Structure of Glucomannan-Protein from the Yeast Cryptococcus Laurentii

Abstract

The structure of an extracellular glucomannan-protein produced by Cryptococcus laurentii was studied. The glucomannan-protein was isolated via its insoluble copper complex. It was homogeneous on free-boundary electrophoresis, contained 91% saccharide, 6.5% protein and 1% phosphorus. It had M_n 21,000. The carbohydrate portion was composed of D-mannose and D-glucose in 33:2 molar ratio. From the results of compositional and methylation analyses, conventional acetolysis, as well as ¹H and ¹³C NMR spectroscopy it was concluded that the glucomannan has an α-(1→6)-linked D-mannopyranosyl backbone having most residues (about 83%) substituted at O-2 with one, two, three or four D-mannopyranosyl units connected by α-(1→2) and α-(1→3) linkages. Moreover, an additional side chain with the α-D-Manp-(1→3)-D-Manp-(1→2)-D-Manp-(1→2)-D-Manp-D-Manp backbone structure in which α-D-glucopyranose residue is linked to O-2 of the mannopyranose unit next to the reducing end. Alkali treatment of glucomannanprotein in the presence of sodium borohydride showed that 87% serine and 83% threonine residues were glycosylated with mannose, mannobiose, and mannotriose.     

Configurational statistics of polysaccharides. VI. Linear (1→4)-linked galactan

The conformational energies for (1→4)-linked α-D- and β-D-galactans have been computed by considering nonbonded, torsional, and electrostatic interactions. The electrostatic interactions are estimated by assigning the charges to various atoms in the molecule by the method of Del Re. The characteristic ratios C_N = 〈r²〉₀/Nl_v² are computed for α-D- and β-D-galactans as a function of the degree of polymerization N and the angle τ at the bridge oxygen atom. These values of characteristic ratios obtained for α-D-galactan are very much higher than for β-D-galactan, indicating that the former assumes a highly extended conformation compared to the latter. The values of characteristic ratios of both these polysaccharides show a decrease with increase in τ similar to that observed for other (1→4)-linked polysaccharides. The calculated values of C_∞ of (1→4)-linked polysaccharides show no correlation with the number of allowed conformations but are affected both by the orientation of the interunit glycosidic bonds and the hindered potential associated with chain units. It has also been shown that the magnitude of the steric factor σ may not be used as an index of flexibility for polysaccharides which differ in type of linkage.     

Doppelt und dreifach funktionalisierte,enantiomerenreine C4-Synthesebausteine aus β-Hydroxybuttersäure, Äpfelsäure und Weinsäure

Enantiomerically Pure Synthetic Building Blocks with Four C-Atoms and Two or Three Functional Groups from β-Hydroxy-butanoic, Malic, and Tartaric Acid The pool of chiral, non-racemic electrophilic building blocks, which are available from simple natural products in both enantiomeric forms is enlarged by the epoxides 3, 5 , and 10 , by the tosylate 12a , and by the aldehydes 18 (cf. symbols A-D , 14 , and Scheme 1). Key steps of the conversions leading from hydroxyacids to the building blocks are: epoxide-opening by triethylborohydride ( 1 → 2a ) and tosylate reduction ( 12a → 12b ); the Mitsunobu inversion ( 2a → 4a ); the reduction of (R, R)-tartaric ester to (R)-malic ester by NBS (N-bromosuccinimide) opening of the benzaldehyde acetal 8 and tin hydride reduction ( 6c → 7c ); the enantiomer enrichment of optically active ethyl β-hydroxy-butanoate through the crystalline dinitrobenzoate 21b . Detailed procedures are given for large scale preparations of the key intermediates. The enantiomeric purities of the building blocks are secured by correlations.     

Structural elucidation and antioxidant activity of a novel heteroglycan from Tricholoma Lobayense

A novel heteroglycan TLH-G was successfully isolated from Tricholoma lobayense cultivated in south China. TLH-G was composed of five monosaccharides, namely, mannose, rhamnose, glucuronic acid, glucose and galactose, and consisted of →1)-β-D-Glcp-(6→ and →1)-α-D-Galp-(3→ motifs. TLH-G had excellent scavenging activities towards 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radicals. Structure-activity relationship analysis demonstrated that glycosidic bond types, monosaccharide composition, and branching degree were more important for the antioxidant activity of polysaccharides from Tricholoma lobayense than other structural factors. All the above results showed that the growth environment played a crucial role in the structure and antioxidant activity of polysaccharides from Tricholoma lobayense.     

