Ammo group

Like hydroxyl groups and ammo groups however halogen substituents possess unshared electron pairs that can be donated to a positively charged carbon This electron donation into the TT system stabilizes the intermediates derived from ortho and from para attack... 

FIGURE 17 11 Imine formation between the aldehyde function of 11 as retinal and an ammo group of a protein (opsin) is involved in the chemistry of vision The numbering scheme in retinal is specifically developed for carotenes and related compounds... 

In base the tetrahedral intermediate is formed m a manner analogous to that pro posed for ester saponification Steps 1 and 2 m Figure 20 8 show the formation of the tetrahedral intermediate m the basic hydrolysis of amides In step 3 the basic ammo group of the tetrahedral intermediate abstracts a proton from water and m step 4 the derived ammonium ion dissociates Conversion of the carboxylic acid to its corresponding carboxylate anion m step 5 completes the process and renders the overall reaction irreversible... 

Aniline is the parent lUPAC name for ammo substituted derivatives of benzene Substituted derivatives of aniline are numbered beginning at the carbon that bears the ammo group Substituents are listed m alphabetical order and the direction of number mg IS governed by the usual first point of difference rule... 

Compounds with two ammo groups are named by adding the suffix diamine to the name of the corresponding alkane or arene The final e of the parent hydrocarbon IS retained... 

Amino groups rank rather low in seniority when the parent compound is identified for naming purposes Hydroxyl groups and carbonyl groups outrank ammo groups In these cases the ammo group is named as a substituent... 

Conjugation of the ammo group of an arylamme with a second aromatic ring then a third reduces its basicity even further Diphenylamme is 6300 times less basic than aniline whereas triphenylamme is scarcely a base at all being estimated as 10 ° times less basic than aniline and 10 " times less basic than ammonia... 

In Its overall design this procedure is similar to the Gabriel synthesis a nitrogen nude ophile IS used m a carbon-nitrogen bond forming operation and then converted to an ammo group m a subsequent transformation... 

Direct nitration of aniline and other arylamines fails because oxidation leads to the formation of dark colored tars As a solution to this problem it is standaid practice to first protect the ammo group by acylation with either acetyl chloride or acetic anhydride... 

After the N acetyl protecting group has served its purpose it may be removed by hydrolysis liberating the ammo group... 

Unprotected arylamines are so reactive toward halogenation that it is difficult to limit the reaction to monosubstitution Generally halogenation proceeds rapidly to replace all the available hydrogens that are ortho or para to the ammo group... 

Decreasing the electron donating ability of an ammo group by acylation makes it possi ble to limit halogenation to monosubstitution... 

Friedel-Crafts reactions are normally not successful when attempted on an aryl amine but can be carried out readily once the ammo group is protected... 

Alkylamines are named m two ways One method adds the ending amine to the name of the alkyl group The other applies the principles of sub stitutive nomenclature by replacing the e ending of an alkane name by amine and uses appropriate locants to identify the position of the ammo group Arylammes are named as derivatives of aniline... 

The carbon that bears the leaving group and a carbon ortho to it become equiva lent m the benzyne intermediate Thus when chlorobenzene 1 is the substrate the ammo group may be introduced with equal likelihood at either position... 

Another structural variation is the replacement of a hydroxyl group m a carbohydrate by an ammo group to give an ammo sugar The most abundant ammo sugar is one of the oldest and most abundant organic compounds on earth N Acetyl d glucosamine is the... 

Ammo acids undergo reactions characteristic of both their amine and carboxylic acid functional groups Acylation is a typical reaction of the ammo group... 

The presence of ammo acids can be detected by the formation of a purple color on treatment with nmhydnn The same compound responsible for the purple color is formed from all ammo acids m which the a ammo group is primary... 

Proline m which the a ammo group is secondary gives an orange compound on reac tion with nmhydnn... 

