A review of studies on bioactive compounds isolated from Sri Lankan flora

The biodiversity of Sri Lanka based on the average number of plant species per 10,000 km has been stated to be much higher than in any other country in Asia. Despite the diversity and the potential economic value of these plants, many have not been investigated for their natural products. Also both the endemic and non-endemic plants species, which have been investigated chemically and biologically show a wide variety of bioactive compounds indicating the high economic potential of the flora. This paper reviews the studies of bioactve compounds isolated from Sri Lankan flora during the period 1980 to date.


INTRODUCTION
The World Conservation Monitoring Centre has designated Sri Lanka as a 'hotspot' in terms of its biodiversity (Caldecott et al., 1994).The indigenous flora of Sri Lanka comprises about 7,500 plant species.Of the recorded 3,154 flowering plant species, 894 (28 %) species are known to be endemic to the island (Wijesundara et al., 2012).There are also records of 336 species of pteridophytes, which include 49 endemics (MOE, 2012), 650 species of lichens belonging to the family Thelotremataceae (41 endemics), 575 mosses (endemism unknown), 303 liverworts (endemism unknown), 1920 species of fungi and some 900 species of algae (Somesekaram et al., 1997).The variety, richness and abundance of Sri Lankan flora and the high percentage of endemic plants -compared to most countries in the region -makes it an ideal location for a systematic drug discovery programme.The early botanical description of Sri Lankan plants is contained in a series of books (Trimen, 1885), which have been revised later (Dassanayake, 1996).Endemic plants in Sri Lanka are within easy access as more than 90 % of them are located in a small area of about 15,000 km 2 in the low country wet zone and the montane zone (Gunatilleke & Gunatilleke, 1990).
A large number of plants with medicinal value has been listed in a compilation, the 'Sinhalese Materia Medica' (Attygala, 1917).Information on the chemistry and the pharmacology of some Sri Lankan and Indian plants (Chandrasena, 1935) and medicinal plants used in Sri Lanka (Jayaweera, 1982) is also documented.
During the past 40 years there have been several investigations on the chemical constituents and antimicrobial and insecticidal effects of Sri Lankan plants, particularly the endemics (Bandara et al., 1989a;1989b;1990b;Hewage et al., 1997;1998).In addition the biological activity of compounds isolated from Sri Lankan lichens have also been determined (Nanayakkara et al., 2005).Tropical lichens, particularly those from Sri Lanka, continue to show a wide variety of biologically active compounds (Orange et al., 2001;Karunaratne et al., 2002;2005;Jayalal et al., 2012).Antiradical and antilipoperoxidative effects of some plant extracts used by Sri Lankan traditional medical practitioners for cardioprotection has been reported by Munasinghe et al. (2001).Arseculeratne et al. (1985) have screened fifty medicinal plants for hepatotoxic activity.In a ground breaking study, the oral hypoglycaemic activity of some Sri Lankan plants have been reported by Karunanayake et al. (1984).The alkaloids found in Sri Lankan plants and their biological activities have been reviewed by Gunatilaka (1999).
However, in many of the early studies on bioactive compounds, the activity determinations were restricted to antibacterial and mosquito larvicidal activities, which are too broad to be useful determinants of high value bioactivities such as, antioxidant, insecticidal, and anticancer activities.These compounds have become important and highly sought after.This review highlights the biological activity of compounds reported from endemic and non-endemic flora of Sri Lanka.

Antioxidant activity
Free radicals play an important role in carcinogenesis through their involvement in breaking the DNA strands.Free radicals also play a role in arteriosclerosis, malaria, in rheumatoid arthritis and could play a role in neurodegenerative diseases and the ageing process (Attaur-Rahman & Choudhary, 2001).
Free radicals are unique bioactive mediators, which account for the tonic relaxation of all types of blood vessels and nonadrenergic and noncholinergic relaxation of the gastro intestinal tract in low concentration.At high concentrations they can damage DNA, RNA, lipids and proteins leading to increased mutations and altered enzymes, which in turn lead to carcinogenesis (Halici et al., 2005).

