Category:TP3P

Revision as of 14:17, 3 August 2010

Phytosterols

Most common phytosterols are campesterol, β-sitosterol, and stigmasterol. Soybean (Glycine max, Fabaceae) is a rich source of phytosterols (about 0.1% of its weight), and is used for semi-synthesis of medicinal steroids ^[1]. Since dietary phytosterols reduce cholesterol levels, they are used as food additives such as for margarine ^[2]. Vitamin D is a family of sterol metabolites generated photochemically in our skin by UV irradiation.

Cardenolides (C23)

The backbone of the foxglove Digitalis (Plantaginaceae) toxins with the androstane skeleton with a γ-lactone ring at C-17. Notable characters are its 14β-configuration in opposition to other steroids (the rings C/D are cis), and the 20(22)-double bond.

When used in small doses, they are extremely valuable clinically for congestive heart failure.

Distribution

Cardenolides occur principally in the related families of Apocynaceae (including Asclepiadaceae). In the milkweed genus Asclepias, these compounds are secreted in the latex and almost every species contains these toxins. Other plant families such as Brassicaceae, Moraceae, Scrophulariaceae, and some monocotyledons (e.g. Urginea in Liliaceae) contain cardenolides.

The 5α-configuration is found in Asclepias (e.g. aspecioside), whereas 5β-configuration is common in the foxglove Digitalis purpurea, Plantaginaceae (e.g. digoxin). In some Asclepias, sugars are attached to the two hydroxyl groups at C-2 and C-3 position to form cyclic bridges (e.g. asclepin, calactin).

Withanolides (C28)

Withanolides were found in the root of Withania Somnifera, also known as Indian ginseng. Its backbone is a highly oxygenated ergostane with a γ-lactone ring linking C-22 and C-26 ^[3]. The configuration of C-22 is usually R.

Brassinolides (C28)

Brassinolides are plant growth-promoting hormones isolated originally from Brassica napus (rape). Its backbone is a highly oxygenated ergostane with the oxygen-expanded B-ring (ε-lactone). This lactone is not essential for plant growth activity (e.g. castasterone) but the 22R, 23R-diol are. The configurations of C-2,3 and 5 are α in brassinolides whereas they are β in ecdysteroids.