Alkaloids are nitrogen-containing small molecules which are mainly found in plants.1) To date, approximately 27 thousand alkaloids have been reported in which 21 thousand were of plant origin.
Since most of the alkaloids exhibit potent bioactivity, they are the main component of many herbal medicines. Some alkaloids are also used as pharmaceuticals. Alkaloids interact with proteins electrostatically due to the positive charge of the nitrogen atoms which facilitates binding to the negative charge of the proteins. Especially, pharmaceutical alkaloids tend to bind to the receptors in neural systems.