Saccharides reduction

Hexosamines, hexosami-nitols and amine-containing di- and tri-saccharides Reduction NaBH, Af-de-acetylation anion exchange chromatography, borate-citrate buffers Donald [239]... 

In his first independent work, Helferich prepared y-hydroxyvaleral-dehyde (4-hydroxypentanal) by reduction and ozonolysis of methylhep-tenone, readily available from citral by a retro-aldol reaction. He was able to show that, similarly to the saccharides, this hydroxyaldehyde exists in... 

An interesting procedure has been proposed for the synthesis of amylose-b-PS block copolymers through the combination of anionic and enzymatic polymerization [131]. PS end-functionalized with primary amine or dimethylsilyl, -SiMe2H groups were prepared by anionic polymerization techniques, as shown in Scheme 56. The PS chains represented by the curved lines in Scheme 56 were further functionalized with maltoheptaose oligomer either through reductive amination (Scheme 57) or hydrosilyla-tion reactions (Scheme 58). In the first case sodium cyanoborohydride was used to couple the saccharide moiety with the PS primary amine group. 

The basic outline of autocatalysed linked metabolism, as described in Chapter 4 (see Table 5.3) was originally and to some extent, still is, from CO (or C02) by reduction leading to fats, saccharides and with NH3 to proteins, according to the scheme... 

Even if the main focus on the research activities were directed towards structural studies on carbohydrates of natural origin, the synthesis of model substances, deriva-tization of oligo- and poly-saccharides, oxidation, and reduction of carbohydrates, and identification of the products all were performed during this time. 

In order to study the reactivity of the nitrogen atom in saccharidic OZT moieties Rollin and co-workers13,55 explored some standard reactions IV-acylation, IV-sulfonylation, IV-vinylsulfonylation by Michael addition, reductive elimination, conjugated addition and cycloaddition. 

Boettger stest analychem A test for the presence of saccharides, utilizing the reduction of bismuth subnitrate to metallic bismuth, a precipitate. bet.gorz. test bohrlum chem A synthetic chemical element, symbolized Bh, atomic number 107 ... 

Reductions with sodium amalgam are fairly mild. Only easily reducible groups and conjugated double bonds are affected. With the availability of sodium borohydride the use of sodium amalgam is dwindling even in the field of saccharides, where sodium amalgam has been widely used for reduction of aldonic acids to aldoses. 

Aliphatic and aromatic sulfides undergo desulfurization with Raney nickel [673], with nickel boride [673], with lithium aluminum hydride in the presence of cupric chloride [675], with titanium dichloride [676], and with triethyl phosphite [677]. In saccharides benzylthioethers were not desulfurized but reduced to toluene and mercaptodeoxysugars using sodium in liquid ammonia [678]. This reduction has general application and replaces catalytic hydrogenolysis, which cannot be used [637]. 

Figure 6.29 Preparation of difluoromethyl saccharides through reduction.

The thioaldonic phenylhydrazides obtained by reduction of saccharide formazans condense with benzaldehyde to give 1,3,4-thiadi-azolines, characterized by their high optical rotatory power.234,235... 

Protocols of peptide chemistry and, to some extent, biooligomer synthesis (e.g., nucleotides, saccharides) are valuable sources of information on this topic with regards to solid-phase synthesis peculiarities. Here we focus on a particular functional group transformation, which takes the role of depro-tecting a masked functionality, namely the nitro-to-amine reduction. This approach provides a versatile tool for planning multistep derivatizations of heterocycles, as exemplified in Fig. 15.45... 

An example belonging to this category is the reduction of some saccharides, in particular aldoses. It is assumed (93) that only the open-... 

Mithramycin shows a completely P-linked chain of D-conflgurated saccharides. This requires a totally different approach for the synthesis which is also done by application of the DBE method. The previously obtained disaccharide 180 is P-glycosylated with the monosaccharide precursor 176 to give the trisaccharide 185. After reductive debromination (Bu3SnH), an acid deformylation deblocked the C-3" position which is oxidized with pyridinium dichromate. Nucleophilic attack at the carbonyl group by methyl lithium affords a 1 1.2 mixture of 186 and 187 none of which is the desired compound [93]. Obviously, the methyl branch is formed exclusively in the axial way. 

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