1,6-Anhydro-N-Acetyl- beta-D-glucosamine in oligosaccharide synthesis: II. synthesis of a spacered Ley tetrasaccharide

3-Aminopropyl glycoside of 3,2'-di-O-alpha-L-fucosyl-N-acetyllactosamine (Ley tetrasaccharide) was synthesized. The glycosyl donor, 2-O-acetyl-3,4,6-tri-O-benzoyl-alpha-D-galactopyranosyl bromide, was coupled with glycosyl acceptor, 1,6-anhydro-2-acetamido-2-deoxy-beta-D-glucopyranose or its 3-O-acetyl derivative, to give the corresponding N-acetyllactosamine derivatives in 20 and 71% yields, respectively. The glycosyl donor was synthesized from 1,2-di-O-acetyl-3,4,6-tri-O-benzoyl-D-galactopyranose, which was obtained by the treatment of benzobromogalactose with sodium borohydride to yield 1,2-O-benzylidene derivative and subsequent removal of benzylidene group and acetylation. Acidic methanolysis of the disaccharide derivatives resulted in the selective removal of one or both acetyl groups to give the disaccharide acceptor bearing hydroxy groups at C3 of the glucosamine residue and C2 of the galactose residue. The introduction of fucose residues in these positions by the treatment with tetrabenzylfucopyranosyl bromide resulted in a tetrasaccharide derivative, which was converted into 3,2'-di-O-alphha-L-fucopuranosyl- 1,6-anhydro-N-acetyllactosamine peracetate after substitution of acetyl groups for benzoyl and benzyl groups. Opening of the anhydro ring by acetolysis resulted in peracetate, which was then converted into the corresponding oxazoline derivative in two steps. Glycosylation of the oxazoline derivative with 3-trifluoroacetamidopropan-1-ol and removal of O-acetyl and N-trifluoroacetyl protective groups resulted in a free spacered Ley tetrasaccharide.     

Synthesis of capsular polysaccharide of Streptococcus pneumoniae type 14. 3. Synthesis of a monomer for polycondensation

Synthesis of a tritylated tetrasaccharide 1,2-O-(1-cyano) ethylidene derivative is described by glycosylation of 3,6-di-O-benzoyl-4-O-(2,4,6-tri-O-benzoyl-beta- D-galactopyranosyl)-1,2-O-[1-(exo-cyano)ethylidene]-alpha-D- glucopyranose with 6-O-acetyl-3-O-benzoyl-4-O-(2,3,4,6-tetra-O-benzoyl-beta- D-galactopyranosyl)-2-deozy-2-phthalimido-D-glucopyranosyl. bromide followed by selective deacetylation and tritylation.     

Synthesis of the tetrasaccharide related to the repeating unit of the antigen from Shigella dysenteriae type 5

Starting from L-rhamnose, D-mannose and 2-amino-2-deoxy-D-glucose hydrochloride, two disaccharide blocks, namely, ethyl 2,4-di-O-benzyl-3-O-[(R)-1-(methoxycarbonyl)ethyl]-alpha-L-rhamnopyranos yl-(1-->3)-2-O-acetyl-4,6-di-O-benzyl-1-thio-alpha-D-mannopyranoside and 2-(trimethylsilyl)ethyl 2-O-acetyl-3,6-di-O-benzyl-alpha-D-mannopyranosyl-(1-->3)-4,6-di-O-benzy l-2-deoxy-2-phthalimido-beta-D-glucopyranoside, were synthesised and then allowed to react in the presence of N-iodosuccinimide and trifluoromethane sulfonic acid to give a tetrasaccharide derivative. This compound was converted into 2-(trimethylsilyl)ethyl 2,4-di-O-benzyl-3-O-[(R)-1-(methoxycarbonyl)ethyl]-alpha-L-rhamno- pyranosyl-(1-->3)-2-O-acetyl-4,6-di-O-benzyl-alpha-D-mannopyranosyl-(1-- >4)-2-O-acetyl-3,6-di-O-benzyl-alpha-D-mannopyranosyl-(1-->3)-2-acetamid o-4,6-di-O-benzyl-2-deoxy-beta-D-glucopyranoside, which on hydrogenolysis, afforded the methyl ester 2-(trimethylsilyl)ethyl glycoside of the tetrasaccharide related to the repeating unit of the O-antigen from Shigella dysenteriae type 5.     

