Erika Castillejos-Ramírez’s research while affiliated with National Autonomous University of Mexico and other places

An infusion from the aerial parts of Justicia spicigera Schltdl., an herb commonly used to treat diabetes, inhibited the activity of protein tyrosine phosphatase 1B (PTP1B). Two undescribed compounds, 2-N-(p-coumaroyl)-3H-phenoxazin-3-one, and 3″-O-acetyl-kaempferitrin, along with kaempferitrin, kaempferol 7-O-α-L-rhamnopyranoside, perisbivalvine B and 2,5-dimethoxy-p-benzoquinone were isolated from the active extract. Their structures were elucidated by a combination of spectroscopic and spectrometric methods. The isolates were evaluated for their inhibitory activity against PTP1B; the most active compounds were 2-N-(p-coumaroyl)-3H-phenoxazin-3-one, and perisbivalvine B with IC50 values of 159.1 ± 0.02 μM and 106.6 ± 0.01 μM, respectively. However, perisbivalvine B was unstable. Kinetic analysis of 2-N-(p-coumaroyl)-3H-phenoxazin-3-one and 2,5-dimethoxy-p-benzoquinone (obtained in good amounts) indicated that both compounds behaved as parabolic competitive inhibitors and bind to the enzyme forming complexes with 1:1 and 1:2 stoichiometry. Docking of 2-N-(p-coumaroyl)-3H-phenoxazin-3-one and 2,5-dimethoxy-p-benzoquinone to PTP1B1-400 predicted a good affinity of these compounds for PTP1B catalytic site and demonstrated that the binding of a second ligand is sterically possible. The 1:2 complex was also supported by the second docking analysis, which predicted an important contribution of π-stacking interactions to the stability of these 1:2 complexes. Finally, an UHPLC-MS method was developed and validated to quantify the content of kaempferitrin in the infusion of the plant.

Infusions and poultices prepared from the aerial parts of Baccharis heterophylla Kunth (Asteraceae) are widely used in Oaxaca (Mexico) for relieving painful and inflammatory complaints. Therefore, the antinociceptive potential of an aqueous extract (31.6–316 mg/kg, p.o.) and essential oil (30–177 µg/paw, i.pl.) of the plant was assessed using the formalin test. Both preparations inhibited the formalin-induced nociception response (100–316 mg/kg and 100–177 µg/paw, respectively) during the test’s second phase. Chemical analysis of the aqueous extract revealed that the major active components were chlorogenic acid (1), 3,4-di-O-(E)-caffeoylquinic acid (2), 3,5-di-O-(E)-caffeoylquinic acid (3), 4,5-di-O-(E)-caffeoylquinic acid (4), 3,5-di-O-(E)-caffeoylquinic acid methyl ester (5), apigenin (6), genkwanin (7), acacetin (8). Compounds 1–5 and 8 are new for B. heterophylla. A high-pressure liquid chromatographic method for quantifying chlorogenic acid (1) and di-caffeoylquinic acids 2–4 in the plant was developed and validated. Analyses of the essential oil and the headspace solid-phase microextraction products, via gas-chromatography-mass spectrometry, revealed that the major volatiles were β-pinene, myrcene, D-limonene, β-caryophyllene, and α-caryophyllene, which have demonstrated antinociceptive properties.

Potential toxic effects in mice of an infusion prepared from the stem bark of Exostema caribaeum was assessed by means of the Lorke procedure. The preparation was not found to be toxic, with the LD50 value estimated to be more than 5 g/kg. This preparation at 100, 300, and 500 mg/kg also caused a significant hypoglycemic effect and a reduction in the postprandial glycemia peak in both normal and nicotinamide/streptozotocin (NA/STZ)-diabetic mice in an oral sucrose tolerance test. Phytochemical analysis of the infusion revealed that the major active principles are 4-phenylcoumarins (2-8) and chlorogenic acid (1). During this process, a new 4-phenylcoumarin was isolated along with several known analogues. The structure of the new compound was established as 5-O-[β-d-xylopyranosyl-(1→6)-β-d-glucopyranosyl]-7,3',4'-trihydroxy-4-phenylcoumarin (2) by spectroscopic means. A simple, efficient, fast, and reliable UHPLC-PDA analytical method for quantifying 4-phenylcoumarins and chlorogenic acid (1) was developed and validated. Parameters assessed for the method validation were selectivity, linearity, the limits of detection (LOD) and quantification (LOQ), precision, and accuracy. It was found that all calibration curves showed good linearity (R(2) > 0.9931), within the range of concentrations tested.

The stem-bark of Exostema caribaeum (Rubiaceae) is widely used in Mexican folk medicine for treating diabetes and malaria. Previous investigations revealed that the active principles of the plant are 4-phenylcoumarins. Hence, a simple and reliable chromatographic method useful for quality control procedures of this valuable herb using UPLC-PDA was developed and validated according to the International Conference on Harmonization (ICH). The method allows simultaneous quantification of 4-phenylcoumarins (2-8) and chlorogenic acid (1) in the crude drug. During this process a new 4-phenylcoumarin (2) was isolated and characterized using 1D and 2D-NMR analyses. R 1 R 2 2 H β-D-xylopyranosyl-(1→6)-β-D-glucopyranosyl 3 H β-D-glucopyranosyl 4 CH3 β-D-xylopyranosyl-(1→6)-β-D-glucopyranosyl 5 CH3 β-D-galactopyranosyl 6 CH3 β-D-glucopyranosyl 7 H 6''-acetyl-β-D-glucopyranosyl 8 CH3 6''-acetyl-β-D-galactopyranosyl