10 research outputs found
Galacto-oligosaccharide Synthesis from Lactose Solution or Skim Milk Using the Ī²-Galactosidase from Bacillus circulans
The synthesis of galacto-oligosaccharides (GOS) catalyzed
by a
novel commercial preparation of Ī²-galactosidase from Bacillus circulans (Biolactase) was studied, and
the products were characterized by MS and NMR. Using 400 g/L lactose
and 1.5 enzyme units per milliliter, the maximum GOS yield, measured
by HPAEC-PAD analysis, was 165 g/L (41% w/w of total carbohydrates
in the mixture). The major transgalactosylation products were the
trisaccharide Gal-Ī²(1ā4)-Gal-Ī²(1ā4)-Glc
and the tetrasaccharide Gal-Ī²(1ā4)-Gal-Ī²(1ā4)-Gal-Ī²(1ā4)-Glc.
The GOS yield increased to 198 g/L (49.4% w/w of total carbohydrates)
using a higher enzyme concentration (15 U/mL), which minimized the
enzyme inactivation under reaction conditions. Using skim milk (with
a lactose concentration of 46 g/L), the enzyme also displayed transgalactosylation
activity: maximum GOS yield accounted for 15.4% (7.1 g/L), which was
obtained at 50% lactose conversion
Well-Defined Oligo- and Polysaccharides as Ideal Probes for Structural Studies
Polysaccharides are the most abundant
organic materials in nature,
yet correlations between their three-dimensional structure and macroscopic
properties have not been established. Automated glycan assembly enables
the preparation of well-defined oligo- and polysaccharides resembling
natural as well as unnatural structures. These synthetic glycans are
ideal probes for the fundamental study of polysaccharides. According
to molecular modeling simulations and NMR analysis, different classes
of polysaccharides adopt fundamentally different conformations that
are drastically altered by single-site substitutions. Larger synthetic
polysaccharides are obtained via a āLEGOā-like approach
as a first step toward the production of tailor-made carbohydrate-based
materials
Well-Defined Oligo- and Polysaccharides as Ideal Probes for Structural Studies
Polysaccharides are the most abundant
organic materials in nature,
yet correlations between their three-dimensional structure and macroscopic
properties have not been established. Automated glycan assembly enables
the preparation of well-defined oligo- and polysaccharides resembling
natural as well as unnatural structures. These synthetic glycans are
ideal probes for the fundamental study of polysaccharides. According
to molecular modeling simulations and NMR analysis, different classes
of polysaccharides adopt fundamentally different conformations that
are drastically altered by single-site substitutions. Larger synthetic
polysaccharides are obtained via a āLEGOā-like approach
as a first step toward the production of tailor-made carbohydrate-based
materials
Well-Defined Oligo- and Polysaccharides as Ideal Probes for Structural Studies
Polysaccharides are the most abundant
organic materials in nature,
yet correlations between their three-dimensional structure and macroscopic
properties have not been established. Automated glycan assembly enables
the preparation of well-defined oligo- and polysaccharides resembling
natural as well as unnatural structures. These synthetic glycans are
ideal probes for the fundamental study of polysaccharides. According
to molecular modeling simulations and NMR analysis, different classes
of polysaccharides adopt fundamentally different conformations that
are drastically altered by single-site substitutions. Larger synthetic
polysaccharides are obtained via a āLEGOā-like approach
as a first step toward the production of tailor-made carbohydrate-based
materials
Well-Defined Oligo- and Polysaccharides as Ideal Probes for Structural Studies
Polysaccharides are the most abundant
organic materials in nature,
yet correlations between their three-dimensional structure and macroscopic
properties have not been established. Automated glycan assembly enables
the preparation of well-defined oligo- and polysaccharides resembling
natural as well as unnatural structures. These synthetic glycans are
ideal probes for the fundamental study of polysaccharides. According
to molecular modeling simulations and NMR analysis, different classes
of polysaccharides adopt fundamentally different conformations that
are drastically altered by single-site substitutions. Larger synthetic
polysaccharides are obtained via a āLEGOā-like approach
as a first step toward the production of tailor-made carbohydrate-based
materials
Well-Defined Oligo- and Polysaccharides as Ideal Probes for Structural Studies
Polysaccharides are the most abundant
organic materials in nature,
yet correlations between their three-dimensional structure and macroscopic
properties have not been established. Automated glycan assembly enables
the preparation of well-defined oligo- and polysaccharides resembling
natural as well as unnatural structures. These synthetic glycans are
ideal probes for the fundamental study of polysaccharides. According
to molecular modeling simulations and NMR analysis, different classes
of polysaccharides adopt fundamentally different conformations that
are drastically altered by single-site substitutions. Larger synthetic
polysaccharides are obtained via a āLEGOā-like approach
as a first step toward the production of tailor-made carbohydrate-based
materials
Strategy for the Enzymatic Acylation of the Apple Flavonoid Phloretin Based on Prior Ī±āGlucosylation
The acylation of
flavonoids serves as a means to alter
their physicochemical
properties, enhance their stability, and improve their bioactivity.