Insecticidal activity
From the early Roman times to the mid 20 th Century pyrethrum, rotenone, nicotine, sabadilla and quassin have been used widely as insect repellents and toxins.The indiscriminate use of synthetic insecticidal compounds has led to deterioration of the environment and they also induce the build up of resistant pest populations, eliminate their natural enemies and facilitate the resultant development of secondary pests.Plants contain a wide diversity of secondary metabolites, some of which play an important role in their defense against pathogens and herbivores (Ware & Whitaker, 2004).Botanicals used as insecticides presently constitute 1 % of the world insecticide market (Rozman et al., 2007).
The investigation of biologically active constituents of Heterodermia leucomelos, a lichen collected from the mossy rocks in the Horton Plains National Park, Nuwara Eliya District, Sri lanka, has led to the isolation of mosquito larvicidal active compound, 3,6-dimethyl- 2-hydroxy-4-methoxybenzoic acid (Figure 6) (90 % moribund after 24 h at 10 ppm) (Kathirgamanathar et al., 2006).Hydroxy benzoic acids are important iron chelators (siderophores), which are secreted by some pathogenic bacteria that grow under low iron conditions (Feistner & Beaman, 1987;Karunaratne et al., 1992).It is known that polar lichen substances are secreted out into the growing medium of the lichens, leading to the intriguing hypothesis that such bioactivities may form part of the chemical defense mechanisms of lichens (Karunaratne et al., 2005).
The two butenolides (Figure 7a) and (Figure 7b) isolated from the CH 2 Cl 2 extracts of three representative species of the endemic genus Hortonia, H. floribunda, H. angustifolia and H. ovalifolia have exhibited potent mosquito larvicidal activity against the 2 nd instar larvae of A. aegypti with IC 50 values of 0.41 and 0.47 ppm, respectively, highlighting the importance and the potency of five membered ring compounds (Ratnayake et al., 2001;Piers & Karunaratne, 1983).alkaloid, N-methyl-6b-(decal-3',5'-trienyl)-3b-methoxy-2b-methylpiperidine (Figure 8), which exhibited MC 50 of 1.0 ppm and LC 50 of 2.1 ppm at 24 h against A. aegypti second instar larvae.The MC 50 and LC 50 of the compound at 24, 48 and 72 h has indicated that a very few of the moribund larvae survived, most dying after about 72 h after treatment (Bandara et al., 2000).
Bergapten (Figure 9) isolated from the stem bark of Limonia acidissima L., (Rutaceae), a medicinal plant widely distributed in Sri Lanka has tested positive for insecticidal activity against Callosobruchus chinensis L. Bergapten has reduced the emergence of adults by 100 % at 0.1 mg level (Bandara et al., 1989b;1990b).
The shot-hole borer, Xyleborus fornicatus Eichh., is a small, wood boring ambrosia beetle and is considered to be the most serious pest of Tea (Camellia sinensis var.assimica) in Sri Lanka.(+)-Usnic acid (Figure 10) has been isolated from an Usnea sp.collected from the surface of a rotting Acacia decurrens Willd., tree in Ambewela, Nuwara Eliya District, Sri Lanka.Healthy adult females of X. fornicatus exposed to different   concentrations of (+)-usnic acid have shown an effect on the growth development of beetles.At 75 and 100 ppm, only 10 and 4 mother beetles have produced progeny, respectively.The galleries constructed in the test media containing (+)-usnic acid have been observed to be of an irregular shape compared to the control (Sahib et al., 2008).
lactones, the methyl ethers of menegazziaic acid and stictic acid were isolated, in addition to glyceryl trilinolate.Usnic acid has exhibited potent antitermite activity against a common tea pest, Glyptotermes dilatatus at low elevations (Kathirgamanathar et al., 2005).
