Salicin-Salicoside; Salicyl alcohol glucoside; Saligenin β-D-glucopyranoside

2.2.3 Salicin

Synonyms Salicoside; Salicyl alcohol glucoside; Saligenin β-D-glucopyranoside.

Biological Source It is obtained from the bark of poplar (Populus) and willow (Salix) and also found in the leaves and female flowers of the willow. It is specifically found in two species of Salix, namely: Salix fragilis and Salix purpurea , belonging to the family Salicaceae. It is also found in the root bark of Viburnum prunifolium L., family : Caprifoliacea and in Spiraea ulmaria, family: Rosaceae.

Geographical Source It grows in China, Europe and in India.

Preparation The powdered bark is macerated with hot water for several hours whereby the glucoside (salicin) and tannin are extracted collectively. The resulting liquid extract is filtered, concentrated under vacuum and treated with lead acetate to remove the tannins as a precipitate. It is subsequently treated with hydrogen sulphite to remove the excess of lead. The clear filtrate is neutralized with ammonia, allowed to concentrate, chilled to obtain the crystals of salicin. The crude salicin may be further purified by treating its solution with animal charcoal and concentrating followed by cooling.

Description It occurs as colourless crystals or prisms or scales. It has a very bitter taste. It is highly soluble in hot water and practically insoluble in ether. It is a levoratatory substance [ (α)_D:–63°].

Chemical Constituents It is hydrolysed in the presence of the enzyme emulsin by yielding one mole each of saligenin (aglycone) and D-glucose as stated below:

When hydrolysis is done in an acidic medium by boiling for a prolonged duration, two moles of saligenin combine together to provide saliretin (water insoluble) with the loss of a mole of water, which may be summarised as shown under:

Chemical Tests

1. It gives an instant bright red colour with concentrated sulphuric acid that fades out on the addition of water.

2. Its hydrolysed product saligenin gives a blue colour with ferric chloride.

3. On oxidation with potassium dichromate and sulphuric acid and heating yields salicylaldehyde having a characteristic odour.

4. It gives specific colours with the following reagents:

Frachde’s Reagent : Violet colour

Mandelin’s Reagent* : Purple red colour

Erdmann’s Reagent** : Bright red colour

Uses

1. It is used as an analgesic

2. It has been employed as a bitter stomachic.

3. It is also used as an antirheumatic agent.

4. It is used as a standard substrate in evaluating enzymes preparations containing β-glycosidase.

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Gaultherin-Monotropitoside; Monotropitin; Methyl salicylate 2-glucoxyloside

2.2.2 Gaultherin

Synonyms Monotropitoside; Monotropitin; Methyl salicylate 2-glucoxyloside.

Biological Source It occurs in the leaves of the Canadian Wintergreen plant Gaultheria procumbens L., in Monotropa hypopitys L., belonging to family Ericaceae It is also found in the bark of Betula lenta L., family Betulaceae; in Spiraea ulmaria L., and S. filipendula L., family Rosaceae.

Geographical Source It grows in the hills of India, Burma and Ceylon.

Description It has a needle-shaped star formation look when crystallised from acetone (99%). It is soluble in water and alcohol.

Chemical Constituents When gaultherin is hydrolysed with 3% H₂SO₄, it forms one mole each of methyl salicylate, D-glucose and D-xylose as shown below:

However, gaultherin (or monotropitin) on being subjected to hydrolysis by the enzyme gaultherase gives rise to the production of one mole each of primeverose [i.e.; 6- (β-D-xyloside)-D glucose] a disaccharide and methyl salicylate.

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Arbutin-Bergenia crassifolia (L.) Fritsch, family Saxifragaceae

2.2.1 Arbutin

Synonyms Ursin; Arbutoside; Uvasol; Uvaursi; Bearberry leaves; Busserole.

Biological source It occurs in the dried leaves of Bergenia crassifolia (L.) Fritsch, belonging to the family Saxifragaceae.

It is also obtained from the dried leaves Uva-Ursi or Bearberry Arctostaphylos uva-ursi (Linné) Sprengel, belonging to family (Ericaceae) and other related plants e.g., coactylis or adenotricha Fernald and McBride (family Ericaceae). Besides, it is extracted from the leaves of blueberry, cranberry and pear trees (Pyrus communis L., family; Rosaceae).

Geographical Source Bearberry is mostly grown in various parts of North and Central Europe, North America, Canada and Scotland.

Description Arbutin occurs in white needles that are promptly soluble in water and ethanol. It is very hygroscopic in nature.

Chemical Constituents The structure of arbutin is given below:

It has a β-D-glucopyranoside function attached to the para position of a phenol.

It yields upon hydrolysis, either by dilute acids or by emulsin, one mole each of D-glucose and hydroquinone.

