Glycine, irradiation

Radiation-induced changes have been studied in a few water-soluble oligopeptides and substituted amino acids. Dale et al. (10) found a higher yield of ammonia from Gly-Gly than from glycine irradiated under similar conditions (x-rays, 0.13M solution, in vacuum) and also a large pH effect, the yield in HC1 being less than one-third of that in neutral solution. The... 

In a less straightforward way, D-glucose (393) underwent a Maillard-type reaction with an excess of glycine (394) under microwave irradiation to afford 5-hydroxy-l,3-dimethyl-2(l/f)-quinoxahnone (395) as a major product, Repetition with labeled reactants suggested that the product contained six carbon atoms from the sugar and four from the amino acid on this evidence, a detailed mechanism has been postulated. 

A family of interesting polycychc systems 106 related to pyrrolidines was obtained in a one-pot double intermolecular 1,3-dipolar cycloaddition, irradiating derivatives of o-allyl-sahcylaldehydes with microwaves in toluene for 10 min in presence of the TEA salt of glycine esters [71]. A very similar approach was previously proposed by Bashiardes and co-workers to obtain a one-pot multicomponent synthesis of benzopyrano-pyrrolidines 107 and pyrrole products 108 (Scheme 37). The latter cycloadducts were obtained when o-propargylic benzaldehydes were utihzed instead of o-allyhc benzalde-hydes, followed by in situ oxidation [72]. 

More recent work shows that the amino acid yield (in particular of glycine) in a CO-N2-H2O atmosphere subject to irradiation with high energy particles is much higher than if spark discharges are used (Kobayaski et al., 1998). These authors thus assume that cosmic radiation could have been an important source of energy for prebiotic syntheses on Earth. 

The process was also applicable to microwave-assisted reactions. Thus, 140a, 140b, and 140 (R1 = z-Pr, R4 = indol-3-ylmethyl) were prepared in a two-step, one-pot synthesis in yields of 55%, 39%, 20%, and with 70%, 73%, 50% ee, respectively. In the first step anthranilic acid was reacted with the appropriate A-BOC-protected amino acid (glycine, L-alanine, and L-valine, respectively) in the presence of P(OPh)3 and dry pyridine under irradiation at 150 °C for 140a or conventional heating at 55 °C for 140b and 140 (R1 = z-Pr, R4 = indol-3-ylmethyl). In the second step the resulting... 

Another example where PEG played the role of polymeric support, solvent, and PTC was presented by the group of Lamaty [72]. In this study, a Schiff base-proteded glycine was reacted with various electrophiles (RX) under microwave irradiation. No additional solvent was necessary to perform these reactions and the best results were obtained using cesium carbonate as an inorganic base (Scheme 7.64). After alkylation, the corresponding aminoesters were released from the polymer support by transesterification employing methanol in the presence of triethylamine. 

Bose et al. [77] compared a similar reaction of the acid chloride of tetrachlor-ophthaloyl glycine 57 with a Schiff base under MW irradiation and conventional... 

Morpholinone 177, derived from allyl glycine, cyclized stereoselectively under UV irradiation (A > 342 nm) in the presence of 9,10-anthracene dicarbonitrile (ADC) and biphenyl (PB) to give compound 176 as a single diastereo-isomer <2001JOC6896> (Scheme 26). 

The oxazinones 74 and 79, already described as chiral glycine templates in Section 11.11.6.3, have been prepared by the PET cyclisation of 252 by irradiation in the presence of 1,4-dicyanonaphthalene as the electron acceptor and methyl viologen as electron-transfer mediator. When the reaction was carried out under strictly anhydrous conditions, compound 79 was isolated, whereas when the reaction was carried out in wet MeCN, compound 74 was the exclusive product (Scheme 33). In any case, the products were obtained with high stereoselectivity, which is the condition required to use them as chiral auxiliaries <2000EJ0657>. 

Figure 23. Morphology of rat aortic smooth muscle cells 48 h after seeding on high-density (A, C, E) and low-density (B, D, F) polyethylene. A, B pristine polymers, C, D plasma-irradiated polymers, E, F polymers irradiated with plasma and subsequently grafted with glycine. Cell membrane stained with Texas Red C2-maleimide, the nuclei counterstained withHoechst 33342. Olympus IX 50 microscope, digital camera DP 70. Bar=200 pm.

Thus, glycine, as part of a peptide chain, was stereocontrol-alkylated by irradiation in the presence of toluene. The new asymmetric center was induced by (S)-alanine moieties in the peptide chain. 

