Sodium dithionite, reductions with

Later, a completely different and more convenient synthesis of riboflavin and analogues was developed (34). It consists of the nitrosative cyclization of 6-(A/-D-ribityl-3,4-xyhdino)uracil (18), obtained from the condensation of A/-D-ribityl-3,4-xyhdine (11) and 6-chlorouracil (19), with excess sodium nitrite in acetic acid, or the cyclization of (18) with potassium nitrate in acetic in the presence of sulfuric acid, to give riboflavin-5-oxide (20) in high yield. Reduction with sodium dithionite gives (1). In another synthesis, 5-nitro-6-(A/-D-ribityl-3,4-xyhdino) uracil (21), prepared in situ from the condensation of 6-chloro-5-nitrouracil (22) with A/-D-ribityl-3,4-xyhdine (11), was hydrogenated over palladium on charcoal in acetic acid. The filtrate included 5-amino-6-(A/-D-ribityl-3,4-xyhdino)uracil (23) and was maintained at room temperature to precipitate (1) by autoxidation (35). These two pathways are suitable for the preparation of riboflavin analogues possessing several substituents (Fig. 4). 

This group is stable to TEA/Pyr and to 80% acetic acid. It is cleaved by reduction with sodium dithionite at pH 7.3. ... 

Fig. 3. Cation-exchange chromatography of protein standards. Column poly(aspartic acid) Vydac (10 pm), 20 x 0.46 cm. Sample 25 pi containing 12.5 pg of ovalbumin and 25 pg each of the other proteins in the weak buffer. Flow rate 1 ml/min. Weak buffer 0.05 mol/1 potassium phosphate, pH 6.0. Strong buffer same +0.6 mol/1 sodium chloride Elution 80-min linear gradient, 0-100% strong buffer. Peaks a = ovalbumin, b = bacitracin, c = myoglobin, d = chymotrypsinogen A, e = cytochrom C (reduced), / = ribonuclease A, g = cytochrome C (oxidised), h = lysozyme. The cytochrome C peaks were identified by oxidation with potassium ferricyanide and reduction with sodium dithionite [47]...

Figure 19.22 Phenolic compounds may be derivatized to contain reactive diazonium groups by nitration with tetranitromethane followed by reduction with sodium dithionite and diazotization with sodium nitrite in dilute HCI.

Reduction with sodium dithionite has been used for conversion of aryl arsonic and aryl stibonic acids to arsenobenzenes [260] and stibinobenzenes in good yields [261]. 

C10H14Oj) C,H. An alternate route leading from 2,3-xylenol to this diether via nitrogen-containing intermediates was explored. The sequence involved the reaction of 2,3-xylenol with nitrous acid (4-nitroso product, mp 184 °C dec.), reduction with sodium dithionite (4-amino product, mp about 175 °C), oxidation with nitric acid (benzoquinone, mp 5 8 °C), reduction with sodium dithionite (hydro-quinone) and final methylation with methyl iodide. The yields were inferior with this process. 

PAMAM dendrimers of generations one to five were decorated on the periphery with naphthalenediimide units (Fig. 6.47) carrying cationic substituents assuring solubility in water. Subsequent reduction with sodium dithionite or forma-mide in aqueous medium [90] led to anion radical sites at the diimide units. These aggregate in solution to form -stacks in the solid state they form electrically conductive films [91]. 

Derivatives of 1,4-dihydronicotinamide (2) and l,4-dihydropyridine-3,5-dicarboxylic acid (8) are obtained from the corresponding pyridines by alkylation followed by reduction with sodium dithionite, as illustrated for (76) in equation (33). The absolutely regioselective reduction by dithionite of pyridinium salts to 1,4-dihydropyridines is true synthetic good fortune most other reducing agents reduce pyridinium salts nonregioselectively and often with reduction beyond the dihydro stage. 

The cation could be isolated by precipitation as the picrate or the reineckate. By reduction with sodium dithionite it could be converted directly into brown-black dibenzene chromium, Cr(C6He)2, w hich can be sublimed 53,54) ... 

