C-4 EPIMERIZATION OF α-D-GLUCOPYRANOSIDE: A FACILE SYNTHESIS OF 4-O-ACETYL-α-D-GALACTOPYRANOSYL DERIVATIVES

An unexpected epimerization resulting from the reaction of α-D-glucopyranosyl derivatives with DAST is described. The reaction of 3,4-di-O-acetyl-1,6-di-O-trityl-β-D-fructofuranosyl 2,3,6-tri-O-acetyl-α-D-glucopyranoside (1), methyl 2,3-di-O-acetyl-6-O-trityl-α-D-glucopyranoside (6), 2,3-di-O-acetyl-6-O-trityl-α-D-glucopyranosyl 2,3-di-O-acetyl-6-O-trityl-α-D-glucopyranoside (13), and 2,3-di-O-acetyl-6-O-tert-butyldiphenylsilyl-α-D-glucopyranosyl 2,3,4,6-tetra-O-acetyl-α-D-glucopyranoside (14) with DAST at 0°C did not give the expected C-4 fluorodeoxy galacto derivatives, but instead, the corresponding 4-O-acetyl-3-hydroxy-α-D-galactopyranosides in yields of 52–78%. When the treatment of 6 was carried out at ?25°C for ～5 min the corresponding diastereomeric 4-O-diethylaminosulfinates (9a,b) were isolated as the major products (40%). Evidence suggests that the epimerization reaction most probably resulted from an intramolecular displacement of the intermediate diethylaminosulfur difluoride ester or diethylaminosulfinyl ester by the neighbouring acetoxy groups.     

Synthesis of Per- and Poly-Substituted Trehalose Derivatives: Studies of Properties Relevant to Their Use as Excipients for Controlled Drug Release

Per- and poly-substituted oligosaccharide derivatives, with trehalose cores, have been prepared and assessed for their potential for use as excipients in controlled-release formulations. The synthesized compounds, generally with acyl and amido substituents, included 6,6′-N,N′ -diamido-6,6′ -dideoxy-α,α -trehalose derivatives, 6,6′ -bis(1,2,3,4-tetra-O-acetyl-β -D-glucopyranuronyl)-α, α -trehalose derivatives, 2,2′,3,3′ -tetra-O-acetyl-6,6′ -bis-(1,2,3,4-tetra-O-acetyl-β-D-glucopyranuronyl)-4,4′ -di-O-acyl-α,α-trehalose, 2, 2′, 3, 3′ -tetra-O-acetyl-6-(1,2,3,4-tetra-O-acetyl-β-D-glucopyranuronyl)-4,4′,6′ -tri-O-acyl-α,α-trehalose, and 2,2′,3,3′,4,4′ -hexa-O-acetyl-6,6′ -bis-(1,2,3,4-tetra-O-acetyl-6-O-succinyl-β-D-glucopyranuronyl)-α,α-trehalose. Compounds were characterized by NMR, IR, MS and optical rotations; elemental analyses; or HRMS. The compounds formed amorphous materials either on fast quenching of melts or on spray drying. Properties, used in the initial assessment of the potential as controlled-release excipients, were log₁₀ P and glass transition, T_g, values.     

Studies on the Thioglycosides of N-Acetyl-Neuraminic Acid 8: Synthesis of S-(α-Sialyl)-(2→ 6)-β-Hexopyranosyl and -(2→ 6')-β-Lactosyl Ceramides Containing β-Thioglycosidically Linked Ceramide

ABSTRACT

Coupling of the sodium salt of S-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-galacto-2-nonulopyranosylonate)-(2→'6)-2,3,4-tri-O-acetyl-1,6-dithio-β-D-glucopyranose (5), -β-D-galactopyranose (8), or S-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→'6)-O-(2,3,4-tri-O-acetyl-6-thio-β-D-galactopyranosyl)-(1→'4)-2,3,6-tri-O-acetyl-1-thio-β-D-glucopyranose (12), which were prepared from the corresponding 1-hydroxy compounds, 1, 2, and 9, via 1-chlorination, displacement with thioacetyl group, and S-deacetylation, with (2S,3R,4E)-2-azido-3-O-benzoyl-1-O-(p-toluenesulfonyl)-4-octadecene-1,3-diol (13), gave the corresponding β-thioglycosides 14, 18 and 22, respectively in good yields. The β-thioglycosides obtained were converted, via selective reduction of the azide group, condensation with octadecanoic acid, and removal of the protecting groups, into the title compounds.     