Malonylated Glycerolipids from the Glandular Trichome Exudate of Ceratotheca triloba

Chemical investigation of the glandular trichome exudate from Ceratotheca triloba (Pedaliaceae) led to the identification of nine 1-O-acetyl-2-O-[(R)-3-acetyloxy-fatty acyl]-3-O-malonylglycerols. Among these, 1-O-acetyl-2-O-[(R)-3-acetyloxyicosanoyl]-3-O-malonylglycerol (7) was the most abundant constituent (41%), followed by 1-O-acetyl-2-O-[(R)-(3-acetyloxyoctadecanoyl)-3-O-malonylglycerol (2; 21%). Compounds having iso- and anteiso-type structures in the 3-acetyloxy-fatty acyl groups in the fatty acyl moiety were also characterized as minor constituents. This is the first report of the isolation of malonylated glycerolipids as natural products.     

Synthesis of a spacer-containing repeating unit of the capsular polysaccharide of Streptococcus pneumoniae type 23F.

The synthesis is reported of 3-aminopropyl 4-O-(4-O-beta-D-glucopyranosyl-2-O-alpha-L-rhamnopyranosyl-beta-D- galactopyranosyl)-beta-L-rhamnopyranoside 3'-(glycer-2-yl sodium phosphate) (25 beta), which represents the repeating unit of the capsular polysaccharide of Streptococcus pneumoniae type 23F (American type 23) [(----4)-beta-D-Glcp-(1----4)-[Glycerol-(2-P----3)] [alpha-L- Rhap-(1----2)]-beta-D-Galp-(1----4)-beta-L-Rhap-(1----)n). 2,4,6-Tri-O-acetyl-3-O-allyl-alpha-D-galactopyranosyl trichloroacetimidate (5) was coupled with ethyl 2,3-di-O-benzyl-1-thio-alpha-L-rhamnopyranoside (6). Deacetylation of the resulting disaccharide derivative, followed by benzylidenation, and condensation with 2,3,4-trio-O-acetyl-alpha-L-rhamnopyranosyl trichloroacetimidate (10) afforded ethyl 4-O-[3-O-allyl-4,6-O-benzylidene-2-O-(2,3,4-trio-O-acetyl- alpha-L-rhamnopyranosyl)-beta-D-galactopyranosyl]-2,3-di-O-benzyl-1-thio - alpha-L-rhamnopyranoside (11). Deacetylation of 11, followed by benzylation, selective benzylidene ring-opening, and coupling with 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl trichloroacetimidate (15) gave ethyl 4-O-[3-O-allyl-6-O-benzyl-4-O-(2,3,4,6- tetra-O-acetyl-beta-D-glucopyranosyl)-2-O-(2,3,4-tri-O-benzyl-alpha-L- rhamnopyranosyl)-beta-D-galactopyranosyl]-2,3-di-O-benzyl-1-thio-alpha-L - rhamnopyranoside (16). Deacetylation of 16 followed by benzylation, deallylation, and acetylation yielded ethyl 4-O-[3-O-acetyl-6-O-benzyl-4-O-(2,3,4,6-tetra-O-benzyl-beta-D-glucopy ran osyl)- 2-O-(2,3,4-tri-O-benzyl-alpha-L-rhamnopyranosyl)-beta-D-galactopyranosyl ]-2,3- di-O-benzyl-1-thio-alpha-L-rhamnopyranoside (20). The glycosyl bromide derived from 20, when coupled with 3-benzyloxycarbonylamino-1-propanol, gave the beta-glycoside (21 beta) as the major product. Deacetylation of 21 beta followed by condensation with 1,3-di-O-benzylglycerol 2-(triethylammonium phosphonate) (27), oxidation, and deprotection, afforded 25 beta.     

