Acetals acyclic sugars

A further useful reaction of dialkyl ditinoacetab involves treatmein with bromine in an aprotic solvent, which effects monobromination at C-l. These brominated intennediates react with such nucleophiles as alcohols to form mixed acetal products [24]. This method has proved especially osefid for the synthesis of nucieoside analogues having acyclic sugar chains attached to the heterocycle [25] (Scheme 5). 

Closely similar results were obtained with various diphenyl dithioacetal acetates (7), with the unsubstituted diethyl dithioacetals (8), and with the aldehydo-pentose peracetates (9) and the tetra-O-acetylaldo-pentose dimethyl acetals (10). Subsequent work in other laboratories has shown the same general principles for the methyl 5-hexulosonates (11) and the pentononitrile tetraacetates (12), two examples where a full series of stereoisomers has been studied. Other workers have investigated isolated examples or partial series (13, 14, 15, 16, 17, 18), and parallel work by x-ray crystallography (19, 20, 21, 22) on acyclic sugar derivatives in the solid state has shown excellent correlation with the general principles outlined here for the molecules in solution. 

Appropriately substituted derivatives of acyclic sugars should behave in the same manner as the alditols. The only examples so far studied are239 2,3-di-0-tosyl-D,L-glycerose and its diethyl acetal, which react as follows ... 

The presence of these acceptor only atoms necessarily interferes with the cooperativity , which favors the formation of the infinite 0-H 0-H 0-H- chains which are so prominent in the crystal structures of the acyclic sugar alcohols. Either the functional character of the acetal or hemi-acetal oxygen atoms is ignored, or the cooperative effect is reduced. As we will see, several different compromises are reached in which three-center hydrogen bonding plays an important part. 

The Action of Diazomethane upon Acyclic Sugar Derivatives. III. A New Synthesis of Ketoses and of their Open Chain (keto) Acetates, M. L. Wolfrom, S. W. Waisbrot, and Robert L. Brown, /. Amer. Chem. Soc., 64, 2329-2331 (1942). 

The importance of parallel 1,3-interactions in determining the favored conformational state of acyclic sugar derivatives in solution was also apparent from n.m.r.-spectral studies of polyhydroxyalkyl-quinoxalines in methyl sulfoxide, and of their acetates in carbon tetrachloride. 

The study of monosaccharides subjected to conditions of methanolysis is considered for two reasons. First, the decomposition of monosaccharides is indicative of the decomposition of monosaccharides liberated during methanolysis second, the ratio of methyl glycosides of a particular standard monosaccharide is the same for the same monosaccharide released during methanolysis (for a particular set of methanolysis conditions), provided that the concentration of sugars is relatively low. Up to four methyl glycosides (the a and )8 anomers of the pyranoside and furan-oside forms) of a particular monosaccharide may be formed the acyclic dimethyl acetal is an additional possibility. The ratios of methyl glycosides of 10 monosaccharides subjected to methanolysis with M hydrogen chloride for 24 h at 80° has been reported. Similar information is also available in another study."... 

A patent application has been presented for Varroa control by means of acyclic and cyclic terpenes, mainly linalool, linalyl acetate, eugenol and anethole total control of the mite was observed when honey bees were fed 50% sugar syrup containing 1% linalool [85],... 

The Smith degradation4 involves reduction of the periodate-oxidized polysaccharide with borohydride, followed by mild hydrolysis with acid. (The periodate oxidation has already been treated in Section 111,1, p. 200.) The modified sugar residues contain acyclic acetal groupings, which are hydrolyzed much faster than the glyco-sidic linkages. The product therefore contains small fragments (such... 

Dialkyl dithioacetal derivatives of ketoses, such as D-fiuctose and L-sorbose, me inaccessible directly from the parent sugars, the ketose undergoing extensive decomposition under the conditions employed for mercaptaladon of aldoses. Such derivatives can, however, be prepared by indirect methods. Acetylation of D-fiuctose [40] and L-soibose with acetic adiydride and zinc chloride [41] leads to good yields of acyclic pentaacetates in which foe ketose carbonyl is not involved in a cyclic acetal. Subsequent treatment of these acetylated derivatives with thiols affords foe acetylated dialkyl dithioacetals in satisfactory yields, and conventional deacetylation affords foe unprotected dialkyl dithioacetals [40,41]... 

---