Synthetic Studies on Sialoglycoconjugates 88: Synthesis of Ganglioside GM3 and GM4 Analogs Containing 2- OR 3-Branched Fatty-Alkyl Residues in Place of Ceramide

ABSTRACT

Each of four ganglioside GM₄ and GM₃ analogues containing 2- or 3-branched fatty alkyl residues in place of ceramide have been synthesized. Coupling of O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-α-D-galactopyranosyl trichloroacetimidate (13) or O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-glacto-2-nonulopyranosylonate)-(2→3)-O-(2,4-di-O-acetyl-6-O-benzoyl-β-D-galactopyranosyl)-(1→4)-3-O-acetyl-2,4-di-O-benzoyl-α-D-glucopyranosyl trichloroacetimidate (14) with 2- or 3-branched fatty-alkyl-1-ols (9-12), prepared from the corresponding branched fatty acids by methyl esterification and reduction, using BF₃Ot₂ gave the corresponding ganglioside analogues (15, 17, 19, 21, 23, 25, 27, 29) in good yields, which were coverted, via O-deacylation and de-esterification, into the title compounds.     

SYNTHESIS OF (2,3,4,6-TETRA-O-ACETYL-α-D-GLYCOPYRANOSYL) THIOPHENE DERIVATIVES AS NEW C-NUCLEOSIDE ANALOGUES[1]

Treatment of 2-(2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl)ethanal (1a) and 2-(2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl)ethanal (1b) respectively with malononitrile in the presence of silica gel provided the corresponding 4-[2,3,4,6-tetra-O-acetyl-α-D-glycopyranosyl]-2-cyanocrotononitriles (2a) and (2b). Starting from 2a and 2b, respectively, cyclizations with sulfur and triethylamine yielded 5-[2,3,4,6-tetra-O-acetyl-α-D-glycopyranosyl]-2-aminothiophene-3-carbonitriles (3a) and (3b). Further cyclizations could be achieved by utilizing of triethyl orthoformate/ammonia to furnish the 6-(α-D-glycopyranosyl)thieno[2,3-d]pyrimidine-4-amines 4a and 4b.     

2-Deoxy-2-C-(2,3-dideoxy-α-d-erythro-hexopyranosyl)-β-d-glucopyranoses: Reinvestigation of Synthesis,Use in Glycosylation,and Conformational Analyses by NMR

Abstract

Conformational investigations using 1D TOCSY and ROESY ¹H NMR experiments on 1,3,4,6-tetra-O-acetyl-2-C-(4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hexopyranosyl)-2-deoxy-β-D-glucopyranose (8) and related disaccharides showed that for steric reasons the C-linked hexopyranosyl ring occurs in the usually unfavoured ¹C₄ conformation and reconfirmed the structure of 1,3,4,6-tetra-O-acetyl-2-C-(4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-enopyranosyl)-2-deoxy-β-D-glucopyranose (5). Glycosylation of 2,3,6-tri-O-benzyl-α-D-glucopyranosyl 2,3-di-O-benzyl-4,6-(R)-O-benzylidene-α-D-glucopyranoside (13) with acetate 8 using trimethylsilyl triflate as a catalyst afforded the α-D-linked tetrasaccharide 14. A remarkable side product in this reaction was the unsaturated tetrasaccharide 2,3,6-tri-O-benzyl-4-O-[4,6-di-O-acetyl-2,3-dideoxy-2-C-(4,6-di-O-acetyl-2,3-dideoxy-β-D-erythro-hexopyranosyl)-α-D-erythro-hex-2-enopyranosyl]-α-D-glucopyranosyl 2,3-di-O-benzyl-4,6-(R)-O-benzylidene-α-D-glucopyranoside (16) where in the C-linked hexopyranosyl ring an isomerization to the β-anomer had taken place to allow for the favoured ⁴C₁ conformation. The tetrasaccharide 14 was deacetylated and hydrogenolyzed to form the fully deprotected tetrasaccharide 18. The ¹ C ₄ conformation of the C-glycosidic pyranose of this tetrasaccharide was maintained as shown by an in depth NMR analysis of its peracetate 19.     

