Anomeric Carbon Atom Research Articles

Carbohydrate Chemistry of the Anomeric Carbon-Sulfur Bond

Abstract Aryl and alkyl S-glycosides and sulfones are ideal precursors of three classes of reactive intermediates : anomeric carbenium, anion, and radical, and thus play a remarkable role in carbohydrate chemistry of the anomeric carbon atom. Reported reactions will include: - A conceptually novel glycosylation reaction based on the activation of thioglycosides by a one electron -transfer reagent - Uses of a novel class of glycosyl donors: anomeric S-xanthates of 2-azido sugars. - Selective synthesis of α and β C-glycosides using anomeric reductive lithiation or reductive samariation of phenyl S-glycosides or sulfones. - Convenient synthesis of substituted pyranoid glycals - Expeditious synthesis of C-disaccharides by Sml2 induced intramolecular coupling reaction of tethered glycosyl phenyl sulfone and exomethylene sugar.

Protonic reactivity of sucrose in anhydrous hydrogen fluoride

Sucrose reacts quantitatively, when dissolved at high concentration in anhydrous hydrogen fluoride, to afford a complex mixture of difructose dianhydrides and their glucosylated derivatives. Oligo- and small poly-saccharides up to dp 14 were detected by FABMS. Oligosaccharides up to dp 4, representing ≈50% of the total mixture, have been isolated and characterized by mass spectrometry, 13C NMR spectroscopy, and comparison with reference oligosaccharides previously obtained by unambiguous synthesis, α- d-Fructofuranose β- d-fructopyranose 1,2′:2,1′-dianhydride is the main spirodioxanyl pseudodisaccharide entity found in the mixture, either free or glucosylated at C-6 and to a lesser extent at C-3, C-4, C-4′ C-6, and C-5′ C-6. Minor spirodioxanyl pseudodisaccharide components are di-β- d-fructopyranose 1,2′:2,1′-dianhydride, which has also been found glucosylated at C-5, α- d-fructopyranose β- d-fructopyranose 1,2′:2,1′-dianhydride, β- d-fructofuranose β- d-fructopyranose 1,2′:2,3′-dianhydride, and the 6,6′-diglucosylated α- d-fructofuranose β- d-fructofuranose 1,2′:2,1′-dianhydride. A 13C NMR examination of the higher mass oligomeric fraction fraction suggests that it may involve 6- O-isomaltooligoglycosyl α- d-fructofuranose β- d-fructopyranose 1,2′:2,1′-dianhydride as the main structural components. The reaction of sucrose in anhydrous HF is believed to proceed through initial selective protonic activation of the tertiary anomeric carbon atom of the fructose moiety, resulting in the quantitative formation of difructose dianhydrides, which subsequently suffer electrophilic substitution by glucopyranosyl oxocarbenium ions generated in a second step by action of the HF.

Simple estimation of the conformational homogeneity of 2,5-disubstituted-1,3-dithianes by means of their1H NMR spectra

A simple method for the correction of free energy differences, ΔG°exp, obtained via the equilibriation of 2-substituted 5-tert-butyl-1,3-dithianes, is proposed on the basis of the 1H NMR data for diastereoisomers. It suggests, in contrast to the opinion of other workers, that these derivatives can be used in order to establish the preference of a substituent connected to the anomeric carbon atom. A simple procedure for the comparison of the amount of twist-boat forms is also demonstrated.

Phosphorus 31P Spin–lattice relaxation times as a tool for the determination of the structure of 1,3‐dithianes with P‐containing substituents at the anomeric carbon atom

AbstractRelaxation times, T, due to the dipolar mechanism of relaxation of 31P nuclei were determined for eight pairs of 1,3‐dithianes with P‐containing substituents at the anomeric carbon atom. The separation of dipole–dipole from the total spin–lattice relaxation could be applied for the unambiguous assignment of configuration of the compounds under investigation. The T relaxation times are smaller for compounds with phosphorus located axially (cis). This observation is discussed in terms of internal rotation around the C‐2 bond and the distances between the phosphorus and axial H‐4,6 protons.

