Reduction with borohydrides

Fenticonazole (106), on the other hand, is used topically to combat a wide variety of dermatophytes and yeasts, particularly Candida albicans. It can be synthesized from 2,4-dichlo-rophenacyl chloride (104) by reduction with borohydride and subsequent displacement with imidazole to give 105. This last undergoes ether formation with p-thiolphenylbenzyl chloride mediated by NaH to produce fcnticonazole (106) [37]. 

Deoxy-l-fluoro-L-glycerol (18) has been prepared by, among other methods, the treatment of 3,4-0-benzylidene-2,5-0-methylene-l,6-di-O-p-tolylsulfonyl-D-mannitol107 (17) with tetrabutylammonium fluoride in acetonitrile, followed by removal of the benzylidene group, periodate oxidation, reduction with borohydride, and hydrolysis. 1,6-Dideoxy-l,6-difluorogalactitol108 was obtained by treatment of 2,3 4,5-di-0-isopropylidene-l,6-di-0-(methylsulfonyl)galactitol with tetra-... 

D-Glucose 6-phosphate is converted enzymically into L-wyo-inositol 1-phosphate (20) in a process which requires NAD+. The base-catalysed cyclization of d-xylo-hexos-5-ulose 6-phosphate (21), followed by reduction with borohydride, leads to (20) and epi-inositol 3-phosphate (22) (Scheme 3).59 This has been put forward as a chemical model for the enzymic synthesis. The phosphorylation of inositols with polyphosphoric acid has been described80 and the p-KVs of inositol hexaphosphate have been determined by 31P n.m.r.61... 

A further synthetic approach to carbon-metal double bonds is based on the acid-catalyzed abstraction of alkoxy groups from a-alkoxyalkyl complexes [436 -439] (Figure 3.11). These carbene complex precursors can be prepared from alk-oxycarbene complexes (Fischer-type carbene complexes) either by reduction with borohydrides or alanates [23,55,63,104,439-445] or by addition of organolithium compounds (nucleophilic addition to the carbene carbon atom) [391,446-452]. 

Chaplin used methanolysis for the analysis of carbohydrates in glycoproteins. His method was a variation of the foregoing procedures, with an improvement of using tert-hvAyX alcohol to remove hydrogen chloride by coevaporation, instead of prolonged trituration with silver carbonate. His method is useful for samples containing uronic acids and lipids. Mononen studied methanolysis, followed by deamination and reduction with borohydride, for determination of the monosaccharide constituents of glycoconjugates. This method was applied to a lipid-free, protein fraction of rat brain. 

In the reductions with borohydrides and boranes the isolation of products differs from that used in the reductions with lithium aluminum hydride, the... 

Reduction of the azepinone ring in 63 can be accomplished selectively. Thus, hydrogenation results in selective 1,4-reduction of the enone moiety and furnishes the corresponding saturated ketone 65. Selective enone 1,2-reduction can be performed with n-BuLi-BHs to produce allylic alcohol 64. Reduction with borohydride is non-selective and gives saturated hydroxyl compound 66 (Scheme 13, Section 2.1.1.5 (2000T9351)). 

The multiplicity of peaks obtained on trimethylsilylation of 3-de-oxy-D-en/fforo-hexosulose has already been mentioned (see p. 24) however, the isomeric 3-deoxyhexitols formed on reduction with borohydride were readily separated as their trimethylsilyl ethers.234 El-Dash and Hodge234 gave a large amount of tabular and graphical data on relative retention-times and showed that, when these values... 

Peroxynitrite reacts with the active site of superoxide dismutase (SOD) to form a nitronium-like species (Fig. 37), analogous to the Fe EDTA reactions described earlier. However, copper in the active site of superoxide dismutase was necessary for the formation of the adduct. Removing copper from the active site by reduction with borohydride and dialysis against 50 mM KCN resulted in no adduct being formed, while restoration of copper to the active site gave back full enzyme activity. To account for the essential role of copper in the active site and the subsequent formation of 3-nitrotyrosine located 18-21 A distal from the active site, we proposed that peroxynitrite is attracted by the same electrostatic force field that draws superoxide into the active site (Beckman et al., 1992 Ischiropoulos et al., 1992b). Peroxynitrite appears to bind to copper in the active site to form a transient cuprous adduct as shown. 

