Silicon-containing amino acids

Successful sila-modification of several peptides leading to new protease inhibitors (03CODD526) stimulated the elaboration of synthetic methods for the preparation of silicon-containing amino acids. Among these compounds a-amino acids-containing silacycles were synthesized... 

In general, sila-heterocycles are believed to be promising candidates for the development of silicon-based dmgs and agrochemicals. For example, the sila-proline ester 184 was prepared as part of a systematic study of silicon-containing amino acids and proteins <2000JOM19>. 

Syntheses of optically active silicon-containing amino acids, particularly, of sila-proline-, imidazolidine-, and oxazolidine-based amino acids 03MI86. 

There is some evidence that chromium (Cr " ), silicic acid (Si(OH)4) or related silicon-based compounds, borate (8407 ), nickel (NP" ), and arsenate (AsOf ) are required inorganic nutrients. However, the available evidence tends to be not convincing to all researchers (Reeves, 1997). The functions of arsenate and nickel are not clear. There is some indication that arsenate is used in the metabolism of sulfur-containing amino acids. An experimentally induced deficiency in arsenate or nickel results in impaired growth. 

Sheehan and another Nobel laureate Khorana showed independently that the mild carbodiimide mediated synthesis is very useful in the condensation reaction of N-blocked amino acids with a different amino acid to form a peptide bond. The O-blocking of carboxylic acid groups in peptide synthesis with amino nucleophiles, such as glycine esters or amides, " or novel silicon containing protective groups is also mediated by carbodiimides. Likewise, alcohols are protected with 4-benzyloxybutyric acid, using EDC/DMPA. ... 

Functionally-substituted disilanes are useful starting materials for silylenes, silicon containing heterocycles or for polymeric silicon-containing materials. The classical method to prepare functionalized disilanes is the cleavage of aryl groups by HCI/AICI3 [1] or by triflic acid [2]. An easier method is the introduction of chloro- or alkoxygroups by replacement of amino substituents. 

One hundred liters of broth were produced in a 150 liter Chemap fermentor. In this fermentation, a marine bacterium (slightly smaller than E. coin was grown to a dry cell density of 10-12 g/1 in 12 to 14 hours. A complex nutrient medium (with about 0.5 g/1 of insolubles) was used which contained a mixture of amino acids, proteins and trace minerals. SAG 4130 (Union Carbide), a silicone and polyglycol mixture, was used for foam control at dosages ranging from 100 to 500 ppm. Total protein at the end of the fermentation was roughly 6 g/1, of which 0.3 to 0.6 g/1 was the protease product. The protease has a molecular weight of about 40,000 daltons. All other proteins are relatively small (less than 10,000 daltons). 

There exist several indirect methods for the spectrophotometric determination of silicon. After extraction of molybdosilicic acid, the Mo has been determined with phenylfluorone [45], or 2-amino-4-chlorobenzenethiol (e = 2.0-10 ) [46]. When silicic acid is added to a solution which contains hydrofluorotitanic acid and H2O2, a yellow titanium peroxide complex is formed. Chloranilic acid has also been used for determination of silicon [47],... 

Preparation of Silicon- and Germanium-Containing a-Amino Acids... 

Summary The silicon-containing a-amino acids (R)- and (S>p-(trimethylsilyl)alanine [(R)- ei and fS -la] as well as the germanium-containing a-amino acids (R)- and (Sj-P-(trimethylgermyl)alanine [(K -lb and fS -lb] were synthesized according to the Schallkopf approach. In addition, rac-p-(trimethylsilyl)alanine (rac-la) was studied by single-crystal X-ray diffraction. 

C -symmetric cyclic carbonate as an optically active CO2 equivalent. This methodology was applied to the asymmetric synthesis of silicon-containing a-amino acid esters, as shown in Scheme 1.49. ... 

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