Dihydroxyacetone selectivity

Figure 6. Selectivity for dihydroxyacetone vs. conversion of glycerol, on PtBi/C, for batch and continuous systems.

Dihydroxyacetone is not stable under the basic conditions preferred for oxidation of the primary function to give hydroxypyruvic acid (reaction e). Under acidic conditions the rate of oxidation of a 1 mol I l aqueous solution is veiy slow (5 mol h l mol i(Pt)). On platinum the initial rate of conversion for reduced concentrations of the starting material (0.3 mol whilst retaining the same amount of catalyst, was 42 mol h mol-i(Pt), as might be expected under non-favourable acidic conditions. Hydroxypyruvic acid is evolved with a selectivity of 82% at 40% conversion (see Figure 11). 

The Pt/C catalyst, compared with Pd/C, showed not only enhanced activity (vide supra) but also reduced selectivity for glyceric acid (only 55% at 90% conversion), favoring dihydroxyacetone formation up to 12%, compared with 8% for the Pd case [48]. The Pt/C catalyst promoted with Bi showed superior yields of dihydroxyacetone (up to 33%), at lower pHs. Glyceric and hydroxypyruvic acids, apparently, are formed as by-product and secondary product, respectively [48], The addition of Bi seems to switch the susceptibility of glycerol oxidation from the primary towards the secondary carbon atoms. 

Bi/Pt atomic ratios (changing from 0.1 to 0.4), as well as the precise preparation procedure of the BiPt/C catalysts, yielded differences in selectivity between glyceric acid, dihydroxyacetone and hydroxypyruvic acid that were not always easy to rationalize [72, 73]. The catalyst preparation procedures using acid-treated carbon (with enhanced number of surface carboxyl groups) are essentially as follows ... 

With the BiPt/C catalyst with a Pt/Bi surface atom ratio of 3, in acidic medium (2 < pH < 4) glycerol could be oxidized with a selectivity of 80% into dihydroxyacetone. It is proposed that the Bi adatoms function as blockers of the Pt(lll) surface, controlling the glycerol surface orientation. 

Ketone donors bearing a-heteroatoms are particularly useful donors for the enamine-catalyzed aldol reactions (Scheme 18). Both anti and syn aldol products can be accessed in remarkably high enantioselectivities using either proline or proline-derived amide, sulfonamide, or peptide catalysts. The syn selective variant of this reaction was discovered by Barbas [179]. Very recently, Luo and Cheng have also described a syn selective variant with dihydroxyacetone donors [201], and the Barbas group has developed improved threonine-derived catalysts 71 (Scheme 18) for syn selective reactions with both protected and unprotected dihydroxyacetone [202]. 

Figure 3. Selectivity of the FDP-aldolase reactions using DHAP vs. dihydroxyacetone/arsenate as a substrate. In the former case, the more stable sugar is obtained due to the reversible nature of the reaction. In the later case, both sugars were obtained in nearly equal amounts, because the reaction was found to be virtually irreversible and the formation of the arsenate ester was rate limiting.

Scheme 8. Selective chemical phosphorylation of dimeric dihydroxyacetone...

Bismethylenedioxy derivatives of hydroxycorticosteroids are produced by the reaction of the dihydroxyacetone function with formaldehyde (Scheme 5.35). Cortisone (10 mg) is suspended in 5.0 ml of chloroform and 1.3 ml of 12 TV hydrochloric acid and 1.3 ml of a 37% solution of formaldehyde are added. The reaction mixture is stirred at 5°C for 48 h and during this time the steroid dissolves. After washing with 1 N sodium hydroxide solution and drying over sodium sulphate, the mixture is filtered through glass-wool and analysed directly. The derivatives are stable and provide symmetric peaks on SE-30, and make it possible to analyse selectively complex mixtures of steroids with a dihydroxyacetone moiety in the molecule [382]. 

Valiolamine (89), an aminocyclitol produced by Streptomyces hygroscopicus var. limoneus, is a potent inhibitor of pig intestinal maltase and sucrase, with IC50 values of 2.2 and 0.049 pM, respectively [107]. Numerous iV-substituted valiolamine derivatives were synthesized to enhance its a-glucosidase inhibitory activity in vitro and the very simple derivative voglibose (90), which is obtained by reductive amination of valiolamine with dihydroxyacetone, was selected as the potential oral antidiabetic agent [108]. Its IC50 values toward maltase and sucrase were 0.015 and 0.0046 pM, respectively. Voglibose (the brand name Basen) has been commercially available for the treatment of type 2 diabetes in Japan since 1994. 

Androsta-l,4-diene-3,17-dione reacted selectively at C-17 with potassium acetylide to give the 17a-ethynyl-17/8-alcohol the dihydroxyacetone side-chain was then elaborated by use of known transformations, without interference from the l,4-dien-3-one system/ Ethynylation of a [16- H]- or [16- H2]-17-oxo-steroid proceeds without loss of label/ ... 

In spite of the abundant literature dealing with carbohydrate transformations, there is relatively little on lower polyols [6]. In the case of glycerol particular attention has been paid to the influence of cocatalysts, like Bi, on the selectivity of Pd and Pt catalysts, which changes the hydroxyl group oxidation from primary to secondary producit dihydroxyacetone with 70 -80% selectivity [7]. 

The principle of potential-dependent selectivity control of a galactose oxidase membrane (Johnson et al., 1982, 1985) using galactose, raffi-nose, and dihydroxyacetone as substrates has been discussed in Section 2.2.2. The change of the redox potential influences all reactions in the same direction. However, since the activity is different towards different substrates the degree of conversion of a particular substrate can be affected by the applied potential. At first the better substrates, e.g. raffinose or galactose, can be measured and at optimal potential all substrates are detected. 

A large number of products can be obtained from glycerol oxidation processes (Scheme 3.7). If the secondary hydroxy group of glycerol is oxidized selectively, dihydroxyacetone (DHA) is formed. DHA has been used for years as an active... 

Figure 17-29. Synthesis of [3, 4 -13C2]-thymidine from [2, 3 -13C2]-dihydroxyacetone phosphate with triosephosphate isomerase (TPI) and D-2-deoxyribose-5-phosphate (DHAP). Asterisks indicate the positions selectively labeled with 13C. Other positions that can be isotopically substituted are marked with , A, and V. Reprinted from Ouwerkerk et al.12511.

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