α-Glucosidase inhibitory activity and in vivo antihyperglycemic effect of secondary metabolites from the leaf infusion of Ocimum campechianum mill.

ETHNOPHARMACOLOGICAL RELEVANCE: Wild basil (Ocimum campechianum Mill.), an aromatic herb of the Lamiaceae family known as "albahaca de monte" (Spanish) or "x'kakaltun" (Mayan) in Yucatan, is used in Mayan traditional medicine to treat diabetes, as well as to alleviate fever symtoms, stomach pain, conjunctivitis, and various skin affections. AIM OF THE STUDY: To isolate and identify the bioactive metabolites responsible for the α-glucosidase inhibitory activity previously detected in the leaf infusion O. campechianum. MATERIALS AND METHODS: The bioassay-guided fractionation and purification of the lyophilized infusion was carried out using a liquid-liquid partition procedure, followed by successive chromatographic purifications of the semipurified fractions. The isolated metabolites were identified by comparing their spectroscopic data with those reported in the literature. The liophylized infusion, together with the semipurified fractions, and the pure metabolites were tested for their antioxidant and α-glucosidase inhibitory activities, as well as their antihyperglycemic effect. RESULTS: Chromatographic purification of the semipurified fractions led to the isolation of the polymethoxylated flavones 5-demethyl nobiletin (1) and 5-demethyl sinensetin (2), together with luteolin (3), methyl rosmarinate (4) and rosmarinic acid (5). Metabolites 4 and 5 appear to be responsible for the α-glucosidase inhibitory activity and the antihyperglycemic effect detected in the lyophilized infusion. A Lineweaver-Burk double reciprocal plot confirmed that the higher α-glucosidase inhibitory activity of 4 is of non-competitive nature. Both 4 and 5 caused a decrease in blood glucose higher than that caused by acarbose, a result that appears to be related to their strong α-glucosidase inhibitory activity. Even though flavonoids 1-3 did not show a good inhibition of α-glucosidase, these products decreased blood glucose in the in vivo model, suggesting a different antihyperglycemic mechanism. CONCLUSIONS: The results confirm both the traditional use of O. campechianum and the importance of the leaf infusion as a potential source of antihyperglycemic agents. The isolation of 5-demethyl nobiletin (1) and 5-demethyl sinensetin (2) from O. campechianum and other Ocimum spp. suggests that polymethoxyflavones can be considered chemotaxonomical markers for the genus.

Natural Products from the Yucatecan Flora: Structural Diversity and Biological Activity.

The Yucatan Peninsula possesses a unique climate, geology, landscape, and biota that includes a distinct flora of over 2300 species; of these, close to 800 plants are used in what is known as Mayan traditional medicine, and about 170 are listed as native or endemic. Even though the flora of the Yucatan peninsula has been widely studied by naturalists and biologists, to date, phytochemical and pharmacological knowledge of most of the plants, including the medicinal plants, is limited. Presently, phytochemical studies carried out on plants from the Yucatecan flora have resulted in the identification of a wide variety of natural products that include flavonoids, terpenoids, polyketides, and phenolics with cytotoxic, antiprotozoal, antibacterial, anti-inflammatory, analgesic, antioxidant, and antifungal activities. This review describes the main findings in over 20 years (1992 to 2018) of exploring the natural product diversity of the Yucatecan flora.

Bioactive dicaffeoylquinic acid derivatives from the root extract of Calea urticifolia

ABSTRACT Calea urticifolia (Mill.) DC., Asteraceae, is a native plant of the Yucatan Peninsula used in traditional medicine to treat inflammation and pain. The bioassay-guided purification of the ethanol root extract allowed the isolation of the main bioactive metabolites, which were identified as an inseparable mixture of thymol (1) and 3-methyl-4-isopropylphenol (2), together with 3,4-O-dicaffeoylquinic acid methyl ester (3), 3,4-O-dicaffeoyl-epi-quinic acid methyl ester (4), 3,5-O-dicaffeoyl-epi-quinic acid methyl ester (5) and 3,5-O-dicaffeoylquinic acid (6). The results showed that the analgesic activity detected in the root extract of C. urticifolia could be attributed mainly to the mixture of 1 and 2 and to the novel 3,4-O-dicaffeoyl-epi-quinic acid methyl ester (4). Alternatively, the similarity on the antiinflammatory and antioxidant activities of the dicaffeoylquinic acid derivatives 3-5 suggests that the former might be related to their ability as radical scavengers.