Chemical constituents and antibacterial activity of Melastoma malabathricum L.

Article abstract of DOI:10.1080/14786419.2010.538395

The aqueous methanolic extracts of Melastoma malabathricum L. exhibited antibacterial activity when assayed against seven microorganisms by the agar diffusion method. Solvent fractionation afforded active chloroform and ethyl acetate fractions from the leaves and the flowers, respectively. A phytochemical study resulted in the identification of ursolic acid (1), 2α- hydroxyursolic acid (2), asiatic acid (3), β-sitosterol 3-O-β-D-glucopyranoside (4) and the glycolipid glycerol 1,2-dilinolenyl-3-O-β-D-galactopyanoside (5) from the chloroform fraction. Kaempferol (6), kaempferol 3-O-α-L-rhamnopyranoside (7), kaempferol 3-O-β-D-glucopyranoside (8), kaempferol 3-O-β-D-galactopyranoside (9), kaempferol 3-O-(2 ,6 -di-O-E-p-coumaryl)-β-D-galactopyranoside (10), quercetin (11) and ellagic acid (12) were found in the ethyl acetate fraction. The structures of these compounds were determined by chemical and spectral analyses. Compounds 1-4, the flavonols (6 and 11) and ellagic acid (12) were found to be active against some of the tested microorganisms, while the kaempferol 3-O-glycosides (7-9) did not show any activity, indicating the role of the free 3-OH for antibacterial activity. Addition of p-coumaryl groups results in mild activity for 10 against Staphylococcus aureus and Bacillus cereus. Compounds 2-5, 7 and 9-12 are reported for the first time from M. malabathricum. Compound 10 is rare, being reported only once before from a plant, without assignment of the double bond geometry in the p-coumaryl moiety.

Full text of DOI:10.1080/14786419.2010.538395

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Chemical constituents and antibacterial
activity of Melastoma malabathricum L.
a
a b
Keng-Chong Wong , Dafaalla Mohamed Hag Ali
& Peng-Lim
a
Boey
a
School of Chemical Sciences, Universiti Sains Malaysia , Penang
1800 , Malaysia
1
b
College of Science , Department of Chemistry, Sudan University
of Science and Technology , P.O. Box 407, Khartoum , Sudan
Published online: 11 Aug 2011.
To cite this article: Keng-Chong Wong , Dafaalla Mohamed Hag Ali & Peng-Lim Boey (2012)
Chemical constituents and antibacterial activity of Melastoma malabathricum L., Natural Product
Research: Formerly Natural Product Letters, 26:7, 609-618, DOI: 10.1080/14786419.2010.538395
To link to this article: http://dx.doi.org/10.1080/14786419.2010.538395
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Natural Product Research
Vol. 26, No. 7, April 2012, 609–618
Chemical constituents and antibacterial activity of Melastoma
malabathricum L.
a
ab
a
Keng-Chong Wong , Dafaalla Mohamed Hag Ali * and Peng-Lim Boey
a
School of Chemical Sciences, Universiti Sains Malaysia, Penang 11800, Malaysia;
b
College of Science, Department of Chemistry, Sudan University of Science and Technology,
P.O. Box 407, Khartoum, Sudan
(
Received 1 April 2010; final version received 23 October 2010)
The aqueous methanolic extracts of Melastoma malabathricum L. exhibited
antibacterial activity when assayed against seven microorganisms by the
agar diffusion method. Solvent fractionation afforded active chloroform
and ethyl acetate fractions from the leaves and the flowers, respectively.
A phytochemical study resulted in the identification of ursolic acid (1),
2ꢀ-hydroxyursolic acid (2), asiatic acid (3), ꢁ-sitosterol 3-O-ꢁ-D-glucopyr-
anoside (4) and the glycolipid glycerol 1,2-dilinolenyl-3-O-ꢁ-D-galactopya-
noside (5) from the chloroform fraction. Kaempferol (6), kaempferol
3
-O-ꢀ-L-rhamnopyranoside (7), kaempferol 3-O-ꢁ-D-glucopyranoside (8),
00
00
kaempferol 3-O-ꢁ-D-galactopyranoside (9), kaempferol 3-O-(2 ,6 -di-O-E-
p-coumaryl)-ꢁ-D-galactopyranoside (10), quercetin (11) and ellagic acid
(12) were found in the ethyl acetate fraction. The structures of these
compounds were determined by chemical and spectral analyses.
Compounds 1–4, the flavonols (6 and 11) and ellagic acid (12) were
found to be active against some of the tested microorganisms, while the
kaempferol 3-O-glycosides (7–9) did not show any activity, indicating the
role of the free 3-OH for antibacterial activity. Addition of p-coumaryl
groups results in mild activity for 10 against Staphylococcus aureus and
Bacillus cereus. Compounds 2–5, 7 and 9–12 are reported for the first time
from M. malabathricum. Compound 10 is rare, being reported only once
before from a plant, without assignment of the double bond geometry in
the p-coumaryl moiety.
Keywords: Melastoma malabathricum; Sendudok; pentacyclic triterpe-
noids; acylated kaempferol glycosides; antibacterial activity
1
. Introduction
Melastoma malabathricum L. (Melastomataceae, Malay name: Sendudok) is a small
shrub widely used in the traditional medicine of Malaysia and Indonesia for treating
diarrhoea, dysentery, leucorrhoea, ulcers and wounds (Burkill, 1966; Perry, 1980).
The methanolic extract of the aerial parts was reported to have a moderate antiviral
activity against HSV-1, a significant activity against Poliovirus and a cytotoxic effect
*Corresponding author. Email: dmhali@hotmail.com; dmhali@sustech.edu
ISSN 1478–6419 print/ISSN 1478–6427 online
ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/14786419.2010.538395
http://www.tandfonline.com

