2.2.1 PHYTOCHEMICAL COMPOUNDS OFAQUILARIA PLANTVariousstudies have been conducted on the bioactive compounds in Aquilaria trees, which is important in discovering therapeuticagent in plant. The most important bioactive constituents of these plants arealkaloids, tannins, flavonoids and phenolic compounds. The phytochemicalcompounds of plants have potentially significant application in human healthcare as well as in corrosion field (Khalil et al., 2013).

It is commonlyknown about the benefits of Aquilariaplant for its medicinal properties by which its application as traditionalmedicine has long been used for centuries. Many earlier literatures have beenpublished discussing on the pharmacology properties of this unique plant. Thereare currently few reports on the benefits of Aquilaria leaves to humans. Theleaves of A. sinensis are known fortreatment of trauma-related illnesses such as fractures and bruises. Meanwhile,the leaves of A. crassna are usefulas a supplement in combating various health conditions such as high bloodpressure, constipation, headache and diabetes, and in treating digestiveailments and as a mild sedative.

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Chemicalcomposition of the leaves of Aquilaria species are reportedly compounds like2-(2-phenylethyl) chromones, phenolic acids, steroids, fatty acids,benzophenones, xanthonoids, flavonoids, terpenoids, nucleosides and alkanes (Adam et al., 2017). Plant materialsof Aquilaria spp. have been reported to exert various bioactivities, includinganti-allergic, anti-cancer, anti-inflammatory, anti-ischemic(cardioprotective),antimicrobial, antioxidant, anti-depressant (effects on the central nervous system)activities, as well as hepatoprotective, laxative and mosquitocidal effects. Although,there are four species dominate the literature, namely, A.agallocha, A.crassna, A.

malaccensis and A.sinensis. The plant materials investigated include leaf, bark,branch, heartwood, oil, stem, stem bark and woody hull (Hashim et al.

, 2016). Ithas been reported that polyphenols and the presence of phenolic compounds aresignificant in antibacterial, anti-candida and antioxidant activities of Aquilaria plant. For instance, detectionof alkaloids in Aquilaria leavesextract is significant as it can be used as antimalaria, analgesics,antispasmodic, bactericidal and stimulants. It also justifies the use of theplant in treating toothache, colic, severe headache, rheumatism and pain duringpregnancy. The detection of alkaloids also indicates its potential use as ananalgesic agent for pain relief. Similarly, another polyphenolic compound,flavonoids, have been reported to have anti-inflammatory action, free radicalscavenging and inhibition of hydrolytic and oxidative enzymes, anti-allergic,anti-cancer, anti-inflammatory and anti-viral. Besides that, the presence ofsaponins, anthraquinones, cardiac glycosides, along with flavonoids couldinhibit tumour growth and protect against gastrointestinal infections.

Moreover,presence of tannins also suggests this plant’s ability as a key role inantidiarrhoeic and antihemorrhagic agent. It is also noted that herbs that havetannins act as astringent in nature, which fasten the healing of wounds andinflamed mucous membranes and could be used for treating intestinal disorderssuch as diarrhoea and dysentery exhibiting antibacterial activity (Khalil et al., 2013). Not to mention, themicrobial effects observed in the more recent pre-clinical studies supportedthe traditional uses where microbial infections could be the cause of diseasessuch as cough, dysentery and leprosy (Hashim et al.

, 2016).Theseseveral classes of phytochemicals (tannin, saponin, flavonoid) found in Aquilaria plant, and records high levelof flavonoid and total phenolic content, were believed to contribute toinhibiting the corrosion of the mild steel in HCl solution. Among theidentified compounds, adenosine was found to be an excellent inhibitor with aninhibition efficiency of up to 62% at a very low concentration (Sin et al., 2017).