Research Square (Research Square),
Год журнала:
2023,
Номер
unknown
Опубликована: Ноя. 2, 2023
Abstract
The
stereoselective
formation
of
1,2-cis
glycosidic
linkages
is
challenging.
currently
most
widely
used
strategy
for
their
installation
uses
4,6-O-benzylidene
protected
building
blocks.
stereoselectivity
this
reaction
thought
to
be
driven
by
a
covalent
intermediate,
which
reacts
via
an
SN2
mechanism.
However,
the
role
cationic
SN1-type
intermediates
in
unclear.
Here,
we
elucidate
structure
glycosyl
cations
carrying
groups
using
cryogenic
infrared
ion
spectroscopy
and
computational
methods.
data
reveal
that
unexpectedly
form
anhydro
cations,
correlates
well
with
outcome
glycosylations.
study
highlights
how
can
unravel
novel
sugar
chemistry
structural
linked
reactions
solution.
Chemical Society Reviews,
Год журнала:
2023,
Номер
52(22), С. 7773 - 7801
Опубликована: Янв. 1, 2023
The
structural
complexity
of
glycans
poses
a
serious
challenge
in
the
chemical
synthesis
glycosides,
oligosaccharides
and
glycoconjugates.
Glycan
complexity,
determined
by
composition,
connectivity,
configuration
far
exceeds
what
nature
achieves
with
nucleic
acids
proteins.
Consequently,
glycoside
ranks
among
most
complex
tasks
organic
synthesis,
despite
involving
only
simple
type
bond-forming
reaction.
Here,
we
introduce
fundamental
principles
bond
formation
summarize
recent
advances
oligosaccharide
synthesis.
Nature Communications,
Год журнала:
2024,
Номер
15(1)
Опубликована: Март 13, 2024
Abstract
Attaining
complete
anomeric
control
is
still
one
of
the
biggest
challenges
in
carbohydrate
chemistry.
Glycosyl
cations
such
as
oxocarbenium
and
dioxanium
ions
are
key
intermediates
glycosylation
reactions.
Characterizing
these
highly-reactive
understanding
their
mechanisms
essential
to
stereoselective
synthesis
complex
carbohydrates.
Although
C-2
acyl
neighbouring-group
participation
has
been
well-studied,
reactive
more
remote
remain
elusive
challenging
study.
Herein,
we
report
a
workflow
that
utilized
characterize
rhamnosyl
1,3-bridged
derived
from
C-3
p
-anisoyl
esterified
donors.
First,
use
combination
quantum-chemical
calculations
infrared
ion
spectroscopy
determine
structure
cationic
intermediate
gas-phase.
In
addition,
establish
exchange
kinetics
highly-reactive,
low-abundance
species
solution-phase
using
chemical
saturation
transfer,
spectroscopy,
correlation
heteronuclear
single-quantum
correlation,
multiple-bond
nuclear
magnetic
resonance
spectroscopy.
Finally,
apply
bacterial
oligosaccharides.
This
combined
approach
finding
answers
fundamental
physical-chemical
questions
application
organic
provides
robust
basis
for
elucidating
The
stereoselectivity
of
glycosidic
bond
formation
continues
to
pose
a
noteworthy
hurdle
in
synthesizing
carbohydrates,
primarily
due
the
simultaneous
occurrence
S
Chemistry - A European Journal,
Год журнала:
2024,
Номер
30(30)
Опубликована: Март 28, 2024
Abstract
The
chemical
synthesis
of
complex
oligosaccharides
relies
on
efficient
and
highly
reproducible
glycosylation
reactions.
outcome
a
is
contingent
upon
several
environmental
factors,
such
as
temperature,
acidity,
the
presence
residual
moisture,
well
steric,
electronic,
conformational
aspects
reactants.
Each
proceeds
rapidly
with
high
yield
within
rather
narrow
temperature
range.
For
better
control
over
glycosylations
to
ensure
fast
reliable
reactions,
systematic
analysis
18
glycosyl
donors
revealed
effect
reagent
concentration,
water
content,
protecting
groups,
structure
activation
temperature.
With
these
insights,
we
parametrize
first
step
reaction
be
executed
reliably
efficiently.
Chemistry - A European Journal,
Год журнала:
2023,
Номер
29(57)
Опубликована: Июль 6, 2023
A
single
acyloxy
group
at
C-2
can
control
the
outcome
of
nucleophilic
substitution
reactions
pyran-derived
acetals,
but
extent
neighboring-group
participation
depends
on
a
number
factors.
We
show
here
that
does
not
necessarily
stereochemical
acetal
with
weak
nucleophiles.
