Steroidal alkaloids have the basic steroidal skeleton with nitrogen-based functional groups attached to the skeleton. More specifically, they are distinguished by their tetracyclic cyclopentanoperhydrophenanthrene skeleton that marks their close relationship with sterols. They fall in two major categories: Solanum alkaloids and Veratrum alkaloids. A Steroidal alkaloid has also been found in Chonemorpha fragrans (Frangipani vine), 'chonemorphine' was used to treat intestinal infections in Wistar rats. (Chatterjee DK et al (1987) Parasitol Res 74, 1, 30-33).
Examples
Apocynaceae steroid alkaloids
The family of apocynaceae alkaloids can be categorized based on their backbone structure, which may include the 5α-pregnane, Δ5-pregnane, or conanine backbone. Typically, these alkaloids feature an amino group or an oxygen compound at the 3rd carbon atom. An illustrative example is latifolinin, which is derived from the conanine backbone. This distinctive structure is characterized by a five-membered ring formed by an amino group bonded to both the 18th and 20th carbon atoms.
Latifolinin is a compound that is naturally present in the bark of Funtumia latifolia. Additionally, the leaves of this plant contain two other compounds, namely funtumin and funtumidin. These compounds belong to the Apocynaceae steroid alkaloids family and share the 5α-pregnan backbone structure.
Batrachotoxins
Batrachotoxins are neurotoxins that are naturally occurring on the dermal surface of poison dart frogs. The photo shows the Phyllobates terribilis. Batrachotoxins share a structural foundation with pregnanes, consisting of 21 carbon atoms, and are distinctive for the amino group attached to the 18th carbon atom, exemplified by batrachotoxin A (see image).
Bufotoxins
The bufotoxins are named after the genus of Bufo. The α-pyranones at the 17th carbon atom are specific for the bufotoxins. The bufotoxin shown here is a sterane derivative with an α-pyranone at the 17th carbon atom and an esterified succinic acid at the 3rd carbon atom with arginine attached.
Buxus steroid alkaloids
Buxus steroid alkaloids are present in the leaves of the common boxwood (Buxus sempervirens). This plant primarily thrives in southern and central Europe. These alkaloids are characterized by an amino group attached to the 3rd and/or 20th carbon atom. Methylation of the amino groups can be partial, complete, or absent. Buxus steroid alkaloids constitute a substantial group of bases, most of which can be categorized into three distinct groups.
Another subgroup of Buxus steroid alkaloids possesses a tetracyclic structure. In these compounds, a bond exists between the 9th and 19th carbon atoms, forming a seven-membered ring (ring B). Buxamine E serves as an example of this group.
The third major group is distinguished by the absence of additional carbon atoms bonded to the 4th carbon atom of the A ring. Buxandonin L is an illustrative member of this category.
The largest group consists of pentacyclic Buxus steroid alkaloids, featuring a core structure based on 4,4,14-trimethyl-9,19-cyclopregnan. Cyclobuxin D is a representative of this particular group.
The Buxus steroid alkaloids buxamine E, buxandoline L, and cyclobuxin D are found in the leaves of common boxwood (buxus sempervirens).
Salamander alkaloids
The toxic salamander alkaloids occur naturally in organisms classified within the genus Salamandra. These alkaloids are derived from 3-aza-A-homo-5β-androstane. One notable example is samandarin (see figure), which may serve as the primary alkaloid depending on the species, although it may not be present in some other organisms at all. Samandarin possesses a distinctive oxazolidine structure within the A ring. Besides samandarin, there are several other steroid alkaloids in Salamandra organisms such as samandaridin, samandarone, and cycloneosamandione.