Amino-acid Protection

The Noc group, developed for amino acid protection, is introduced with the acid chloride (Et3N, H2O, dioxane, 2 h, 20°, 61-95% yield). It is cleaved with Pd(Ph3P)4 (THF, A, A -dimethyibarbituric acid, 8 h, 20°, 80% yield). It is not isomerized by Wilkinson s catalyst, thus allowing selective removal of the allyl ester group. 

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

The Paloc group was developed as an amino acid protective group that is introduced with the p-nitrophenyl carbonate (H2O, dioxane, 68-89% yield). It is exceptionally stable to TFA and to rhodium-catalyzed allyl isomerization, but it is conveniently cleaved with Pd(Ph3P)4 (methylaniline, THF, 20°, 10 h, 74-89% yield). ... 

L Lapatsanis, G Milias, K Froussios, M Kolovos. Synthesis of A-2,2,2,-(trichloro-ethoxy carbonyl)-L-amino acids and A-(fluorenylmethoxycarbonyl)-L-amino acids involving succinimidoxy anion as a leaving group in amino acid protection. Synthesis 671, 1983. 

Parmar et al have developed a method for resolving racemic mixtures of a variety of natural and nonnatural amino acids using the ethyl ester of the amino acid protected at the amino position hy the formation of a Schiff base with an aromatic aldehyde such as /)-chlorobenzaldehyde. Both chymotrypsin and Lip such as porcine Lip gave good yields of the L-amino acid which precipitates out of solution as the amino acid ester released from the imine is cleaved by the hydrolase. 

Amino Acid Protecting Groups Suitable for Solution Synthesis Protecting Groups Suitable for Solid-Phase Synthesis on HMFS Resin... 

As an example, liquefied mixtures are easily formed by using some amino acids protected with acetyl, Boc-, Fmoc- and Z-groups. Some authors have called the resulting systems eutectic mixtures , but this term should be reserved for the textbook definition as the composition of minimum melting point that freezes isothermally at the eutectic temperature. Hence we refer to them as eutectic melts . 

Neale, P. J., Banaszak, A. T., and Jarriel, C. R., Ultraviolet sunscreens in Gymnodinium sanguineum (Dinophyceae) mycosporine-like amino acids protect against inhibition of photosynthesis, J. Phycol., 34, 928, 1998. 

An amino acid protected only at the N atom and a different amino acid in which only the C02H group is protected do not react with each other to form a peptide bond. On the contrary, they form an ammonium carboxylate in a fast acid/base reaction (Figure 6.29). Ammonium car-boxylates can in principle be converted into amides by strong heating. Thus, for example, in the industrial synthesis of nylon-6,6, the diammonium dicarboxylate obtained from glutamic acid and hexamethylenediamine is converted to the polyamide at 300 °C. However, this method is not suitable for peptide synthesis because there would be too many undesired side reactions. 

Mahmoudi A, Nazari K, Khosraneh M et al (2008) Can amino acids protect horseradish peroxidase against its suicide-peroxide substrate Enzyme Microb Technol 43 329-335... 

It intercepts the activated ester first and the new intermediate does not racemize, mostly because the reaction is highly accelerated by the addition of HOBt. The second amino acid, protected on the carboxyl group, attacks the HOBt ester and gives the dipeptide in a very fast reaction without racemization. 

The scheme of classical peptide SPS is shown in Fig. 2.1. The first step is the attachment of the first amino acid onto the resin, usually via the carboxylic group with both the amino and the side-chain functions of the a-amino acid protected (step 1). The inverse strategy, where the amino group would be linked to the resin and the carboxyl would be protected, has seldom been used because extensive racemization occurs during repeated resin-bound carboxylate activations (3) this limits the accessibility of C-terminal modified peptides that are biologically relevant. However, several recent reports (4-7) describe the SP modification of the peptide C-terminus using the more reliable C-to-N direction for peptide synthesis. 

The linker was prepared by hooking the aldehyde 2.14 (68) onto the support and then performing a reductive amination with the first a-amino acid protected as an allyl... 

Standard amino acid protecting groups that were used routinely in BOC-peptide synthesis. For Lys the -nitrogen has the potential to cyclize. We sometimes protect this with the fluorenylmethyloxycarbonyl (FMOC) protecting group. 

Amino acid-protecting groups such as benzyloxycarbonyl and t-butoxycarbonyl groups are cleaved by BBr3. 

Patrikeev et al. also employed imprinted silicas for thin layer chromatography. The silica was mixed with plaster and immobilised on a plate for use in the separation and identification of gramines [31] and for the resolution of amino acid derivatives [29]. In the latter experiment it was found that the influence of the amino acid protective group, dinitrophenol, was too dominant to allow the separation of... 

Weinberg JM, Venkatachalam MA, Roeser NF, Davis JA, Varani J, Johnson KJ. Amino acid protection of cultured kidney tubule cells against calcium ionophore-induced lethal cell injury. Fab Invest 1991 65 671-678. 

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