Oxygen hydroxyacylation

ACID-BASE RELATIONSHIPS OXYGEN, OXIDES 0X0 ANIONS d-2-HYDROXY-ACID DEHYDROGENASE (S)-2-HYDROXY-ACID OXIDASE 3-HYDROXYACYL-CoA DEHYDROGENASE /3-HYDROXYACYL THIOESTER (or, ACP) DE-HYDRASE... 

Cobalt complexes derived from Schiff bases 388 catalyzed the hydroxyacylation of electron-deficient alkenes (Fig. 90) [431, 432]. Thus, methyl acrylate 387 reacted with aliphatic aldehydes 386 in the presence of 5 mol% of the in situ generated catalyst, molecular oxygen, and acetic anhydride to 2-acyloxy-4-oxoesters 389 in 56-77% yield. When acetic anhydride was omitted, the yields of products were lower and mixtures of the free hydroxy compounds and acylated compounds resulting from Tishchenko reactions were obtained. Electron-rich alkenes did not undergo the transformation, since the addition of the acyl radical is much slower. The acylcobalt species inserts oxygen instead and acts as an epoxidation catalyst. 

Bertolasi and coworkers have related the OH chemical shifts of o-hydroxyacyl aromatics to the oxygen-oxygen distance. A plot of 50H vs. the oxygen-oxygen distance (Ro-o) in A shows a reasonable linear relationship (equation 1). 

Whereas mitochondrial oxidation utilizes NAD" and flavoproteins coupled to the oxidative phosphorylation system, the glyoxysomal system differs in two m jor respects (Fig. 5). First, the flavoprotein reduced in the acyl-CoA dehydrogenase step is oxidized directly by molecular oxygen with the formation of HjOj, which is then degraded by catalase second, NADHj produced in the oxidation of 2-hydroxyacyl-CoA is not reoxidized in the glyoxy-somes thus an external NAD -NADH redox system is required. 

The insertion of a single double bond by an oxygen-independent process has recently been shown to be even more intimately associated with fatty acid synthesis, when a 3-cw-dehydratase, acting at the hydroxyacyl-ACP level, was characterized as an inherent activity of an unusual synthetase complex from Brevibacterium ammoniagenes (Kawaguchi and Okuda, 1977). In this case, oleoyl-CoA has been defined as the product, since unsaturation is retained at the C-9 position. 

Figure 2. Schematic diagram of the second reaction of the fatty acid P-oxidation pathway catalyzed by co/i enoyl-CoA hydratase. Compounds 1 and 2 are 2-mmr-enoyl-CoA and L-3-hydroxyacyl-CoA, respectively. The protonated Glu transfers a proton to the a carbon of the substrate on the re face, whereas the deprotonated Glu" attracts a proton from water whose oxygen makes a nudeopbilic attack on the P-carbon of the substrate. The amino group of Gly" in the peptide backbone acts as a l rogen donor to form a hydrogen bond with the carbonyl oxygen so that an electronic rearrangement occurs in the acryloyl portion of the sul trate. The transition state is shown in the square brackets The product, L-3-hydroxyacyl-CoA, can then leave the active site. Two general acid-base functional groups, the ycarboxyl groups of Glu and Glu , play a major part in the hydratase catalysis...

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