AMMO

Monomeihylamine, methylamine, CH3NH2-Colourless, inflammable gas with an ammo-niacal odour, very soluble in water, m.p. 

Colourless liquid with a characteristic ammo-niacal smell m.p. 9 C, b.p. 106°C. Miscible with water. It is present in pepper as the alkaloid piperine from which it can be obtained by healing with alkali. It can also be prepared by the reduction of pyridine, either electrolytically or by other means. Piperidine is a strong base, behaving like the aliphatic amines. 

Example Miller and Rich investigated the conformational consequences of substitution s on an amino acid in cyclosporin A. an importan t iininunosnppressive dnig. One of th e ammo acids iii this cyclic iin decapeptide is (2.v, ir. 4r, 5f )-3-nydroxy-4-methyl-2-(methylamino)-6-octenoic acid (MeBmtli. It is essential for biological activitv. 

Some amides, ammo acids, di and polycimino compounds, amino alcohols... 

Ether solution. Contains water- insoluble amines. Aqueous solution. Will possess ammo, niacal odour of water-soluble amines present. Distil as long as distillate is alkaline to recover volatile water-soluble amines. 

You will have noticed that, throughout this chapter, the heteroatom has always been hie nucleophile. There is one way to use nitrogen as an electrophile however and this provides a good synhion for ammo acid synthesis ... 

From their respective pK s we see that acetic acid is a stronger acid than ammo mum ion Therefore the equilibrium lies to the right K is greater than 1... 

Example A common misconception is that the conjugate base of a weak acid is strong This is sometimes but not always true It is true for example for ammo nia which is a very weak acid (pK 36) Its conjugate base amide ion (H2N ) is a much stronger base than HO It is not true however for acetic acid both acetic acid and its conjugate base acetate ion are weak The conjugate base of a weak acid will be strong only when the acid is a weaker acid than water... 

Some of the most important organic compounds in biochemistry are the a ammo acids rep resented by the general formula shown... 

A quote from a biochemistry text IS instructive here This IS not an easy reaction in or game chemistry It is how ever a very important type of reaction in metabolic chemistry and is an integral step in the oxidation of car bohydrates fats and several ammo acids G L Zubay Biochemistry 4th ed William C Brown Publishers 1996 p 333... 

This reaction is catalyzed by an enzyme called a dehydratase and is one step along the pathway by which plants convert glucose to certain ammo acids... 

The term chiral recognition refers to a process m which some chiral receptor or reagent interacts selectively with one of the enantiomers of a chiral molecule Very high levels of chiral recognition are common m biological processes (—) Nicotine for exam pie IS much more toxic than (+) nicotine and (+) adrenaline is more active than (—) adrenaline m constricting blood vessels (—) Thyroxine an ammo acid of the thyroid gland that speeds up metabolism is one of the most widely used of all prescription... 

Because diastereomers are not mirror images of each other they can have quite different physical and chemical properties For example the (2R 3R) stereoisomer of 3 ammo 2 butanol is a liquid but the (2R 3S) diastereomer is a crystalline solid... 

Draw Fischer projections or make molecular models of the four stereoisomeric 3 ammo 2 butanols and label each erythro or threo as appropriate... 

An unknown acetylenic ammo acid obtained from the seed of a tropical fruit has the molec ular formula C7H11NO2 On catalytic hydrogenation over platinum this ammo acid yielded homoleucme (an ammo acid of known structure shown here) as the only product What is the structure of the unknown ammo acid" ... 

Firefly lucifenn is an example of an azole that contains a benzene ring fused to the five membered ring Such structures are fairly common Another example is benzimidazole present as a structural unit m vitamin B12 Some compounds related to benzimidazole include purine and its ammo substituted derivative adenine one of the so called het erocychc bases found m DNA and RNA (Chapter 28)... 

Very strongly activating —NH2 (ammo) Ortho para directing... 

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... 

The first organometallic compounds we encountered were compounds of the type RC=CNa obtained by treatment of terminal alkynes with sodium amide m liquid ammo nia (Section 9 6)... 

These reactions are normally carried out in liquid ammo nia because that is the sol vent in which the sodium salt of the alkyne is prepared... 

An example of a biologically important aide hyde is pyridoxal phosphate which is the active form of vitamin Bg and a coenzyme for many of the reac tions of a ammo acids In these reactions the ammo acid binds to the coenzyme by reacting with it to form an imine of the kind shown in the equation Re actions then take place at the ammo acid portion of the imine modifying the ammo acid In the last step enzyme catalyzed hydrolysis cleaves the imme to pyridoxal and the modified ammo acid... 

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... 

A standard method for the preparation of an a ammo acid uses a bromo carboxylic acids as the substrate and aqueous ammonia as the nucleophile... 

Phthalimide has been piepaied in 95% yield by heating the com pound foimed on reaction of phthalic anhydiide (Section 20 5) with excess ammo nia This compound has the moleculai foimula C8H10N2O3 What is its stiuctuie ... 

Step 4 Protonation of the tetrahedral intermediate at its ammo nitrogen... 

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