ChemInform Abstract: gem‐Difluorinations versus 1,2‐Migration and Fragmentation in the Reaction of 2‐ and 3‐Uloses with DAST. Influence of Stereochemistry at the Anomeric Carbon Atom.

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Gem-Difluorination versus 1,2-migration and fragmentation in the reaction of 2- and 3-uloses with DAST. Influence of stereochemistry at the anomeric carbon atom

gem-Difluorination versus 1,2-migration and fragmentation in the reaction of 2- and 3-uloses with DAST. Influence of stereochemistry at the anomeric carbon atom

CONFORMATIONAL PREFERENCE IN 1,3-DITHIANES CONTAINING PHOSPHONIUM AND PHOSPHINO SUBSTITUENTS AT THE ANOMERIC CARBON ATOM

Abstract The synthesis and conformational analysis of 1, 3-dithiane, 5,5-dimethyl-1,3-dithiane, 5-tert-butyl-1,3-dithiane and 4,6-dimethyl-1,3-dithiane containing different phosphonium and phosphino groups at the anomeric carbon atom are described.

Neue Untersuchung über Inhaltsstoffe aus Aloe- und Rhamnus-Arten, XIII [1] / A New Investigation on Constituents of Aloe and Rhamnus Species, XIII [1

Rhamnus purshianus D. C., 10-Hydroxyaloins A/B, Oxanthrone Glucosyls, Quinonoids, Anthranoids The absolute configurations of the diastereomeric 10-hydroxyaloins, which may be regarded as parent structures for other naturally occurring oxanthrone-C-glucosyls, have been established as 10R, 16 R (A) and 10 S, 16 R (B) by an X-ray structure analysis of the A-octaacetyl derivative (C 16 is the anomeric glucosyl carbon atom). The determination was confirmed by CD spectroscopic comparison with the structural analogues aloins A and B, which should prove useful for making future configurational assignments within this class of compounds. A conformational analysis by the use of a molecular modeling method based on force-field calculations reveals the presence of an extra- and an intra-form, the extra-form of which is energetically preferred.

The oxygen-18 isotope shift in carbon-13 NMR spectroscopy. 14. Kinetics of oxygen exchange at the anomeric carbon of D-ribose and D-2-deoxyribose

The kinetics of the oxygen-exchange reaction of the anomeric carbon atoms of D-ribose and D-2 deoxyribose (2-deoxy-D-erythro-pentose) were compared using the 18 O isotope induced shift in 13 C NMR spectroscopy. Measurements were made at a number of temperature and pH values. The oxygen-exchange reaction for these sugars is strongly pH-dependent, displaying regions of acid, water, and base catalysis. The results are analyzed in terms of steric and inductive effects on the hydration kinetics of the open-chain forms and by comparison with the hydration reaction of simple aldehydes

Complexes of carbohydrates with metal cations. XVI•Di-D-fructose and di-L-sorbose dianhydrides

Di-D-fructose 2′, 1:2,1′-dianhydrides form complexes with metal cations if the two anomeric carbon atoms have the same configuration. Such anomers have the central 1,4-dioxane ring in a flexible form; complex formation involves O-1, O-1′, O-3, and O-3′, as confirmed by the X-ray crystal structure of the strontium complex of the β,β-dipyranose anomer. The α,β-anomers, and dianhydrides containing only furanose rings, do not form such complexes. Keywords: difructose dianhydrides, complex formation with cations, crystal structure of complex, chromatographic separation on ion-exchange resins.