On warming, further reactions occur. The S ion causes bond scission and the formation of —CH..S radicals. Other radicals (such as glycine residue, —CO—CH—NH—) also change, with a transfer to the sul-fydryl group. This would appear to represent one form of radiation protection. Similar results can be expected in irradiated organic polymers containing sulfur. 

Glycine, methionine, glycylglycine, and glycylmethionine solutions were selected for study primarily on the basis of electron spin resonance studies of irradiated proteins (16, 22,23,43), peptides (6), and amino acids (25) which show ... 

These four compounds were also selected because they were commercially available in pure form and reasonably soluble in unbuffered solutions at room temperature. In addition, the radiation chemistry of glycine, glycylglycine, and methionine has been studied at room temperature (4, 5, 6, 12, 36, 49, 50, 51). Also, sulfur-containing amino acids have been suggested by chemical-irradiation flavor correlation studies (4, 21, 38, 44f 49, 50, 53) as being related to irradiation flavor. 

Preparation and Irradiation of Solutions. Glycine, methionine, glycylglycine, and glycylmethionine were obtained from Nutritional Biochemicals Corp., Cleveland, Ohio, and used without further purification. All samples dissolved completely in deionized distilled water to give colorless solutions, except glycylmethionine which had a pale yellow color. Each solution was within 0.2 pH unit of its isoelectric pH (5.5 to 6.0). 

Methionine and glycylmethionine interfered in the ammonia determination, and although color developed, no ammonia yields are reported for these compounds. A fine precipitate also appeared on nesslerizing some of the irradiated glycylglycine solutions, which prevented their analysis. The ammonia yields for glycine solutions were so low they were at the... 

The perhydroxy radical formed on the y-carbon atom (Reactions 30 and 31) is a likely precursor of aspartic acid, which we have found in yields of G = 1.1 when PGA was irradiated in 0.1% solution in 02. Further oxidation and a decarboxylation step would be required to give aspartic acid. However, it is not yet known whether the aspartic acid is formed solely as a result of irradiation it may be formed from a labile precursor during acid hydrolysis of the polymer. Our results differ from those reported by Friedberg and Hayden, who found high yields of aspartic acid in PGA irradiated in the absence of 02 we found only traces of aspartic acid from solutions of PGA irradiated under N2 (Figure 3). Glycine formation was not affected by the presence of 02. 

Only three new amino acids were found (by automatic amino acid analysis) in poly-D,L-alanine after irradiation in 0.1% solution in the absence of O2 with doses to 5 Mrads. All were in yields less than G = 0.02. The first was eluted before aspartic acid and was therefore acidic the second was eluted in the position of aspartic acid, and the third in the position of glycine. We have not been able to confirm the identities of these products by TLC because of the low yields. The products found by amino acid analysis could not account for the discrepancy between amide-like ammonia formed (G = 0.66) and alanine destroyed (G = 1.9). Aspartic acid is formed when alanine is irradiated in solution 26), and it is likely that the carboxylation reaction proposed by these authors also accounts for the observed aspartic acid formation in PDLA. 

The presence of O2 during irradiation of PDLA (0.1% solution, 1 atm. O2), increased the amino acid destruction G = —1.9 in N2 and 2.1 in O2) and the formation of amide-like ammonia (G = 0.66 in N2, 2.0 in O2). The acidic amino acid formed in N2 was not found in samples irradiated in O2, but the amount of aspartic acid was increased. It is possible that O2 converted the precursor of the unknown acidic amino acid into aspartic acid. The small amount of glycine apparently was not affected. 

We have found that the yields of certain products from PGA irradiated in 1% aqueous solution under vacuum are reduced by altering the pH below 4. Thus the yield of D-glutamic acid decreased from G = 0.45 at pH above 5 to less than one-third of this value at pH 3.9 glycine (G = 0.1 at pH 7) could not be detected in samples irradiated at pH 3.9. 

It was at this stage that Whiffen and co-workers succeeded in unravelling the very involved spectrum obtained from X-irradiated single crystals of glycine in terms of the planar radical... 

Treatment with the nickel(II) complex of the tripeptide glycine-glycine-histidine in the presence of magnesium monoperoxyphthalate Visible light irradiation in the presence of tris(bipyridyl)ruthenium(II) dication and ammonium persulfate Ethylmercury phosphate Fluorescein... 

The glycine-derivative radical generated by this process was found to react with a benzyl radical, which was generated from toluene under similar reaction conditions. Thus, irradiation of a solution of N-acetylglycine ethyl ester and toluene in acetone led to the formation of DL-N-acetylphenylalanine ethyl ester (70),... 

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