Hydroxycarboxylic acids from hydrolysis

GC/MS has also been used to investigate acidic and neutral fractions (after alkaline hydrolysis, separation and trimethylsilylation) of a resinous sample collected from a flint flake dated back to the lower Palaeolithic (roughly 200 000 BC) and recovered near Arezzo in Italy [11]. The results show that the organic material recovered on the flint flake was a pitch obtained from birch bark by a pyrolysis type process. In fact, the main components of the acidic fraction are a series of linear a,oo-dicarboxylic acids ranging from 16 to 22 carbon atoms and a series of oo-hydroxycarboxylic acids ranging from 16 to 22 carbon... 

The presence of oe-hydroxycarboxylic acids together with a-aminoacids could lead to an estimate of the local concentration of ammonia when these molecules were synthesised. Such an estimation method implies the assumption that the syntheses of the two classes of molecules were simultaneous and started from the same organic substrate, i.e. aldehydes25 . From aldehydes, aminoacids can be obtained by the Strecker synthesis (aldehyde, HCN, NH3 in aqueous solution), while hydroxyacids can be synthesised from the cyanhydrin synthesis (aldehyde + HCN) followed by a hydrolysis. Nevertheless, it must be emphasised that all aminoacids detected in carbonaceous chondrites cannot be obtained by the Strecker synthesis. This remark limits the interest of the previous arguments concerning the concentration of NH3 during the accretion phase. 

The bienzymatic approach described above could also be advantageously applied to the synthesis of (R)-2-hydroxycarboxylic acids in cases where no satisfactorily enantioselective nitrilase is available (Figure 16.5). The best enantioselectivity in the hydrolysis of lb, for example, was 92% ee. The enantioselectivity of the hydroxynitrile lyase from ahnonds (PaHnL) in the synthesis of lb is also less then perfect [13], but we found that a combiCLEA of PaHnL and NIT-106 quantitatively converted 2b (O.IM starting concentration) into 3b with ee>99% R (reaction in 90 10 DlPE-buffer pH 5.5, as before) with very little (>3%) amide formation. 

Dioxinones Obtained by Resolution or Prepared with a Chiral Auxiliary. 2-Phenyl-4//-1,3-dioxin-4-ones (15) derived from formylacetate or acetoacetate can be readily prepared in enantiopure form by preparative resolution " on cellulose triacetate. These have been used for Michael additions and hydrolysis to long-chain p-hydroxycarboxylic acids, for example the tride-canoic acid (16) from (/ )-(15a). The cuprate adducts formed with the methylphenyldioxinone (i f-flSb) can be hydrogenolyti-cally cleaved directly to p-branched p-hydroxy acids with benzyl protection of the hydroxy functional group see (17) in eq 9. ... 

Aromatic hydroxycarboxylic acids, especially salicylic acid, have a wide range of applications, for example, as valuable raw materials and intermediates in the production of pharmaceutical chemicals. Originally, salicylic acid was synthesized by the Kolbe-Schmitt reaction [57], which consists of two steps (1) the synthesis and purification of alkali metal phenoxides and (2) carboxylation (Scheme 4.4). Another possible synthetic method is via the attack of a trichloromethyl cation (generated by a copper catalyst from carbon tetrachloride) on the phenoxide anion, followed by hydrolysis of the C—Cl bonds with concentrated sodium hydroxide, because it is fairly difficult to replace an aromatic hydrogen with carboxyl functionality [58]. 

Monascus ruber and at Merck Sharpe Dohme from Aspergillus terreus. Both mold metabolites are extremely effective in lowering plasma concentrations of LDL. The active form of each is the 5-hydroxycarboxylic acid formed by hydrolysis of the 5-lactone. 

Lactones occur as natural odorants in aU major food commodities, including meat and meat products, milk, dairy products, cereals, fruits, vegetables and various beverages, such as tea, wine and spirits. Odour-active compounds in foods are y-and 5-lactones derived from aliphatic saturated and unsaturated y-hydroxycarboxyHc and 5-hydroxycarboxylic acids derived from fatty acids or sugars, but some lactones also arise from other precursors (e.g. mint lactone is a terpenoid compound and pantolactone is produced by hydrolysis of pantothenic acid via pantoic acid). Some lactones derived from aromatic hydroxycarboxyhc acids are also common compounds. The most important representatives of these compounds are phthahdes that are 3fL-isobenzofuran-l-ones (8-98) and coumarins (8-99) that are 2fL-l-benzopyran-2-ones (5-lactones of 2-hydroxycinnamic acids). 

The principle of enolate controlled stereochemistry can be demonstrated by use of the chiral acetate 83. When doubly deprotonated (R)- and (S)-HYTRA 83 reacts with enantiomerically pure 3-benzyloxybutanal 99 the (R)-configured acetate enolate attacks the aldehyde 99 (irrespective of its chirality) predominantly from the Re face so that, after hydrolysis, anti hydroxycarboxylic acid 100a results. On the other hand, the (S)-configured enolate of 83 attacks the enantiomerically pure aldehyde preferentially from the Si side to give syn carboxylic acids 100b with comparable selectivity, as shown in Scheme 1.22 [175]. 

Hydrolysis of chiral cyanohydrins offere an interesting general route to (/ )- and (5)-2-hydroxycarboxylic acids. In concentmted hydrochloric acid (JR)- and (5)-cyanohydrins derived from aldehydes and ketones are easily hydrolyzed to give the corresponding (R)-... 

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