Haploscleridamine, a novel tryptamine-derived alkaloid from a sponge of the order haplosclerida: an inhibitor of cathepsin K.

As part of a search for novel inhibitors of cathepsin K, the MeOH extract of a Micronesian sponge of the order Haplosclerida was shown to be active. Bioassay-guided fractionation of the extract yielded halitoxins, tryptamine, and a novel tryptamine-derived alkaloid, haploscleridamine (1). The tetrahydro-beta-carboline structure of haploscleridamine (1) was elucidated through spectral techniques. Haploscleridamine (1) was found to be an inhibitor of cathepsin K with an IC(50) of 26 microM.