Activation amino groups

The retention and the peak asymmetry of benzoic acid also indicate the inertness of the bonded phase. If basic compounds remain on the surface or are used as reagents, the peak asymmetry of benzoic acid is poor. The peak height is lower than that of the same quantity of o-toluic acid.3,4 This phenomenon is observed if the basic catalyst that was used in the synthesis process has not been completely washed off the stationary phase or if active amino groups remain. This type of column is not suitable for the separation of acidic compounds. 

In general, amino-containing compounds are poor partners in CM due to their tendency to coordinate to the metal catalyst, even when late-transition metal systems are employed. To preserve catalyst activity, amino groups are therefore typically masked as cyanides, carbamates, amides, or phthalimides. In substrates where iV-coordination to the catalyst is less favored, such as with hindered /V-aryl-/V-allylamines, no protecting group is required. 

Here Phe is an isotopically labeled residue. Although such reactions suggested the possibility of some kind of activated amino group on the tyrosine that is cut off in the initial cleavage of the unlabeled substrate, it is more likely that the released tyrosine stays in the active site,383 while the acetyl-Phe fragment exchanges with acetyP-Phe. 

Deamination (62) or trinitrophenylation (63) of two amino groups (a-amino group of N-terminal alanine and -amino group of a lysine residue) retains the activity. Amino groups have nothing to do with the activity. 

Investigations show that the active amino group of acetoacetate decarboxylase—the one that is concerned with the formation of the ketimine intermediate—has an especially low pK (26, 27). Model experiments revealed that amines of low pK are the best nonenzymic catalysts in particular, cyanomethylamine led to a rate of decarboxylation that is only a few orders of magnitude less than that for the enzymic system (28, 29, 30). 

Activated amino groups, such as those found in 4-pyridylmethyl-amines299 or 2-pyridyltrimethylammonium iodide (254),94 are reductively removed in acid solution. The reduction of the latter requires protonation of the ring to obtain sufficient activation. 

Other aromatic amines with TICT-active amino groups include naphthyl-amines like DMANCN, which shows a well-separated dual fluorescence, and DANCA or related dyes which are used as fluorescence probes (sensing micropolarity) in biological investigations. In the latter case, only one (red-shifted) band (or two strongly overlapping bands) can be seen. 

Transaldolase transfers a 3-carbon keto fragment from sedoheptulose 7-phos-phate to glyceraldehyde 3-phosphate to form erythrose 4-phosphate and fructose 6-phosphate (Fig. 29.9). The aldol cleavage occurs between the two hydroxyl carbons adjacent to the keto group (on carbons 3 and 4 of the sugar). This reaction is similar to the aldolase reaction in glycolysis, and the enzyme uses an active amino group, from the side chain of lysine, to catalyze the reaction. 

This modification of poly(HS-co-MMA) aimed to add an active amino group to the copolymer by reacting it with ethylenediamine (EDA). The aminated poly(HS-co-MMA) was expected to show high reactivity to aldehyde and esters. 

Starting with p-toluidine (p-methylaniline), however, the strongly activating amino group directs bromination to its ortho positions. Removal of the amino group (deamination) gives the desired product. 

Chain extenders can also be substituted with bio-based components in the synthesis of waterborne PUs. For example, chitosan, a derivative of abundant naturally occurring polysaccharides that has active amino groups, can be used to chain-extend waterborne PUs in water. Chitosan possesses unique biological properties such as nontoxicity, biocompatibility, anticoagulant properties, and biodegradability. Waterborne PU films synthesized with chitosan as a chain extender exhibited excellent mechaiucal and anti-coagulating properties, as well as antibacterial and antifungal activities [63]. 

The overly active amino group can be deactivated, as shown in Figure 14.89, by acylating it through reaction with acetyl chloride to give acetamidobenzene. 

Anisic acid was used with benzoxazole, whereas /i-toluic acid was more suited for benzothiazole derivatives. Formamides bearing pyrrolidine, piperidine, and morpholine derivatives were viable coupling partners however, amido- and ester-substituted substrates were unreactive. Notably, an optically active formamide could function as a coupling partner without racemization, suggesting that optically active amino groups could be incorporated onto heterocyclic systems via this process (eq 19). 

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