Squalene is the immediate biological precursor of all triterpenoids. Triterpenoids form a large group of natural products which includes Steroids and consequently sterols, they derived from C30 precursors.

• Nearly 200 different triterpene skeletons are known from natural sources and represent structurally cyclization products of Squalene.
• In 1934, Robinson proposed a direct cyclization of squalene to the Steroid molecule.
• In 1936, Nobel laureate researcher Paul Karrer described the biochemical structure of squalene for the First time.
• It has major specificities, which are related to Anti-Cancer properties, the maintenance of the oxidation/antioxidation balance, and its Anti-Aging capabilities.

• Squalene epoxide (2,3-oxidosqualene) is produced by the enzyme squalene epoxidase which use NADPH and oxygen to oxidize squalene.
• This metabolic step is the First in sterol biosynthesis leading to the formation of lanosterol or cycloartenol.
• Squalane is a completely saturated derivative of squalene and largely used as a component in many cosmetic products.
• It is obtained by hydrogenation of squalene extracted from Olive Oil.

• The large group of steroids (including sterols) are present in very small amounts in bacteria but at larger amounts in plants and animals, while the hopanoids are very abundant in prokaryotes where they replace Cholesterol.
• steroids are modified triterpenes which derived also from squalene by cyclization, unsaturation and substitution.
• The nucleus of all steroids is the tetracyclic C17 hydrocarbon 1,2-cyclopentanoperhydrophenanthrene (gonane or sterane) substituted by methyl groups at C10 and C13, and an alkyl side-chain at C17.
• steroids may possess a nucleus derived from the former one by one or more C-C bond scissions or ring expansions or contractions.

• Gonane and three (3) examples of Basic Unsubstituted Steroids are shown below.

• R=H (cholestane)
• R=Me (ergostane)
• R=Et (stigmastane)

Unsaturated Steroids with most of the skeleton of cholestane containing a 3b-hydroxyl group and an aliphatic side chain of 8 or more carbon atoms attached to position 17 form the group of sterols.