Besides, the leaves also contain methyl arbutin, quercetin, gallic acid, ursolic acid and tannin. However, arbutin forms a complex with hexamethylenetetramine that may be used as a means to separate it from methylarbutin.

Chemical Tests

1. Arbutin yields a blue colouration with ferric chloride solution.

2. Its presence in crude drug may be detected by frist moistening the powdered tissues with dilute HCl, warming cautiously over a watch glass on a low flame and carefully collecting the sublimate as crystals of hydroquinone that forms on another watch glass.

Important Features The presence of gallotannin usually helps in preventing certain specific enzyme, for instance: b-glucosidase from splitting arbutin that justifiably explains why the crude plant extracts are more effective therapentically, as compared to pure arbutin.

Uses

1. It is used as a diuretic.

2. It finds its application as an antiseptic agent on the urinary tract.

3. It also exerts astringent actions.

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Phenol Glycosides

2.2 Phenol Glycosides

A variety of phenol glycosides are widely distributed in nature. It has been found that quite a few simple phenol glycosides have their aglycone portion loaded with either phenolic moieties or more often with alcoholic moieties or carboxylic acid functions. Invariably, the natural vegetative plant products, such as: Willow bark (containing Salicin) and Bearberry leaves (containing arbutin) have been employed therapeutically since ages, the former as antipyretic and the latter both as urinary antiseptic and as diuretic.

A few frequently used phenol glycosides commonly found in natural plant products are described below; such as: Arbutin; Gaultherin; Salicin; Populin; Glucovanillin.

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Inhibition of Tumor Cells Interacting with Stromal Cells by Xanthones Isolated from a Costa Rican Penicillium sp.

Shugeng Cao†, Douglas W. McMillin‡, Giselle Tamayo§, Jake Delmore‡, Constantine S. Mitsiades*‡, and Jon Clardy*†

† Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, United States

‡ Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, United States

§ Unidad Estrategica de Bioprospeccion, Instituto Nacional de Biodiversidad (INBio), Santo Domingo de Heredia, Costa Rica

J. Nat. Prod., Article ASAP

DOI: 10.1021/np2009863

Publication Date (Web): March 29, 2012

CR1642D, an endophytic isolate of Penicillium sp. collected from a Costa Rican rainforest, was identified through a high-throughput approach to identify natural products with enhanced antitumor activity in the context of tumor–stromal interactions. Bioassay-guided separation led to the identification of five xanthones (1–5) from CR1642D. The structures of the xanthone dimer penexanthone A (1) and monomer penexanthone B (2) were elucidated on the basis of spectroscopic analyses, including 2D NMR experiments. All of the compounds were tested against a panel of tumor cell lines in the presence and absence of bone marrow stromal cells. Compound 3 was the most active, with IC50 values of 1–17 μM, and its activity was enhanced 2-fold against tumor cell line RPMI8226 in the presence of stromal cells (IC50 1.2 μM, but 2.4 μM without stromal cells).

full text article 

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Senna-Senna leaf; Sennae folium; Tinnevelley Senna; Indian Senna

2.1.5 Senna

Senna was first used in the European medicine as early as the 9th or 10th century by the Arabs. An Egyptian native Issae Judaeus (850 to 900 A.D.) was reported to be the pioneer in bringing and introducing the drug to Egypt from Mecca,

Synonyms Senna leaf; Sennae folium; Tinnevelley Senna; Indian Senna;

Biological Sources Senna is the dried leaflets of Cassia senna L. (Cassia acutifolia Delile, (Alexandria senna), or of Cassia angustifolia Vahl (Indian or Tinnevelley Senna) belonging to the family Leguminoseae. However, the modern taxonomists recommend to club together both the commonly available species of senna, namely: Alexandria senna and Thinnevelley senna—under one name as Senna alexandria Mill.

Geographical Source C. acutifolia grows wild in the vicinity of Nile River (Egypt) extending from Aswan to Kordofan; whereas, C. angustifolia grows wild in the Arabian Peninsula, Somalia, India, and Northwest Pakistan. In India the drug is cultivated in Southern part- Tinnevelly, Mysore and Madurai; Northern part- Jammu, Western part Pune and Kutch region of Gujrat.

Preparation After a duration of 2-3 months of sowing the Alexandra senna is harvested both in April and in September by cutting off the tops of the plants approximately 15 cm from the ground level and subsequently allowing them to dry in the sun. Later on, the unwanted stems and pods are segregated from the leaflets with the help of sieves using mechanical vibrators. The portion that passes through the sieves, is now ‘tossed’ carefully, whereby the leaves are colleted on the surface and the relatively heavier stalk fragments at the bottom. The dried leaves are now graded, packed in bags and stored in dry place. The commercial drug at present is distributed through Port Sudan located on the Red Sea, and from the Port of Tuticorin, in India.

