Aminoacid kinds

The expression homochiral in its original meaning concerns isometric molecules of various kinds with the same configuration, for example, the (i,)-aminoacids. There were propositions to use this word in a narrow sense, as the equivalent of enantiopure. For a discussion, see Ref. 6, p. 215. 

Similar results were observed by Davies and McKervey in the tandem Mn02 oxidation-Wittig reaction of alcohols derived from (3-aminoacids, which can somehow be considered to belong to a semi-activated kind.30... 

Substrate for this kind of Evans auxiliary is the aminoacid (/ )-phenylalanine, which is reduced to the alcohol 23 and exposed either to carbon disulfide in combination with triethylamine and sodium hydroxide to synthesize 19 or to diethylcarbonate and potassium carbonate to form oxazolidin-2-one 24. 

Moreover, the isomeric distributions of aminoacids and hydroxyacids seem to suggest that radical reactions, must also be taken into account (see paragraph 5.4). Presently, it remains impossible to determine if this kind of processes played a role during the accretion process or later. 

The most important of the peptidic phosphatase inhibitors are the microcystins and nodularin. Mycrocystins are heptapeptides characterised by the sequence cyclo(D-Ala-X-D-e/7t/i/ o-P-methylisoAsp-Y-Adda-D-isoGlu-iV-methyldehydroAla), where X and Y are different L-aminoacids, and Adda is the abbreviation of the P-aminoacid [25,35,85,95]-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4(E),6(E)-dienoic acid. In the most common microcystin, namely microcystin-LR, X is Leu and Y is Arg. This kind of compounds was considered to be the highly hepatotoxic principle of the cyanobacteria genera Microcystis, Artabaena and Oscillatoria. Apart Jfrom the variations represented by X and Y, other differences arising jfrom the demethylation of aminoacids, lead to the existence to more than fifty microcystins. The rare acid Adda is also... 

Pollen extract contains serveral kinds of organic substances carbohydrates, sporo-pollenines, aminoacids, proteins, nucleic acids, alkaloids, carotenes, flavonoids, organic acids, phytosterols and plant hormones. Furthermore, there are several trace elements such as manganese, cobalt, nickel, copper, zinc and silica. 

Out of 16 permutations of the first two bases, 8 fully specify the aminoacid without regard to the third base for example, TCT, TCC, TCA, and TCG all code for the aminoacid serine, so if the first two bases are TC the diird one can be anydiing. Of the other eight, six result in a two-way selection for example, CAT and CAC code for histidine, but CAA and CAG code for glutamine. Putting the third base into two classes in diis way makes chemical sense, as T and C have similar structures (and are known as pyrimidine bases), whereas A and G have a different kind of structure (and are known as purine bases). These structures can be seen in Figure 2.1. 

Figure 25-7. Cross-link structure of gelatin-sUoxane hybrids. The cross-links involved grafting of 3-glycidoxypropyl-trimethoxysilane (GPSM) molecules to the aminoacid residues of the gelatin chains as well as their condensation to yield Sk-O-Si bonds. AAl and AA2 represent different kinds of aminoacid residues of gelatin.

Three kinds of chiral components were mainly used in stereoelective type initiators alcohols, glycols and aminoacids. 

In every living cell proteins are assembled on ribosomes by the co-polymerization of about 20 kinds of aminoacids, all with the same L-optical configuration (see Fig. 5.7). The molecular weight of proteins varies from about 6000 to well over a million daltons, but all have the common struaure shown in Fig. 4.2, where R represents the familiar side-chains, such as methyl (for alanine) and p-hydroxybenzyl (for tyrosine). The Atlas of Protein Sequence and Structure (National Biomedical Research Foundation, Georgetown University, Washington, D.C), published at intervals, contains the aminoacid sequences of many hundreds of proteins. 

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