Tocoyena hispidula (Rubiaceae) is popularly known as “flor-do-cerrado” and “jenipapinho”. It is a shrub found in the North (Pará) and Northeast (Piauí and Maranhão) regions of Brazil and used to pain intestine and uterine inflammation combat. The Rubiaceae family has as chemotaxonomic markers iridoids, anthraquinones and indole alkaloids. The present work reports iridoids and coumarins isolated from T. hispidula.
The EtOH extract from the stem (48 g, 3.5%) was obtained by maceration. In a aliquot of 41 g of the EtOH extract was added MeOH, and the soluble part was subjected to silica gel filter column chromatography using hexane, CHCl3, EtOAc and MeOH. The CHCl3 fraction (2.5 g) was subjected to silica gel column chromatography using Hex/EtOAc. CC65, CC82 and CC72 subfractions were purified by Sephadex LH-20 column chromatography to provide compounds 1 (17.8 mg), 2 (2.0 mg) and 3 (46.0 mg) respectively. The EtOAc fraction (2.5 g) was applied on a Stracta column (C18, 10 g), yielding MeOH/H2O 1:1, MeOH and CHCl3 fractions. The MeOH/H2O 1:1 fraction (1.35 g) was subjected to Sephadex LH-20 column chromatography. The A7 subfraction (683 mg) was purified on semipreparative HPLC (RP-18), isocratic (20% MeOH/ACN 1: 1 and 80% H2O, λ 240 nm), affording a mixture of 4a and 4b compounds (19.7 mg). The A10 subfraction (285 mg) was subjected to Sephadex LH-20 column chromatography and silica gel to obtain compound 5 (21.0 mg).
Structural determination of substances 1-5 was performed by 1H and 13C NMR spectroscopic analysis and compared with the literature (Figure 1). Compound 1, coumarin scopoletin, an important phytoalexin in plants, which exhibits antitumor, hypolipidemic and spasmolytic activity. Compound 2 is an coumarin (fraxidin), for which antimicrobial and antileishmania activities are reported. Compound 3 is the morindolide noriridoid. Noriridoids are a class of metabolites rarely found from natural sources. Compounds 4a and 4b are a diastereomeric mixture of iridoids. Compound 5 is genipin, an iridoid with anti-inflammatory, anticancer, antithrombotic, antibacterial action among others. Genipin is used to prepare a series of blue pigments used in the food industry.
In the present work, the compounds scopoletin (1), fraxidin (2), morindolide (3), the diastereoisomeric mixture of iridoids (4a and 4b) and genipin (5) were isolated and identified. These compounds are being reported to first time in the genus Tocoyena.