Amino acids methyl group oxidation

Oxidation of the hydroxyl group, after protection of the amine group by ben2oylation, gives amino acids (7), eg, oxidation of 2-amino-2-methyl-l-propanol to 2-methylalanine [62-57-7] (CH )2CNH2COOH. 

The salts of some enamines crystallize as hydrates. In such cases it is possible that they are derived from either the tautomeric carbinolamine or the amino ketone forms. Amino ketone salts (93) ( = 5, 11) can serve as examples. The proton resonance spectra of 93 show that these salts exist in the open-chain forms in trifluoroacetic acid solution, rather than in the ring-closed forms (94, n = 5, 11). The spectrum of the 6-methylamino-l-phenylhexanone cation shows a multiplet at about 2.15 ppm for phenyl, a triplet for the N-methyl centered at 7.0 ppm and overlapped by signals for the methylene protons at about 8.2 ppm. The spectrum of 93 ( = 11) was similar. These assignments were confirmed by determination of the spectrum in deuterium oxide. Here the N-methyl group of 93 showed a sharp singlet at about 7.4 ppm since the splitting in —NDjMe was much reduced from that of the undeuterated compound. 

Transformation of the amino nitriles to the corresponding amino acids, with removal of the dioxane ring, is carried out in two steps. Treatment with concentrated hydrochloric acid results in the hydrolysis of both the nitrile and the acetal group, and in cyclization to the corresponding 3-substituted 5-hydroxyniethyl-3-methyl-2-oxo-6-phenylmorpholinc hydrochlorides. Oxidative cleavage with 2 N sodium hydroxide solution, air and Raney nickel at 120 CC (ca. 30 h) delivers the hydrochlorides of the free a-methylamino acids in high yield. 

The decarboxylation of the caesium salt of 9-methylanthracene-10-acetic acid occurs at an even lower potential (0.7 V) and affords the dimer as well as the methyl ether (Eq. 40) [342], The low oxidation potentials for the decarboxylation of 54 (0.13 to 0.77 V) [306a] and 55 (—0.17 V) [306b] indicate too, that the initial electron transfer occurs from the amino or aryl group rather than from the carboxylate. 

Penicillamine reacts with pyridoxal-5-phosphate to form a thiazolidine derivative, and is able to displace many amino acids from their Schiff base complexes, forming stable compounds of this type. The reactivity of the thiol group of penicillamine is less than that of cysteine, probably because of steric hindrance by the adjacent methyl groups of penicillamine, which in consequence is less rapidly oxidized in vivo [7]. 

A method involving SPE was developed for the determination of ten A-nitroso amino acids in cured meat products. These compounds were derivatized with diazomethane followed by O-acylation of hydroxyl groups with acetic anhydride-pyridine reagent. The methyl esters and their acylated derivatives were separated by GC on a DB-5 fused silica capillary column and quantified with a TEA-CLD specific for the nitric oxide derived from the thermal denitrosation of nitrosamines recovery exceeded 75% at the 10 ppb level579. 

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