Carboxyl protection

To direct the synthesis so that only Phe Gly is formed the ammo group of phe nylalanme and the carboxyl group of glycine must be protected so that they cannot react under the conditions of peptide bond formation We can represent the peptide bond for matron step by the following equation where X and Y are amine and carboxyl protecting groups respectively... 

The Dppe group was developed for carboxyl protection in peptide synthesis. It is formed from an N-protected amino acid and the alcohol (DCC, DMAP, 3-12 h, 0°, It). It is most efficiently cleaved by quatemization with Mel followed by treatment with fluoride ion or K2CO3. The ester is stable to HBr/AcOH, BF3 Et20, and CF3CO2H. ... 

Developed as a carboxyl protective group for peptide synthesis because of its stability to hydrogenolysis and acidic conditions, the acetol (hydroxy acetone) ester is prepared by DCC coupling (68-92% yield) of the acid with acetol. It is cleaved with TBAF in THF. ... 

Relative Lability of Aspartic Acid )8-Carboxyl Protective Groups ... 

Carboxyl Protective Group Abbreviation Deprotection time... 

This active ester was used for carboxyl protection of Fmoc-serine and Fmoc-threonine during glycosylation. The esters are then used as active esters in peptide synthesis. 

No synthesis of (3) appears in the original paper so we may speculate on the success of these or other ideas. Route (a) is much shorter as no carboxyl protection is necessary if we are ready to waste the first mole of ylid. 

Elevation of lung gjutathione by oral supplementation of L-2-oxathiazolidine-4-carboxylate protects against oxygen toxicity in protein-energy malnourished rats. FASEB J. 6, 3101-3107. 

Enzyme Labile Carboxyl Protecting Groups Choline Ester (OCho)... 

To overcome these difficulties in the selective deprotection and chain extension, several carboxyl-protecting groups, namely, allyl (16,32), benzyl (43,44), tert-butyl (42), 2-bromoethyl (45), 2-chloroethyl (45), heptyl (46), 4-nitrophenyl (47,48), and pentafluorophenyl (49) for L-serine/L-threonine have been introduced or applied. Similarly, amino-protecting groups for L-serine/L-threonine that have proved useful for the synthesis of glycopeptides are tm-butyloxycarbonyl (50), 9-fluorenylmethoxycarbonyl (43,44,48), 2-(2-pyridyl)ethoxycarbonyl (51), 2-(4-pyridyl)ethoxycarbonyl (44,52), and 2-triphenylphosphonioethoxycarbonyl (53). Some applications of these groups have been discussed in earlier reviews (7-11). 

Different Amino and Carboxyl Protecting-Group Combinations of L-Serine/L-Threonine Used for Glycopeptide Chain-Lengthening... 

RW Roeske. Carboxyl protecting groups, in The Peptides Analysis, Synthesis, Biology, Vol. 3, pp 101-136, Academic Press, New York, 1981. 

Carboxyl protection of the second amino acid is usually achieved by conversion to an ester using an appropriate alcohol and acidic catalyst (see Section 7.9.1). Although methyl and ethyl esters... 

The metalation of phenoxazine has also been investigated, but in contrast to phenothiazine, direct lithiation at C-l can only be achieved in very low yield (58JA2195 68JMC807). Fortunately, however, the carboxylate protection method is just as efficient as that with phenothiazine, and the... 

Some Amine and Carboxyl Protecting Groups Used in Peptide Syntheses... 

SCHEME 7. 2,2,2-Trichloroethyl protection of carboxyl Protection and deprotection. 

Briand, B., Kotzur, N., Hagen, V. and Beyermann, M. (2008) A new photolabile carboxyl protecting group for native chemical ligation. Tetrahedron Letters, 49, 85-87. 

While the conventional carboxylate protecting groups interfere with the course of the reaction, the enantioselective epoxidation on the oxazole 77b followed by photo-oxygenation and hydrolysis of triamide 78b affords the ester 79 in good yield with the desired stereochemistry [76b], Starting from alkoxyoxazoles, rearrangement to dioxetanes [75b] or dioxazoles [75] has been observed, and a simple and high-yield route for stable 377-1,2,4-dioxazoles 80 has been described (Sch. 46) [77]. 

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