The first report of chemical and biological study of essential oil from Begonia reniformis leaf ( Begoniaceae )

60 Eclética Química Journal, 42, 2017 ISSN: 1678-4618 DOI: 10.26850/1678-4618eqj.v42.1.2017.p60-64 ABSTRACT: Species of the genus Begonia are expensive ornamental plants. There have been few reports of chemical studies with the Begonia species. Here we report the first chemical and biological study of essential oil for a species of Begonia. The essential oil of the Begonia reniformis leaf obtained by hydrodistillation was analyzed via GC-MS and twenty-one compounds were identified. Sesquiterpenes silphiperfol-4,7(14)-diene and β-vetispirene were the major ones with a percentage of 15.7 and 21.0%, respectively. The oil showed weak activity against bacteria Bacillus subtilis and Pseudomonas aeruginosa with minimum inhibitory concentrations of 625μg/mL for each of the two bacteria. The first report of chemical and biological study of essential oil from Begonia reniformis leaf (Begoniaceae)


Introduction
The family Begoniaceae is characterized by flowering plants that consist of two genera, Begonia and Hillebrandia, with about 1500 species occurring in all parts of the world 1,2 .The genus Hillebrandia is classified as monotypic because it consists of only one specie Hillebrandia sandwicensis, a plant endemic of the Hawaiian Islands 3 .The species of the genus Begonia can be native or horticultural hybrids and are popular as houseplants due to the diversity in their floral form and leaf shape which adds commercial value to their species 4 .In Brazil there are about 213 Begonia species, mainly found in the Atlantic Forest, of which 186 are endemic 5,6 .
The chemistry and biological potential of the Begonia species is poorly explored with rare studies available in the literature.In an investigation of the phytochemistry of leaf extracts of Begonia malabarica, the compounds friedelin, epi-friedelinol, β-sitosterol, luteolin, quercetin and β-sitosterol-3-β-Dglucopyranoside were isolated 7 .From the Begonia picta species, the following flavonoids were isolated: vitexin, iso-vitexin, orientin, iso-orientin and 1,3dihydroxy-6,7-dimethoxyxanthone.The compounds orientin and iso-orientin were also identified, both of which showed potent antioxidant activity with IC 50 values of 54.0 and 53.4 μmol/L, respectively, when compared with a trolox positive control with an IC 50 value of 96.1 μmol/L 8 .In other phytochemical studies, different classes of anthocyanins were isolated from the extracts of flowers of the Begonia sp species, while several steroids and flavonoids were isolated from B. evansiana and B. malaba-rica species 7,9,10  the few reports available point to flavonoids and steroids as chemotaxonomic metabolites for the genus.
In relation to studies on the chemistry of the essential oil obtained from the Begonia species, to our knowledge there are no reports, this work is the first to describe the chemical constituents of the essential oil for a Begonia species, the Begonia reniformis, a species that is part of the Brazilian flora.To date, we have found no chemical study previously reported for this plant.

Material botanic
Begonia reniformis specimens were collected on the Campus of the Rural Federal University of Pernambuco, in the city of Recife, State of Pernambuco in the Northeastern of Brazil, in August 2016.The Instituto Agronômico de Pernambuco -IPA was asked to make the botanical identification and a voucher specimen was deposited at the Dárdano de Andrade Lima Herbarium of the IPA (90664).

Obtaining of essential oils
The essential oil was obtained from fresh leaf (250 g) via hydrodistillation using a Clevenger-type apparatus.The distillation was carried out for 3 h.The oil obtained was treated with Na 2 SO 4 .

Analysis of essential oil
The essential oil was analyzed by GC-MS with a programmed temperature of 60-240ºC at 3ºC min rate in a Gas Chromatograph (Varian 431-GC) equipped with a fused-silica capillary column (30 m × 0.25 mm i.d.× 0.25 μm) coated with DB-5 and coupled to a Mass Spectrometer (Varian 220-MS).The detailed conditions of GC-MS analysis have been previously reported by our research group 11,12 .Identification of the chemical constituents was carried out using the Van den dool and Kratz 13 equation and comparing with published mass spectra 14 .