Synthesis of 2-S-dioxo isosteres of purine and pyrimidine nucleosides. I. Alkyl and glycosyl derivatives of 3,5-diamino-4H-1,2,6-thiadiazine 1,1-dioxide

Preparation of alkyl and glycosyl derivatives of 3,5-diamino-4H-1,2,6-thiadiazine 1,1-dioxide (1) is described. Reaction of 1 with dimethyl sulfate gave the 4-methyl and 2,4-dimethyl derivatives. With benzyl chloride and allyl bromide C-4 substituted compounds were obtained. Reaction of the disilyl derivative of 1 with either 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide or 1,2,3,4,6-penta-O-acetyl-β-D-glucopyranose in the presence of Friedel-Crafts catalysts afforded the α and β anomers of the N-2 nucleoside and the β-O-glucoside. When the reaction was performed with 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D-ribofuranose, a β-C-glycoside and the α and β anomers of the N-2 nucleoside were obtained. The structure of the corresponding nucleosides were elucidated by ¹H nmr and uv by comparing the latter with those of the alkyl derivatives.     

Synthesis of 1-O-(Methylthio)thiocarbonyl Sugar Derivatives Bearing Acyl Protective Groups Using Phase Transfer Catalysis Methods

Abstract

2,3,4,6-Tetra-O-acetyl-D-glucopyranose (1) was successfully transformed to an anomeric mixture of 2,3,4,6-tetra-O-acetyl-1-O-(methylthio)thiocarbonyl-D-glucopyranose (2) by liquid - liquid and solid - liquid phase transfer methods. Similar anomeric free sugar derivatives bearing acetyl or benzoyl protective groups were also smoothly converted to the corresponding 1-O-(methylthio)thiocarbonyl derivatives. Thermal rearrangement of 1-O-(methylthio)thiocarbonylfuranose derivatives proceeded well to give 1-S-methylthiocarbonyl-1-thiofuranose derivatives.     

Chemical-Enzymatic Synthesis of A Branched Hexasaccharide Fragment of Type Ia Group B Streptococcus Capsular Polysaccharide

ABSTRACT

A branched hexasaccharide fragment of type Ia group B streptococcal polysaccharide, α-NeuAc(2→3)-β-D-Gal(1→4)-β-D-GlcNAc(1→3)-[β-D-Glc(1→4)]-β-D-Gal(1→4)-β-D-Glc-OMe (13), has been synthesized by chemical-enzymatic procedures. Chemical synthesis of a pentasaccharide, β-D-Gal(1→4)-β-D-GlcNAc(1→3)-[β-D-Glc(1→4)]-β-D-Gal(1→4)-β-D-Glc-OMe (12), was achieved from glycosyl donor, 4-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-3,6-di-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl trichloroacetimidate (9), and acceptor, methyl O-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-(1→4)-O-(2,6-di-O-benzyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (6), by block condensation in 41% yield. Following enzymatic sialylation of 12 at the 3-O-position of its terminal galactopyranosyl residue using recombinant α-(2→3)-sialyltransferase and CMP-NeuAc afforded 13 in 59% yield.     

Synthesis and Properties of New Thiacalixarene Derivatives with Palladium Ion

Three new thiacalix[4]arene derivatives, 5,11,17,23-tetra-tert-butyl-25,27-di(2-hydroxyethoxy)-26,28-dihydroxythiacalix-{}[4]arene (2), 5,11,17,23-tetra-tert-25, 26,27,28-tetrakis[(methylcarboxyl)methoxy]thiacalix[4]arene (3),5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(2-hydroxy-1-propanoxy)thiacalix[4]arene (4), were synthesized for the first time. The coordination properties of thiacalix[4]arene(1) and its derivatives (2 and 4) were investigated by detecting the interactions betweenthese compounds and two palladium complexes, cis-[Pd(en)(H₂O)₂]²⁺ and cis-[Pd(dtco-3-OH)(H₂O)₂]²⁺, by means of electrospray ionization mass spectrometry (ESI-MS) technique.     

