5-Keto-Mannose (D-Lyxo-Hexos-5-Ulose) in Aqueous Solution-Isomeric Composition Dominated by α/β D-Fructofuranose Related Structures

Abstract

Selective C-6 hydroxyl triphenylmethylation of methyl 2,3-O-isopropylidene-α-D-mannofuranose (1), followed by C-5 hydroxyl oxidation and sequential removal of protecting groups in aqueous acid, yielded D-lyxo-hexos-5-ulose (5-keto-mannose, 5) as a mixture of isomeric forms. The isomeric mixture of 5 in D₂O solution was carefully examined using ¹H and ¹³C NMR techniques and structural assignments were made for seven isomers. The most prevalent form of 5 observed was the ketofuranose isomer 2S, 5R-D-lyxo-hexo-5,2-furanos-5-ulose 1-hydrate (5a, 52%), with its 2S, 5S-ketofuranose anomer (5b) being the next most abundant (14%). Also identified in the mixture were the α and β-hexofuranos-5-uloses 5c (6%) and 5d (< 2%), the pyranose structure 1R,5R-lyxo-hexopyranos-5-ulose 5e (10%), and the anhydro isomer 1R,5R-1,6-anhydro-D-lyxo-hexopyranos-5-ulose (5f, 5%), present in ¹ C ₄ conformation. Limited spectral information suggests that the remaining isomer 5g (8%) is a hydrated acyclic aldehyde form of 5.     

The Isomeric Composition of 6-Deoxy-D-XYLO-Hexos-5-Ulose in Aqueous Solution as Determined by 1H and 13C NMR

Abstract

Acid hydrolysis of 6-deoxy-1,2-O-isop ropylidene-α-d-xylo-hexo-furanos-5-ulose (4) yielded gummy 6-deoxy-d-xylo-hexos-5-ulose (1) as an isomeric mixture of two furanose forms, 6-deoxy-α-d-xylo-hexo-furanos-5-ulose and 6-deoxy-β-d-xylo-hexofuranos-5-ulose, and a pyranose structure 1R, 5R-6-deoxy-d-xylo-hexopyranos-5-ulose. The combined percentage (64%) of the furanoses represents an unusually large amount of free carbonyl form for a sugar when compared to simple hexoses and 2-hexuloses. Isomeric structures were determined in deuterium oxide solution by ¹H and ¹³C NMR.     

Syntheses of Pyrazole Iso-C-Nucleosides

ABSTRACT

3-O-Benzyl-6-deoxy-1,2-O-isopropylidene-α-D-xylo-hexofuranos-5-ulose (1) and 3,6-dideoxy-1,2-O-isopropylidene-α-D-glycero-hex-3-enofuranos-5-ulose (6) reacted with carbon disulfide and methyl iodide under basic conditions to give the α-oxoketene-S,S-acetals 2 and 7, respectively. Treatment of 2 and 7 with hydrazine hydrate yielded the pyrazole derivatives 3 and 8, respectively.     

Synthesis of (Z)-3-Deoxy-3-(1,2,3,6-Tetradeoxy-3,6-Imino-L-Arabino-Hexitol-1-C-Ylidene)-D-Xylo-Hexose Derivatives. First Examples Of Homo-(1→3)-C-Linked Iminodisaccharides.

ABSTRACT

Cross-aldolisation of 3,6-[(tert-butoxy)carbonyl]imino-2,3,6-trideoxy-4,5-O-isopropylidene-L-arabino-hexose (10) with 1,6-anhydro-2-O-benzyl-3-deoxy-β-D-erythro-hexopyrano-4-ulose (6) generates, after water elimination, a single enone 11 that is reduced selectively into an allylic alcohol 12, deprotection of which affords methyl (Z)-3-deoxy-3-(1,2,3,6-tetradeoxy-3,6-imino-L-arabino-hexitol-1-C-ylidene)-β-D-xylo-hexofuranoside (1) and (Z)-1,6-anhydro-3-deoxy-3-(1,2,3,6-tetradeoxy-3,6-imino-L-arabino-hexitol-1-C-ylidene)-β-D-xylo-hexopyranose (14).     

