5 research outputs found
Expeditious Microwave-Assisted Synthesis of 5âAlkoxyoxazoles from αâTriflyloxy Esters and Nitriles
A rapid and general access to diversely substituted 5-alkoxyoxazoles <b>2</b> (i.e., R<sup>1</sup>, R<sup>2</sup> = alkyl, phenyl) from
easily accessible α-triflyloxy/hydroxy esters <b>1</b> and nitriles with good yields (41â76%) is reported. The versatility
of the cyclization is shown for a range of substrates with high selectivity
toward triflates over mesylates and proved to be compatible with sensitive
functional groups. As an illustration of this transformation, the
first synthesis of the recently isolated hydroxypyridine methyl multijuguinate <b>4</b> was achieved in four steps through a hetero DielsâAlder
reaction of the 5-alkoxyoxazole and acrylic acid, followed by a protodecarboxylation
reaction
Thermally Controlled Decarboxylative [4 + 2] Cycloaddition between Alkoxyoxazoles and Acrylic Acid: Expedient Access to 3âHydroxypyridines
A modified Kondratâeva cycloaddition involving an unprecedented thermally controlled metal-free decarboxylative aromatization affords an expedient access to natural 3-hydroxypyridine/piperidine systems
Metal-Free Decarboxylative Hetero-DielsâAlder Synthesis of 3âHydroxypyridines: A Rapid Access to <i>N</i>âFused Bicyclic Hydroxypiperidine Scaffolds
A complete
experimental and theoretical study of the thermally
controlled metal-free decarboxylative hetero-DielsâAlder (HDA)
reaction of 5-alkoxyoxazoles with acrylic acid is reported. This strategy
offers a new entry to valuable 2,6-difunctionalized 3-hydroxypyridines
from readily available 2- and 4-disubstituted 5-alkoxyoxazoles. The
reaction conditions proved compatible with, among others, ketone,
amide, ester, ether, and nitrile groups. The broad functional group
tolerance of the protocol allows a rapid and versatile access to both
hydroxyindolizidine and hydroxyquinolizidine derivatives via a pyridine
dearomatization strategy
Kondratâeva Ligation: DielsâAlder-Based Irreversible Reaction for Bioconjugation
Diversification of existing chemoselective
ligations is required
to efficiently access complex and well-defined biomolecular assemblies
with unique and valuable properties. The development and bioconjugation
applications of a novel DielsâAlder-based irreversible site-specific
ligation are reported. The strategy is based on a Kondratâeva
cycloaddition between bioinert and readily functionalizable 5-alkoxyoxazoles
and maleimides that readily react together under mild and easily tunable
reaction conditions to afford a fully stable pyridine scaffold. The
potential of this novel bioconjugation is demonstrated through the
preparation of fluorescent conjugates of biomolecules and a novel
FoÌrster resonance energy transfer (FRET)-based probe suitable
for the in vivo detection and imaging of urokinase-like plasminogen
activator (uPA), which is a key protease involved in cancer invasion
and metastasis
Synthesis, Biological Evaluation, and <i>in Vivo</i> Imaging of the first CamptothecinâFluorescein Conjugate
The first synthesis and photophysical
properties of a fluorecently
labeled camptothecin derivative, namely, camptothecin-FI (CPT-FI),
an antitumoral agent that targets topoisomerase I, are reported. The
preparation of this fluorescent conjugate is based on a highly convergent
and flexible approach which enables the rapid chemical modification
of the AB ring system of this fragile pentacyclic alkaloid, aimed
at introducing an anchoring point to graft the fluorophore. The selection
of a fluorescein analogue as the reporter group has enabled us to
get the first green-emitting CPT conjugate exhibiting valuable spectral
properties and retaining biological properties of native CPT. Indeed,
in biological models, i.e., glioma cell lines U87 and/or T98, the
kinetics of cell endocytosis, as well as the efficacy of CPT-FI were
compared to those of CPT. CPT-FI fluorescence was measured in the
cytosolic compartment of T98 glioma cells from 5 min treatment and
remained detectable until 48 h. As CPT, CPT-FI drastically inhibited
glioma growth and cell cycle but exhibited a reduced affinity as compared
to the native CPT. <i>In vivo</i> and <i>ex vivo</i> imaging studies of CPT-FI intratumoraly injected into a model of
NIH-3T3 murine tumor xenografts in nude mice, showed accumulation
around the injected site area, which is very promising to target tumors
and follow biodistribution <i>in vivo</i>