Synthesis of trisaccharide methyl glycosides related to fragments of the capsular polysaccharide of Streptococcus pneumoniae type 18C.

The synthesis is reported of methyl 3-O-(4-O-beta-D-galactopyranosyl-alpha-D- glucopyranosyl)-alpha-L-rhamnopyranoside (1), methyl 2-O-alpha-D-glucopyranosyl-4-O-beta-D-glucopyranosyl-beta-D- galactopyranoside (3), methyl 3-O-(4-O-beta-D-galactopyranosyl-alpha-D-glucopyranosyl)-alpha-L- rhamnopyranoside 3"-(sn-glycer-3-yl sodium phosphate) (2), and methyl 2-O-alpha-D-glucopyranosyl-4-O-beta-D- glucopyranosyl-beta-D-galactopyranoside 3-(sn-glycer-3-yl sodium phosphate) (4), which are trisaccharide methyl glycosides related to fragments of the capsular polysaccharide of Streptococcus pneumoniae type 18C ([----4)-beta-D- Glcp-(1----4)-[alpha-D-Glcp-(1----2)]-[Glycerol-(1-P----3)]-beta-D-Galp - (1----4)-alpha-D-Glcp-(1----3)-alpha-L-Rhap-(1----]n). Ethyl 4-O-acetyl-2,3,6-tri-O-benzyl-1-thio-beta-D-glucopyranoside (10) was coupled with benzyl 2,4-di-O-benzyl-alpha-L-rhamnopyranoside (6). Deacetylation of the product, followed by condensation with 2,4,6-tri-O-acetyl-3-O-allyl-alpha-D-galactopyranosyl trichloroacetimidate (18), gave benzyl 2,4-di-O-benzyl-3-O-[2,3,6-tri-O- benzyl-4-O-(2,4,6-tri-O-acetyl-3-O-allyl-beta-D-galactopyranosyl)-alpha- D- glucopyranosyl]-alpha-L-rhamnopyranoside (19). Acetolysis of 19, followed by methylation, deallylation (----22), and further deprotection afforded 1. Condensation of methyl 2,4-di-O-benzyl-3-O-[2,3,6-tri-O-benzyl-4-O-(2,4,6-tri- O-acetyl-beta-D-galactopyranosyl)-alpha-D-glucopyranosyl]-alpha-L- rhamnopyranoside (22) with 1,2-di-O-benzyl-sn-glycerol 3-(triethyl-ammonium phosphonate) (24), followed by oxidation and deprotection, yielded 2. Condensation of ethyl 2,3,4,6-tetra-O-benzyl-1-thio-beta-D-glucopyranoside (27) with methyl 3-O-allyl-4,6-O-benzylidene-beta-D-galactopyranoside (28), selective benzylidene ring-opening of the product, coupling with 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl trichloroacetimidate (31), and deallylation afforded methyl 6-O-benzyl-4-O-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl)-2-O- (2,3,4,6-tetra-O-benzyl-alpha-D-glucopyranosyl)-beta-D-galactopyranoside (33). Deprotection of 33 gave 3, and condensation of 33 with 24, followed by oxidation and deprotection, gave 4.     

Synthesis of 1,3-Dl-O-Acetyl-5-O-Benzoyl-2-O -(O-Carboran-1-Ylmethyl)- D-Ribofuranose. A General Precursor for the Preparation of Carborane-Containing Nucleosides for Boron Neutron Capture Therapy

Abstract

An eight-step synthesis of 1,3-di-O-acetyl-5-O-benzoyl-2-O-(o-carboran-1-ylmethyl)-D-ribofuranose 9 was carried out from 1,2:5,6-O-isopropylidene-α-D-allofuanose 1. Condensation of 9 with trimethylsilyl protected uracil in the presence of trimethylsilyl trifluoro-methanesulfonate, and subsequent deblocking of the resulting 1-[3-O-acetyl-5-O-benzoyl-2-O-(o-carboran-1-ylmethyl)-D-ribofuranosyl]uracil 10 (>95& β-configuration) by alkaline hydrolysis, yielded 1-[2-O-(o-carboran-1-ylmethyl)-β-D-ribofuranosyl]uracil 11.     

