Aloe-emodin anthrone

R = C02H, rhein anthrone R = CH2OH, aloe-emodin anthrone... 

Barbaloin was first isolated in 1851, but an acceptable structure was not proposed until 1952, when Miihlemann showed that condensation of aloe-emodin anthrone Ql,8-dihydroxy-3-(hydroxymethyl)anthrone, 7, R = CH2OH] with tetra-O-acetyl-a-D-glucopyranosyl bromide in acetone in... 

The biogenesis of barbaloin has not yet been studied, but its synthesis gives rise to some legitimate speculations thereon. A phenoxide ion can be alkylated on an oxygen atom or on a carbon atom, as shown in the reaction sequence below which reaction predominates depends on the phenol, the conditions employed, and the alkylating agent used. The glycosylation of the anion from aloe-emodin anthrone is an example of reaction b, whereas... 

Isobarbaloin appears to be an isomer of barbaloin, and degradative experiments give the same results as with barbaloin thus, Ldger - has shown that, on prolonged, acid treatment, isobarbaloin gives aloe-emodin and D-arabinose. It yields aloe-emodin anthrone on treatment with aqueous borax, and consumes 2 moles of periodic acid per mole. The ultraviolet spectrum of isobarbaloin is identical with that of barbaloin, showing that it, too, has an anthrone structure. The infrared spectrum of isobarbaloin shows only minor differences from that of barbaloin. From these data, it seems likely that isobarbaloin and barbaloin differ only in their stereochemistry. 

The synthesis of barbaloin from aloe-emodin anthrone and tetra-0-acetyl-a-D-glucopyranosyl bromide leads to one product only, and no isobarbaloin is formed. It seems justified to assume that this product is a /3-D-glycopyranosyl derivative in which case, one possible explanation of the isobarbaloin-barbaloin relationship is to presume that isobarbaloin is... 

Anthraquinones have been reported to be the main active components in Cassia tora, including aloe-emodin, anthrone, aurantiobtusin, chrysophanic acid,... 

Aromatic natural products of polyketide origin are less prevalent in plants compared with microorganisms. The majority of the plant constituents that contain aromatic stmctures are known to arise from the shikimate pathway (see below). Unlike those derived from the shikimate pathway, aromatic products of the polyketide pathway invariably contain a meta oxygenation pattern because of their origin from the cyclization of polyketides. Phenolic compounds such as chrysophanol-anthrone (Bl), and emodin-anthrone (B2), and the anthraquinones, aloe-emodin (B3) and emodin (B4) (Fig. 2), are products of the polyketide pathway and are found to occur in some plants of the genera Cassia (Leguminosae) (21), Rhamnus (Rhamnaceae) (22), and Aloe (Liliaceae) (23). The dimer of emodin-anthrone (B2), namely hypericin, (B5) is a constituent of the antidepressant herbal supplement, St. John s wort (Hypericumperforatum, Hy-pericaceae) (24). 

The primary active ingredients of cascara sagrada include cascarosides A, B, C, and D, but barbaloin, chrysaloin, chryophanol, emodin, and aloe-emodin are also present (Tyler, 1994 Anonymous, 1996). The anthrone glucofrangulin is present in the cortex of the European species Rhamni frangula (De Witte, 1993). As with senna and aloe constituents, these anthrones produce an active secretion of water and electrolytes within the lumen of the small intestine. In addition, the anthrones inhibit absorption of water and electrolytes from the large intestine. This causes an increase in the volume of bowel contents, and strengthens the dilatation pressure in the intestine to stimulate peristalsis (Anonymous, 1996). 

This synergistic effect in mice results from synergistic stimulation of large intestinal transit and large intestinal water secretion [15,16], Recently, several investigations have been performed to determine whether intracaecally administered rhein-anthrone and anthraquinones such as aloe-emodin, Fig. 

The antioxidant properties of naturally occurring anthraquinones and anthrones were evaluated using different model systems. For example, the antioxidant activity of these compounds was studied on the inhibition of peroxidation of linoleic acid. These results suggest that the antioxidant mechanism for two anthraquinones, emodin, Fig. (4) and aloe-emodin, Fig. (2), possibly depends on scavenging hydroxy radicals, while the pro-oxidant... 

E Cascarae cortex (5-7) samples are characterized by anthrone glycosides two pairs of yellow fluorescent cascarosides A/B (Rf 0.05-0.15) and cascarosides C/D (R, 0.2-0.25). The cascarosides A/B dominate. The amount of yellow fluorescent aloin (T2), deoxyaloin (R, 0.65) and the red-brown fluorescent aglycones emodin, aloe-emodin, chrysophanol (solvent front) varies. Four blue fluorescent naphthalide derivatives are detectable in the R, range 0.3-0.45. 

SoiMiooideo. A group of yellow, homo- and heterodi-meric anthrone glycosides, the aglycones (sennidins) of which are derived from the monomers ifaein and aloe-emodin. 

Plants of the genus Aloe contain a reduced form of aloe-emodin as the C-glucoside of the corresponding anthrone, which is called aloin. Lemon yellow aloin is a mixture of two isomers. The major product (S)-aloin or (S)-P-D-glucopyranoside-aloe-emodin is referred to as aloin A (or barbaloin, 9-162), the (l )-isomer is aloin B (isobarbaloin). Related glycosides called aloinosides a and b contain a-L-rhamnopyranose bound by an O-glycosidic bond to the hydroxymethyl group at C-3. 

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