ABSTRACT
Conobea scoparioides (Plantaginaceae) is an herbaceous plant known as "pataqueira" that grows wild in seasonally wet areas of the Amazon region. It is used for aromatic baths and anti-protozoan remedies by the Brazilian Amazon native people. The main volatile compounds identified in the essential oil of "Pataqueira" were the phenolic monoterpenes thymol and thymol methyl ether and their precursors, the monoterpene hydrocarbons α-phellandrene and p-cymene. A hydrotalcite synthesized from blast-furnace slag exhibited a 3:2 (Mg/Al) molar ratio, and this layered double hydroxide (LDH) was evaluated as a catalyst in converting the main monoterpenes of the "Pataqueira" oil. This action significantly increased the thymol content, from 41% to 95%, associated with the percentual reduction in other main components, such as thymol methyl ether, α-phellandrene, and p-cymene. The LDH reaction showed a strong tendency towards producing hydroxylated derivatives, and its behavior was similar to the hypothetical plant biosynthetic pathway, which leads to the production of the monoterpenes of "Pataqueira" oil. Thymol and its derivatives are potent antiseptics applied in pharmaceutical and hygienic products as antibacterial, antifungal, and antioxidant properties, among others. The present work reports a natural source with a high thymol content in aromatic plants from the Amazon, with evident economic value.
ABSTRACT
O óleo essencial das folhas e ramos finos frescos e secos de Hyptis crenata forneceu os seguintes rendimentos, 1,4 por cento e 0,9 por cento. Os constituintes voláteis principais foram ±-pineno (22,0 por cento; 19,5 por cento), 1,8-cineol (17,6 por cento; 23,2 por cento), ²-pineno (17,0 por cento: 13,8 por cento), cânfora (4,7 por cento; 11,6 por cento), limoneno (5,4 por cento; 4,4 por cento) e ³-terpineno (3,5 por cento; 2,4 por cento), totalizando mais de 70 por cento nos óleos. A atividade de seqüestro do radical DPPH para o extrato metanólico (CE50, 16,7 + 0,4 µg/mL) foi comparável ao do BHT (19,8 ± 0,5 µg/mL) mostrando uma significante atividade antioxidante. Os óleos apresentaram baixa atividade. O teor de fenólicos totais (TP, 373,0 + 15,9 mg GAE/g) e equivalente trolox (TEAC, 226,8 + 0,5 mg TE/g) confirmaram a atividade antioxidante do extrato metanólico, que pode ser atribuída à presença de compostos fenólicos polares. No teste com larvas de camarão as concentrações letais para o óleo e extrato metanólico foram 6,7 + 0,2 µg/mL e 13,0 + 3,7 µg/mL, respectivamente, fornecendo importante evidência de suas atividade biológicas.
The essential oils of fresh and dried leaves and fine stems of Hyptis crenata furnished the following yields: 1.4 percent and 0.9 percent. The main volatile constituents were ±-pinene (22.0 percent; 19.5 percent), 1,8-cineole (17.6 percent; 23.2 percent), ²-pinene (17.0 percent; 13.8 percent), camphor (4.7 percent; 11.6 percent), limonene (5.4 percent; 4.4 percent) and ³-terpinene (3.5 percent; 2.4 percent), totalizing more than 70 percent in the oils. The DPPH radical scavenging activity (EC50, 16.7 + 0.4 µg/mL) of the methanol extract was comparable to BHT (19.8 ± 0.5 µg/mL) showing a significant antioxidant activity. The oils showed low activities. The amount of total phenolics (TP, 373.0 + 15.9 mg GAE/g) and trolox equivalent (TEAC, 226.8 + 0.5 mg TE/g) confirmed the antioxidant activity of the methanol extract that can be attributed to the presence of polar phenolic compounds. In the brine shrimp bioassay the lethal concentrations (LC50) for the oil and methanol extract were 6.7 + 0.2 µg/mL and 13.0 + 3.7 µg/mL, respectively, providing important evidence of their biological activities.