The hot petrol extracts of the roots of Croton lacciferus L., has shown significant insecticidal activity against Aphis cracciuora Koch.The extract, when chromatographed over silica gel and eluted with petrol-chloroform has yielded three ent-kauranoids, two of which are new natural products.The two new kauranoids (Figure 11a & b) have been tested using the microapplicator method for insecticidal activity against A. cracciuora maintained in the laboratory on one-weekold potted cowpea, Vigna unguiculata L. These two compounds have shown a moderate insecticidal activity against A. craccivora at a dose of 5 ppm/insect causing 61 and 62 % mortality, respectively, of adult female aphids after 24 h (Bandara et al., 1988a).
Diploclisia glaucescens (Blume) Diels (Memspermaceae) is a creeper growing in the mid-country regions of South India and Sri Lanka.Ecdysterone (Figure 12) along with a bidesmosidic triterpenoid saponin have been isolated from the methanol extract of the stem of D. glaucescens in a yield of over 0.46 %.It possessed insecticidal activity against groundnut aphid, Aphis craccivora with an LD 50 value of 18 mg/kg (Bandara et al., 1989c;d).
Croton aromaticus L., (Euphorbiaceae), a widely distributed plant in Sri Lanka, is used in ethnomedical preparations and in traditional agriculture.The air-dried and powdered roots of C. aromaticus have been subjected to sequential solvent extraction.The petroleum ether extract was chromatographed over silica gel when (-)hardwickiic acid (Figure 13) was isolated in 0.8 %.The aphidicidal activity of the compound has been evaluated using the microapplicator method.The compound at a dose of 5 ppm/insect has caused 62 % mortality of adult female aphids after 24 h (Bandara et al., 1987).

Antibacterial activity
The search for new antibiotics with hitherto unknown modes of action remains an urgent priority as microbial resistance to antimicrobial agents continues to unfold as one of the most difficult problems facing the physicians dealing with infectious diseases (Ristuccia & Cunha, 1984).Bacteria are capable of passing genetic information between species through a process called conjugation.This property and the relatively short generation time have been important and led to the current situation in which the control of pathogenic bacteria has been difficult.In 1961, outbreaks of methicillin resistant Staphyloccocus aureus (MRSA) were sporadic and the introduction of new antibiotics kept the bacteria at bay.Since then, MRSA has acquired resistance to virtually all antibiotics in clinical use including cephalosporins, tetracyclines, aminoglycosides, erythromycin and the sulfonamides (Neu, 1992).
Four lichen species, Parmotrema grayana Hue, Cladonia sp., Heterodermia obscurata (Nyl.), and Roccella montagnei Bel, collected from different locations in Sri Lanka have been investigated: P. grayana from the stem bark of palm tree [Roystonea regia (Kunth) O.F. Cook (syn.R. elata, R. floridana)]; Cladonia sp., from rocks in the Labukelle region, Central Province; H. obscurata from the rocks in the Beragala region, Central Province and R. montagnei from coconut palm trees (Cocos nucifera L.).Atranorin (Figure 14) isolated from all four lichen species has exhibited a moderate antibacterial activity against Escherichia coli, Bacillus subtilis and Salmonella typhi at a concentration of 100 µg/mL in the agar well diffusion method with inhibition zones of 13, 12 and 12 mm, respectively.Sekikaic acid (Figure 15) isolated from H. obscurata has shown a moderate antibacterial activity against E.coli, B. subtilis and S. typhi at a concentration of 100 µg/mL in agar well diffusion method with an inhibition zone of 16 mm.
