Acid-base reactions amino acids

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. 

Folic acid plays the central role in one-carbon metabolism and is directly or indirectly involved in the biosynthesis of nucleic acid bases and amino acids. In plants and microbes, the various folate derivatives involved in one-carbon metabolism originate from dihydropterin derivatives, via the enzymes 7,8-dihydropteroate and dihydrofolate synthase (Figure 5.18). 7,8-Dihydrofolate then undergoes reduction to 5,6,7,8-tetra-hydrofolate (THF), which can become substituted with formyl, methylene, or methyl groups for utilization in one-carbon donor reactions. ... 

Mutation. For industrial appHcations, mutations are induced by x-rays, uv irradiation or chemicals (iiitrosoguanidine, EMS, MMS, etc). Mutant selections based on amino acid or nucleotide base analogue resistance or treatment with Nystatin or 2-deoxyglucose to select auxotrophs or temperature-sensitive mutations are easily carried out. Examples of useful mutants are strains of Candida membranefaciens, which produce L-threonine Hansenu/a anomala, which produces tryptophan or strains of Candida lipolytica that produce citric acid. An auxotrophic mutant of S. cerevisiae that requires leucine for growth has been produced for use in wine fermentations (see also Wine). This yeast produces only minimal quantities of isoamyl alcohol, a fusel oil fraction derived from leucine by the Ehrlich reaction (10,11). A mutant strain of bakers yeast with cold-sensitive metaboHsm shows increased stabiUty and has been marketed in Japan for use in doughs stored in the refrigerator (12). 

Hydrolyses of aminopyridopyrimidines to the corresponding pyridopyrimidones by means of acid, base, and nitrous acid have been reported. 4-Amino compounds are stable to nitrous acid, but are much more labile than the 2-amino derivatives toward acid- or base-catalyzed hydrolysis. The aminochloro-pyrido[2,3-d]pyrimidine (160) has been converted into the 2,4-dianilino analog (161) by reaction with aniline." ... 

It is interesting to note that in the reaction of (188) with [TcOCU] , the 0x0 group is replaced by a doubly deprotonated amino group. The mixed imido-amido Tc complex [Tc(app)Cl2(Happ)j (263) was synthesized and structurally characterized with Re. Neutral, mixed amino-phosphino ligands can stabilize the soft [Tc=N] + core in the expected way, whereas the harder [Tc=0] + core imposes subsequent acid/base reactions. Stabilization is then mainly achieved by deprotonation, in order to compensate for the relatively high charge. ... 

In the absence of substrates, the aldehyde group of pyridoxal phosphate is covalently bound to a lysine residue of the transaminase (1). This type of compound is known as an aldimine or Schiffs base. During the reaction, amino acid 1 (A, la) displaces the lysine residue, and a new aldimine is formed (2). The double bond is then shifted by isomerization. 

This procedure was improved 123 for the synthesis of building units based on amino acids other than Gly, but with nonfunctionalized side chains (Table 6). To suppress the 3-elim-ination and racemization side reactions, triflates of a-hydroxycarboxylic acid esters 124 34 (L = OTf, Scheme 19) were used as substrates for the nucleophilic substitution. In order to prevent polyalkylation, the nucleophilic amine of to-BocNH- or co-tBu02C-alkylamines 33 were temporarily protected with the benzyl group. 115116 This protection also improved the yields and purity of Gly-based building units. In this case commercially available benzyl bromoacetate 34 (L=Br) was used as the substrate. In both cases the nucleophilic sub-... 

Not surprisingly, chiral formamides emerged as prime candidates for the development of an asymmetric variant of this reaction. A selection of the most efficient amide catalysts based on amino acids is shown in Figure 7.4 representative examples of enantioselective hydrosilylation are collected in Tables 7.7 and 7.8. Proline-derived anilide 82a and its naphthyl analogue 82b, introduced by Matsu-mura [3c], produced moderate enantioselectivity in the reduction of aromatic ketimines with trichlorosilane at 10 mol% catalyst loading (Table 7.7, entries 1 and 2). Formamide functionality proved to be crucial for the activation of the silane, as the corresponding acetamides failed to initiate the reaction. 

Simulation Results. A onc-dimensional simulation model based on the Nernst-Planck and Poisson equations [14, in which all the acid-base reactions occurring in the membrane are taken into account, has been used to give a qualitative description of the pH step titration process. In these simulations, a pH step is applied outside a 2 mm thick stagnant layer, which is assumed to be present in front of an 8 mm thick membrane. Diffusion coefficients in the membrane are assumed to be 4/10 of those in water (this value is based on experience with ion step experiments). Lysozyme, used as a model protein, is assumed to contain 11 carboxylic groups (pKa = 4.4), 2 imidazole groups (pKa = 6.0), and 9 amino groups (pKa = 10.4) per molecule. Concern... 

Imines are particularly common as intermediates in many biological pathways, where they arc often called Schiff bases. The amino acid alanine, for instance, is metabolized in the body by reaction with the aldehyde pyridoxal phosphate (PLP), a derivative of vitamin Bg, to yield a Schiff base that is further degraded. 

All enzyme-catalyzed reactions that involve proton transfer use acid or base catalysis, so most enzyme active sites contain acidic or basic amino acid side chains that participate in catalysis. Because enzyme-catalyzed reactions take place close to pH 7, only fairly weak acids and bases are available, as shown in Fig. 7. 

The potential use of Cp2TiCl2 in the treatment of neoplasia has been reported.2022 The reaction of Cp2TiCl2 with phosphorus- and sulfur-based [3-amino acid analogs under atmospheric conditions has also been described.2023 The reactions of Cp2TiCl2 with organometallic acetylferrocene thiosemicarbazones to give bimetallic products have been reported. Physicochemical and spectral studies have been carried out in order to establish a correlation between the biological activity and the structures of the compounds.1525... 

Alkaloids are basically nitrogen bases. The amino acids act as building blocks for the biosynthesis of alkaloids. Majorities of the alkaloids contain a pyridine, quinoline, and isoquinoline or tropane nucleus and are responsible for physiological effects in man or in animal. The side chains in alkaloids are derived from terpene or acetate. Alkaloids have basic properties and are alkaline in reaction, turning red litmus paper blue. 

The Oppolzer sultam 35-1 (Scheme 35, reaction (101) [84] reacts with even higher stereoselectivies and is easier to remove. The main domains of the Oppolzer sultam are conjugate 1,4-additions or simple double bond additions [Scheme 35, reactions (102) and (103)] [85], which show diastereoselectivities of >95% in most cases. Scheme 36 presents examples of persistent, restorable and selfimmolative auxiliaries which are all based on amino acids or amino alcohols, finders RAMP-SAMP [86] is attached to ketones or aldehydes in form of a hydrazone 36-1 which is used for highly stereoselective electrophilic a-alkyla-tions. After the reaction the auxihary is removed via ozonolysis which generates the nitrosamine 36-2 first. In an ensuing step this is reduced to the original auxiliary. In Schollkopf s bislactim ether alkylations [Scheme 36, reaction (105)]... 

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