1.3- Dicyclohexylcarbodiimide Links

Write an equation for the linking of two protected amino acids with dicyclohexylcarbodiimide (DCC). 

Fig. 13. Synthesis of (3-linked asparagines glycosides (a) dicyclohexylcarbodiimide (DCC) and l-hydroxybenzotriazole(HOBt) coupling (98), (b) pentafluorophenyl (OPfp) ester of aspartic acid derivative coupling (97).

There are three main reasons to suggest a specific function of subunit III in proton translocation. First, Casey et al. [171] showed that modification of this subunit with dicyclohexylcarbodiimide (DCCD) blocks proton translocation, but has little effect on electron transfer. Similar results have been obtained with the reconstituted oxidase from the thermophilic bacterium PS3 [164]. Prochaska et al. [160] showed that DCCD binds mainly to Glu-90 of the bovine subunit III, which is predicted to lie within the membrane domain and hence to be a site analogous to the DCCD binding site in the membranous fj, sector of the ATP-synthase (Fig. 3.8 see also Ref. 85). Since the latter is a part of a proton-conducting channel in ATP synthase, subunit III was thought to have the same function. However, there is one essential difference between the two phenomena. Modification of the membranous glutamic residue in by DCCD leads also to inhibition of ATP hydrolysis in the complex, as expected for two linked reactions. In contrast, DCCD has little or no effect on electron transfer in cytochrome oxidase under conditions where H translocation is abolished. Hence, DCCD cannot simply be judged to block a proton channel in the oxidase. More appropriately, it decouples proton translocation from electron transfer. 

The next stage is to link the carboxyl group of the second amino acid on to the amino group of the first. The Boc group (Chapter 24) is usually used for amino group protection in the Merrifield method and DCC (dicyclohexylcarbodiimide) is used to activate the new amino acid. Here is a summary of this step, using symbols again for polymer and spacer. 

Since pyrrolidinodiphosphines, e.g., Ph-CAPP, and BPPM, gave excellent stereoselectivities, we prepared a series of new chiral pyrrolidinodiphosphines, in which the nitrogen atom of PPM (, 11) is linked up with a variety of a-aminoacyl groups. The rhodium complexes with these ligands may serve as good bio-mimetic models of reductase when they are anchored on polymers especially polyamides. a-Aminoacyl-PPMs ( ) were prepared by the condensation of PPM with an N-CBZ-a-amino acid or an N-CBZ-dipep-tide in the presence of dicyclohexylcarbodiimide (DCC) and 1-hy-droxybenztriazole (HOBT)(eq. 3). 

Figure 2.2 Modern solid phase peptide synthesis. Process begins with a-N terminal Fmoc deprotection of resin bound C-terminal amino acid residue with piperidine (mechanism illustrated). Peptide link formation follows (typical solvent Al-methylpyrrolidone [NMP]) by carboxyl group activation with dicyclohexylcarbodiimide (DCC) (mechanism illustrated) in presence of hydroxybenzotriazole (HOBt). HOBt probably replaces DCC as an activated leaving group helping to reduce a-racemization during peptide link formation. Other effective coupling agents used in place of DCC/HOBt are HBTU 2-(lH-benzotriazol-l-yl)-l,l,3,3-tetramethyluronium hexafluorophosphate Py-BOP benzotriazole-l-yl-oxy-tns-pyrrolidino-phosphonium hexafluorophosphate. The Process of a-N deprotection, and peptide link formation, continues for as many times as required (n-times), prior to global deprotection and resin removal.

EC microc q)sules were linked onto cotton via grafting with 1,2,3,4-butanetetracarboxylic acid (BTCA). The mercerized cotton was immersed in treatment baths with different concentrations of EC microcapsules and BTCA for reduction of curing temperature the catalysts cyanamide (CA) and N,N -dicyclohexylcarbodiimide... 

To circumvent this uncertainty without use of the caesium salt procedure, hydroxymethyl [87] or aminomethyl functions on the polymer can be reacted with carboxylic partners in an esterification reaction [207] or peptide bond formation with the aid of condensing agents like carbonylbisimidazole [88], dicyclohexylcarbodiimide [89] or others. For this purpose in the author s laboratory the use of symmetric anhydrides [3] of the N-protected amino acids to be attached to the support was found to be most effective [90], especially in the formation of activated esters on the gel phase with phenolic hydroxyl functions [38]. By this procedure, on 0.5% cross-linked polystyrenes, load levels up to 1.5 millimoles/g of the support are reached. 

In step 3, the next N-protected amino acid is linked to the first one. This is accomplished with the aid of dicyclohexylcarbodiimide (DCC). DCC is able to link carboxyl and amino groups in a peptide bond in the process, the DCC is converted to dicyclohexylurea. The mechanism of this step is described in Figure 17.8. 

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