Amino acids photochemical reactions

Topics of relevance to the content of this chapter which have been reviewed during the year include photoactive [2]rotaxanes and [2]catenanes, photochemical synthesis of macrocycles, phototransformations of phthalimido amino acids, photoaddition reactions of amines with aryl alkenes and arenes, photoreactions between arenenitriles and benzylic donors, photostability of drugs, polycyclic heterocycles from aryl- and heteroaryl-2-propenoic acids, photoreactions of pyrroles, photoamination reactions in heterocyclic synthesis, switching of chirality by light, photochromic diarylethenes for molecular photoionics and solid state bimolecular photoreactions. 

Bensasson, R., Goldschmidt, C. R., Land, E. J., Truscott, T. G., Triplet Excited State of Furocoumarins Reaction with Nucleic Acid Bases and Amino Acids, Photochem. Photobiol. 1978, 28, 277 281. 

Bensasson, R.V., Land, E.J., and Salet, C. (1978) Triplet excited state of furocoumarins reaction with nucleic acid bases and amino acids, Photochem. Photobiol., 27, 273-280. 

A similar reaction sequence starting from tryptophan yields 1-methyl-3,4-dihydro-)3-carbohne-3-carboxylic acid (465). This compound has been shown to undergo photochemical oxidation to l-methyl-)3-carbohne-3-carboxyhc acid (466). Such a sequence of events may account for the biogenetic origin of the amino acid 466. 

Reaction selectivity of the parent ortho-QM has also been explored with a variety of amino acid and related species.30 In these examples, the rates of alkylation and adduct yields were quantified over a range of temperatures and pH values. The initial QM3 was generated by exposing a quaternary benzyl amine (QMP3) to heat or ultraviolet radiation (Scheme 9.10). Reversible generation of QM3 was implied by subsequent exchange of nucleophiles at the benzylic position under alternative photochemical or thermal activation.30 Report of this work also included the first suggestion that the reversible nature of QM alkylation could be used for controlled delivery of a potent electrophile. 

A direct formation of 5-22 [e. g., of 2-amino-4-cyclopentene-l,3-diol (5-22, Nu = OH)], is observed if the photochemical reaction of 5-19 is performed under acidic conditions using HC104. After acetylation, the formed diacetate can be isolated in about 25 % yield. 

A group at the Bach Institute in Moscow was able to isolate a flavine pigment (an isoalloxacine derivative) from the polymer obtained by heating a mixture of three amino acids (glutamic acid glycine lysine = 8 3 1) this exhibited photochemical acivity (e.g., redox reactions such as electron transfer to acceptors with lower Eo values) under both aerobic and anaerobic conditions (Kolesnikov and Kritsky, 1999). 

It is still unclear what kind of radiation sources can lead to asymmetric reactions. Jeremy Bailey from the Anglo-Australian Observatory in Epping, Australia, investigated which astronomical objects could be considered radiation sources (Bailey et al., 1998 Bailey, 2001). It was possible in laboratory experiments to generate a small enantiomeric excess of some amino acids by using circularly polarized UV light (Norden, 1977). This asymmetric photolysis involves photochemical decomposition of both d- and L- enantiomers, but at different rates, so the more stable form tends to survive. This process must be subject to autocatalytic multiplication. 

The literature presents a large number of examples concerning the use of known oxazolidinones as chiral auxiliaries in many kinds of reactions. Rare is the use of A-amino derivatives of oxazolidinones, which were used to synthesise new A-acylhydrazones 207. Radical addition reactions occurred with high diastereoselectivity <00JA8329>. The use of glycolate oxazolidinones 210 proved to be efficient for the enantioselective preparation of a-alkoxy carboxylic acid derivatives . Photochemical reaction of vinyl... 

A. Shafferman and G. Stein, The effect of aromatic amino acids on the photochemistry of a disulfide Energy transfer and reaction with hydrated electrons, Photochem. Photobiol. 20, 399-406 (1974). 

The mechanism of the photochemical alkylation shows particular characteristics as regards the formation of alkyl radicals, the reaction of these radicals with the heteroaromatic substrates, and the rearomatization of the intermediate products. A variety of alkylating agents (hydrocarbons, alcohols, amines, carboxylic acids, amino acids) have been used for photochemical and y-ray-induced alkylation. " ... 

