Usefulness of the Peptide Segment Separation Method for Asparagine-Rich Protein Syntheses. Synthesis of Malaria Vaccine Analogs Having the Repeated Unit of l-Asparaginyl-l-Alanyl-l-Asparaginyl-l-Prolyl

Abstract

Abstract In order to demonstrate the usefulness of “the peptide segment separation method” for syntheses of Asn-rich proteins, the central area of circumsporozoite protein of human malaria parasite plasmodium falciparum, Boc–(Asn–Ala–Asn–Pro)n–OBzl (n=2, 3, 4, 6, 9, 12, and 18), were prepared by the coupling reactions of H–(Asn–Ala–Asn–Pro)k–OBzl (k=1, 2, 3, 6, 9, and 12) with Boc–(Asn–Ala–Asn–Pro)m–OH (m=1, 3, or 6) using DCC and HOBt as coupling reagents. The peptide chains are separated into peptide segments by the tertiary peptide bonds of Asn–Pro moieties and they are assembled by the sequence of Asn–Ala–Asn separated by a Pro residue. Regardless of the increase in the peptide chain lengths of the amino and carboxyl components, the coupling reactions in DMF or NMP were achieved in high yields. The excellent solubility of the peptides in highly polar solvents was preserved in spite of the tendency for an Asn residue to have a high potential for aggregation through hydrogen bond formed by the side-chain amide group. The purification of the peptide series by recrystallization could be completely achieved and HPLC on a gel filtration column showed all the peptides to be monodisperse.