Aglycone skeletons

Chromatographic analysis of glycoalkaloids can be performed in a number of ways (321,322). The intact compounds can be analyzed by GC after derivatization (323). After hydrolysis the aglycone skeleton can be examined by GC without the need of derivatization (324). For routine determinations of the glycoalkaloids present in potato tubers, HPLC is probably the method of choice. Column acidity caused by active silanol sites on the packing surface strongly influences the chromatographic separation of Solanum alkaloids. In fact, basic compounds react with... 

Figure 1. Aglycone skeletons of fungitoxic steroidal saponins and Solanum glycoalkaloids.

Acyl carrier protein, fatty acid synthase sequence, 45-46 Acyl carrier protein derivatives, desaturation, 13,l4f Acyl lipids, formation, 47-48 Aglycone skeletons saponins, 288f Solanum glycoalkaloids, 288f... 

For our anthracycline synthesis, the anionic cycloaddition reaction of the homophthalic anhydrides and quinone dienophiles, leading to the aglycone skeletons of anthracyclines, plays a key role. Table 1 shows the results of the cycloaddition reactions of the homophthaUc anhydrides with quinone... 

The oxidative formation of p-benzoquinones from anilides such as 7-108 was used for the synthesis of the core scaffold of the natural products elisabethin A (7-106) and pseudopterosin A aglycone (7-107) (Scheme 7.30). Exposure of anilide 7-108 to DMP [53] led to the formation of the o-imidoquinone 7-109, which underwent an intramolecular Diels-Alder reaction to give 7-110 in 28% yield after hydration. In a competitive pathway, the p-quinone 7-111 is also formed from 7-108, which on heating in toluene again underwent an intramolecular Diels-Alder reaction to give cycloadduct 7-112 in 25% overall yield. Hydrolysis of 7-112 furnished the carbocyclic skeleton 7-113 of elisabethin A (7-106). 

An interesting approach to unususal glycosides (with relatively large carbocyclic aglycon) from lactose was proposed by Thiem s group.85 They postulated a conversion of the glucose part into the cyclooctanone skeleton (Fig. 64). Similar approach to the glucose derivative provided non-substituted cyclooctane.86... 

Ginsenosides with a few exceptions share a similar basic structure, consisting of a saturated 1,2-cyclopentanoperhydrophenanthrene (sterane or gonane) steroid nucleus. They are classified into two groups by the skeleton of aglycones, namely dammarane-type and oleanane-type. Ginsenosides... 

A C9-C14 cycHzation forms the ring C and leads to the amphilectane skeleton which is foimd for instance in pseudopterosins A-F (10, aglycone) [10] isolated from Pseudopterogorgia elisabethae extracts stemming from a Bahamian collection site (Fig. 5). This class of natural products can be characterized as... 

Elisabethol (13) [4] shows the same stereochemistry as the pseudopterosin aglycone 10. Elisabatins A-C (14,15,16) [ 14] have the same amphilectane skeleton found in the aglycone portion of the pseudopterosins. The elisabatins are unique among the amphilectane-type diterpenoids because they possess an unusually high unsaturation number that leads to extended aromatic conjugation. 

Most of the triterpenoid glycosides isolated so far from holothurians present a sugar chain of two to six monosaccharide units linked to the C-3 of the aglycone, which is usually based on a holostanol skeleton [3p,20S-dihydroxy-5a-lanostano- 18,20-lactone] (1), Fig.(l) [1]. 

Flavonoids constitute a large class of polyphenols found in fruits and vegetables that share a common skeleton of phenylchromane. This basic structure allows a large number of substitution patterns leading to several subclasses of flavonoids, such as flavonols, flavones, flavanones, flavanols, anthocyanidins, isoflavones, dihydroflavonols, and chalcones. Among the diverse flavonoid subclasses, flavonols (especially quercetin) and flavanols (catechins) are the most abundant in our food. Flavonols are present in foods as diverse glycosides, whereas flavanols are usually found as aglycones. 

The biosynthesis of 1 follows a pattern seen for all bisindoles that have been biosynthetically investigated thus far [17, 163, 164] two molecules of L-tryptophan (123) are oxidized and then dimerized to give an initial bisindole skeleton (Fig. 24). Historically, the biosynthesis of staurosporine (121) has been investigated in parallel with that of rebeccamycin (124), a related bisindole. Both molecules are thought to be biosynthesized through nearly identical routes to give the aglycone... 

---