Description

Features Alexandria senna Tinnevelley senna

Colour : Pale greyish green Yellowish green

Odour : Slight Slight

Taste : Mucilagenous slightly bitter Mucilagenous, bitter and

and characteristic characteristic

Size : Length = 2-4 cm, Length = 2.5-5cm

Width = 7-12 mm; Width = 3-8 mm

Shape : Ovate -lanceolate; Lanceolate

Texture : Thin and brittle Thin and flexible

Chemical Constituents The principle active constituents of senna are four sennosides A, B, C and D, which are the dimeric glycosides having their aglycones composed of either rhein and/or aloe-emodin moieties i.e.; 10, 10’-bis (9, 10-dihydro-1, 8-dihydroxy-9-oxoanthracene-3-carboxylic acid). The structure of the above four glycosides are as given below:

Besides, relatively small quantities of monomeric glycosides and free anthraquinones are also present in senna pods, such as: rhein–8-glucosides, rhein-8-diglucoside, aloe emodin-8-glucoside, aloe-emodin anthrone diglycoside, rhein, aloe-emodin and isorhamnetin.

It also contains kaempterol (a phytosterol), mucilage, resins, myricyl alcohol, chrysophanic acid, calcium oxalate and salicylic acid.

Specific method of extraction for the sennosides: Exclusively for commercial purposes, the sennosides are extracted as their corresponding calcium sennosides in varying strengths because of its enhanced stability.

Methodology: The drug powder (about 80-100 mesh size) is duly macerated with either 80% acetone or 90% methanol for a period of 6 hours, followed by 2 hours with cold water. This process helps to achieve an extract that contains between 17-18% sennosides and enables to extract about 65% of sennosides from the crude drug.

The sennosides and other anthracene derivatives may be extracted by the help of a mixture of polyethylene glycols (in 70% v/v ethanol) and solutions of non-ionic surfectants.

However, the isolation of individual sennosides may be achieved by employing non-polar synthetic resins having porous structural features. Alternatively, the drug powder is macerated with citric acid in methanol which is followed by a repeated extraction with a mixture of methanol, toluene and ammonia. The resulting extract is treated with a concerntrated solution of calcium chloride to salt out the sennosides as their respective calcium salts.

Chemical Tests

1. Modified Borntrager’s Test: It gives a pink to red colouration for the presence of anthraquinone glycosides (see under section 4.2.1.1).

2. The mucilage of senna gives a distinct red colouration with Ruthenium Red solution.

Substituents and Adulterants Tinnevelley senna is invariably found to be adulterated with the

following three cheaper varities of senna namely:

(a) Dog senna ie; Cassia abovata,

(b) Palthe senna ie; Cassia auriculatad, and

(c) Arabian Senna or Mecea senna or Bombay senna i.e.; wild variety of Cassia angustifolia Vahl. from Southern Arabia.

Dog senna : It contains approximately 1% of anthraquinone derivatives.

Palthe senna : It contains no anthraquinone glycosides

Arabian senna : It is brownish-green in appearance.

Uses

1. Senna and its branded preparations, for instance: Glaxenna^R (Glaxo); Pursennid^(R) (Sandoz); Helmacid with senna^(R) (Allenburrys); are usually employed as purgative in habitual constipation. The glycosides are first absorbed in the small intestinal canal after which the aglycone portion gets separated and ultimately excreted in the large intentine (colon). The released anthraquinones irritate and stimulate the colon thereby enhancing its peristaltic movements causing bulky and soft excretion of faces.

2. The inherent action of senna is associated with appreciable griping , and therefore, it is generally dispensed along with carminatives so as to counteract the undesired effect.

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Frangula-Buckthorn bark; Alder buckthorn; Black dogwood; Berry alder; Arrow wood; Persian berries

2.1.4 Frangula

Synonyms Buckthorn bark; Alder buckthorn; Black dogwood; Berry alder; Arrow wood; Persian berries;

Biological Source Frangula bark is the dried bark of Rhamnus frangula Linne belonging to the family Rhamnaceae.

Geographical Source The plant is a shrub which grows abundantly in Europe, the Mediterranean coast of Africa and Western Asia.

Preparation The preparation of frangula bark resembles to that of cascara bark (see section 2.1.3). Just like the cascara bark, the frangula bark must be aged for at least a period of one year before it is used therapeutically so as to permit the reduced forms of the glycosides with harsh action to be oxidised to comparatively milder forms.