The Cannizzaro reaction, that is, the base-catalysed disproportionation of a carbonyl compound to an alcohol and a carboxylic acid, has gained some importance as an economically viable alternative to the reduction with borohydrides. However, the reaction is restricted to carbonyl compounds without any a-hydrogen, which do not undergo competing aldol reactions. Thus, mainly aromatic aldehydes are used for this kind of transformation. The protocols developed for microwave applications typically involve solvent-free conditions using alumina as the solid support. Under these conditions, a significant acceleration of the reaction was achieved. 

The a-amination of aldehydes and subsequent reduction to form oxazolidinones (Scheme 7.6) was developed by the Jorgensen group [7]. In the presence of 10 mol% L-proline as catalyst a variety of aldehydes reacted with azodicarboxylates, 3a and 3a, affording the oxazolidinones 7 after subsequent reduction with borohydride and cyclization. Selected examples of the synthesis of products 7, which were obtained in yields up to 92% and with enantioselectivity up to 95% ee, are shown in Scheme 7.6. 

In most cases, uronic acids are liberated from acidic polysaccharides by hydrolysis leading to irreproducible concomitant formation of lactones. Several methods to circumvent this problem have been published describing conversion of the uronic acid into methyl esters followed by reduction with borohydride or borodeuteride reagents and subsequent hydrolysis and GC-MS detection [129]. Other techniques are based on the liberation and quantification of carbon dioxide. Direct determination of uronic acid residues in hydrolyzates has frequently been performed according to colorimetric assays, which are rather insensitive and have thus mostly been replaced by high-performance anion exchange chromatography (HP-AEC) methods [130-132]. 

On the other hand, why does a single diastereoisomer of this organomercury compound give a mixture of dia stereoisomers (68 32) on reduction with borohydride in the presence of acrylonitrile ... 

FiO. 11. Ckwnplex formation between the 2-electron-reduced (EHi) form of E. coli glutathione reductase and NADPH. EH2 was produced by anaerobic reduction with borohydride time was allowed for the slight excess of borohydride to react with water before beginning the titration with NADPH. 1, Oxidized 2, EHi 3, EHa-f-0.45 equivalent NADPH 4, EHi-1-0.90 equivalent NADPH and 5, EH -1-2.75 equivalents NADPH. 

Another potential side reaction of the enediol(ate) intermediate is formation of the dicarbonyl compound, l-deoxy-D-glycero-2,3-pentodiulose 5-phosphate, resulting from p-elimination of the Cl-phosphate due to improper stabilization and/or premature dissociation of enediol(ate) from the enzyme active site. This compound has been characterized by reduction with borohydride, oxidation with H2O2, complexation with o-phenylenediamine, and 13C-NMR (23, 34). The p-elimination product is not detected in reactions with wild-type R. rubrum Rubisco but is formed in substantial amounts with mutants in which the Cl-phosphate ligands are substituted, demonstrating the required role of these amino acid side chains in stabilizing the enediol(ate) intermediate (34-35). 

Figure 2. Product analysis of K329A turnover reactions in the absence of amine (A) or in the presence of 400 mM ethylamine (B). Other reaction constituents at pH 8 were 20 pM K329A protomer, 1 mM EDTA, 10 mM MgCl2, 415 mM bicine, 19.6 mM NaHC03, 10% glycerol, and 250 pM [l- H]RuBP. Reactions were quenched after 4 h by reduction with borohydride.

With some 4-substltuents reduction with borohydride does not proceed past the dihydro adduct even in protic solvents. Certain l-(2-nitrophenylmethyl)isoquinolinium salts, e.g. (73), have been found to undergo substituent cleavage on reduction with borohydride. ... 

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