Methanolyis of lecanoric acid isolated from Cladonia sp., H. obscurata and P. grayana, has yielded the mononuclear aromatic compound methyl orsellinate (Figure 16), which exhibited a moderate antibacterial activity against E. coli, B. subtillus and S. typhi (Thadani et al., 2012).(Figure 19), isolated from the stem bark of Garcinia mangostana L., has been found to be active against vancomycin resistant Enterococci (VRE) and methicillin resistant Staphylococcus aureus (MRSA) with MIC values of 6.25 and 6.25 to 12.5 µg/mL, respectively.hydrochloride (VCM) against MRSA has been observed.commercially available antibiotics such as ampicillin and minocycline has also been discovered.combination with GM against VRE and in combination with VCM against MRSA might be useful in controlling VRE and MRSA infections (Sakagami et al., 2005).
Vatica affinis Thw., is a dipterocarp species endemic to Sri Lanka.The cold acetone extracts of the bark and timber of this species have been chemically investigated isolated from the extract by using silica gel preparative plates.A silica column chromatography of the extract has yielded a second compound vaticaffinol (Figure 21b), when the column was eluted with acetone-benzene study has shown antibacterial activity towards Oxford Staphylococcus and Escherichia coli when tested by the filter paper disc method in Mueller Hinton Agar medium (Sotheeswaran et al., 1985).
Calophyllum moonii Wight., is an endemic species to Sri Lanka.Calozeyloxanthone (Figure 22) has been re-isolated from the root bark of C. moonii and was tested for antibacterial activity against vancomycinresistant Enterococci (VRE) and vancomycin-sensitive Enterococci (VSE).Results of the study has indicated that calozeyloxanthone is strongly active against both tested species with MIC values of 6.25 and 12.5 µg/mL, respectively.Further, a marked synergism between calozeyloxanthone and vancomycin hydrochloride (VCM) against VRE has been observed (Sakagami et al., 2002).
Litsea gardneri L., is a moderate sized endemic plant in Sri Lanka.Alkaloids extracted from the defatted bark of L. gardneni have been tested for antibacterial activity against E. coli and S. aureus using the modified tube dilution technique.Four alkaloids have been isolated and the activity was observed only for laurolitsine (Figure 23) (against S. aureus), the minimum inhibitory concentration being 250 µg/mL (Bandara et al., 1989e).

Antifungal activity
Synthetic fungicides are currently used as the primary means for the control of plant disease.
However, alternative control methods are needed due to the negative public perceptions regarding the use of synthetic chemicals such as resistance to fungicides among fungal pathogens, and the high development cost of new chemicals.The use of plant-derived products as disease control agents have been studied, since they tend to have a low mammalian toxicity, less environmental effects and wide public acceptance (Lee et al., 2007).Preventing fungal decay in organic fruits after harvest is an increasing challenge, and novel preservation approaches, which comply with organic food standards need to be developed.and papaya has been determined using thin layer chromatography (TLC) bioassay.Plumbagin has shown higher antifungal activities against A. tunis (inhibition area = 4.5 cm 2 ), B. theobromae (inhibition area = 0.8 cm 2 ), Fusarium sp.(Inhibition area = 2.5 cm 2 ), and C. gloeosporioides (Inhibition area = 4.5 cm 2 ) compared to that of standard antifungal agent benlate (Adikaram et al., 2002).On a spore germination assay conducted against C. gloeosporioides, a plumbagin solution at and above 31 µg/mL has caused total inhibition with an IC 50 value of 6.86 µg/mL, whereas at 50 µg/mL of the standard benlate required for the total inhibition (IC 50 = 44 µg/mL) (Adikaram et al., 2002) was higher.assay against Clodosporium clodosporioides.It was found that discretine was moderately active (MID = 30 µg/spot), while nordicentrine was highly active (6 µg/ spot) when compared with the standard antifungal agent, benomyl, with an MID value of 1 µg/spot (Puvanendran et al., 2008).
From the hexane extract of the lichen Heterrodermia microphylla, atranorin (Figure 14) has been isolated and the results of quantitative spore germination assay indicated the antifungal activity of atranorin against C. gloeosporioides and C. musae with percentage germination values of 58.2 and 26.2, respectively, while the percentage germination for benlate was 33.3 (Bombuwala et al., 2008).
