Alkaloids are a group of naturally occurring chemical compounds (natural products) that contain mostly basic nitrogen atoms.Alkaloids are often divided into the following major groups:
1.True alkaloids---Which contain nitrogen in the heterocycle and originate from amino acids.Their characteristic examples are atropine, nicotine, and morphine. This group also includes some alkaloids that besides nitrogen heterocycle contain terpene (e.g., evonine) or peptide fragments (e.g. ergotamine). This group also includes piperidine alkaloids coniine and coniceine although they do not originate from amino acids.
2.Protoalkaloids are the ones which contain nitrogen and also originate from amino acids. Examples include mescaline, adrenaline and ephedrine.
3.Pseudalkaloids – alkaloid-like compounds that do not originate from amino acids. This group includes, terpene-like and steroid-like alkaloids, as well as purine-like alkaloids such as caffeine,theobromine, theacrine and theophylline.