Histidine benzylation

Amino-acid Protection. - Carboxyamidomethyl (CAM) esters have been shown to be useful protecting groups in a-chymotrypsin and papain-catalysed peptide hydrolysis and synthesis.5 10 1,3-Dioxans (582) can be obtained from Na-protected serine derivatives by acid-catalysed transacetalation and are sufficiently robust to survive both amino deprotection and peptide coupling reactions. 11 (L)-Histidine benzyl ester can be prepared as the ditosylate salt... 

The phenolic hydroxyl group of tyrosine, the imidazole moiety of histidine, and the amide groups of asparagine and glutamine are often not protected in peptide synthesis, since it is usually unnecessary. The protection of the hydroxyl group in serine and threonine (O-acetylation or O-benzylation) is not needed in the azide condensation procedure but may become important when other activation methods are used. 

With H2/Pd-C, the normal conditions for benzyl group removal, it is difficult to remove the benzyl group on histidine without also causing reduction of other aromatic groups that may be present. ... 

Weitere Untersuchungen befaBten sich mit den optischen Eigenschaften von Poly-l-benzyl-L-histidin und Poly-L-histidin (175) sowie der basenkatalysierten Bildvuig von cyclischen Verbindungen aus Poly-L-asparaginsaure- 8-benzylester und Poly-L-glutamin-y-benzylester (173). 

Chiral calix[4]arene podands were made using A-benzyl histidine methyl ester.33 These histidyl calixarenes 12a,b were studied in complexation experiments with Co(H), but no use was made of their chirality. The same is true for a chiral calix[4]arene capped tetraphenyl porphyrin which is C4-symmetrical due to the four L-alanine derived linkers.34... 

Sheehan J, Cruickshank PA. Notes- a convenient synthesis of water-soluble carbodiimides. J. Org. Chem. 1961 26 2525-2528. Windridge GC, Jorgensen EC. 1-hydroxybenzotriazole as a 67. racemisation-suppressing reagent for the incorporation of im-Benzyl-histidine into peptides. J. Am. Chem. Soc. 1971 17 6318-6319. 68. 

The assignment of screw-sense in other helix-forming polypeptides is based on studies of the dispersion of optical rotation and in most cases it has been found to be right-handed for the L-enantiomorph (Urnes and Doty, 1961). Notable exceptions are poly-/8-benzyl-L-aspartate and poly-1-benzyl-L-histidine which form somewhat unstable helices of opposite screw-sense. 

Trimethylsilyl chloride also gives the N -product alone in simple models, but this is probably the consequence of thermodynamic control in any event N -trialkylsilyl derivatives are much too labile to be useful as stepping stones to N"-alkylhistidines. The only thoroughly studied example of exclusive mono-N -derivatization is the reaction of acetic anhydride with acylhistidine esters, when thermodynamic control appears to operate. Thus, N -(benzyl-oxycarbonyl)histidine methyl ester gives only the M-acetyl derivative, providing a third kind of intermediate which is useful for N"-alkylation with reactive halides (see Section 2.6.2.3).1 1... 

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