An investigation into the use of cobalt chelates in peptide synthesis : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science, Massey University, Palmerston North.
Preparative scale samples of [ Co(en)2
]C1 using the method of Bailar (27) and [ Co(en)2
]Cl from CoCl6
were produced. The carbonate complex was also prepared from [ Co(en)2
]C1, using the method described by Buckingham (21). [ Co(en)2
]Cl was then converted to [ Co(en)2
]Br. Alanato, Phenylalanato, Nεnitroarginato, Valinato, Prolinato and O-Benzylaspatato complexes were synthesised from [Co(en)2
]Br using a modification of Meisenheimers method outlined by Dekkers (26). Isoleucinato, Phenylalaninato,Nε nitroarginato, O-benzyl-aspatato and O-benzyltyrosinato complexes were also prepared under non solution conditions described by Dekkers (26). The formation of glycinatobis(ethylene-diamine)cobalt(III) complex preparation by a modified Meisenheimer method, was used as model reactions to optimise the source of base, pH conditions, solvent conditions and reaction times. The use of methyltri- flouromethane sulfonic acid and triflouromethane sulfonic acid in methanol, to alkylate the amino-acido-bis(ethylene-diamine)cobalt(III) complex was demonstrated. The conditions required to optimise the yield of the condensation of these methylated amino acid cobalt(III) with amino acid esters or peptide esters, was established, and the conditions necessary for the rapid ion exchange separation of the products investigated. The most suitable of the methods for the removal of the peptide from the cobalt(III) complexes, described by Dekkers, was established and Gel Filtration separation of the peptide products demonstrated. Problems with the instability of some peptide complexes, especially Co(en)2
, were encountered and possible solutions tested. The synthesis using cobalt chelates of the amino acids of PhePheOC6
had thus been attempted and the isolated products were submitted for amino.