Carbohydrate Complexities

Nicotinic acid is found in plants associated with both peptides and polysaccharides. For example in wheat bran, two forms are described a peptide with a molecular weight of approximately 12,000 and a carbohydrate complex that is called niacytin. Polysaccharides isolated from wheat bran have been found to contain 1.05% nicotinic acid in bound form. Hydrolysis yielded a fragment identified as P-3-O-nicotinoyl-D-glucose (25). 

R. O. Duthaler, A. Hafner, M. Riediker in Asymmetric C-C Bond Formation with Ti-, Zr-, and Hf-Carbohydrate Complexes in Organic Synthesis via Organometallics, K. H. Dotz, R.W Hoffmann, Eds., pp 285-310, Vieweg, Braunschweig 1990. 

The conclusion that solid-state spectra provide evidence for a lignin-carbohydrate complex is of special interest. Solid-state spectra of lignin fractions obtained by ball milling and extraction with dimethyl sulfoxide exhibit carbohydrate signals and vice... 

Sweetness is a quality that defies definition, but whose complexity can be appreciated merely by examining the molecular structures of those compounds that elicit the sensation. They come in all molecular shapes and sizes, and they belong to such seemingly unrelated classes of compounds as aliphatic and aromatic organic compounds, amino acids, peptides and proteins, carbohydrates, complex glycosides, and even certain inorganic salts. 

Saponins and phenolics also have anti-microbial properties (Chung et ah, 1998) and have been associated with reduced rumen functions (Klita et al., 1996 Reed, 1995), thereby limiting the nutrient quality of forages. Also, carbohydrate complexes with hgnins and other compounds reduce carbohydrate utilization by rumen bacteria (Cornu et al., 1994). The influence of such anti-microbials on rumen functions can affect small intestine characteristics by altering nutrient concentrations (Barry and McNabb, 1999). 

CORNU A, BESLE J M, MOSONi p, GRENET E (1994) Lignin-carbohydrate complexes in forages structure and consequences in the ruminal degradation of cell-wall carbohydrates. Reprod Nutr Dev. 34 385-98. 

KIYOHARA H, MATSUMOTO T, YAMADA H (2000) Ligniu-carbohydrate complexes intestinal immune system modulating ingredients in kampo (Japanese herbal) medicine, juzen-taiho-to. Planta Med. 66 20-24. 

Dropkin, V.H. and Bird, A.F. (1978) Physiological and morphological studies on secretion of a protein-carbohydrate complex by a nematode. International Journal for Parasitology 8, 225-232. 

All compounds have a precise and often highly specific function to fulfil, and in animals many of them are concerned also with the protection of the body against agents of disease. The problems of immunity and of enzyme systems involve the consideration of protein-carbohydrate complexes so that structural studies in the group now need to be undertaken seriously. 

S. Ravaud, X. Robert, H. Watzlawick, R. Haser, R. Mattes, and N. Aghajari, Trehalulose synthase native and carbohydrate complexed structures provide insights into sucrose isomerization, /. Biol. Chem., 282 (2007) 28126-28136. 

Covalently bonded chiral auxiliaries readily induce high stereoselectivity for propionate enolates, while the case of acetate enolates has proved to be difficult. Alkylation of carbonyl compound with a novel cyclopentadienyl titanium carbohydrate complex has been found to give high stereoselectivity,44 and a variety of ft-hydroxyl carboxylic acids are accessible with 90-95% optical yields. This compound was also tested in enantioselective aldol reactions. Transmetalation of the relatively stable lithium enolate of t-butyl acetate with chloro(cyclopentadienyl)-bis(l,2 5,6-di-<9-isopropylidene-a-D-glucofuranose-3-0-yl)titanate provided the titanium enolate 66. Reaction of 66 with aldehydes gave -hydroxy esters in high ee (Scheme 3-23). 

In principle, mass spectrometry is not suitable to differentiate enantiomers. However, mass spectrometry is able to distinguish between diastereomers and has been applied to stereochemical problems in different areas of chemistry. In the field of chiral cluster chemistry, mass spectrometry, sometimes in combination with chiral chromatography, has been extensively applied to studies of proton- and metal-bound clusters, self-recognition processes, cyclodextrin and crown ethers inclusion complexes, carbohydrate complexes, and others. Several excellent reviews on this topic are nowadays available. A survey of the most relevant examples will be given in this section. Most of the studies was based on ion abundance analysis, often coupled with MIKE and CID ion fragmentation on MS " and FT-ICR mass spectrometric instruments, using Cl, MALDI, FAB, and ESI, and atmospheric pressure ionization (API) methods. 

In the PPA-a-AI 1 complex, a flexible loop of the enzyme, which would normally contact the substrate, is pushed outward to allow entry of the inhibitor, and one of the key aspartate residues is held in a conformation similar to that observed in the free enzyme. Therefore, some changes relative to the carbohydrate complex are required in order to accommodate the inhibitor. The structurally mimetic interactions within the catalytic site are supplemented by other specific protein-protein interactions, with a substantial buried surface area at the interface, involving 50 residues of the enzyme [171]. 

Lignin—Carbohydrate Complexes from Poplar Wood... 

OVEREND AND JOHNSON Lignin—Carbohydrate Complexes from Poplar 271... 

Table I. Properties of Populus deltoides Lignin-carbohydrate Complexes...

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