12 research outputs found
Synthesis of α-D-GalpN3-(1-3)-D-GalpN3: α- and 3-O-selectivity using 3,4-diol acceptors
No full textThe motif α-D-GalpNAc-(1-3)-D-GalpNAc is very common in Nature and hence its synthesis highly relevant. The synthesis of its azido precursor has been studied and optimized in terms of steps, yields and selectivity. It has been found that glycosylation of the 3,4-diol acceptor is an advantage over the use of a 4-O-protected acceptor and that both regio- and anomeric selectivity is enhanced by bulky 6-O-protective groups. The acceptors and donors are made from common building blocks, limiting protective manipulations, and in this context, unavoidable side reactions
Scalable Synthesis of Anomerically Pure Orthogonal-Protected GlcN<sub>3</sub> and GalN<sub>3</sub> from d‑Glucosamine
No full textAn improved and scalable
synthesis of orthogonally protected d-glucosamine and d-galactosamine building blocks from
inexpensive d-glucosamine has been developed. The key reaction
is an inversion/migration step providing access to a fully orthogonal
protecting group pattern, which is required for microbial oligosaccharide
synthesis. The method can be carried out on a multigram scale as several
of the reactions can be purified by crystallization to give anomerically
pure products
Molecular Heterojunctions of Oligo(phenylene ethynylene)s with Linear to Cruciform Framework
No full textElectrical transport properties of molecular junctions are fundamentally affected by the energy alignment between molecular frontier orbitals (highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO)) and Fermi level (or work function) of electrode metals. Dithiafulvene (DTF) is used as substituent group to the oligo(phenylene ethynylene) (OPE) molecular wires and different molecular structures based on OPE3 backbone (with linear to cruciform framework) are achieved, with viable molecular orbitals and HOMO-LUMO energy gaps. OPE3, OPE3-DTF, and OPE3-tetrathiafulvalene (TTF) can form good self-assembled monolayers (SAMs) on Au substrates. Molecular heterojunctions based on these SAMs are investigated using conducting probe-atomic force microscopy with different tips (Ag, Au, and Pt) and Fermi levels. The calibrated conductance values follow the sequence OPE3-TTF > OPE3-DTF > OPE3 irrespective of the tip metal. Rectification properties (or diode behavior) are observed in case of the Ag tip for which the work function is furthest from the HOMO levels of the OPE3s. Quantum chemical calculations of the transmission qualitatively agree with the experimental data and reproduce the substituent effect of DTF. Zero-bias conductance, and symmetric or asymmetric couplings to the electrodes are investigated. The results indicate that improved fidelity of molecular transport measurements may be achieved by systematic studies of homologues series of molecular wires applying several different metal electrodes.</p
Glycosyl Fluorides as Intermediates in BF<sub>3</sub> center dot OEt<sub>2</sub>-Promoted Glycosylation with Trichloroacetimidates
No full textSynthesis and pharmacological evaluation of DHβE analogs as neuronal nicotinic acetylcholine receptor antagonists
No full textDihydro-β-erythroidine (DHβE) is a member of the Erythrina family of alkaloids and a potent competitive antagonist of the α4β2-subtype of the nicotinic acetylcholine receptors (nAChRs). Guided by an X-ray structure of DHβE in complex with an ACh binding protein, we detail the design, synthesis, and pharmacological characterization of a series of DHβE analogues in which two of the four rings in the natural product has been excluded. We found that the direct analogue of DHβE maintains affinity for the α4β2-subtype, but further modifications of the simplified analogues were detrimental to their activities on the nAChRs
A strategic approach to [6,6]-bicyclic lactones: application towards the CD fragment of DHβE
No full textWe report an effective synthetic protocol to access [6,6]-bicyclic lactone moieties through a regio- and stereoselective intramolecular Mizoroki–Heck cross-coupling reaction followed by a 6π-electrocyclization. This method enabled the first synthesis of the elusive CD fragment of the Erythrina alkaloid DHβE. Preliminary pharmacological evaluations support the notion that the key pharmacophores of DHβE are located in the A and B rings
Synthesis and Pharmacological Evaluation of DHβE Analogues as Neuronal Nicotinic Acetylcholine Receptor Antagonists
No full textDihydro-β-erythroidine
(DHβE) is a member of the Erythrina
family of alkaloids and a potent competitive antagonist of the α4β2-subtype
of the nicotinic acetylcholine receptors (nAChRs). Guided by an X-ray
structure of DHβE in complex with an ACh binding protein, we
detail the design, synthesis, and pharmacological characterization
of a series of DHβE analogues in which two of the four rings
in the natural product has been excluded. We found that the direct
analogue of DHβE maintains affinity for the α4β2-subtype,
but further modifications of the simplified analogues were detrimental
to their activities on the nAChRs
Erythrina Alkaloid Analogues as nAChR AntagonistsA Flexible Platform for Leads in Drug Discovery
No full textErythrina Alkaloid Analogues as nAChR Antagonists-A Flexible Platform for Leads in Drug Discovery
No full textErythrina alkaloids and their central nervous system effects have been studied for over a century, mainly due to their potent antagonistic actions at β2-containing nicotinic acetylcholine receptors (nAChRs). In the present work, we report a synthetic approach giving access to a diverse set of Erythrina natural product analogues and present the enantioselective total synthesis of (+)-Cocculine and (+)-Cocculidine, both found to be potent antagonists of the β2-containing nAChRs.</p
A comprehensive study of extended tetrathiafulvalene cruciform molecules for molecular electronics:synthesis and electrical transport measurements
No full text
