Oxidation of proline

A -Pyrroline has been prepared in low yield by oxidation of proline with sodium hypochlorite (71), persulfate (102), and periodate (103). A -Pyrroline and A -piperideine are products of enzymic oxidation via deamination of putrescine and cadaverine or ornithine and lysine, respectively (104,105). This process plays an important part in metabolism and in the biosynthesis of various heterocyclic compounds, especially of alkaloids. 

Murahashi and co-workers (49) extensively studied the synthesis of nitrones such as 29 by a decarboxylative oxidation of proline derivatives (Scheme 12.12). However, these nitrones were primarily used in nucleophilic addition reactions rather than 1,3-dipolar cycloadditions. Others have synthesized cyclic nitrones 30 and 31 having a chiral center adjacent to the nitrogen atom (50,51). Saito and co-workers (51) applied nitrone 31 in reactions with fumaric and maleic acid... 

Another hydroxylated product of OH modification of proline is 5-hydroxy-2-aminovaleric acid, arising from oxidation of proline and arginine residues (A20) (Fig. 4). 

Oxidation of proline and arginine residues leads also to formation of glutamate semialdehyde and, upon its further oxidation, to pyroglutamic acid (A9). Oxidized proline produces also 2-pyrrolidone (K6) (Fig. 5). 

Fig. 4. Oxidation of arginine. 5-Hydroxy-2-aminovaleric acid, which is the arginine oxidation end product, may also be produced during oxidation of proline.

Scheme 11 Oxidation of proline causes ring opening with the resultant formation of glutamic semialdehyde...

The oxidation of proline by intact plant tissues has been well established (Barnard and Oaks, 1970 Durzan and Ramaiah, 1971 Stewart, 1972). After infiltration of [ C]proiine, the formation of [ C]glutamic, organic acids, and CO2 was observed. The pathway for these transformations goes by the following sequence ... 

Another enzymatic oxidation of proline has recently been described by Boggess et al. (1978). They found isolated mitochondria from several higher plants (barley, com, wheat, soy, and mung bean) could oxidize proline to glutamate, organic acids, and CO2. Pyrroline-5-carboxylate was apparently the primary product of this reaction. The reaction required O2 and could not be carried out anaerobically with a pyridine nucleotide acceptor. The for L-proline with the mitochondrial system was 5 mAf. Boggess et al. (1978) were not able to solubilize this system. Treatment with Triton X-100 yielded inactive preparations. 

Only 20 of the 22 a-amino acids in Table 24.1 are actually used by cells when they synthesize proteins. Two amino acids are synthesized after the polyamide chain is intact. Hydroxyproline (present mainly in collagen) is synthesized by oxidation of proline, and cystine (present in most proteins) is synthesized from cysteine. 

The surface of quartz catalyzes the air Oxidation of //-proline to hydroxyproline, Indicating that some type of activated, oriented, and speciric adsorption may be involved (274). It is therefore noteworthy that the hydroxyproline excreted in the urine of miners with silicosis was 31% higher than in normal individuals. The total hydroxyproline in blood and urine served as an ind ( of fibrosis activity (275). 

An active intermediate in the oxidation of proline by particles from rabbit kidney appears to be glutamic-y-semialdehyde (III). The iso-HC=0... 

There is a. ccTtain amount of evi(l(Mic( that tlu semialdehydo of glutamic acid is the intermediate formy the loss of the 5-araino group of ornithine. This evidence is the isolation of what was presumed to be the 2,4-dinitrophenylhydrazone of the semialdehyde upon partial oxidation of proline by the cyclophorase system. The glutamic acid semialdehyde can be expected to condense readily to pyrroline carboxylic acid, and reduction of this compound would yield proline (Fig. 2). 

In the oxidation of proline, glutamic acid is formed and in the oxidation of hydroxyproline, y-hydroxyglutamic acid is formed. Other intermediates are glutamic-y-semialdehyde and y-hydroxyglutamic-y-semi-aldehyde. These findings suggest the pattern of catabolism shown in Fig. 13. 

Effects of cationic (cetylpyridinium chloride, CPC) and anionic (SDS) micelles on the rate of reaction of chromium(VI) oxidation of formaldehyde have been studied in the presence and absence of picolinic acid. Cationic micelles (CPC) inhibit whereas anionic micelles (SDS) catalyze the reaction rates that could be attributed to electrostatic interactions between reactants (cationic metal ions and catalyst H+) and ionic head groups of ionic micelles. Experimentally determined kinetic data on these metaUomicellar-mediated reactions have been explained by different kinetic models such as pseudophase ion-exchange (PIE) model, Monger s enzyme-kinetic-type model, and Piszkiewicz s cooperativity model (Chapter 3). The rate of oxidation of proline by vanadium(V) with water acting as nucleophile is catalyzed by aqueous micelles. Effects of anionic micelles (SDS) on the rate of A-bromobenzamide-catalyzed oxidation of ethanol, propanol, and n-butanol in acidic medium reveal the presence of premicellar catalysis that has been rationalized in light of the positive cooperativity model. ... 

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