Chemical Constituents The seed, bark and rootbark of Rhamnus species, specifically in Alder Buckthorn (Rhamnus alnifolia L’ Her.); in Rhamnus carthartica L., in Rhamnus purshiana DC (Cascara sagrada) consists of the two important glycosides Frangulins A and B, which were initially thought to be isomeric compounds. Later on two more glycosides known as glucofrangulns A and B have also been reported . However, the structures of Frangulins A* and B** along with Glucofrangulins A and B are given below:

Besides, frangulin the frangula bark contains emodin (see Section 4.2.1.2) and chrysophanic acid as shown below:

--------------------------------------------------

* Horhammer, Wagner, Z. Naturforsch, 27B, 959, 1972.

** Wagner, Demuth, Tetrahedron Letters, 5013, 1972.

Substituents/Adulterants As the activity of Frangula Bark corresponds to that of cascara sagrada, it finds a good substitute and comparable usage in Europe and the Near East. Interestingly, the drug substances obtained from the ripe and duly dried fruits of Rhamnus catharticus Linn., are invariably employed in Europe and the Near East for their recognised cathartic therapeutic activity.

Uses It is mostly used as a cathartic.

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Cascara Sagrada-Sacred bark; Chitten bark; Chittin bark; Purshiana bark; Persian bark; Bearberry bark; Bearwood; Cascara bark; Cortex Rhamni purshianae

2.1.3 Cascara Sagrada

Interestingly, the very name ‘cascara sagrada’ is Spanish for the sacred bark; Rhamnus is the ancient classical name for buckthorn, and Purshianus was attributed as a mark of honour and respect to the great German botanist Friedrich Pursch.

Synonyms Sacred bark; Chitten bark; Chittin bark; Purshiana bark; Persian bark; Bearberry bark; Bearwood; Cascara bark; Cortex Rhamni purshianae.

Biological Source Cascara sagrada is the dried bark of Rhamanus purshiana DC., belonging to

family Rhamnaceae, from which a naturally occurring cathartic is extracted. It is usually collected at least one year prior to its use.

Geograhical Source It is invariably obtained from cultivated as well as wild shrubs and small trees grown in Northern Idaho, West to Northern California, North Carolina, Oregon, in Kenya and Western Canada.

Preparation The bark is collected, during the dry season (April to August) from the 8 to 9 years old trees that have gained a height of 16-18 meters with their stems having a diameter of 8 to 10 cm, by inflicting longitudinal incisions on the fully developed stems. In usual practice, the coppicing technique is employed for the collection of bark. The bark is carefully stripped off from the branches and the stems. They are subsequently allowed to dry in shade by putting their inner-surface facing the ground so as to permit the completion in the enzymatic conversion of the anthranol derivative i.e., glycosides (an emetic principle) to its anthraquinone derivative usually present in the fresh drug, thereby exerting a milder cathartic activity. During this span of one year the drug must be duly protected from rain or humid environment so as to check the growth of mould.

Description

Colour : Outside-purplish brown; Inside reddish brown.

Odour : A typically nauseatic odour.

Taste : Persistently bitter.

Size : Occurs in varying sizes of thickness between 1 to 4 mm.

Shape : Mostly occurs in quills or channels. Also available in small, flat and broken segments.

However, internally the bark exhibits longitudinal striations; whereas externally the bark appears to be quite smooth and usually displays the presence of seattered lenticles, lichens and cork. Besides, mostly insects and liveworts are found on the exterior surface of the bark.

Chemical Constituents The cascara sagrada bark is found to contain two major types of anthracene compounds, namely:

(a) Normal O-Glycosides These are based on emodin like structures and constitute about 10 to 20% of the total glycosides, and

(b) Aloin-like C-Glycosides These comprise of about 80 to 90% of the total glycosides.

The two C-glycosides are known as barbaloin and deoxybarbaloin (or chrysaloin) as given below:

The main active constituents are four glycosides usually designed as Cascarosides A, B, C and D. From extensive and intensive studies of these cascarosides by optical rotary dispersion (ORD) technique it has been established that the cascarosides A and B are solely based on optical isomers of barbaloin ; whereas cascarosides C and D on optical isomers of deoxybarbaloin. However, from a close inspection of all the four basically primary glycosides of barbaloin and deoxybarbaloin it may be revealed that they possess the characteristic features of O-glycosides as well as C-glycosides.

Salient Features The sailent features of the various glycosides are as follows:

(i) About six anthracene derivatives isolated and identified in the drug belong to the category of O-glycosides which are solely based on emodin,

(ii) Dried cascara bark normally produces not less than 7% of the total hydroxyanthracene derivatives, calculated as cascaroside A, and

(iii) The remaining cascarosides must make up at least 60% of this total quantum.

Perhaps the presence of a ‘lactone’ in the drug attributes a bitter taste to it.

