Diterpenes aglycones

Stevioside and rebaudioside A are diterpene glycosides. The sweetness is tainted with a bitter and undesirable aftertaste. The time—intensity profile is characteristic of naturally occurring sweeteners slow onset but lingering. The aglycone moiety, steviol [471 -80-7] (10), which is the principal metaboHte, has been reported to be mutagenic (79). Wide use of stevia ia Japan for over 20 years did not produce any known deleterious side effects. However, because no food additive petition has been presented to the FDA, stevioside and related materials caimot be used ia the United States. An import alert against stevia was issued by the FDA ia 1991. In 1995, however, the FDA revised this import alert to allow the importation and use of stevia as a diet supplement (80), but not as a sweetener or an ingredient for foods. Several comprehensive reviews of stevia are available (81,82). 

Recently, Mander and coworkers [122] reported the total synthesis of sordaricin (4-347), the aglycone of the potent antifungal diterpene sordarin which was first isolated in 1971 from the ascomycete Sordaria araneosa. Two approaches were explored the first method utilized a possible biogenetic Diels-Alder reaction the second was based on a domino retro-Diels-Alder/intramolecular Diels-Alder process. Thus, heating of 4-348 led, with extrusion of cyclopentadiene, to a 1,3-butadiene as intermediate which underwent an intramolecular Diels-Alder reaction to give the desired 4-349 as the main product, together with a small amount of 4-350 (Scheme 4.77). 

Nonacosanol,beta-D-glucoside of beta-sitosterol, sugiol (a diterpene ketone), and several glycosides and aglycones have been isolated. 

Several cwt-kaurenoid diterpene glycosides with steviol as a common aglycon have been isolated from Stevia rebaudiana, which is native to subtropical and tropical South America and Central America.23-27 Among the... 

Fig. 2A In a Steviae folium BuOll extract (.1) the. sweet-tasting diterpene glycosides are found as four grey zones in the R, range 0.1-0.3 with rebaudioside A (T2) at R, 0.2 and stevioside (Tl) at R, 0.3. The three weak grey zones in the upper R, range 0,75 up to the. solvent front are due to less polar diterpene glycosides and aglycones.

Pseudopterosins. Diterpene glycosides (P A-L) from the sea whip Pseudopterogorgia elisabethae living in the tropical Atlantic. P occur as aglycones not only in the form shown but also as the 7)8-epimers and the enantiomers. The sugar residue at 0-8 or 0-9 can be D-xylo-, L-fuco-, and D-arabinopyranosyl which may be acetylated in the 2-, 3-, or 4-position. 

Figure 7.29 Citrus fruit are a rich source of terpenoids including the Cio diterpenes (+)- and (—)-limonene and a number of more complex limonoids which are distinctive in that the glucosides are tasteless while the aglycones have a bitter taste.

Figure 32. Stevia diterpene, stevioside, its aglycone, steviol, and a mutagenic derivative, 15-oxo-steviol.

Kohda, H., O. Tanaka, and K. Nishi Diterpene—glycosides of Stevia paniculata Lag. Structures of aglycones. Chem. Pharm. Bull. 24, 1040 (1976). 

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