Synthesis and Properties of 1-(3,4-DI-O-Acetyl-2-Deoxy-2-Hydroxyimino-D-Threo-Pentopyranosyl)Pyrazoles

ABSTRACT

3,4-Di-O-acetyl-2-deoxy-2-nitroso-α-D-xylo-pentopyranosyl chloride (2) reacts with pyrazole to afford 1-[3,4-di-O-acetyl-2-deoxy-2-(Z)-hydroxyimino-α- (3) and β-D-threo-pentopyranosyl]pyrazole (4). The products of condensation were modified at C-2 or C-3 to give pyrazole derivatives with 3-azido-2,3-dideoxy-2-hydroxyimino-pentopyranosyl (5,7,8,9,10), 2-acetoxyimino-2,3-dideoxy-β-D-glycero-pentopyranosyl (12,13), β-D-lyxo- (14), β-D-xylopentopyranosyl (15) structures and 2,3-dihydro-2-pyrazol-1-yl-6H-pyran-3-one oximes (6,11). The conformation of the sugar residue and configuration at the anomeric centre and of the hydroxyimino group were established on the basis of ¹H NMR and polarimetric data.     

Isomérisations en chimie des sucres. II Fermetures de cycles par attaque nucléophile intramoléculaire sur des carbones sp2 à caractère électrophile: Furannoses hybridés sp2 en C3

When heated with one equivalent of H₂O, the 1,2: 5,6-di-O-isopropylidene-α-D-ribo- and -xylo-hexofuranos-3-uloses loose one molecule of acetone and yield the 3, 6-anhydro-1, 2-O-isopropylidene-α-D-ribo- and -xylo-hexofuranos-3-ulose ketohydrols. The carbonyl group of the starting material seems to provide some kind of intramolecular electrophilic assistance to the hydrolysis of the 5, 6-O-isopropylidene group. When the oxygen of the carbonyl group is replaced by cyanomethylene, an analogous cyclisation takes place under base catalysis, provided that C6 bears a free hydroxyl group.     

Behaviour of the Primary Nitro Group Under Denitration Conditions

ABSTRACT

Treatment of per-O-acetylated or acetalated glycosylnitromethanes derived from the common hexoses and pentoses with tributyltin hydride and a catalytic amount of a radical initiator [1,1′-azobis(cyclohexanecarbonitrile)] in refluxing benzene easily afforded the corresponding glycosylmethanal oximes in 84-97% yields. Per-O-acetylated C-β-glycopyranosylmethanal oximes were employed for synthesis of versatile C-β-glycopyranosyl cyanides of the β-D-gluco, β-D-manno, β-D-galacto, β-D-xylo, and β-L-rhamno configurations.     

Synthèse et réactions de didésoxy-5,6-halogéno-6-α-D-xylo-hepténo-5-furannurononitriles. Communication préliminaire

Synthesis and reactions of 5,6-dideoxy-6-halogeno-α-D-xylo-hept-5-eno-furanurononitriles The 5,6-dideoxy-6-chloro-, 6-iodo- and 6-fluoro-3-O-methyl-α-D -xylo-hept-5-eno-furanurononitriles have been prepared, their properties described as well as the methods used for the assignment of the configuration of the geometrical isomers. Some new reactions of the 6-bromo analog ( 1 ) of these compounds are reported. For example, when reacted with 2-mercaptoethanol or N,N′-dimethyl-ethylenediamine in the presence of NaOH, 1 gave the corresponding six-membered ring, stereo-isomers of an oxathiane or of a perhydrodiazine respectively. When the base used was Et₃N and the binucleophile the N-methyl-ethanolamine or the N,N′-dimethyl-ethylene-diamine the major product was a cyano-enamine which could be hydrolysed to a β-cyanoketone or cyclized to a five-membered ring, an oxazolidine or an imidazolidine respectively.     

Highly Stereoselective Synthesis of a C2-Symmetric 2,2′-Bipyridine Derived from Glucose

2-Bromo-6-lithiopyridine adds stereoselectively to the β-face of 1,2;5,6-di-O-isopropylidene-α-D-glucofuranos-3-ulose (2) to provide compound 5 in 50% yield as a single diastereomer. Compound 5 can be coupled to form novel C₂-symmetric 2,2′-bipyridine 7, the first example of a C₂-symmetric bipyridine that derives chirality from glucose.     