Syntheses and reactions of 5-O-acetyl-1,2-anhydro-3-O-benzyl-alpha-D-ribofuranose and beta-D-lyxofuranose, 5-O-acetyl-1,2-anhydro-3,6-di-O-benzyl- and 1,2-anhydro-5,6-di-O-benzoyl-3-O-benzyl-beta-D-mannofuranose, and 6-O-acetyl-1,2-anhydro-3,4-di-O-benzyl-alpha-D-glucopyranose and -beta-D-talopyranose

The title compounds 5-O-acetyl-1,2-anhydro-3-O-benzyl-alpha-D-ribofuranose and 5-O-acetyl-1,2-anhydro-3-O-benzyl-beta-D-lyxofuranose, and 6-O-acetyl-1,2-anhydro-3,4-di-O-benzyl-alpha-D-glucopyranose and 6-O-acetyl-1,2-anhydro-3,4-di-O-benzyl-beta-D-talopyranose, and 5-O-acetyl-1,2-anhydro-3,6-di-O-benzyl-beta-D-mannofuranose and 1,2-anhydro-5,6-di-O-benzoyl-3-O-benzyl-beta-D-mannofuranose have each been synthesized from the corresponding 2-O-tosylate and 1-free hydroxyl intermediates by base-initiated intramolecular S(N)2 ring closure in almost quantitative yields. Acetyl and benzoyl groups were not affected in the ring closure reactions. Condensation of 6-O-acetyl-1,2-anhydro-3,4-di-O-benzyl-alpha-D-glucopyranose and 5-O-acetyl-1,2-anhydro-3,6-di-O-benzyl-beta-D-mannofuranose with 1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranose in the presence of ZnCl2 as the catalyst afforded the 1,2-trans-linked 6-O-acetyl-3,4-di-O-benzyl-beta-D-glucopyranosyl-(1-->6)-1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranose and 5-O-acetyl-3,6-di-O-benzyl-alpha-D-mannofuranosyl-(1-->6)-1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranose as the sole products in satisfactory yields, while condensation of 5-O-acetyl-1,2-anhydro-3-O-benzyl-beta-D-lyxofuranose with 3-O-benzyl-1,2-O-isopropylidene-alpha-D-xylofuranose yielded the 1,2-trans-linked 5-O-acetyl-3-O-benzyl-alpha-D-lyxofuranosyl-(1-->5)-3-O-benzyl-1,2-O-isopropylidene-alpha-D-xylofuranose as the sole product in a good yield. The 6-O-acetyl group in the glycosyl donor, 6-O-acetyl-1,2-anhydro-3,4-di-O-benzyl-alpha-D-glucopyranose, did not influence the stereoselectivity of the ring-opening-coupling reaction.     

Synthesis of an aza analogue of 2-deoxy-D-ribofuranose and its homologues.

Azasugars were obtained in one-pot reactions by catalytic reduction reactions of amino group precursors in aldosugars followed by intramolecular reductive amino alkylation reactions. (3R,4S)-4-[(1S)-1,2-Dihydroxyethyl]pyrrolidin-3-ol was obtained from D-xylose by two different strategies through 3-C-cyano-3-deoxy-D-ribo-pentofuranose or 3-C-azidomethyl-3-deoxy-D-ribo-pentofuranose in 6 and 16% overall yields, respectively. The oxidative cleavage of the diol group in the corresponding Fmoc-azasugar followed by deprotection afforded (3R,4R)-4-(hydroxymethyl)pyrrolidin-3-ol. (3R,4S)-4-[(1S,2R)-1,2,3-Trihydroxypropyl]pyrrolidin-3-ol was synthesized from diacetone-D-glucose through 3-deoxy-3-C-nitromethyl-D-allose and the overall yield was 7%.     

