Ergosterol and Stigmasterol

 

Rajah Serfoji Govt. College (Autonomous), Thanjavur – 613 005 

SEMESTER – III

Organic  Chemistry - III Code: R3PCH6

UNIT - V     Steroids

Ergosterol (ergosta-5,7,22-trien-3β-ol) a crystalline steroid alcohol C28H44O that occurs especially in yeast, molds, and ergot and is converted by ultraviolet irradiation ultimately into vitamin D2 is a sterol found in fungi, and is a component of fungal cell membranes, serving many of the same functions that cholesterol serves in animal cells. Because fungi cannot survive without ergosterol, the enzymes that create it in fungi have become important targets for drug discovery. Ergosterol is provitamin form of vitamin D2; exposure to ultraviolet (UV) light causes a chemical reaction that produces vitamin D2

                                                                                                Ergosterol

Ergosterol (ergosta-5, 7, 22-trien-3β-ol) is a sterol found in fungi, and named for ergot, the common name of members of the fungal genus Claviceps from which ergosterol was first isolated. Ergosterol is a component of yeast and other fungal cell membranes, serving many of the same functions that cholesterol serves in animal cells. Because ergosterol is present in cell membranes of fungi, yet absent in those of animals, it is a useful target for antifungal drugs. Ergosterol is also present in the cell membranes of some protists, such as trypanosomes. This is the basis for the use of some antifungals against West African sleeping sickness.

Amphotericin B, an antifungal drug, targets ergosterol. It binds physically to ergosterol within the membrane, thus creating a polar pore in fungal membranes. This causes ions (predominantly potassium and protons) and other molecules to leak out, which will kill the cell. Amphotericin B has been replaced by safer agents in most circumstances, but is still used, despite its side effects, for life-threatening fungal or protozoan infections.

Miconazole, itraconazole, and clotrimazole work in a different way, inhibiting synthesis of ergosterol from lanosterol. Ergosterol is a smaller molecule than lanosterol; it is synthesized by combining two molecules of farnesyl pyrophosphate, a 15-carbon-long terpenoid, into lanosterol, which has 30 carbons. Then, two methyl groups are removed, making ergosterol. The "azole" class of antifungal agents inhibit the enzyme that performs these demethylation steps in the biosynthetic pathway between lanosterol and ergosterol.

Ergosterol is a biological precursor of vitamin D₂, the chemical name of which is ergocalciferol. Exposure to ultraviolet light causes aphotochemical reaction that converts ergosterol to ergocalciferol.

This happens naturally to a certain extent, and many mushrooms are irradiated after harvest to increase their Vitamin D content. Fungi are also grown industrially so that ergosterol can be extracted and converted to Vitamin D for sale as a dietary supplement andfood additive.

Preparations of irradiated ergosterol containing a mixture of previtamin and D vitamin were called Viosterol .

Stigmasterol (also known as Wulzen anti-stiffness factor) is one of a group of plant sterols, or phytosterols, that include β-sitosterol, campesterol, ergosterol (provitamin D₂), brassicasterol, delta-7-stigmasterol and delta-7-avenasterol, that are chemically similar to animal cholesterol. Phytosterols are insoluble in water but soluble in most organic solvents and contain one alcohol functional group.

Stigmasterol 

Stigmasterol is an unsaturated plant sterol occurring in the plant fats or oils ofsoybean, calabar bean, and rape seed, and in a number of medicinal herbs, including the Chinese herbs Ophiopogon japonicus (Mai men dong), in Mirabilis jalapa and American Ginseng. Stigmasterol is also found in various vegetables, legumes, nuts, seeds, andunpasteurized milk. Pasteurization will inactivate stigmasterol. Edible oils contains higher amount than vegetables. Phytosterols normally are broken down in the bile.

Stigmasterol is used as a precursor in the manufacture of semisyntheticprogesterone, a valuable human hormone that plays an important physiological role in the regulatory and tissue rebuilding mechanisms related to estrogen effects, as well as acting as an intermediate in the biosynthesis of androgens, estrogens, andcorticoids. It is also used as the precursor of vitamin D₃.