The marine environment has been explored in the search for new bioactive compounds over the last 50 years, becoming a highly important and rich source of potent molecules and drug leads reported to possess a wide scope of activities. Alkaloids constitute one of the largest classes of natural products and are synthesized by terrestrial and marine organisms on all evolutionary levels. Alkaloids are usually present in an organism as a mixture consisting of several major and a few minor compounds of the same biosynthetic origin and differing only in functional groups. This group of compounds has apparently evolved as a defense mechanism against predators and as a result alkaloids are often highly potent and toxic molecules. 1 Marine invertebrates have proven to be an outstanding source of active molecules, one of the most promising being indole alkaloids. Although many of these marine alkaloids closely resemble the endogenous amines (serotonin, dopamine, or histamine), their potential affinity to various neurological targets and consequential impact on animal behavior is virtually unexplored.

Indole alkaloids, their activity, synthesis, and potential use in medicine have been already reviewed in several articles. 2 In this review, we provide information on current and potential pharmaceuticals including small molecule natural indole alkaloids, their biological properties, structure-activity relationship studies, and especially their potential for the treatment of neurological disorders.