The
1,2-trans
selectivity
increased
increasing
reactivity
incoming
nucleophile.
This
trend
suggests
intermediacy
both
cis-fused
dioxolenium
ions
and
oxocarbenium
in
stereochemistry-determining
step.
In
addition,
as
electron-donating
ability
neighboring
decreased,
preference
for
products
increased.
Computational
studies
how
barriers
ring-opening
reaction
transition
states
to
provide
change
capacity
C-2-acyloxy
Molecules,
Год журнала:
2025,
Номер
30(2), С. 218 - 218
Опубликована: Янв. 7, 2025
Using
methods
of
DFT,
we
investigated
the
effect
electron
withdrawing
and
donating
groups
on
relative
stability
tentative
glycosyl
donor
reaction
intermediates.
The
calculation
shows
that
by
changing
stereoelectronic
properties
protecting
group,
can
influence
dioxolenium
type
intermediates
up
to
10
kcal
mol−1,
increasing
nucleophillicity
4-O-Bz
intermediate
becomes
more
stable
than
a
triflate–donor
pair.
We
exploited
this
mechanism
design
galactosyl
donors
with
custom
O2
O4,
outcome
cyclohexanol.
showed
no
change
in
product
distribution,
which
suggests
neighboring
group
participation
takes
precedence
over
remote
due
kinetic
barriers.
The Journal of Organic Chemistry,
Год журнала:
2025,
Номер
90(4), С. 1585 - 1596
Опубликована: Янв. 15, 2025
Nucleophilic
substitution
reactions
of
C-2-acyloxy
furanosyl
acetals
can
be
highly
diastereoselective.
We
here
show
that
the
presence
a
less
electron-donating
p-nitrobenzoyloxy
group
at
C-2
acetal
use
to
control
1,2-trans
stereoselectivity
with
higher
than
analogue
more
benzoyloxy
group,
just
as
what
was
observed
in
pyranosyl
system.
Computational
results
support
reaction
manifold
involving
both
open
oxocarbenium
ions
and
cis-dioxolenium
provide
1,2-cis
products.
Participation
by
C-2-(p-nitrobenzoyloxy)
forms
stabilized
ion
reacts
incoming
nucleophile
readily
The
relative
stability
versus
is
much
system
result
lower
energy
penalty
for
forming
cis-fused
[5,5]-bicyclic
dioxolenium
ion.
Beilstein Journal of Organic Chemistry,
Год журнала:
2025,
Номер
21, С. 369 - 406
Опубликована: Фев. 17, 2025
Stereoselective
glycosylations
are
one
of
the
most
challenging
tasks
synthetic
glycochemists.
The
protecting
building
blocks
on
glycosides
contribute
significantly
in
attaining
required
stereochemistry
resulting
glycosides.
Strategic
installation
suitable
groups
C-2
position,
vicinal
to
anomeric
carbon,
renders
neighbouring
group
participation,
whereas
distal
C-3,
C-4,
and
C-6
positions
often
claimed
exhibit
remote
participation
with
carbon.
Neighbouring
being
widely
studied
help
glycochemists
design
protocols
for
multistep
synthesis
complex
oligosaccharides
turn,
standardise
process
glycosylation
towards
a
particular
stereochemical
output.
While
has
been
quite
effective
achieving
produced
glycosides,
exhibits
comparatively
less
efficacy
complete
stereoselectivity
reactions.
Remote
is
still
highly
debated
topic
scientific
community.
However,
implementing
participating
role
reactions
practised
achieve
better
stereocontrol
facilitate
formation
synthetically
glycosidic
linkages.
Communications Chemistry,
Год журнала:
2025,
Номер
8(1)
Опубликована: Март 7, 2025
The
stereoselective
introduction
of
glycosidic
bonds
is
one
the
greatest
challenges
in
carbohydrate
chemistry.
A
key
aspect
controlling
glycan
synthesis
glycosylation
reaction
which
linkages
are
formed.
outcome
governed
by
a
reactive
sugar
intermediate
-
glycosyl
cation.
Glycosyl
cations
highly
unstable
and
short-lived,
making
them
difficult
to
study
using
established
analytical
tools.
However,
mass-spectrometry-based
techniques
perfectly
suited
unravel
structure
gas
phase.
main
approach
involves
isolating
intermediate,
free
from
external
influences
such
as
solvents
promoters.
Isolation
allows
examining
their
integrating
orthogonal
spectrometric
spectroscopic
technologies.
In
this
perspective,
recent
achievements
gas-phase
research
on
highlighted.
It
provides
an
overview
used
probe
methods
for
interpreting
spectra.
connections
between
data
mechanisms
solution
explored,
given
that
reactions
typically
performed
solution.
