Amino sugars catalyst

Nitro sugars have been broadly used as precursors of the corresponding amino sugars, most of them naturally occurring and biologically relevant compounds. The standard procedure involves a catalytic hydrogenation and several catalysts have been used for this purpose. 

Raney Nickel was also used as the catalyst for the reduction of nitro sugars to amino sugars by hydrogenation.87 Under these conditions, nitro sugar 127 was reduced to amino sugar derivative 128, without removal of the benzyl protecting group. Compound 128 was finally converted into azepane 129 (Scheme 39).88... 

Finally, carbohydrate ligands of enantioselective catalysts have been described for a limited number of reactions. Bis-phosphites of carbohydrates have been reported as ligands of efficient catalysts in enantioselective hydrogenations [182] and hydrocyanations [183], and a bifunctional dihydroglucal-based catalyst was recently found to effect asymmetric cyanosilylations of ketones [184]. Carbohydrate-derived titanocenes have been used in the enantioselective catalysis of reactions of diethyl zinc with carbonyl compounds [113]. Oxazolinones of amino sugars have been shown to be efficient catalysts in enantioselective palladium(0)-catalyzed allylation reactions of C-nucleophiles [185]. 

Pyridine is used in catalytic amounts and acylpyridinium salts are assumed to be the reactive acylating agents. The method can be applied to the synthesis of both symmetrical and unsymmetrical acid anhydrides. " These can also be obtained in many cases directly from the acid halide and the sodium carbox-ylate without using a solvent or a catalyst. Tiiis approach has been described for a number of mixed acid anhydrides. Thus acetic palmitic anhydride (70%), butyric myristic anhydride (81%) and caproic lauric anhydride (85%) were prepared by heating the components for 2 h at 90 °C. 75 These anhydrides were successfully employed for the N-acylation of amino sugars. 7 ... 

Primary amine formation is equally well promoted in alkaline medium, e.g., aqueous ethanolic NaOH solution, that selectively poisons the catalyst for hydrogenolysis reactions. However, saturated NH3/alcohol solutions best afford almost quantitative yields of primary amines from catalytic reduction of nitriles. Ammonia adds to imine 1 to give a 1,1-diamine, which is hydrogenolyzed to the primary amine. In the presence of NHj, finely divided Ni can be used, platinized finely divided Ni for the hydrogenation of hindered nitriles, and rhodium-on-alumina for sensitive compounds. Mild reduction of 3-indoleacetonitrile to tryptamine [equation (c)] is effected at RT over 5% rhodium-on-alumina in 10% ethanolic NH3 with little side reaction , and branched chain amino sugars are conveniently prepared using this selective hydrogenation [equation (d)] . 

On comparing the reactions of 2-amino-2-deoxyaldoses and 1-amino-l-deoxyketoses with 8-dicarbonyl compounds, which yield pyrroles (Scheme A, X = NH, A -alkyl, or A -aryl), with the reactions of the nonnitrogenous aldoses and ketoses with the same compounds, which yield furan derivatives (Scheme A, X = 0), it may be noted that the changes of bonds are the same. It seems reasonable, therefore, to assume that both processes proceed through the same, or at least similar, mechanisms. From the experimental point of view, the main differences between these two reactions concern rates and catalysts. Aldoses and ketoses react very slowly in the absence of such acidic catalysts as zinc chloride and ferric chloride. The reactions of the amino sugars are much faster and are usually performed under neutral or slightly basic conditions. 

Hetero-Diels-Alder reactions have been used in the construction of amino-sugars, asymmetry being induced by the use of either a chiral Lewis acid catalyst or a chiral auxiliary. Thus, the 3-amino-hexuronic acid derivatives 61 were obtained with high de and ee using a copper(II) triflate catalyst with a chiral bisoxazoline ligand. 4-Amino-4-deoxy-D-erythrose and 4-amino-4,5-dideoxy-L-lyxose (63), the latter a potent inhibitor of a-L-fucosidase, were obtained from the D-pyroglutamic add-containing diene 62 (Scheme 19). ... 

In 2004, Pizzarello and Weber studied a water-based prebiotic model of sugar syntheses from glycoaldehyde and formaldehyde in the presence of nonracemic alanine or isovaline. They demonstrated that the configuration of tetroses is affected by the chirality of the amino acid catalyst. 

The first use of vinylidene-metal species in C-C bond formation with a ruthenium catalyst was reported by Trost in 1990. Since then, the use of vinylidene-Rh species in organic synthesis has been extended to the formation of heterocycles through cycloisomerization of alkynols and alkynyl anilines. For example, the cycloisomerization of alkynol 455, leading to the formation of pyran 456 was used for the synthesis of amino sugar 457 (Scheme 2-51). ... 

Enders et al. also reported direct asymmetric Mannich reactions starting from the protected ketone 14 [10]. Several protected carbohydrates and amino sugars were assembled in a three-component reaction. Alongside L-proline (1) they employed the L-hydroxyproline-based catalyst 17 (Scheme 5.10). This catalyst proved to be beneficial in terms of reaction rate due to superior solubility properties. Remarkably, the addition of water had a positive effect on the stereoselectivity in case catalyst 17 was employed. 

---