Soluble protein chaperone that recognizes N-glycans and mediates quality control of glycoprotein folding in the endoplasmic reticulum. Membrane-bound protein chaperone that mediates quality control of protein folding in the endoplasmic reticulum. C-type lectinsĪ class of Ca ++-dependent lectins recognizable by a characteristic sequence comprising their carbohydrate recognition domain. BiofilmĬommunity of bacteria that adheres to a moist surface (e.g., surface of ponds or teeth). The process is used to cleave O-glycans from Ser or Thr residues. The cleavage of a C-O or C-N bond positioned on the beta carbon with respect to a carbonyl group. Azido sugarĪ monosaccharide to which an azido group has been introduced synthetically. AzideĪ functional group comprising three nitrogen atoms bound in a linear arrangement (N 3). AvidityĪ measure of the combined strength of interaction from the multiple affinities of a multivalent complex. Rapid method for the chemical synthesis of oligo- and polysaccharides on a solid support. AntennaĪ branch of an oligosaccharide emanating from a “core” structure. Stereoisomers of a monosaccharide that differ only in configuration at the anomeric carbon of the ring structure. The carbon atom of a monosaccharide that bears the hemiacetal functionality (C-1 for most sugars C-2 for sialic acids). Amino sugarĪ monosaccharide in which a hydroxyl group is replaced by an amino group. AldoseĪ monosaccharide with an aldehyde group or potential aldehydic carbonyl group (by definition, this is the C-1 position). Non-carbohydrate portion of a glycoconjugate or glycoside that is glycosidically linked to the glycan through the reducing terminal sugar. The related term hemagglutination denotes the specific case wherein the cells are red blood cells. The clumping of cells in the presence of a protein (e.g., antibody or lectin). AffinityĪ measure of the strength of interaction between a receptor and its ligand. AdhesinĪ protein on the surface of bacteria, viruses, or parasites that binds to a ligand present on the surface of a host cell. If the hemiacetal is a sugar, the acetal is a glycoside. AcetalĪn organic compound derived from a hemiacetal by reaction with an alcohol. From that point of view, the stereoelectronic component of the anomeric effect plays a unique role in guiding reaction design.Gene locus comprising three major allelic glycosyltransferases that generate the A, B, and O blood groups. This analysis paves the way for the broader discussion of the omnipresent importance of negative hyperconjugation in oxygen-containing functional groups. For example, negative hyperconjugation can unleash the “underutilized” stereoelectronic power of unshared electrons ( i.e., the lone pairs) to stabilize a developing positive charge at an anomeric carbon. In these situations, the role of orbital interactions increases to the extent where they can define reactivity. Even when many factors contribute to the observed structural and conformational trends, electron delocalization is a dominating force when the electronic demand is high ( i.e., bonds are breaking as molecules distort from their equilibrium geometries). Stereoelectronic thinking can reconcile quantum complexity with chemical intuition and build the conceptual bridge between structure and reactivity. Why are such questions inherently controversial? How to describe a complex quantum system using a model that is “as simple as possible, but no simpler”? What is a fair test for such a model? Perhaps, instead of asking “who is right and who is wrong?” one should ask “why do we disagree?”. We will use recent controversies regarding the origin of the anomeric effect to start a deeper discussion relevant to any electronic effect. We show that the complete hyperconjugative model remains superior in explaining the interplay between structure and reactivity. After providing the background related to the relevant types of hyperconjugation and a brief historic outline of the origins of the anomeric effect, we outline variations of its patterns and provide illustrative examples for the role of the anomeric effect in structure, stability, and spectroscopic properties. Herein, we will use a classic conformational “oddity”, the anomeric effect, to discuss the value of identifying the key contributors to reactivity that can guide chemical predictions. The task becomes even more difficult when multiple approaches based on different physical premises disagree in their analysis of a multicomponent molecular system. Understanding the interplay of multiple components (steric, electrostatic, stereoelectronic, dispersive, etc.) that define the overall energy, structure, and reactivity of organic molecules can be a daunting task.
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