Casanthranol is the purified version of a mixture of anthranol glycosides highly water-soluble and duly extracted from cascara sagrada. It has been reported that each gramme of casanthanol contains not less than 200 mg of the entire hydroxyanthracene derivative, calculated as cascaroside A, out of which not less than 80% of the respective derivatives mainly consists of cascarosides.

Chemical Test It gives a positive indication with Modified Borntrager’s test because of the presence of C-glycosides.

Substituents/Adulterants The barks of Rhamanus californica and R. fallax are generally used as a substitute for cascara sagrada bark. Sometimes the frangula bark is also used as a substitute for this drug. However, the former types of barks (Rhamnus species) exhibit a more uniform coat of lichens along with broader medullary rays when compared to the original drug species.

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Rhubarb-Rheum; Radix rhei; Rhubarb rhizome

2.1.2 Rhubarb

Synonyms: Rheum; Radix rhei; Rhubarb rhizome.

Biological Source: Rhubarb is the rhizome and roots of Rheum officinale Bail., R. palmatum L., Rheum emodi Wall ; R. webbianum Royle, belonging to the family Polygonaceae. The rhizome and roots are mostly collected from 6-7 year old plants just prior to the following season. They are commercially available either with intact cortex or partially decorticated.

Geographical Source It is obtained largely from cultivated as well as wild species of Rhubarb grown in regions extending from Tibet to South East China. It is also found in Germany and several European countries. In India it is grown extensively in Kashmir, Kullu, Sikkim, Uttar Pradesh, Panjab. It is also found in Nepal. It is cultivated in Southern Siberia and North America.

Preparation The rhizomes are collected either in spring or in autumn from 6 to 10 year old plants., grown at an altitude of more tha 3, 000 meters. These are duly cleaned, decordicated and dried. The relatively larger rhizomes are cut into small pieces either longitudinally or transversely. The cut fragments are threaded and dried in the shade. They are also dried artifically in an atmosphere of hot wooden boxes and exported for commercial consumption.

Description Rhubarb is usually found to be compact, rigid, cylindrical conical or barrel shaped with 8-10 cm length and 3-4 cm thickness. They appear to be mostly longitudinally wrinkled, ridged or furrowed; whereas a few of them do exhibit transverse annulations or wrinkles. Interestingly, the flat pieces are prepared from large rhizomes that are normally cut longitudinally and, therefore, they appear to be largely as plano-convex with tapering at both ends. These two varieties of pieces possess a sharp characteristic odour and a bitter astringent taste. The surface is often smeared with a bitter yellowish powdery substance, which on being removed gives rise to a rather smooth surface that appears to be pale brown to red in colour.

Chemical Constituents Rhubarb essentially contains mainly the anthraquinone glycosides and the astringent components. The former range between 2 to 4.5% and are broadly classified into four categories as stated below:

(a) Anthraquinones with —COOH moiety—e.g., Rhein; Glucorhein;

(b) Anthraquinones without —COOH moiety—e.g., Emodin; Aloe-Emodin; Chrysophanol; Physcion;

(c) Anthrones and Dianthrones of Emodin—as shown below:

(d) Heterodianthrones—e.g. Palmidin A, B, and C, which are produced from two different anthrone molecules, as stated under:

Palmidin A : Aloe-emodin anthrone + Emodin anthone

Palmidin B : Aloe-emodin anthrone + Chrysophanol anthrone

Palmidin C : Emodin anthrone + Chrysophanol anthrone

However, the astringet portion of rhubarb chiefly comprises with the following components, namely: gallic acid as α- and β-glucogallin; tannin as d-catechin and epicatechin.

Rhubarb in addition to the above constituents, consists of rheinolic acid, pectin, starch, fat and calcium oxalate. The calcium oxalate content ranges between 3-40% in various species of rhubarb which reflects directly on the corresponding ash values (i.e., total inorganic contents).

Chemical Tests

1. The Rhubarb powder on being treated with ammonia gives rise to a pink colouration.

2. Rhubarb gives a blood-red colouration with 5% potassium hydroxide.

3. It gives a positive indication with modified Borntrager’s test (see under Aloes).

Uses

1. It is used mainly in the form of an ointment in the treatment and cure of chronic eczema, psoriasis and trichophytosis—as a potent keratolytic agent.

2. It is employed as a bitter stomachic in the treatment of diarrhoea.

3. It is also used as a purgative.

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Aloes

2.1.1 Aloes

Synonym: Aloe

Biological Source: Aloe is the dried latex of leaves of various species of Aloes, namely:

Aloe barbadensis Miller (or Curacao Aloe);

Aloe ferox Miller (or Cape Aloe);

Aloe perryi Baker (or Socotrine Aloe);

Aloe africana Miller and Aloe spicata Baker (or Cape Aloe).

All these species belong to the family Liliaceae.

