P-Hydroxypropionate

P-Hydroxy acids lose water, especially in the presence of an acid catalyst, to give a,P-unsaturated acids, and frequendy P,y-unsaturated acids. P-Hydroxy acids do not form lactones readily because of the difficulty of four-membered ring formation. The simplest P-lactone, P-propiolactone, can be made from ketene and formaldehyde in the presence of methyl borate but not from P-hydroxypropionic acid. P-Propiolactone [57-57-8] is a usehil intermediate for organic synthesis but caution should be exercised when handling this lactone because it is a known carcinogen. 

There are two pathways for the degradation of nitriles (a) direct formation of carboxylic acids by the activity of a nitrilase, for example, in Bacillus sp. strain OxB-1 and P. syringae B728a (b) hydration to amides followed by hydrolysis, for example, in P. chlororaphis (Oinuma et al. 2003). The monomer acrylonitrile occurs in wastewater from the production of polyacrylonitrile (PAN), and is hydrolyzed by bacteria to acrylate by the combined activity of a nitrilase (hydratase) and an amidase. Acrylate is then degraded by hydration to either lactate or P-hydroxypropionate. The nitrilase or amidase is also capable of hydrolyzing the nitrile group in a number of other nitriles (Robertson et al. 2004) including PAN (Tauber et al. 2000). 

Nevertheless, malonyl-CoA is a major metabolite. It is an intermediate in fatty acid synthesis (see Fig. 17-12) and is formed in the peroxisomal P oxidation of odd chain-length dicarboxylic acids.703 Excess malonyl-CoA is decarboxylated in peroxisomes, and lack of the decarboxylase enzyme in mammals causes the lethal malonic aciduria.703 Some propionyl-CoA may also be metabolized by this pathway. The modified P oxidation sequence indicated on the left side of Fig. 17-3 is used in green plants and in many microorganisms. 3-Hydroxypropionyl-CoA is hydrolyzed to free P-hydroxypropionate, which is then oxidized to malonic semialdehyde and converted to acetyl-CoA by reactions that have not been completely described. Another possible pathway of propionate metabolism is the direct conversion to pyruvate via a oxidation into lactate, a mechanism that may be employed by some bacteria. Another route to lactate is through addition of water to acrylyl-CoA, the product of step a of Fig. 17-3. Tire water molecule adds in the "wrong way," the OH ion going to the a carbon instead of the P (Eq. 17-8). An enzyme with an active site similar to that of histidine ammonia-lyase (Eq. 14-48) could... 

Urinary organic acid analysis is useful for differentiating isolated carboxylase deficiencies from the biotin-responsive multiple carboxylase deficiencies. P-Hydroxyisovalerate is the most common urinary metabolite observed in isolated P-methylcrotonyl-CoA carboxylase deficiency, biotinidase deficiency, biotin holo-carboxylase synthetase deficiency, and acquired biotin deficiency. In addition to P-hydroxy-isovalerate, elevated concentrations of urinary lactate, methylcitrate, and P-hydroxypropionate are indicative of multiple carboxylase deficiency. 

Titanium homoenolates of alkyl propionates.18 Treatment of 1-alkoxy-l-trimeth-ylsiiyloxycyclopropanes (l)19 with TiCl4 results in moderately air-sensitive, thermally stable, purple solids formulated as 2, but probably dimeric. They are oxidized by air to alkyl p-hydroxypropionates in good yield. 

Ansede JH, PellechiaPJ, Yoch DC. (1999). Metabolism of acrylate to p-hydroxypropionate and its role in dimethylsulfoniopropionate lyase induction by a salt marsh sediment bacterium, Alcaligenes faecalis M3A. Appl Environ Microbiol, 65, 5075-5081. 

A remarkable acceleration effect on the ring-opening of various epoxides with HCo(CO)4 was achieved by the addition of small amounts of Lewis bases such as alcohols (ethanol, butanol) [8]. In this maimer, the hydroformylation of propylene oxide was accelerated by a factor of 100. An improvement of conversion was also observed in the presence of acetone, diethyl ether, or THE (tetrahydrofu-ran). Low reaction temperatures stimulated hkewise the selective formation of hydroxy aldehydes. With styrene, mainly isomeric diols were obtained because of the high reducing power of the cobalt catalyst. Epichlorohydrin yielded mainly ethyl y-chloro-P-hydroxypropionate. The relative reactivity of the olefin oxides toward these hydroformylation conditions was found to be in the following order (Figure 6.15). 

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