Amino acids, basicity stereochemistry

Systematic substitutive nomenclature may be used to name all organic molecules. However, those that are of animal or vegetable origin have often received trivial names, such as cholesterol, oxytocin and glucose. Biochemical nomenclature is based upon such trivial names, which are either substitutively modified in accordance with the principles, rules and conventions described in Chapter 4, Section 4.5 (p. 70), or transformed and simplified into names of stereoparent hydrides, i.e. parent hydrides of a specific stereochemistry. These names are then modified by the rules of substitutive nomenclature. Three classes of compound will be discussed here to illustrate the basic approach carbohydrates amino acids and peptides and lipids. For details, see Biochemical Nomenclature and Related Documents, 2nd Edition, Portland Press, London (1992). 

The basic concepts of stereochemistry were independently developed by varft Hoff and Le Bel in 1874. Based on their findings Emil Fischer suggested that biological macromolecules are composed of chiral l amino acids and d sugars and in 1894 proposed his famous key and lock hypothesis that two chiral molecules interact through shape complementarity with each other and are therefore stereospecific [15]. 

Now we can add the next amino acid using its correct codon, but we want to show the process in general so we shall use the general structure in the margin. All amino acids have the same basic structure and differ only in the group R Both structures are the same and have the same (S) stereochemistry. 

The following is a summary of the representation and description of basic stereochemistry. See also the relevant entries in Chapter 5, especially nnder amino acids and carbohydrates. 

Fig. 2.1. a. Basic chemical structure and stereochemistry of L-amino acids, b. Polymeric structure of proteins and peptides constructed from monomeric units. 

Rehearsal of some basic amino acid and enzyme chemistry plus revision of stereochemistry (Chapter 16) and asymmetric synthesis (Chapter 45). 

The next codon of RNA directs the ribosome to add the next amino acid, linked to the previous one in the chain by an amide bond. Amino acids used to make proteins have the same basic structure and stereochemistry, shown in the margin, and differ only in the group R. 

A Lewis acid-induced aza-Diels-Alder reaction between the /3-lactam-imine 295 and 3,4-di hydro-2//-pyran gives the two diastereomeric pyranoquinolines 296 and 297. Under basic conditions, these products rearrange to the amino-substituted pyranoindolizinones, 298 and 299, respectively, with retention of stereochemistry (Scheme 74) <2003CEJ3415>. 

Lyapova, Pojarlieff, and Kurtev (52) have studied the N —0 and 0—N acyl migration in 1-amino-l, 2,3-triphenylpropanols under acidic and basic conditions respectively. They found a great difference in the ease of migration which depends on the relative stereochemistry of the substrate and the degree of substitution of the nitrogen atom (NH or NCH3). 

Acetylation of delectine yielded an jV,0-diacetyldelectine (160). Basic hydrolysis of delectine gave a parent amino alcohol (161) and anthranilic acid. Treatment of alkamine (161) with methyl iodide and sodium hydride afforded derivative 162, which was identical with 0,0-dimethyllycoc-tonine. Soviet chemists also reported the isolation of 0,O-dimethylly-coctonine (162) from the same plant. The complete assignments of all functional groups and their stereochemistry were made on the basis of comparisons of H NMR and mass spectral data with those of other lycoc-tonine-type alkaloids. 

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