Regioselective Syntheses of New Tri-and Tetrasaccharides by Transglycosylation of Trichoderma Viride β-Glucosidase

ABSTRACT

A new β-glucosidase, which was partially purified from Trichoderma viride cellulase, catalyzed a transglycosylation reaction of cellobiose to give β-D-Glcp-(1→6)-β-D-Glcp-(1→4)-D-Glcp 1 and β-D-Glcp-(1→6)-β-D-Glcp-(1→6)-β-D-Glcp-(1→4)-D-Glcp 2, regioselectively. Furthermore, the enzyme converted laminaribiose and gentiobiose into β-D-Glcp-(1→6)-β-D-Glcp-(1→3)-D-Glcp 3 and β-D-Glcp-(1→6)-β-D-Glcp-(1→6)-D-Glcp 4, respectively. Selective β-(1→6) transglycosylation was achieved.     

Conformational Analysis of C-Disaccharides using Molecular Mechanics Calculations

ABSTRACT

Relaxed-residue energy maps based on the MM3 force field were computed for the methyl glycosides of eight C-linked D-glucosyl disaccharides: the two-bond axial-equatorial linked disaccharides β-kojibioside [(1→2)α–], β-nigeroside [(1→3)α–] and β-maltose [(1→4)α–], the two-bond equatorial-equatorial linked disaccharides β-sophoroside [(1→2)β–], β–laminarabioside [(1→3)β-], β–cellobioside [(1→4)β–] and the three-bond-linked (1→6) disacharides C-isomaltoside and C-gentiobioside. Optimized structures were calculated on a 20° grid spacing of the torsional angles about the C-glycosidic bonds and the final isoenergy surfaces were based on 11664 conformations, for the two-bond-linked disaccharides and 69984 conformations for the three-bond-linked disaccharides. Boltzmann-weighted ³J coupling constants were calculated and compared to the experimental values. They are satisfactory except for maltose where hydrogen bonds cause an over-estimation of the energy differences between the conformers. The energy maps are similar to maps of the corresponding O-disaccharides, but there are differences in the locations and the relative energies of the minima. The preferred conformations of the C-glycosidic bonds are as if they were conforming to the exo-anomeric effect but are closer to staggered conformations than shown by the MM3 results for the O-linkages.     

Structural Elucidation of an Elicitor-Active Oligosaccharide,LN-3, Prepared from Algal Laminaran

Abstract

The primary structure of an elicitor-active oligosaccharide, LN-3, prepared from partially hydrolyzed algal laminaran was determined by means of the analyses of glycosyl-linkage, fragments by acetolysis, and glycosyl-sequence. The elicitor-active oligosaccharide, LN-3, is a pyridylaminated hepta-β-d-glucoside which was shown to have the following linear structure: β-d-Glcp(1→6)-β-d-Glcp(1→3)-β-d-Glcp(1→3)-β-d-Glcp(1→3)-β-d-Glcp(1→6)-β-d-Glcp(1→3)-Glc-PA.     

Spectres RMN des Polysaccharides et de leurs Dérivés: Influence des Substituants sur le Déplacement Chimique 13C

Methyl and acetyl substituent effects on ¹³C chemical shift have been determined on (α 1→3), (α 1→4), (β 1→3) and (β 1→4) linked polysaccharides such as pseudo-nigerane, β-cyclodextrine, amylose, laminarane and cellulose. Methyl α- and β-D -glucopyranoside have been used as monomer model compounds. Shift determination of hydroxylated and substituted polysaccharides requires unambiguous assignment of their ¹³C spectra. Selective heteronuclear spin decoupling and the isotope effect of deuterated hydroxyl have been used as assignment techniques.     