6
10
K.-C. Wong et al.
IC50 ꢀ 25 mg mlꢁ ) on murine cell lines (Lohezic-Le Devehat, Bakhtiar, Bezivin,
1
(
Amoros, & Boustie, 2002). The ethanolic extract of the stem bark and leaves was
found to be potentially antinociceptive, acting at both the peripheral and central
levels in mice (Sulaiman, Somchit, Israf, Ahmad, & Moina, 2004). The flowers were
shown to contain antioxidant and cytotoxic flavonoids (Susanti et al., 2007).
Previous phytochemical studies have revealed the presence of malvidin
0
3
,5-diglucoside (Lowry, 1976), 4 -methylpeonidin 7-O-ꢁ-D-glucoside (Mohandoss
&
Ravindran, 1993), kaempferol (Das & Kotoky, 1988; Mohandoss & Ravindran,
993; Susanti et al., 2007), kaempferol 3-O-ꢁ-D-xyloside (Mohandoss & Ravindran,
1
1
0
0
00
993), kaempferol 3-O-glucoside, kaempferol 3-O-(2 ,6 -di-O-p-trans-coumaroyl)
glucoside and naringenin (Susanti et al., 2007), p-hydroxybenzoic acid and gallic acid
(
(
Das & Kotoky, 1988) in the flowers, ꢁ-sitosterol and melastomic acid in the roots
Manzoor-I-Khuda, S.A. Chowdhury, Reza, & A.K. Chowdhury, 1981), quercetin
3
-O-ꢀ-L-rhamnosyl-(1!2)-ꢁ-D-galactoside (Dinda & Saha, 1988), 1-octyl doco-
sanoate, 11-methyl-1-tritriacontanol (Dinda & Saha, 1986) in the aerial parts,
2-methyl-1-tritriacontanol, ꢁ-sitosterol, ursolic acid (Das & Kotoky, 1988) and
3
several tannins (Yoshida, Nakata, Hosotani, Nitta, & Okuda, 1992a, 1992b) in the
dried leaves. The extensive use of M. malabathricum in traditional medicine led us to
carry out further phytochemical investigations of this plant, guided by antibacterial
activity assay. In this article we report the isolation of 12 compounds from
M. malabathricum, some of them possessing antibacterial activity. Nine of the
isolated compounds are reported for the first time in this plant.
2
2
. Results and discussion
.1. Extraction and isolation
The aqueous methanolic extracts of the fresh leaves and flowers of M. malabathricum
L. were evaluated for antibacterial activity by the agar diffusion method. Guided by
this activity, solvent fractionation and isolation were carried out by silica gel and
Sephadex column chromatography using different solvent systems. The isolated
structures were confirmed by comparison of their spectral data (UV, IR, MS,
1
13
H- and C-NMR) with literature data (Collins, Pilotti, & Wallis, 1992; Furuya,
Orihara, & Hayashi, 1987; Kriwacki & Pitner, 1989; Li, Elsohly, Hufford, & Clark,
999; Mabry, Markham, & Thomas, 1970; Markham, Ternai, Stanley, Geiger, &
Mabry, 1978; Sakakaibara, Kaiya, Fukuda, & Ohki, 1983; Seo, Tomita, & Tori,
981; Ternai & Markham, 1976; Yamagishi et al., 1988), 2D NMR, chromato-
1
1
graphic methods (GC–MS, TLC, PC) and chemical analyses.
The chloroform fraction (fr-2) of the aqueous methanolic extract of the leaves
(
3
ext-1) gave ursolic acid (1), 2ꢀ-hydroxyursolic acid (2), asiatic acid (3), ꢁ-sitosterol
-O-ꢁ-D-glucopyranoside (4) and glycerol 1, 2-dilinolenyl-3-O-ꢁ-D-galactopyrano-
side (5). The ethyl acetate fraction (fr-3) of the aqueous methanolic extract of the
flowers (ext-2) afforded kaempferol (6), kaempferol 3-O-ꢀ-L-rhamnopyranoside (7),
kaempferol 3-O-ꢁ-D-glucopyranoside (8), kaempferol 3-O-ꢁ-D-galactopyranoside
00
00
(
9), kaempferol 3-O-(2 ,6 -di-O-E-p-coumaryl)-ꢁ-D-galactopyranoside (10), querce-
tin (11) and ellagic acid (12). The triterpenoids (2–4), glycolipid (5), flavonoids
7, 9–11) and ellagic acid (12) are reported for the first time from M. malabathricum.
(

