groups.