Syntheses of trisaccharide CDE and tetrasaccharide BCDE fragments found in orthosomycins

1,5-Anhydro-3- O-benzyl-2,6-dideoxy-4- O-(3,4-di- O-benzyl-2,6-dideoxy-β- d- arabino-hexopyranosyl)- d- arabino-hex-1-enitol ( 17), which corresponds to the BC fragment of various orthosomycins, was prepared from phenyl 2,3-di- O-benzyl-6-deoxy-4- O-(3,4-di- O-benzyl-2,6-dideoxy-β- d- arabino-hexopyranosyl)-1-thio-β- d-glucopyranoside ( 16) by reductive lithiation. The synthesis of 16 involved a stereoselective coupling of phenyl 2,3-di- O-benzyl-6-deoxy-1-thio-β- d-glucopyranoside ( 9) and 1,2-di- O-acetyl-3,4-di- O-benzyl-6-deoxy-β- d-glucopyranose ( 14) followed by deoxygenation at C-2′. Glycosylation of methyl 2- O-benzyl-6-deoxy-4- O-methyl-β- d-galactopyranoside ( 25) with 3,4,6-tri- O-acetyl-2-deoxy-2-phthalimido-β- d-glucopyranosyl trichloroacetimidate, followed by deamination at C-2′, led stereospecifically to methyl 2- O-benzyl-6-deoxy-4- O-methyl-3- O-(3,4,6-tri- O-acetyl-2-deoxy-β- d- arabino-hexopyranosyl)-β- d-galactopyranoside ( 26). The 2-deoxy unit of 26 was then modified by consecutive axial introduction of a C-Me group at position 3′, protection of HO-3′, and deoxygenation at C-6′, in order to obtain methyl 3- O-(3- O-benzoyl-2,6-dideoxy-3- C-methyl-β- d- arabino-hexopyranosyl)-2- O-benzyl-6-deoxy-4- O-methyl-β- d- galactopyranoside ( 39), which corresponds to the DE fragment of orthosomycins. A glycosyloxyselenation-oxidation-elimination sequence was performed on 39 and either 1,5-anhydro-3,4-di- O-benzyl-2,6-dideoxy- d- arabino-hex-1-enitol ( 40) or 1,5-anhydro-3- O-benzyl-2,6-dideoxy-4- O-(3,4-di- O-benzyl-2,6-dideoxy-β- d- arabino-hexopyranosyl)- d- arabino- hex-1-enitol ( 17) to give the CDE tri- and BCDE tetrasaccharide fragments, respectively. Each fragment contained the spiro-ortholactone junction with an ( R) configuration at the anomeric carbon atom of the C-unit.

Formation of α-Deoxyadenosine in Polydeoxynucleotides Exposed to Ionizing Radiation under Anoxic Conditions

When poly(dA), poly(dA-dT), and salmon testis DNA were gamma-irradiated under nitrogen, the major deoxyadenosine damage product (excluding liberated adenine) was identified as the alpha-anomer of deoxyadenosine. The yields of alpha-deoxyadenosine from poly(dA), poly(dA-dT), and salmon testis DNA irradiated with a dose of 500 Gy under anoxic conditions were 1.5, 1.3, and 1.3%, respectively. No alpha-deoxyadenosine was detected after irradiation under oxic conditions. The presence of nucleotides with the alpha-configuration at the anomeric carbon atom in the DNA chain may have a significant effect on its tertiary structure and possibly modify its biological activity.

Reactions of 3-[formula omitted]-acetyl-2-[formula omitted]-[formula omitted]-tolylsulfonyl-D-[formula omitted]- and -[formula omitted]-[formula omitted]-hex-1-enitol derivatives with nucleophiles; the SN2′ mechanism is proved firstly in glycal derivatives

Reactions of the title compounds with sodium methoxide and sodium borodeuteride were found to proceed mainly via the SN2′ mechanism; nucleophiles selectively attacked the anomeric carbon atom from the same side of the leaving acetoxyl group at C-3.

