Glycine, masking

El fazepam (80) not only is a tranquilizer, but also stimulates feeding in satiated animals. One of several syntheses involves reaction of benzophenone derivative with a glycine equivalent masked as an oxazolidine-2,5-dione (79). ... 

The early syntheses of allokainic acid had as a key step a ring closure of a diester derived from glycine. The presence of the masked isopropenyl chain... 

Monofluoroalanine is accessible, as a racemate, by means of either classical methods or fluoromethylation of a masked glycinate anion by a monofluorohalo-genomethane (CH2C1F). ... 

Schdllkopf and cowoikers have pioneered the development of anions of another type of masked carboxylic acid derivative, i.e. bislactim ethers such as (159), derived from (5)-valine and glycine or alanine, for the asymmetric synthesis of amino acids. As shown in Scheme 78, compounds such as... 

Protein-probe interactions, e.g., by DNA-binding proteins, or charge interactions between positively charged proteins (evident from binding of labeled nonspecific probes) and nucleic acid can be masked by acetylation or glycine treatments (see below). 

Another method for asymmetric alkylation of a masked glycine was reported by Yamada, and is shown in Scheme 3.13 [72]. In this example of a chiral glycine enolate, the Schiff base of tert-hniy glycine and an a-pinene-derived ketone is dilithiated with two equivalents of LDA. Presumably, the lithium alkoxide is chelat-... 

Intermediate (5)-l is simply yV-benzyl-4-fluorophenylglycine that has been capped with an ethylene unit. The original synthesis in which 4-fluorophenylacetic acid was transformed to the corresponding chiral oxazolidinone 6 is depicted in Scheme 2. Masked a-azido acid 7 was formed diastereoselectively from this intermediate. Hydrolysis and azide reduction afforded enantiomerically pure (5)-4-fluorophenyl glycine (8). Reductive amination with benzaldehyde introduced the V-benzyl unit and subsequent A, 0-dialkylation with ethylene dibromide provided chiral oxazinone 1. 

In human nutrition, free amino acids play an important role in aromatisa-tion, as flavour enhancers, and as sweeteners. Monosodium glutamate, in concentrations of 0.1-0.4%, is probably the most prominent flavour enhancer for spices, soups, sauces, meat and fish. (L)-Cysteine amplifies the flavour of onions. Glycine is used to mask the aftertaste of saccharin. Whereas (L)-amino acids may taste slightly bitter, the (D)-enantiomers have a sweet taste. This is in general also true for the corresponding di- and oligopeptides - except for the methyl ester of (L)-aspartyl-(L)-phenylalanine (Aspartame). 

The new reaction of formate mentioned above did not take place in all experiments. In several instances, the ratio of formate glycine incorporation approached 2 1, and the formate label was approximately equally distributed between C2 and 0. It was observed in these latter experiments that purine synthesis de novo (as measured by the incorporation of NH2CH2C"00H into C4) took place much more rapidly than in the experiments demonstrating unequal formate incorporation. It was believed that rapid synthesis de novo of the purine ring was masking the enzymatic exchange reaction of formate with inosinic acid. 

The a-C-furanosylglycine derivative 47 was prepared in 37% overall yield by use of iV-Boc-r-butyldimethylsilyloxypyrole as a masked glycine anion, as shown in Scheme 8. Condensation of 4,6-0-benzylidene-D-glucose with nitroethane in the presence of DBU and 2-hydoxypyridine as 1,3 proton transfer catalyst gave, after reduction, the (a-aminoethyl) P-D-C-glucoside derivative 48. Further C-disaccharides are referred to in Chapter 3. 

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