Ishwarane (Figure 28) has been isolated from the CH 2 Cl 2 extract of three Hortonia spp.viz., H. angustifolia, H. floribunda and H. ovalifolia.This compound has displayed a moderate antifungal activity against C. cladosporioides with a 23 mm inhibition zone diameter compared with that of the standard antifungal agent benor (37 mm inhibition zone diameter) in TLC bioassay.This activity has been further corroborated by using germination inhibition assay and found that Ishwarane totally inhibited the germination of C. cladosporioides spores at concentrations higher than 6.25 ppm (Ratnayake et al., 2008).
In the search for active principles from the roots of Eupatorium riparium Regel, methylripariochromene A (Figure 29) has been isolated from n-hexane extract and was tested against C. gloeosporioides.It has exhibited antifungal activity comparable to that of the commercial fungicide, benlate in TLC bioassay.Results obtained from the germination inhibition bioassay corroborated that methylripariochromene A and benlate had the same degree of antifungal activity against C. gloeosporioides (Bandara et al., 1992).

Anticancer activity
Cancer has no geographic, national, religious or other boundaries.Each year over 6.5 million people are diagnosed with cancer worldwide (Culotta & Koshland, 1993).Natural products and their semisynthetic analogues have provided some of the most effective and widely used chemotherapeutic agents for cancer (Cordel, 1978).This is exemplified by such compounds as Taxol ®, the Vinca alkaloids, vinblastine, vincristine, the podophyllotoxin analogues etoposide and teniposide, the camptothecin analogues topotecan, and CPT-11, the microbial products bleomycin, mitomycin C, the anthracyclines adrimycin and daunorubicin.Importantly, these anticancer compounds are highly complex that they would not have emerged from a synthetic programme alone or from the combinatorial approach to drug discovery.Thus, natural products approach continues to be important for the development of new anticancer drugs as it is complementary to synthetic and biosynthetic approaches.
Two new members of a family of highly modified phenylalanine diketopiperazine, ambewelamide A and B (Figure 39) have been isolated from the CH 2 Cl 2 extract of Usnea sp., found in Ambewela, Sri Lanka.Of the two compounds, ambewelamide A exhibited potent in vitro cytotoxicity against murine leukemia P388 cells with an IC 50 value of 8.6 ng/mL and showed significant in vitro antineoplastic activity against P388 cells (percentage T/C 140 at 160 µg/kg) (Williams et al., 1998).
A flabelliferin (Figure 40) isolated from the methanol: water (1:1) extract of Borassus flabellifera L., flour was introduced into micro wells containing melanoma cells.A 13 % inhibition of the cell growth has been observed for the isolated compound at the concentration of 100 µg/mL on the melanoma cell line, while the reference compound, doxorubicin resulted in a 63 % inhibition of cell growth at the concentration of 20 µg/mL (Keerthi et al., 2009).
Seselin (Figure 33) isolated from Pleiospermium alatum Radlk., has shown detectable activity against a yeast strain rad 52, at a dose of 500 µg/mL.Further, seselin has shown selective activity against the rad 52 yeast strain as compared with the wild-type RAD + strain, indicating that it functions as a DNA-damaging agent.Seselin was also weakly active in a mammalian cytotoxicity assay against Vero monkey cells, with an IC 50 value of 12 µg/mL (Gunatilaka et al., 1994).
The other compound isolated from Pleiospermium alatum was xanthyletin (Figure 41), which has shown somewhat higher activity in the wild-type RAD + cell line (IC 50 value = 21 µg/mL) suggesting that its cytotoxicity is due to some other mechanism than the DNA damage (Gunatilaka et al., 1994).