Natural Product Research
611
Compound (10) is uncommon, being reported only once before in a related
species (Chou & Liao, 1982), but the configuration of the olefinic function of the
p-coumaryl moiety was not specified (CAS Registry Number: 84461-47-2). In this
study the olefinic protons of the two p-coumaryl groups were observed as
0
00
000
two pairs of doublets at 7.69 and 6.38 ppm (3 , 2 ), and 7.39 and 6.05 ppm
0000 0000
(3 , 2 ) with a coupling constant (J) 15.9 Hz (Figure S1). The large value of J
indicated the E-configuration of the p-coumaryl moiety (Silverstein, Bassler, &
Morrill, 1991).
12
13
1
H
COOH
1
R1
OH
6
„
3
O
3
HO
HO
HO
1
„ O
5
6
R2
OH
1
2
3
: R1 = H, R2 = Me
4
: R1 = OH, R2 = Me
: R1 = OH, R2 = CH OH
2
1
5
OH
9
R'
O
O
OH
O
OH
OH
6
1
O
2
O
R
O
O
1
HO
HO
O
O
OH1
3
1
15
OH
O
S
G
5
12
R1
4
„ OH
OH
O
4„„„
1
„
7
O
O
1„„„
HO
7'''
HO
O
O
OH
1
„„ O
3
O
OH
5
OH
OR2
O
OH
6„„
OH
O
O
1„„„„
6
: R1 = R2 = H
7
: R1 = H, R2 = rha
4„„„„
8
: R1 = H, R2 = glc
: R1 = H, R2 = gal
1: R1 = OH, R2 = H
7''''
HO
9
1
10
Scheme 1. Compounds 1 to 12.

