Acetals Derived from Carbohydrate Hydroxy-groups

Acetals Derived from Carbohydrate Hydroxy-groups 

Such methylene derivatives as (50)—(52) were obtained when suitably protected monosaccharides reacted with dichloromethane in a two-phase system in the presence of a phase-transfer catalyst.  

---

Acetals Derived from Carbohydrate Hydroxy-groups... 

In addition to the approach outlined in Scheme 4, several other approaches to the synthesis of glycofuranosides have been reported during the past year. Hanessian and Banoub have used cyclic amide acetals derived from vicinal diols as the source of the aglycone in condensations with l-0-acetyl-2,3,5-tri-0-benzoyl-jS-D-ribofuranose in the presence of stannic chloride (Scheme 5). Disaccharide derivatives are obtained when the cyclic amide acetal is derived from carbohydrate vicinal diols (Scheme 6), and selective methanolysis of the formate ester exposed an hydroxy-group that can be subjected to further manipulation or glycosylation. 2,3,5-Tri-0-benzoyl-a)8-L-arabinofuranosyl bromide or chloride has been condensed with 4-nitrophenyl 2,3-di-O-acetyl-a-L-arabinofuranoside to yield, after deacylation, 4-nitrophenyl 5-O-a-L-arabinofuranosyl-a-L-arabino-furanoside, with jS-peltatin A [isolated from podophyllin Podophyllum peltatum)] in glycosidation of the phenolic 8-OH group in an attempt to reduce... 

Elforts have been made to characterize the nature and content of individual components that are present in the low-molecular-mass fraction of the total mill effluents, which include the spent chlorination and alkali extraction stage liquors [2,4]. Approximately 456 types of compounds have been detected in the conventional bleach effluents, of which 330 are chlorinated organic compounds [22]. The compounds may be lumped into three main groups, namely, acidic, phenolic, and neutral (Table 2). Acidic compounds are further divided into the five categories of acids fatty, resin, hydroxy, dibasic, and aromatic acids. The most important fatty acids are formic and acetic acids. The dominant resin acids are abietic and dehydroabietic acids. Among the hydroxy acids identified, glyceric acid predominates. Dibasic acids such as oxalic, malonic, succinic, and mafic acids are derived from the lignin and carbohydrate fraction... 

---