The stem bark of Pleurostylia opposita Wall., has been extracted with MeOH/CH 2 Cl 2 (1:1 v/v).Size extrusion of the purified extract yielded two sesquiterpene pyridine alkaloids, oppositines A (Figure 43a) and B (Figure 43b).Oppositines A and B when exposed to the cancer cell line HCT-116 (human colon tumor) have shown moderate cytotoxicity against HCT116 cell lines with EC 50 values of 27 ± 2 and 26 ± 3 µM, respectively (Whitson et al., 2006).
The lichen Parmotrema sp.(Parmeliaceae), collected from Labukelle, Central Province, Sri Lanka, has been sequentially extracted into methanol and the extract has shown significant in vitro kinase inhibitory activity.Bioassay-guided fractionation of the Parmotrema sp., extract has led to the isolation of depside inhibitors.A new depside (Figure 44a) has been isolated along with   exhibited moderate inhibition of purified recombinant Plk1 kinase with IC 50 also observed at high ATP concentrations, suggesting the potential for activity in a cellular environment.The depsides when tested against a panel of 23 other recombinant inases were found to possess up to 30-fold selectivity toward Polo-like kinase-1 (Williams et al., 2011).

Oral hypoglycaemic activity
Diabetes mellitus is a chronic of carbohydrate, fat, and protein metabolism (Anirban Abdul, 2005).
A defective or deficient insulin secretory response causes impaired carbohydrate (glucose) use and the resultant hyperglycaemia is a typical feature of diabetes mellitus.It is the fourth leading cause of death in developed countries and diabetes mellitus affects more than 5 % of the world's population, making it one of the most common non communicable diseases (2001).
There are more than 220 million persons affected with diabetes in the world today, and by 2025, the number is expected to approach 300 million (Simon, 2010).
A standard treatment uses drugs such as sulphonyl ureas, biguanides and thiazolidinediones, which more insulin.However, undesired consequences of prolonged use of sulphonylureas and other drugs include long term angiogenic side effects, which result due to chronic exposure to increased insulin levels (Bebernitz et al., 2001).
A large number of medicinal plants used in the control of diabetes mellitus have been reported (Bailey & Day, 1989;Marles & Farnsworth, 1994).Although these plants may represent alternatives to developing new oral hypoglycaemic agents, appropriate and unambiguous ethnobotanical information is needed to exploit them.Salacia reticulata Wight., is an indigenous plant, which grows in the Dry Zone forests of Sri Lanka.Known as kothala himbutu, this herb is used for the treatment of diabetes in ayurvedic medicine.A polyhydroxylated cyclic 13-membered sulfoxide, salacinol (Figure 45a) has been isolated from an aqueous extract of S. reticulata through bioassay guided separation.Salacinol has shown potent inhibitory activities on isomaltase, and the inhibitory effects on serum glucose levels in maltose and sucrose-loaded rats (in vivo) have been found to be more potent than that of acarbose, a inhibitory activity of salacinol is also reported (IC 50 : maltase, 3.2 mg/mL; sucrase, 0.84 mg/ mL; isomaltase, 0.59 mg/mL).Interestingly, the organic extracts of the plant contained triterpenoids (Gunatilaka et al., 1993;Tezuka et al., 1993;1994;Dhanabalasingham et al., 1996).
Several studies on the chemistry of S. reticulata have been conducted using S. reticulata var.diandra, a variety endemic to Sri Lanka (Karunaratne, 2013).According to the current literature (Dassanayake, 1996), this variety is now elevated to the species level (S.diandra).
-Glucosidase inhibitors have proved useful in the reduction of postprandial hyperglycaemia by suppressing the absorption of glucose, being effective in the treatment of type II diabetes and obesity (Raskin et al., 2007).The current interest in these compounds has been extended to a diverse range of diseases, including lysosomal storage disorders, cancer and special attention has been given to those compounds with anti-HIV activity (Kouam et al., 2006).Because of their promising therapeutic potential, -glycosidase inhibitors are being searched from natural

Sperm motility enhancing activity
Globally, infertility affects about 50 to 80 million couples at some point of their reproductive lives with a variety of biological and behavioural determinants (World Health Organisation, 2003).There is a need and a demand for new sperm stimulants to be used in asthenozoospermia and in some assisted reproductive programmes.In many parts of the world, efforts are now being aimed at investigating the therapeutic efficacy of locally available medicinal herbal plants.The beneficial role of medicinal plants in the treatment of male infertility has been numerously indicated (Saalu et al., 2006;2009a;2009b;2010).