Geographical Source

Curacao, Barbados, Aruba : Curacao Aloes or Barbados Aloes and Bonaire (West Indian Islands)

Cape Town (South Africa) : Cape Aloes

Socotra and Zanzibar Islands : Socotrine or Zanzibar Aloes

It is also cultivated in Europe and the North West Himmalayan region in India.

Preparation

General Method The leaves are transversely cut at the base and the incised ends placed downwards in a ‘V’ shaped trough having a hole at its bottom. The latex drains down the trough and is collected in individual receptacles placed beneath. The latex is evaporated in a kettle made of copper till it attains such a consistency that it may be poured into metallic ingots where it gets solidified. When the latex is concentrated gradually and then cooled slowely, it gives rise to an opaque product. The aloe thus obtained is termed as ‘hepatic’ or ‘livery’ aloe. If the latex is concentrated rapidly, followed

by sudden cooling the resulting product appears to be transparent and relatively brittle in nature. The broken surface has a vitreous or glassy surface. Such a product is commonly known as ‘vitreous’, ‘lucid’ or ‘glassy’ aloe.

Description

Chemical Constituents Aloe-emodin occurs in the free state and as a glycosides in various species of Aloe and also in Rheum (Rhubrb). Curaeao aloes contains about two and half times the amount of aloe emodin when compared to cape-aloes.

Interestingly, the glycosides of anthranols, dianthrones, and oxanthrones i.e., the reduced

derivatives of anthraquinones, invariably found in various plant substances. These plant products do make an appreciable contribution to the inherent therapeutic values of the naturally occurring substances. The structural relationships of emodin are represented as shown in Figure 4.3.

Both anthrones and anthranols mostly occur either as free or combined as glycosides. From a close look at their respective structures it may be observed that they are reduced anthraquinone derivatives. Both anthrone and anthranol are isomeric in nature; however, the latter may be partially converted to the former, which is essentially a non-fluorecent substance and is not soluble in alkaline solutions. Generally, the anthrones are converted on oxidation into their corresponding anthraquinones, namely: oxanthrone and dianthrone. Hence, it has been observed that prompt oxidation usually takes place in the powdered crude drug rather than the rhizomes itself.

Besides, aloin (or barbaloin) the aloes also contain isobarbaloin (Curacao aloes), β-barbaloin) = (Cape aloes), aloe emodin and resins. The principal resin present in the aloes is known as aloesin.

γ-Coniceine, which is a piperidine alkaloid is found in Aloe gililandii, A. ballyi, and A. ruspoliana (Liliaceae)

Aloe yields not less than 50% of water soluble extractives. It also contains volatile oil to some extent that imparts a characteristic odour to it.

Chemical Tests The overall chemical tests for aloes may be divided into two separate heads, namely: (a) General Tests, and (b) Special Tests

(a) General Tests: For this prepare a 0.1% (w/v) aqueous solution of aloes by gentle heating, add to it 0.5g of Kiesulgur and filter through. Whatman Filter Paper No. 42 and preserve the filtrate for the following tests:

1. Borax Test (or Schoenteten’s Reaction): To 5 ml of the above test solution add 0.2 g of pure borax and heat gently till it gets dissolved. Transfer a few drops of the resulting solution into a test tube filled with distilled water, the appearance of a green coloured fluoroscence due to the formation of aloe emodin anthranol shows its presence.

2. Bromine Test: When equal volumes of the test solution and bromine solution are mixed together, it yields a pale-yellow precipitate due to the production of tetrabromaloin.

3. Modified Borntrager’s Test: It is known that aloin (or barbaloin) belongs to the class of Cglycoside which does not undergo hydrolysis either by heating with dilute acid or alkali, but it may be decomposed with ferric chloride due to oxidative hydrolysis. Hence, the Modified Borntrager’s test employing FeCl₃ and HCl is used as stated below:

First of all heat together 0.1 g of powdered aloe with about 2 ml of FeCl₃ solution(5% w/v) and 2 ml of dilute HCl (6N) in a test tube over a pre-heated water bath for 5 minutes. Cool the contents and extract the liberated anthraquinone with carbon tetrachloride. Now carefully separate the lower layer of CCl₄ and add to it ammonia solution. The appearance of a rose-pink to cherry red colour confirms its presence.

(b) Special Tests

1. Nitrous Acid Test: Crystals of sodium nitrite together with small quantity of acetic acid when added to 5 ml of the above test solution of aloe, the following observations are noted:

(a) Curacao Aloes: A sharp pink to caramine colour due to the presence of isobarbaloin.

(b) Cape Aloes: A faint pink colour due to isobarbaloin.

(c) Socotrine and Zanzibar aloes: Colour comparatively lesser change in colour.

