Aspartic acid sidechains

Note In the Burgess route, the alkyl bridge (two carbon atoms) comes from the aspartic acid sidechain, whereas the Nanchen and Pfaltz route introduces the alkyl bridge with the chloroacetic acid chloride (linker length variable). 

Sidechain conservatism may be split up into at least two kinds 1) substitutions which conserve sidechain bonding forces - providing similar electrostatic, hydrophilic, or hydrogen bonding interactions, and 2) substitutions conserving secondary structure propensity. For instance, substitution of glutamic acid with aspartic acid conserves charge, but this could have a considerable effect upon the secondary structure propensity of the peptide. 

The identities of the two VL complexes are not known with certainty, but the available evidence suggests the -557 ppm-type products arise from monodentate reaction at the carboxylate group, whereas the -544 ppm products derive from monodentate reaction at the nitrogen functionality. Additional products from amino acids with reactive sidechains, as found in serine or aspartic acid, have not been reported.51V chemical shifts for products formed with histidine are similar to those observed for other amino acids, except that an additional signal (-571 ppm) has been observed [66],... 

Amino acids have two functional groups, the carboxylic group and the amino group, which can be converted to surfactant with a reactive molecule bearing a hydrophobic chain. Amino acids with reactive sidechains, such as lysine, arginine, aspartic acid, and glutamic acid, offer opportunities for the molecular design of AAS. 

Itoh, M. Peptides. I. Selective protection of a- or sidechain carboxyl groups of aspartic and glutamic acid. A facile synthesis of p-aspartyl and y-glutamyl peptides. Chem. Pharm. Bull. 17, 1679 (1969). 

References to polypeptides bearing long alkyl sidechains are almost confined to the esters of poly(a,L-glutamic acid) (PyAG-n) and poly (a or p,L-asparfic acid) (PpAA-n or PaAA-n) whose chemical stmctures are depicted in Fig. 1. In these compounds the alkyl sidechain is connected to the mainchain by a carboxylate group that is directly anchored to the backbone in the case of poly(P-peptide)s and through a methylene or ethylene spacer in poly (a-aspartate)s and poly(a-... 

---