Natural steroid stigmasterol

Crude fats and oils consist primarily of glycerides. However, they also contain many other hpids in minor quantitites. Com oil, for example, may contain glycerides plus phosphoUpids, glycolipids, many isomers of sitosterol and stigmasterol (plant steroids), several tocopherols (vitamins E), vitamin A, waxes, unsaturated hydrocarbons such as squalane and dozens of carotenoids and chlorophyll compounds, as well as many products of decomposition, hydrolysis, oxidation, and polymerization of any of the natural constituents. 

It will be noted that stigmasterol also represents a commercial route to progesterone. This abundant plant sterol that is readily available from soybean with its C22-C23 double bond, easily converts to progesterone in four steps and has therefore become a preferred substrate for various steroidal drugs. Cholesterol itself, which is the natural substrate for all mammalian steroid hormones, and is readily available from various sources (e.g., wool grease), is now also convertible to desirable steroid intermediates utilizing biotransforma-tion chemistry. The same is true of P-sitosterol (Chapter 11), which is another plant sterol available from soybean. 

Steroids are widespread in nature, and those present in Aristolochia species are mostly derivatives of P-sitosterol and stigmasterol. P-Sitosterol (610) and its glucoside (611) were frequently encountered in several Aristolochia species (Table 22). P-Sitosterone (612), 3-one derivative of P-sitosterol was found in A. zollingeriana only [245], Stigmasterol (613) and its derivatives stigmast-4-en-3-one (614), 3P-... 

Aldehyde 1032 has been used as a chiral template for the side chain of (255, 26)-di-hydroxycholecalciferol (1036), a metabolite of natural vitamin D3 (Scheme 153) [225]. The chain is introduced by a Wittig coupling of the stigmasterol-derived phosphorane 1033 with aldehyde 1032 to give olefin 1034 as an E/Z isomeric mixture. This is of no consequence, since the double bond is eventually reduced. Transformation of the stigmasterol steroid unit to the 7,8-didehydrocholesterol derivative 1035 followed by photochemical—thermal isomerization furnishes the vitamin D3 framework. 

---