Synthetic Studies on Sialoglycoconjugates 89: Synthesis of Ganglioside GM3 and KDN-GM3 Containing Different Carbon-Chain Length Fatty Acyl Groups at the Ceramide Residue

ABSTRACT

Ganglioside GM₃ and KDN-ganglioside GM₃, containing hexanoyl, decanoyl, and hexadecanoyl groups at the ceramide moiety have been synthesized. Selective reduction of the azido group in O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→3)-O-(2,4-di-O-acetyl-6-O-benzoyl-β-D-galactopyranosyl)-(1→4)-O-(3-O-acetyl-2,6-di-O-benzoyl-β-D-glucopyranosyl)-(1→1)-(2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (1) and O-(methyl 4,5,7,8,9-penta-O-acetyl-3-deoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→3)-O-(2,4-di-O-acetyl-6-O-benzoyl-β-D-galactopyranosyl)-(1→4)-O-(3-O-acetyl-2,6-di-O-benzoyl-β-D-glucopyranosyl)-(1→1)-(2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (2), coupling with hexanoic, decanoic, and hexadecanoic acids, O-deacylation, and de-esterification gave the title gangliosides GM₃ (11→13) and KDN-GM₃ (14→16) in good yields. On the other hand, O-deacylation of 1 and subsequent de-esterification gave 2-azido-sphingosine containing-GM₃ analogue 17, which was converted into lyso-GM₃, in which no fatty acyl group was substituted at the sphingosine residue, by selective reduction of the azido group.     

A Convenient Synthesis of 2, 3 - DI- O - Acetyl-1, 6 - Anhydro- β - D – Glucopyranose

Abstract

1, 2, 3-Tri-O-acetyl-6-O-benzyl-4-O-chloroacetyl-α- and -β-D-glucopyranose (4α β)were derived from 1, 2, 3-tri-O-acetyl-4, 6- O -benzyl-idehe-β-D-giucopyranose (1) in two steps. Compound 1, 1, 2, 3-tri-O -acetyl-β-D-glucopyranose (2), and 4α,β were subjected to the cyclization reaction using Lewis acids ( SnCl₄ and BF₃-etherate), to give corresponding 1, 6-anhydro derivatives.     

Synthetic Antigens: Synthesis of 4-Aminophenyl O-α-D-Mannopyranosyl-(1→2)-O-α-D-mannopyranosyl-(1→6)-O-α-D-Mannopyranoside and A Related Di- and A Trisaccharide

Abstract

4-Nitrophenyl 2,3-O-isopropylidine-α-D-mannopyranoside 2 was condensed with O-(2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl)-(1→2)-3,4,6-tri-O-acetyl-α-D-mannopyranosyl bromide 1 and 2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl bromide 11 in the presence of mercuric cyanide. Products were deprotected to yield, respectively, 4-nitrophenyl O-α-D-mannopyranosyl-(1→2)-O-α-D-mannopyranosyl-(1→6)-α-D-mannopyranoside 6 and 4-nitrophenyl O-α-D-mannopyranosyl-(1→6)-α-D-mannopyranoside 14. The 4-nitrophenyl group of 6 was reduced to give title trisaccharide. Bromide 1 was also condensed with methyl 2,3,4-tri-O-benzyl-α-D-manopyranoside 3 in the presence of silver trifluoromethanesulfonate and tetramethylurea to give protected trisaccharide derivative which was deprotected to furnish, methyl O-α-D-mannopyranosyl-(1→2)-O-α-D-mannopyranosyl-(1→6)-α-D-mannopyranoside 10. The identities of all protected and deprotected compounds were supported by ¹H and ¹³C NMR spectral data.     

The different modes of chiral [1,2,3]triazolo[5,1‐b][1,3,4]thiadiazines: crystal packing,conformation investigation and cellular activity