C-glycosylic derivatives. XV. Vinylogues of homo-C-glycosides

1,2-O-Isopropylidene-3-O-methyl-α-D-xylo-pentodialdo-1,4-furanose and its 3-O-benzyl analog have been reacted with pyridinyl-3-methylenetriphenylphosphorane and benzimidazolyl-2-methylenetriphenylphosphorane. The unsaturated sugars so obtained are vinylogs of homo-C-glycosides whose conformation is easily determined. They constitute useful model compounds for pharmacologic studies.     

Preparation of L-Lyxo-Hexos-5-Ulose Through C-3 Epimerization of Bis-Glycopyranosides of L-Arabino-Hexos-5-Ulose1

Abstract

The unreported title compound and its 2,6-di-O-benzyl derivative have been prepared from methyl β-D-galactopyranoside through a sequence involving the bisglycoside methyl 2,6-di-O-benzyl-5-O-methoxv-β-D-galactopyranoside 8, the precursor of L-orabino-hexos-5-ulose, that was converted to the L-lyxo series by inversion at C-3. The inversion was achieved in acceptable yields by selective triflation, followed by displacement with benzoate, and by an oxidation/reduction sequence. Whereas 2,5-di-O-benzyl-L-lyxo-hexos-5-ulose exists entirely as a mixture of the two anomeric 1,4-furanosic forms, the unprotected hexos-5-ulose involves at equilibrium in CD₃CN/D₂O at least eight tautomers, one of which is predominant.     

Stereoselective Synthesis of 3-C-Branched-Chain Sugars by Aldol Reaction of Furanos-3-Uloses with Acetone

Abstract

Aldol reaction of 1,2-O-isopropylidene-5-O-tertbutyl-dimethylsilyl-α-D-erythro-pentofuranos-3-ulose (1) with acetone in the presence of aqueous K₂CO₃ afforded 3-C-acetonyl-1,2-O-isopropylidene-5-O-tertbutyl-dimethylsilyl-α-D-ribofuranose(2). Similar reaction of 1,2:5, 6-di-o-isopropylidene- α-D-ribo-hexofuranos-3-ulose (3) afforded 3-C-acetonyl-1,2:5, 6-di-o-isopropylidene- α-D-allofuranose (4) and (1R, 3R, 7R, 8S, 10R)-perhydro-8-hydroxy-5,5,10-trimethyl-2,4,6,11,14-pentaoxatetracyclo[8,3,1,0^1,8,0^3,7] tetradecane. The stereochemistry of the new chiral centers were determined by ¹H NOE experiments.     

Dérivés C-glycosyliques. XXIV. Glycosyl-4-thiazoles

4-C-glycosylthiazoles have been prepared by reacting thiourea or thioacetamide with a 6-S-benzyl-6-chloro-1,2-O-isopropylidene-3-O-methyl-α-D-xylo-6-thiohexofuranos-5-ulose (7). The latter compound which constitutes an interesting synthetic intermediate in carbohydrate chemistry has been obtained by successive oxidation and chlorination of 6-S-benzyl-1,2-O-isopropylidene-3-O-methyl-α-D-6-thioglucofuranose.     

Efficient Synthesis of 2′-Deoxy-β-D-furanosyl C-Glycosides. Palladium-Mediated Glycal-Aglycone Coupling and Stereocontrolled β- and α-Face Reductions of 3-Keto-furanosyl Moieties

ABSTRACT

Efficient routes for selective syntheses of 2′-deoxy-β-D-furanosyl C-glycosides have been developed and demonstrated by preparation of the isomers 5-[2′-deoxy-β-D-ribo- (=arabino)furanosyl]-1,3-dimethyl-2,4(1H,3H)-pyrimidinedione and 5-[2′-deoxy-β-D-xylo-(=lyxo)furanosyl]-1,3-dimethyl-2,4(1H,3H)-pyrimidinedione. The syntheses involved regio-and stereospecific palladium-mediated coupling of a new glycal, 1,4-anhydro-2-deoxy-3-O-[(1,1-dimethylethyl)diphenylsilyl]-D-erythro-pent-1-enitol with an appropriate aglycone derivative to form a single 2′-deoxy-3′-keto-β-D-furanosyl C-glycoside (as the corresponding silyl enol ether). Following desilylation, the ketone group of the furanosyl ring was reduced stereo-selectively in either of two ways: by delivery of hydride from (a) the most hindered face of the carbonyl carbon using sodium (triacetoxy)borohydride or (b) the least hindered face using potassium tri-(sec-butyl)borohydride.     

