Protecting enzymatically removed

The heptyl ester was developed as an enzymatically removable protective group for C-terminal amino acid protection. 

Scheme 7. Spacer-based enzymatically removable protecting groups...

Synthesis of the Palmitoylated and Farnesylated C-Terminal Lipohexapeptide of the Human N-Ras Protein by Employing an Enzymatically Removable Urethane Protecting Group, H. Waldmann, E. Nagele, Angew. Chem. 1995,107, 2425-2428, Angew. Chem. Int. Ed. 1995, 34, 2259-2262. 

Braun, P., Waldmann, H., and Kunz, H. (1992) Selective enzymatic removal of protecting functions heptyl esters as carboxy protecting groups in glycopeptide synthesis. Synlett 1, 39 10. 

An additional interesting acyl-type -protection is the phenylacetyl group that is enzymatically removed with penicillin G acylase (see Section 2.5). 

In these protease-catalyzed cleavages of the C-terminal protecting groups, it has to be taken into consideration that an undesired hydrolysis of peptide bonds can occur, especially if unnatural and poor substrates are subjected to enzyme-mediated transformations. The use of enzymes which cannot cleave amides at all enables this undesired side reaction to be overcome. This principle has been realized in the development of the heptyl (Hep) ester [13,14,48,49] as carboxyl protecting group, which can be enzymatically removed by means of lipases (Fig. 10). 

A further possibility for the enzymatic removal of C-terminal blocking groups is opened up by the application of enzymes which generally display a high esterase/ protease ratio. Such a biocatalyst is the alkaline protease from Bacillus subtilis DY which shows similarities to Subtilisin Carlsberg. For this enzyme the ratio of esterase to protease activity is >105. It selectively removes methyl, ethyl and benzyl esters from a variety of Trt-, Z- and Boc-protected di- and tripeptides and a pentapeptide at pH 8 and 37 °C (Fig. 18-9) (91l... 

Hep),14-9, 31, 32, 98-1001 the 2-bromoethyl (EtBr) I4-6, 31, 32, 1011 and the p-nitrobenzyl (PNB) esters11021 as carboxy protecting groups for peptide synthesis which can be enzymatically removed by means of lipases or esterases, respectively (Fig. 18-11). 

Figure 18-13. Use of hydrophilic esters as solubilizing enzymatically removable protecting groups for the synthesis of characteristic protein fragments.

Selective enzymatic removal of protecting groups from 1,6-anhydropyranoses. 

Protection of carboxyl groups as carbalkoxy(ethoxy)methyl esters Enzymatic removal of the protective group... 

At the beginning of the 1990s, Houston Industries developed an enzymatic process ( Enzymatic Coal Desulfurization ) protected in Canada and US [83,84], Although, the application was focused to coal desulfurization it may also be applicable to crude oil and fossil fuel-derived liquids. The processes claim the removal of both, organic as well as inorganic sulfur species. The process was described as using ground coal (10-50 p,m) slurried with water, while the oil was treated in an aqueous emulsion. 

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