Cribrostatin 6, a dark blue cancer cell growth inhibiting constituent of the Republic of Maldives marine sponge Cribrochalina sp. has been isolated, and its structure (shown below) elucidated, based on a combination of RMS, high field (500 MHz, HMBC, and GOESY experiments) 15N, .sup.1H- and 13C NMR, and X-ray crystal structure analyses. Cribrostatin 6 also was found to inhibit the growth of a number of pathogenic bacteria and fungi.