Chemical constituents of Asparagus.

Asparagus species (family Liliaceae) are medicinal plants of temperate Himalayas. They possess a variety of biological properties, such as being antioxidants, immunostimulants, anti-inflammatory, antihepatotoxic, antibacterial, antioxytocic, and reproductive agents. The article briefly reviews the isolated chemical constituents and the biological activities of the plant species. The structural formula of isolated compounds and their distribution in the species studied are also given.

INTRODUCTION

Asparagus species, belonging to the family Liliaceae, are native medicinal shrubs valued for their medicinal properties. The genus Asparagus includes about 300 species around the world. The roots of Asparagus are the main source of the drug shatawar, the crude drug also used for increasing the secretion of milk and improving appetite in lactating women. Ripe fruits of Asparagus curillus cause abortion, tuberous roots with honey are given in dysuria, diabetes, and dysentery.[1] The roots of Asparagus racemosus are bitter, sweet oleaginous, cooling, and indigestible, appetizer, and are useful in dysentery, tumors, inflammation, biliousness, leprosy, epilepsy, and night blindness.[2] In Unani system, the roots are used as laxatives, tonic, aphrodisiac, galactogogue, and in disease of kidney and liver. Shoots contain thiophene, thiazole, aldehyde, ketone vanillin, asparagusic acid, and its methyl and ethyl esters used as flavors. Flowers and mature fruits contain quercetin, rutin (2.5% dry basis), and hyperoside, and the leaves contain diosgenin and quercetin-3-glucuronide. A. racemosus roots mainly contain 4 saponins, for example, shatavarin I–IV, the glycosides of sarsasapogenin. Roots of A. racemosus are also used against jaundice.

The bark exhibited antibacterial and antifungal activity. The powdered roots contain 2.95% protein, 5.44% saponins, 52.89% carbohydrate, 17.93% crude fiber, 4.18% inorganic matter, and 5% oil. The root of Asparagus officinalis is more diuretic than its shoot, and the root is recommended in dropsy and is a powerful cardiac sedative. Its roots have been used as a remedy for schistosomiasis and tuberculosis. The roots of Asparagus filicinus are considered as tonic, astringent, and vermifuge. In India and China, this plant is given as a powerful diuretic in cholera and rheumatism.[3] Ancient Grecians and Romans used Asparagus for its diuretic properties. It helps flush out the kidneys and help in the prevention of the formation of kidney stones. Chinese pharmacists save the best Asparagus roots for their families and friends, believing that it will increase feelings of compassion and love. In India, it is used to promote fertility, reduce menstrual cramping, and increase milk production in nursing mothers. Asparagus acts to increase cellular activity in the kidneys and thus increases the rate of urine production.

CHEMICAL CONSTITUENTS

The major bioactive constituents of Asparagus are a group of steroidal saponins. This plant also contains vitamins A, B1, B2, C, E, Mg, P, Ca, Fe, and folic acid. Other primary chemical constituents of Asparagus are essential oils, asparagine, arginine, tyrosine, flavonoids (kaempferol, quercetin, and rutin), resin, and tannin.

Shatavarin IV is a glycoside of sarsasapogenin having 2 molecules of Asparagus rhamnose and 1 molecule of glucose [Figure 1]. The major bioactives (Chemical constituents) of Asparagus species are shown in Figure 2. Sarsasapogenin and shatavarin I-IV are present in roots, leaves, and fruits of Asparagus species. Synthesis of sarsasapogenin in the callus culture of A. racemosus was also reported.[4] A new isoflavone, 8-methoxy-5,6,4’-trihydroxyisoflavone-7-O-β-D-glucopyranoside was also reported from A. racemosus previously.[5] The isolation and characterization of polycyclic alkaloid called asparagamine,[6] a new 9,10-dihydrophenanthrene derivative named racemosol and kaempferol were also isolated from the ethanolic root extract of A. racemosus.[7] Oligofurostanosides (curillins G and H) and spirostanosides (curilloside G and H) [Figure 2] have been isolated from the roots and sarsasapogenin from leaves of A. curillus. Isolated compounds and biological activities of Asparagus species are listed in Table 1.

Figure 1

Structures of sarsasapogenin and its glycosides

Figure 2

Isolated compounds from Asparagus species

Table 1

Isolated compounds and activities of the different parts of Asparagus species

PROPERTIES

The structural complexity of saponins results in a number of physical, chemical, and biological properties. Saponins are usually amorphous substances having a high molecular weight. These are soluble in water and produce foam but organic solvents, such as chloroform, acetone, and ether inhibit their foaming property. Solubility of saponins is also affected by the properties of the solvent (as affected by temperature, composition, and pH), whereas water, alcohols (methanol, ethanol), and aqueous alcohols are the most common extraction solvents for saponins. Due to the presence of a lipid-soluble aglycone and water soluble sugar chain in their structure (amphiphilic nature), saponins are surface active compounds with detergent, wetting, emulsifying, and foaming properties. In aqueous solutions surfactants form micelles above a critical concentration called critical micelle concentration (cmc).

Saponins possess a variety of biological properties, namely, being antioxidants, immunostimulants, antihepatotoxic, antibacterial, useful in diabetic retinopathy, anticarcinogenic, antidiarrheal, antiulcerogenic, antioxytocic, and reproductive agents. Many saponins are known to be antimicrobial to inhibit mould and to protect plants from insects. They may be considered as defense system and have been included in a large group of protective molecules found in plants named phytoanticipins or phytoprotectants. Saponin-rich plants have been found to improve growth, feed efficiency, and health in ruminants.[8]

CONCLUSION

The literature survey revealed that the steroidal saponins are the main biologically active constituents of genus Asparagus. There is a wide disparity in the structures of bioactive compounds ranging from sulfur containing carboxylic acids, chalcones, steroidal sapogenins, and saponins.