Ylides du soufre dérivés de sucres Communication préliminaire

S-Methylation of 6-S-benzyl-6-deoxy-1,2-O-isopropylidene-3-O-methyl-α-D-xylo-6-thiohexofuranos-5-ulose ( 1 ) gave the expected sulfonium salt 2 which on alcaline treatment yielded the stable sulfur ylide 3 . This compound constitutes an useful synthetic intermediate in carbohydrate chemistry. On heating in 1,2-dimethoxyethane, it underwent a Stevens rearrangement which led to an extension of the carbon chain of the sugar and, reacted with Michael acceptors, it gave cyclopropanation reactions.     

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.     

HALOACETYLATED ENOL ETHERS: 16[5] REGIOSPECIFIC SYNTHESIS OF 5-TRICHLOROMETHYL-PYRAZOLES

ABSTRACT

The regiospecific synthesis and isolation of three series of 5-trichloromethyl-pyrazoles 2f–j, 3a–j and 4a–j from the cyclocondensation of 1,1,1-trichloro-4-alkoxy-3-alken-2-ones (1a–f) or trichloroacetyl containing β-diketones (1g–j) with dry hydrazine and phenyl-hydrazine is reported. It was established by ¹H- and ¹³C-NMR spectroscopy that the 5-hydroxy-5-trichloromethyl-4,5-dihydro-1H-pyrazole intermediates 2a–j were formed quantitatively.     

Molecular CsF5 and CsF2+

D_5h star‐like CsF₅, formally isoelectronic with known XeF₅^? ion, is computed to be a local minimum on the potential energy surface of CsF₅, surrounded by reasonably large activation energies for its exothermic decomposition to CsF+2 F₂, or to CsF₃ (three isomeric forms)+F₂, or for rearrangement to a significantly more stable isomer, a classical Cs⁺ complex of F₅^?. Similarly the CsF₂⁺ ion is computed to be metastable in two isomeric forms. In the more symmetrical structures of these molecules there is definite involvement in bonding of the formally core 5p levels of Cs.     

Molecular CsF5 and CsF2+

D_5h star‐like CsF₅, formally isoelectronic with known XeF₅⁻ ion, is computed to be a local minimum on the potential energy surface of CsF₅, surrounded by reasonably large activation energies for its exothermic decomposition to CsF+2 F₂, or to CsF₃ (three isomeric forms)+F₂, or for rearrangement to a significantly more stable isomer, a classical Cs⁺ complex of F₅⁻. Similarly the CsF₂⁺ ion is computed to be metastable in two isomeric forms. In the more symmetrical structures of these molecules there is definite involvement in bonding of the formally core 5p levels of Cs.     

Triallylborane and some its analogs as ligands in transition metal π-complexes: theoretical investigations

The structure, stability, and potential existence of chromium complexes with triallylborane B(CH₂—CH=CH₂)₃ and its analogs with coordination of the Cr atom to three double bonds are discussed. Complexes LCr(CO)₃ are studied where L = (C₃H₅)₃CH, (C₃H₅)₃B, (C₃H₅)₃BNMe₃, [(C₃H₅)₃BF]−, (C₂H₄)₃, C₆H₆, (C₃H₅)₃CPh, (C₃H₅)₃B(NC₅H₅). The calculations are carried out in DFT terms in approximations PBE/3z and BP86/TZ2P. The calculated dissociation energies of the studied complexes into the fragments Cr(CO)₃ and L range from 48.3 to 63.0 kcal mol⁻¹ (BP86/TZ2P) and from 54.2 to 66.9 kcal mol⁻¹ (PBE/3z). Ligands (C₃H₅)₃ER (ER = CPh, B(NC₅H₅)) can form two isomeric complexes A and B due to coordination of tricarbonylchromium to either three double bonds or benzene or pyridine ring. In the former case, isomer A is less stable as compared to isomer B, while in the latter case isomer Ais more stable. The possibility of selective synthesis of one of these isomers, namely, tris(η²-allyl)pyridineborane complex, is predicted.