Further methods [205] successfully employed to synthesize fuUeropyrroUdines include acid-catalyzed [213] or thermal [214] desilylation of trimethylsilyl amino derivatives, tautomerization of a-aminoesters of immonium salts [215] and imines [216, 217], reaction with aldehydes in the presence of aqueous ammonia [218], reaction with oxazolidinone [204] or photochemical reaction with some amino derivatives [219-223], The reaction with amino acids and aldehydes was also carried... 

Asymmetric synthesis, either enantioselective or diastereoselective, has seldom been performed by photochemical reactions. One of the first examples that may be classified as a photochemical asymmetric synthesis is the photoalkylation of the most simple amino acid, glycine. Elad and Sperling 220) demonstrated that, if glycine is part of a polypeptide chain, there is good control (up to 40 % e.e.) in the creation of the new chiral center. A radical mechanism operates after the first step of photoinitiation of the process. 

The protoberberine alkaloid, xylopinine, has been synthesized in an optically active form by Kametani et al.22 ). A key reaction in this synthesis was the photochemical cyclization of the optically active amino acid derivative 1,2,3,4-tetrahydro-6,7-dimethoxy-3-methoxycarbonyl-1 -methylene-2-veratroylisoquinoline with 1,3... 

To understand the fundamental photochemical processes in biologically relevant molecular systems, prototype molecules like phenol or indole - the chromophores of the amino acids tyrosine respective trypthophan - embedded in clusters of ammonia or water molecules are an important object of research. Numerous studies have been performed concerning the dynamics of photoinduced processes in phenol-ammonia or phenol-water clusters (see e. g. [1,2]). As a main result a hydrogen transfer reaction has been clearly indicated in phenol(NH3)n clusters [2], whereas for phenol(H20)n complexes no signature for such a reaction has been found. According to a general theoretical model [3] a similar behavior is expected for the indole molecule surrounded by ammonia or water clusters. As the primary step an internal conversion from the initially excited nn state to a dark 7ta state is predicted which may be followed by the H-transfer process on the 7ia potential energy surface. 

Ekpenyong Kl, Shetlar MD (1979) Photochemical reactions of cytosine N-methyl analogs in alcoholic solutions. Photochem Photobiol 30 455-461 Elad D (1976) Photoproducts of purines. In Wang SY (ed) Photochemistry and photobiology of nucleic acids. Academic Press, New York, pp 357-380 Elad D, Rosenthal I (1969) Photochemical alkylation of caffeine with amino-acids. Chem Commun 905-906... 

Fig. 18.4. Mechanism for the photochemical reaction of a benzophenone-coated ITO-modified optical fiber with a C-H bond of an amino acid side chain of the hepatitis C virus. The virus can act as an antigen for the detection of the anti-HCV antibody. After the immunoreaction, the subsequent binding of a marker, a secondary peroxidase-labeled antibody, allowed to catalyze a chemiluminescence reaction for the receipt of an optical signal.

Gan et al. used amino acids such as piperidino acetic acid or morpholino acetic acid in photochemical reactions with C60 [231,232]. Whereas the reaction of the ester derivatives of the amino acids result in the formation of pyrrolidine-fused C6o derivatives, the reaction of the free amino acids give the 1-substituted l,2-dihydro[60]fullerenes 57a-b (Scheme 22). In a typical experiment a methanol solution of the amino acid 56a-b was added to a toluene solution of C6o and irradiated with a 250 W overhead projector lightbulb. Prolonged irradiation led to multiadducts. To avoid hydroxylation of C60 the pH of the amino acid solution should be no more than 9.0. 

Amino acid derivatives react with C6o both thermally and photochemically to yield different products. Gan et al. intensively studied the photochemical reactions of C6o and amino acid derivatives such as sarcosine esters, glycine esters, and iminodiacetic esters [268], The thermal reaction of the sarcosine ethyl ester 98 led to the formation of a 4 1 mixture of two products, the major being compound 99 and the minor being compound 100 containing two ester functionalities (Scheme 43). 

Availability is not the only constraint on substrate consumption. The value of a substrate is also related to the resources needed to convert the molecule into an intermediary metabolite. Thus in aerobic environments, monosaccharides and amino acids are readily consumed under anaerobic conditions, heterotrophic metabolism is largely fueled by small organic acids. Some taxa consume other types of substrates as long as they are reasonably abundant. Important examples include P-proteobacteria that consume phenols, a significant component of DOM inputs originating from plant material, and methylotrophs that consume single carbon compounds produced by anaerobic metabolism, photochemical reactions, and oxidation of methyl and methoxy substituents (Giovannoni and Rappe, 2000). 

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