Synthesis of an xylosylated rhamnose pentasaccharide, the repeating unit of the O-chain polysaccharide of the lipopolysaccharide of Xanthomonas campestris pv. begoniae GSPB 525

A xylosylated rhamnose pentasaccharide, alpha-L-Rhap-(1-->3)-[beta-L-Xylp-(1-->2)-]-alpha-L-Rhap-(1-->3)-[beta-L-Xylp-(1-->4)]-L-Rhap, the repeating unit of the O-chain polysaccharide (OPS) of the lipopolysaccharides of Xanthomonas campestris pv. begoniae GSPB 525 was synthesized by a highly regio- and stereoselective way. Thus coupling of 1,2-O-ethylidene-beta-L-rhamnopyranose (1) with 2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl trichloroacetimidate (2) to give (1-->3)-linked disaccharide (3), subsequent benzoylation, deethylidenation, acetylation, 1-O-deacetylation, and trichloroacetimidation afforded the disaccharide donor 11. Condensation of 11 with 1 yielded 2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl-(1-->3)-2-O-acetyl-4-O-benzoyl-alpha-L-rhamnopyranosyl-(1-->3)-1,2-O-ethylidene-beta-L-rhamnopyranose (12), and selective deacetylation of 12 yielded the trisaccharide diol acceptor 15. Coupling of 15 with 2,3,4-tri-O-benzoyl-alpha-L-xylopyranosyl trichloroacetimidate (16), followed by deprotection, gave the target pentasaccharide 19.     

Synthesis of a cyanoethylidene derivative of 3,6-anhydro-d-galactose and its application as glycosyl donor

Starting from 1,2,4-tri-O-acetyl-3,6-anhydro-alpha-d-galactopyranose, 4-O-acetyl-3,6-anhydro-1,2-O-(1-cyanoethylidene)-alpha-d-galactopyranose (7) was synthesized by treatment with cyanotrimethylsilane. Additionally, 3,4-di-O-acetyl-1,2-O-(1-cyanoethylidene)-6-O-tosyl-alpha-d-galactopyranose was prepared from the corresponding bromide and both cyanoethylidene derivatives were used as donors in glycosylation reactions. The coupling with benzyl 2,4,6-tri-O-acetyl-3-O-trityl-beta-d-galactopyranoside provided exclusively the beta-linked disaccharides in approximately 30% yield. The more reactive methyl 2,3-O-isopropylidene-4-O-trityl-alpha-l-rhamnopyranoside gave with donors 3 and 7 the corresponding disaccharides in nearly 60% yield. Furthermore, the synthesis of 3,6-anhydro-4-O-trityl-1,2-O-[1-(endo-cyano)ethylidene]-alpha-d-galactopyranose, which can be used as a monomer for polycondensation reaction is described.     

Synthesis and conformational analysis of the repeating units of bacterial spore peptidoglycan

Deprotection of the fully blocked disacharide allyl O-(2-amino-4,6-O-benzylidene-3-O-[(R)-1-carboxyethyl]-2-deoxy-beta-D-glucopyranosyl-1',2-lactam)-(1-->4)-2-acetamido-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranoside by selective de-O-allylation and parallel removal of the benzylidene and O-benzyl groups is described. The resulting beta-muramyl lactam-(1-->4)-GlcNAc disaccharide is characterised as the per-O-acetylated derivative by 1H and 13C NMR spectroscopy and X-ray structure analysis. Conformational analysis about glycosidic bond of repeating units of bacterial spore cortex is based on experimental data and molecular modelling.     