Furanose ring anomerization: A kinetic study of the 5-deoxypentoses and 5- O-methylpentoses

The anomerization of 5-deoxy- l-pentoses ( 1– 4) and 5- O-methyl- d-pentoses ( 5– 8) in aqueous solution has been studied by 13C saturation-transfer n.m.r. (s.t.-n.m.r.) spectroscopy, using compounds substituted with 13C at the anomeric carbon atom. Unidirectional rate-constants of ring-opening ( k open) and ring-closing ( k close) have been obtained for these compounds under identical solution conditions (50m m acetate buffer, pH 4.0 at 60°), and have been compared to those measured for the d-tetroses ( 9 and 10) and the four d-pentose 5-phosphates ( 11– 14). Based on these comparisons, several correlations between furanose structure and reactivity have been revealed, and models have been proposed to explain the observed kinetic behavior of compounds 1– 10. The effect of exocyclic structure on acid-catalyzed rate-constants was also examined by comparing the behavior of 5-deoxy- l-(1- 13C)-lyxose and 5- O-methyl- d-(1- 13C)lyxose. Some consideration has been given to identifying the factors (enthalpic and entropic) that may play roles in determining the effect of structure on anomerization reactivity.

Type-specific polysaccharides of Cryptococcus neoformans. N.m.r.-spectral study of a glucuronomannan chemically derived from a Tremella mesenterica exopolysaccharide

A glucuronomannan (GM) was derived by removal, through Smith degradation, of xylose from the native (3- O-acetylglucurono)xylomannan exopolysaccharide isolated from Tremella mesenterica. 13C-N.m.r. chemical shifts measured at various pD values were compared for p-nitrophenyl β- d-glucopyranosiduronic acid ( 1) and two GMs ( 2 and 3) differing in GlcA content (Man:GlcA; 2, 10:1; and 3, 5:1). Also measured and compared were p K a values for 1 and 2. One-dimensional and two-dimensional (COSY and HETCOR) n.m.r. data allowed unambiguous assignments of pD-sensitive chemical shifts due to 2- O-β- d-Glc pA substituents attached to a (1→3)-linked α- d-Man p backbone. The p K a and n.m.r. data indicated that the CO 2H groups in either GM are independent of each other, and are similar in behavior to those of p-nitrophenyl β- d-glucopyranosiduronic acid molecules. The n.m.r. data confirmed the previous, chemically deduced, structural role of Glc pA in the native polysaccharide from T. mesenterica, and indicated that significant pD-induced changes occur in the stabilities of the glycosidic orientations in the GM. Previous 13C-n.m.r. assignments for 2- O-β- d-Glc pA in polysaccharides derived from Cryptococcus neoformans serotype A-variant were confirmed, except for the signal due to the anomeric carbon atom. This signal is now known to be pD-sensitive. In acidic solutions, it is coincident with the signal (104.5 p.p.m.) due to the anomeric carbon atoms of the unsubstituted α- d-Man p backbone residues. In basic solutions, the 2- O-β- d-Glc pA anomeric carbon resonance is shifted upfield by ∼0.2 p.p.m., and is observed as a separate signal.

Conformational calculations for the α and β anomer of 2,3,4-tri- O-acetyl- d-arabinopyranosyl azide

The 2,3,4-tri- O-acetyl-α- and -β- d-arabinopyranosyl azide anomers were studied by the semiempirical quantum-chemical PCILO method. Rotational energy maps for the azide group and the three acetyl groups established the lowest energy minima for the two anomers. Two minima each were found for the azide group setting. The geometry around the anomeric carbon atom was optimized for each conformer. It was observed that the lowest minima found were in the range showing the exo-anomeric effect.

Conversion of Digitoxin (2) Into synthetically Useful Derivatives of Digitoxose (1) (2,6-Dideoxy-D-ribo-Hexose)

Abstract An efficient procedure is described for the conversion of digitoxin (2) into 1,3,4-tri-O-benzoyl-2,6-dideoxy-β-D-ribo-hexopyranose (4). This conversion allows digitoxin (2) to become a viable source of 2,6-dideoxy sugars since the tribenzoate 4 is readily converted into synthetically useful derivatives. One type of derivative, exemplified by t-butyl 2,6-dideoxy-β-D-ribo-hexopyranoside (17), is an unprotected glycoside and thus easily permita structural modification at C-3 and C-4. A second type of derivative formed from 4 is one capable of glycosidic coupling at the anomeric carbon atom. Examples of this latter type are 3,4-di-O-benzoyl-2,6-dideoxy-α-D-ribo-hexopyranoayl chloride (7) and ethyl 3,4-di-O-benzoyl-2,6-dideoxy-1-thio-O-D-ribo-hexopyranoside (13).

