Composition of Essential Oil from Leaves and Flowers of Justicia calycina from the Amazon Rainforest, Brazil

Published in Khimiya Prirodnykh Soedinenii, No. 5, September–October, 2020, pp. 794–795.

In Brazil, the family Acanthaceae is represented by 41 genera, the most numerous of which is Justicia L., with approximately 700 species distributed in tropical and pantropical regions. Although Brazil has a high number of species from this family, with 126 in the genus Justicia L. alone [[1]], phytochemical studies on native species of the Amazon region are scarce [[2]]. Justicia calycina (Nees) V.A.W. Graham is an herbaceous, perennial plant with large, bright flowers and cystoliths on the leaves. The species grows mainly in the Amazon forest and Cerrado (savanna) biome on the banks of rivers with little shade [[3]]. Commonly known in the Amazon region as "sara-tudo" and "quebra corrente," the leaves and stems are used in folk medicine in the form of an infusion, decoction, and maceration for stomachache and the relief of inflammatory processes [[4]].

Plants of the genus Justicia are known for the production and accumulation of alkaloids, lignans, flavonoids, and terpenoids [[2]], including essential oils [[5]]. The popular use of species of Justicia to treat inflammatory processes was recently confirmed with an aqueous extract of the leaves from Justicia acuminatissima (Miq.) Bremek, which is a heterotypic synonym of J. calycina [[6]]. To the best of our knowledge, J. calycina has not previously been investigated for the identification of the chemical constituents of its essential oil. This paper reports, for the first time, the chemical composition of the essential oils from the leaves and flowers of J. calycina found growing wild in the Amazon Rainforest in the state of Rondonia, Brazil.

The essential oils obtained through conventional hydrodistillation of the fresh leaves and flowers of J. calycina exhibited a light yellow color. The yield on a fresh weight basis was 0.05 ± 0.02% for leaves and 0.04 ± 0.01% for flowers. The oils were submitted to CG-MS for the determination of the constituents. The flower oil exhibited greater chemical diversity.

Sixty-three and forty-four compounds were identified in the leaf and flower oils, accounting for 98.40% and 96.36% of the total oil, respectively (Table 1). The oils are basically composed of monoterpenes and sesquiterpenes, with a predominance of the latter in both oils. The main constituents were α-copaene (11.33% of leaf oil; 6.66% of flower oil), β-caryophyllene (15.87% of leaf oil; 12.11% of flower oil), and bicyclogermacrene (11.84% of leaf oil; 10.94% of flower oil). Other constituents identified in significant amounts were β-pinene (5.06% of leaf oil), prezizaene (2.11% of flower oil), γ-cadinene (2.21% of flower oil), elemol (2.31% of flower oil), limonene (5.62% of leaf oil; 2.42% of flower oil), 2-epi-β-funebrene (2.56% of leaf oil; 2.20% of flower oil), γ-elemene (2.81% of leaf oil; 3.10% of flower oil), and α-selinene (3.61% of leaf oil; 3.24% of flower oil).

Percentage of Chemical Constituents Identified in Essential Oils from Justicia calycina, Yield (%) ± SD

aRetention indices calculated from retention times in relation to those of a series of n-alkanes on a 30 m DB-5 capillary column. RI: retention index, SD: standard deviation, MS: mass spectrum, CI: co-injection with authentic standards. Method of identification: RI, MS and *RI, MS, Cl.

Fresh leaves and flowers of J. calycina were collected in the morning from adult specimens (5 m in height) at locations with streams in the City of Colorado do Oeste, state of Rondonia, Brazil, in April 2017. The plant was identified by Francismeire Bonadeu of the Instituto Federal de Rondonia. A voucher sample was deposited in the COOE Herbarium of the Instituto Federal de Rondonia under No. COOE 475. The extraction, analysis, and chemical identification of the compounds of the oils from the fresh leaves and flowers were performed as described previously by [[7]].