Synthesis of new sulfonamide inhibitors of carbonic anhydrase

Four different derivatives of aromatic sulfonamides have been synthesized: 1,2-bis[(4-sulfonamidobenzamide)ethoxy]ethane (SBAM), 1,2-bis[(4-sulfonamidobenzoate)ethoxy]ethane, 1,2-bis[(2,4-dichloro-5-sulfonamidobenzamide)ethoxy]ethane, and 1,2-bis[(2,4-dichloro-5-sulfonamidobenzoate)ethoxy]ethane. SBAM is a most potent inhibitor on ciliary epithelium carbonic anhydrase and is approximately 13 times more active against carbonic anhydrase isoform II than against isoform I.     

Synthesis and biological evaluation of novel hexahydro-pyrido[3',2':4,5]pyrrolo[1,2-a]pyrazines as potent and selective 5-HT(2C) receptor agonists

Further lead optimization efforts on previously described 1,2,3,4,10,10a-hexahydro-1H-pyrazino[1,2-a]indoles led to the new class of 5,5a,6,7,8,9-hexahydro-pyrido[3',2':4,5]pyrrolo[1,2-a]pyrazines culminating in the discovery of (5aR,9R)-2-[(cyclopropylmethoxy)methyl]-5,5a,6,7,8,9-hexahydro-9-methyl-pyrido[3', 2':4,5]pyrrolo[1,2-a]pyrazine 18 as a potent, full 5-HT(2C) receptor agonist with an outstanding selectivity profile and excellent hERG and phospholipidosis properties.     

Synthesis of [18F]SU11248, a new potential PET tracer for imaging cancer tyrosine kinase

N-[2-(Diethylamino)ethyl]-5-[(Z)-(5-[18F]fluoro-2-oxo-1,2-dihydro-3H-indol-3-ylidene)methyl]-2,4-dimethyl-1H-pyrrole-3-carboxamide, a new potential positron emission tomography tracer for imaging cancer tyrosine kinase, has been prepared by the nucleophilic substitution of the nitro-precursor N-[2-(diethylamino)ethyl]-5-[(Z)-(5-nitro-2-oxo-1,2-dihydro-3H-indol-3-ylidene)methyl]-2,4-dimethyl-1H-pyrrole-3-carboxamide with K18F/Kryptofix 2.2.2 followed by a simple chromatography methodology combined solid-phase extraction with high-performance liquid chromatography purification procedures in 15-25% radiochemical yields.     

Synthesis and anticandidal activity of some imidazopyridine derivatives

New hydrazide derivatives of imidazo[1,2-a]pyridine have been synthesized and evaluated for anticandidal activity. The reaction of imidazo[1,2-a]pyridine-2-carboxylic acid hydrazides with various benzaldehydes gave N-(benzylidene)imidazo[ 1,2-a]pyridine-2-carboxylic acid hydrazide derivatives. Their anticandidal activities against Candida albicans and Candida glabrata (isolates obtained from Osmangazi University, Faculty of Medicine, Eskisehir, Turkey), Candida albicans (ATCC 90028), Candida utilis (NRLL Y-900), Candida tropicalis (NRLL Y-12968), Candida krusei (NRLL Y-7179), Candida zeylanoides (NRLL Y-1774), and Candida parapsilosis (NRLL Y-12696) were investigated.     

Nucleosides,IV1 Synthesis and Properties of 2-Metylthio-Naphthimidazole-Ribonucleoside

Abstract

The synthesis of 2-Methylthio-1-(β-D-ribofuranosyl) naphthimidazole has been accomplished by condensation of 2-methylthio-1-trimethylsilylnaphthimidazole(3) with 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D-ribofuranose(4) in the presence of trimethylsilyl triflate in 1,2-dichloroethane, followed by subsequent debenzoylation. Structural proofs are based on elementary analysis, UV- and ¹H-NMR-spectra.     