Structural Studies on Galactomannans From Brazilian Seeds

Abstract

Chemical structures of galactomannans from the native Brazilian species, M. scabrella, S. barbatiman and S. parahy-bum were studied. Their seeds, on aqueous extraction, furnished high yields of viscous galactomannans, whose mannose to galactose ratios were 1.1:1, 1.5:1, and 3.0:1, respectively. The polysaccharides were analysed by methylation, periodate oxidation and chromium trioxide oxidation. The results, confirmed by ¹³C NMR spectroscopy, indicated expected structures of legume galactomannans, namely a polymeric main chain of (l→4) -linked β-D-mannopyranosyl residues substituted at 0–6 by single unit α-D-galactopyranosyl side-chains. ¹³C NMR spectra showed clear splitting of the O-substituted resonances of C-4 of the β-D-mannosyl residues depending on the nearest-neighbour probabilities, indicating a random arrangement of the D-galactosyl groups in all of the three galactomannans.     

Structural study on a bioactive fructan from the root of Achyranthes bidentata Blume

The structure of a saccharide component (Abs),with pronounced activity of improving immunity system,isolated from the root of Achyranthes bidentata Blume,a traditional Chinese herbal medicine,was studied.Based on 13C NMR,HPLC,and methylation analyses,Abs was shown to be a mixture of short-chain fructans with an average dp of 8,containing more (2→6) than (2→1) linked β-D-fructofuranosyl residues,with branching at O-6 or O-1 of 18% of the D-fructofuranoeyl residues.     

Thiosugars Iii. Stereoselective Approach to β-(1→2)-2,3-Dideoxy-2-C-Acetamidomethyl-2-S-Thiodisaccharides From Levoglucosenone

ABSTRACT

β-(1→2)-2,3-Dideoxy-2-C-acetamidomethyl-2-S-thiodisaccharides were synthesized in four steps by a stereoselective base catalyzed Michael addition reaction of 1-thiosugars to α-nitroalkene 4a, a new chiral synthon from levoglucosenone. It was followed by the reduction of the nitro group with a sodium borohydride/cobalt chloride complex and the hydrolytic opening of the 1,6-anhydro ring.     

Quantitative Analysis of Caffeoylquinic Acids and Styrylpyrones in Sweetia panamensis Bark by UPLC

Six secondary metabolites from the methanolic extract of Sweetia panamensis (Fabaceae) bark were isolated and characterised. Along with the pyrones desmethylangonine β-d-O-glucopyranoside and desmethylangonine β-d-O-glucopyranosyl-(1→6)-O-β-d-glucopyranoside, already reported in this species, 5-O-caffeoylquinic acid (chlorogenic acid), 4-O-caffeoylquinic acid, 3-O-caffeoylquinic acid and the isoflavonoid 5-O-methylgenistein 7-O-β-d-glucopyranoside were isolated for the first time from S. panamensis. Additionally, an LC-ESI-MS qualitative analysis was performed and an ultra performance liquid chromatography (UPLC) method was developed and validated for the determination of these compounds. The UPLC method was applied to the quantitative analysis of plant samples. Pyrones and caffeoylquinic acids resulted to be the main compounds in the extract; in particular desmethylangonine β-d-O-glucopyranosyl-(1→6)-O-β-d-glucopyranoside was the most abundant compound.

     

A One-Step Procedure for Facile Preparation of D-Glucopyranosides with a free 2-OH from O-Peracetylated β-D-Glucopyranose

ABSTRACT

Glycosylations and deacetylations of 2-O-acetyl of O-peracetylated β-D-glucopyranose were realized in one step by reactions with 4.0 equivalents of alcohols and 1.5 equivalents of trifluoroborane etherate. Thus, various β-D-glucopyranosides with a free hydroxyl group on C-2 were conveniently prepared and applied for synthesis of Glcl → 2 linked disaccharides.

     

Efficient water‐soluble drag reducing star polymers with improved mechanical stability