The development of new fertility regulating drugs from medicinal plants is an attractive proposition.Natural plant substances possessing mild inherent estrogenic or anti-estrogenic properties offer themselves as effective non-conventional sources of contraception with less deleterious side effects.Many plants and herbs have also been reported to have potential antifertility properties (Casey, 1960).Many of these plant products having inherent estrogenic or anti-estrogenic effects possibly bring about alterations in tubal transport of blastocyst or hormonal milieu of the uterus making the uterine environment hostile for implantation or fetal development.
A non-steroidal contragestative agent (Figure 48) has been isolated from the MeOH-CH 2 Cl 2 (1:1) crude extract of the Sri Lankan marine red algae, Gelidiella acerosa.Contragestative effects of this compound assessed in pregnant rats has shown 80 % contragestative activity without any overt clinical signs of toxicity (Premakumara et al., 1996).

Anti-inflammatory activity
Although, no bioactive compounds in this category have been isolated so far, Sri Lankan studies on the antiinflammatory activity is significant because bioassays carried out on crude extracts have shown the potential of Sri Lankan plants having anti-inflammatory activity.
Leaves of Argyreia populifolia Choisy (Convolvulaceae) is used in the traditional medicine for inflammation in joints and arthropod bites.The anti-inflammatory activity of the leaves have been evaluated using carrageenan-induced paw oedema test in rats.A 10 mL/kg oral dose of fresh juice of the leaves significantly impaired the initial phase of the acute inflammatory response (by 33%) in this model.The juice has shown a marked anti-histamine activity when assessed using histamine-induced vascular permeability test.It has been concluded that the leaf juice has an antiinflammatory activity mediated via antihistamine action, justifying its use in traditional medicine (Ratnasooriya & Dharmasiri, 2001).
The anti-inflammatory of an aqueous leaf extract (ALE) of Ixora coccinea (Rubiaceae) in rats after oral administration (500, 1000 and 1500 mg/kg) has also been investigated.This has been done using the carrageenan-induced paw oedema (acute inflammatory model) and cotton pellet granuloma tests (chronic inflammatory model).In the former test, ALE significantly reduced both early and late phases of the inflammatory response and also the oedema maintained between the two phases.In the latter test, it has significantly suppressed granuloma formation (only highest dose tested).Collectively, the results has shown a promising anti-inflammatory activity against both acute and chronic inflammation (Ratnasooriya et al., 2005).The anti-inflammatory activity of methanolic leaf extract (MLE) of I. coccinea Linn.(Rubiaceae), has also been investigated.It has been found that the methanolic leaf extract has a dose-dependent anti-inflammatory activity in carrageenan-induced rat paw oedema model (r 2 = 0.7; p < 0.01) (Handunnetti et al., 2009).
Trichosanthes cucumerina Linn.(Cucurbitaceae), is one of the medicinal plants often used in Sri Lankan traditional medicine.The anti-inflammatory activity of the hot water extract and its fractions of T. cucumerina have been evaluated by the use of carrageenan-induced paw oedema model in Wistar rats.Apart from the lowest dose of the HWE, other tested doses (500, 750, of the inflammation, most pronounced at 5 hours after the injection of carrageenan.The anti-inflammatory effect induced by 750 mg/kg was comparable to that of the reference drug, indomethacin at 4 and 5 hours (Arawwawala et al., 2010).