The crystal structures of four new chiral [1,2,3]triazolo[5,1‐b][1,3,4]thiadiazines are described, namely, ethyl 5′‐benzoyl‐5′H,7′H‐spiro[cyclohexane‐1,6′‐[1,2,3]triazolo[5,1‐b][1,3,4]thiadiazine]‐3′‐carboxylate, C₁₉H₂₂N₄O₃S, ethyl 5′‐(4‐methoxybenzoyl)‐5′H,7′H‐spiro[cyclohexane‐1,6′‐[1,2,3]triazolo[5,1‐b][1,3,4]thiadiazine]‐3′‐carboxylate, C₂₀H₂₄N₄O₄S, ethyl 6,6‐dimethyl‐5‐(4‐methylbenzoyl)‐6,7‐dihydro‐5H‐[1,2,3]triazolo[5,1‐b][1,3,4]thiadiazine‐3‐carboxylate, C₁₇H₂₀N₄O₃S, and ethyl 5‐benzoyl‐6‐(4‐methoxyphenyl)‐6,7‐dihydro‐5H‐[1,2,3]triazolo[5,1‐b][1,3,4]thiadiazine‐3‐carboxylate, C₂₁H₂₀N₄O₄S. The crystallographic data and cell activities of these four compounds and of the structures of three previously reported similar compounds, namely, ethyl 5′‐(4‐methylbenzoyl)‐5′H,7′H‐spiro[cyclopentane‐1,6′‐[1,2,3]triazolo[5,1‐b][1,3,4]thiadiazine]‐3′‐carboxylate, C₁₉H₂₂N₄O₃S, ethyl 5′‐(4‐methoxybenzoyl)‐5′H,7′H‐spiro[cyclopentane‐1,6′‐[1,2,3]triazolo[5,1‐b][1,3,4]thiadiazine]‐3′‐carboxylate, C₁₉H₂₂N₄O₄S, and ethyl 6‐methyl‐5‐(4‐methylbenzoyl)‐6‐phenyl‐6,7‐dihydro‐5H‐[1,2,3]triazolo[5,1‐b][1,3,4]thiadiazine‐3‐carboxylate, C₂₂H₂₂N₄O₃S, are contrasted and compared. For both crystallization and an MTT assay, racemic mixtures of the corresponding [1,2,3]triazolo[5,1‐b][1,3,4]thiadiazines were used. The main manner of molecular packing in these compounds is the organization of either enantiomeric pairs or dimers. In both cases, the formation of two three‐centre hydrogen bonds can be detected resulting from intramolecular N—H…O and intermolecular N—H…O or N—H…N interactions. Molecules of different enantiomeric forms can also form chains through N—H…O hydrogen bonds or form layers between which only weak hydrophobic contacts exist. Unlike other [1,2,3]triazolo[5,1‐b][1,3,4]thiadiazines, ethyl 5′‐benzoyl‐5′H,7′H‐spiro[cyclohexane‐1,6′‐[1,2,3]triazolo[5,1‐b][1,3,4]thiadiazine]‐3′‐carboxylate contains molecules of only the (R)‐enantiomer; moreover, the N—H group does not participate in any significant intermolecular interactions. Molecular mechanics methods (force field OPLS3e) and the DFT B3LYP/6‐31G+(d,p) method show that the compound forming enantiomeric pairs via weak N—H…N hydrogen bonds is subject to greater distortion of the geometry under the influence of the intermolecular interactions in the crystal. For intramolecular N—H…O and S…O interactions, an analysis of the noncovalent interactions (NCIs) was carried out. The cellular activities of the compounds were tested by evaluating their antiproliferative effect against two normal human cell lines and two cancer cell lines in terms of half‐maximum inhibitory concentration (IC₅₀). Some derivatives have been found to be very effective in inhibiting the growth of Hela cells at nanomolar and submicromolar concentrations with minimal cytotoxicity in relation to normal cells.     

Organometallic derivatives of sugars

Stable organometallic derivatives of glucose were prepared either by treatment of 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranose with organometallic hydroxides R₃ MOH and oxides R₂ MO or by the reaction between 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide with R₃SnSLi.     

Syntheses of N-Acyl and N-Alkoxycarbonyl Derivatives of 2-Alkoxycarbonylamino-2-deoxy-D-glucose

Abstract

N-Acyl and N-alkoxycarbonyl derivatives of l, 3, 4, 6-tetra-O-acetyl-2-alkoxy-carbonylamino-2-deoxy-β-D-glucopyranose have been synthesized using mixed anhydrides and symmetrical or disymetrical pyrocarbonates. These derivatives have been used as donors in 1, 2-trans-glycosylation reactions promoted by Lewis acids. Besides the expected (β-D-glycosides, cyclisation and rearrangement side-products were often encountered in such glycosylations.     

