Benzyloxycarbonyl group modified

In the Boc method (Figure 5-14), the a-amino group is protected with a t-butyl-oxycarbonyl (Boc), and the e-amino group of lysine by a modified benzyloxycarbonyl group (Z). C-terminal activation is achieved with N,N -dicyclohexylcarbodiimide (DCCI) and 1-hydroxybenzotriazole (HOBt). 

Peptides that display a terminally located aldehyde function in their structure constitute another group of modified peptide enzyme inhibitors. The sequence benzyloxycarbonyl-Pro-Phe-CHO fulfils the known primary and secondary specificity requirements of chymotrypsin and has been found to be a potent reversible inhibitor of this proteolytic enzyme (Walker et al. 1993). Further, protease inhibitors comprising terminally located aldehyde function are antipain, leupeptin, chymostatin, and elastatinal. In addition, also phos-phoramidon, bestatin, puromycin, and amastatin represent modified peptides which can reversibly inhibit enzymes. 

The monoaminomonophosphonic acids, either in the free state or, very often, as their diethyl esters, have been resolved by the usual techniques of repeated crystallization of appropriate salts those of L-(+)-tartaric acid (2,3-dihydroxybutanedioic acid) or its mono-or di-benzoyl derivativesor of D-(-)-mandelic acid, have been widely employed the use of di-O-benzoylated L-tartaric anhydride, which is based on the separation of diastereoisomeric amides (111), has also been employed to a limited extent. In selected cases, such as the monoaminomonophosphonocarboxylic acids or A -acylated (aminoalkyl)phosphonic acids, resolution following salt formation with organic bases has also been carried out ephedrine, quinine and both enantiomers of l-phenylethylamine have all been used. In many cases, only one enantiomer of the (aminoalkyl)phosphonic acid (or diester) has been isolated in optically pure form. Sometimes, the acidity of the substrate, and hence choice of base for resolution, can be modified by using a mono- (as opposed to di-) ester or (or even in addition to) protection of the amino group as, for example, the phthalimido, benzyloxycarbonyl (cbz) or r r -butyloxycarbonyl (boc) derivative. Resolved di- and mono-esters can be hydrolysed to the free acids under acidic conditions, and A -protection can also be removed through the customary procedures. 

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