Anomers nomenclature

Figure 3.5 750 MHz 1 H continuous-flow HPLC-NMR spectrum of an equilibrium mixture of transacylated glucuronides of 4-fluorobenzoic acid. The nomenclature 271 -a denotes the 1 proton in the a-anomer of the 2-O-acyl glucuronide...

As pointed out on page 276, the nomenclature of tetraacetyl-/S-D-glucopyranosylbenzene (IV), its anomer,66 and related compounds was based on their specific rotations in accordance with Hudson s conventions,63 and not on the actual stereochemical configurations of the phenyl group about the anomeric centers. Thus, for example, it has not been known if the rotationally designated /3-D-xylopyranosylbenzene (LX), actually possesses the configurational tram /3-structure (LXI), or cis a-structure (LXII). 

Nitriles, a-amino, mutarotation of, 13 Nitrogen compounds, of cyclic monosaccharides, 115 — 232 Nojirimycin, 116,132,133 Nomenclature, of enzymes, 306 Nuclear magnetic resonance anomer determination by, 43 characterization of anhydrodeoxyaldi-tolsby, 74,77,79... 

Lactose is hydrolyzed by the membrane-bound enzyme lactase. The enzyme is also known as a -galactosidase because its action involves the cleavage of the P-anomer of galactose from its 1 4 bond with an a-anomer of glucose. Note this arrow nomenclature for the bond or linkage between the two monosaccharides. 

Anomeric carbon (Section 22.2C) The hemiacetal or acetal carbon in the cyclic form of a carbohydrate. The anomeric carbon can have either the a or /3 stereochemical configuration (using carbohydrate nomenclature), resulting in diastereomeric forms of the carbohydrate called anomers (a-anomers and /3-anomers). Anomers differ on/y in the stereochemistry at the anomeric carbon. 

Scheme 11.13. A representation of a portion of the pathway of gluconeogenesis. The 6-phosphate of glucose is considered capable of hydrolysis to glucose with the appropriate hydroiyase (EC 3.1.3.9) catalyst. The anomer shown is a (because the hydroxyl on the ano-meric carbon is cis or syn to the hydroxyl at C5, Scheme 11.14). A caution concerning nomen-ciature is needed. In the acyclic form, it is clear which carbon is number six. Cyclization to the six-membered ring pyranose (oxane) (or furanose [oxolane] when the five-membered ring forms) leaves ns with a nomenclature problem since the carbon that was C-1 (the ano-meric carbon) is often referred to as C-1 in both structures that involve formation of bonds to that carbon as well as in reactions that may occur at that carbon. However, it will be recalled (Chapter 5) that the nomenclature of cyclic ethers (and other heterocycles) generally requires that the heteroatom (or a heteroatom if more than one is present) receive the lowest number. So, the lUPAC and the lUBMB numbering system is used for archiving purposes, while the trivial nomenclature is commonly used in the literature. Both systems will be found here as appropriate.

General Discussion. Although calcium chloride compounds of both the a- and /S-anomers have been crystallized 38), only one crystalline anomer of the sugar itself is known, and this has been usually designated as the jS-anomer, following the nomenclature of Hudson. 

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