Compared with natural flavonoid glycosides, the acylation of nonglycosylated
flavonoids presents greater challenges since they contain fewer reactive
sites. In this work, we propose an efficient strategy to solve this
problem based on a first Ī±-glucosylation step catalyzed by a
sucrose phosphorylase, followed by acylation using a lipase. The method
was applied to phloretin, a bioactive dihydrochalcone mainly present
in apples. Phloretin underwent initial glucosylation at the 4ā²-OH
position, followed by subsequent (and quantitative) acylation with
C8, C12, and C16 acyl chains employing an immobilized lipase from Thermomyces lanuginosus. Electrospray ionization-mass
spectrometry (ESI-MS) and two-dimensional nuclear magnetic resonance
spectroscopy (2D-NMR) confirmed that the acylation took place at 6-OH
of glucose. The water solubility of C8 acyl glucoside closely resembled
that of aglycone, but for C12 and C16 derivatives, it was approximately
3 times lower. Compared with phloretin, the radical scavenging capacity
of the new derivatives slightly decreased with 2,2-diphenyl-1-picrylhydrazyl
(DPPH) and was similar to 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic
acid) (ABTSā¢+). Interestingly, C12 acyl-Ī±-glucoside
displayed an enhanced (3-fold) transdermal absorption (using pig skin
biopsies) compared to phloretin and its Ī±-glucoside
Interactions of Bacterial Cell Division Protein FtsZ with C8-Substituted Guanine Nucleotide Inhibitors. A Combined NMR, Biochemical and Molecular Modeling Perspective
FtsZ
is the key protein of bacterial cell-division and target for
new antibiotics. Selective inhibition of FtsZ polymerization without
impairing the assembly of the eukaryotic homologue tubulin was demonstrated
with C8-substituted guanine nucleotides. By combining NMR techniques
with biochemical and molecular modeling procedures, we have investigated
the molecular recognition of C8-substituted-nucleotides by FtsZ from <i>Methanococcus jannaschii</i> (Mj-FtsZ) and <i>Bacillus
subtilis</i> (Bs-FtsZ). STD epitope mapping and trNOESY bioactive
conformation analysis of each nucleotide were employed to deduce differences
in their recognition mode by each FtsZ species. GMP binds in the same
anti conformation as GTP, whereas 8-pyrrolidino-GMP binds in the syn
conformation. However, the anti conformation of 8-morpholino-GMP is
selected by Bs-FtsZ, while Mj-FtsZ binds both anti- and syn-geometries.
The inhibitory potencies of the C8-modified-nucleotides on the assembly
of Bs-FtsZ, but not of Mj-FtsZ, correlate with their binding affinities.
Thus, MorphGTP behaves as a nonhydrolyzable analog whose binding induces
formation of Mj-FtsZ curved filaments, resembling polymers formed
by the inactive forms of this protein. NMR data, combined with molecular
modeling protocols, permit explanation of the mechanism of FtsZ assembly
impairment by C8-substituted GTP analogs. The presence of the C8-substituent
induces electrostatic remodeling and small structural displacements
at the association interface between FtsZ monomers to form filaments,
leading to complete assembly inhibition or to formation of abnormal
FtsZ polymers. The inhibition of bacterial Bs-FtsZ assembly may be
simply explained by steric clashes of the C8-GTP-analogs with the
incoming FtsZ monomer. This information may facilitate the design
of antibacterial FtsZ inhibitors replacing GTP
Enzymatic Synthesis of a Novel Neuroprotective Hydroxytyrosyl Glycoside
The
eco-friendly synthesis of non-natural glycosides from different
phenolic antioxidants was carried out using a fungal Ī²-xylosidase
to evaluate changes in their bioactivities. Xylosides from hydroquinone
and catechol were successfully formed, although the best results were
obtained for hydroxytyrosol, the main antioxidant from olive oil.
The formation of the new products was followed by thin-layer chromatography,
liquid chromatography, and mass spectrometry. The hydroxytyrosyl xyloside
was analyzed in more detail, to maximize its production and evaluate
the effect of glycosylation on some hydroxytyrosol properties. The
synthesis was optimized up to the highest production reported for
a hydroxytyrosyl glycoside. The structure of this compound was solved
by two-dimensional nuclear magnetic resonance and identified as 3,4-dihydroxyphenyl-ethyl-<i>O</i>-Ī²-d-xylopyranoside. Evaluation of its biological
effect showed an enhancement of both its neuroprotective capacity
and its ability to ameliorate intracellular levels of reactive oxygen
species
Highly Diastereoselective Multicomponent Synthesis of Spirocyclopropyl Oxindoles Enabled by Rare-Earth Metal Salts
The synthesis of polysubstituted spirocyclopropyl oxindoles
using
a series of rare-earth metal (REM) salts is reported. REMs, in particular
Sc(OTf)3, allowed access to the target compounds by a multicomponent
reaction with high diastereoselectivity (ā¤94:6:0:0). Density
functional theory calculations on the model reaction are consistent
with the observed selectivity and revealed that the special coordinating
capabilities and the oxophilicity of the metal are key factors in
inducing the formation of one main diastereoisomer