Solubilizing protecting groups

On the other hand, selected di- and tripeptides can be synthesized enzymatically using solubilizing protecting groups on a large scale, even in a continuous process1118-1201 (cf. 12.5.3.4.1, p. 832-833). In addition, the solid-to-solid conversion has proven to be a very useful method for the synthesis of selected short peptides which fulfil the requirements for this special synthetic procedure (cf. 12.5.3.4.2, p. 838-839). 

Block copolymers as solubilizing protecting groups in peptide synthesis were prepared by Bayer et aL [51]. They used 3,5-diisocyanatobenzyl cMoride and 3-nitro-3-azapentane-l,5-diisocyanate as reagents for the syntheris of the copol-ymeric supports ... 

The protecting groups are also used to solubilize synthetic intermediates in organic solvents, e.g. methylene chloride. Chromatography is then possible on a larger scale, since silica gel can be used as adsorbent. Six synthetic strategies have been developed (H. Kdster, 1979) ... 

The aims of inserting a thiazolidine-4-carboxylic acid (4-thiaproline, Thz, 11) residue into peptide chains are similar to those discussed for the 4-oxaproline analogue in Section 9.2.3.4.I. Thiazolidine-4-carboxylic acid (11), particularly when disubstituted at the C5 position of the proline ring, can act as a cysteine precursor and concomitantly as an amide backbone protecting group (see Section 23.2.4). Its solubilizing properties derive from its preference for the cis configuration of the Xaa-Thz bond. 169-172 ... 

The most common reagent for introducing the terf-butoxycarbonyl (Boc) protecting group is the pyrocarbonate B0C2O. This is employed here in aqueous alkaline medium to which has been added the solubilizing agent dioxane. 

A. Fischer, A. S. Bommarius, K. Drauz, and C. Wandrey, A novel approach to enzymatic peptide synthesis using highly solubilizing N -protecting groups of amino adds, Biocatalysis 1994, 8, 289-307. 

Thus, in this method the stepwise synthesis proceeds on the soluble polymer, as in the liquid phase method the only difference is in the coupling step where the carboxyl component is an insoluble polymeric active ester. The use of the solubilizing C-terminal macromolecular protecting group overcomes the limitations encountered in the original application of the polymer reagent method of peptide synthesis. However, due to the steric limitations characteristic of the polymer-polymer interactions, the attainment of quantitative coupling in each step of the synthesis can be difficult in this method. 

The synthesis of the amprenavir derivative, which is equipped with a solubilizing phosphate group, takes a slightly different course from that used for the prototype. The protected intermediate 5 used in the synthesis of 12 is allowed to react with benzyloxycarbonyl chloride to provide the... 

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