6
12
K.-C. Wong et al.
2
.2. Antibacterial activity
The aqueous methanolic extracts of the leaves (ext-1) and flowers (ext-2) of
M. malabathricum exhibited antibacterial activity when tested by the agar diffusion
method (Table 1). From ext-1 an active precipitate (fr-1) was obtained which was
extracted with chloroform to give fraction fr-2. Five compounds (1–5) were isolated
from fr-2 of which 1–4 are triterpenoids active against some of the tested
microorganisms, while 5 is an inactive glycolipid. Compound 3, at concentrations
ten times those of refampicin, showed activity against Bacillus cereus comparable to
that shown by this reference antibiotic (Table 1). ext-2 was extracted with ethyl
acetate to give fraction fr-3 from which seven compounds (6–12) were obtained.
Among these are two flavonols (6 and 11) and ellagic acid (12), which are active
compounds, and three kaempferol 3-O-glycosides (7–9), which did not show any
activity indicating the role of the free 3-OH for antibacterial activity. The seventh
compound is the diacylated kaempferol 3-O-glycoside (10). It appears that the
addition of two p-coumaryl groups results in a mild activity for 10 against
Staphylococcus aureus and B. cereus as shown in Table 1. The presence of p-coumaryl
group has been seen before to dramatically increase the dermatitis activity of
astragalin (Loggia, Negro, Bianchi, Romussi, & Tubaro, 1989). The results of
extracts and pure compounds which possess partial activity are reported within
parentheses in Table 1.
3
3
. Experimental
.1. General
Melting points were determined using a Gallenkamp apparatus. FTIR spectra were
recorded on a Perkin–Elmer System 2000 spectrometer. EI–MS and GC–MS were
recorded on a Hewlett Packard 5989 A. NMR spectra were recorded in deuterated
methanol (Sigma Chem. Co.), chloroform (Aldrich) or pyridine (Merck), by a Bruker
Avance 300 or a Bruker Avance 400 spectrometer operated at 300 and 400 MHz
1
13
for H NMR and 75 and 100 MHz for C NMR, respectively. UV spectra of the
flavonoids were measured in methanol, using a Jasco-V-530 UV/Vis spectro-
photometer as described in Mabry et al. (1970). TLC was carried out on pre-coated
silica gel 60 F250 plates (Merck). Column chromatography was carried out using
silica gel (Riedel-deHaen 230-400 mesh, ASTM) and Sephadex LH-20 (Sigma-
Aldrich). Paper chromatography was carried on Whatman No. 54. All solid
compounds isolated were purified by recrystallisation in acetone (1, 2, 3 and 4),
methanol (6, 8, 9 and 12) or acetone-chloroform (7 and 10). Compound 5 was
purified by repeated CC.
3
.2. Plant material
M. malabathricum was collected from Penang Island, Malaysia. The plant was
identified by Professor Lai-Keng Chan, School of Biological Sciences, Universiti
Sains Malaysia, where a voucher specimen (No. 10613) was deposited.

Natural Product Research
613

6
14
K.-C. Wong et al.

