Sugar relative reactivities

Competition Experiments of Ley Ley examined product distributions to obtain relative reactivity values (RRVs) for both rhamnose and mannose sugars with benzyl, 3,4-cyclic diacetals, and benzoyl groups. Using a limiting amount of acceptor (1 equiv), two donors were added in excess (2 equiv each), followed by the addition of activator (NIS/TfOH, 2 equiv) (Scheme 11.13). After quenching the reaction, the product distribution was analyzed by -NMR. 

Cowie, G.L., J.I. Hedges, and S.E. Calvert. 1992. Sources and relative reactivities of amino acids, neutral sugars, and lignin in an intermittently anoxic marine environment. Geochimica et Cosmochimica Acta 56 1963-1978. 

K. K. Sen Gupta, A. Sanyal, P. S. Tribedi, and S. Sen Gupta, Kinetic behaviour and relative reactivities of some aldoses, amino sugars and methylated sugars towards permanganate in perchloric acid medium, J. Chem. Res. (S), (1993) 484-485. 

The effect of variation of sugar configuration on the rate of hydrolysis of a number of methyl glycosides has been studied by several groups of work-ers.7n.7i The relative reactivities collected by Shafizadeh and Thompson are shown in Table XII. These results have been discussed by Foster and Overend and by Edward, on the basis of mechanism a of Fig. 4. 

The reduction of chlorodeoxy sugars has been achieved [31,32] in high yield by means of tributyltin hydride in the presence of 2,2 -azobis(2-methylpropionitrile). The reaction with methyl 2,3-di-0-acetyl-4,6-dichloro-4,6-dideoxy-a-D-galactopyranoside at 60°C gave [31] methyl 2,3-di-0-acetyl-6-chloro-4,6-dideoxy-ot-D-xylo-hexopyranoside as the main product. A free-radical mechanism has been proposed [33] for the reduction of alkyl halides by organotin hydrides. In accordance with this proposal, the presence of the radical initiator 2,2 -azobis(2-methylpropionitrile) was essential for the reduction of chlorodeoxy sugars moreover, the relative reactivities of the two chlorine atoms in methyl 2,3-di-0-acetyl-4,6-dichloro-4,6-dideoxy-a-D-galactopyranoside follow a free-radical order. 

These important factors constitute the proper strategy for the regioselective protection of the remaining active centers of the molecules as their reactivity varies significantly. Thus, the relative reactivity of the various -OH groups upon stereoselective tosylation of 1,6-anhydro sugars decreases according to the determined order as depicted inO Fig. 1 [27]. 

The relative reactivity toward sodium of the hydroxyl groups at the various carbon atoms of a sugar has been exploited in order to prepare selected derivatives. By the addition of one molar equivalent of sodium to 4,5-0-isopropylidene-D-fucose dimethyl acetal in ethyl ether, followed by benzyl chloride, Schmidt and Wernicke were able to isolate a 42 % yield of 2-0-benzyl-4,5-0-isopropylidene-D-fucose dimethyl acetal. Freudenberg and Noe reacted molar equivalents of 1,2-0-isopropylidene-a-D-glucofuranose and sodium in boiUng dioxane. Subsequent reaction with benzyl chloride, and acetylation, gave a 29 % yield of crystalline 5,6-di-0-acetyl-3-0-benzyl-1,2-0-isopropylidene-a-D-glucose. 

Second, the relative reactivities of Ru(IV)0 ", RudlDOH, and Os(IV)0 show that guanine oxidation is much more facile than sugar oxidation. This observation suggests that all oxidants that cleave DNA... 

Cowie, G.L., Hedges, J.I. and Calvert, S.E. (1992) Sources and Relative Reactivities of Amino-Acids, Neutral Sugars, and Lignin in an Intermittently Anoxic Marine Environment. Geochimica et Cosmochimica Acta, 56, 1963-1978. 

Relative Reactivity Values (RRVs). which are the experimentally determined values relating the reactivities of the BB s to the stamdard sugar... 

Basic chemical research, best done in academic institutions or by contract research organizations, was needed first in order to obtain sucrochemicals of the nature envisioned by Dr. Hass. Thus, early work in sucrochemistry was funded by the Sugar Research Foundation in such research laboratories. An exploratory project oriented towards discovering the fundamental chemistry of sucrose and other carbohydrates had been supported previously at the Massachusetts Institute of Technology from 1943 to 1950. The main purpose of the project, however, was to train carbohydrate chemists and to apply classical carbohydrate chemistry more broadly to sucrose and its close relatives. None of the derivatives produced and studied were found to be of practical importance in later sucrochemical studies, although a number of patent applications were filed and patents issued. Some of these studies were continued in several other laboratories during the early 1950 s, and a number of additional studies were undertaken to elucidate the relative reactivities of the various reactive entities, determine reaction kinetics and to try to make new and possibly useful derivatives. An intensive search was undertaken to find mutual solvents for both hydrophilic sucrose and hydrophobic reactants. 

The organotin derivative (7) was prepared from D-mannose, and some reactions involving Sn-Li exchange were studied, while the relative reactivities of some C-triphenylstaimyl-carbohydrate derivatives in iodine-induced phenyl-tin bond cleavage reactions have been determined. Nucleophilic addition of a carbanionic carborane to a number of sugar aldehydes has provided adducts that were used in attempts to increase the water solubility of carborane - antibody complexes with a view to localising boron on tumors prior to... 

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