We describe here the first example of the synthesis of 4‐arm star poly(acrylic acid) for use as a water‐soluble drag reducing agent, by applying Cu(0)‐mediated polymerization technique. High molecular weight 4‐arm star poly(tert‐butyl acrylate) (M_n = 3.0–9.0 × 10⁵ g mol^?1) was first synthesized using 4,4′‐oxybis(3,3‐bis(2‐bromopropionate)butane as an initiator and a simple Cu(0)/TREN catalyst system. Then, 4‐arm star poly(tert‐butyl acrylate) were subjected to hydrolysis using trifluoroacetic acid resulting in water‐soluble 4‐arm star poly(acrylic acid). Drag reduction test rig analysis showed 4‐arm star poly(acrylic acid) to be effective as a drag reducing agent with drag reduction of 24.3%. Moreover, 4‐arm star poly(acrylic acid) exhibited superior mechanical stability when compared with a linear poly(acrylic acid) and commercially available drag reducing polymers; Praestol and poly(ethylene oxide). The linear poly(acrylic acid), Praestol, and poly(ethylene oxide) all showed a large decrease in drag reduction of 8–12% when cycled 30 times through the drag reduction test rig while, in contrast, 4‐arm star poly(acrylic acid) demonstrated much higher mechanical stability. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 335–344     

1H NMR Studies of Hydroxy Protons of ASN- and Ser-Linked Disaccharides in Aqueous Solution

ABSTRACT

The hydroxy protons of β-D-GlcpNAc-(1→4)-β-D-GlcpNAc, β-D-GlcpNAc-(1→4)-β-D-GlcpNAc-N-Asn, β-D-Galp-(1→3)-α-D-GalpNAc-O-Me and of β-D-Galp-(1→3)-α-D-GalpNAc-O-Ser in aqueous solution have been investigated using ¹H NMR spectroscopy. The chemical shifts, coupling constants, temperature coefficients, exchange rates and NOEs have been measured. The O(3)H proton of β-D-GlcpNAc-(1→4)-β-D-GlcpNAc and β-D-GlcpNAc-(1→4)-β-D-GlcpNAc-N-Asn, and the O(2')H proton of β-D-Galp-(1→3)-α-D-GalpNAc and β-D-Galp-(1→3)-α-D-GalpNAc-O-Ser have values which differ significantly from the other hydroxy protons. Both these hydroxy protons are shielded when compared to those of the corresponding monosaccharide methyl glycosides. This shielding is attributed to the proximity of these protons to the O(5') oxygen and to the 2-acetamido group, respectively. In β-D-GlcpNAc-(1→4)-β-D-GlcpNAc and β-D-GlcpNAc-(1→4)-β-D-GlcpNAc-N-Asn, the O(3)H proton has restricted conformational freedom with a preferred orientation towards the O(5') oxygen, and is protected from exchange with the bulk water through a weak hydrogen bond interaction with O(5'). In β-D-Galp-(1→3)-α-D-GalpNAc-O-Me and β-D-Galp-(1→3)-α-D-GalpNAc-O-Ser, the O(2')H is protected from exchange with the bulk water by the 2-acetamido group. The conformations of the disaccharides are not affected by the amino acid, and no interaction in terms of hydrogen bonding between the sugars and the amino acid residue could be observed.     

Formation of nanotubes and secondary assemblies of cyclodextrins induced by BBOT

The study of cyclodextrin nanotubes is a significant topic among the self-assembly behaviors of cyclodextrins. We report herein the interaction of 2,5-bis(5′-tert-butyl-2-benzoxazoyl)thiophene (BBOT) with α-, β-, γ-cyclodextrins (CDs). It has been discovered that the reaction patterns of BBOT with CDs are remarkably different. β-CD forms a simple inclusion complex with BBOT in a stoichiometry of 1:2 (guest:host). β-CD forms a 1:1 inclusion complex with BBOT at its low concentration. At higher concentration of BBOT, the nanotube and secondary assembly of β-CD are formed. As for γ-CD, the nanotube and secondary assembly are formed within the whole concentration range of BBOT studied. The structure of γ-CD nanotubes is different from that of β-CD nanotubes to a certain extent.

     

Synthesis of Polyacrylamide Copolymers Containing (1→6)-Branched (1→3)-β-D-Linked Tri- and Tetra-Saccharides Related to Schizophyllan

Abstract

The allyl β-glycosides of a trisaccharide O-β-D-Glcp-(1→3)-O-[β-D-Glcp-(1→6)]-β-D-Glcp and of a tetrasaccharide O-β-D-Glqp-(1→3)-O-[β-D-Glqp-(1→6)]-O-β-D-Glcp-(1→3)-β-D-Glcp, corresponding to the branching point or the repeating unit of antitumor (1→6)-branched-(1→3)-β-D-glucans, have been synthesized starting from ethyl 2-O-benzoyl-4,6-O-benzylidene-l-thio-α-D-glucopyranoside and copolymerized in a radical reaction with acrylamide to obtain polyacrylamide copolymers containing the tri-and tetra-saccharides for immunochemical studies of schizophyllan.     