2. Nitric Acid Test: The Test solution of aloes when made to react with nitric acid, it gives rise to various shades of colour due to different types of aloes available commercially as shown below:

Caracao Aloe : Deep brownish red

Cape Aloes : Initial brownish colour changing to green

Socotrine Aloes : Pale brownish yellow

Zanzibar Aloes : Yellowish brown

3. Cupraloin Test (or Klunge’s Isobarbaloin Test): To 10 ml of a 0.4% (w/v) aqueous solution of aloe add a drop of the saturated solution of copper sulphate, immediately followed by 1 g of NaCl and 20 drops of ethanol (90% v/v). It produces different shades of colours depending on the variety of aloes used:

Carocao Aloes : A wine red colour lasting for few hours,

Caoe Aloes : A faint colouration changing to yellow quickly,

Socotrine Aloes : No colouration

Zanzibar Aloes : No colouration

Uses

1. Though, both aloes and aloin are official drugs, the former is mostly used as a purgative by exerting its action mainly on colon, whereas the latter is generally prepared over the former now-a-days.

2. Aloes find its usefulness as an external aid to painful inflammatory manifestations.

3. It constitutes an important ingredient in the ‘Compound Tincture of Benzoin’ (or Friar’s Balsam).

4. Aloe gel made from the mucilaginous latex of A. vera is frequently employed in the treatment and cure of radiation burns to get immediate relief from itchings and pains.

5. Aloe usually causes gripping and is, therefore, administered along with carminatives.

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Anthracene Glycosides (or Anthraquinone Glycosides)

2.1 Anthracene Glycosides (or Anthraquinone Glycosides)

Anthracene glycosides represent a major class of glycosides. They are abundantly found in various dicot plant families, such as: Ericaceae, Euphorbiaceae, Leguminoseae, Lythreaceae, Polygonaceae, Rhamnaceae, Rubiaceae and Verbenaceae to name a few. Interestingly, some monocots belonging to the family Liliaceae also exhibits the presence of anthracene glycosides. Besides, they are also present in certain varieties of fungi and lichens.

A plethora of glycosides having their aglycone moieties closely related to anthracene are present in noticeable amounts in a variety of drug substances, for instance: aloe, cascara, frangula, sagrada and senna. These drugs are invariably employed as cathartics.

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CLASSIFICATION GLYCOSIDES

2 CLASSIFICATION

In reality, the most befitting classification of glycosides is rather a hard-nut-to-crack. In case, the classification is to be governed by the presence of sugar moiety, a good number of rare sugars are involved, if the aglycone function forms the basis of classification, one may come across groups from probably all major categories of plant constituents identified and reported. Of course, a therapeutic classification offers not only a positive edge over the stated classification but also affords an excellent means from a pharmaceutic viewpoint, but it grossly lacks a host of glycosides which are of great pharmacognostic interest.

The most acceptable classification of glycosides is based on the chemical nature of the aglycone moiety present in them, namely:

(i) Anthracene glycosides

(ii) Phenol glycosides

(iii) Steroid glycosides

(iv) Flavonoid glycosides

(v) Coumarin and Furanocoumarin glycosides

(vi) Cyonogenetic glycosides

(vii) Thioglycosides

(viii) Saponin glycosides

(ix) Aldehyde glycosides

(x) Bitter glycosides

(xi) Miscellaneous glycosides

All these different categories of glycosides would be discussed individually with appropriate examples in the sections that follows:

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C-Glycosides

1.4 C-Glycosides

The C-glycosides may be designated as shown under:

CH HO—C₆H₁₁O₅——> C—C₆H₁₁O₅ C-Glycoside

C-Glycosides are present in a variety of plant substances, such as: aloin in Aloe; cascaroside in Cascara.

(i) Aloin or Barbaloin:

(ii) Cascarosides (A, B, C and D):

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N-Glycosides

1.3 N-Glycosides

The N-glycosides may be represented as shown below:

=N—H HO—C₆H₁₁O₅——>  =N—C₆H₁₁O₅N-Glycoside

The most typical example of N-glycosides is the nucleosides, wherein the respective amino group of the base ultimately reacts with —OH group ribose/deoxyribose.

Examples: Adenosine: It is widely distributed in nature e.g.; from yeast nucleic acid.

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S-Glycosides

1.2 S-Glycosides

The S-glycosides are normally designated as below:

—SH HO—C₆H₁₁O₅——>  S—C₆H₁₁O₅S-Glycoside

The presence of S-glycosides is more or less restricted to isothiocyanate glycosides, such as: Sinigrin, obtained from black mustard seeds. (i.e., Brassica campestris Family: Cruciferae)

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O-Glycosides

1.1 O-Glycosides

The O-glycosides are usually represented as follows:

—OH  HO—C₆H₁₁O₅ ——>  —O—C₆H₁₁O₅O-Glycoside

These are most abundantly found in nature in the higher plants, such as: senna, rhubarb and frangula.

