P. Rijoa,b, J. Chumbob, A. Oliveirab, M.C. Costab,d, B. Rodríguezc and M.F. Simõesa
a Fac. Farmácia, iMed-UL, Univ. de Lisboa, Lisboa, Portugal, b Escola Superior de Saúde Ribeiro Sanches (ERISA), R. Fernando
Palha, 69, 1900-693, Lisboa, Portugal, cInst. Química Orgânica, CSIC, c. Juan de la Cierva 3, E-28006, Madrid, Spain, d
Laboratório Nacional de Energia e Geologia, I.P., Estrada da Portela, Bairro do Zambujal – Alfragide, Apartado 7586 - 2720-866,
Amadora.
The genus Plectranthus (Lamiaceae) consists of about 350 species, distributed from Africa through Asia to Australia. Several species are used as
folk medicine for skin irritations and nausea, also as antiseptics and vermicide.1 The main metabolites of this genus Plectranthus L’Herit belong
to phenolics and terpenoids classes. Within this last class, diterpenes are well-represented by a great variety of oxidized abietanes, namely with
phenolic functions. Several similar diterpenes, have shown antioxidant activities. The knowledge of free radical mediation in several human
pathological processes encouraged the use of diterpenes as natural drugs to prevent and treat some human diseases, namely atherosclerosis
and cancer cells proliferation, besides its known utility in food industry.2
Here we report the isolation, structure elucidation of two known diterpenoids, parvifloron D (1) and 7α-acetoxy-6β,12-dihydroxy-8,12abietadiene-11,14-dione (2) from P. ecklonii Benth. and P. grandidentatus, respectively, and their antioxidant abilities. The activities of the
compounds were measured by the α,α-diphenyl-β-picrylhydrazyl (DPPH) method. The percentage of DPPH radical reduction by abietanes 1
and 2 was evaluated at different concentrations in a spectrophotometric assay1. Both diterpenoids 1 and 2 showed a dose dependent
scavenging activity.
Measurement of DPPH Radical Scavenging Activity:
Parvifloron D (1) and 7α-acetoxy-6β,12-dihydroxy-8,12-abietadiene-11,14-dione (2)
100.00
90.00
DPPH radical scavenging activity (%) =
[(Abscontrol - Abssample)/(Abscontrol)] x 100
80.00
DPPH Inhibition (%)
70.00
BHT
Parvifloron D 1
Quercetin
Royleanone 2
60.00
50.00
where Abscontrol was the absorbance of DPPH radical +
methanol, Abssample was the absorbance of DPPH radical +
sample/standard. The scavenging activity was expressed in
terms of IC50, the concentration of the samples required to
give a 50% reduction in the intensity of the signal of the
DPPH radical. The results were done at least in triple.
40.00
30.00
20.00
10.00
0.400
0.380
0.360
0.340
0.320
0.300
0.280
0.260
0.240
0.220
0.200
0.180
0.160
0.140
0.120
0.100
0.080
0.060
0.040
0.020
0.00
0.000
A solution of test compound in methanol (500 μL) was
added to an methanol solution of DPPH radical (0.100 mM,
500 μL). The reaction mixture was vortexed thoroughly and
left in the dark at room temperature for 30 min. The
absorbance
of
the
mixture
was
measured
spectrophotometrically at 516 nm. Quercetin and BHT
were used as the standards. The ability to scavenge DPPH
radical was calculated by the following equation:
Concentration(mM)
Compounds
IC50 (mM)
BHT
0,1050 ± 0,0070
Quercetin
0,0075 ± 0,0010
Parvifloron D (1)
0,1125 ± 0,0177
7α-acetoxy-6β,12-dihydroxy-
1,8500 ± 0,0707
8,12-abietadiene-11,14-dione (2)
Parvifloron D 1 showed antioxidant properties equivalent
(IC50 0.1125 ± 0.0177 mM) to BHT but lesser than quercetin
reference.
The IC50 of royleanone 2 (1.8500 ± 0.0707 mM) revealed
antioxidant ability inferior to butylated hydroxytoluene
(BHT) reference.
We intend to improve antioxidant properties of Abietane 1
and some of its new derivatives through synthetic
strategies targeting relevant biological activities which are
under study.
References:
1 Y. Narukawa, et al., 2001, Chem. Pharm. Bull. 49, 9, 1182—1184. 2 C. Gaspar-Marques et al., 2008, Nat. Prod. Res., 22, 167–177.
Acknowledgments: To the students Helena Santos, Telma Gama e Mª Inês Carvalho (ERISA), FCT-MCES (I&D nº 8/94, grant nº SFRH/BD/19250/2004);
CYTED (Project X.11: PIBATUB); CICYT (grant nº CTQ2006-15279-C03-02).