With Vicinal Diols

Acetone has been used as the organic solvent but can cause problems due to the formation of acetonides with vicinal diols in slightly acid conditions (lU,15). After the aqueous methanol extraction, the homogenate is filtered and the methanol removed from the filtrate under reduced pressure at 1+0° or below. At this stage it is common to buffer the aqueous residue, usually with potassium phosphate. With some tissues, for example liquid endosperm, it is convenient to extract directly with a buffer solution at about pH 8 resulting in a cleaner extract (16). 

Borate buffers The useful pH range for borate buffers is 8.5-10.0. Boric acid is poisonous in high concentration, and it complexes with vicinal diols like ribose. 

The affinities observed for complexes between amides and anions are remarkably parallel to those found for the interactions between such anions and carbohydrate models. The data in Tab. 2.1 show the same affinity increase in the sequence r
strong acceptor as the result of two geometrically matching hydrogen bonds with vicinal diols. The formation of two almost linear and parallel hydrogen bonds is also responsible for the efficiency of the guanidinium residue for carboxylate complexation in artificial receptors [101] as well as in proteins (cf. Chapter 6) [102]. 

Remark All substances with vicinal diol groups (sugars, sugar alcohols, glycosides etc.) yield a yellow-green fluorescence with this reagent. In order to determine which zones are produced by sugars the plate can be sprayed later with... 

Substituted phenacyl bromides (61) were condensed with vicinal diols (62), and the resulting bromoketals (63) were then coupled with sodium 1,2,4-triazole in dimethyl formamide solution. 

Several useful one-pot procedures employing the reaction of tosyl chloride with vicinal diols have been used to form epoxides. Treatment of variously substituted diols with 1 equiv of tosyl chloride and sodium hydroxide in monoglyme provides access to a variety of 1-alkynyloxiranes (R and/or being terminal or substituted alkynes) in moderate to good yield (eq 15). ... 

Almost all of the Mo and W enzymes show paramagnetic pentavalent forms that can be studied by methods such as EPR spectroscopy, and EPR in particular has been extensively used to study the enzymes. Beeause the pentavalent form is typieally only a fraction of the total metal present, few parallel studies using XAS have been reported. Rhodobacter DMSO reduetase, however, is one notable exeeption. In this case there are two different forms that show essentially 100% of Mo as the Mo(v) form. The first is an inhibited species, which forms with vicinal diols such as glycerol, and is a stable Mo(v) entity that is resistant to both oxidation and reduction. This species was studied in the first XAS report on DMSO reductase, and was fou nd to be a six-coordinate complex with four equivalent sulfurs and two Mo-0 bonds, probably from the vicinal diol coordinated to Mo(v). The stability of this spe-eies means that it has little catalytic relevance, but the second quantitatively Mo(v) DMSO reductase species is formed by reduction with the alternative substrate trimethylamine Af-oxide (TMAO). This substrate forms the most... 

Lead tetraacetate-2,7-dichlorofluorescein (A) lead tetraacetate (saturated solution) in glacial acetic acid (B) 2,7-dichlorofluorescein in water (1%, m/v, or lower, down to 0.2%, if background interferes with detection) A and B are mixed 1 1 (v/v), then toluene (19 1, v/v) is added Plate is dipped in reagent for 10s, then heated at 100°C for 3 min All carbohydrates with vicinal diol groups, oxidized by lead tetraacetate, are detected fluorimetric scanning (excitation 313nm, emission 366 nm) 50-100pmol... 

Attempts to elicit equatorial vs equatorial selectivity were only partially successful (with vicinal diols) when an NPOE was used as glycosyl donor, whereas armed donors were less discriminating [93, 95],... 

Boronic acids form reversible complexes with vicinal diols in aqueous media as shown below. This strategy has been incorporated into receptors for saccharides. It typically takes a few minutes for these equilibria to be achieved in solution. Given this simple observation, do you expect the study of these binding events to be on the slow or fast exchange time scale on a 300 MHz H N MR spectrometer Do you exjject to see different resonances for the boronic acid and the boronate ester, or an average of the signals Explain your answer. 

The Pd(PhCN)2Cl2-promoted reaction of 1,3-cyclohexane-dione with one molecule of alcohol gave 3-alkoxycyclohex-2-enone, which may further react with a second molecule of alcohol affording 1,3-dialkoxybenzene (eq 173). Underthesamecondi-tions, 1,2-cyclohexanedione reacted with vicinal diols to provide 2,3-dialkyl-2,3-dihydrobenzo[b][l,4]dioxine (eq 174). ... 

Routine formol-calcium fixed, paraplast-embedded, five micron thick, tissue sections were generally used throughout our studies, but cryostat- or paraplast-embedded sections fixed in any manner that does not interfere with vicinal diols may be used equally well. Sections must be floated onto clean, grease-free slides. This should avoid the loss of sections during staining. Chrome alum gelatin (see below) may be used if sections become detached. 

Several alternative routes have been suggested, which in some cases are especially useful to prepare alkyl derivatives of EDOT with substitution at the dioxane ring. The most important of these alternative pathways appears to be the acid catalyzed transetherification of 3,4-dimethoxythiophen (or other lower alkoxythiophenes) with vicinal diols. - ° The Williamson ether synthesis can lead to low yields particularly in the case of long chain 1,2-dibromoalkanes due to the competing elimination reactions instead of nucleophilic substitution, resulting in a-olefins or a-acetylenes. Although... 

An alternative strategy for the synthesis of piperazines vras reported by Madsen and co-workers and uses the [Cp IrCl2]2 catalytic sj tem to effect an iridium catalysed cyclocondensation of vicinal diamines with vicinal diols (Scheme 12.51). Interestingly, the cyclocondensation can be catalysed by either acid or base however, sodium bicarbonate was utilised for convenience. 

Scheme 12.51 Coupling of vicinal diamines with vicinal diols provides piperazines.

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