Examples: Rhein-8-glucoside obtained from rhubarb.

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INTRODUCTION GLYCOSIDES

1. INTRODUCTION

Glycosides, in general, are defined as the condensation products of sugars with a host of different varieties of organic hydroxy (occasionally thiol) compounds (invariably monohydrate in character), in such a manner that the hemiacetal entity of the carbohydrate must essentially take part in the condensation. It is, however, pertinent to state here that the polysaccharides are also encompassed in this broad-based overall definition of glycosides. The noncarbohydrate moiety is usually termed as aglycone (or aglycon), or a genin.

The rather older or trivial names of glycosides usually has a suffix ‘in’ and the names essentially included the source of the glycoside, for instance: strophanthidin from Strophanthus, digitoxin from Digitalis, barbaloin from Aloes, salicin from Salix, cantharidin from Cantharides, and prunasin from Prunus. However, the systematic names are invariably coined by replacing the “ose” suffix of the parent sugar with “oside”. The stereochemical anomeric prefix a or b and the configurational prefix (D- or L-) immediately precede the sugar nomenclature, and lastly the chemical name of the aglycone precedes the name of the sugar. It may be expatiated with the help of the following examples:

(a) Aloin (or Barbaloin): 10-Glucopyranosyl-1, 8-dihydroxy-3-(hydroxymethyl)-9 (10H)-anthracenone;

(b) Salicin: 2-(Hydroxymethyl) phenyl- -D-glucopyranoside;

(c) Amygdalin: D-Mandelonitrile–β-D-glycosido-6- β-D-glucoside;

(d) Digitoxin: 3-[0-2, 6-Dideoxy- β-D-ribo-hexopyranosyl -(1-> 4)-O-2, 6-dideoxy-β-D-ribohexopyranosyl (1->4), 2, 6-dideoxy-β-D-ribo hexopyranosyl) oxy]-14-hydroxycard- 20(22)-enolide.

Interestingly, the glycosides may be regarded as internal acetate. The two series of stereoisomeric glycosides are usually termed as β and β glycosides. Thus, taking into consideration the simple example of methyl D-glucosides, these a and b structures may be represented as shown below:

Figures 4.1 and 4.2 represent the open-chain structure, cyclic structure and boat configuration

of methyl–a-D-glucoside and methyl–β-D-glucoside respectively. In this particular instance the glycosidic likage is established by dehydration involving a hydroxy group of the aglycone portion (i.e., methyl alcohol) and the hydroxyl group on the hemiacetal carbon of the carbohydrate (in question), thereby ultimately resulting into the formation of an acetal type of structure.

α-Configuration If the —OCH₃moiety (generalized as OR′) is in opposite steric sense as the—CH₂OH moiety on C-5 (for D-family sugars), the glycosidic structure is designated as α-configuration.

β-Configuration If the -OCH₃ moiety is in the same steric sense as the CH₂OH group on C-5, the glycosidic structure is designated as β-configuration.

It has been observed that the substantial quantum of naturally occurring glycosides essentially possess the stereo-configuration. However, this observation may be further expatiated with the help of the following typical examples of β-amygdalin and β-salicin:

Sailent Features (b-Amygdalin):

(i) Glycosidic linkage is b-because it is hydrolysed by emulsin (an enzyme),

(ii) The linking oxygen is on the same side of the plane of the ring as the CH₂OH moiety on C-5.

(iii) It contains several asymmetric C atoms i.e., chiral centres, and

(iv) It is optically active.

Salient Features (b-Salicin):

1. Hydrolysed by emulsin, hence it has b-configuration,

2. The linking oxygen is on the same side of the plane of the ring as the CH2OH moiety on C-5,

3. It has several chiral centres, and

4. It is optically active.

Glycosides, are found to exert a wide spectrum of therapeutic actions, both in modern medicines and in traditional medicaments, ranging from cardiotonic, analgesic, purgative, and anti-rheumatic, demulcent and host of other useful actions.

The Glycosidic Linkages The exact point of linkage between the carbohydrate (sugar) and non carbohydrate (aglycone) moieties is an ‘oxygen bridge’ that essentially connects the reducing group present in carbohydrate to either an alcoholic or a phenolic group present in the non carbohydrate.

Such glycosides are collectively termed as O-glycosides. However, if the ‘O’ is replaced by ‘S’ it is called S-glycosides; if replaced by ‘N’ is known as N-glycosides; and if replaced by ‘C’ is termed as C-glycosides.

These four types of glycosides shall be described briefly at this juncture with appropriate examples from the domain of medicinal plants.

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