Amino fragmentation

Zincke-type salts derived from other aromatic nitrogen heterocycles also undergo Zincke reactions. The isoquinolinium salt 6 (Scheme 8.4.16) permitted incorporation of a phenyl ethylamine chiral auxiliary, providing salt 48. In this context and others (vide infra), Marazano and co-workers found that refluxing -butanol was a superior solvent system for the Zincke process. Additionally, the stereochemical integrity of the or-chiral amino fragment was reliably maintained. 

The mild reaction conditions and the obviously high potential driving force of the ketene Claisen rearrangement recommended the use of the process for more complex systems. The first series of this type of reaction suffered from severe limitations. On the one hand, only electron-deficient ketenes added to the allylamines, and useful yields of the lactams had exclusively been achieved by employing dichloroketene [57, 58 a]. On the other hand, the rearrangement was restricted to either monosubstituted olefins in the amino fragment or the... 

With these results available, it was not difficult to substitute the chlorine atom in compounds 91 with an additional equivalent of a primary or secondary amine in methanol [ 11,57] to obtain a, -diaminoesters 106 with different amino fragments (Scheme 35). 

The dihydro derivatives provide entirely analogous spectra except that the fragments which include the dihydro-p-hydroxystyrylamine nucleus and these occur at + 2 mass units. Amino fragments and the ion m/e 135 (C8H9ON) give useful structural information the ions v and w are ascribed to hydroxyproline. 

Some structure elucidation methods often have been used in the past and should also be recommended for future use. The Hofmann degradation is one of these reactions another is the use of a KOH melt to hydrolyze (amide) bonds. This method is well-known for determining the nature of the polyamine. One must keep in mind, however, that in addition to the cleavage of polyamine substituent bonds, the polyamines themselves are degraded, and smaller amino fragments can be detected. Therefore, a careful analysis of the product is necessary. 

An alternative method for the simultaneous derivatization of both carboxylic and amino fragments in amino acids known since the 1990s implies the interaction of these analytes with chloroformates. It leads to the esterification of carboxy groups together with the formation of iV-ethoxycarbonyl derivatives (Fig. 

From these data it was concluded that pepsin has an extended active site being able to accomodate specifically five amino acid residues of the substrate. The orientation of the substrate molecule relative to the ethanol binding loci in pepsin crystals has been determined. Pepsin mechanism includes "amino-enzyme" formation which chemically is not an amide, formed by the enzyme carboxyl with the amino fragment of the substrate. 

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