In vitro assay for antimicrobial activity
The antimicrobial potential of essential oil obtained of B. reniformis leaves was evaluated against the bacteria Staphylococcus aureus (ATCC 6538), Bacillus subtilis (ATCC 6633), Escherichia coli (UFPEDA 224) and Pseudomonas aeruginosa (ATCC 416) as well as against the fungi Candida albicans (ATCC 1007) and Candida utilis (ATCC 1009).The microorganisms were maintained in nutrient agar (NA), stored at 4 °C.The antimicrobial activity evaluation was performed by determination of the values of minimum inhibitory concentrations (MIC) as previously reported 11,12 .The antimicrobials Metronidazol and Fluconazol were used as the positive control.

Results and discussion
Essential oil (78 mg) from a mass of the fresh leaves of B. reniformis (250 g) was obtained with a yield of 0.03%.The chemical profile of essential oil of B. reniformis leaves obtained by GC-MS showed two major peaks at 22.2 and 28.1 minutes with relative concentrations of 15.7 and 21.0%, respectively (Figure 1).Major peaks at 22.2 and 28.1 minutes were identified as sesquiterpenes silphiperfol-4,7( 14)-diene and β-vetispirene, respectively.A total of 21 compounds were identified representing 84.8% of the analyzed oil (Table 1), such as (-)-cis-cadine-1(6),4diene (7.1%), ishwarane (3.9%), Guaiol (8.0%), cismuurola-3,5-diene (3.5%), trans-muurola-3,5-diene (3.7%), dauca-5,8-diene (4.3%) and β-atlantol (2.9%).To our knowledge there has been no report of chemical and biological studies of the essential oils of species from Begoniaceae family that has included the genera Begonia and Hillebrandia.The major compound of essential oil from B. reniformis leaves, sesquiterpene βvetispirene, has been previously reported in the essential oils from Vetiveria zizanioides (Poaceae) roots 15 , and its occurrence in other plant species is rare.The second major oil compound has been reported in about fifteen plant species, such as Remirea maritima (Cyperaceae), Piper amalago (Piperaceae), Artemisia vulgaris (Asteraceae), Clinopodium vulgare (Labiatae) and Lomatium rigidum (Apiaceae) [16][17][18][19][20]    The essential oil of B. reniformis leaf was evaluated against six microorganisms including fungi, grampositive bacteria and gram-negative bacteria to determine the MIC values by the agar dilution method.The samples of natural source as extract and essential oil that show MIC values lower than100 μg/mL are characterized as strong antimicrobial agent.The samples with MIC values ranging from 100-500, 500-1000 and over 1000 μg/mL are considered to be moderately weak, or non-active, respectively, against fungi and bacteria according to criteria in the literature 21 .The results in Table 2 show that the oil was biologically active against gram-positive bacteria B. subtilis and gram-negative bacteria P. aeruginosa with MIC of 625μg/mL for each of the two bacteria, this is considered to be weak activity.

Conclusions
The first study on the chemical composition of the essential oil for a species of the Begoniaceae family showed sesquiterpenes as the major constituents in the B. reniformis leaf.The sesquiterpenes silphiperfol-4,7(14)-diene and β-vetispirene were the majority and these are rare in the essential oil of plant.The essential oil showed weak antimicrobial activity against the bacteria B. subtilis and P. aeruginosa.

Figure 1 .
Figure 1.Chromatogram of essential oil of the B. reniformis leaf obtained via GC-MS.
. Despite limited studies of the chemistry of the Begonia species,

Table 1 .
Chemical constituents identified in the essential oil of the B. reniformis leaf.Compounds are listed in ascending order of their retention times.AI: Arithmetic index.b Arithmetic index as determined on non-polar DB-5 column.c Arithmetic index of the literature.d,e Determined by the fragmentation pattern of their respective mass spectra. a

Table 2 .
Values of the MIC obtained for essential oil from the B. reniformis leaf towards bacteria and fungi