Malaysiatin, the first cyclic heptapeptide from a marine sponge

Abstract Malaysiatin ( 1 ), the first homodetic cycloheptapeptide from a marine source, has been isolated from the cytotoxic and antimicrobial extracts of the marine sponge Pseudaxinyssa sp. , collected in Borneo. The unusual structure of malaysiatin, which contains homodipeptide and homotripeptide fragments, was elucidated by extensive spectroscopic analysis that suggests an all-L stereochemistry.