2.2.1 PHYTOCHEMICAL COMPOUNDS OF
AQUILARIA PLANT

Various
studies have been conducted on the bioactive compounds in Aquilaria trees, which is important in discovering therapeutic
agent in plant. The most important bioactive constituents of these plants are
alkaloids, tannins, flavonoids and phenolic compounds. The phytochemical
compounds of plants have potentially significant application in human health
care as well as in corrosion field (Khalil et al., 2013). It is commonly
known about the benefits of Aquilaria
plant for its medicinal properties by which its application as traditional
medicine has long been used for centuries. Many earlier literatures have been
published discussing on the pharmacology properties of this unique plant.

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There
are currently few reports on the benefits of Aquilaria leaves to humans. The
leaves of A. sinensis are known for
treatment of trauma-related illnesses such as fractures and bruises. Meanwhile,
the leaves of A. crassna are useful
as a supplement in combating various health conditions such as high blood
pressure, constipation, headache and diabetes, and in treating digestive
ailments and as a mild sedative.

Chemical
composition of the leaves of Aquilaria species are reportedly compounds like
2-(2-phenylethyl) chromones, phenolic acids, steroids, fatty acids,
benzophenones, xanthonoids, flavonoids, terpenoids, nucleosides and alkanes (Adam et al., 2017). Plant materials
of Aquilaria spp. have been reported to exert various bioactivities, including
anti-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).

It
has been reported that polyphenols and the presence of phenolic compounds are
significant in antibacterial, anti-candida and antioxidant activities of Aquilaria plant. For instance, detection
of alkaloids in Aquilaria leaves
extract is significant as it can be used as antimalaria, analgesics,
antispasmodic, bactericidal and stimulants. It also justifies the use of the
plant in treating toothache, colic, severe headache, rheumatism and pain during
pregnancy. The detection of alkaloids also indicates its potential use as an
analgesic agent for pain relief. Similarly, another polyphenolic compound,
flavonoids, have been reported to have anti-inflammatory action, free radical
scavenging and inhibition of hydrolytic and oxidative enzymes, anti-allergic,
anti-cancer, anti-inflammatory and anti-viral. Besides that, the presence of
saponins, anthraquinones, cardiac glycosides, along with flavonoids could
inhibit tumour growth and protect against gastrointestinal infections. Moreover,
presence of tannins also suggests this plant’s ability as a key role in
antidiarrhoeic and antihemorrhagic agent. It is also noted that herbs that have
tannins act as astringent in nature, which fasten the healing of wounds and
inflamed mucous membranes and could be used for treating intestinal disorders
such as diarrhoea and dysentery exhibiting antibacterial activity (Khalil et al., 2013). Not to mention, the
microbial effects observed in the more recent pre-clinical studies supported
the traditional uses where microbial infections could be the cause of diseases
such as cough, dysentery and leprosy (Hashim et al., 2016).

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