Our preferred method of sialic acid profiling is to use the DMB / HPLC system. The first step is release of the sialic acids from the glycoprotein by mild acid hydrolysis (typical conditions are incubation with 2 mol dm acetic acid for 2 h at 80 °C) followed by fluorescent labeling using DMB and stabilization of the tagged conjugates by reduction with sodium dithionite. Analysis of the DMB labeled sialic acids is done by HPLC with a C18 column and fluorescence detection (.7ex = 295nm,.7em= 352 nm). 

Subjecting the total matrix to chemical treatment may be an effective method for detection of fingerprint derivatives, without actual isolation of the analytes. Thus, for example, colored yams can be tested for the presence of forbidden azo dyes by subjecting them to partial reduction with sodium dithionite, followed by FTIR of the reduced yam and detecting the characteristic peaks of restricted PAA. This method was applied to forensic testing of textiles which were dyed with forbidden azo dyes (Section n.B.5)196. 

NH4OH gave 9. Oxidation of 9 with cupric acetate afforded 5-deoxy-L-arabinosone 10, followed by reaction with acetone oxime and 5% NH4OH to produce the a-keto aldoxime 11. Reaction of 11 with EtOCOCH(NH2)CN in ethanol afforded 12, which was treated with sodium methoxide and guanidine hydrochloride to afford 13. Reduction with sodium dithionite in aqueous solution buffered to pH 7 gave L-eryt/iro-biopterin (2). 

Of the many other methods we can mention the preparation of biospecific adsorbents utilizing trichloro-5-triazine [120], coupling via thiol-disulfide interchange with activated thiolated support [121] or via azide formation [122]. The attachment of affinants containing the aromatic residues can be carried out by means of diazonium groups [87,123]. The coupling of the affinant onto the silinized glass after the reactions with p-nitrobenzoylchloride followed by reduction with sodium dithionite was described by Weetall and Filbert [124]. 

Hydroxy anthranilic Acid (5-OH-AA). This was synthesized from m-hydroxybenzoic acid by coupling with diazotized rosaniline and subsequent reduction with sodium dithionite. The recrystallized product had a melting point of 242°C. (dec.). 

The iron in xanthine oxidase is related to the ferredoxins and there are eight iron atoms per molecule [30]. The oxidised xanthine oxidase appears to contain all eight atoms in the low-spin (S = 0) Fe(II) state as the small unique quadrupole split spectrum is not affected by magnetic fields. Reduction with sodium dithionite (Na2S204) results in severe magnetic broadening... 

Figure 4.21 Tyrosine reactive probes. Nitration of tyrosine by reaction with tetranitromethane, followed by reduction with sodium dithionite, to yield an o-aminotyrosine.

Lounasmaa et al. ° have continued their investigations into the synthesis of indoloquinolizidine derivatives, with particular reference to vallesiachotamine models. The most advanced work in this area to date involves synthesis (Scheme 9) of the closely related vallesiachotamine derivative (75). The critical stage in this synthesis was the reduction of the pyridinium salt (76) by means of sodium dithionite, which, in buffered (NaHC03) solution, allowed the isolation of the dihydropyridine derivative (77). Cyclization of (77) in the presence of acid gave, preferentially, the desired 3H,15H-trans-isomer (75), as had previously been established " in model systems. Alternatively, alkylation of the unsaturated ester (78) with tryptophyl bromide gave the pyridinium salt (79), which, on reduction with sodium dithionite in aqueous methanol, gave a mixture of (75) and the uncyclized tetrahydropyridine derivative (80). >yhen the sodium dithionite reduction medium was buffered (with NaHCOa), and the dihydropyridines so obtained were cyclized in acid, the products were the tetracyclic geometrical isomers of structure (81) (Scheme 9). 

R. Fornasier, F. Marcuzzi, M. Parmagnani, U. Tonellato, Stereoselective reduction with sodium dithionite of conjugated enones in the presence of j8-cyclodextrin and its heptakis(2,6-di-0-methyl) derivative as host compounds or phase transfer agents, J. Inclusion Phenom. Mol. Recognit Chem., 1994, 18, 81-92. 

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