Cationic ring-opening polymerization of new 1,6-anhydro-β-lactose derivatives

Synthesis and cationic ring-opening polymerization of new 1,6-anhydro-β-lactose derivatives such as hexa-O-methylated (LSHME), tert-butyldimethylsilylated (LSHSE), and benzylated 1,6-anhydro-β-lactoses (LSHBE) were first investigated. The disaccharide monomers were prepared by methylation, tert-butyldimethylsilylation, and benzylation of 1,6-anhydro-β-lactose, respectively. It was found that LSHME was readily polymerized with such Lewis acid catalysts as PF₅ and SbCl₅ to give stereoregular 2,3-di-O-methyl-4-O-(2′,3′,4′,6′-tetra-O-methyl-β-D -galactopyranosyl)-(1→6)-β-D -glucopyranans which are comb-shaped polysaccharide derivatives. However, LSHSE and LSHBE had almost no polymerizability. It was revealed that the ring-opening polymerizability of the anhydrodisaccharide monomers was influenced by the steric hindrance of the hydroxyl-protective groups. Ring-opening copolymerization of LSHME with 1,6-anhydro-2,3,4-tri-O-benzyl-β-D -glucopyranose (LGTBE) in various ratios of monomer feeds was also examined to afford the corresponding copolymers. Structural analyses of the monomers and polymers were carried out by means of high resolution nuclear magnetic resonance spectroscopy.     

A new myrsinol-type diterpene polyester from Euphorbia dracunculoides Lam

A new myrsinol-type diterpene polyester, 14-deoxo-3β-O-propinoyl-2α,5α,7β,15β-tetra-O-acetyl-14α-O-benzoyl-myrsinol (1), and its known analogue, 14-deoxo-3β-O-prorionyl-5α,15β-di-O-acetyl-7β-O-nicotinoyl-myrsinol-14β-acetate (2), together with a monoterpenoid, pubinernoid A (3), two indole alkaloids, neoechinulin A (4) and dihydroxyisoechinulin A (5), two benzene derivatives, siringin (6) and (3-methoxyphenyl) acetic acid (7), were isolated from the 70% acetone extract of the aerial parts of Euphorbia dracunculoides Lam. Their structures were elucidated on the basis of spectroscopic evidence and comparison with literature reports. The absolute configuration of 1 was deduced by comparing experimental and calculated ECD spectra. Among them, compounds 4 and 5 were first obtained from the plant source. In addition, the ¹³C NMR data of compound 2 was reported for the first time.     

Unexpected synthesis of a naphthylsilole

The reaction of 1,4-dilithiotetraphenylbutadiene (2) with 1,1′-dichloro-2,3,4,5-tetraphenyl-1-silole (3) leads to 2,3,4,5-tetraphenyl-1-(1,2,3-triphenylnaphthalen-4-yl)-1H-silole (5) instead of the expected octaphenyl-1,1′-spirobisilole (1). The reaction of 2 with SiC1₄ in dioxane produced 1 in low yield, confirming results reported earlier.     

Synthesis of Sialyl Lewis X Ganglioside Analogs Containing A Variable Length Spacer Between the Sugar and Lipophilic Moieties 1

Abstract

Five sialyl Lew is X ganglioside analogs containing 4-(2-tetradecylhexadecanoylamino)benzyl group in place of ceramide and a variety of lengths of ethylene glycol chains as the spacer, have been synthesized. Glycosidation of O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-glacto-2-nonulopyranosylonate)-(2→3)-O-(4-O-acetyl-2,6-di-O-benzoyl-β-D-galactopyranosyl)-(1→4)-O-[(2,3,4-tri-O-acetylα-L-fucopyranosyl)-(1→3)]-2,4-di-O-benzoyl-α-D-glucopyranosyl trichloroacetimidate (13) with oligo ethyleneglycol monobenzyl ether derivatives 9, 10, 11 and 12, prepared from the corresponding oligo ethyleneglycols by 4-nitrobenzylation, reduction and N-acylation with 2-tetradecylhexadecanoic acid, using boron trifluoride etherate gave the corresponding glycolipid derivatives 14, 15, 16 and 17. A similar glycosidation of 13 with 4-nitrobenzyl alcohol gave the 4-nitrobenzyl glycoside 18, which was converted via reduction of nitro group and N-acylation into the corresponding glycolipid derivative 19. Compounds 14-17 and 19 were transformed into the title compounds by O-deacylation and hydrolysis of methyl ester group in good yields.