FIGURE 27 5 Tyrosine is the biosynthetic precursor to a number of neurotransmit ters Each transformation IS enzyme catalyzed Hydroxy lation of the aromatic ring of tyrosine converts it to 3 4 dihyd roxyphenylalanine (l dopa) decarboxylation of which gives dopamine Hy droxylation of the benzylic carbon of dopamine con verts It to norepinephrine (noradrenaline) and methy lation of the ammo group of norepinephrine yields epi nephrine (adrenaline)... 

A key biochemical reaction of ammo acids is their conversion to peptides polypeptides and proteins In all these substances ammo acids are linked together by amide bonds The amide bond between the ammo group of one ammo acid and the carboxyl of another IS called a peptide bond Alanylglycme is a representative dipeptide... 

By agreemenl peplide slruclures are wrillen so lhal Ihe ammo group (as H3N— or H2N—) IS al Ihe left and Ihe carboxyl group (as C02 or CO2H) is al Ihe righl The... 

Several chemical methods have been devised for identifying the N terminal ammo acid They all take advantage of the fact that the N terminal ammo group is free and can act as a nucleophile The a ammo groups of all the other ammo acids are part of amide linkages are not free and are much less nucleophilic Sanger s method for N terminal residue analysis involves treating a peptide with 1 fluoro 2 4 dimtrobenzene which is very reactive toward nucleophilic aromatic substitution (Chapter 23)... 

The reaction is earned out by mixing the peptide and 1 fluoro 2 4 dmitrobenzene in the presence of a weak base such as sodium carbonate In the first step the base abstracts a proton from the terminal H3N group to give a free ammo function The nucleophilic ammo group attacks 1 fluoro 2 4 dmitrobenzene displacing fluoride... 

To direct the synthesis so that only Phe Gly is formed the ammo group of phe nylalanme and the carboxyl group of glycine must be protected so that they cannot react under the conditions of peptide bond formation We can represent the peptide bond for matron step by the following equation where X and Y are amine and carboxyl protecting groups respectively... 

Protect the ammo group of the N terminal ammo acid and the carboxyl group of the C terminal ammo acid... 

Deprotect the ammo group at the N terminus and the carboxyl group at the C terminus... 

The reactivity of an ammo group is suppressed by converting it to an amide and ammo groups are most often protected by acylation The benzyloxycarbonyl group O... 

Section 27 17 Peptide bond formation between a protected ammo acid having a free carboxyl group and a protected ammo acid having a free ammo group can be accomplished with the aid of N N dicyclohexylcarbodiimide (DCCI)... 

These relationships are general Hydroxyl substituted purines and pyrimidines exist in their keto forms ammo substituted ones retain structures with an ammo group on the ring The pyrimidine and punne bases m DNA and RNA listed m Table 28 1 follow this general rule Beginning m Section 28 7 we 11 see how critical it is that we know the cor rect tautomeric forms of the nucleic acid bases... 

In addition to illustrating the mechanics of translation Figure 28 12 is important m that It shows the mechanism of peptide bond formation as a straightforward nude ophilic acyl substitution Both methionine and alanine are attached to their respective tRNAs as esters The ammo group of alanine attacks the methionine carbonyl displac mg methionine from its tRNA and converting the carbonyl group of methionine from an ester to an amide function... 

FIGURE 28 12 Translation of mRNA to an ammo acid sequence of a protein starts at an mRNA codon for methionine Nucleophilic acyl substitution transfers the N formylmethionme residue from Its tRNA to the ammo group of the next ammo acid (shown here as alanine) The process converts an ester to an amide... 

L Ammo acid (Section 27 2) A descnption of the stereochem istry at the a carbon atom of a chiral ammo acid The Fis cher projection of an a amino acid has the ammo group on the left when the carbon chain is vertical with the carboxyl group at the top... 

N terminus (Section 27 7) The amino acid at the end of a pep tide or protein chain that has its a ammo group intact that IS the a ammo group is not part of a peptide bond... 

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