Natural Product Research
615
3
.3. Extraction and isolation
Fresh leaves (3 kg) were homogenised in MeOH–H O (4 : 1) at room temperature.
2
The slurry was filtered and the filtrate was concentrated under reduced pressure at a
ꢂ
temperature540 C to 1/10 of its original volume, using a rotary evaporator, to give
the methanolic extract (ext-1) (193.5 g). When chilled and centrifuged, (ext-1) gave
the precipitate (fr-1) (40.2 g). The precipitate (fr-1) was defatted with petroleum ether
and extracted with chloroform (300 mL ꢃ 2 and 200 mL ꢃ 2). The chloroform extract
(fr-2) (16.1 g) was fractionated by silica gel column chromatography (200 g), eluting
with chloroform–acetone–methanol (18 : 6 : 1), chloroform–acetone–methanol
10 : 9 : 1) and acetone successively. The eluent was collected in 25 mL fractions.
(
Fractions 15–19, which eluted with chloroform–acetone–methanol (18 : 6 : 1), yielded
ursolic acid (1) (405 mg). Fractions 25–30 yielded 2ꢀ-hydroxyursolic acid (2) (96 mg).
Fractions 46–50, which eluted with chloroform–acetone–methanol (10 : 9 : 1), yielded
asiatic acid (3) (42.5 mg) and glycerol 1, 2-dilinolenyl-3-O-ꢁ-D-galactopyranoside (5)
(1.35 g). Fractions 68–75, which eluted with acetone, yielded ꢁ-sitosterol 3-O-ꢁ-D-
glucopyranoside (4) (111 mg).
The purple-magenta flowers (250 g) were defatted with petroleum ether and
extracted with MeOH–H O (9 : 1) at room temperature. The solvent was removed
2
ꢂ
under reduced pressure at a temperature540 C to give a solid (ext-2) (13.0 g) which
was extracted with ethyl acetate. The ethyl acetate extract (fr-3) (1.0 g) was
fractionated on a Sephadex LH-20 column (20 g) using methanol. The eluent was
collected in 20 ml fractions. Fractions 7–9 were chromatographed on a silica gel
column (60 g) using dichloromethane–acetone–methanol (10 : 10 : 2), yielding kaemp-
ferol (6) (21 mg), kaempferol 3-O-ꢀ-L-rhamnopyranoside (7) (37 mg), kaempferol
3
(
-O-ꢁ-D-glucopyranoside (8) (52 mg) and kaempferol 3-O-ꢁ-D-galactopyranoside (9)
8 mg). Fractions 10–12 precipitated ellagic acid (12) (14 mg) on concentration, while
00
00
kaempferol 3-O-(2 ,6 -di-O-E-p-coumaryl)-ꢁ-D-galactopyranoside (10) (41 mg) was
recovered from the resulting solution. Fractions 13–15, on passing through a
Sephadex LH-20 column eluting with methanol, yielded quercetin (11) (5 mg).
3
.4. Spectral data
00
00
Kaempferol 3-O-(2 ,6 -di-O-E-p-coumaryl)-ꢁ-D-galactopyranoside (10): Pale yellow
ꢂ
powder, m.p. 194 C (dec) (CH COCH –CHCl ); IR (KBr) ꢂ : 3391, 1696, 1654,
max
3
3
3
ꢁ
1
630, 1604, 1589, 1513, 1444, 1359, 1259, 1204, 1171, 1080, 982, 830 cm ; EI-MS m/z
1
(
(
(
rel. int.): 432 (0.2), 342 (0.7), 311 (2.4), 286 (42.0), 258 (4.6), 257 (5.3), 229 (6.6), 213
6.2), 164 (35.8), 147 (41.2), 121 (28.3), 91 (19.5), 65 (12.4) and 44 (100); UV ꢃmax nm
MeOH): 268, 299, 313, 353, 366, (MeOH þ NaOMe): 274, 310, 366, (MeOH þ
AlCl ): 276, 315, 398, (MeOH þ AlCl /HCl): 278, 317, 392, (MeOH þ NaOAc): 275,
3
3
1
2
99, 314, 370 and (MeOH þ NaOAc/H BO ): 268, 301, 317, 365; H NMR
3
3
(methanol-d , 400 MHz) ꢄ (ppm): 6.05 (d, 1.9, 1 H, H-6), 6.21 (d, 1.9, 1 H, H-8),
4
0 0 0 0 00
.93 (d, 8.8, 2 H, H-2 ,6 ), 6.86 (d, 8.8, 2 H, H-3 ,5 ), 5.50 (d, 8.0, 1 H, H-1 ), 5.37 (dd,
7
1
1
1
6
0
0
00
00
00
.6, 8.0, 1 H, H-2 ), 3.78-3.84 (m, 1 H, H-3 ), 3.88 (d, 2.9, 1 H, H-4 ), 3.78-3.84 (m,
00
00
H, H-5 ), 4.37 (dd, 3.2, 11.5, 1 H, H-6 ), 4.19 (dd, 4.0, 11.5, 1 H, H-6 ), 6.38 (d, 15.9,
000
0
00
000 000
H, H-2 ), 7.69 (d, 15.9, 1 H, H-3 ), 7.46 (d, 8.6, 2 H, H-5 ,9 ), 6.81 (d, 8.6, 2 H, H-
0000
0
00 000
0000
,8 ), 6.05 (d, 15.9, 1 H, H-2 ), 7.39 (d, 15.9, 1 H, H-3 ), 7.26 (d, 8.6, 2 H,
13
0000 0000
0000 0000
H-5 ,9 ) and 6.78 (d, 8.6, 2 H, H-6 ,8 ); C-NMR (methanol-d , 75 MHz)
4

