Aciculitins A−C: Cytotoxic and Antifungal Cyclic Peptides from the Lithistid Sponge Aciculites orientalis

The lithistid sponge Aciculites orientalis contains three cyclic peptides, aciculitins A−C ( 1 − 3 ), that are identical except for homologous lipid residues. The structure of the major peptide, aciculitin B ( 2 ), was elucidated by interpretation of spectroscopic data. The aciculitins consist of a bicyclic peptide that contains an unusual histidino-tyrosine bridge. Attached to the bicyclic peptide are C 13 −C 15 2,3-dihydroxy-4,6-dienoic acids bearing d -lyxose at the 3-position. The structures of aciculitamides A ( 4 ) and B ( 5 ), which are artifacts obtained earlier from this sponge, are also presented. The aciculitins 1 − 3 inhibited the growth of Candida albicans and were cytotoxic toward the HCT-116 cell line.