New circulin macrocyclic polypeptides from Chassalia parvifolia

Four new macrocyclic polypeptides were isolated and identified from an extr act of the tropical tree Chassalia parvifolia. Circulins C-F are 29-30 amin o acid cyclic peptides in which the entire primary amino acid chain is cova lently cyclized via peptide bonds. Their structures were deduced from a com bination of FABMS analyses, N-terminal Edman degradation, endoproteinase di gestion, and amino acid analyses. All the peptides share a high degree of s equence homology and contain six cysteine residues forming three intramolec ular disulfide bridges. Circulins C-F inhibited the cytopathic effects of i n vitro HIV-1 infection with EC50 values of 50-275 nM.