6
16
K.-C. Wong et al.
ꢄ (ppm): 158.4 (C-2), 134.7 (C-3), 179.2 (C-4), 162.9 (C-5), 100.4 (C-6), 167.0 (C-7),
0 0 0 0 0
5.0 (C-8), 158.3 (C-9), 105.3 (C-10), 122.7 (C-1 ), 132.1 (C-2 ,6 ), 116.3 (C-3 ,5 ), 161.5
9
0 00 00 00 00 00 00
(C-4 ), 101.1 (C-1 ), 74.0 (C-2 ), 73.2 9 C-3 ), 70.6 (C-4 ), 75.0 (C-5 ), 64.2 (C-6 ),
000 000 000 000 000 000
68.8 (C-1 ), 115.2 (C-2 ), 147.0 (C-3 ), 127.2 (C-4 ), 131.2 (C-5 ,9 ), 116.8
1
000 000 000 0000 0000 0000 0000
(C-6 ,8 ), 161.3 (C-7 ), 168.8 (C-1 ), 114.5 (C-2 ), 146.7 (C-3 ), 127.0 (C-4 ),
0000 0000 0000 0000 0000
31.2 (C-5 ,9 ), 116.8 (C-6 ,8 ) and 161.3 (C-7 ) (see also Supplementary
Figures S1–S6).
1
3
.5. Acid hydrolysis of compounds 4 and 5
Four mg of 4 and 10 mg of 5 were separately placed in a 50 mL round bottom flask.
Ten millilitres of 2 M HCl in methanol were added and the mixture was refluxed on a
ꢂ
water bath (80 C) for three hours, and then cooled and diluted with 5 mL of water.
The aglycones were extracted with chloroform (5 mL ꢃ 3) while the aqueous layer
gave the monosaccharides after evaporation under reduced pressure. The sugars
were identified by comparison with authentic monosaccharides on PC using solvent
systems butanol–acetic acid–water (4 : 1 : 5, top layer) and butanol–toluene–pyridine–
water (5 : 1 : 3 : 3), and silica gel TLC, using butanol–acetic acid–diethyl ether–water
(9 : 6 : 3 : 1).
3
.6. Acid hydrolysis of the flavonoids 7–10
Three milligrams of each compound were dissolved in 150 mL MeOH and 150 mL 2 M
ꢂ
H SO was added. After letting it stand for 20 min at 100 C, the MeOH was
evaporated off and 1 mL of water was added. The aqueous layer was extracted 3
2
4
times with 300 mL Et O to afford the aglycone, while the aqueous layer was
2
neutralised with CaCO , collected using a Pasteur pipette and concentrated to give
3
the sugars. The sugars were identified by comparison with authentic monosaccha-
rides on silica gel TLC, using the solvent systems n-butanol–acetic acid–diethyl
ether–water (9 : 6 : 3 : 1) and ethyl acetate–acetic acid–methanol–water (13 : 4 : 3 : 3).
3
.7. Trans-esterification of compound 5 and 10
Three to nine milligrams of each compound were placed in a 5 mL round bottom
flask. 0.5 mL of 2 M methanolic sodium hydroxide was added and the mixture was
ꢂ
refluxed for 5 min on a water bath (80 C). 0.5 mL of BF solution (10% in methanol)
3
was then added and the reflux was continued for 2 min, followed by the addition of
1
mL of heptane and further refluxing for 1 min. The mixture was then cooled,
transferred into a small test tube and after addition of a small amount of a saturated
solution of sodium chloride, gently swirled and allowed to separate. The organic
layer, which contained the methyl ester, was collected by a Pasteur pipette. The
methyl esters were identified by comparison of their retention times and mass spectra
with those of authentic methyl linolenate and methyl (E)-p-coumarate by TLC and
GC–MS analyses.

Natural Product Research
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3
.8. Antibacterial activity
Antibacterial activity was carried out by the agar diffusion method (Barry, 1991).
Different concentrations of the test materials were prepared in DMSO and 5 mm
diameter wells in the agar were filled with 60 mL of each sample. Refampicin was
used as the reference compound. Seven microorganisms were used: Staphylococcus
aureus ATCC 25923, Bacillus subtilis NCTC 8236, Bacillus cereus ATCC 10876,
Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 17853, Salmonella
typhi (lab. strain) and Klebsiella pneumoniae (lab. strain). The microorganisms were
provided by the Microbiology Laboratory, School of Pharmaceutical Sciences,
Universiti Sains Malaysia, Malaysia. The experiments were carried out in duplicate.
Supplementary material
Additional spectral data relating to this article is available online, alongside
Figures S1–S6.
Acknowledgements
The authors acknowledge the research grant (no. 304/PKIMIA/633132) provided by
Universiti Sains Malaysia, that has resulted in this article. Thanks are due to Dr Pazilah
Ibrahim of the School of Pharmaceutical Sciences, Universiti Sains Malaysia, for helping in
carrying out the antibacterial activity. USM-TWAS Postdoctoral Fellowship awarded to
Dafaalla Mohamed Hag Ali is gratefully acknowledged.
References
Barry, A.L. (1991). Procedures and theoretical considerations for testing antimicrobial agents
in agar media. In V. Lorian (Ed.), Antibiotics in laboratory medicine (3rd ed., pp. 1–23).
Baltimore: Williams and Wilkins.
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Kuala Lumpur: Ministry of Agriculture and Cooperatives.
Chou, C.J., & Liao, C. (1982). Phytochemical and pharmacological studies on the flower of
Melastoma candidum D. Don forma albiflorum J. C. Ou. Guoli Zhongguo Yiyao
Yangjiuso Yanjiu Baogao, 69–129. Abstract retrieved from SciFinder (Accession
No. 1983:77988).
Collins, D.J., Pilotti, C.A., & Wallis, A.F.A. (1992). Triterpene acids from some Papua New
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