Synthesis of a trisaccharide component of the capsular polysaccharide of Streptococcus pneumoniae type 19F

2-O-[4-O-(2-Acetamido-2-deoxy-beta-D-mannopyranosyl)-alpha-D- glucopyranosyl]-alpha,beta-L-rhamnopyranose, a structural component of the capsular polysaccharide of Streptococcus pneumoniae type 19F, has been synthesized by sequential glycosylation reactions using the glycosyl acceptor 2,2,2-trichloroethyl 3,4-di-O-benzyl-alpha-L-rhamnopyranoside (prepared from the known 2-O-acetyl-3,4-di-O-benzyl-alpha-L-rhamnopyranosyl chloride), and the glycosyl donors 4-O-acetyl-2,3,6-tri-O-benzyl-alpha-D-glucopyranosyl chloride and 4,6-di-O-acetyl-2-azido-3-O-benzyl-2-deoxy-alpha-D-mannopyranosyl bromide (prepared in seven steps from the known methyl 2-azido-4,6-O-benzylidene-2-deoxy-alpha-D-altropyranoside). The corresponding 8-(methoxycarbonyl)octyl glycoside has also been synthesized, by coupling of 8-(methoxycarbonyl)octyl trifluoromethanesulfonate and the sodium salt of 2-O-[4-O-(2-acetamido-4,6-di-O-acetyl-3-O-benzyl-2-deoxy-beta-D- mannopyranosyl)-2,3,6-tri-O-benzyl-alpha-D-glucopyranosyl]-3,4-di-O- benzyl-alpha,beta-L-rhamnopyranose.     

3,4-anhydro-1,2-O-isopropylidene-beta-D-tagatopyranose and 4,5-Anhydro-1,2-O-isopropylidene-beta-D-fructopyranose

3,4-Anhydro-1,2-O-isopropylidene-beta-D-tagatopyranose (8) and 4,5-anhydro-1,2-O-isopropylidene-beta-D-fructopyranose (10) have been prepared by treatment of 3,5-di-O-acetyl-1,2-O- isopropylidene-4-O-toluene-p-sulfonyl-beta-D-fructopyranose with methanolic sodium methoxide. The structures of 8 and 10 were assigned by 1H and 13C NMR spectroscopy and that of 10 by X-ray crystallography; both exist in half-chair conformations. Compounds 8 and 10 interconvert in aqueous sodium hydroxide, giving a ratio of 1:2 at equilibrium. The monoacetates of 8 and 10 (5-O-acetyl-3,4-anhydro-1,2-O-isopropylidene-beta-D-tagatopyranose and 3-O-acetyl-4,5-anhydro-1,2-O-isopropylidene-beta-D-fructopyranose) undergo stereospecific epoxide ring opening in 80% acetic acid to give mainly the axial monoacetates 5-O-acetyl-1,2-O-isopropylidene-beta-D-fructopyranose and 4-O-acetyl-1,2-O-isopropylidene-beta-D-tagatopyranose, respectively.     

Synthesis of the pentasaccharide related to the repeating unit of the antigen from Shigella dysenteriae type 4 in the form of its methyl ester 2-(trimethylsilyl)ethyl glycoside

Starting from D-mannose, D-glucose and L-fucose, the pentasaccharide derivative methyl 2,3,4-tri-O-benzyl-alpha-L-fucopyranosyl-(1-->3)-2-O-acetyl-4,6-O-benzylidene-alpha-D-mannopyranosyl-(1-->3)-2-O-acetyl-6-O-benzyl-4-O-(2,3,4-tri-O-benzyl-alpha-L-fucopyranosyl)-alpha-D-mannopyranosyl-(1-->4)-[2-(trimethylsilyl)ethyl 2,3-di-O-benzyl-beta-D-glucopyranosid]uronate was synthesized. This compound with two alpha-mannopyranosyl units was transformed, via Walden inversion and subsequent deprotection, into the alpha-D-glucosamine-type target compound, namely methyl alpha-L-fucopyranosyl-(1-->3)-2-acetamido-2-deoxy-alpha-D-glucopyranosyl-(1-->3)-2-acetamido-2-deoxy-4-O-(alpha-L-fucopyranosyl)-alpha-D-glucopyranosyl-(1-->4)-[2-(trimethylsilyl)ethyl beta-D-glucopyranosid]uronate which is related to the repeating unit of the O-antigen from Shigella dysenteriae type 4.