Methyl 3,4-dihydroxybenzoate (Protocatechuic acid methyl ester)

Phenolics from Lagotis brevituba Maxim

A phytochemical investigation on Lagotis brevituba led to the isolation and characterisation of 11 phenolic compounds: p-hydroxy-benzoic acid 1, methyl 3,4-dihydroxybenzoate 2, vanillic acid 3, protocatechuic acid 4, caffeic acid 5, glucose ester of (E)-ferulic acid 6, p-coumaric acid 7, vanillin 8, diosmetin-7-O-β-d-glucoside 9, chrysoeriol 10 and luteolin 11. Their structures were elucidated using spectroscopic methods and by comparison with data in the literature. Compounds 1-6 were first obtained from the genus Lagotis, and compounds 1-9 were isolated from L. brevituba for the first time. Compound 4 and 11 displayed remarkable antioxidant activities against DPPH radical (IC50 = 5.60 ± 0.09, 27.5 ± 0.06 mg/L, respectively), which were superior to positive control rutin. And compound 11 was also superior to rutin in ABTS assay (IC50 = 2.04 ± 0.13 mg/L).

The Hypoxia Mimetic Protocatechuic Acid Ethyl Ester Inhibits Synaptic Signaling and Plasticity in the Rat Hippocampus

During hypoxia a number of physiological changes occur within neurons including the stabilization of hypoxia-inducible factors (HIFs). The activity of these proteins is regulated by O₂, Fe²⁺, 2-OG and ascorbate-dependant hydroxylases which contain prolyl-4-hydroxylase domains (PHDs). PHD inhibitors have been widely used and have been shown to have a preconditioning and protective effect against a later and more severe hypoxic insult. In this study we have investigated the neuroprotective effects of the PHD inhibitor, protocatechuic acid ethyl ester (ethyl 3,4, dihydroxybenzoate: EDHB), as well as its effects on synaptic transmission and plasticity in the rat hippocampus using electrophysiological techniques. We report for the first time, an acute concentration-dependent and reversible inhibitory effect of EDHB (10-100 μM) on synaptic transmission in the dentate gyrus but not Cornu Ammonis 1 (CA1) region which does not affect cell viability. This effect was attenuated through the application of the NMDA or GABA_A receptor antagonists, AP-5 and picrotoxin in the dentate gyrus. There were no changes in the ratio of paired responses after EDHB application suggesting a post-synaptic mechanism of action. EDHB (100 μM), was found to inhibit synaptic plasticity in both the dentate gyrus and CA1 regions. Application of exogenous Fe²⁺ (100 μM) or digoxin (100 nM) did not reverse EDHB's inhibitory effect on synaptic transmission or plasticity in both regions, suggesting that its effects may be HIF-independent. These results highlight a novel modulatory role for the PHD inhibitor EDHB in hippocampal synaptic transmission and plasticity. A novel post-synaptic mechanism of action may be involved, possibly involving NMDA and GABA_A receptor activation.

Chemical Constituents from Xanthium mongolicum

Objective: To investigate the chemical constituents from Xanthium mongolicum.
Methods: The constituents were isolated and purified by silicagel,Sephadex LH-20 column chromatography. Their structures were identified on the basis of spectral data and physiochemical characteristics.
Results: Ten compounds were isolated and identified as hexadecanoic acid( 1), methyl 3, 4-dihydroxybenzoate ( 2), protocatechuic aldehyde( 3), caffeic acid methyl ester( 4), vanillic acid( 5), 4-hydroxybenzoic acid( 6), caffeic acid ethyl ester( 7), chlorogenic acid( 8), caffeic acid( 9), 3, 4-di-O-caffeoylquinic acid( 10).
Conclusion: Compounds 1 ~ 5,7 and 10 are isolated from this plant for the first time.