Improved purification and further characterization of an isomalto-dextranase from Arthrobacter globiformis T6.

A highly purified isomalto-dextranase (EC 3.2.1.94) was simply separated from the cell-free culture broth of Arthrobacter globiformis T6 by CM-cellulose column chromatography and characterized further. The purified enzyme was essentially homogeneous on PAGE and SDS-PAGE as well as isoelectric focusing. The enzyme was an acidic protein with pI 5.15. E1%1cm at 280 nm was 24.6. The molecular weight of the enzyme was estimated to be about 69, 000 by SDS-PAGE. No carbohydrate moiety seemed to be associated with the enzyme protein. The optimum pH and temperature of the enzyme was pH 5.3 and 65°C, respectively. The enzyme was completely stable over the range of pH 3.0-8.0 at 4°C for 24 hr, and retained about 90% of its original activity after heating at 60°C for 10 min. Inactivation of the enzyme was found to be partial with 5mM Ag+, and complete with 5 HIM Hg2+, Fe3+, KMnO4, and NBS. The enzyme split dextran, retaining the α-configuration of the anomeric carbon atoms in the hydrolysis products. The Km value of the enzyme for dextran was 0.038%. Isomaltitol was a potent competitive inhibitor (Ki=0.79 mM)

C-1 lithiation of c-2 activated glucals

Direct lithiation of the readily available 2-benzyloxy and the2-phenylthio glucals 1 and 7 at the anomeric carbon atom leads to intermediates reacting with different electrophiles. Subsequent removal of the phenylthio group in compounds 9a , b with Raney-nickel and diastereospecific 1-hydrogen- and 2-hydroxy-transfer with the BH 3•SMe 2/H 2O 2, NaOH system provides a convenient entry into functionalized C-glucopyranosides.

Synthesis of l-(4- 2H)erythrose, l-)1- 13C, 5- 2H)arabinose and l-(2- 13C, 5- 2H)arabinose and identification of the intermediates by 2H and 13C-N.M.R. spectroscopy

l-(1- 13C, 5- 2H)Arabinose ( 6D) and l-(2- 13C, 5- 2H)arabinose ( 8D) have been synthesized by degradation of 2,3- O-isopropylidene-α- l-rhamnofuranose ( 2) to l-(4- 2H)erythrose ( 5β, 5αD), with subsequent chain elongation to 6D plus l-(1- 13C, 5- 2H)ribose ( 7D), the latter being converted into 8D. Intermediates were identified by complete assignment of the 13C chemical shifts employing carbon-carbon and carbon-deuterium coupling constants, deuteration shifts, differential isotope-shifts, and deuterium spectra. The anomeric carbon atoms of 2 and 2,3- O-isopropylidene- l-(1- 2H) erythrose ( 4D) gave only single 13C resonances, suggesting that these two compounds exists in only one major anomeric configuration, clarifying previously reported work. The synthesis of 2,3- O-isopropylidene- l-(1- 2H)rhmanitol ( 3D) facilitated the assignment of the signals in the 13C spectra of the nondeuterated analog. Specific deuterium-enrichment and the observed carbon-deuterium coupling ( 1 J C,D ∼22 Hz) not only served to identify the deuterated carbon atom unambiguously in 3 but also permitted assignment of closely spaced resonances. The deuterium spectrum of 2,3- O-isopropylidene- l-(1- 2H)erythrofuranose ( 4D) showed only a single resonance, indicating preponderance of one anomer, in accord with the observation of a single C-1 resonance in the 13C spectrum.