Simple amino acids

Typical values for pAlg are in the range of 9.0 to 9.8. At physiological pH, the a-carboxyl group of a simple amino acid (with no ionizable side chains) is completely dissociated, whereas the a-amino group has not really begun its dissociation. The titration curve for such an amino acid is shown in Figure 4.7. 

Thomson MOW Click Organic Interactive to learn to estimate isoelectric points for simple amino acids and peptides. 

In the case of simple amino acids and dipeptides, esterification of the carboxyl groups occurs on heating in toluene with the appropriate bis(triorganotin) oxide or triorganotin hydroxide 481, 482), the water being removed azeotropically. 

Substitued Benz[f]isoindoles of Simple Amino Acids... 

A number of less elaborate but, nevertheless, quite interesting systems have also been reported where just simple amino acids play a relevant role. Among them is an intriguing report by Komiyama s group [54] in which they describe RNA hydrolysis achieved as a result of the cooperation between carboxylate and ammonium ions. They prepared conjugates of glycine (or iminodiacetate) with an-... 

Phosphazene polymers can act as biomaterials in several different ways [401, 402,407]. What is important in the consideration of skeletal properties is that the -P=N- backbone can be considered as an extremely stable substrate when fluorinated alcohols [399,457] or phenoxy [172] substituents are used in the substitution process of the chlorine atoms of (NPCl2)n> but it becomes highly hydrolytically unstable when simple amino acid [464] or imidazole [405-407] derivatives are attached to the phosphorus. In this case, an extraordinary demolition reaction of the polymer chain takes place under mild hydrolytic conditions transforming skeletal nitrogen and phosphorus into ammonium salts and phosphates, respectively [405-407,464]. This opens wide perspectives in biomedical sciences for the utilization of these materials, for instance, as drug delivery systems [213,401,405,406,464] and bioerodible substrates [403,404]. 

In cytochrome-c [PtCU]2- binds to methionine 65 on the outside of the protein (64). Again the chloride is probably displaced as the reagent is applied in phosphate buffer. Dickerson and co-workers consider that the platinum is oxidized to a Pt(IV) complex but this seems unlikely as it does not occur in the reaction of [PtClJ2- with simple amino-acids. 

Abelson (1956) carried out experiments using atmospheres containing CCb, (CO), N2, (NH3), H2 and H2O and detected small amounts of simple amino acids, the formation of which was prevented by adding oxygen. Many of the Miller-Urey experiments involved various energy sources and were carried out in the liquid and solid states as well as on gas mixtures. 

The preceding discussion is based on an individual acidic or basic group, but molecules can posses more than one such group, e.g., simple amino acids (Fig. 2.7). It... 

Natural products derived from amino acids form a broad and divergent group, including simple amino acid derivatives, alkaloids, and small, often cyclic, polypeptides. Simple amino acid derivatives, which are not uncommon in algae, are often oxidation or rearrangement products of one of the 20 common amino acids. Alkaloids and polypeptides are more complex in their structural modifications. 

A semi-synthetic metalloenzyme that catalyses the enantioselective hydrolysis of simple amino acid esters has been reported. Iodoacetamido-l,10-phenanthroline (238) was interacted with a cysteine residue in adipocyte lipid binding protein (ALBP) to produce the conjugate ALBP-Phen (239), which was converted into its Cu(II) complex. The ALBP-Phen-Cu(II) was found to catalyse the enantioselective... 

Peptides and proteins are composed of a-amino acids linked by amide bonds (see Section 13.1). Their properties, for example the ability of enzymes to catalyse biochemical reactions, are dependent upon the degree of ionization of various acidic and basic side-chains at the relevant pH. This aspect will be discussed in more detail in Section 13.4, but, here, let us consider a simple amino acid dissolved in water at pH 7.0. An a-amino acid has an acidic carboxylic acid group and a basic amine group. Both of these entities need to be treated separately. 

The pH at which the concentration of the zwitterion is a maximum is equal to the isoelectric point pi, strictly that pH at which the concentrations of cationic and anionic forms of the amino acid are equal. With a simple amino acid, this is the mean of the two pAT values ... 

Hine has demonstrated that simple amino acids, such as glycine and p-alanine, are not capable of intramolecular deprotonation in the reaction with isobutyraldehyde-2-d (Scheme 8) [62], Apparently, the carboxylate moiety in the iminium ion intermediate 29 is a relatively weak base and, as such, external bases, present in the buffer used (e.g. acetate ions), are largely responsible for the formation of the enamine intermediate 30. 

Type A enamine catalysts include simple amino acids, such as proline 6, and most of their derivatives (such as the tetrazole 44 and various sulfonamides, e.g. 45). They are typically used for aldol, Mannich, a-amination and a-oxygenation reactions - these are all reactions where the electrophile can readily be activated by hydrogen bonding (Scheme 12) [8, 9, 12, 46],... 

The third method of separating optically active substances by combining them with optically active bases or acids had not been employed with any success until E. Fischer took up this question, the study of the optically active amino acids being his first work upon the chemical constitution of the proteins. The non-success of this method was in all probability due to the small affinity which the simple amino acids themselves have for combining with acids and bases even the attempts to separate the monoaminodicarboxylic acids, which are fairly strong acids, were not successful. 

B. Although titration curves for proteins are complex because of their multiple acidic and basic groups, their behavior can be illustrated by titration of a simple amino acid such as alanine (Figure 2-1). 

Although the most generally useful heterocycles for the alkylation of simple amino acids by this method are the imidazolidinones84, oxazolidinones have the advantage of being much more readily hydrolyzed. (S)-a-Methylmethionine was prepared by this latter method from the parent amino acid 85,86. The oxazolidinone 1885 [mp 126.4-127.2 °C [a]D +61.8 (e = 1, CHC13)] prepared in 24-30% yield from (S)-methionine, was methylated using LDA and iodomethane in satisfactory yield. 

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 spectrum of structural mutations that can convert a proto-oncogene into an oncogene is very diverse. Both simple amino acids changes in the coded protein and larger structural changes are observed. In particular, viral oncoproteins demonstrate multiple mutations compared to their cellular coimterparts, linked to important and far-reaching structural and fimctional changes. 

Simple amino acid degradation products aldehydes, sulphur compounds (e.g. hydrogen sulphide, methanethiol), nitrogen compounds (e.g. ammonia, amines)... 

Deamination appears to proceed equally rapidly both in the presence and absence of oxygen. Stein and Weiss (S18) examined this phenomenon and deduced that deamination can be accompanied by both oxidation and reduction. In the absence of oxygen the H atom, rather than the HO radical is the effective agent. This mechanism is satisfactory for the simple amino acids (glycine, alanine, and serine) studied by these workers. With the more complex amino acids yields of ammonia become less and side chains may be preferentially broken. 

Covalent linkage of amino acid, peptide or protein moieties onto the hydrolyzed and/or oxidized polymers (Control and Oxidized starches) was examined for its ability to improve the potential for microregion lipophilicity within the carbohydrate polymer. Proteinaceous materials are often strongly surface active (39) and may, if carefully selected, contribute positively to wall material characteristics. This selection process was carried-out using maltodextrins (DE 10 and/or 25) as the carbohydrate framework and various amino acid-derived materials as the function-altering accessory, ranging from gelatin and casein proteins to simple amino acids. 

---