Vitex negundo L. (Verbenaceae) is a small tree, of which the water extract of fresh mature leaves is used internally and externally in ayurveda medicine as antiinflammatory, analgesic and anti-itching agents.The early phase (2 hours) of carrageenan-induced rat paw oedema was significantly (p < 0.01) suppressed in an inversely does-dependent (r 2 = 1, p < 0.01) manner by fresh mature leaf extract (EC 50 = 2 g/kg).In the formaldehyde-induced rat paw oedema test, the 2.5 and 5 g/kg leaves have significantly (p < 0.05) suppressed the inflammation on days 4 -6 of the test (Dharmasiri et al., 2003).
The anti-inflammatory potential of Sri Lankan black tea (Camellia sinensis L.) (Theaceae) has been determined using both acute (carrageenan-induced paw oedema) and chronic (formaldehyde-induced paw oedema and cotton pellet granuloma test) rat inflammatory models.Three doses of black tea brew (BTB) [84 mg/mL, equivalent to 1.5 cups; 168 mg/mL, equivalent to 3 cups; and 501 mg/mL, equivalent to 9 cups] made using high grown unblended dust grade No: 1 black tea samples were orally administered to rats (n = 6 -9/ dose/test).The results have shown that Sri Lankan BTB possesses marked and significant (p < 0.05) oral anti-inflammatory activity against both acute and chronic inflammation.This anti-inflammatory activity was dose-dependent in the carrageenan-induced paw oedema test and cotton pellet granuloma test.Further, in the carrageenan paw oedema model, the anti-inflammatory activity of BTB was almost identical to the green tea brew of both Chinese and Japanese types (Ratnasooriya & Fernando, 2009).
In Sri Lankan traditional medicine a decoction of leaves and stems of Anisomeles indica (Lamiaceae) is claimed to possess anti-inflammatory activity.Three doses of the freeze-dried decoction of a pre-flowering plant (E1) (125, 250 and 500 mg/kg) and one dose of the decoction of a plant at flowering stage (E2) (500 mg/kg) were orally administered to rats.The anti-inflammatory activity has been evaluated using the carrageenaninduced paw edema, formaldehyde-induced paw oedema and adjuvant-induced paw oedema models in rats.E1 demonstrated a significant (p < 0.01) and dose-dependent anti-inflammatory effect in all three models, while E2 did not demonstrate significant anti-inflammatory activity (Dharmasiri et al., 2002).

Miscellaneous activity
Mikania scandens B. L. Rob., is a common invasive plant in Sri Lanka and other South Asian countries.Preliminary investigation of a number of plant extracts for allelopathic activity using seed germination inhibition bioassay has shown promising bioactivity of the water extract of the aerial parts of M. scandens.Activity-guided fractionation of the M. scandens extract led to the isolation of the highly allelopathic active compound mikanolide (Figure 49), with an MIC of 0.083 µM/mL.This plant could be used to develop as an environment friendly natural herbicide, either in crude form as shredded plant material or as pure mikanolide, which is the major constituent (~ 0.02 %) in the plant (Piyasena & Dharmaratne, 2013).

CONCLUSION
Bioactive compounds ranging from alkaloids, terpenoids, aromatic compounds and lichen specific metabolites isolated from Sri Lankan flora exhibits the potential of the Sri Lankan flora as an economic resource.In light of these findings, a comprehensive investigation of bioactive compounds of Sri Lankan endemic plants has now become of prime importance.

Figure 12 :Figure 13 :
Figure 12: Structure of ecdysterone The methanol extract of the brown seaweed, Stoechospermum marginatum C. Agardh, grown in seas around the Northern part of Sri Lanka has been found to inhibit the growth of Staphylococcus aureus in the standard disk method.Fractionation of the active extract has led to the isolation of an antibacterial compound whose structure has been established to be 19-acetoxy-5,15,18-trihydroxyspata-13,16-diene (Figure17) (DeSilva et al., 1982).