Adenine, amination

Ammonia reacts with the ketone carbonyl group to give an mine (C=NH) which is then reduced to the amine function of the a ammo acid Both mine formation and reduc tion are enzyme catalyzed The reduced form of nicotinamide adenine diphosphonu cleotide (NADPH) is a coenzyme and acts as a reducing agent The step m which the mine is reduced is the one m which the chirality center is introduced and gives only L glutamic acid... 

Chemical Name 9-/3-D-arabinofuranosyl-9H-purine-6-amine monohydrate Common Name Adenine arablnoside spongoadenosine Structural Formula ... 

The sugar component in RNA is ribose, and the sugar in DNA is 2 -deoxy-ribose. (The prefix 2 -deoxv indicates that oxygen is missing from the 2 position of ribose.) DNA contains four different amine bases, two substituted purines (adenine and guanine) and two substituted pyrimidines (cytosine and thymine). Adenine, guanine, and cytosine also occur in RNA, but thymine is replaced in RNA by a closely related pyrimidine base called uracil. 

Amine bases in nucleic acids can react with alkylating agents in typical Sjsj2 reactions. Look at the following electrostatic potential maps, and tell which is the better nucleophile, guanine or adenine. The reactive positions in each are indicated. 

A 12), 0-(thymin-l-yl)ethyldodecyldimethylamrnonium chloride), 25 (T12), j3-(theophyllin-7-yl)ethyldodecylammonium chloride, 26 (TH12), j3-(adenin-9-yl)-ethyloctadecyldimethylammonium chloride (A 18), and /3-(thymin-l-yl)ethylocta-decyldimethylammonium chloride (T18)47. These model compounds were prepared by the Menschutkin reaction of dodecyldimethyl amine or octadecyldimethylamine with chloroethylated bases. 

Attached by a covalent bond to carbon atom 1 of the deoxyribose ring is an amine (and therefore a base), which may be adenine, A (22) guanine, G (23) cytosine, C (24) or thymine, T (25). In RNA, uracil, U (26), replaces thymine. The base bonds to carbon atom 1 of deoxyribose through the nitrogen of the —NH— group (printed in red) and the compound so formed is called a nucleoside. All nucleosides have a similar structure, which we can summarize as the shape shown in (27) the lens-shaped object represents the attached amine. 

Amines, amino acids, amides [1, 2] e.g. chloramphenicol, creatine, adenine, guanine histidine, phenylalanine, sphingosine... 

As might be expected, the add-catalyzed silylation-amination of the free purine-bases such as hypoxanthine 242 (R=H) and guanine 242 (R=NH2) proceeds, via 243, to the corresponding substituted adenines 244 in high yields [64] (Scheme 4.24). 

Adenine as an isolated molecule has no symmetry elements and therefore might mathematically be considered chiral however, as in the case of glycine (Section 1.2.1), this description is not useful in chemistry since the enantiomers differ only by inversion through the weakly pyramidal nitrogen atom of the amine functionality, the main body of the molecule being planar. The inversion corresponds to a low-frequency vibration and a low-energy barrier such that single enantiomers... 

One of the most important reactions of purines is the bromination of guanine or adenine at the C-8 position. It is this site that is the most common point of modification for bioconjugate techniques using purine bases (Figure 1.53). Either an aqueous solution of bromine or the compound N-bromosuccinimide can be used for this reaction. The brominated derivatives then can be used to couple amine-containing compounds to the pyrimidine ring structure by nucleophilic substitution (Chapter 27, Section 2.1). 

Reaction of 6-halopurines with Michael acceptors under Heck conditions gives N- -substituted hypoxanthine derivatives <00CCC797>. Reactions of a series of 1-aminobenzimidazoles and l-amino-3-methylbenzimidazolium chlorides with 2,4-pentanediones afford pyridazino[l,6-a]benzimidazoles and 2-pyrazolylanilines, the product ratio depending on conditions and on the electronic character of the substituents at the benzene moiety <00BMC37>. Cyclization reactions of adenine derivative 75 with different amines or hydrazine afford tricyclic polyaza compounds 76 <00CCC1109>. 

There are four bases in DNA guanine, thymine, cytosine and adenine. Each has a ketone C=0 group in which the oxygen is quite electronegative and bears an excess negative charge <5 , and an amine in which the electropositive hydrogen atoms bear an excess... 

The transport of amino acids at the BBB differs depending on their chemical class and the dual function of some amino acids as nutrients and neurotransmitters. Essential large neutral amino acids are shuttled into the brain by facilitated transport via the large neutral amino acid transporter (LAT) system [29] and display rapid equilibration between plasma and brain concentrations on a minute time scale. The LAT-system at the BBB shows a much lower Km for its substrates compared to the analogous L-system of peripheral tissues and its mRNA is highly expressed in brain endothelial cells (100-fold abundance compared to other tissues). Cationic amino acids are taken up into the brain by a different facilitative transporter, designated as the y system, which is present on the luminal and abluminal endothelial membrane. In contrast, active Na -dependent transporters for small neutral amino acids (A-system ASC-system) and cationic amino acids (B° system), appear to be confined to the abluminal surface and may be involved in removal of amino acids from brain extracellular fluid [30]. Carrier-mediated BBB transport includes monocarboxylic acids (pyruvate), amines (choline), nucleosides (adenosine), purine bases (adenine), panthotenate, thiamine, and thyroid hormones (T3), with a representative substrate given in parentheses [31]. 

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