Synthesis of 8-Methoxycarbonyloctylβ-Glycosides of Tri-and Tetrasaccharides Related to Schizophyllan and Neoglycoproteins Therefrom

Abstract

The 8-methoxycarbonyloctyl β-glycosides of the trisaccharides O-β-d-Glcp-(1 → 6)- O-β-d-Glcp-(1 → 3)-d-Glcp and O-β-d-Glcp-(1 → 3)-O-[β-d -Glcp-(1 → 6)]-d-Glcp and of the tetrasaccharide O-β-d-Glcp-(1 → 3)-O-[β-d-Glcp-(1 → 6)]-O-β-d-Glcp-(1 → 3)-d-Glcp, corresponding to the fragments of schizophyllan, have been synthesized by using mono- to tetrasaccharide 1-thioglycosides as glycosyl donors, each bearing a participating benzoyl group in the 2-position, and N-iodosuccinimide and silver triflate as promoter. Saponification of the tri- and tetrasaccharide β-glycosides, followed by attachment to bovine serum albumin of the resulting sugar derivatives having a carboxyl group at the aglycon terminal, provided neoglycoproteins for immunological studies of the polysaccharide.     

NMR characteristics of α-D-Man-(1→2)-D-Man and α-D-Man-(1→3)-D-Man mannobioses related to <Emphasis Type="Italic">Candida albicans</Emphasis> yeast mannan structures

Candida albicans mannans are highly perspective polysaccharides for pharmaceutical and biomedical industry. However, they have not been fully characterized. Generally, the larger, acid-stable part of these complex polymers mostly contain α- (and a few β-) linked mannoses. According to this statement all ¹H–¹³C NMR crosspeaks of α-(1→2) and α-(1→3) mannobioses in d₂-water as model disaccharides were assigned (and in d₆-DMSO—partial assignment). It is clearly shown that it is possible to differentiate the type, configuration and position of the glycosidic linkage i.e. α-(1→2) or α-(1→3) by one bond heteronuclear correlated spectroscopy methodology. Subsequently we compared the reference NMR data and isolated dimer fraction from Candida albicans and concluded that it is exclusively composed of α-(1→2) mannobiose. Notably α-(1→2) linkages as the branching points in the mannan polysaccharide structure imply rather spatially rigid orientation of its sidechains.     

A Flexible Stereoselective Synthesis of the Spirosesquiterpenes (±)-β-Acorenol, (±)-β-Acoradiene, (±)-Acorenone-B and (±)-Acorenone via an Intramolecular Ene-Reaction

The racemic spirosesquiterpenes β-acorenol ( 1 ), β-acoradiene ( 2 ), acorenone-B ( 3 ) and acorenone ( 4 ) (Scheme 2) have been synthesized in a simple, flexible and highly stereoselective manner from the ester 5 . The key step (Schemes 3 and 4), an intramolecular thermal ene reaction of the 1,6-diene 6 , proceeded with 100% endo-selectivity to give the separable and interconvertible epimers 7a and 7b . Transformation of the ‘trans’-ester 7a to (±)- 1 and (±)- 2 via the enone 9 (Scheme 5) involved either a thermal retro-ene reaction 10 → 12 or, alternatively, an acid-catalysed elimination 11 → 13 + 14 followed by conversion to the 2-propanols 16 and 17 and their reduction with sodium in ammonia into 1 which was then dehydrated to 2 . The conversion of the ‘cis’-ester 7b to either 3 (Scheme 6) or 4 (Scheme 7) was accomplished by transforming firstly the carbethoxy group to an isopropyl group via 7b → 18 → 19 → 20 , oxidation of 20 to 21 , then alkylative 1,2-enone transposition 21 → 22 → 23 → 3 . By regioselective hydroboration and oxidation, the same precursor 20 gave a single ketone 25 which was subjected to the regioselective sulfenylation-alkylation-desulfenylation sequence 25 → 26 → 27 → 4 .